摘要:

Matrix Isolation Studies on Reactions of Metal Atoms The Characterisation of Cu(O,) and Cr(O,) BY J. H. DARLING AND J. S. OGDEN* M. B. GARTON-SPRENGER Inorganic Chemistry Laboratory South Parks Road Oxford Received 5th September 1973 When copper or chromium vapour is condensed in low temperature matrices containing a few mole % oxygen several new i.-r. bands may be observed. This paper shows through the use of l80 substitution that one species common to both systems is the bis-superoxide molecule M(02)*; the structure of this species is discussed in the light of other metal superoxide complexes. Matrix isolation is now well established as a technique for studying chemical reactions between metal atoms and simple ligands and in particular a number of metal atom/O reactions have been investigated in this way.Thus Andrews et al. in a series of papers 1-5 on alkali metal atom/O matrix reactions have characterised species such as LiO, KO and CsO using vibrational spectroscopy. Bos et aL6-have identified molecular GeO and SnO formed in similar circumstances and more recently Ozin et aL8* and Darling lo have extended this type of study to transition metal/O systems and have demonstrated the existence of the binary dioxygen complexes M(0,) and M(O,) (M = Ni Pd Pt). This paper describes some of our experimental results on the copper atom and chromium atom/O matrix reactions and discusses their interpretation. EXPERIMENTAL The Knudsen furnace low temperature cryotip and i.-r. spectrometer used for this work have been described previously.l In these experiments samples of elemental copper or chromium (99.99 % pure) were heated in alumina or tantalum sample holders to temperatures -1400-1500K and the vapours deposited on a cooled (20 K) CsI window with a large excess of matrix. In a series of preliminary experiments both argon and krypton doped with various proportions of oxygen (1 to 10 %) were used as matrices but the simplest spectra were obtained using a mixture of 10 % oxygen in argon and the results described below refer in general to these conditions unless otherwise stated. In order to aid spectral assignments several l8O enrichment experiments were carried out using both " scrambled " and " unscrambled " samples of oxygen prepared as described previo~sly.~The l60 I80 atom ratio was varied in the range 0.7 to 1.2 but the molar composition of the final matrix gas was kept constant at 90 % Ar 10 % total 02.Research grade 1602 and Ar were obtained from the British Oxygen Co. and l80enriched oxygen gas (84 % 1802 16 % l6O l80)was supplied by Miles Laboratories Inc. Matrices were deposited at rates -10 millimol/h and with metal vapour pressures Torr the matrix ratio was typically -lo00 :1. All infra-red spectra were recorded at 20 K and new spectral features due to metal atom/02 reactions were usually visible after -30 min deposition under the above conditions. RESULTS When copper vapour was co-condensed at 20K with a large excess of argon containing 10 % 1602 a prominent sharp absorption was observed at 1109cm-' 75 76 CU(O2)2 AND Cr(02)2 together with a much weaker sharp feature at 1087cm-l and a broad absorption centred at 850 cm-l.Traces of H,O CO and C02 were also present in the matrix. The broad feature at 850 cm-1 was -30 cm-l wide and resembled the types of absorption typically found in extended solids or large polymeric species but the other new features at 1109 and 1087 cm-l were 3 cm-l wide and typical of simple matrix isolated molecules. The relative intensities of these two bands however were found to vary depending upon experimental conditions and in particular the strong bond at 1109 cm-l was relatively less intense in matrices containing lower proportions of oxygen whilst the weak feature at 1087 cm-1 was correspondingly enhanced.This suggests that these sharp bands cannot both arise from the same molecular species and for the purposes of this paper attention is focused on the band at 1109 cm-1 which was particularly prominent in 90 % Ar+ 10 % 0 matriceq. In some experi- ments this band appeared as a partially resolved doublet (1 110.0 and 1107.5 cm-l) but this phenomenon was not always reproducible and is attributed to a matrix effect. TABLE1.-VIBRATION FREQUENCIES (cm-l) OF ISOTOPICALLY SUBSTITUTED cU(o2)2 SPECIES IN ARGON MATRICES observed a calculated assignment unscrambled scrambled calc. I b calc. I1 -1144.5 1144.2 16 16 Cu 16 16 -1133.5 1 134.5 1 134.4 16 16 Cu 16 18 (1134.5 (1134.1 16 16 Cu 18 16 11 30.5 1130.5 1131.1 1130.8 16 16 Cu 18 18 1112.3 11 12.8 18 16 Cu 16 18 {1112.3 {1112.1 18 16 Cu 18 16 11 12.3 1111.4 16 18 Cu 18 16 1 109.0 1109.0 1109.0 1108.9 16 16 Cu 16 16 -1102.5 1102.3 1102.6 18 16 Cu 18 18 {1102.3 (1 101.5 16 18 Cu 18 18 1087.5 (vw)1087.5 1087.3 1087.6 16 16 Cu 16 18 {1087.3 (1086.8 16 16 Cu 18 16 1077.8 1078.2 18 16 Cu 16 18 {:X:Cl: {1077.7 -1078.0 18 16 Cu 18 16 1077.3 16 18 Cu 18 16 -1079.1 1078.8 18 18 Cu 18 18 1058.0 1058.0 (sh) 1058.0 1057.8 16 16 Cu 18 18 -1054.5 1055.1 1055.0 18 16 Cu 18 18 (1055.1 (1054.9 16 18 Cu 18 18 1045.5 1045.5 1045.6 1045.5 18 18 Cu 18 18 (a) frequency accuracy k1cm-'.(6) assuming Koo = 5.983 and K&,oo = 0.189 mdyn/A respectively ; and putting all other potential constant equal to zero. (c) assuming a GVFF with KOO = 6.13 K00,oo = 0.175 KcU-o = 1.0 KcU-o,cu-o = 0.05 KO-O.Cu-O(adj) = 0.4 mdYn/A-The result of l80enrichment at 10 % total oxygen concentration was to produce a very broad (-50 cm-l) polymer type band centred at -830 cm-' and a number of intense sharp bands in the frequency region 1000-1 150 cm-l which were clearly associated with the pure l60 band at 1109 cm-l.A typical spectrum obtained after condensing copper vapour with argon containing unscrambled oxygen (4.2 % 1602 5.0 % 1802, 0.8 % l60 l80) is shown in fig. l(a). Four prominent bands are present at 1130.5 1109.0 1058.0 and 1045.5 cm-l together with a weak central feature at J. H. DARLING M. B. GARTON-SPRENGER AND J. S. OGDEN I I I I I IS0 1050 (C) (a obsd obsd caIcd caIcd 7-r-1 I FIG.1.-1.-r.spectra obtained after co-condensing (a)copper with 90 %Ar 4.2 % l6O2 5 % 0.8 % I60I8O; (b) copper with 90 % Ar 3 % 1602 2 % "02 ; (c) chromium with 5 % 160180 09 %Ar 5.6 % 1602 3.8 %1802 0.6 % l60l8O;(d)chromium with 90 %Ar 3.2 % 1602 1.8 % 1802 5 % l60I8O. 78 1087.5 cm-'. In contrast fig. l(b) shows the more complicated spectrum obtained using isotopically scrambled oxygen. A total of eight distinct bands may now be observed in this region and the frequencies of these are given in table 1. The spectra obtained from the chromium vaporisations showed several similarities to the copper system. When chromium was condensed with an excess of argon containing 10 % 1602, two prominent features were observed in the region above 1000 cm-l at 1153.8 and 1134.4 cm-l and a much weaker band was sometimes present at 11 11 .O cm-I.Below 1000 cm-l an intense sharp band was observed at 971.5 cm-l and this was accompanied by a weaker feature at 939.5 cm-l. Altering the proportion of oxygen in the matrix again resulted in changes in relative band intensities and a detailed discussion of the behaviour of all the bands on l80enrichment is beyond the scope of this paper. However the isotope patterns produced in the region above 1000 cm-l were very similar to those observed in the copper system and were studied in detail. Fig. l(c) shows a typical spectrum obtained using unscrambled oxygen. TABLE2.-vIBRATION FREQUENCIES (Cm-') OF ISOTOPICALLY SUBSTITUTED Cr(02)2 SPECIES IN ARGON MATRICES observed a calc.I * calculated assignment unscrambled scrambled calc. I1 -1153.7 1153.7 16 16 Cr 16 16 1146.7 1146.9 1146.9 16 16 Cr 16 18 {1146.9 {1146.8 16 16 Cr 18 16 1145.3 1145.7 1145.6 16 16 Cr 18 18 1 134.4 1 134.4 1135.2 1135.1 16 16 Cr 16 16 1 121.2 1122.0 18 16 Cr 16 18 1121.2 1121.3 18 16 Cr 18 16 1121.2 1120.6 16 18 Cr 18 16 11 14.7(vw) 11 14.7 11 14.5 1115.1 18 16 Cr 18 18 {11 14.5 {1113.9 16 18 Cr 18 18 11 lO.O(vw) 1109.7 16 16 Cr 16 18 16 16 Cr 18 16 18 16 Cr 16 18 -1103.4 18 16 Cr 18 16 16 18 Cr 18 16 -1087.8 1087.8 18 18 Cr 18 18 1078.0 -1077.8 1077.7 16 16 Cr 18 18 1077.3 1076.7 18 16 Cr 18 18 {1076.7 16 18 Cr 18 18 1070.8 1070.8 1070.3 1070.2 18 18 Cr 18 18 (a) frequency accuracy k0.5cm-'.The bands at 1146.7 and 1077.3 were approximately 3 cm-I broad. (b) assuming Koo = 6.171 KOO,OO= 0.1 rndyn/A respectively and putting all other potential constants equal to zero. (c) assuming a GVFF with Koo = 6.320 K00,oo = 0.088 Kcr-o = 1.0 Kcr-0,Cr-o = 0.05 &34,-00(adj) = 0.4 mdYn/A-The highest frequency band at 1153.8 (labelled X) had no comparable l80 counter-part and remains unassigned but the five remaining bands form a pattern similar to that in fig. l(a) and their frequencies are given in table 2. Fig l(d) shows a corresponding spectrum using scrambled oxygen. Here a total of eleven bands may be observed but three of these were very weak and not always reproducible and we believe that only the seven bands listed in table 2 are associated with the pure l60 79 J.H. DARLING M. B. GARTON-SPRENGER AND J. S. OGDEN band at 1134.4 cm-l. The band widths in this system were typically 1.5-2.0 cm-' apart from the two absorptions at 1146.7 and 1077.3 cm-l which were N 3 cm-' wide. One additional experiment was carried out on the chromium system in an attempt to assess the magnitude of the extinction coefficient of these bands. It is known that when chromium vapour is co-condensed with matrices containing CO binary chromium carbonyls are formed which in general have large CO extinction coefficients in the terminal CO stretching region. When chromium was condensed with argon containing -10 %O2and -1 %CO the i.-r. spectrum showed absorptions in both the 1100-1200 cm-I range (1134.4 and 1153.8 cm-l) and in the terminal CO region (1991 1967 and 1940 cm-l) of comparable intensity.None of the bands listed in tables 1 and 2 showed any fine structure attributable to metal isotope effects and this suggests that they are primarily 0-0vibrations. SPECTRAL INTERPRETATION The analysis of the oxygen isotope spectra shown in the figure follows the pro- cedure described by Darling and Ogden l2 in their description of the frequency and intensity patterns expected for isotopically substituted carbonyls. This approach assumes a Cotton-Kraihanzel type of force field for the ligand vibrations and has recently been successfully applied l3 in the characterisation of Pt(N2)2. By analogy with this work the four line pattern observed here in fig. l(a) is characteristic of weakly coupled 0-0 vibrations in a bis-dioxygen complex CU(O~)~ which contains two equivalent O2groups.The four prominent bands are correspondingly assigned 1045.5 cm-l CU('~O~)~, as 1109 cm-l CU('~O~)~ 1130.5 and 1058.0 cm-' Cu('602) ('802). In this high frequency separation approximation,l only two force constant parameters are available to generate these frequencies and knowledge of the I6O2:1802isotope ratio allows one to calculate in addition the expected intensity pattern. The line diagram accompanying fig. l(a) shows the theoretical spectrum calculated using a principal 0-0force constant KO =5.983 mdyn/& an interaction constant Koo,oo =0.189 mdyn/& and the known isotope ratio. The frequency fit in particular is very satisfactory and table 1 (calc.I) shows that the observed bands are all reproduced to within 1 cm-'. These calculations were carried out assuming a linear model for Cu(O,), with no coupling between the 0-0and Cu-0 modes. However using this approximation exactly the same four line spectrum could also arise from three alternative geometries :the planar C2hstructure 0 0/\ cu 0 \/ 0 and the eclipsed (D2,Jand staggered (D&)configurations in which both O2 ligands are symmetrically side-on bonded and any discussion of the structure of CU(O~)~ must therefore take these possibilities into consideration. Fig l(b) shows the same region of the spectrum obtained after co-condensing copper vapour with argon containing scrambled oxygen and the accompanying diagram shows the line spectrum calculated using the high frequency approximation and again assuming no coupling.The same values of KO and satisfactorily reproduce the additional five bands. (calc. I table 1) and the intensity agreement is quite good. However at this stage the possibility of distinguishing between side-on and end-on bonding arises since the high frequency separation approximation of zero coupling CU(O212 AND Cr(O,) between the 0-0 and Cu-0 modes will not hold exactly and if it breaks down significantly one might expect to see evidence of linkage isomerism in an end-on bonded molecule such as (1602) CU(~~O~~O), where the vibration frequencies of 160-160-Cu-160-1 8O would be slightly different from those of 60-160-Cu-180-160.Ewerimentally however no band splitting could be detected due to this effect and the band assigned to Cu(1602)(160180) at 1087.5cm-l was the same width (-3 cm-l) as that due to CU('~O,)~. This might be taken as evidence that there is no linkage isomerism in these molecules and that the O2 ligand is side-on bonded but this conclusion cannot be reached without considering two additional factors the " natural " line width of these absorptions and the magnitude of the linkage isomer splitting. A number of calculations were therefore carried out on the linear Cu(O,) model using a completely general valence force field. Various sets of potential constants were chosen so as to generate Cu-0 frequencies at about 300 em-l and to reproduce the observed 0-0 absorptions.Coupling between the 0-0 and Cu-0 vibrations could take place through off diagonal elements in both the 9and %' matrices and the results of one of these calculations are given in table I (calc. 11). From these results it is clear that the various linkage isomers do have slightly different vibration frequencies but that the magnitude of the splitting can be quite small and might easily remain unresolved in a band -3 cm-I wide. This result was not totally unexpected since Pimentel l4 has shown that the 0-0 vibrations in F-160-180and F-1SO-160 may differ by only 1.5 cm-l but it means that one cannot dismiss the possibility of end-on bonding in this system. The interpretation of the corresponding chromium atom/O spectra (fig. 1(c) and (d))follows exactly the same procedure.In the high frequency separation approxima- tion two force constants adequately reproduce all the observed frequencies (table 2 calc. I) and the intensity agreement is satisfactory if one realizes that the broader bands at 1146.7 and 1077.3 cm-l each consist of two overlapping peaks. There is no definitive evidence of linkage isomerisation using scrambled oxygen but similar GVFF calculations (table 2 calc. 11) indicate that the effect of this on the 0-0 frequencies could again be quite small. One final point remains concerning the number of metal atoms in these species. Copper and chromium vapour are both essentially monatomic and we have assumed that only one metal atom is involved in these reactions. However it is possible that some metal atom clustering takes place in the matrix prior to oxidation and that these species should be formulated as MX(OJ2.This question could only be resolved by an analysis of the metal-ligand vibrations and for the purposes of this paper we shall takex = 1. DISCUSSION These experiments indicate that when copper or chromium vapour is condensed at low temperatures in argon containing 10 % oxygen molecular bis dioxygen species M(02) are formed. The principal 0-0 stretching constants in these molecules are close to 6.0 mdyn/& and this suggests an 0-0 linkage similar to that present in the superoxide ion for which l5 KO = 6.2 mdyn/A. These compounds might be formulated as di-superoxides (0,)-M2+(0,)-but we cannot distinguish rigorously between end-on and side-on bonding.Ozin et al. favour side-on bonding in their discussion of the bis-superoxide complexes of Ni Pd and Pt but we believe that it is possible to argue in favour of end-on bonding on the basis of comparisons with other systems. J. H. DARLING M. 3. GARTON-SPRENGER AND J. S. OGDEN 8J The structure of matrix isolated lithium superoxide is fairly well established as being Li+( 1)-from i.-r. and Raman data.l* The 0-0 vibration in this molecule at 1097.4 Gm-' is reported to be very weak in the i.-r. and to be almost unaffected by changing the lithium isotope mass. substitution produces frequency shifts expected for an essentially isolated O2 vibration. In contrast the Li-0 band at 743.8 cm-l is strong in the i.-r.These observations are completely consistent with a C, structure since to a first approximation there is no molecular dipole change associated with the pure 0-0 vibration and this mode is only detectable in the i.-r. by virtue of rather weak coupling with the Li-0 mode of the same (A,) symmetry. If side-on bonding is present in CU(O~)~ and Cr(02), one might therefore conclude that the extinction coefficients of the observed 0-0 vibrations are quite low and that intense metal -02 vibrations lie below the limit of our spectrometer (200 cm-l). However the experi- ment in which chromium atoms were condensed with a matrix containing both 0 and CO indicates that the extinction coefficients of the 0-0 and C-0 vibrations are the same order of magnitude suggesting end-on 0 bonding.It is therefore interesting to compare these results with related experimental data for some dioxygen complexes of co-ordinated cobalt where exactly the same bonding problem remained unresolved until quite recently. Although the majority of 1 1 transition metal/O complexes are known to be side-on bonded,16 a number of cobalt complexes are now known in which molecular oxygen is believed to be end-on bonded. In particular Basolo et a1.l7*l8 have studied the i.-r. and e.s.r. spectra of a series of compounds with the general formula N N'-ethylene-bis(acetylacetoniminide)Co(B)(O& where B may be H20 DMF or substituted pyridine. These complexes all exhibit a very intense 0-0 vibration in the frequency region 1120-1 140 cm-l and the magnetic data indicates a bent Co-0-0 linkage.Similar conclusions have been reached by Ochiai l9 from e.s.r. studies on related salicylaldehyde derivatives and Rodley and Robinson have recently confirmed this geometry in their crystal structure determination of the benzoyl derivative.,O Here the O2 ligand is end-on bonded (Co-0-0 = 126") and the 0-0 bond length is very close to that found in the free superoxide ion. Both the intensity and general position of the 0-0 vibrations in these complexes suggest that the metal-0 linkage in Cu(02) and Cr(02) is very similar. Our spectroscopic results would then indicate C2hzigzag configurations for these molecules and this structure could also be adopted by the other binary transition metal di-superoxides known.9* lo From the viewpoint of high temperature chemistry these simple molecules would seem to be important intermediates in transition metal atom/02 reactions and it would be interesting to explore whether similar superoxo species also play a part in the initial oxidation of metal surfaces.In most cases this may be a very transient step prior to dissociative chemisorption but it is interesting to note that the oxidation of cadmium 21 gives CdO rather than CdO and that there is some evidence for non- dissociative chemisorption in the oxidation of thallium., We gratefully acknowledge the financial support of the Central Electricity Generat- ing Board for this work. L. Andrews J. Chem. Phys. 1969 50,4288. L. Andrews and R. R. Smardzewski J.Chem. Phys. 1973 58,2258. L. Andrews J. Phys. Chem. 1969,73 3922. L. Andrews J. Chem. Phys. 1971,54,4935. R. R. Smardzewski and L. Andrews J.Phys. Chem. 1973,77,801. A. Bos J. S.Ogden and L. Orgee to be published. A. Bos and J. S. Ogden J.Phys. Chem. 1973,77 1513. H. Huber and G. A. Ozin Canad.J. Chem. 1972,50,3746. H. Huber W. Klotzbucher G. A. Ozin and A. Vander Voet Canud.J. Chem. 1973,51,2722. lo J. H. Darling D. Phil. thesis (Oxford 1973). J. S.Anderson and J. S. Ogden J. Chem. Phys. 1969,51,4189. l2 J. H. Darling and J. S. Ogden J.C.S. Dalton Trans. 1972 2496. l3 D. W. Green J. Thomas and D. M. Gruen J. Chem. Phys. 1973,58,5453. l4 P. N. Noble and G. C. Pimentel J. Chem. Phys. 1966,44 3641. l5 F. J. Blunt P. J. Hendra and J. R.Mackenzie Chem. Cunzm. 1969,278. l6 V. J. Choy and C. J. O'Connor Coord. Chem. Rev. 1972,9,145. l7 A. L. Crumbliss and F. Basolo J. Amer. Chem. Soc. 1970,92 55. l8B. M. Hoffman,D. L. Diemente and F. Basolo J. Amer. Chem. SOC.,1970 92,61. l9 F. I. Ochiai J. Znorg. Nucl. Chem. 1973,35 1727. 2o G. A. Rodley and W. T. Robinson Nature 1972 235,438. 21 D. Michell and A. P. Smith Phys. Stat. Sol. 1968 27,291. 22 J. S. Ogden A. J. Hinchcliffe and J. S. Anderson Nature 1970 226,940.

ISSN:0301-5696    

DOI:10.1039/FS9730800075

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Determination of Dissociation Energies of Alkaline-Earth Chlorides Bromides and Hydroxides by Flame Photometry V. G. RYABOVA BY L. V. GURVICH,* AND A. N. KHITROV Institute for High Temperatures of the U.S.S.R. Academy of Sciences Moscow U.S.S.R. 127412 Received 17th September 1973 The ratio of the integral intensity of the bands MX and lines M where M = CaySr Ba and X = C1 Br and OH was measured in the spectra of 16 flames aHz+bOz +cNz+dHzO with additives of chlorine or bromine (T=1810-2580K). On the basis of these measurements it was found (in kcal mol-I) Do(CaC1) = 94.1& 1.6 ; Do(SrCl)= 95.6+ 1.8 ; Do(CaBr) = 75.7+ 5.4 ; Do(SrBr) = 78.4+4.4 ; Do(Ca-OH) = 96+ 3 Do(Sr-OH) = 95f3 Do(BaCl) = 106.8 +2.2 ; Do(BaBr) = 87.5f2.2 ; Do@a-OH) = 111 rt 4. The ratio of an atomic line intensity of M in the spectrum of flame without halogen to its intensity in the presence of halogen was investigated.The data obtained indicate that in the flame besides the monohalogenide and dihalogenide there is formed at least one metallic compound which contains 1 atom of halogen apparently MXOH. The approximate values of the bonding energies in the molecules MClz MBrz MClOH and MBrOH were determined. There are described in the literature two widely used methods of investigation of high-temperature reactions for subsequent determination of the equilibrium constants and enthalpies of these reactions and the dissociation energies of the molecules taking part therein. One of them is based on the mass-spectrometric study of the equilibrium of the reactions in the Knudsen cell the other is based on spectrophotometric studies in flames usually the equilibrium between the metal atoms injected into the flame with the products of combustion.The dissociation energies of separate molecules obtained by both methods are in some cases in fair agreement (for halogenides and hydroxides of alkali metals In Ga and T1) while in other cases (oxides of alkaline-earth metals) disagreements are large. The mass-spectrometric and spectrophoto- metric investigations of the dissociation energies of fluorides and chlorides of CaySr and Ba 1-6 resulted in systematic discrepancies. In all cases the values Do(MX) found by flame photometry were higher while the values Do(MX-X) were lower than those obtained in the mass-spectrometric measurements.Since the values d(MX) in flames during the spectrophotometric investigations were determined 4-6 on the basis of indirect data the above discrepances could be caused by the presence in the flames of other metal compounds containing 1 atom of halogen. This paper aims to eliminate these discrepancies by means of a modified spectrophotometric method and to study the dissociation energies of chlorides bromides and hydroxides of alkali-earth metals. To perform this study there was selected a group of rich hydrogen+air flames of a variable composition similar to those used in earlier studies.7-9 83 DISSOCIATION ENERGIES THEORETICAL RELATIONS As shown ea~-lier,~*lO in rich hydrogen-air flames an equilibrium of the bio- molecular exchange reactions of atoms M with the flame gases M+HX +MX+H (1) is obtained.Here X = OH 0,F or C1 (the last two if halogens or their compounds be injected into the gas mixture). The enthalpy of reaction (1) can be found by the 3rd-law method when the absolute values of the partial pressures of all components in (1) and the equilibrium constants Kl are specified or by the 2nd-law method if the dependence of Kl or some proportional values is investigated within some interval of temperatures. If in a flame spectrum the spectral transitions of the atom M and the molecule MX are observed simultaneously the equilibrium constant of reaction (1) can be written as where Z(MX) and Z(M) are the integral intensities of the spectral transitions of MX and M B(T) is the coefficient depending on the observed spectral transitions C is a coefficient that does not depend on the temperature but does include the prob- abilities of the corresponding transitions their frequencies the parameters of the recording optical system etc.Determination of the absolute value of C and there- fore Kl is as a rule impossible particularly because of the absence of the data on the probabilities of the transitions for the molecules MX. However the value Kl/Ccan be calculated by measuring the ratio I(MX)/Z(M) computing B(T) and determining the values p(H) and p(HX) or their ratio. If these data can be obtained for an adequately wide temperature interval the value AH(1) for an average temperature T can be determined by the second-law method from If in the spectrum MX the integral intensity of a single rotational line is measured the coefficient B(T)takes the form where c2 = 1.438 83 cm is the second radiation constant Tis the flame temperature Q(MX) and Q(M) are the partition functions of MX and M Too+ G,(u) +F,(J) and Emare the energies (in cm-l) for those states of MX and M from which corresponding transitions are observed.When the integral intensity of a whole band MX is measured the expression for B(T)assumes the form where Q:ot(MX) is the rotational partition function of MX in a vibrational state with a quantum number zi of the upper electronic state of the observed transition. L. V. GURVICH V. G. RYABOVA AND A. N. KHITROV It is obvious that if the bands of the molecules MX and MY are observed in the flame spectra the enthalpy for reaction MX+HY = MY+HX (6) can be found from the measurements of Z(MY)/Z(MX).The enthalpies of the metal atom reactions with halogens in hydrogen-air flames can be determined also by another method. If a bivalent atom M forms compounds with halogen by reactions M+HX + MX+H (1) MX+HX +MX,+H (7) no other compounds of metal with halogen being present in the flame the ratio of the line intensity in flame spectrum without halogen Zo(M)to its intensity in the presence of halogen Z’(M) is defined by the relation Here po(M) is the partial pressure of the metal in the flame without halogen and p@M) is the sum of the partial pressures of all metal compounds in the flame.The latter can easily be calculated by the ratio p(CM) = ~(M)n(H,0)/55.5ZNi (11) where c(M) is the molar concentration of the metal salts solution injected into the flame n(H20) is the number of moles H20 in the unburned gas per mole O2 and ENt is the number of moles of the components in the combustion products per mole O2 in the unburned gas (see table 1). In those cases when besides MX there are formed one or several compounds of the metal with one halogen atom the expression for Al assumes more complex form (see below). EXPERIMENTAL The measurements were done in 16 rich hydrogen-oxygen-nitrogen flames with tempera- tures from 1810 to 2580 K. The flames were burnt on a burner of the Meker type with 2 coaxial shield flames as was described in ref.(7)-(9). The compositions of combustible mixtures were checked by means of calibrated capillary- type flowmeters. They are listed in table 1. The accuracy of finding the content of each component in the mixture is better than 3 %. The metals were injected into the flames by means of the Lundegard sprayer in the form of diluted solutions of their salts. For this purpose a strictly constant amount of N2 is blown through the sprayer. The amount of water fed into the flame was determined by means of CaCl traps put on the burner during free-of-flame experiments when nitrogen was blown through the sprayer and the burner. Chlorine was introduced into the flame from a container through a calibrated glass capillary tube with a differential pressure gauge filled with H2S04.In order to create standard conditions for the experiment the capillary tube was placed in an ultrathermostat. Bromine was added to unburned gases in the form of vapours of CH2Br2 or C2H5Br with a current of nitrogen blown through a bubbler filled with the bromine-containing liquid. The bubbler was thermostatted in the ultrathermostat. The quantity of substance fed into the flame per unit time with a specified amount of nitrogen at a given temperature of the thermostat was calculated by weighting the bubbler before and after the calibrating experi- ments. The accuracy of determining the amount of halogen thus added to the flame was better than 5 %. TABLE1.-FLAMECOMPOSITIONS AND TEMPERATURES (1 atm = 101.325 kPa) flame unburned gas T/K burned gas lO&Hz)*/ 12LH20)*/ lOp(N2)'l lO$:W/ lytgH)t/ SNt Hz 02 N2 H20 Calc.expt. atm VC 4 1 4 0.030 1974 1860 2.49 2.53 4.98 0.296 3.20 8.03 VIIC 3.5 1 4 0.028 2070 1930 1.99 2.69 5.31 0.547 3.38 7.53 IVC 3 1 4 0.026 21 62 201 5 1.42 2.88 5.69 0.746 3.19 7.03 z VIC 2.5 1 4 0.025 2240 21 30 0.764 3.09 6.12 1.23 3.oo 6.53 v1 M 0 Vd 4 5 0.033 1818 1745 2.21 2.25 5.53 0.124 3.37 9.03 2 > VIId 3.5 5 0.03 1888 1815 1.76 2.38 5.86 0.162 3.12 8.53 r-l H IVd 3 5 0.030 1964 1885 1.24 2.53 6.23 0.258 2.79 8.03 0 VIIIb 4.5 3 0.017 2100 1975 3.32 2.69 3.99 0.813 6.78 7.52 Z Vb 4 3 0.01 6 2192 2070 2.84 2.87 4.27 1.41 7.35 7.02 VIIb 3.5 3 0.013 2291 2190 2.29 3.08 4.60 2.51 7.45 6.49 IVb 3 3 0.012 2396 2310 1.65 3.32 4.97 4.11 7.09 6.02 VIb 2.5 3 0.011 2495 2430 0.909 3.57 5.41 5.50 7.38 5.52 VIIIa 4.5 1 2 0.013 2300 2210 3.81 3.08 3.06 3.71 9.92 6.51 Va 4 1 2 0.012 2400 2320 3.29 3.32 3.31 6.23 10.5 6.01 VIIa 3.5 1 2 0.011 2505 2450 2.67 3.59 3.60 10.3 12.7 5.53 IVa 3 1 2 0,010 2610 2580 1.95 3.87 3.94 15.6 17.6 5.06 * The equilibrium partial pressure at experimentally measured temperature of the burned gas.t The partial pressure obtained by the "lithium method ". $ The number of moles in burned gas per mole O2in unburned gas mixture. L. V. GURVICH V. G. RYABOVA AND A. N. KHITROV Flame temperatures at a height of 15 to 40-60 mm from the reaction zone were measured by the Na Li and Ca line-reversal method. The results of measurements using the lines of different elements agree for each flame within 15 K.The temperature was maintained con- stant within the same range from 15 up to 40-60 mm above the reaction zone. The measured temperatures are given in table 1. They are considerably lower than the calculated adiabatic temperatures of these flames presented in the same table-this is typical for a flame on an intensively cooled burner made from capillary tubes. The composition of the products of combustion was calculated theoretically at a measured flame temperature. The equilibrium partial pressures of H20 H2 N2 and H so found are given in table 1. As is well-known in rich hydrogen-air flames p(H) can considerably exceed the equilibrium values. Therefore the values p(H) were also found experimentally by the " lithium method " described in ref.(9). To this end the values of p(Li) formed due to the injection of a solution of LiCl into the given flame were determined by the absolute intensity of the line Li 6707 A in the flame spectra 20 and 30 mm above the reaction zone. Assuming that in the flames used in the experiment p@Li) = p(Li)+p(LiOH) the values p(H) were calculated from the equilibrium constants of the reaction * Li+ H20 + LiOH+ H (12) and the values ofp(Li) p(Li0H) andp(H20). Values of obtained p(H) at a height of 20 mm above the reaction zone are given in table 1. The errors do not exceed 25 %. OPTICAL MEASUREMENTS Measurements of the ratio of the integral intensity of the molecular bands of MX where X = C1 Br and OH and the lines of the atoms M where M = Ca Sr and Ba in the flame spectra were made by photographic techniques.The spectra were registered by a ISP-51 TABLE 2.-THE SPECTRAL TRANSITIONS SELECTED FOR MEASUREMENTS OF I(M) atom AiA transition 10-8 Am Is-1 Ca 4227 'P1-1So 1.84 Sr Ba 4607 5535 'P,-'So'P1-'So 1.60 1.01 TABLE 3.-THE SPECTRAL TRANSITIONS SELECTED FOR THE MEASUREMENTS OF (MX) molecule transition CaCl 5934 B2C -+x2z (0-0,l-1,2-2) SrCl 6359 A2n++ x2z (0-0,l-1,2-2) BaCl 5240 A2rI+.+ x2z (0-0,l-1,2-2) CaBr 6103 B2Z -+ X2C (0-0 1-1,2-2) SrBr 6418 B2Z + X2Z (1-0,2-1,3-2) BaBr 5208 c2n33 x2z (1-1,2-2,3-3) CaOH 5360 CT* 3 x2z (1-1,2-2.3-3) 5540 ? SrOH 6230 ? 6074 ? BaOH 4870 ? 5120 ? instrument with a camera f = 270 mm. The flame was focused at the slit of the spectro- graph at full size and a sample was cut from the flame image 20 mm above the reaction zone.An " isopanchromatic " film type 15-800 was used as photographic material. On each spectrogram there were taken spectra of 4 flames and a 9-stage optical wedge. Given in * K12was calculated for &(LiOH) = 104 kcal/moi ; the probcbility for the line Li 6707A transition was taken to be 3.6 x lo7s-l.J1 DISSOCIATION ENERGIES tables 2 and 3 are the wavelengths and some characteristics of the spectral transitions used in these measurements. The relative intensities of the atomic line and molecular band were found by the density intensity calibration curve plotted by the optical wedge at the wavelength of the line (or band) due to the microdensitometric measurement of the spectrograms.The band line and wedge were measured using a constant width of microdensitometer slit. The width was selected so that practically all the molecular band (group of bands) was within the slit of the micro- densitometer. The variation of the sensitivity of the photographic materials with the wave- length was not taken into account since it does not depend on the temperature of the radiation source and the corresponding coefficient is included into the value C in eqn (3). I IC 20 30 104p(HCl)/atm FIG.1.-Variation of I,,(M)/I‘(M) withp(HC1). a,Ca in flame VIId ; b Sr in flame VIId ; c Ba in flame VIId ; a’ Ca in flame IVc ; b’ Sr in flame IVc ; c’ Ba in flame IVc. The dependence of the ratio Io(M)/I’(M) on the quantity of halogen added to the given flame was measured by a photoelectric method.For this purpose the image of the flame was focused at the input slit of a YM-2 monochromator at a fullisize and a 1 mrn sample was cut from the image 20 mm above the reaction zone by means of the Hartman diaphragm. A photomultiplier(FEU-18 or FEU-22)was placed behind output slit of the monochromator. The signal from the photomultiplier was fed to a d.c. amplifier and was measured by a digit31 voltmeter. The typical results of these measurements are presented in fig. 1 and 2. RESULTS If traces of alkaline-earth metals are injected into rich hydrogen-air flames the resonance line of atoms M as well as bands of molecules MO and MOH are present in the flame spectra.’ 4-16 When small amounts (0.01-0.1 %) of chlorine or bromine are added to pre-mixed gas the band systems of monohalide molecules MX appear in the flame spectra as well and the intensities of atomic lines as well as molecular bands L.V. GURVICH V. G. RYABOVA AND A. N. KHITROV I 0 10 20 30 104p(HBr)/atm FIG.2.-Variation of lo(M)/I’(M) with p(HBr). a Ca in flaw VIId ; bySr in flame VIId ; c Ba in flame VIId ; a’ Ca in flame IVc ; b’ Sr in flame IVc ; c’ Ba in flame IVc. of MO and MOH decrease. Therefore the dissociation energies of halides and hydroxides of alkaline-earth metals can be obtained by the methods described above. MONOHALOGENIDES OF METALS The results of measurements of the values I(MX)/I(M) in the spectra of 16 flames when small amounts of Cl, C2H,Br and CH2Br2 and diluted solutions of metal salts (0.01 M CaCl, 0.002 M SrCl and 0.009 M BaCl,) were added to the mixtures feeding the flames are given in tables 4 and 5.The relative integral intensities of the resonance lines of the metals given in table 2 and of the typical groups of 3 bands of molecules MX given in table 3 were measured. Each value of log Z(MX)/I(M) is an average from 3-5 spectrograms. For BaBr the independent measurements were made by the bands of the subsystems C2n+-X2Z and C211,-X2E. The values p(HX) were calculated on the basis of the measurements of the amount of halogen (or a halogen-containing material) injected into the flame according to the relation PWX) = P(W/U +P(H)/K,) (13) where K1,is the equilibrium constant for the reaction HZ+X eHX+H (14) whilep(CX) = rn/CN,and rn is the number of gram-atoms of halogen in the unburned gas per mole of O2 The values B(T)given in tables 4 and 5 are calculated by the ratio (9,taking into account that there was measured the total integral intensity of three bands with u’ = 0,l and 2 or v’ = 1 2 and 3 Thus in the case of all three chlorides and CaBr the exponential term in (5) assumes the form TABLE 4.-RESULTS OF DETERMINATION OF IOg Kl/C FOR REACTION M+HCl+ MCI+ H (1 atm = 101.325 kPa) ilame atm log B(T) log KIIC atm log B(T) log KIIC atm log B(T) log K1 IC vc 1.33 0.125 -2.033 -1.527 1.04 0.115 -1.702 -1.097 1.19 0.372 0.666 1.469 VIIC 1.33 0.088 -1.843 -1.451 1.04 0.123 -1.620 -0.983 1.19 0.41 2 0.667 1.532 IVC 1.34 0.095 -1.829 -1.371 1.04 0.065 -1.522 -0.970 1.20 0.456 0.67 I 1.552 g VIC 1.36 0.001 -1.703 -1.357 1.03 0.068 -1.407 -0.871 1.21 0.462 0.666 1.523 > Vd 1.31 0.278 -2.204 -1.517 1.03 0.328 -1.857 -1.025 1.17 0.423 0.671 1.553 2 YIId 1.32 0.253 -2.105 -1.479 1.03 0.273 -1.765 -1.011 1.18 0.493 0.668 1.583 1Vd 1.33 0.232 -2.000 -1.445 1.03 0.220 -1.672 -1.017 1.18 0.517 0.666 1.555 Z YIIIb 1.29 -0.280 -1.886 -1.437 2.32 0.175 -1.575 -0.934 1.42 0.090 0.664 1.439 Vb 1.29 -0.325 -1.775 -1.344 2.32 0.096 -1.467 -0.970 1.43 0.109 0.662 1.483 2 VIIb 1.17 -0.449 -1.644 -1.289 2.10 -0.062 -1.349 -0.861 1.29 0.030 0.660 1.450 m IVb 1.17 -0.574 -1.526 -1.317 2.10 -0.127 -1.285 -0.840 1.29 O.OO0 0.658 1.397 VIb --2.05 -0.133 -1.143 -0.720 1.26 0.014 0.655 1.436 VIITa 1.17 -0.547 -1.624 -1.244 2.11 -0.162 -1.331 -0.820 1.30 -0.071 0.660 1.473 Va 1.17 -0.659 -1.506 -1.215 2.12 -0.306 -1.234 -0.844 1.30 -0.138 0.662 1.43 1 VIIa 1.17 -0.774 -1.407 -1.144 2.11 -0.409 -1.129 -0.756 1.30 -0.223 0.655 1.424 IVa --2.05 -0.580 -1.033 -0.679 1.26 -0.264 0.65 1 1.531 TABLE 5.-RESULTS OF DETERMINATION OF log K,/C FOR REACTION M+HBr $ MBr+ H (1 atm = 101.325 kPa) Flame atm log B(T) log Ki IC atm log B(T) log KiIC atm vc 1.24 0.152 -2.151 -1.591 1.35 0.120 -1.816 -1.326 8.74 0.100 0.735 1.394 VIIC 1.20 0.023 -2.056 -1.583 1.37 0.005 -1.732 -1.338 8.51 0.060 0.732 1.391 IVC 1.17 0.088 -1.942 -1.419 1.37 -0.01 5 -1.631 -1.280 8.55 0.070 0.727 1.369 VIC 1.04 -0.023 -1.803 -1.368 1.22 -0.055 -1.509 -1.172 7.57 0.115 0.724 1.441 Vd 1.03 +0.110 -2.336 -1.712 1.19 +0.150 -1.978 -1.374 7.30 0.155 0.733 1.553 VIId 1.05 0.244 -2.228 -1.512 1.21 0.090 -1.882 -1.381 7.46 0.160 0.738 1.519 Wd 1.04 0.226 -2.1 16 -1.460 1.13 0.080 -1.785 -1.313 7.49 0.165 0.734 1.470 VIIIb 1.60 -0.182 -2.070 -1.619 1.70 -0.240 -1.677 -1.310 9.15 -0.075 0.730 1.532 Vb 1.59 -0.212 -1.873 -1.422 1.72 -0.225 -1.571 -1.166 9.25 -0.105 0.727 1.522 VIIb 1.45 -0.383 -1.734 -1.46 1.54 -0.380 -1.448 -1.144 8.29 -0.245 0.723 1.432 IVb I .42 -0.529 -1.607 -1.438 1.51 -0.430 -1.336 -1.095 8.13 -0.250 0.719 1.410 VIb 1.19 -0.459 -1.491 -1.158 --6.80 -0.270 0.71 6 1.482 VIIIa --1.67 -0.410 -1.429 -1.065 8.98 -0.245 0.723 1.521 Va --1.68 -0.405 -1.327 -0.936 9.03 -0.340 0.723 1.449 VITa ----8.54 -0.470 0.715 1.419 IVa ---I -7.18 -0.575 0.709 1.524 DISSOCIATION ENERGIES The values of log K,/C obtained for 6 monohalogenides are also listed in tables 4 and 5.As an example in fig. 3 is shown the dependence of log Kl/Con T-' for CaCl and CaBr. The values of AHl(T) calculated by the second law method are presented in table 6. From table 6 it is clear that the data obtained for CaBr and SrBr are a -1.0 6 2l -1.0 4.0 4.5 5.0 5.5 104 KT-1 FIG.3.-Variation of log Kl/Cwith T-' for CaCl and CaBr. a CaCl ; b CaBr. much less reliable than for 4 other molecules. This is explained by the fact that in the flame spectra the bands of CaBr and SrBr are partially overlapped by the bands of hydroxides of the same metals and this hinders the measurements particularly in hotter flames.~.-ENTHALPIE~ TABLE OF REACTION (1) FOR MC1 AND MBr (1 cal = 4.184 J) AH1(T)*/kcal mol-1 AHI(O)*/kcal mol-* CaCl 10.6k0.7 S.lkO.7 SrCl 9.2+ 0.8 6.6+ 0.8 BaCl -2.9+ 1.O -4.6+ 1.O CaBr 13.1 +2.6 11.O+ 2.6 SrBr 10.5k2.1 8.3k2.1 BaBr 0.9+ 0.9 -0.7+0.9 * The errors are standard deviations. Also given in table 6 are the values Hl(0)obtained with the values of H(T)-H(0) for HX H and M from ref. (12) and for MX calculated with the molecular constants recommended in ref. (13). The latter were also used for calculation of the values B(T)in tables 4 and 5. MONOHYDROXIDES OF METALS The measurement of the ratio Z(MOH)/Z(M) in the flame spectra makes it possible to determine the values log Kl/Cand the enthalpy for the corresponding reactions.The measurements of the values Z(M0H) were performed on the bands given in table 3 and the measurements of Z(M) were made on the lines given in table 2. The values of log Z(MX)/I(M) are given in tables 7 and 8 the results of the measurement TABLE 7.-RESULTS OF DETERMINATION OF IOg Ki/C FOR REACTION Ca+ HzO CaOH+H flame A= 6230A A = 5540A log Z(MW-4M) log B(T) * log B(T)t log KIIC * log Ki IC t log-I(MWI(M) log B(T) * log B(T)t log K11C * log KllC t vc 0.267 -1.895 -0.724 -3.525 -2.355 0.585 -1.224 -0.054 -2.537 -1.367 VIIC 0.311 -1.784 -0.595 -3.374 -2.185 0.645 -1.137 0.052 -2.392 -1.204 IVC 0.359 -1.649 -0.438 -3.258 -2.047 0.791 -1.029 0.183 -2.236 -1.024 Vlc 0.3 80 -1.485 -0.246 -3.1 18 -1.879 0.847 -0.898 0.341 -2.064 -0.824 Vd 0.289 -2.108 -0.972 -3.644 -2.507 0.586 -1.393 -0.256 -2.63 1 -1.495 VIId 0.345 -1.983 -0.827 -3.521 -2.364 0.630 -1.294 -0.138 -2.547 -1.390 IVd 0.380 -1.854 -0.676 -3.418 -2.254 0.719 -1.192 -0.014 -2.430 -1.253 VIIIb 0.057 -1.711 -0.510 -3.299 -2.049 0.388 -1.078 0.123 -2.286 -1.085 Vb 0.048 -1.569 -0.344 -3.1 14 -1.889 0.448 -0.965 0.260 -2.110 -0.885 VIIb 0.019 -1.402 -0.149 -3.001 -1.747 0.443 -0.832 0.422 -2.007 -0.753 IVb 0.017 -1.249 0.032 -2.903 -1.622 0.468 -0.707 0.573 -1.911 -0.630 VIb 0.078 -1.108 0.199 -2.715 -1.408 0.537 -0.594 0.713 -1.741 -0.434 VIIa -0.071 -1.376 -0.117 -2.941 -1.682 0.335 -0.811 0.448 -1.970 -0.71 1 Va -0.118 -1.237 0.047 -2.855 -1.571 0.284 -0.699 0.585 -1.915 -0.631 VIIa -0.197 -1.087 0.224 -2.734 -1.423 0.244 -0.577 0.734 -1.783 -0.472 IVa -0.285 -0.948 0.389 -2.575 -1.238 0.216 -0.464 0.873 -1.589 -0.252 * calculated for bent model of CaOH ; t calculated for linear model of CaOH.TABLERESULTS OF DETERMINATION OF log K1/c FOR REACTION M+ H20 + MOH+ H (M = Sr and Ba) flame SrOH BaOH log EX) I(M) I(M) log B(T)* log NT) t log KiIC * log KI IC t log -I(MW log B(T)* log b(T)t log KjIC * log KI/C t vc 0.372 -1.038 0.160 -2.552 -1.354 -0.089 1.581 2.75 I -0.46 0.764 VIIC 0.425 -0.944 0.250 -2.419 -1.226 0.004 1.575 2.764 -0.322 0.S68 IVC 0.516 -0.839 0.363 -2.282 -1.081 0.115 1.568 2.779 -0.285 0.926 z v1 * VIC 0.624 -0.722 0.513 -2.088 -0.853 0.255 1.563 2.803 -0.195 1.045 tn 2 Vd 0.403 -1.200 -0.210 -2.640 -1.450 -0.205 1.595 2.732 -0.434 0.703 9 VIId 0.387 -1.105 0.086 -2.027 -1.436 -0.147 1.586 2.742 -0.443 0.713 r! IVd 0.450 -1.03 0.190 -2.569 -1.376 -0.041 1.579 2.756 -0.420 0.757 0 VIIIb ---0.311 1.572 2.773 -0.335 0.866 m Vb 0.225 -1.697 0.434 -2.151 -0.934 -0.271 1.567 2.792 -0.297 0.928 2 td VIIb 0.232 -0.661 0.592 -2.047 -0.794 -0.193 1.563 2.817 -0.247 1.007 2 v1 IVb 0.300 -0.543 0.737 -1.914 -0.634 -0.124 1.561 2.842 -0.234 1.047 m VIb 0.377 -0.433 0.874 -1.739 -0.432 -0.004 1.560 2.867 -0.127 1.180 VIIIa 0.140 -0.641 0.617 -1.995 -0.736 -0.283 1.563 2.821 -0.214 1.044 Va 0.133 -0.529 0.753 -1.897 -0.614 -0.276 1.561 2.844 -0.21 5 1.068 VIIa 0.105 -0.420 0.891 -1.765 -0.454 -0.257 1.560 2.871 -0.147 1.164 IVa 0.062 -0.307 1.030 -1.581 -0.250 -0.260 1.559 2.897 -0.043 1.295 L.V. GURVICH V. G. RYABOVA AND A. N. KHITROV by the band at 5120 A for BaOH being not included into the table to save space. In contrast to monohalogenides of alkaline-earth metals the interpretation of the data obtained for MOH is very difficult since the analysis of their spectral transitions is still not available and even the structures of the molecules MOH are unknown. For preliminary treatment of the experimental data the values B(T)in eqn (3) were calculated under the assumption that the observed band of each molecule is a transition between the single vibrational levels of the upper and ground states. The calculations were made for 2 models of the molecule MOH-linear and bent-with estimated values of the constants given in table 18.Therefore two versions of the values B(T) and the corresponding values log Kl/C are given in tables 7 and 8. Fig. 4 illustrates 0-9-IG-G -2.0 -I I c 3.8 4.3 4.4 5.3 104~/~ FIG.4.-Variation of K1/Cwith T-' for CaOH. a,Ca+H,O = CaOH+ H by the band 6230 A; 6,Ca + H2O = CaOH+ H by the band 5540 8 ; c CaCl+ H20 = CaOH+ HCI by the band 6230 A ; - tCaOH = 180" - - - LCaOH = 105". the dependences of log K1/Con T-I for CaOH obtained from measurements by the bands at 5540A and 6230A for two models of the molecule. Given in table 9 are the values Hl(T)calculated by the second-law method for both models of the molecule MOH as well as the corresponding values H,(O).The latter were obtained using the values H(T)-H(0) for MOH calculated with the constants given in table 18 and for M H and H2Q from ref. (12). As seen in table 9 the difference in the values H(T)-H(0) for the linear and bent models of MOH substantially compensates for the corresponding difference in the values B(T). MEASUREMENTS OF THE DEPENDENCE I&f)/Z'(M) The variations of the intensity of the resonance lines of metal atoms in flame spectra were investigated under conditions when the content of halogen in the un-burned gas was varied from to 0.4 %. Typical examples of the variation of TABLE ~.-ENTHALPIES OF REACTION (1') AND BOND ENERGIES M-OH (kcal mol-I) (1 cal = 4.184 J) U CaOH SrOH BaOH LMOH = 105" LMOH = 180" LMOH= LMOH= LMOH = 105" LMOH = 180" 1 = 5540A f = 6230A A =; 5540A 1 = 6230A 105" 180" 1 = 4870A I = 5120A 1 = 4870A 3.= 5120A AHl(T) * 25.8k0.7 26.3k0.7 30.7k0.8 31.010.7 27.650.7 31.5k0.7 9.310.8 12.3k0.8 14.1k0.8 17.3+0.8 AHdO) * 23.3k0.7 23.8k0.7 25.410.8 25.7k0.8 25.0k0.8 26.010.8 7.4-LO.8 10.4k0.8 9.3k0.8 12.5k0.8 D,(M-OH) * 95.250.7 94.7k0.7 93.110.8 92.8k0.8 93.5k0.7 92.5k0.7 111.1+0.8 108.110.8 109.2k0.8 106.0+0.8 z 94+ 1.5 93+ 1.5 108.6k2.1 96 95 110 99 96 114 * errors are standard deviations. t correction is included for transitions from 10 vibrational levels of excited state. $ from the measurements for reaction (19). L. V. GURVICH V. G. RYABOVA AND A. N. KHITROV Zo(M)/Z’(M) with the values p(HX) where p(HX) were calculated by ratio (13) are given in fig.1 and 2. The values of the coefficients Al and A2 in eqn (8) calculated by least squares on the basis of results of measurements in different flames are presented in table 10. TABLECOEFFICIENTS A1 AND Az IN EQN (8) OBTAINED BY THE LEAST SQUARE METHOD (1 atm = 101.325 kPa) atom Ca flame vc Io(M)/Z’\W =f[~(HCf)l10-2 Al/atm-10-4 Az/atm-2 5.3k2.1 25.0+ 6.3 5.2+ 2.7 24.3 +7.1 IVC 5.1k0.7 4.1k1.3 2.4+ 0.9 19.6k2.6 VIId VIIIb 10.9+ 1.3 6.3 k0.6 10.4k4.2 4.7& 2.0 6.4f 1.9 3.6+ 1.1 41.O+ 6.8 25.0k4.5 VIIb 4.2+ 1.1 3.7k 1.6 - - IVb - - 2.5+ 1.0 10.4+ 3.6 VIIIa 3.2k0.4 4.6+ 1.9 1.4+ 0.4 S.l+ 1.7 Va 3.5k0.8 0.7+ 0.2 - - VIIa 2.0+ 0.8 1.2k0.3 c - Sr vc 11.O+ 3.7 16.0+ 5.2 5.7+ 1.5 72.0+ 5.4 IVC - - 5.7+ 1.1 36.0k4.1 VIC 6.0+ 1.8 3.5+ 1.1 - - VIId 11.O+ 4.0 77.0+ 7.0 14.0+ 2.6 86.0+ 11.0 VIIIb - - 1.1k0.3 30.0+ 10.0 IVb - - 4.9+ 1.o 7.9k41.0 VIIIa 2.1k0.7 7.2+ 1.4 - - VIIa - - 4.7k0.6 5.0+ 2.4 Ba vc 23.0* 2.0 23.0k2.0 13.0+ 5.0 77.0+ 19.0 IVC 5.85 0.5 35.Of20.0 - - VIId VIIIb 20.0+ 6.0 4.1k2.0 68.0k 20.0 54.0+ 8.0 14.0+ 7.0 9.8+ 2.0 190.0+ 33.0 30.0+ 7.7 IVb 3.1k0.4 2.9+ 1.5 3.4k0.7 7.0+ 2.0 VIIIa 4.3k0.5 5.0+ 1.9 4.5+ 0.6 18.0+ 2.1 VIIa 1.8f 0.2 1.7+ 0.7 - - * errors are standard deviations.To calculate the equilibrium constants Kl and K from the values Al and A2,it is necessary to know the values p@M) and po(M). The partial pressure of the metal in flames in the absence of the halogen po(M) given in tables 11 and 12 were determined on the basis of measurements of the absolute intensities of their atomic lines in the flame spectra by the method described earlier.’ The values of the absolute proba- bilities of spectral transitions l1 used in the calculations are given in table 2.The values p@M) were calculated by the ratio (1 1) referring to the concentrations of the used solutions of salts and the data of table 1. They are also listed in tables 1 1 and 12. The comparison of the values Kl calculated by the relation with the values K1calculated by the equation UO) R In K = A@*(T)-T and the values AHl(0) given in table 6 has Shawn the presence of systematic dis-agreements. In all cases the values K1 found through Al are higher than those S8-4 TABLE11.-DETERMINATION OF THE VALUES K FOR CHLORIDES OF Ca Sr AND Ba (1 atm = 101.325 kPa) flame Ca Sr Ba 107~;wi (MI/ lO*p(ZM)/ 10lOPo(M)/ 107A;M)/ Ki K7 lo a4om atm K1 K7 atrn K7 vc 6.64 1.36 50.0 16.2 13.6 1.51 9.0 17.4 6.06 58.2 14.1 IVC 6.74 1.69 19.2 --5.93 6.00 55.3 65.4 VIC --2.10 13.9 2.12 10.0 --VIId 27.5 6.64 1.26 19.4 17.6 13.5 1.44 39.7 17.7 5.89 59.2 57.0 VIIIb 16.4 3.95 1.64 31.9 --11.5 3.56 56.0 136.0 VIIb 7.20 3.64 2.09 49.5 ----IVb ----2.08 3.30 50.6 41.9 VIIIa 12.1 3.62 2.13 63.1 5.00 7.23 2.30 44.7 5.25 3.26 52.2 55.7 I Va 9.60 3.66 2.39 12.7 ---VIIa 10.2 3.68 2.71 26.3 --2.92 3.31 48.6 60.5 TABLE12.-DETERMINATION OF THE VALUES OF K FOR BROMDES OF Ca Sr AND Ba (1 atm = 101.325 kPa) flame ca Sr Ba 109pa;&M)I 1O7~@M)/ 1O9~o(M)/ 1O8pGM)/ 107p(=w atm K1 K7 atm atm K1 K7 atm K1 vc 25.0 6.64 0.59 112 16.2 13.6 1.39 42.3 6.06 18.9 IVC 8.58 6.74 0.77 204 4.98 13.8 1.72 58.2 -VIC -----VIId 27.5 6.64 0.54 181 17.6 13.5 1.28 49.8 5.89 18.3 VIIIb 16.4 3.95 0.72 390 10.6 7.89 1.63 39.1 3.56 19.2 I I VIIb ----IVb 4.79 3.66 1.16 343 1:83 7.29 2.39 60.5 3.30 19.8 VIIIa 12.1 3.62 1.02 234 --3.26 19.7 Va -----VIIa -3.60 7.35 2.73 60.6 - DISSOCIATION ENERGIES calculated through eqn (1 5) and the discrepancies for all compounds particularly for chlorides and BaBr considerably exceed the values due to the possible errors in Al and AH,(O).This apparently indicates that in the flames besides the molecules MX at least one compound with one atom of halogen is formed by alkaline-earth metals.Thus the values Kl AH1 and Do(MX) cannot be determined from the values Al. Values of A2 listed in table 10 make it possible to determine the equilibrium constant of reaction (7). The required values of Kl were calculated by relation (15) using Hl(0) from table 6. They are presented in tables 11 and 12 together with K7 = A2P2(WP@M)l&Po(M). The enthalpies of reactions (7) and the corresponding values Do(MX-X) were calculated from values of K7 obtained by the 3rd-law method. TABLEI3.-BOND ENERGIES (MX-X) OBTAINED FROM K1 (kd m0I-l) (1 cal = 4.1843) flame Do(CaC1-Cl)/kcal mol-1 Do(SrCI-Cl)/kcal mol-1 Do(BaCl-Cl)/kcal mol-1 D (CaBr-Br)/Real mol-1 Do(SrBr-Br)/kcal mol-1 Do(BaBr-Br)/kcal mol-1 vc 121 111 111 107 103 104 IVC 119 - 117 111 106 - VIC - 112 - - - - VIId 118 115 113 108 107 107 VIIIb 120 - 120 113 104 107 VIIb 124 - - - - - IVb - - 116 115 107 110 VIIIa 125 118 117 113 - 112 Va 118 - - - - - VIIa 122 - 119 - 108 - 3rd law average* 2ndlaw 121+2.6 112+8 11423.1 103+40 116k 3.2 97+ 10 11123.1 82+ 7 106+ 1.9 go+ 4 l08* 3.1 83+ 9 * errors are standard deviations.HYDROXIHALOGENIDES OF METALS The data analysis has shown that if under experimental conditions in the flames only two compounds with one halogen atom are formed by alkaline-earth metals these compounds would be monohalogenide MX and hydroxihalogenide MXOH. The latter can be formed through the following balanced reactions MX+H,O +MXOH+H (16) and MOH+HX e MXOHfH. (17) If no other compounds of the investigated metals containing 1 atom of halogen but MX and MXOH are formed in flames the coefficients Al are connected with the values Kl 6 and Kl through the relations where Ki is the equilibrium constant of the reaction M+H,O +MOH-tH.TABLEIA-EQUILIBRIUM CONSTA U'S FOR EACTIONS (16) AND (17) Bame Ca sr Ba chloride-. bromide chloride bromide chloride bromide K; KI6 K17 K16 K17 K; Ki6 K17 K16 K17 K; K16 K17 K16 Kr 7 vc 0.044 0.41 13 0.96 13 0.045 0.26 8.7 0.15 4.6 3.0 0.55 11.0 0.92 5.7 -IVC 0.075 0.83 19 1.0 10 -0.32 3.8 0.36 5.3 -A VIC -- - 0.56 11.0 ---VIId 0.036 0.84 29 1.5 22 0.037 0.20 7.8 0.32 11.0 2.8 0.44 9.4 0.99 6.5 VIIIb 0.061 1.5 41 1.6 19 --1.1 3.6 0.35 -5.5 2.7-14.0 VIIb 0.126 1.8 30 -----IVb ----1.3 5.3 1.3 13.0 3.7 14.0 VIXIa 0.133 1.4 23 1.5 11 0.14 0.40 6.6 --4.8 1.5 17.0 4.6 19.0 Va 0.178 1.8 25 -----VIIa 0.249 1.2 13 --1.5 6.0 1.8 1.8 - TABLE15.-BOND ENERGIES Do(MX-OH) AND Do(MOH-X) IN kml mOl-' OBTAINED FROM Ki6 AND K1 (1 cal= 4.184 J) flame CaCl-OH CaOH-CI SrCI-OH SrOH-Cl BaCl-OH BaOH-CI CaBr-OH CaOH-Br SrBr-OH SrOH-Br BaBr-OH BaOH-Br vc 112 110 102 107 108 104 113 93 105 89 113 90 IVC 113 112 -105 101 112 92 106 90 VIC -101 108 ----VIId 115 113 101 107 107 104 115 95 109 92 115 92 VIIIb 116 114 -105 101 114 94 111 96 116 94 VIIb 116 114 -----IVb --108 104 -109 93 116 94 VIIIa 114 113 99 106 109 106 112 93 -118 95 Va 115 113 -----VIIa 112 111 -108 105 -109 93 3rd law * average 114k1.6 112k1.5 101+1.3 107k0.8 107k1.6 104+1 113+1 93+ 1 108+2 92+ 3 116+2 93+2 2ndlaw* 113+6 113+6 look3 109+6 104rfI6 99+6 109+6 97+ 8 99+ 10 SO+ 9 98+ 6 76_+ 7 * errors are standard deviations.L. V. GURVICH V. G. RYABOVA AND A. N. KHITROV Values of KI6and Kl calculated from Al p(i)and Klare presented in table 14. The values Ki were obtained from eqn (1 5). Using these data third law calculations of AH16(0)and AHl,(0) were made and corresponding approximate values of Do(MX-OH) and Do(MOH-X) are presented in table 15. DISCUSSION For determining the enthalpy of reactions and the dissociation energies by the methods described in this paper the correct definition of the flame temperatures the values po(M) and p(XM) and the accurate measurements of the integral intensities of the bands are all important.The absence of systematic errors in the measured temperatures was verified by measurement of the intensity of the D-lines of Na in flame spectra. By presenting logI(Na) as function of T-l the excitation energy of the 2Pstate of Na was obtained as 48.6 kcal mol-l in good agreement with 48.5 kcal mol-1 from ref. (1 8). In order to check the accepted methods of determining po(M) and p(CM) the values of po(Na) were determined from the absolute intensity measurements of the D-lines of Na in the spectra of 16 flames when a 9.6 x M solution of NaCl was injected into the flame. According to the available data in the flames used in the experiments apart from the hottest sodium is present mainly in the form of atoms Na and small amounts of ions Na+.Therefore the sum p,(Na) and p(Na+) must be equal to the value p(CM) found by ratio (1 1). Comparison of the corresponding values for 16 flames shows that in all the flames except VIb these values are in agree- ment within 10 % while in the flame VIb where one can expect additional formation of NaOH they agree within 20 %. In order to check the absence of errors associated with the measurements of the band integral intensities the latter were measured with different microdensitometer slit widths. Furthermore a number of measurements (for BaBr and MOH) were performed with different bands. In all cases there was obtained adequate agreement. The values of the dissociation energies and the bond energies are given in table 16 while the corresponding enthalpies of formation are presented in table 17.TABLE 16.-DISSOCIATION ENERGIES AND BOND ENERGIES* IN kcal mOl-' (1 cal = 4.184 J) Ca 94.1k1.6 121 + 5 215 75.7k5.4 111+6 187 Sr 95.6+ 1.8 114+ 6 210 78.4+ 4.4 106+ 5 186 Ba 106.8+ 2.2 116+ 6 223 87.5k2.0 l08+ 6 196 Do(M4H) Do(MC14H) Do(MOH-Cl) Do(M0HCl)t DdMBr-OH) Do(M0H-Br) Do(M0HBr)t Ca Sr 96+3 95+3 114+ 4 101+ 4 112+4 107+4 208 200 113+5 l08+ 6 9345 92+ 6 189 186 Ba 111+4 107+4 104f 5 214 116+5 93+6 204 * errors are doubled standard deviations. t dissociation energy of MOHX on M + X+ OH. MONOHALOGENIDES OF METALS The dissociation energies of monochlorides of Ca Sr and Ba obtained from the measurements of log I(MX)/I(M) in the spectra of 16 flames are in good agreement with the mass-spectral data.2 Owing to the performance of the measurements 104 DISSOCIATION ENERGIES within a wide interval of temperatures (greater than 700 K) these data are apparently more accurate than are the mass-spectral data.There are no published experimental data of the dissociation energies of mono- bromides of these metals. The values D,(BaBr) obtained during the measurement of the values logI(MX)/I(M) by the bands of the subsystems 211+-X2Z and TABLE 17.-sTANDARD ENTHALPIES OF FORMATION AHf (9,298.15K)/k=l M01-l (1 ail = 4.184 J) CaCl -23.0& 1.8 * SrCl -28.2&2.0 BaCl -34.6+2.5 CaClz -116.0+ 5.0 SrC12 -114.0f 6.0 BaCl2 -122.0+ 6.0 CaBr -7.0+ 5.6 SrBr -13.1 f4.6 BaBr -17.4f 2.5 CaBrz -92.02 8.0 SrBr2 -97-027.0 BaBr2 -W.O+ 6.0 CaOH -45.0+ 3.0 SrOH -46.6+ 3.0 BaOH -59.0+4.0 CaClOH -129.0+ 5.0 SrClOH -124.0+ 5.0 BaClOH -133.0+ 6.0 CaBrOH -11 1.O+ 6.0 SrBrOH -112.0+ 6.0 BaBrOH -125.0+ 7.0 * errors are doubled standard deviations.The calculations are based on standard enthalpies of formation from ref. (22) and AH (Ca g 0) = 42.5k0.2)kcal mol-' ; AH (Sr g 0) = (39.2k0.5)kcal mol-1 ; AH;-(Ba g 0) = (44.0+1.0) kcal mol-l. 2113-X2Z agree within the range of 0.2 kcal mol-l. Table 6 presents the average value of these measurements. The values Do(CaBr) and D,(SrBr) listed in table 16 need to be improved since the measurements of I(MBr) were complicated by partial overlapping of the bands of MBr and MOH. MONOHYDROXIDES OF METALS The interpretation of the experimental data for I(MOH)/I(M) in the flame spectra is rather difficult both due to the absence of the analysis of the observed spectral transitions so that it is impossible to calculate the coefficient B(T)with good precision and to the absence of the molecular constant data for MOH.The latter introduces errors into the calculations of B(T)values and furthermore into the values H(T)-H(0) necessary for the transition from AH,(T) to AH1(0). However these uncertainties partially compensate each other in the process of calculation of AH(0) and Do. The values AHl(T) given in table 9 are calculated under the assumption that the observed spectral transitions are transitions from the single vibrational levels of the excited states to the level 000 of the ground state.The structural parameters of MOH in the excited state required for calculating B(T)were taken to be identical to those in the ground state. Thus there were obtained 2 sets of the values B(T) log Kl/C, AH,(T)and AHl(0),i.e. for the bent and linear models of these molecules. From table 9 it is clear that the results of measurements by different bands and the results of calculationsfor different models are in adequate agreement. The errors introduced into the value AHl(0) and D,(MOH) by the assumption that the bands of MOH in the flame spectra are connected with transitions between the single vibrational levels might be significant. To estimate their magnitude the valuesB(T)were calculated on the understanding that the observed bands are sequences associated with one of the vibrations of the molecule MOH and that there occur transitions from the vibrational levels 0 < v' < 10 of the upper electronic state.Values of D,(M-OH) found in this way exceed those obtained from tables 7 and 8 by 1-3 kcal mol-1 depending on the vibration of MOH to which the corresponding L. V. GURVICH V. G. RYABOVA AND A. N. KHITROV transitions are related. Since it is not possible unambiguously to relate the observed bands to any specific vibration in table 9 there are presented the values D,(M-OH) increased by 2 kcal mol-l compared with the originally found values. When alkaline-earth metals and chlorine are injected into the hydrogen+ air flames the bands of the molecules MOH and MCl are simultaneously observed in the flame spectra.The measurements of I(MOH)/I(MCl) make it possible to find the enthalpy of reaction MX+H20 +MOH+HX (19) and to obtain independent data for D,(M-OH). The corresponding measurements were performed and values of D,(M-OH) so obtained are also given in table 9. These values exceed the values calculated from log Ki9/C. The values D,(M-OH) listed in table 16 have been obtained by taking into account the measurements of log Kl/Cand log K,,/C. These values of D,(M-OH) are in satisfactory agreement with the data obtained lgm21on the basis of indirect measurements. DIHALOGENIDES OF METALS The values of D,(MX-X) calculated by the 3rd law method from K7 are given in table 13. This table shows the great scatter of data obtained from the measure- ments in different flames (the standard deviations of the values A reach 50 %; this indicates the low accuracy of the measurements).For CaBr and SrBr, the values K7 contain an additional error due to the inaccuracy in the value Kl calculated with AH,(O) listed in table 6. The values of D,(MBr-Br) also contain uncertainties due to the absence of experimental data of the molecular constants of MBr,. Some idea of validity of the values Do(MX-X) and Do(MX2) presented in table 16 can be given by the comparison of D,(MX-X) calculated by the 2nd and the 3rd law methods (see table 13). The comparison of the calculated values Do(MCJ2) with the results of the mass-spectral measurements indicates that the latter are 2-4 kcal mol-1 lower.HYDROXYHALOGENIDES OF METALS The values of D,(MX-OM) and D,(MOH-X) calculated by the 3rd law method from K16and K17 are given in table 15. The accuracy of determining the coefficients Al is as a rule higher than A2 and the scatter of Do obtained in different flames is lower than for D,(MX-X). However it does not confirm a high accuracy of D,(MX-OH) and D,(MOH-X) since they depend on estimated molecular con- stants of these compounds (see Appendix) and the assumption that only 2 metallic compounds containing one atom X (MX and MXOH) are present in the flames. It should be noted however that good agreement between the values of D,(MXOH) calculated as B,(MX) +D,(MX-OH) and D,(M-OH) +D,(MOH)X apparently supports the absence of large errors in the interpretation of the experimental data.Some idea of the accuracy of the determination can be given by comparison of the values calculated by the 3rd and 2nd law methods (see table 15). It is very desirable to verify the obtained values D,(MX-OH) and D,(MOH-X) by an independent method first of all by means of a mass-spectrometric study. It must be noted that these data indicate that in the systems containing an alkaline- earth metal hydrogen oxygen nitrogen and chlorine or bromine a considerable (in some cases predominant) part of the metal can occur in the form of MXOH. DISSOCIATION ENERGIES APPENDIX The thermodynamic functions of the compounds discussed in the present paper in the ideal gas state were calculated by ordinary methods. Functions for MX were calculated with molecular constants in an anharmonic oscillator-nonrigid rotor approximation.The thermodynamic functions of the other gases were calculated in a rigid rotor-harmonic oscillator approximation. The molecular constants of MOH were estimated for 2 models of these molecules and are presented in table 18. Given in table 19 are the molecular constants of MC12 (from ref. (2)) and MBr2 (estimated). TABLE1 ESTIMATED MOLECULAR CONSTANTS OF MOH LMOH = 180" LMOH = 105" molecule r(M-O)/A r(O-H)/A vl/cm-1 v2(2)/cm-1 v3lcm-1 vllcm-1 vzlcm-l v3/~m-~ CaOH 2.00 0.96 3700 300 600 3700 1300 600 SrOH 2.20 0.96 3700 300 500 3700 1300 500 BaOH 2.20 0.96 3700 300 450 3700 1300 450 TABLEMOL MOLECULAR CONSTANTS OF MX2 metal chlorides bromides r(M-X)/A LMOH vl/cm-1 vzlcrn-1 v3lcrn-l r(M-X)/A LMOH vllcm-1 vzlcm-1 v3lcm-1 Ca 2.51 180" 217 64(2) 402 2.67 180" 150 40(2) 300 Sr 2.67 140" 269 44 300 2.82 180" 125 30(2) 250 Ba 2.82 120" 255 35 260 2.99 140" 175 25 180 The thermodynamic functions of MXOH were calculated using the estimated values of the molecular constants also for 2 models of these molecules.In one model LMOH was taken equal to 105" in the other model 180". The parameters of the angle OMX were accepted to be the same as in the molecules XMX the vibrational frequencies were also taken equal to the frequencies of the corresponding vibration in MX2 and MOH. D. L. Hildenbrand J. Chem. Phys. 1968,48 3657. D. L. Hildenbrand J. Chem. Phys. 1970,52,5751. T. C. Ehlert G. D. Blue J.W. Green and J. L. Margrave J. Chem. Phys. 1964,41,2250. L. V. Gurvich and V. G. Ryabova Tepl. Vys. Temp. 1964,2,215. 'V. G. Ryabova and L. V. Gurvich Tepl. Vys. Temp. 1965,3,652. V. G. Ryabova and L. V. Gurvich Tepl. Vys. Temp. 1964,2,834. 'L. V. Gurvich and V. G. Ryabova Tepl. Vys. Temp. 1964,2,540. C. G. James and T. M. Sugden Proc. Roy. SOC.A 1958,248,238. E. Bulewicz and T. M. Sugden Trans. Faraday SOC.,1956 52 1481. lo T.M. Sugden Trans.Faraday SOC.,1956,52,1465. l1 K. C. Brog T. G. Eck and H. Wieder Phys. Rev. 1967 153,91. l2 L. V. Gurvich G. A. Khachkuruzov V. A. Medvedev et al. Thermodynamic Properties of Individual Substances (Nauka Publishers 2nd Edn.,Moscow 1962). Spectroscopic Data Relative to Diatomic Molecules ed. B. Rosen (Pergamon Press London 1970).14A. G. Gaydon Proc. Roy. SOC.A 1955,231,437. l5E. M. Bulewicz Nature 1956 177 670. l6 J. Van der Hurk T.Hollander and C. T. J. Alkemade J. Quant. Spectr. Rad. Transfer 1973 13 273. l7 Yu. I. Ostrovsky and N. P.Penkin Optics Spectr. 1961 XI 565. C. E. Moore Atomic EnergyLevels Vol. I (Nat. Bur. Stand. U.S.A.). l9 V. G. Ryabova and L. V. Gurvich Tepl. Vys. Temp. 1965,3 318. 2o D. N. Cotton and D. R. Jenkins Trans. Faraday Soc. 1968,64,2988. 21 P. J. Kalf Dissertation (Rotterdam 1971). 22 Report of the ICSU-CODATA Task Group on key values for thermodynamics J. Chem. Thermodyn. 1972,4,331.

ISSN:0301-5696    

DOI:10.1039/FS9730800083

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Studies of High Temperature Species by Infra-red and Raman Spectroscopy BYI. R. BEATTIE," D. EVERETT, S. B. BRUMBACH R. Moss AND D. NELSON Department of Chemistry The University Southampton SO9 5NH Received 5th September 1973 Several cells for studying gas-phase vibrational spectra at high temperatures are described. The Raman spectrum of gaseous tin dichloride is obtained in a cell which is potentially capable of exten- sion to 1500°C. The Raman spectrum of niobium pentafluoride as a function of temperature has been obtained in a sapphire cell with a gold O-ring seal capable of being operated at temperatures in the region of 750°C. The infra-red spectrum in a thermal gradient cell which is usable to 1000°C is presented for aluminium tribromide. Applications of tunable lasers to high temperature infra-red spectroscopy are briefly discussed.In this paper we shall consider conventional vibrational spectroscopy at uncon- ventional temperatures. It is not our purpose to deal with flames shock-heated gases molecular beams or plasmas although all are relevant to the work to be described here. Previous studies of high teznperature species by molecular spectroscopists have been mainly by direct observation of heated gases or by the study of species isolated in an inert substrate at low temperatures. The loss of rotational degrees of freedom in a matrix although at first sight a disadvantage may in practice be advantageous. Bands become much sharper and hence it is frequently possible to distinguish iss- topically different molecules.In this way it may be possible to determine the for- mula of a matrix-isolated fragment and its molecular shape. However matrix isolation spectroscopy has the disadvantage of introducing "matrix effects " which will affect the observed vibrational frequencies relative to those of the free molecule and may affect the gross molecular shape. The disadvantages of high temperature spectroscopy are the difficulty of the experiment and the diffuseness of many bands. The experimental difficulties occur because of problems of cell design including window materials and associated gaskets. There is also the problem of the random thermal noise. Fig. 1 shows the general form of black body radiation at 600,1000 and 1600 K as a function of wavelength.' Note that the radiation scale is logarithmic and that a change from 1000 to 1600 K at 0.5 pm (the approximate wavelength of the argon laser lines principally used for Raman studies) causes an increase in background radiative intensity by roughly five orders of magnitude.By contrast at 10pm (a wavelength of interest in infra-red studies) the background is high at both temperatures but relatively unaffected by the change in temperature. Despite such difficulties Braune and Engelbrecht obtained gas-phase Raman data for the mercury dihalides in a classical piece of work as early as 1932. In 1956 Klemperer and Lindeman obtained the infra-red spectra of gaseous HgC12 and HgBr2 using a cell described by Klemperer earlier the same year. These were the first molecules that might reasonably be regarded as high temperature species to have their gas-phase vibrational spectra studied.107 HIGH TEMPERATURE SPECTROSCOPY In conventional gas-phase Raman spectroscopy the Raman scattering from a point defined by the incident focused laser beam is collected and passed to the mono- chromator. With a collection angle of 60" a suitable cell design would be that of fig. 2. Two features of this design can be improved upon. The wall of the tube con- taining the sample can be thinned say by a factor of ten thereby allowing an increase of cell temperature by roughly 100" for the same thermal noise. Secondly the rear "window '' can be maintained at a lower temperature than the front "window ". Ar 5 10 AlPm FIG.1.-Monochromatic intensity (Jnlerg CM-~s-l) of the hemispherical radiation of a perfect black body as a function of wavelength (A/pm). The point Ar represents the frequency of the princi- pal lines of an argon laser. a = 600 K b = lo00 K c = 1600 K. Thereby the spectrometer " sees "less radiation from the rear window and none from the furnace walls. The only criterion for the temperature of the cooler window is that the vapour in the cell shall not condense out. The actual temperature is not important as the Raman scattering is observed from the heated gas at the point of the focused laser beam. Silica cells are convenient and may be used routinely to temp- eratures of the order of 1000°Cas this material is transparent to the (visible) exciting and Raman radiation.Above 1OOO"Cthe shot noise component of the background radiation becomes serious. Phase-sensitive detection systems may be used to remove the broad background spectrum but in the absence of signal averaging techniques do not improve the signal to noise ratio. In infra-red spectroscopy the problems of high temperatures are much more difficult to overcome. Even at 500 K background radiation from windows is becom- ing serious and many "plastic '' window materials are molten at this temperature. Semi-conductors such as silicon deteriorate rapidly in transmittance as the temperature increases and even crystal quartz at 100cm-l shows a decrease in transmittance between 300 and 700 K of roughly a factor of In addition there is the problem of obtaining inert gasket materials which are stable to high temperatures.For I. R. BEATTIE S. B. BRUMBACH D. EVERETT R. MOSS D. NELSON 109 transmittance studies it is convenient if the incident radiation is chopped before the sample. In designing an instrument for such studies it is clearly advisable to have parallel light if possible and to remove the cell as far as possible from the detector to reduce thermal noise from the furnace cell and windows. t lL FIG.2.-Section through furnace (F) and sample cell (C) for a high temperature gas-phase Raman study. 0 and R represent observation and Raman collection ports respectively L represents the laser beam. The broadening of observed bands as the temperature increases is a more funda- mental problem.In the Raman effect the principal bands in a spectrum usually arise from totally symmetric modes. In vibrational infra-red and Raman spectroscopy the difference between the rotational constants in the upper and lower states is frequently very small. As a result of this Q-branches of totally symmetric modes usually fall on top of one another resulting in line-like spectra in the Raman effect even in the gas phase with the apparent absence of 0 P and R S branches. This behaviour is frequently found even for asymmetric rotors where not all Q-branches are coincident. However in the infra-red effect intense bands do not conform to one particular type. Frequently Q-branches are weak or absent and it is normal to observe rota- tional fine structure in infra-red gas-phase spectroscopy.In certain cases for example in parallel bands of symmetric tops line-like Q-branches may be obtained. As with the Rarnan effect the ratio of the intensity in the Q-branch to other branches is a function of the moments of inertia of the molecule under study. Because P and R (and 0 and S) branches consist of a series of lines spaced by factors related to the rotational constants the effect of temperature on broadening of these branches is appreciable. This is predominantly due to increased population of higher rotational levels at higher temperatures. Clearly the effect is less serious HIGH TEMPERATURE SPECTROSCOPY for initially line-like Q-branches. Thus the generalisation may be made that the effect of high temperatures on observed Raman spectra in terms of broadening is usually much less serious than in comparable infra-red spectra.RAMAN SPECTROSCOPY AT HIGH TEMPERATURES (6l)UP TO 1ooo"c Raman spectroscopy up to 1000°C is relatively routine for gaseous species which do not react with vitreous silica. Using elementary techniques high quality spectra can be obtained.6 For compounds which react with silica sapphire is an alternative which is inert and transparent to visible radation.' The cell described here can be used to at least 750°C and with suitable gasket materials formally to the melting point of sapphire (about 2000°C) although before that temperature could be reached background radiation would become prohibitive. FIG.3.The high temperature sapphire cell.The cell and furnace are shown in fig. 3. The essential features of the cell are a high-temperature gold O-ring seal plus a low-temperature (water cooled) Teffon O-ring or metal (nickel or Monel) gas-filled O-ring seal. Condensation in the region of the cooled seal is avoided by making the sapphire plug of sufficient length that it can be used effectively as a part of the furnace insulation. In this way the temperature gradient from the hot zone to the cooled zone occurs through the sapphire plug. The plug is kept under pressure on the gold O-ring seal. Similarly a smaller inde- pendent pressure is exerted on the water-cooled seal. An example of the use of this cell is given in fig. 4 which shows the results of a variable temperature Raman study (in the niobium-fluorine stretching region) for gaseous niobium pentafluoride.8 The results closely parallel those on antimony pentafluoride and show the formation 1.R. BEATTIE S. B. BRUMBACH D. EVERETT R. MOSS D. NELSON 111 of monomeric NbF from the originally polymeric material. The spectrum is unchanged from 500 to 600°C. On the basis of gas-phase and matrix infra-red experiments a C4vshape has been attributed to monomeric NbF5.I0 However in the interpretation of these matrix experiments it was assumed that monomeric NbF was present in the infi-a-red gas-phase experiments conducted at about 100°C. It is I I 1 750700 750X30 I -750 700 750 700 cm-' FIG.4.-The Raman spectrum of niobium pentafiuoride in the 700cm-I region as a function of temperature.a = 230"C,b = 350°C c = 40O0C d = 450°C. likely that monomeric NbF was not isolated in the matrix experiments. The situa- tion closely parallels that of SbF and although the evidence is slight the observation of a single intense polarized Raman band in the niobium-fluorine stretching region for monomeric NbF does not disagree with the presence of the expected D3,,mono-mer. It is interesting to note that Jones and Van Schalkwyk were unable to obtain complete dissociation to monomeric TaF even at 530°C. The ease of monomer formation for the pentafluorides of vanadium niobium and tantalum thus follows the order VF % NbF5>TaF,. (b) ABOVE 1ooo"c Above 1000°Ccontainer problems in terms of background random noise become so serious that a change in cell design becomes desirable.Unfortunately in the absence of resonance conditions the Raman effect is relatively weak so that concen- trations of greater than 0.1 atmospheres and preferably of the order of 1 atmosphere HIGH TEMPERATURE SPECTROSCOPY are desirable. We find that stable jets can be obtained from modified Knudsen cells using an internal heated carrier gas stream and a cooler external stream of gas. Pre-heated argon flows over the heated sample and then issues from an orifice where it A FIG.5.-Modified Knudsen cell for gas-phase Raman studies. A is made of alumina. forms a jet which is surrounded by another argon stream flowing around the cell (see fig. 5). The jet has a region of the order of 1.5 cm in length where no particulate material is visible.It is in this region that the focused laser beam is used to study the Raman scattering. As there is no heated container near the collection angle of the n I I I s 433 303 200 100 cm-l FIG.6.-The Raman spectrum of gaseous SnClz using the cell shown in fig. 5. lens background radiation is low. Induction heating of the cell is convenient to obtain rapid response and to keep the nozzle of the cell at a sufficiently high temper- ature. Fig. 6 shows the Rman spectrum of gaseous SnCl obtained using this cell in conjunction with photon counting. INFRA-RED SPECTROSCOPY AT HIGH TEMPERATURES Isothermal cells rapidly become impractical for high temperature infra-red studies using conventional spectrometers because of radiation from the windows.Several alternative approaches are then possible one of these being to use cool or relatively cool windows. Klemperer in 1956 used borosilicate tubes approximately 1.2 m long and 4.5 cm in diameter. Only the centre 20 cm of the cell was heated and through- out the whole experiment an argon pressure of one atmosphere was maintained. The windows at the extreme ends of the tubes were at room temperature. This type of approach has also been used extensively by Stafford and co-workers.l' They used 1 m mullite (2A1203 SO2)tubes directly sealed to borosilicate glass at each end and again heated only the centre portion of the cell. To reduce the effects of background I. R. BEATTIE S. B. BRUMBACH D. EVERETT R.MOSS D. NELSON 113 radiation when making absorption measurements the light was chopped prior to entering the cell. Argon was again used as a buffer gas to act as a diffusion barrier. During studies of emission spectra (in which complications arise due to the frequency-cubed factor in intensity leading to non-observation of low-frequency bands) self absorption of radiation was reduced by a controlled flow of buffer gas through the cell Assijgunent of bands using such a cell relies on the dependence of band intensity during temperature cycling and also dependence of band intensity oa pressure. Such experiments are by no means isothermal. Crystals grow in cooler portions of the tube and the formation of smokes or fogs of finely divided solid particles or droplets is difficult to avoid.Results from such studies are open to question and the technique is difficult. More recently Hanst Early and Klemperer l2 in studies of gaseous B203 designed a multi-reflection high temperature cell of the White type.13 Because of the ex- tended path length (four to eighty traverses in multiples of four of a three foot long furnace tube) it is possible to work at appreciably lower pressures than those used in the conventional single pass cell. Under these conditions it appears that nucleation in the gas phase diminishes rapidly and most of the condensation occurs at the walls of the cell. An alternative method to avoid the formation of smokes and the presence of carrier gas is the use of a thermal gradient cell for materials which have adequate vapour pressures (for infra-red studies) at temperatures up to 250°C.The cell is shown in fig. 7. Note that silicon windows can be sealed directly into borosilicate F FIG.7.-Thermal gradient infra-red cell. S graded seal; Q silica tube; B borosilicate tube; W silicon windows ; T sample tube and furnace ; F high temperature furnace ; H heaters for borosilicate portion of tube. glass. The central portion of the cell is heated to temperatures up to IOOO'C but the windows are not allowed to reach greater than 250°C. In this way only vapour is present in the cell and no inert gas is required as a diffusion barrier. The disad- vantage is that one is looking for diflerences in a spectrum as a function of tempera- ture. The cooler gas is always present.Some results for A12Br6+2A1Br3 which were obtained using this cell are presented in fig. 8. An alternative approach is to use a flowing pre-heated carrier gas which carries the heated sample into the cell situated inside a furnace. The material is then constantly swept away at the "window " ends of the tube by a cross-flowing curtain of hot inert gas. This approach avoids the problem of smoke or fog formation but is relatively expensive in terms of loss of material. Using this technique Sole and HIGH TEMPERATURE SPECTROSCOPY Walker l4 have studied emission and absorption spectra of for example ZnCl at 700°C. In an attempt to design a more nearly isothermal cell eqeriments were carried out on a double gas curtain cell operating at ambient pressure in an inert gas atmosphere.This is shown in fig.9. The material under examination plus inert gas diluent fills the cell. Any material diffusing to the ends is removed by the hot curtain of argon gas. The outer curtain of cold gas enables conventional window materials to be used. 8 s 'E" 8 2 c) 280 400 cm-I FIG.&-Partial infra-red spectrum of aluminium tribromide vapour in the thermal gradient cell. 4 4 C C FIG.9.Infra-red double gascurtain cell. W windows;C cold curtain inlets ;H inlet for curtain gas to be heated by furnace surrounding sample. I. R. BEATTIE s. B. BRUMBACH D. EVERETT R. MOSS D. NELSON 115 Using this cell the antisymmetric stretching mode of HgC12 at 41 5 cm-l was observed.In designing cells of this type it is important to ensure that the spectrometer can not "see " the furnace walls. CONCLUSIONS AND FUTURE WORK Direct observation of vibrational spectra of hot vapours has the attraction that formally all species present will be observed with their characteristic spectra under the prevailing experimental conditions. The design of Raman cells for high temper- ature studies has reached the situation where Raman spectroscopy is routine to 1OOO"C and where using gas jets it will probably be possible to work up to 1500°C without major problems arising. Progess in the infra-red region has been much less satis- factory. All the cells described so far have problems for example the double curtain cell is difficult to stabilize.Probably the most satisfactory approac;h to date is that of Sole and Walker.14 A possible major development in absorption spectroscopy is the recent discovery of tunable lasers potentially capable of working in the infra-red region from 4000 cm-l to about 250cm-l using alkali metal vapours as the non-linear device to mix the frequencies from two tunable dye lasers pumped by a nitrogen 1a~er.l~ Using lasers the infra-red beam diameter can be of the order of a few millimetres so that it is possible to design a cell with small holes as windows. Thus using a very slow gas stream in to the cell isothermal conditions can be obtained without the formation of smokes or fogs (fig. 10). Further if the beam is highly collimated the detector can FIG.10.-Proposed cell for use at high temperatures with a tunable infra-red laser.W windows. be spaced well away from the cell from which it can be protected by a screen with a small hole in it to allow passage of the laser beam. As the black body radiation decreases as the square of the distance from the detector for a highly collimated laser beam in the region of a four-order of magnitude change in the background relative to the signal should be readily available. If suitable high temperature window materials and gaskets were available there would be no reason why hot windows should not be used in a true vacuum isothermal cell. Unfortunately the only obvious window material for such studies is diamond and this does not seal directly into silica. It is interesting to note in this connection that a borosilicate glass cell with specially thinned ends as windows (0.12 to 0.20 mm thick) was used to 4.7 pm at temperatures up to 400°C.16More recently a silica cell with specially thinned ends (0.03 to 0.10 mm) was described for studying spectra above 2100cm-1 and below 200cm-l at temperatures up to 1200"C.17 Thus the spin-flip Raman laser which can operate in the region below 100 cm-l could be used for high resolution studies using all-silica cells at temperatures up to 1200°C.Finally it is worth mentioning the use of molecular beams. Isentropic expansion from a high pressure region through a nozzle to a low pressure region leads to rapid cooling of samples via standing shock waves. Translational temperatures of the order of a few degrees Kelvin and vibrational/rotational temperatures of the order of 60 K can be obtained in these supersonic jets.The disadvantage of such studies is the HIGH TEMPERATURE SPECTROSCOPY formation of molecular clusters in the jets. However the use of less drastically cooled molecular beams is attractive for the study of high temperature molecules possibly with added diluent gases. The use of multi-reflection techniques say with lo3 reflections and tunable lasers is potentially extremely powerful. It is unlikely that one will be able to work at low enough pressures to avoid collision and Doppler broaden- ing but nonetheless the spectra should be much sharper than those normally obtained at high temperatures. We thank Mr. P. J. Jones Mr.G. J. Van Schalkwyk and Dr. L. E. Alexander for permission to use unpublished work. We also thank Prof. Bray for helpful discussion and Dr. J. Barnes for help in preliminary experiments on the cells discussed here. We thank S.R.C. and the Gas Council for financial support. F. E. Fowle International Critical Tables of Numerical Data ed. E. W. Washburn (McGraw Hill NewYork 1929). H. Braune and G. Engelbrecht 2.phys. Chem. 1932 B19,303. W. Klemperer and L. Lindeman J. Chem. Phys. 1956,25 397. W. Klemperer J. Chem. Phys. 1956 24 353. 0.K. FiIippov and N. G. Yaroslavskii Optics Spectr. 1963 15 299. See for example I. R. Beattie and J. R.Holder J. Chem. SOC. A 1969,2655 ; I. R. Beattie and J. R. Horder 1.Chem. SOC.A 1970,2433. 'L. E. Alexander and I. R.Beattie J. Chem. SOC.A 1972 1745. * P. J. Jones and G. J. Van Schalkwyk unpublished observations ; G. J. Van Schalkwyk Ph. D. Thesis (Southampton University 1973); L. E. Alexander I. R. Beattie and P. J. Jones J. Chem. SOC. A 1972 210; L. E. Alexander Ph.D. Thesis (Southampton University 1972). L. E. Alexander and I. R. Beattie J. Chem. Phys. 1972 56 5829. lo N. Acquista and S. Abramowitz J. Chem. Phys. 1972 56 5221. l1 B. G. Ward and F. E. Stafford Inorg. Chem. 1968 7 2569 ; T. V. Iorns and F. E. Stafford J. Amer. Chem. SOC.,1966 88. 4819. l2 P. L. Hanst V. H. Early and W. Klemperer J. Chem. Phys. 1965 42 1097. l3 J. U. White J. Opt. SOC.Amer. 1942 32 285. l4 M. J. Sole and P. J. Walker J. Phys. E. 1970 3 394. l5 P. P. Sorokin J. J. Wynne and J. R. Lankard Appl. Plzys. Letters 1973 22 342 ; J. J. Wynne P. P. Sorokin and J. R. Lankard Laser Engineering and Applications Conference Washington D.C. 1973. l6 F. A. Cotton and L. T. Reynolds J. Am:r. Clzem. Soc. 1958 80 269. A. A. Mal'tsev and G. K. Selivanov Inst. Exp. Tech. 1971 14 1767.

ISSN:0301-5696    

DOI:10.1039/FS9730800107

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

GENERAL DISCUSSION Dr. P. L. Timms (University of Bristol) said I wish to report a new method of carrying out reactions between metal atoms and compounds which is proving to be a useful alternative to the established co-condensation procedure. Dr. R. Mackenzie in my group is developing the technique. We evaporate the metal inside an evacuated 2-1. Pyrex flask which is being rotated and which contains a slurry or solution of the reactant in an inert solvent. The choice of solvent and the temperature at which the solution is kept is governed by the need to maintain a high vacuum. Our operating temperatures lie in the range from 0 to -196°C. The solution or slurry is very well mixed by the rotation; we adjust the speed of rotation until there is a small pool of liquid on the bottom of the flask with the bulk of the liquid held in a continuously renewed film on the walls.Speeds of rotation are 40-80rev/min. In a run we vaporize 0.5-1.0 g of metal in 30-90 min and condense this into 50-200 ml of a 10 % solution or slurry of the reactant. The process could be readily scaled-up or made continuous. We have prepared tetrakis(tripheny1phosphine)nickel(0) under two different sets of conditions 10 % solution in Silicone 704 at 0°C Ni(g)+P(C 6H5)3-i-Ni[P(C6H5)314 slurry in methyl- cyclohexane at -120°C Based on the nickel the yield was greater than 25 % from the methylcyclohexane slurry and at least as high from the Silicone 704 solution although recovery of the crystalline product was more difficult in the latter case.Triphenylphosphine could be used in a co-condensation experiment but the inlet temperature would have to be greater than 200°C. Clearly it is somewhat easier to use the rotating flask technique in this case but the advantage of the new method over the co-condensation method is more obvious when the compound which one wants to react with a metal vapour is essentially involatile or is too unstable to be volatilized. I am grateful to Dr. M. L. H. Green of Oxford University for demon- strating the feasibility of a rotating reactor although his apparatus was built for co-condensation experiments. Dr. H. A. Skinner (University of Munchester) said With reference to Timms’s paper there is evidence 1* that hexamethylbenzene binds more strongly than does benzene to Cr.Has the co-condensation method been adapted to prepare compounds of the type Cr(C6(CH3) and CI-(C,(CH,)~)PF~? Is it his impression that the de- fluorination of PF by Fe atoms occurs at very low temperatures or only on warming of the solid Fe/PF co-condensate? Dr. P. L. Timms (Uiziversity of Bristol) said In reply to Skinner although we have not yet used hexamethylbenzene in co-condensation reactions we believe it J. A. Connor H. A. Skinner and Y. Virmani J.C.S. Faraday I 1973 69 1218. G. E. Herberich and J. Muller J. Organurnetul.Chem. 1969 16 111 117 GENERAL DISCUSSION should react readily with chromium atoms. It is a relatively involatile ligand and lends itself to use in solution or as a slurry in our rotary reactor apparatus.We have plans to react it with manganese iron and cobalt atoms as well as with chromium atoms. Regarding the reaction of iron with PF, I suspect that defluorination occurs at the moment of co-condensation of an iron atom and a PF3 molecule. Once iron is coordinated to other PF molecules its ability to cause defluorination is probably much diminished. The mass spectra of many Fe-PF complexes show ions in which transfer of fluorine from phosphorus to iron has apparently occurred e.g. (PF,),FeFz. Mrs. D. L. S. Brown (University of Manchester) said I would like to report preliminary results on the thermal decomposition and iodination of chromium hexa(trifluorophosphine). We are indebted to Dr. Timms of Bristol University for supplying a small sample of this compound for these preliminary studies.Cr(PF,) was observed to decompose in the microcalorimeter at temperatures above 300°C. It is not decomposed in argon gas at 260°C. It is however attacked by iodine vapour at 260°C. The product is a black powder which analyzed as CrIn with n in the range 2.5-2.8. The iodine balance in these experiments indicated there is little if any formation of the compound PF312. The thermal decomposition gave a thin greyish metallic deposit but less clean and shiny than that observed from thermal decomposition of Cr(C0)6. The AH for isothermal decomposition at 25°C was about 60-65 kcal mol-l. This refers to the formation of PF,(g) and Cr(meta1). From iodination measurements the corresponding AH was higher being about 70 kcal mol-l.This corresponds to an average Cr-PF bond energy of about 25 kcal mol-1 for Cr(PF,),(d -+ Cr(d + 6PF3(d at 25°C. This is slightly less than Cr-CO in Cr(CO),. However further work is needed to establish that the iodination reaction is without complications from side- reactions. Since these if occurring are almost certainly exothermic the preliminary value 25 kcal mol-l per Cr-PF bond is to be regarded as a lower limit. Dr. P. L. Ths (University of Bristol) said With regard to the paper by Darling et al. the formulae of matrix-isolated dioxygen complexes of transition metals appear to be M(0,) and M(O,),. In contrast dinitrogen and carbon monoxide form more extended series of complexes under matrix isolation conditions. Why is the limit with dioxygen M(O,), especially when this limit applies equally to complexes con- taining “ end-on ” or ‘‘ side-on ” bonded oxygen? Dr.J. S. Ogden (University of Oxford) said In reply to Timms this type of complex was onfy discovered just over a year ago and only half a dozen or so transi-tion metal/O matrix reactions have been investigated in any detail. It would there- fore be premature to conclude that M(O,) was the limit of complexity. However there does seem to be one significant difference between these dioxygen complexes and the more familiar carbonyls or nitrogenyls as we have indicated these M(O,) species are probably best thought of as superoxo complexes in which the metal is in a positive oxidation state and for some metals (e.g. Cu) the magnitude of the third ionization potential would probably prohibit complexes of stoichiometry M(O,),.Another factor to be considered is that one is never certain whether matrix co-condensation reactions of this type are thermodynamically controlled or kinetically controlled and previous work on metal atom/CO matrix reactions has GENERAL DISCUSSION 119 shown that the species formed depend to some extent on the temperature of the deposition surface and on the proportion of CO present. One might therefore expect that for some metals with well characterized +I11 oxidation states (e.g. Cr) one should be able to observe species such as M(O,), and these should be most readily formed by reaction with pure oxygen co-condensed at a temperature -27 K where a limited amount of diffusion could take place.Dr. H. A. Skinner (University of Manchester) said Rittner and others have shown that the dissociation energies of alkali halide diatomic molecules compare satisfactorily with values from calculations of the Born-Mayer type by treating the molecules as ion-pairs with allowance for mutual polarization of the ions in contact. The dissociation energies given by Gurvich for the alkaline-earth rnonohalides can be examined in like manner for which it would seem that the ion-pair model is less convincing for these molecules. The Rittner model relates the experimental dissociation energy D(M -X) to the combination of the attractive coulombic term (C = e2//re-[IM-Ex])and the smaller attractive term from mutual polarization with the repulsive Born-Mayer ion-contact term.Comparing the molecules NaCl and CaCI we note that the coulombic term C in Na+Cl- exceeds D(Na -Cl) whereas in Ca+Cl- it is less than D(Ca -C1) (IM-EX)! D('-x)l (C-D)l rdii kcal mol-1 Clkcal mol-1 kcal mol-1 kcal mol-1 NaCl 2.36 30 111 98 +13 CaCl 2.44 53 83 94 -11 To achieve the experimental D(Ca-C1) from the ion-pair model thus requires a large polarization contribution-much larger than in alkali chlorides. Such a considerable distortion of the ion-pair by polarization may be regarded in another way in terms of configurational interaction between "non-polarizable" ion-pair M+X- and covalent M*-X where M*refers to the excited divalent state of the M atom.2 The ionic model X-M2+X-for the alkaline earth dihalides CaCl, SrC1 and BaCl does give values for the coulombic term C slightly larger than the bond dis- sociation energy sum (Dl+Dz) even when allowance is made for angular structures in SrC1 and BaCl,.There is however little to spare and taking account of the Born-Mayer repulsion it would again seem necessary to require substantial polar- ization. The polarized ionic model is perhaps marginally better for the dihalides than for the monohalides but the angular structures in themselves indicate that it is inadequate. Miss E. M. Bulewicz (University of Swansea) said Atomic line-intensity measure- ments in flames in the presence of halogens have been previously used in the deter- mination of the dissociation energies of metal halides.3* Moreover the paper of Gurvich et al.covers almost the same ground-except for the use of intensity measure- ments on molecular emission bands-as a recent paper by Schofield and S~gden.~ The results obtained and the conclusions reached are similar except that these authors do not claim to have established that the monohalide formed in addition to MX is necessarily MXOH. Yet the present paper makes no reference to this work. E. S. Rittner J. Chem. Phys. 1951,19 1030. H. A. Skinner Trans. Faraday Soc. 1949,45,20. E. M. Bulewicz L. F. Phillips and T. M. Sugden Trans. Faraday Soc. 1961,57,221. K.Schofield and T. M. Sugden Trans. Faraday SOC.,1971,67,1054. GENERAL DISCUSSION Alkaline earth metals catalyze free radical recombination.This effect might be present in the cooler flames used with the highest values of p(CM) employed viz. of the order of atm. This would make the actual values of [HI in the presence of an alkaline earth metal lower than those determined by the LilLiOH method in a flame containing Li only. The ratio [HI actual/[H]would decrease with increasing height in the flame. The tacit assumption is made in this paper that all the emission observed atomic and molecular is thermal. The assumption is probably justified here for atomic lines away from the reaction zone (particularly in hotter flames). However there is some doubt as to whether the hydroxide emission is thermal or chemiluminescent (see e.g. ref. (3)); there appears to be no evidence on the mechanism of excitation of the halide spectra.Dr. H. A. Skinner (University of Manchester) said For molecules which dissociate on heating (such as Al,Br +2AlBr3) are high-temperature spectral studies advan- tageous for the measurement of the dissociation equilibrium constant and its vari- ation over a range of temperature? Prof. I. R. Beattie (University of Southampton) said The difficulty in making quantitative measurements of such equilibria lies principally in the contribution of hot bands to the total intensity. However Raman studies on hot gases are readily made to 1000°C in constant-volume systems and yield results of considerable semi- quantitative intere~t.~ 'D. H. Cotton and D. R. Jenkins Trans. Faraday SOC.,1971 67 730. P. J. Padley and T. M. Sugden,7thInt. Symp. Combustion (Butterworths London 1959) p. 235. D. H. Cotton and D. R.Jenkins Trans. Faraday SOC.,1968,64,2988. I. R. Beattie and J. R. Horder J. Chem. Suc. A 1969 2655.

ISSN:0301-5696    

DOI:10.1039/FS9730800117

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Mass Spectrometer Studies of Al+H20 Reactions in Effusion Cells and in Atmospheric H2+02 Flames BY MILTONFARBER," M. A. FRISCH R. D. SRIVASTAVA AND S. P. HARRIS Space Sciences Inc. Monrovia California U.S.A. Received 30th August 1973 A two-fold mass spectrometer study of the A1 +H20reactions in effusion cells and in atmospheric Hz+Ot flames was conducted. The flame studies yielded a Dg of 119.5 f5 kcal/mole for A10 in agreement with the results of previous thermochemical and spectroscopic investigations. A discus-sion concerning the discrepancy between the data obtained in these and previous flame experiments is presented. The major Al-0-H species in both the effusion and the flame studies was NOH with a AHfZ9* of -42.7+2 kcal/mole. The flame studies also produced other suboxides of alu-minum,as well as the species A102H for which a AHf298of -90+ 5 kcal/mole was obtained.Considerable controversy has existed for several years concerning the high tem- perature chemistry and thermodynamics of reactions involving Al and H20. Widely discrepant data have been reported by various investigators. For example the dissociation energy of A10 obtained from effusion experiments has differed by as much as 100 kJ from the results of recent spectroscopic measurements of aluminium additives in flames. The identity of the major Al-0-H flame species as well as their thermodynamics has also been in dispute. A wide discrepancy exists regarding the results of two groups of experiments (1) Knudsen effusion Langmuir evaporation transpiration spectroscopic and mass spectrometric ; and (2) combustion and flame spectroscopy.6-8 Concerning the dissociation energy of AlO the controversy involves an A10 bond energy differing by a maximum of only 5 or 6 kcal among the various types of experiments in group (l) which in turn differ by as much as 20 kcal with those of group (2).Gurvich and Veyts were among the early workers who examined the behaviour of aluminum in flames. Recently papers by Jensen and Jones and Newman and Page reported results of studies of aluminum additives to H2+N2+O2 flames. Jensen and Jones obtained -5+ 10 kcal for AHfZ9&lO which is in agreement with the second and third law D; values of 601 & 34 kJ and 5892 75 kJ respectively reported by Newman and Page.These three papers 6-8 recommend a value for the heat of formation of A10 which is 20 kcal more negative than the spectroscopic value of 16.57 kcal/mole obtained by Tyte and MacDonald and Innes (DZ = 506 kJ/mol) and the value of 17.0 kcal/ mole obtained by Farber et aZ.,3in an effusion-mass spectrometer study under neutral conditions of the vapour species over alumina in the temperature range 1943-2093 K. Gole and Zare recently studied the visible chemiluminescence in a cross-beam experiment involving a thermal beam of aluminium atoms -1700 K intersecting an uncollimated beam of ozone molecules 300K and reported a minimum value of 17.6 kcal/mole for AHf298A10. In carrying out a rotational analysis of two emission bands found near 2500 and 2800 A MacDonald and Innes deduced that the observed spectra corresponded to emission from two highly-excited states of A10 to a common 121 122 MASS SPECTROMETER STUDIES OF Al+H,O lower state lying only 5300cm-' (0.66eV) above the A10 ground state.On the assumption that both the upper and ground states dissociate to the same separated atom limit they added the 0.66 eV to the original dissociation energy obtained by Tyte (4.54 ev) which resulted in a D;of 5.20 eV (16.57) kcal/mole for AHf). Gole and Zare state that this 08value is also an upper limit since the dissociation of the excited states to products other than the ground-state atoms would only lead to the determination of a lower dissociation energy. Thus their recommended value is between 16.5 and 17.5 kcal/mole.Brewer and Searcy established from an effusion weight loss experiment that the most negative value for the heat of formation of A10 was 9.5 kcal/mole based on the interpretation that the weight loss was due entirely to the formation of AlO. Trans-piration and other Knudsen experiments 9* confirmed these weight-loss data. Both Jensen and Jones and Newman and Page could account for only a small quantity of the total amount of aluminum introduced into the flame as being either A1 or A10 species. Newman and Page calculated that the partial pressure of A10 was 1 x atm and that the total partial pressure of the A1 in all forms was 1.5 x ; i.e. the total A10 and A1 concentration was less than 1 % ofthe A1 species. Jensen and Jones found that the total A1 concentration was 4.8 x 1014 atoms whereas the A10 concentration was 1.4x lo1 molecules ~m-~ or approximately 3 % of the total concentration of Al.Both investigators attempted to use the A1 and A10 information obtained from the spectroscopic measurements to decide empirically what major A1 species were in the flame. Jensen and Jones plotted double logarithmic plots of the peak intensities of A10 and Al against the mass of the aluminum isopropoxide added to the reservoir and obtained straight lines of a gradient 1.0 within the limits of experimental error. They concluded from these plots that there was only 1 atom of A1 present in each molecule of the dominant species formed by A1 in the flames and listed the species Al A10 A102 HA102 AlOH A1(OH)2 A1(OH)3 and AlH as candidates for the major concentrations.Applying competitive reaction criteria for these various species they concluded that the major Al-containing species in the flames was A1(OH)2. Newman and Page made similar calculations and determined that HA10 would be the predominant species. However a final note in their paper acknowledged the work of Jensen and Jones and stated that they were in agreement that the bulk of aluminium present was most probably in the form of A1(OH)2. In view of the significant differences in the results obtained among the various investigators a two-fold study of the reactions involving A1 with H20was undertaken at this laboratory to clarify the thermodynamics and identify the species formed. The first phase was an effusion-mass spectrometer investigation at temperatures above 2000 K followed by a four-stage differentially pumped mass spectrometer study of A1 vapour added to H2+O2flames.EXPERIMENTAL PROCEDURES AND METHODS OF CALCULATION EFFUSION STUDIES The dual vacuum chamber quadrupole mass spectrometer apparatus employed for the effusion-mass spectrometer studies as well as the experimental procedures and methods of calculation have been described previ~usly.~* lo*l1 The alumina effusion cell was25.4 mm long and was attached to an alumina rod. The cell had an inside diameter of 6.8 mm and employed an elongated orifice 0.986 mm in diameter by 6.6mm long for beam collimation. Since the magnitude of the AlOH species ion intensity was initially unknown high purity D&) was used instead of Hz to avoid obtaining erroneous values as a result of any contribution by COz impurities (a.m.u.44). The cell M. FARBER R. D. SRIVASTAVA M. A. FRISCH AND s. P. HARRIS 123 pressure for the D2was held at 6 x atm by means of a variable leak. In addition to the reactions of D2 with alumina a study was made employing D20(g). The appearance potential of the AlOD+ species was found to be 7.55-1eV. The apparatus and experimental procedures for the effusion weight loss studies have also been reported previously.12* l3 A rhenium boat containing two pieces of sapphire was placed inside a rhenium cell which had an effusion orifice of 1.828 mm diameter and 10mil thickness. Blank runs were made by heating the cell to the desired temperature.The rhenium cell was fitted into a tantalum holder having a small orifice to prevent back diffusion. This holder was connected to a tantalum flow tube which in turn was connected to an H2 reservoir. FLAME STUDIES Construction and assembly of a four-stage differentially pumped vacuum system was necessary to accomplish the operation of a flame at a pressure of 1 atm and to obtain simul- taneously the mass spectra of the ''frozen "combustion species produced in the atmospheric flame." This system provided a pressure variation from 1 atm in the flame to lo-' atm at the mass spectrometer. The aluminum additive was introduced into the flame in the form of aluminum isopropoxide Al(C,H,O (m.p. 118C b.p. 140C) and aluminum iodide AIIB(m.p.191C b.p. 360C). The relative ion intensities of the various flame species were corrected for cross-section and mu1 tiplier efficiencies as described previously. 39 14-' THERMODYNAMIC RESULTS MASS SPECTROMETER AND EFFUSION STUDIES FOR AH,AlOH(g) Ion intensities were obtained in the temperature range 1833-2240 K for the species involved in the reaction of D2(g) with Al,03(c) including D2 D D20 OD AIOD AlO AID A120 0 and 02. The reactions of interest included and The ion intensities and the computed equilibrium constants for the reactions with D2(g) and A1203(c) are presented in table 1. Fig. I and 2 show the log K versus 1/T for reactions (1)-(2). Second-law heats of reaction were obtained from a least-squares treatment of the data.TABLE1.-ION INTENSITIES AND EQUILIBRIUM CONSTANTS FOR THE REACTION OF A1203(C) WITH D2(g) ion intensities X 10-13/A run T/K D D2 D2O A1 AlOD A120 K1 K2 k3 K4 I 1833 2700 46000 1425 23 55 3.34 x 10-2 2.70~ 105 2.81 x 10-4 1910 1999 4140 6560 38500 30900 5340 23400 59 200 28 1 924 6.06 x 10-2 1.41 x 10-1 * 8.48 x 105 2.76~ 106 2.43 x 10-4 1.10~ 10-4 * 2088 8750 22500 41500 324 2830 2.23 x 10-1 7.08 X 106 1.54~10-4 2149 2149 10700 35200 15300 154000 98000 96400 520 1500 11100 8900 3.27 x 10-1 2.99x 10-1 * 1.61 x 107 1.73 x 107 1.91 x 10-4 2 1898 14440 265000 170 3300 99 112 4.25 x 10-2 * 0.51 1.48 x 106 1.85 x 10-4 2018 2085 29950 37700 220000 150000 580 1000 8400 13800 378 552 388 692 1.41 x 10-1 2.12x 10-1 0.63 0.44* 8.17 x 106 1.96 x 107 1.80~ 10-4 1.64~10-4 2170 48300 114000 1570 23500 1075 1095 3.99~ 10-1 0.67 4.44 x 107 1.26 x 10-4 2240 61300 89000 1785 35000 1505 1915 5.57~10-1 0.66 9.47 x 107 1.28 x 10-4 * discarded.MASS SPECTROMETER STUDIES OF A1-t HzO -0.2c 4.6 5.O 5.4 T-I x 104/~-1 FIG.1.-Log of equilibrium constant for the reaction 3A1203(c)+3Al(g)+ +D2(g)= NOD@) as a function of the reciprocal temperature. The heat of formation of AIOD(g) was computed from the two chemical equilibria involving different molecular species (reactions (1) and (2)). Reaction (2) is iso- molecular and therefore pressure independent. Calculations were included for 4 -4 4.8 5.2 5.6 ~-1 x 104/~-1 FIG.2.-Log of equilibrium constant for the reaction AI20(g)+D2O(g)= 2A10D(g) as a function of the reciprocal temperature.M. FARBER R. D. SRIVASTAVA M. A. FRISCH AND s. P. HARRIS 125 reactions (3) and (4) to substantiate experimental validity since the DE of deuterium and hydrogen is well known and numerous recent experimental results 3*l7 have established the heat of formation of A120(g) to within 1-2 kcal/mole. Thermo-dynamic results are expressed in calories where one thermochemical calorie equals 4.184 international joules. The heat of formation of A120(g) at 298 K from reaction (4) was calculated as -34.3&2 kcal/mole. A second-law bond-energy value of 104.4+ 1.5 kcal/mole was obtained for D2 at an average temperature of 2040 K. TABLE 2.-EXPERIMENTAL DATA FOR THE REACTION OF H2 WITH A1203(C) total Al203(c) totai no.(~HJofmoles total no. of (n&03) moles T/K timelrnin weight losslmg blank/rng A1203 lost per hour of H2 passed per hour 2013 230 1.o 0.2 2.049~ 4.297 x 2055 230 1.45 0.5 2.431 x 4.297 x 2106 230 3.O 1.35 4.221 x 4.~6~10-3 2150 230 7.0 4.2 7.162x 4.~6~10-3 2200 230 17.8 13.7 10.490x 4.594~10-3 The average second-law AHf2000values for AlOD(g) -50.4+ 1 kcal/mole for reactions (1) and (2) respectively. were -50.7+3 and Reduction to 298 K using tabulated heat content data l8 yielded an average value of -43.7 kcal/mole. Since deuterium compounds are approximately 1 kcal/mole more stable than their hydrogen analogue a value of -42.7 +2 kcal/mole for AHf298A10H(g)was obtained. The results of six molecular-flow effusion experiments involving the reaction of H2 with A1203(c)in the temperature range 2013-2353 K are presented in table 2.Mass balance equilibria and the assumption that AlOH was the major Al-0-H species produced led to an average third-law value of -49.3 kcal/rnole for AH,AlOH(g) at 2100 K. This reduced to -43.6k2.2 kcal/mole at 298 K. MASS SPECTROMETER STUDIES OF A1 ADDITIVES IN Hz-I-02 FLAMES The procedures used previously for other additive studies lo were employed to measure the bond energy of AlO,to identify the Al-0-H species formed in the flame and to determine thermodynamic data for these molecules. Aluminum was intro-duced into the flame in the form of vapourized aluminum isopropoxide and alurnin- urn iodide. A typical mass spectrometer tracing of an atmospheric H2 +O2 flame $8 I I 11 I II 11 17 18 32 12 1617 I I a.m.u.a.m.u. tracing A tracing B FIG.3.-Relative intensities of major flame species of the HP+O2flame at a temperature of 2250 K. (Ionization energy of 20 eV was employed to prevent fragmentation. The relative intensities in tracing B have been amplified 10 times over those of tracing A.) MASS SPECTROMETER STUDIES OF Al+H,O (fig. 3) shows the relative intensities of the species HzO H2 H O2and OH. Mass spectrometer intensities of the major aluminum species present in the flame at a calculated temperature of 2250f 100 K are shown in fig. 4 5 and 6. Fig. 4 and 5 depict results employing Al13 ; fig. 6 involves the Al(C3H,0)3 studies. IEt11.5 eV H+ IE=8eV 1 4 I I I 44 43 27 a.m.u. FIG.4.-Mass spectrometer intensities of A1 species in the H2+02flame at average temperature of 2250 K.The aluminum was introduced into the flame as AIIj vapour at a concentration of 0.5 '%. The amplification was reduced by a factor of 20 on the left of the dotted line. Aluminum isopropoxide produces C02 which has the same molecular weight as AlOH. Therefore it was necessary to obtain relative intensity data for AlOH below the appearance potential for CO,' (13.8 eV).19 The appearance potentials for AlOH+ and A10+ as determined in the effusion-mass spectrometer experiments are 7.5+ 1 and 9.5+ 1 eV respectively. Obtaining ion intensities below 13 eV therefore eliminated contributions of CO,' intensities to the mass 44peak. Fig. 4 is a tracing of the sweep from a.m.u.25 to a.m.u. 50 during an interval of 40s. The ionization energy was initially set at 8 eV to obtain an Al+ intensity at 2 eV above its appearance potential of 6 eV. When the mass value reached the point depicted by the dotted line during the sweep interval the ionization energy was changed to 11.5 eV to measure the relative intensities of AlO+ and AlOHf at 2-3 eV above their appearance potentials. At that time the amplification factor was reduced by 20. Thus the approximate ratio of AlO+/Al+ was 20 as can be seen from fig. 4. When higher ionization energies were employed relative intensities of some species increased whereas others decreased due to fragmentation. For example fig. 5 shows that the ion intensity of Al+ increased considerably when an ionization energy of 18 eV was employed.The Arf (resulting from an 0.5 % impurity in the oxygen) which has an appearance potential of 16.7 eV,I9 can also be seen at a.m.u. 40. M. FARBER R. D. SRIVASTAVA M. A. FRISCH AND s. P. HARRIS 127 IE= 10 eV A&O+ At a.m.u. FIG.S.-Mass spectrometer intensities of AI species in the H2+O2flame at an average temperature of 2250K. The aluminum was introduced into the flame as AI13 vapour at a concentration of 0.5 %. The amplification was reduced by a factor of 10 on the left of the dotted line. r A~OH" I HALO; AeO* ~~~~~~~~~ ~~~ I It I I 60 59 44 43 MASS SPECTROMETER STUDIES OF &+H,O Fig. 6 shows a mass scan from a.m.u. 40 through a.m.u. 65. As can be seerf no peak corresponding to A1(OH)2 (a.m.u.61) is discernible above the noise level; however peaks at a.m.u. 59 and a.m.u. 60 corresponding to AIO and HOAlO are apparent. Although the intensities shown in fig. 4 were obtained with the mass spectrometer sweeping the appropriate mass range each peak was also studied at an electron energy 2 eV above its appearance potential while the mass spectrometer was centred on the peak of interest. Oscilloscpe tracings were obtained for the three principal peaks Al+ AlO+ and AlOH+ (fig. 7). The ratios are approximately equal to those shown in fig. 4. Isomolecular reactions involving the various relative ion intensities can be written to obtain free energies. The reaction Wg)+H2W) = A10(d +H2(9) (5) would yield a free energy and lead to a bond energy of AIO.The equilibrium constant = 1AIO+1Hf/1A1+1H20+ was calculated from the ratios of 0.1 for IH;/IH20+and 20 for IAlo+/IAl+ which yielded a free energy of reaction AG of -3.08 kcal at 2250 K. A AHf298 value of -1.7 kcal was obtained employing published free-energy functions.18 This yielded a value of 18.555 kcal/mole or for AHf298A10(g) a D; of 119.5f:5 kcal/mole. From the reaction AW) +H2O(g) = AlO2(g)+H2(d (6) a AG of 7.4 kcal is calculated at 2250 K leading to a value of -41.6+ 5 kcal/mole for AHfzs8A102(g). This is in agreement with the recently published thermochemical value of -44.3&2 k~al/mole.~ Two isomolecular reactions involving the species AlOH can be written AWg) +H,(d = AlOH(9) +H(9) (7) and AlW +H20(9) = AlOH(9) +H(9).(8) The experimental ratios of the ion intensities for reaction (7) were found to be 4 and 0.1 respectively for the ratios IAIOH+/IA,O+ and IH+/IH2+.A free energy of reaction of 4.1 kcal was calculated at 2250 K leading to a AH298of -6.4 kcal employing published free energy functions. Using AHf298values of 52.1 kcal/mole for H and 17.0kcal/mole for A10,3 a value of -41.555 kcal/mole was obtained for AHf298A10Hg). Ion intensity ratios of 80 for ZAIOH+/ZAl+ and 0.01 for zH+/IH20+ yielded a value of 1.0kcal for the AG for reaction (8) at 2250 K. This led to a AH298 of -8.1 kcal. A value of -40.05 5 kcal/mole for AHf298A10H(g) was calculated employing published AHf298 values of 52.1 kcal/mole for H(g) -78 kcal/mol for Al(g) and -57.8 kcal/mole for H,0(g).18 The thermodynamic data for AlOH obtained from the flame spectra confirmed the results of the effusion and mass spectroscopic measurements described above.This heat of formation supports a structural configuration of the molecule as A1-0-H. For this structure Gurvich and Veyts estimated a value of 1305 10 kcal/mole for the A1-OH bond which leads to -42 kcal/mole for AHfAIOH. A limiting value for the heat of formation of HOAlO was calculated from the effusion-mass spectrometer experiments based on the assumption that a partial pressure of atm for HOAlO would have been detected in the mass spectrometer. FIG.7.-Relative intensities of Al+ AlO+ and AIOH+ in the Hz+O2flame at an average temperature of 2250K.The amplification factor of the Al+ intensities was 20 that of the A10+ and 50 that of tbe AIOH+. Ionization energies employed for the intensity measurements were 11.5 eV for AlO+ 10 eV for AlOH+ and 8 eV for Al+. [Toface page 128 M. FARBER R. D. SRIVASTAVA M. A. FRISCH AND S. P. HARRIS 129 This assumption resulted in a limit value of -104 kcal/mole for AHf298HOA10(g). It is possible to calculate a value for the heat of formation of HOMO from the ion intensities shown in fig. 6. The peak at a.m.u. 60 possibly HOAlO is the same relative height as the A10+ intensity peak. These intensities lead to 20.5 & 5 kcal for AG at 2250 K for the reaction AlO(g)+H,O(g) = HOAlO(g)+Wg) (9) yielding a calculated AHfZg8HOAIO(g) value of -90 & 5 kcal/mole.DISCUSSION The bond energy value of 119.5+5 kcal/mole for A10 obtained in these studies confirms the results of the numerous thermochemical and spectroscopic investigations. However there is a difference of over 20 kcal/mole with those obtained in the flame studies by Gurvich and Veyts,6 Jensen and Jones,7 and Newman and Page.8 As mentioned in a recent publication,20 in the work of Jensen and Jones and Newman and Page this discrepancy may be attributable to the f number employed which they took from an investigation by Vanpee et aL2' of aluminium additives to cyanogen+oxygen flames. Vanpee et al. observed strong blue-green AlO emission bands and assumed that equilibrium was not present in the flame. Employing the line absorption method of Ladenburg and Reiche,, they calculated the Al(g) con-centration as 20 % of the total Al additive concentration and attributed the remaining A1 species to AlO.Using this A10 concentration and population distribution in A2nstate given by Tyte they calculated anfnumber of (3.7+ 3) x MacDonald and Innes2 have since determined that the observed spectra of Tyte were due to emission from two highly excited states to a common lower state. From the flame species composition given by Vanpee et aZ.,21we calculated an A10 concentration of 5 x mole fraction for an additive total mole fraction of A1 of 2.6 x This concentration would yield an f number of approximately 1x Since they observed very strong C2 Swan bands and CN emission in the red and violet spectral regions although the calculated mole fraction of CN was only 1 x it is entirely possible that the calculated equilibrium concentration of A10 in a highly excited state would be sufficient to produce the emission intensities observed.The reduction of the A10 concentrations by a factor of 100 would bring the Jensen and Jones and Newman and Page results into agreement with those obtained in the thermochemical spectroscopic and current flame studies. The mass spectrometer investigations of the effusion and flame reactions are in agreement in that the major A1-0-H species formed is the AlOH molecule with a somewhat smaller concentration of HOAlO. If the dihydroxide Al(OH) existed at a.m.u. 61 it did not exhibit ion intensities sufficiently above the noise level to be detected in the H,+02 flame spectra.Calculations based on an effusion-mass spectrometric study of the vapour species over A120 indicated that in addition to the species A1 and AlO the suboxides A102 Al,O and A1202would be present as well as the hydroxy compounds AlOH and HOA10. Gurvich and Veyts estimated 575 kJ/mol-l (137 kcal) for Dg from the measured concentration of the free metal species and the known delivery of the metal to their acetylene flame. This estimate was based on the assumption that the free metal and the monoxide were the only major species present in the flame gases. The concentra- tion attributed to A10 could be reduced by the concentration ofthese other A1 species thereby lowering the value for DE considerably. Thus the conclusion of Jensen and Jones and Newman and Page that Al A10 and one other molecule containing S8-5 MASS SPECTROMETER STUDIES OF Al+H,O Al-0-H atoms were the only species present is considerably oversimplified.Also their conclusion that the compound Al(OH) is the major flame species is highly speculative. This research was partially supported by the Department of the Navy Office of Naval Research Material Sciences Division Power Program. D. C. Tyte Proc. Phys. SOC.,1967 32 827. J. K. MacDonald and K. K. Innes J. MoI. Spectr. 1969 32 501. M. Farber R. D. Srivastava and 0. M. Uy J.C.S. Furuduy I 1972 68,249. J. L. Gole and R. N. Zare J. Chem. Phys. 1972,57 5331. L. Brewer and A. W. Searcy J. Amer. Chem. SOC.,1951 73 5308. L. V. Gurvich and I.V. Veyts Dokl. Akad. Nuuk S.S.S.R. 1956,108,659. ’D. E. Jensen and G. A. Jones J.C.S. Faruduy I 1972,68,259. R. N. Newman and F. M. Page Combustion and Flame 1971,17 149. von Wartenberg 2.anorg. Chem. 1952,269,76. lo M. Farber and R. D. Srivastava Combustion and Flume 1973,20 33 ; ibid. 1973 20 43. l1 M. Farber and R. D. Srivastava J.C.S. Furuduy I 1973 69 390. l2 M. Farber Margaret A. Frisch and H. C. KO,Trans. Faraduy Soc. 1969,65 3202. l3 M. A. Greenbaum J. N. Foster M. L. Arin and M. Farber J.Phys. Chem. 1963,67,36. l4 R. F. Pottie J. Chem. Phys. 1966 44 916. l5 A. C. H. Smith E. Caplinger R. H. Neynaber E. W. Rothe and S. M. Trujills Phys. Rev. 1962,127,1674. l6 S.Lin and F. E. Stafford J. Chem. Phys. 1968,48 3885. l7 K. R. Thompson High Temp.Sci. 1973,5,62. JANAF ThermochemicaE Tables (Dow Chemical Co. Midland Michigan). l9 U.S. Dept. of Commerce Nat. Bur. Stand. Publ. NSRDS-NBS 26 Ionization Potentials and Heats of Formation of Gaseous Positive Ions June 1969. 2o R. D. Srivastava 0. M. Uy and M. Farber J.C.S. Furuday II 1972 68 1388. 21 M. Vanpee W. R. Kineyko R. Caruso Combustion and Flume 1970 14,381. 22 R. Ladenburg and F. Reiche Ann. Physik 1913,42,181.

ISSN:0301-5696    

DOI:10.1039/FS9730800121

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Mass Spectrographic Study of Solid Iron-Cobalt Alloys BY B. B. ARGENT,* P. E. BLOOMFIELD, R. H. MOOREAND D. ROBINSON Dept. of Metallurgy University of Sheffield Received 14th September 1973 The activities of iron and cobalt in face-centred cubic iron-cobalt alloys have been determined using a Knudsen Cell and double-focussing mass spectrometer. Difficulties due to changes in the absolute sensitivity of the mass spectrometer were overcome by making measurements of the ratio of the intensities Z(56Fe+)/Z(59C~+) using an analysis developed by Belton and Fruehan.’ Activities at 1 500 K approximately obey Raoult’s law and are in excellent agreement with previous work.2* The equilibrium diagram for the iron-cobalt system exhibits a complete series of face centred cubic (7) solid solutions above 1260 K and an extensive body centred cubic (a) solid solution region at lower temperature^.^'^ There have been measure- ments of the enthalpies of mixing of liquid iron-cobalt s enthalpies of solidi- fication,’ enthalpies of formation of y alloy^,^ enthalpies of formation of a alloys lo and of the combined enthalpies of the a to y transformations and ferro- to para- magnetic changes.g* These data apart from the work of Tozaki et aZ.,s have been critically assessed by Muller and Hayes ; they conclude that the maximum enthalpy of formation for the liquid alloys at 1 873 K is -2 424 J mol-l at xco = 0.5 for the y alloys at 1 473 K is -1 312 J mol-1 at xco = 0.5 for the a alloys at 1 143 K is -6 964 J mol-1 at x, = 0.4.The work of Tozaki and his collaborators on the iron-cobalt system is in complete agreement with that of Predel and Mohs.’ Belton and Freuhan measured activities of iron and cobalt in liquid alloys using a Bendix time of flight mass spectrometer and a Knudsen cell.Their results show positive deviations from Raoult’s law for the cobalt component with a maximum value offco = 1.24 at x, = 0.3 ; for the iron component there are negative deviations for x, = 0-0.4 with a minimum value of fFe = 0.97 and positive deviations for x, > 0.4 with a maximum value offFe = 1.59 at infinite dilution in cobalt. Activi-ties of iron in a and y alloys have been measured by Satow Kachi and Iwase using a gaseous equilibration technique based on the equilibrium Fe (pure or in alloys) +H20 + FeO +H2 and by Normanton using a solid state electrochemical cell based on lime stabilised zirconia Fe FeOlZrO,( + CaO)lFeO Fe-Co.Although negative deviations are shown for a phase alloys the iron activities approxi- mately obey Raoult’s law for y phase alloys. The present study was undertaken to check the results on the y phase alloys and as part of a programme to assess the performance of a high resolution mass spectro- meter at temperatures where the partial pressures of the components were in the range 10-5-10-1 Pa. A description of the instrument and details of preliminary 131 S8-5’ IRON-COBALT ALLOYS experiments on the variation of source sensitivity with the composition of the gases in the source region was presented at the 1971 Symposium on Metallurgical Chemistry organized by the National Physical Laboratory and Brunel University ; these studies have now been completed and will be published separately.For the purposes of this paper it is sufficient to note that under certain conditions of operation the source sensitivity can vary by up to 20% with variations in the partial pressure of carbon monoxide. This gas is desorped from the hot furnace in quantities signifi- cantly affecting the sensitivity at temperatures > 1 300 K. The arguments leading to the choice of a high resolution mass spectrometer for studies where the partial pressures are low have been presented by Argent and Powers.12 They essentially rest on the difficulty of making adequate correction for background hydrocarbon species when complete resolution is not achieved.EXPERIMENTAL The aIloys were made by vacuum melting the required quantities of 99.9 % iron and 99.8 % cobalt; analyses are given in table 1. Turnings of the alloys were contained in liners machined from the alloy fitted in molybdenum cells and covered with tungsten plates containing the effusion orifice. The orificc areas were w0.2 mm2; appropriate corrections were made for the fact that the orifices were slightly diverging truncated cones.13 An MS703 K mass spectrometer manufactured by AEI Ltd. was used in these investigations. TABLE DATA ON IRON-COBALT ALLOYS * 1.-EXPERIMENTAL (standard states pure face centred cubic iron and cobalt at 1 500 K) analysed composition t 1 500K 1 330 K-1 530K xco me In (IFe/ko) fco fFe AHs,co/kJ mol-1 $ AHs .Fe/kJ mol-1 $ 0.0462 0.0961 0.0961 0.197 0.288 0.399 0.399 0.495 0.587 0.689 0.689 0.803 0.890 0.942 1.Ooo 1.Ooo 0.952 0.902 0.902 0.800 0.701 0.597 0.597 0.504 0.409 0.309 0.309 0.196 0.108 0.0557 4.057 2.403 1.930 0.950 0.534 -0.030-022}1 -0.246 -0.955 -1.905 0.96 1.07 0.99 0.97 0.97 1.02 1.04 1.07 0.98 0.98 1.oo 1.oo 0.99 1.01 1.01 1.01 0.97 0.95 0.90 1.17 1.18 0.96 438 (+15) 453 (+_18) 430 (+26) 420 (& 8)408 (k16) 430 +8) 435 (+19) 424 (+9) 426 (k9)400 (+7) 406 (+7) 398 (+24) 439 (+24) 430 (+14) 414 (+8) 393 (+6) 401 (+25) 402 (+17) 390 (rfi36) 386 (+11)394 (t-21) 406 (rfi 12) 406 (+10) 393 (+36) 406 (+,11)388 (+8) 384 (+5) 397 (+15) 404(+18) 414 (+16) * weighted mean of experiments on two days.t maximum impurities detected 0.2wt % Ni 0.05 wt % C,0.03 wt % 02. $ bracketed values represent 95 % confidence limits. It was operated at a resolution (M/AM)of 4 OOO (10 % valley definition) with an extraction field of -7.1 kV ; ionisation of the molecular beam was carried out at -35 V with a trap current of 300 PA. The temperature of the Knudsen cell could be maintained to f0.3 K over 0.5 h at 1 500 K ; equalisation of the top and bottom temperatures of the cell was achievable to within 0.3 K. Tests on thermocouples before and after use indicate that syste- matic errors are no greater than +1.5 K to -0.5 K. B. B. ARGENT P. E. BLOOMFIELD R. H. MOORE AND D. ROBINSON 133 Experiments were carried out over two days and in each case 10-12 estimates of the ratio Z(s6Fe+)/I(sgCo+)were obtained over the temperature range 1 330 K to 1 530 K.Correc-tions were made for variations in sensitivity due to changes in background pressure caused by desorption of carbon monoxide from the furnace using calibration curves determined in separate experiments. Although the instrumental sensitivity was not sufficiently stable to justify combining results obtained on separate days reproducibility was good on any one day. The least squares technique was used to fit equations to the experimental data loglo [(IS6Fe+)Ts/K] = a+BK/T log10 [~("CO+)TS/K] = c+dK/T. Values of the enthalpy of sublimation of iron and cobalt were derived from the parameters b and d. The equations were also used to obtain estimates of the intensities of iron and cobalt at a standard temperature of 1 500 K.Activity coefficients of cobalt and iron at 1500K were obtained using Belton and Fruehan's technique for integrating ratios of the ion intensities e.g. xco =xco In fco = -1 xFed{ln [1(56Fe+)/1(59Co+)] -In (xF,/xco)). T/K 1500 1450 1400 1350 co Fe 104 KIT FIG.1.-Plot of loglo(156~e+ Ts/K) and log10 (159c0+ Ts/K)against lo4K/Tfor an alloy with xc0 = 0.942. The lowest experimental point for iron corresponds to a partial pressure of -2.5 x Pa. IRON-COBALT ALLOYS RESULTS The heats of sublimation of iron and cobalt from the pure metals and from the alloys are given in table 1. 95 % confidence limits are also shown ; they are based on the regressions used to fit the log (Z+Ts/K) against lo4 K/T plots (fig.1). Replicate runs using different cells were carried out for the pure metals and for the alloy x, = 0.1 (table 2) ; from this information it appears that the heats of sublima- tion are reproducible to 6 %. The mean values for the pure metals agree with the literature values l4 to within 5 kJ mol-1 AH,(Co 1 430 K) = 414 kJ mol-l AH,(Fe 1 430 K) = 398 kJ mol-l. TABLE 2.-REPRODUCIBILITY AND ACCURACY OF MEASURED HEATS OF SUBLIMATION number of assessed experimental . 1 330 K-1 530 K value 14 at component alloy runs AHs,Fe/kJmol-1 * AHs,co/kJ mol-1 * 1 430 K Fe pure Fe 5 393 (+8) 398 co pure Co 6 414 (+21) 414 Fe x(-J = 0.096 5 392 (+13) co XG = 0.096 5 427 (+24) * bracketed values represent 95 % confidence limits.Ratios of the ion intensities for iron and cobalt in the alloys at 1 500 K are shown in table 1. Integration of the plot of the Belton and Fruehan function shown in fig. 2 was carried out using the trapezoidal rule. Integration was carried out from point to point rather than along an arbitrarily chosen smooth curve ; for compositions where duplicate measurements had been made the mean value of the function was I-,,,P 0 \ 9" P m i \o I P'O 0.8 1.2 1.6 0.8 1.2 1.6 In (156~~ + /159c0+)-In (XF~/XC~ FIG.2.4~2)Plot of the Belton and Fruehan integration function for the alloys in table 1 at 1 500 K. The solid points were obtained under different experimental conditions but show the same trend. (b)A similar integration plot for Belton and Fruehan's liquid iron-cobalt alloys at 1 863 K.0, This work f.c.c. alloys 1 500 K; 0 this work f.c.c. alloys 1 500 K using a different experimental technique ; 0 Belton and Fruehan liquid alloys at 1 863 K. B. B. ARGENT P. E. BLOOMFIELD R. H. MOORE AND D. ROBINSON 135 used. The values of the function at xFe= 0 and x, = 0 were assumed to be equal to the values at xFe= 0.05 and x, = 0.05 respectively ; this is equivalent to assuming that Henry’s law holds at up to 5 % solute. If instead the curves are directly efirapolated the maximum difference produced in the calculation of activity co-efficients is only 5 %. The values deduced for the activities of iron and cobalt relative to the pure face-centred cubic elements at 1 500 K are shown in fig.3. Values of aFeat 1 293 K determined by Satow Kachi and Iwase,2 at 1 373 K determined by Normanton and at 1 863 K determined by Belton and Fruehan are shown for comparison. 0.5-8 XFe FIG.3.-Plot of UF= and aco against XFe (standard states pure face centred cubic iron or cobalt at the stated temperatures). 0 1 500 K ; A Satowet d2aFe 1 293 K ; V ,Normanton3 Thiswork UF~ a~~1 373 K; 0,this work uco 1 500 K; 0,Belton and Fruehanl aco 1 863 K (n.b. standard states pure liquids). It is difficult to estimate the precision of activities obtained by the integration technique of Belton and Fruehan. In the present case the maximum difference in In [Z( 56Fe+)/Z(5gCo+)],when experiments have been duplicated using two different samples of the same alloy is 0.10 i.e.11 % in the ratio of the intensities. On the basis of this precision and the excellent agreement with results obtained by two different experimental techniques an accuracy of 15 % is proposed for the activities determined in this investigation. DISCUSSION The precision of heats of sublimation determined in this investigation is not sufficient to warrant determining partial enthalpies of formation for comparison with the values quoted by Miiller and Hayes1 The activities are in good agreement with previous work on solid alloys and support the view that the behaviour of the y-solutions is close to ideal. However it is not easy to reconcile these observations with Belton and Fruehan’s work on liquid alloys which suggests significant positive deviations from Raoult’s law.Similar positive deviations are predicted by Kaufman IRON-COBALT ALLOYS and Nesor,15 but their model uses Belton and Fruehan's liquid data quoted in Hultgren's assessment,14 as part of its data base. Consider an alloy x, = 0.30. Co Cpure f.c.c. 1 473 K) = Co (xco = 0.30 f.c.c. 1 473 K) (1) AG1 = -14 71 1 J. mol-l (this work-ideal) AH1 = -2 791 J mol-l (Miiller and Hayes 9 :. AS1 = +8.092 J mol-l K-l Co (pure liquid 1 873 K) = Co (pure f.c.c. 1 473 K) (2) AH2 = -31 798 J rnol-l (Hultgren et all4) AS2 = -18.41J mol-1 K-l CO(xc0 = 0.30 f.C.C. 1 473 K) = CO(~c,= 0.30 f.C.C. 1 763 K) (3) AH3 = +11 086 J mol-l AS3 = +6.864 J mol-1 K-l (estimated on the basis of Norrnanton's Cpmeasurements).Co (xc0 = 0.30 f.c.c. 1 763 K) = Co (xc,= 0.30 liquid 1 763 K) (4) AH4 = +12 919 J mol-1 (Predel and Mohs ') AS = +7.328 J mol-1 K-l Co (xco = 0.30 liquid 1 763 K) = Co (xco = 0.30 liquid 1 873 K) (5) AH5 = +4 455 J mol-l ASg = +2.451 J mol-l K-l (estimated assuming Cp,co= 40.50 J mol-1 K-l). :. Co (pure liquid 1 873 K) = Co (xc = 0.30 liquid 1 873 K) (6) i= 5 AH6 = C AHi = -6 129Jmol-' i= 1 i= 5 As6 = ASi ='+6.325 J rno1-l K". i= 1 This value of AH6 may be compared with estimates made from Predel and Mohs original data points. These suggest a minimum value of -5 440 J mol-1 and a maximum of -5 920 J mol-l. This agreement gives confidence in deriving the following value of AGco and the activity coefficient for cobalt in the liquid alloy AGco = -17 976 J mol-1 aco(x, = 0.30 1 873 K) = 0.3144 fcO(xc = 0.30 1 873 K) = 1.05.This compares with Belton and Fruehan's value of 1.24 forf, at 1 863 K. Miodownik has recently 16* l7 sought to explain the negative excess entropies observed in some face centred cubic iron alloys on the basis of a suggestion 18-20 that there are two electronic configurations of iron atoms in a face centred cubic lattice. In pure iron the antiferromagnetic state (spin = 0.5 pB) is the ground state although the upper level can be excited thermally. The addition of more than 30-40 % nickel or cobalt leads to a reversal of the order of the levels with the ferro- magnetic state (spin 2.8 pB) being stabilized. Information on the separation of the levels AE = EFerro-EAntiferro, can be obtained from data on the Curie temperature either measured directly or extrapolated from other alloys.Thus for iron-cobalt alloys,20*21 T,= 113.512f-ZJI In (/3+1) B. B. ARGENT P. E. BLOOMFIELD R. H. MOORE AND D. ROBINSON 137 where T' is the Curie temperature ZT is the number of nearest neighbours with spin aligned in the direction favoured by the sign of the exchange integral and 2.l is the number whose spin is opposed B is the Bohr rnagneton number (= 2s). The appro- priate parameters are as the spin on the cobalt = 1.7 pB where a = exp (-AEIRT). TABLE3.-PARTIAL MAGNETIC ENTROPIES FOR IRON IN FACE CENTRED CUB LC IRON-COBALT ALLOYS CALCULATED USING THE TWO GAMMA STATE MODEL SFe(mag.T)-Sw(mag. O>/ XFe xco AE/kJ mol-1 J mol-1 K-1 * 1.o 0.0 3.35 8.455 0.9 0.1 2.51 8.487 0.8 0.2 1.34 8.516 0.7 0.3 0.0 8.527 0.6 0.4 -2.18 8.498 0.5 0.5 -4.86 8.394 0.4 0.6 -8.04 8.188 0.3 0.7 -10.90 7.955 0.2 0.8 -12.90 7.768 0.1 0.9 -26.50 6.478 * ground state antiferromagnetic. -0.2 d I & 7 -0.4 L-( 0 E b w' @ -0.c 4 -0.E XFe FIG.4.-Excess entropies of mixing for iron-cobalt alloys at 1 500 K compared with predictions based on the " two gamma state " model. A,predicted values ; 0,observed values. (Obtained from Miiller and Hayes heats of mixing and ideal excess free energies of mixing.) Table 3 summarizes values of AE for the iron-cobalt alloys. With the two state system envisaged for the iron atoms the magnetic entropy can be calculated using IRON-COBALT ALLOYS where g,/g = 1.79 the ratio of the degeneracies of the two levels.Values of are also included in table 3. If the differences between these values and the value for pure iron are taken to be the excess partial quantities for iron integration gives the excess integral entropies. These values are plotted in fig. 4 for comparison with those calculated from Muller and Hayes enthalpies and our observation that AGE x 0. The experimental values are more negative than those calculated using the “two gamma state ” model but the fact that the sense and approximate magnitude are correctly predicted lends weight to the suggestion that magnetic effects are a major consideration in the face centred cubic iron-cobalt alloys.The authors’ thanks are due to the Science Research Council for financial support and to Mr. M. J. Ellis and Mr. F. Cooke for assistance with the experimental work. G. R. Belton and R. J. Fruehan J. Phys. Chem. 1967,71 1403 T. Satow S. Kachi and K. Iwase Sci. Rep. Res. Inst. Tohoku Univ. Ser. A 1956 8 502. A. S. Normanton private communication. M. Hansen and K. Anderko Constitution ofBinary Alloys (McGraw-Hill New York 2nd ed. 1958). G. B. Harris and W. Hume-Rothery J. Iron Steel Inst. 1953 174 212. A. Hellawell and W. Hume-Rothery Phil. Trans. A 1957 249 417. ’B. Predel and R. Mohs Arch. Eisenhiittenwesen 1970 41 143. * Y. Tozaki Y. Iguchi S. Ban-ya and T. Fuwa Chemical Metallurgy of Iron and Steel (Iron and Steel Institute London 1973).F. Muller and F. H. Hayes J. Chem. Thermodynamics 1971 3 599. lo W. Steiner and 0. Krisement Arch. Eisenhiittenwesen 1962 33 877. l1 F. Korber W. Oelsen and H. Lichtenberg Mitt. Kaiser- Wilhelm-Inst. Eisenforsch Diisseldorf 1937 19 131. l2 B. B. Argent and P. Powers J. Shefield Univ. Met. SOC. 1968 7 51. l3 R. D. Freeman and J. G. Edwards The Characterisation of High Temperature Vapours Ed. J. L. Margrave (Wiley New York 1967) Appendix C. l4 R. Hultgren P. D. Anderson R. L. Orr and K. K. Kelley Selected Values of the Thermo- dynamic Properties of Metals and Alloys (Wiley New York 1963) and subsequent supplements. l5 L. Kaufman and H. Nesor 2.Metallkunde 1973 64,249. l6 A. P. Miodownik Acta Met. 1970 18 541. l7 A. P. Miodownik Chemical Metallurgy of Iron and Steel (Iron and Steel Institute London 1973). l8 R. J. Weiss and K. J. Tauer Phys. Rev. 1956 102 1490. l9 L. Kaufman E. V. Clougherty and R. J. Weiss Acta Met. 1963 11 323. 2o R. J. Weiss Proc. Phys. SOC.,1963 82 281. 21 A. P. Miodownik Scripta Met. 1969,3,931.

ISSN:0301-5696    

DOI:10.1039/FS9730800131

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Atomization Energies of Phosphorus Oxides BY s. SMOES AND J. DROWART Physical Chemistry Laboratory Free University of Brussels B 1050 Brussels Belgium Received 11th December 1973 The study by the mass-spectrometric Knudsen-cell method of the vapours in equilibrium with metal oxide+metal phosphide systems at 1000-1700K made possible the identification of the mole- cules P203,P2O4 P205and P306. Their atomization energies were determined as well asthose of the phosphorus oxides prevalent at low temperatures. These are :P2O3 2055 k15 PZO4 :25304 18 Pz05 3020+22 P306 4012+24 P406 4385 (f40 -60) P40, 4956+23 P40s 5516+25 P409 6066rtr.27 kJ mol-'. One of the problems in chemistry at high temperatures remains the identification of the molecules present in the gas phase of binary and more complicated systems and the determination of their thermodynamic properties.Both goals can be achieved by the mass-spectrometric analysis of the ions produced by electron impact from the neutral species in molecular beams formed by the Knudsen effusion method. This procedure indeed gives access to the simultaneous determination of the chemical identity of the molecules and of their partial pressures. These in turn permit the calculation of reaction enthalpies dissociation energies and heats of formation by the relations based on the second and third laws of thermodynamics. When as for the phosphorus +oxygen system the vapour at low temperatures is composed of complex species such as P4Ol0 through P407,1-3 simpler molecules can be formed both by increasing the temperature and by reducing the chemical activities of the constituent atoms.When the various molecules can be sequentially made to be of importance in the gas phase the investigation of their behaviour under electron impact their identifica- tion and the determination of their thermodynamic properties is facilitated. The study of various metal phosphide +metal oxide systems made it possible to realize this and to identify the molecules P203 P204 P205and P306in addition to the already known molecules PO and P02,4 and P406to P4010.1-3 EXPERIMENTAL The mass spectrometer Knudsen cell assembly and experimental procedures have already been described. The diaphragm separating the cell from the ion sourcewas cooled by circulating liquid nitrogen.So doing insured that for all molecular ions P,O; except P,O6+ P302 and P305+,the intensity profile measured with the moveable beam defining slit,5 was the same as for Ag+. The molybdenum Knudsen cells used without insert had cylindrical channel type effusion orifices 0.8 mm diam. 1.0-1.2mm long. The condensed phases placed within the cells were MOP synthesized from the elements and either Fez03 (mole ratio 1/2 expt I) C00(1/2 expt 2) or Mo03(1/3,expt 3 ;111 expt 4 inconsecutive parts a 6 and c ; 1 /I quantitative vaporization). Pressure calibrations were made by quantitative vaporization of known amounts of silver and integration of the ion currents mostlycarried out simultaneously with the study of the phosphorus oxides. In view of the low pressures of the AgPOz molecule its contribution to the weight loss was neglected.In the system with 139 ATOMIZATION ENERGIES OF PHOSPHORUS OXIDES initial nominal composition MOP+ Moo3 where the main component of the vapour is P203 absolute pressure measurements were simultaneously performed and also by intensity integration and weight loss determination. For the latter a first weighing was made after the molecules P407-P4010 initially present due to slight excess of phosphorus had been vapor- ized. The second weighing was made after the complete vaporization of the silver added. These measurements thus yielded an experimental value for the ratio of the sensitivities S(Ag)/S(P,O3). The result is S(Ag)/S(P203) = 12.3 at 14 eV and 7.4 at 19 eV.It is to be noted that S being proportional to the cross-section and multiplier yield S(P2O3) given above corresponds to the partial cross-section for the process P2O3 +e+P20$ +2e and not to the total ionization cross-section. The same relative sensitivity was used for Pz04 P205and P306 which by analogy to P203 and P406 through P4Ol0 are expected to also fragment appreciably under electron impact. For the molecules P407 through P4010 compensation of the sensitivities was assumed in the reactions given in table 2. For the molecules PO PO2 and P2 relative sensitivities taking multiplier yields and molecular effects into account were estimated earlier and for P4 estimated here in the same fashion. The values are S(Ag)/S(PO)/S(P02) = 1.0/1.2/0.3 at 14 eV and S(Ag)/S(PO)/S(l?O,)/ S(P2)/s(P4) = 1.0/1.8/1.0/2.2/2.7 at 19 eV.RESULTS IDENTIFICATION OF THE MOLECULES The ions formed by electron impact from the species in the molecular beams and their approximate ionization (IP) or appearance potentials (AP) are summarized in table 1 which also gives their relative intensities and the P203pressures. Reaction with silver further led to the observation of AgPOf (AP = 13.9eV) AgP02+(IP = 9.3 eV) and impurities to that of NaPO+ (AP = 13.1 eV) NaPO; (IP = 8.6 ev) and KPO;. During the initial stages of the experiments in the MoPfMoO systems the gaseous species of the Moo3 system were also observed ; at the highest temperatures gaseous MoPO and MoPO were further identified. 1.-APPEARANCE TABLE POTENTIALS AND RELATIVE ION INTENSITIES I(expt 1) a Z(expt 2) Z(expt 3) a Z(expt 44 a I(expt 4b) b z(expt 4c) b APIeV 1670 K 1317 K 1362 K 1032 K 1316K 1316K 9.5k0.5 1C 1 Id le 1 1 and 13.5f 1.0 11.5f0.5 6.0~ lo-' 0.10 0.34 8.1 x 10-4= 5.0x 10-2 4.5 x 10-2 and 15.4f 1.0 11.4+ 0.5 8.6 x 1.25 15.4f 0.5 2.6 x 2.5 x 10.4-t 0.5 2.4~ lo-" 0.27 0.25 0.55 0.17 10.8L-1.0 5.9 x 10-3 G 2 x 10-4 12.0k 1.0 4.8 x 10-4 g 2 x 10-4 12.3f1.O 3.6 x 7.2 x 15.0+ 1.0 4.5 x 10-3 2.1 x 10-2 10.0f0.5 3.5 x 10-2 Q 10-2 f ~9.0~ 10-4f 11.45 0.5 66 x f 4.0 x 11.9 f0.5 Q 10-4 f 7.3x 10-2 12.4k0.5 2.3 x 1.5 x 10-1 P40 13.0k0.5 7.0x 1.8 x P0)203) /atm 9.3 x 10-8 2.2 x 10-5 9.5x 10-6 1.1 x 10-4 1.2x 10-5 a Ionization energy of 19 eV; b 14 eV; CI(Fe+) = 0.9 and I(FeO+) = 1.9x ; dcorrected for fragmentation uncorrected 2.1 ; =fragment from PzO3 (see fig.1) ; finterference from re-evaporation. S. SMOES AND J. DROWART Mutual comparison of the ionization potentials and comparison with the ioniza- tion and appearance potentials in the literature indicates that PO+ and PO (except in expt 4a) P2+ P203+ P204+,P205+,P306+ (except in expt 4a) P4+ P407+ through P401+o,NaPO; KPOZ and AgP0; are parent ions formed by direct ionization from the corresponding neutral molecules. P20Z+ and P30; are considered to be fragment ions. f /h FIG.1.-Time dependence of the ion intensities at 1032 K (expt 4u). Identification of the neutral molecules P409,P408 P407 and in particular Pz03 could be confirmed accepting Pi P4+and P401+0 to be parent ions from the variation of theirintensity I(at 19 eV) as function of the evolution with time t of the activities of phosphorus and oxygen at constant temperature.Fig. 1 shows that log1 varies linearly with t with the following relative coefficients a Pi 1.00 ; P4f 2.00 ; P40?o 0.57 set equal to 4a(P)+lOa(0); P40$ 0.70 (calc. 0.71); P408+,0.87 (calc. 0.86); P407+,0.99 (calc. 1.00); P3O; 0.69 (calc. 0.50); P306+,0.87 (calc. 0.64); P203+ 0.59 (calc. 0.57); PO; 0.58 during the first two hours (calc. 0.21); PO 0.58 (calc. 0.36). Simultaneously it is shown that under the conditions of the experiment P307+ and P30$ are fragment ions formed mainly from P409 and P408respectively and that PO+ and PO$ are fragment ions from P203.(The appearance potentials of P20$ Poi and PO+ from P401 are 28,23 and 24 eV respectively and can therefore S8-6 TABLE 2.-REACTION ENTHALPIES AND ATOMIZATION ENERGIES (kJm0l-l) expt reaction T/K interval AHij(I1) AHZ(II1) molecule 1 1590-1 696 -85+12f FeO 2 1197-1377 -8530+ 550/T+ 4.9f 0.4 1591 13 e 149_+8 PO2 4a 1032 -3.9 -232&7 P4 1032 21.4 -<-233.9 P406 <4416+18 1032 0.7 233.14 P407 4956+ 23 1032 -0.5 -13-15 P408 5516+25 1032 -0.9 -6516 P409 6066+ 27 1032 1.o -1133.17 P203C2" 2061_$18 -123k 17 Cs 2051f18 2 P2O3 = PO+PO2 1197-1377 -18 920+ 550/T+ 7.5k0.4 369+ 18 3875 14 P203C2 2067+ 15 368+ 18 3773- 14 2056+ 15 CS 3 1151-1374 -19 780) 560/T+ 8.5k0.5 385) 18 379& 14 P203C2 2058+ 15 384+ 18 369+ 14 CS 20483-15 4b 11 49-1 3 1 5 -20 000+350/T+8.7+0.3 389-4- 16 379& 14 P203C2 2058+ 15 387+ 16 369+ 14 2M8+ 15 CS 4c 1186-1386 -19 350+300/T+8.1+0.2 377+ 16 380+ 14 P203C2" 2059+ 15 376+ 16 370+ 14 2049f 15 CS 3 PzO4 = 2P02 121 5-1374 -18 700)710/T+9.2+0.5 3683- 20 364k 14 P204D2h 2536+ 17 369+ 20 3453.14 cs 2517+ 18 3 1272-1 374 see fig.3 -280f18 P205 3O20f 22 3 1295-1344 see fig. 2 7533-20 P306 4012f24 0 Reaction enthalpy at 0 K obtained by the second law ; b reaction enthalpy at 0 K obtained by the third law ; C dissociation or atomization energy obtained from AH($(III); d the uncertainties cited are twice the standard deviation ; the uncertainties in AH6(II) include those in AH?O in the temper- ature (0.5 %) and in H+-Ho"; f the uncertainties take into account for AHO(III) twice the standard deviation from the mean the uncertainty in the temperature the estimated uncertainty in the product of the cross sections (100 %) and in the free energy functions and for 08 the uncertainty in the atomiza- tion energies of the reference molecules.S. SMOES AND J. DROWART not be formed from the latter at 19 eV even if a(P,O,) =a(P4010). Towards the right in fig. 1 PO; tends to become a parent ion. EQUILIBRIUM CONSTANTS REACTION ENTHALPIES AND ATOMIZATION ENERGIES Because of the absence of information on the thermodynamic properties of the condensed phases actually present and of the bivariant behaviour of the systems investigated only homogeneous gas-phase reactions are considered (table 2).The -1 I I -6 *# 4 P*03 = PO + PO2 0% -7 @ -8 M 0 4 X I I -9 =3 Pop -io 1 \ I 1 7.5 8.0 8.5 T-1 x 104/1(-1 FIG.2.-Temperature dependence of the equilibrium constants A expt 2 ; X expt 3 ;V ,eXPt 46 ; 0,expt 4c. equilibrium constants are summarized in fig. 2 and 3 typical individual pressures or ratios of pressures being given in table 1 and in fig. 1. The numerical values of the free energy functions and enthalpies used in the calculation of the reaction enthalpies are taken from the literature or estimated as discussed in the appendix. The Van t'Hoff relation is used only if the equilibrium in question couM be studied over a ATOMIZATION ENERGIES OF PHOSPHORUS OXIDES -1 -2 @-4 M 0 CI -5 -6 5 ~-1x 1041~4 FIG.3.-Temperature dependence of the equilibrium constants.sufficiently extended temperature interval and is not corrected for possible variation of the ionization cross-sections with temperature. The dissociation or atomization energies are derived from the reaction enthalpies using Dg(P,) =485.3k4,' D:(PO) =593.0+8,4 both based on spectroscopic and thermodynamic determinations D:,a,(P02) = 1086.2&1lY4 Di,at(P4) = 1195rf 8,' and D6,at(P4010)=6601 k8 kJ mo1-1.8 DISCUSSION Among the atomization energies determined in this study comparison with literature results can be made for the molecules Pq PO2 P406 through P4OlO. D:(P4) = 1202+10 Dg(P0,) = 1092+11 determined both by the second and third laws and Dg(Fe0) =412+ 14 kJ mol-I compare very favourably with Dg(P,) = 1195+8,8 DE(P0,) = 1086+11,4 and Dg(Fe0) =406+12,1° and 414k20kJ rn01-l.~ (The latter value is corrected to the same free energy function as used here).Simultaneously the exchange reaction FeO(g) +PO(g) =Fe(g) +PO2@) shows the consistency between the dissociation energies of the molecules PO PO2 and FeO. For P407,P408and P409the determination of the atomization energies is based on the reactions P40n(g) =~~/~~)P401o~g)+(1 -n/lO)P,(g) n =7 8 9. S. SMOES AND J. DROWART The calculation of the atomization energies of these molecules depends thus on D&at(P4010)given in the JANAF Tables. The value 6601 f8 kJ mol-1 is however confirmed by the consistency in the atomization energy of P203 deduced from the reactions P203(g) = PO(g) +P02(g) and P2O3(g) = 0.3 P4010(g)+0.4 P2(g) and from the reaction P4OlO(g)+2PO(g) = 6P02(g),which yields D;,at(P4010) = 6587 f 40 kJ mol-l.For P407 P408 and P4og a first comparison can be made between the second law reaction enthalpies measured in ref. (1) and those calculated from the atomization energies in table 2 for the reactions P4og(g) +P407(g) = 2 P4O8(g) AH = AH6080 = -5 1OY1 AH = -10 (table 2). P408(g)+P401o(g) = 2 P,Og(g) AH; = AH5030 = -5f AH6080 = -23f 12,l AH = -15 (table 2). p4°9(9) +p4°8(g) = p4°10(g) f p4°7(g) AH; = AH6080 = 22+ 16,l AH = 25 kJ mol-1 (table 2). In fact the calculation of the enthalpy differences associated with the reactions employed for these molecules in table 2 requires only relative pressures i.e.ion intensities so that the data in ref. (1) can also be used to calculate the same reaction enthalpies. The important point thereby is that the temperature in ref. (1) (423- 673 K) differs markedly from that here. The result with D8,at(P4010)= 6601 f8 is respectively D;,,,= 4969 5498 and 6051 kJmol-l for P407 P408 and P4og in satisfactory agreement with the present results. For P406 re-evaporation probably due to recombination of Pz03 made it possible to determine only an upper limit to the true pressure and thus an upper limit to the atomization energy. A number of conclusions can however already be drawn therefrom. The JANAF Tables give on the basis of the heat of formation of P406(Z)and the heat of vaporization of P,O,(g) the value D8,at(P406)= 4934 kJ mol-l which is difficult to reconcile with the present information.By using the heat of combustion AH298 = -1343 kJ mol-lyll AH~gs,f(P4010, of P406 (c) to P~O~O(C) c),~ and the heat of vaporization of P406,there results D8,,t(P406) = 4318f35 kJ mol-I. This may however be a lower limit since combustion l1 of P406 was incomplete. From the appearance potential for the process P4010(g)+e+P40i(g) +40(g)+2e 32.6f 0.5 eV and the ionization potential of P406,10.6f0.5 ev there follows Dz,at(P406)= 4477+ 75 kJ mol-l.l Finally extrapolation of the atomization energies of P4010 through P407 yields D6,at(P406)= 4385 kJ mol-l. It is thus probable that the upper limit derived here is quite close to the atomization energy of P406 for which the value D;,at(P406) = 4385 (+40 -60) kJ mol-1 is proposed which implies AH&8,r(P406yc)= -1662 (+40 -60) kJ mol-l.Important results in this investigation are considered to be the identification and the determination of the atomization energies of the molecules P203 P204 P205 and P306. P203 and P205 are if not necessarily structurally at least formally the monomers of the molecules P406 and P4Olo. As mentioned above P406(g)was observed as a re-evaporation product whenever P203was important in the vapour. There is thus reason to believe that there are little or no kinetic limitations to the dimerization of P203to P406 which is thermodynamically highly favoured at low 3.-FREE TABLE ENERGY FUNCTIONS(-(Go-H")/T)/Jmol-I K-') AND ENTHALPIES ((Hf- Hi)/J mol-l) TIK p2odCs) PZodc~v P204(D2h) pZ%(ca) Pzos P306 p407 p408 p40u 298 258.5 250.5 254.7 268.7 270.7 277.1 287.4 298.8 303.5 1OOO 339.5 331.1 347.0 361.1 376.7 407.0 446.2 470.0 487.0 1200 354.5 346.1 364.7 378.9 397.5 433.7 479.4 505.9 525.7 1400 367.6 359.4 380.4 394.6 416.0 457.5 509.1 538.1 560.4 H2098-H 16 100 15 600 17 300 17 200 19 200 21 500 25 100 27 100 29 0oO HY3OO-H 110 800 111 800 132300 132800 155800 200600 250200 271 200 292400 3 0 P c m S.SMOES AND J. DROWART 147 temperatures. Likewise P204 and P306 may be considered to be the dimer and the trimer of PO2 of which P408 is the tetramer. Although the agreement between the second and third law enthalpies for the reactions leading to the atomization energies of P203 and P204 are satisfactory it can not be used to choose between the two structures envisaged nor to exclude completely free rotations analogous to those attributed to N2O3 N204 and N205.' Until further information becomes available D;,at(P203) = 2055 k15 Dg.at(P204) = = 2530+ 18 D&at(P205)= 3020+22 DGYat(P3O6)40123-24 kJ mol-1 are retained.Another result of interest is the observation of gaseous ternary compounds of high stabilities for which the preliminary values are D;,,t(NaP02) = 1395&40 Dg,at (KPO,) = 1375 +40 D;,,t(AgP02) = 1345+40 Dg,,,(SnPO,) = 1450&40 kJ mol-1 (observed in connection with the study of PO(g) 4). It is likely that similar molecules occur in many other high temperature systems such as flames.The authors thank Mrs. Y. Elsen and Mr. R. Huguet for assistance with the measurements and the evaluation of the data. They acknowledge support from the Fund for Collective Fundamental Research Belgium. APPENDIX THERMODYNAMIC FUNCTIONS For the atom Fe and for the molecules P2,8 P4,8 PO,' PO2:* P406,' P4010,~ and FeO,S the thermodynamic functions given in the references cited were used. For the remaining molecules the thermodynamic functions were calculated with the usual statistical mechanical formulae for the rigid rotor harmonic oscillator using estimated structures and vibration frequencies. These structures were estimated by analogy with those of the corres- ponding N-0 molecules taking angles and interatomic distances in P406 and P4010 into account 0 0 000 0 0 \/\/ \/ P2O3 \// (Cs) P-P or P P (C2J; P2O4 P-P (&)or \ /\ 0 0 0 0 0 0 000 \/ \/ \/ \/ P P (CJ; Pz05 P p (C2")./ // \\ 0 0 0 The O=P=O O=P-0 O=P-P and P-0-P angles are respectively 134 117,110 and 105". The P-0 distance adopted is 143 or 148 pm depending on whether P is tri or penta- valent ; while the P-0 and P-P distances are 165 and 205 pm. For P306 a plane hex- agonal P303 structure was used with an apical oxygen atom on each phosphorus atom and distances as above. The vibration frequencies adopted by comparison with those in the N-0 P406 and P4OlOmolecules are P2O3(CS) 150 130 110 65 50 30 25 (2) 20 mm-1 ; P203(C20) 130 110 80 65 50 (2) 40 30 lOmm-'; PZO4(&) 150 130 110 (2) 65 (2) 50 40 30 25 (2) 2Om-l; P204(Cs) 150 130 110 80 65 (2) 50(2) 40 30 25 10mn1-l; P,05(C2,) 150 130 110 (2) 80 65 (2) 50 (3) 40 30 25 10 mm-' ; P306(&) 140 (3) 97 (3) 65 (2) 60 (2), 45 (2) 40 (3) 35 (3) 300 (3) mm-l.For the molecules P407 through P409 the thermodynamic functions were linearly inter- polated between those for P406 and P4O10 taking differences in symmetry numbers into account. The numerical values of the thermodynamic functions are given in table 3. ATOMIZATION ENERGIES OF PHOSPHORUS OXIDES D. W. Muenow 0. M.Uy and J. L.Margrave J. Zmrg. Nucl. Chem. 1970,32,3459. A. Hashizume N. Wasada and T. Tsuchiya Bull. Chem. SOC.Japan 1966,39,150. L. W. Daash J. N. Weber M. A. Ebner and G. Sparrow J.Mass.Spectr. Zon Phys. 1969,2 500. J. Drowart C.E. Myers R. Szwarc A. Vander Auwera-Mahieu and 0.M. Uy,J.C.S. Faraday Trans. ZZ 1972,68 1749. J. Drowart A. Pattoret and S. Smoes Proc. Brit. Ceram. SOC.,1967 8 67. J. Drowart and P. Goldhger Angew. Chem. (Int. Ed.) 1967 6 581. 'J. Berkowitz M. G. Inghram and W. A. Chupka J. Chem. Phys. 1957,26,842. * JANAF Thermochemical Tables 2nd edn. (NSRDSand NBS 37 1971). L. Brewer and G. M. Rosenblatt Ado. High. Temp. 1969 2,l. lo G. Balducci G. De Maria M. Guido and V. Piacente J. Chem. Phys. 1971,55,2596. S. B. Hartley and J. C. McCoubrey Nature 1963,198,476 ;S. B. Hartley W. S.Holmes J. K. Jacques M. F. Mole and J. C. McCoubrey Quart. Rev. 1963 17,204.

ISSN:0301-5696    

DOI:10.1039/FS9730800139

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Active Aluminas Prepared by Plasma Vaporization BY M. F. BARRETT,D. C. HAVARD,I. G. SAYCE," B. SELTON AND R. WILSON Division of Inorganic and Metallic Structure National Physical Laboratory Teddington Middlesex Received 17th September 1973 Ultrafine alumina powders with hydroxylated surfaces have been prepared by a technique similar to that which earlier yielded thixotropically active silicas. The method involves vaporization of alumina under reducing conditions from a plasma-heated centrifugal furnace followed by oxidation with oxygen water vapour or carbon dioxide. The product is mainly yAl,O with an appreciable proportion of amorphous material. Surface areas measured by the BET method are in the range 100-160 m2 g-' while a typical water-content determined thermogravimetrically was 5.5 % by weight.The factors controlling product properties are discussed and these properties are compared with those of commercially available fine powders. Oxide powders with high surface area are widely used in industry for applications ranging from thixotropic agents and reinforcing fillers to catalysis and ceramic fabrication. Silica is one of the most widely used ultrafine powders and many of its applications depend on the highly hydroxylated surface which can be achieved with this oxide. While there are several methods available for the production of surface- active silicas some of the most highly dispersed materials result from the vapour phase hydrolysis of silicon compounds typically by the controlled combustion of silicon tetrachloride vapour in an oxy-hydrogen flame.Recently however comparable materials have been obtained by a route involving the reductive vaporization of pure silica in a thermal plasma followed by reoxidation of the vapour in the presence of water. This route avoids the preparation and handling of chlorine-containing compounds and promises to permit considerable economies if used on a large scale. Active aluminas have likewise found a range of applications mainly in the manu- facture of ceramic materials. In particular fine boehmite (A1203 .H20)powders may be dispersed in aqueous solutions and at suitable pH yield viscous sols which are used in certain refractory ceramic formulations and in the manufacture of polycrystalline fibres. Artificial boehmite powders are generally prepared by precipitation methodsY3 but other ultrafine alumina powders have been prepared by vapour phase routes.Again vapour phase hydrolysis of aluminium chloride in an oxy-hydrogen flame has been used,4 as has oxidation of an aluminium halide in an oxygen pla~ma.~ More recently the plasma evaporation of alumina has been investigated and has yielded submicron alumina powders at power consumptions of about 13 kWh/kg with the promise of considerably lower power consumptions on development. These powders were however less finely divided than the silica powders produced earlier consisting typically of a mixture of y-and &aluminas with surface area around 79 m2/g indicating a mean diameter (assuming spherical particles of density 3.4 g/ cm3) of about 22 nm.The object of the present work was to investigate methods of reducing the particle size of the powder and if possible to produce a highly hydroxyl- ated product comparable to the thixotropic silicas previously prepared. 149 ALUMINAS BY PLASMA VAPORIZATION CONDENSATION CONDITIONS The ultimate particle size of oxide species synthesised in flames has been interpreted as resulting from an interplay of the two factors homogeneous nucleation rate and growth rate.' Recent work however leads to the conclusion that the critical nucleus size may be of molecular dimensions and that the growth phase is all important8 In particular the ultimate particle size is determined by the time which elapses between the start of the reaction and the solidification of the oxide droplet.After that time Brownian collisions no longer lead to assimilation of one droplet by another in a process of coalescence but merely to aggregation of discrete particles. I I temp/K FIG. 1.-Molar quantities of major aluminium-containing species (Xi)present at equilibrium of system (A1203+2C) at one atmosphere total pressure (JANAF data lo). While these arguments have been applied to the condensation of thixotropic silicas,8 they do not account for the growth processes occurring during the early stages of condensation. In fact thixotropic silicas may well not form directly from small molecular species. The reaction path may involve production of small hydroxylated molecules followed by formation of hydroxylated polymer molecules which are then dehydrated to yield the well known Aerosil-type gel structure.Evidence for such a mechanism is provided by a recent patent in which arc-vaporized silicon monoxide was reacted with water vapour. The product was an intermediate containing both silane and silanol groups which on heating lost water and yielded a thixotropic powder comparable to conventional Aerosil silica. This process appears somewhat analogous to that proposed for carbon black formation where the soot particle is believed to grow by condensation of a tarry hydrocarbon droplet which evolves hydrogen until a solid particle results.' M. BARRETT D. HAVARD I. SAYCE B. SELTON R. WILSON 151 Whatever the growth mechanism the theories are in agreement with practice in predicting that the initial flame temperature is of major importance in determining ultimate particle size and that by reducing the flame temperature the particle size of the product will be reduced and its surface area increased.The present method of fine powder synthesis involves reductive distillation of the oxide and combustion of metallic and lower oxide species downstream of the furnace. In order to ascertain the most probable vapour species the equilibrium partial pressures were calculated from JANAFdata,l O by using a computer programme which determines equilibrium conditions by a process of free energy minimization. The calculation neglected the possible existence of oxy-carbide species in the liquid phase and employed an alumina to carbon mole ratio of 1 :2,this having been found in the previous study to give the most rapid distillation rate.Under these conditions the most important vapour species in a system at one atmosphere total pressure are shown in fig. 1. In the present work the distillation is carried out at temperatures in the region 2400 to 2600 K at which the major vapour species are A120(g) and Al(g) as suggested previously. In practice the distillation is carried out in the presence of an excess of nitrogen. The form of the equilibrium curves is then similar but as expected the monatomic species becomes relatively more important than the molecular vapour species. Recently a new value has been proposed for the standard enthalpy of formation of AlO(g).l Substituting this for the JANAF value causes a significant increase in the relative partial pressure of AlO(g) at the higher temperatures at the expense of other aluminium containing vapour species ; however AlO(g) makes only a small contri- bution below 2700 K.Production of the oxide powder requires reoxidation of the hot reduced vapour and this takes place at the exit of the furnace where oxidant gas is introduced. The flame temperature in the oxidation zone could be lowered by dilution with inert gas but preliminary experiments indicated that large volumes were required and that this approach would cause overloading of the particle collection facility. More satisfactory would be the use of an oxidant in which the vapour species have a lower heat of combustion yielding a lower flame temperature.Two such oxidants have been used in the present study carbon dioxide and water vapour. The enthalpy of combusion of A120(g) in carbon dioxide at 298 K (to form y-A1203 and carbon monoxide) is -229.3 kcal mol-l and in water (to form y-A1203) and hydrogen is -249.0 kcal mol-l compared with -396.0 kcal mol-1 in oxygen. Furthermore if the oxidant gas is present in excess its dissociation may be employed to buffer the flame temperature. Computer calculations indicate that at one atmos- phere total pressure carbon dioxide is 50 % dissociated (to CO 0 and 0,) at about 3060 K while water is 50 % dissociated (to H OH H2,0,and 0,) at about 3350 K. In fact under the conditions employed in typical experiments flame temperatures are likely to have been considerably below these temperatures.Typical vaporization rates correspond to vaporization of the following stoichiometric ratios Al,03 ; C :N2(plasma gas) = 1 :2 :20. Using JANAF data the equilibrium concentrations of the various species were calculated for a temperature of 2400 K. The gaseous species concentrations were then used in a further calculation in which the species were hypothetically reacted in an adiabatic flame with an excess of oxygen carbon dioxide or water. The quantities of oxidant were chosen to correspond to (approxi- mately) experimental values. Thus per mole of alumina used in the above equilibrium calculation were taken O2 50moles at 300K C02 40moles at 300K or H20 40 moles at 400 K.In this way approximate adiabatic flame temperatures were 152 ALUMINAS BY PLASMA VAPORIZATION computed corresponding to the synthesis conditions of the three powders discussed below ; these flame temperatures were 0 1788 K C02 1409 K and H20 1664K. EXPERIMENTAL The stream of aluminium vapour species was obtained using a centrifugal plasma furnace essentially similar to that employed in the earlier work.6 In this technique the alumina moulding composition (Cawoods Refractories " Alufused W " 99.3 % A1203)was mixed in molar ratio 1 :2 with finely divided carbon (British Acheson Petroleum Coke flour 97-98 % C) as reducing agent and cast in the form of a hollow cylindrical furnace core of dimensions 300 mm long 38 mm internal diameter 122 mm external diameter.After firing under nitrogen atmosphere at 850°C the composite cylinder was placed in the centri- fugal plasma furnace and rotated about a horizontal axis at some 450 r.p.m. while strongly heated internally using a d.c. plasma. Typical torch conditions were N280 l/min at STP input power -25 kW torch efficiency -90 %. The evaporation rate varied during the course of each experiment as the furnace first heated up and later became depleted of alumina however a typical evaporation rate under these conditions would be some 20 g/rnin of alumina. This vaporization rate corresponds approximately to the stoichiometry used in the calculations above i.e. A1203 :C :N2 21 1 :2 :20. The hot exhaust gases were rapidly mixed with the selected oxidant via a set of two or three jets and within a water-cooled reactor vessel downstream of the furnace.After reaction the products were cooled by passing through a water-cooled heat exchanger and cyclone which removed any larger particles. The product-laden gases were then led through an agglomerator (a series of baffles in a water-cooled tube which forced the gas through a tortuous path) and the powder was finally collected at a temperature of 120-180°C in a specially developed bag-filter unit. All metal parts of the quench and collection system in contact with products were of water-cooled copper or stainless steel. When water vapour was used as oxidant this was introduced as steam (-138"C 35 p.s.i.). The quench and collection equipment was cooled using warm water (-50'C) in order to prevent premature condensation of moisture which could have wetted the powder product.The properties of three products from this equipment will be discussed. First for comparison purposes an ultrafine alumina prepared by reaction of the reduced product with oxygen secondly with carbon dioxide and finally with water vapour. As the latter material appears to be of greatest potential interest this product was selected for more detailed study the results of which are recorded below. RESULTS CHARACTERISATION OF PRODUCTS X-ray powder photographs of all three products indicate the presence of y-Al,O and amorphous material. There is a small proportion of S-Al2O3present in the oxygen-quenched material corresponding to the higher flame temperature under these conditions.There appears to be an increasing proportion of amorphous product in the series O2<H20<C02,corresponding to a decrease in flame tempera- ture. Typical surface areas measured by nitrogen BET 12* l3 single point determination using a Micromeritics Automatic Surface Area Analyser Model No. 2200 showed a corresponding trend. Thus typical values for powders quenched in oxygen water and carbon dioxide were 72 123 and 137 m2 g-1 respectively. A particular water- quenched product was selected for more detailed study. The surface area of this sample was determined from the adsorption isotherm shown in fig. 2 measured with a BET apparatus which was constructed for standards work. A linear BET fitwas noted between the relative pressure limits of 0.05 and 0.25 and using a value of 0.162nm2for the area occupied by each molecule of absorbed nitrogen the surface M.BARRETT D. HAVARD I. SAYCE B. SELTON R. WILSON 153 area was found to be 132.0k0.4m2 g-l. The plot shows negligible hysteresis indicating the absence of appreciable mesoporosity. Fig. 3 shows an a plot for the powder,14 compared with Degussa silica TK 800 as reference. The latter powder is FIG.2.-"Ti trogen adsorp tion/desorption is0therm for water-quenched alumina. one of the IUPACISCIJNPL surface area standards.l For mesoporous materials significant positive deviation from linearity would be expected at higher values of a, whereas for microporous materials a negative deviation would be expected. The absence1of significant deviation confhms the non-porous nature of the present product.I so I I I I I I 0 cc,(T K 800) FIG.3.-as plot (reference Degussa silica TK 800) for water-quenched alumina. An electron micrograph of the water-quenched material (fig. 4(a))shows that the individual particles are approrrjmately spherical with the particles aggregated in clusters. It is possible with difficulty to disperse these in certain solvents and isolated 154 ALUMINAS BY PLASMA VAPORIZATION particles may occasionally be seen. The form of the powder is similar to that of a non-hydroxylated silica gel obtained by condensation from a flame or plasma. It contrasts markedly with the highly aggregated appearance of a hydroxylated fumed silica. Fig.4(b) shows a micrograph of a thixotropic silica obtained by plasma vaporization and quenching in an environment containing water vapour.2 This product has a characteristic web-like structure with substantial necking between individual particles. X-ray powder photographs showed both silicas to be amorphous. diamlnm FIG.5.-Histogram of particle size distribution for water-quenched alumina. A histogram showing the particle size distribution of the water-quenched material is shown in fig. 5. This was taken from an electron micrograph. The specific surface area determined from the micrograph l6 is 108 m2g-l substantially lower than that determined from the nitrogen adsorption isotherm. This discrepancy is not unexpected and indicates either a surface roughness of the particles or an inability to take full account of the smaller particles in an electron micrograph.Furthermore a statistically reliable result would only be obtained by averaging the data from a number of representative micrographs. Thermo-gravimetric analysis of the water-quenched product gives a weight loss of 5.5 % between 20 and 1000"C with the bulk of the loss occurring between 80 and 200°C. Permitting the samples to cool in air to 20°C results in a weight gain of 2.75 % over 24 h. These weight changes are the result of loss and later re-adsorption of water. Some indication as to the nature of this process may be obtained from spectroscopic studies. Transmission infra-red spectra of pressed discs of all three aluminas showed a very broad intense band between 2600 and 3750 cm-l.Such bands are common to silicas aluminas and several other inorganic oxides and result from the overlapping bands due to 0-H stretch vibrations from hydroxyl groups bound to surface Al atoms and from adsorbed molecular water.17* l8 A less intense and narrower peak at 1630 cm-l is attributed to the bending frequency of molecular water. The broad band exhibits a small shoulder at 369Ocm-l which is attributed to bonded -OH groups. The alumina samples were heated in air at various temperatures between 100 and 1000°C. On cooling the broad band (2600 to 3750 cm-l) and the band at 1630 cm-l were found to have decreased in intensity and the shoulder at 3690 cm-l was now clearly resolved. This treatment did not however reduce any of the above peaks to zero intensity.A typical spectrum of water-quenched alumina after heating at 750°C for 24 h is shown in fig. 6. FIG.4.-Electron~micrographs of plasma-produced powders (a)water-quenched alumina ; (6)thixo-tropic silica. [Toface page 154 M. BARRETT D. HAVARD I. SAYCE B. SELTON R. WILSON 155 The persistence of these peaks suggests either that the adsorbed water is particu- larly difficult to remove even at 1000°C,a suggestion not supported by the thermo- gravimetric analysis or alternatively that rehydration of the water-free surface occurs rapidly. In order to avoid such rehydration the infra-red adsorption of the wavenumber/cm-l 4000 3500 3000 25001800 1600 I400 FIG.6.-Infra-red spectrum of water-quenched alumina after heating in air for 24 h at 750°C and then cooling to 20°C.pressed discs was studied while heating under vacuum in a cell similar to that described by Harrison and Lawrence.lg Under vacuum both the peaks ascribed to molecular water and that ascribed to bonded -OH groups were reduced to near zero intensity by heating at temperatures as low as 100OC. The spectrum in fig. 7 is typical being recorded after heating under reduced pressure (0.3 Torr)at 140°Cfor 3-5 h and cooling under vacuum to room temperature. The twin peaks at 2820 and 2900 cm-l were observed consistently in several samples and have not been identified wavenumber /cm-l 4000 3500 3000 2500 I I I I FIG. 7.-Infra-red spectrum of water-quenched alumina after heating at 140°C under vacuum (0.3 Torr) 3.5 h and then cooling to 20°C.ALUMINAS BY PLASMA VAPORIZATION The comparative ease of dehydration of all three aluminas contrasts with observa- tions by other workers on y-A1203 aerogels.2o It is possible that removal of bonded hydroxyl groups is facilitated in discs formed under pressure because the increased proximity of these groups aids their condensation. Such an effect has been observed in pressed discs of Cab-0-Sil silica.21 However in the present work all hydroxyl groups appear to have been removed at a much lower temperature. loo-PH FIG.8.-Viscosity of a 10 % by weight aqueous suspension of water-quenched alumina as a function of pH. The availability of surface hydroxylation for interparticulate hydrogen bonding finds important application in the use of fine powders as thickening agents.The ability of the water-quenched alumina to act in this way is demonstrated in fig. 8. Viscosity measurements were made using a Ferranti Portable Viscometer Model VM on a 10 weight per cent aqueous suspension of alumina the pH being adjusted by addition of dilute solutions of hydrochloric acid and ammonia. To facilitate mixing the suspensions were prepared at low pH values. Viscosity measurements were made at the lowest possible shear rates (8.73 s-l for viscosity values greater than 2P) compatible with the instrument. At the higher pH values the suspensions displayed non-Newtonian characteristics and viscosity values at pH greater than 5 in fig.8 must be regarded as minimal values. The sharp increase in viscosity at pH 5.9 is noteworthy and may be compared with a similar increase at pH 6.2 observed for suspensions of Cabot Alon,22 a commercial fumed alumina similaf to Degussa Alumina C prepared by flame hydrolysis of aluminium ~hloride.~ The presence of residual hydrochloric acid or chlorine on the surface of Alon presumably accounts for the lower pH (4.4) of the 10 % suspension in water compared with that of a similar suspension of the present water-quenched alumina (pH 7.7). M. BARRETT D. HAVARD I. SAYCE B. SELTON R. WILSON 157 CONCLUSIONS High surface area alumina powders have been prepared by plasma vaporization and condensation. Despite attempts to prepare a highly hydroxylated product the hydroxylation which has been achieved is readily removed on heating; however rehydration also occurs readily in moist air.The morphology characteristic of hydroxylated silica aerogels prepared by flame or plasma routes has not been achieved with alumina under comparable conditions. Although hydroxylated alumina species have been proposed,lO* l1 it would appear that their stability or ability to form polymeric chains is lower than that of their counterparts in silicon chemistry If more highly hydroxylated aluminas are to be produced by this route it would appear that reoxidation of the vapour species must be achieved at temperatures lower than those employed in the present work. The present products have been characterised and found to be closely comparable to commercial fumed aluminas.They are however uncontaminated by halogens and have a somewhat higher surface area than those quoted for commercial products. It would appear that submicron aluminas could be prepared by this route at a commer- cially competitive price should a demand exist for this type of product. The authors gratefully acknowledge the contribution of Dr. R. E. Shawyer of the Division of Quantum Metrology National Physical Laboratory who carried out the thermodynamic computations discussed in this paper. R. Bode H. Ferch and H. Fratzscher Kautschuk u. Gummi Kunststofe 1967 20 578. D. A. Everest I. G. Sayce and B. Selton Symposium on Electrochemical Engineering New- castle-upon-Tyne 1971 I. Chem. E. Symposium Series ed.J. D. Thornton (Institute of Chem- ical Engineers London 1973) vol. 2 p. 108. W. H. Gitzen Alumina as a Ceramic Material (American Ceramic Society Columbus Ohio 1970) p. 13. K. A. Loftmann Ultrafine Particles ed. W. E. Kuhn (Wiley New York 1963) p. 196. T. I. Barry R. K. Bayliss and L. A. Lay J. Mat. Sci. 1968 3,229. D. A. Everest I. G. Sayce and B. Selton J. Mat. Sci. 1971 6 218. R. W. Hermsen and R. Dunlap Combustion Flame 1969,13,253 G. D. Ulrich Combustion Sci. Tech. 1971 4 47. A. Jlligen (sic) and W. Neugebauer G. Offen. 1932 291/1971. lo JANAF Thermochemical Tables (U.S. Department of Commerce National Bureau of Stand-ards 2nd ed. 1971). l1 D. E. Jensen and G. A. Jones J.C.S. Faraday I 1972 68,259. l2 S. Brunauer P. H. Emmett and E. Teller J.Amer. Chem. SOC. 1938 60 309. l3 B.S. 4359 Methods for the Determination of Specific Surface ofPowders Part 1 (British Standards Institution London 1969). l4 K. S. W. Sing Surface Area Determination ed. D. H. Everett and R. H. Ottewill (IUPAC Butterworth London 1970) p. 25. D. H. Everett G. D. Parfitt K. S. W. Sing and R. Wilson J. Appl. Chem. Biotechnol. 1974 24 199. l6 T. Allen Particle Size Measurements (Chapman and Hall Ltd. London 1969). l7 M. L. Hair Infra-red Spectroscopy in Surface Chemistry (Edward Arnold Ltd. London 1967). L. H. Little Infra-red Spectra of Adsorbed Species (Academic Press London and New York 1966). l9 F. R. Harrison and J. J. Lawrence J. Sci. Instr. 1964 41 693. 2o J. B. Peri and R. B. Hannan J.Phys. Chem. 1960,64,1526. R. S. McDonald J.Phys. Chem. 1958,62,1168. 22 Cabot Corporation Technical Literature.

ISSN:0301-5696    

DOI:10.1039/FS9730800149

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Transport of Beryllium in Beryllium Dichloride Vapourt BY P. GROSS*AND R. H. LEWN Fulmer Research Institute Limited Stoke Poges Buckinghamshire Received 4th September 1973 Experiments on the transport of beryllium in beryllium dichloride vapour at about 1x atmospheres have been made in the temperature range from 1250 to 1500K. The transport can well be interpreted as resulting from the reaction Be(s)+BeC12(g) = 2BeCl(g) (1) and agrees with that extrapolated from previous transport experiments by Greenbaum Arin Wong and Farber between 1570 and 1725K. A third law analysis of all the experiments leads to AH&,? ,BeCl(g) = 1.7 k0.7 kcal/mol. This interpretation of the transport experiments can however not be reconciled with mass spectroscopic equilibrium measurements by Hildenbrand and Theard which led to AH:298,BeCl(g) = 13.1+2.2 kcal/mol.Second law analysis of the transport expetiments interpreted as resulting from Be(@+BeCLCg) = (BeCl)z(g) (2) is much less satisfactory than that from (1) and their third law analysis according to (2) with a reason- ably estimated entropy for (BeC1)2(g) leads to a well defined enthalpy of reaction 2 (z= *1.2), but to an enthalpy of dimerisation of about -90 kcal which is much more negative than one can expect. The transport of beryllium in beryllium dichloride vapour of about 1 Torr pressure between 1573-1723 K has been studied by Greenbaum Arin Wong and Farber (referred to subsequently as GAWF). The authors evaporated solid beryllium dichloride from a container through a connecting tube into a beryllia Knudsen cell charged with liquid beryllium.They assumed that the reaction BeCl,(g) +Be(1) = 2BeCl(g) (191) occurs and calculated the pressures of beryllium dichloride and beryllium mono- chloride from the weight loss from the beryllium dichloride container and the weight loss from the effusion cell after correction for the evaporation of the beryllium. By third law analysis of their experiments the authors obtained AH&98BeCl(g) = 2.0+ 0.8 kcal/mol. A few years later Hildenbrand and Theard (in the following HT) published the results of experiments in which they passed hydrogen chloride gas into the Knudsen cell of a mass spectrometer which contained aluminium and beryllium (between 1380 and 1550 K) and measured the intensities of the lines Be+ BeClf BeCl; AI+ and AlCl+ at ionising energies of 2 and 5 eV above threshold.From the equilibrium constant of the two isomolecular reactions Be(g) +AlCl(g) = BeCl(g) +Al(g) (2) Be(g) +BeC12(g) = 2BeCl(g) (1 €9 t This research has been sponsored in part by the Air Force Office of Scientific Research through the European Office of Aerospace Research EOAR United States Air Force under Contract NO.F 61052-70-C-0021). Further details are given in a report submitted to the European Office of Aerospace Research (R. 163/SR/8) in JuIy 1971 which is obtainable from the National Technical Information Service Springfield Va. 22151 USA. 158 P. GROSS AND R. H. LEWIN they derived by third law enthalpies of formation of beryllium monochloride gas which are practically identical with each other [AHf"zss,BeCl(g) = 15.3k2.0 and 14.1& 2.5 kcal/rnol] but about 1 1 & 2 kcal/mol more positive than that obtained by GAWF.This corresponds to a calculated transport of beryllium which is only a few per cent of that actually found by GAWF. No reason for the discrepancy is apparent. Features of the experiments by GAWF with which fault may be found but which can hardly explain the large discrepancy are (i) Some beryllium and beryllium monochloride can diffuse backward into the tube connecting the beryllium dichloride evaporator with the Knudsen cell and thus lead to a wrongly calculated too high monochloride pressure. (ii) The total pressure was rather high for molecular flow through their orifice but this may diminish the error mentioned under (i).EXPERIMENTAL APPARATUS AND PROCEDURE Some non-evident error in either of the investigations may have occurred and experiments are reported here which are similar to those by GAWF in which in an all-alumina apparatus beryllium dichloride at a pressure not exceeding 0.35 Tom and usually much lower was led into a Knudsen cell containing solid beryllium. However only that part of the beryllium removed from the effusion cell by reaction and evaporation that passed through the Knudsen orifice was absorbed in a platinum or nickel absorber and determined spectrographically so that the beryllium monochloride or beryllium vapour which diffused back into the con- necting tube cannot falsify the calculated pressure.The molecular effusion apparatus is shown in fig. 1 (a and b) which with its legend is self explanatory. ANALYSIS For the analysis of the beryllium absorbed the absorber sheet was washed in distilled water cut into sections and dissolved in aqua regia for spectrographic analysis of the solutions. Traces of aluminium were found and also determined spectrographically. It is assumed that they had been transferred into the condenser by the reactions AI2O3(s)+ 2Be(s)+ BeC12(g) = 3BeO(s)+ 2AlC1 (3) 2AlCl+ Pt(excess) = 4/3Al(diss. in Pt excess)+ 2/3A1Cl3(g). (3a) The solutions of the sheets in aqua regia were made up to contain standard concentrations of platinum (or nickel) and the relative intensities of suitable lines of beryllium and aluminium were compared with those of solutions of the same concentration of platinum and containing various known amounts of beryllium and aluminium.The error of the concentrations thus determined is considered to be in general not greater than .t10per cent.* MATERIALS BERYLLIUM CHLORIDE Selected crystals of the purest obtainable beryllium chloride (Brush Beryllium Company) were sublimed twice through a glass filter at about 400°C in vacuum. The purified chloride condensed as crystals in Pyrex tubes which were sealed off immediately after distillation. All operations involving the distilled beryllium chloride were carried out in a glove box through which carefully dried air was circulated. BERYLLIUM The beryllium was either super-purity crystals obtained as a gift from " Pechiney " Paris through the courtesy of Dr.C. Roy or a high purity beryllium (99.8 %) "swarf " standing on a 30 mesh sieve purchased from the Royal Ordnance Factory Cardiff. * As far as Dossible error limits are twicethe standard deviationof the mean. 160 BERYLLIUM TRANSPORT IN BERYLLIUM DICHLORIDE FIG.[l(u).-Pyrex envelope. The molecular effusion apparatus was suspended on thin alumina rods inside the 1Ocm diameter Pyrex tube S. R U W platinum wound furnaces designed to have a small thermal capacity and no gas absorbing parts TR TU TW polished nickel radiation shields ; M metal end plate ; 0,sealing ring ; X connection to the ionisation gauge (pressure about Torr when the system was cold and about lo-' Torr when the furnaces were at temperature) ; NW NU NR connections to furnaces HIC H2C connections to thermocouple; V connection through cold trap to high vacuum oil diffusion pump.FIG.l(b).-Molecular effusion apparatus made entirely from recrystallised alumina. A beryllium dichloride evaporator ; B beryllium dichloride ; C nickel gauze ; E alumina connecting tube ; F alumina pluck ; G beryllium (crystals or swarf) ; H1 H2 platinum-30 % rhodium-platinum thermocouples measuring and controlling the temperature of the effusion cell and the BeCl evaporator to within f 3.0"C; I effusion hole (cross section measured under the microscope length determined from X-ray photographs) ; J condensation zone ; K platinum or nickel absorber ; L1 alumina temperature distributor L2 copper temperature distributor ; d ... d typical temperature distribution measured by a sliding thermocouple in a dummy apparatus with an enlarged effusion hole. TRANSFER AND CHECK EXPERIMENTS Apart from the transfer experiments two types of blank experiments have been carried out. To check the whole experimental arrangement and procedure five experiments on the evaporation of beryllium were mslde in the same apparatus in the range 1280-1500K in the absence of beryllium chloride. The evaporated beryllium was absorbed on platinum absorbers. The average ratio between calculated and experimental pressures was 1.12 and if one of the experiments is excluded the average ratio = 1.02 Secondly it appeared in the course of the experiments that some beryllium was absorbed on the absorbers when beryllium chloride was passed through an identical apparatus which had not been used for beryllium transport and did not contain any beryllium.Blank experiments with approxi- mately the same amount of beryllium chloride as in the equilibrium experiments were there- fore made at various temperatures and the amount of absorbed beryllium determined. RESULTS Details of the transport experiments are given in table 1. For the evaluation of the equilibrium constant (KJ of the reaction Be($ +BeCl,(g) = 2BeCl(g) (1 s) from the experiments adjustments have to be made to the total amount of deposited P. GROSS AND R. H. LEWIN beryllium (Be) for the beryllium directly (Be ev) evaporated and for the beryllium absorbed (Be abs) from the dichloride.For the evaluation of the beryllium dichloride pressure the amount lost from the beryllium dichloride container has to be corrected for that consumed by reaction (l) and further for that small amount of beryllium dichloride which presumably reacts with the formation of aluminium monochloride (reaction (3a)). TABLE 1.-TRANSFEREXPERIMENTS AND THEIR EVALUATION A = orifice area w = Clausing factor BeC12 = BeC12 evaporated Be = total beryllium in absorber A1 = in absorber (mmol equivalents BeCl,) Be evap. = Be abs. = Be evaporated Be absorbed from BeCl p12= pressure of BeC12,pll = pressure of BeCl Kl= equilibrium constant for the reaction Be(s)+BeC12(g) = 2BeCl(g). Duration inNo. 1 was 14 100 s in all others 14 400. Theevaporation from the BeCI2 container during its heating up and cooling down period was negligible.no. T/K Alcmzl03 w BeC12 mmol Be mmolx 102 A1 mmolx4 Be(ev)mmolx 102 Be(abs)mmolx 102 2’12 atmx 104 2’11 atmx 105 K1 atmx 107 1 1253 10.0 0.80 3.27 5.64 0.12 0.39 1.85 1.96 0.324 0.536 2 1278 5.42 0.80 2.13 4.32 0.062* 0.40 1.18 2.35 0.472 0.948 3 1278 6.65 0.57 0.47 2.71 0.032 0.35 0.27 0.56 0.406 2.94 4 1278 6.65 0.57 0.98 2.26 0.062* 0.35 0.55 1.19 0.268 0.604 5 1388 6.65 0.57 0.946 18.6 0.038 3.80 0.53 1.05 2.94 82.30 6 1388 3.20 0.90 0.974 8.51 0.155 2.88 0.55 1.36 1.37 13.8 7 1398 5.41 0.80 0.709 21.6 0.038 5.20 0.40 0.611 2.90 138 8 1398 5.41 0.80 0.502 15.5 0.000 5.20 0.28 0.482 1.83 695 9 1498 1.87 0.90 0.54s 31.1 0.056 12.4 0.31 1.01 8.61 734 10 1498 1.87 0.90 0.928 26.0 0.054 12.4 0.52 2.38 6.16 159 * not analysed average taken.For a scrutiny of the quantitative agreement between GWAF’s results and ours their experimental pressures have been recalculated and the equilibrium constants Klreferring to unstable solid beryllium derived from them. The order of magnitude of the equilibrium constants of this investigation (fig. 2 0) agrees with those found by GAWF (fig. 2 a). Both sets of results (GAWF) and our own have been subjected singly and combined to least square treatment to give log Kl = -A1/T+ B1. Table 2 gives the values for Al and B1thereby found their standard error the standard error of the estimate and Fisher’s I; values as a measure of the correlation between log K and 1/T.The table also gives the estimated equilibrium constants at 1500 K i.e. a little below the lowest temperature of the experiments by GAWF and at the upper end of our own; the agreement between the two estimated equilibrium constants is good (it is also not too bad at the two extreme ends of the temperature range fig. 2). From the Al values the corresponding values for the enthalpy of reaction 1 at 298 K and their uncertainty limits have been derived and are also given in table 2. Although they differ appreciably from each other their difference is well within the rather wide uncertainty limits. For a more reliable value for the enthalpy of reaction (1) the equilibrium constants obtained by GAWF and those found in this investigation have been subjected to a third law analysis using JANAF’s values of (FF-Hgg8)/Tfor Be(s) BeCl,(g) and BeCl(g).The results are given in table 3 (3rd column) which shows that the two sets of data are in agreement with each other. The final value for the standard enthalpy of reaction (1) at 298 K AHFl,298 = -89.3kO.8 kcal/mol (which is just compatible with that in table 2) with AHf0298BeC12(g) = -86.0k2.5 leads to a standard 162 BERYLLIUM TRANSPORT IN BERYLLIUM DICHLORIDE 104 KIT FIG.2. enthalpy of formation of beryllium monochloride gas of BeCl(g) = 1.6+ 1.3 kcal/mol. The results of GAWF’s and our investigations are therefore incompatible with those of HT which lead to values of Kl that are only 1.5 x of ours. TABLE2 GAWF a this investigation b combined a+b 20.10 22.54 20.75 3.34 5.22 1.67 9.01 10.78 9.43 2.03 3.85 1.13 0.103 0.343 0.258 145 75 616 4.08 4.47 3.98 96.4 106.3 98.7 15.3 23.9 7.6 3.6 11.3 6.3 7.2 4.4 2.0 1.8 7.2 3.5 4.4 3.2 1.4 1.o 27.6 39.8 P.GROSS AND R. H. LEWIN In a short discussion of the paper by GAWF HT remark that “the difference may be due to additional unrecognised processes which could increase the beryllium transport thereby causing GAWF to over-estimate the BeCl concentration ” but also find that the “discrepancy is puzzling and disturbing ” TABLE3 T/K -log K1 AH:l,29g/kcal mol-1 -log Ks AH;s,298/kcal mol-I 1253 7.27 91.7 1.93 21.8 1278 7.02 91.9 1.91 22.5 1278 6.53 89.1 1.29 18.5 1278 7.23 93.2 1.81 21.6 1388 5.09 87.5 0.71 16.4 1388 5.86 92.3 1.16 19.3 1398 4.86 86.6 0.48 15.1 1398 5.16 88.5 0.58 15.7 1498 4.13 87.5 0.15 13.6 1498 4.80 90.6 0.745 17.7 - part mean 89.9 18.2 twice standard deviation & 1.5 1.8 1573 3.75 89.0 0.43 5 16.3 1574 3.72 88.6 0.49 16.7 1575 3.78 89.3 0.68 18.2 1603 3.60 89.5 0.53 17.3 1636 3.33 89.2 0.53 18.7 1664 3.04 88.4 0.29 16.2 1695 2.71 87.5 0.23 16.0 1696 2.73 87.6 0.20 14.95 1722 2.61 87.9 0.05 21.6 1724 2.89 90.3 0.96 18.7 part mean 88.7 17.5 twice standard deviation k0.6 1.2 total mean 89.3 17.85 twice standard dev.total & 0.8 1.1 The possibility of complex formation cannot be excluded but it is clear that for any polymerisation the entropy loss would have to be over-compensated by a com- paratively greater enthalpy of association.Nevertheless in order to investigate the possibilities of polymerisation we have calculated from all the available transport experiments equilibrium constants for the following reactions Be(s) +BeC12(g) = (BeCl),(g) 3Be(s)+3BeC12(g) = 2(BeCl),(g) Be(s) +3BeC12(g) = 2Be2Cl,(g) Be +2BeC12(g) = Be,C14(g) assuming that they do not occur simultaneously. The beryllium monochloride found in some experiments is so high that the formation of the molecules Be2C13 or Be3C14 eqn (7) and (8) respectively would absorb more beryllium dichloride than was introduced into the cell. We have further subjected the equilibrium constants BERYLLIUM TRANSPORT IN BERYLLIUM DICHLORIDE of reactions (5)-(8) to a least square second law analysis.In reactions (6) to (8) the fit of the regression of log Kon l/Tis very bad and only for reaction (5) it is acceptable though it is very much worse than in the case of reaction (1) (see table 2). In view of the unreliability of second law least square treatment of equilibrium data we have tried to subject all the data for reaction (5) K5 to a third law treatment. This is not possible unambiguously because data for the derivation of the molar heat capacities (entropies and enthalpies) of the double molecule are not available. We have therefore made an estimate of these magnitudes for a planar dimer molecule (Be2Cl,) on the basis of data for monomer beryllium chloride gas and monomer and dimer alkali-particularly lithium-chloride gas.The estimated values all valid at 1500 K are Cp" = 19.3 cal K-l mol-1 (Hf500-&,8) = 22.75 kcal/mol and S;500= 101.50 cal K-l mol-l. With these estimates one arrives at the individual values of AH:5,298 given in table 3 (last column) and obtains for the standard heat of reaction (5) at 298 K from our own from those of GAWF and the combined set of experiments = 18.2rfI 1.8 17.5+ 1.2 and 17&* 1.1 kcal/mol respectively. The standard error in the enthalpy of reaction thus derived is acceptable and with the standard enthalpy of formation of beryllium dichloride gas one obtains Be2Cl,(g) = -68.2+ 2.7 kcal/mol. This value is very much more negative than one can expect since with BeCl(g) = 13.1 k2.2 from HT it would give for the standard enthalpy of association in dimer beryllium chloride AH&298,Be2Cl,(g) = -94.3 3.5 kcal/mol which is nearly 18 kcal/mol more negative than the sum of the enthalpies of association in (LiCl),(g) [AH~ss,2gs(LiCl),(g) = = -50 kcal/mol] and in (Li,) [AH&s,298(Li)2(g) -26.4 kcal/mol].This discrepancy cannot be explained as deriving from the choice of a too small value for the standard entropy of (BeCl),. If one increases Si'500(BeCl)2(g) by 5.5 cal K-l mol-l for which there is no justification one obtains AH;5,298 = 26.1 which leads to AH&298 = -86 which is still 10 kcal/mol too negative. We thank M. Farber D. Hildenbrand and M. Krauss for helpful discussions. We thank Mr. D. Nicholas for the spectrographic analysis and express our gratitude to the U.S.Air Force Office of Scientific Research who sponsored this research through the European Office of Aerospace Research. M. A. Greenbaum M. L. Arin M. Wong and M. Farber J. Phys. Chem. 1964,68,791. D. L. Hildenbrand and L. P. Theard J. Chem. Phys. 1969,50,5350. 0. Kubaschewski and W. A. Dench Acta Met. 1955,3 339. E. A. Gulbransen and K. F. Andrew J. Electrochem Suc. 1952 97 383; R. B. Holden R. Speiser and H. L. Johnston J. Amer. Chem. Sue. 1948,70,3897. JANAF Thermochem. Tables 2nd edn. NSRDS and NBS 37 (1971). P. Gross C. Hayman P. D. Greene and J. T. Bingham Trans. Faraday Suc. 1966 62 2719 and JANAF Tables.

ISSN:0301-5696    

DOI:10.1039/FS9730800158

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

GENERAL DISCUSSION Prof. F. M. Page (University of Aston in Birmingham) said I would point out that our determination of the bond energy of A10 does not depend on the choice of a value for thefnumber. We may use our results to calculate anfnumber which agrees with Vanpee.2 The calculation of Farber is a two-edged weapon. I presume that the mass spectrometer used is the same as that described in Combustion and FZame 3-which I would prefer to describe as a three-stage vacuum system with atmospheric control since the first stage controls the pressure at which the flame burns. Would Farber state what that pressure was and further what allowance for reactions occurring in the sampling nozzle were made?4 These reactions may affect not only the aluminium species but also the flame gas constituents which are unlikely to be at equilibrium.Finally what steps were taken to establish the flame tempera- ture at the sampling point? I have long pondered on the difference between the flame and the mass spectrometric bond energies for AlO and I would stress that the three published flame values are supported by a great deal of unpublished observa- tions on sensitivity in flame photometric analysis. Prof. J. Drowart (Vrije Universiteit Brussels) said With respect to the dissociation energy of the molecule AlO the results of exchange eq~ilibria,~~' of partial pressure measurements in the A1203 system * and of chemiluminescence or laser-induced fluorescence lo in reactions in molecular beams are all in good mutual agreement.The shock-tube data l1 may be further re-interpreted to give together with the other results a quite accurate value for D8(AlO). The exchange equilibrium 5* AlO(g)+Ti(g) = Al(g)+TiO(g) AH; = -36.3 kcal/mol yields Dfj(A10) = 121.5k2.5 kcal/mol. This result is based on Dg(Ti0) = 157.8f 1.0 l2kcal/mol itself confirmed by exchange equilibria with GeO for which AH8 = +2.8 l3 and -0.1 kcal/mol were determined. D8(GeO) = 156.4rf:1.5 kcal/mol,14 derived from thermochemical cycles based on the vaporization of GeO (amorphous) and of Ge(c)+GeO,(hex) has in the meantime been confirmed by the study of the exchange equilibrium with SnO which yields D8(GeO) = 157.5+ 1.5 kcal/mol. For SnO the spectroscopic value Dg(Sn0) = 125.7& 1 kcal/mol in agreement R.N. Newman and F. M. Page Combustion and Flame 1971,17,149. M. R. Kineyko A. R. Caruso and M. Vanpee Combustion and FZame 1970,14,381. M. Farber and R. D. Srivastava Combustion and Flame 1973 20 33. A. N. Hayhurst and N. R. Telford Proc. Roy. Soc. A 322,483. W. Van Campenhout Licence Thesis (Vrije Universiteit Brussels 1970). J. Drowart S. Smoes and T. Walec to be published. 'D. L. Hildenbrand Chem. Phys. Letters 1973 20 127. M. Farber R. D. Srivastava and 0. M. Uy J.C.S. Faraday I 1972 68,249. J. L. Gole and R. N. Zare J. Chem. Phys. 1972,57,5331. lo R.N.Zare Ber. Bunsenges to be published. l1 D. C. Tyte Proc. Phys. SOC.,1967,92 1134. l2 J. Drowart P. Coppens and S. Smoes J. Chem. Phys. 1969,50,1046. l3 P. J. Hampson and P. W. Gilles J. Chem. Phys.1971,55 3712. l4 P. Coppens S.Smoes and J. Drowart Trans. Faraday Soc. 1967,63,2140. B. Rosen Spectroscopic Data Relative to Diatomic Molecules (Pergamon Press Oxford 1971). 166 GENERAL DISCUSSION with thermochemical data from the vaporization of the Sn(2) + SnO,(c) system,l is used. That the exchange reactions, AWg) + O(d = Al(d + 02(d and A1W) + S(g) = AKg) + Wg) yield slightly lower values for DZ(AlO) 1 17.8 3 and 118.6f2.5 kcal/mol respec- tively may be related to differences in assumptions concerning relative ioniza- tion cross-sections a. With o(AlO)/a(Al) N 0.7 as for several other oxide^,^ o(O2)/o(0)= 1.8,4 and o(S0) 2~ +[o(S>+a(O)] (by extension of qualitative argu- ments given elsewhere 9 rather than a(AlO)/a(Al) = a(O,)/a(O) = a(SO)/a(S),2 D6(AlO) = 121.8k3 and 121.1 f2.5 kcal/mol are deduced from the above reactions.The lower wavelength limit of the chemiluminescence produced by the reaction Al(g) + 03(d + Aw-7)+ O,(g) studied under single collision conditions using molecular beam techniques yields DZ(Al0) 2 118.3 1.5 kcal/mol.6 This value depends however on assumptions concerning the relative kinetic energies of the reactants and products which can be modified to yield DZ(Al0) 2 120.1 1.5 kcal/mol.' Furthermore there are indica- tions of weak shoulders in the luminescence spectrum,6 which suggest that in addition to the vibrational level v' = 18 in A10(B2X+) on which the above limit is based also the level v' = 19 is formed which would yield DZ(Al0) 2 120.5+ 1.5 kcal/mol.More recent measurements of the laser-induced fluorescence studied in order to identify the vibrational energy of A10 formed in the reaction AKg) + 02m -+ AlO(g) + O(g) yield DZ(Al0) 2 120.6+ 1 kcal/mol. The limit of the continuous absorption by AlO(g) produced in shock experiments has been located at 2729 f5 A,* from which combined with the excitation energy of the A211i state of A10 D6(AIO) < 119.9 kcal/mol has been deri~ed.~ The absorp- tion curves in ref. (8) show however pronounced edges at 2655 and 2705 f5 A. The difference between the corresponding energies 725 cm-l agrees closely with the vibrational quantum in the A2111i state of AlO 720 ~m-l.~It is therefore proposed here that ;1 = 2655 and 2705A correspond to the absorption limits from v' = 0 and D' = 1 in A1O(A2I&) and that the fact that these can be distinguished implies that the upper state to which the transition takes place can hardly be re- pulsive.combined as previou~ly,~ with the term value for the A2nlstate above v = 0 in the X2X+ ground state of A10 < B6(AlO) < 122.1 kcal/mol is then ob-tained this upper limit being probably close to the actual dissociation energy. Comparison of the various thermochemical values DZ(A10) = 121.5,1° 121.8 and 121.1 (ref. (2) revised) and 119.4kcal/mol,ll briefly discussed above and of the R. Colin J. Drowart and J. Verhaegen Truns. Furuduy Soc. 1965,61 1364. D. L. Hildenbrand Chem. Phys. Letters 1973 20 127. R. J. Ackermann and E. G. Rauh J. Chem. Thermodyn. 1973,5,331.W. L. Fite and R. T. Brackman Phys. Rev.,1959,113 815. J. Drowart C. E. Myers R. Szwarc A. Vander Auwera-Mahieu and 0. M. Uy J.C.S. Faraday II 1972,68,1749. J. L. Gole and R. N. Zare J. Chem. Phys. 1972 57 5331. ' R. N. Zare Ber. Bmenges to be published. D. C. Tyte Proc. Phys. SOC.,1967 92 1134. J. K. McDonald and K. K. Innes J. Mol. Specfr. 1969 32 501. lo J. Drowart S. Smoes and T. Walec to be published. l1 M. Farber R. D. Srivastava and 0. M. Uy J.C.S. Faraduy I 1972 61 249. GENERAL DISCUSSION spectroscopic values D6(AlO) 2 120.6,l and D8(A10) < 122.1 kcal/mol thus shows excellent agreement and suggests that D8(AlO) = 121.4+ 1 kcal/mol should be quite accurate. Dr. H. A. Skinner (University of Manchester) said From thermal data given by Farber et al.bond dissociation energies of selected A1-0 bonds (kcal mol-') in different molecules compare as follows Al-0 = 120 HOAl-0 = 105 Al-OH = 131 04-0 = 118 OAl-OH = 118 AlO-A1 = 130 There is not a large spread of values over these examples although there would seem to be scope for considerable variation in the multiple bond character in these different A10 bonds. Possibly the binding energy in A10 is dominated by the ionic character less so by double bond character. I presume bond lengths are not available for comparison purposes? Prof. J. Drowart (Vrije Universiteit Brussels) said The possibility of deducing or corroborating the structures of the molecules P203 P204 and P205 by comparing the measured atomization energies with the sum of the bond energies suggested by Skinner was actually examined.It seems that no conclusive evidence for either of the alternate structures retained in the paper can be gained by this procedure which requires knowledge of the -P=O -P-0-and -P-P-bond strengths. The -P=O bond strength was estimated by comparing the smooth decrease in atom- ization energies in going from P4OlO to P407 which correspond to D8,at(P,OJ- D8,at(P40,1) = 535 550 and 560 kJ/mol for n = 10 9 and 8 respectively. The average 550-t-20kJ/mol is very similar to the -P=O bond strength in various X3P0 compounds where the extreme values are 520 and 650 kJ/mol. This bond strength is furthermore quite comparable with the dissociation energy of the mole- cule PO. The -P-0-bond strength was deduced from the estimated atomization energy of P406 itself taken to be 570 kJ/mol less than that of P407on the basis of the above smooth decrease.The -P-0- bond strength so obtained 365 kJ/mol is scarcely different from the value 380 kJ/mol deduced from (RO)3P compounds.2 With a value of 200 kJ/mol for the P-P- bond deduced from the atomization energy of P4 it can now be verified that the reconstructed atomization energies of P203,Pz04 and P205do not differ sufficiently to distinguish the alternate structures. A limiting factor is that the absence of experimental structural data for these mole- cules does not enable one to use correlations with variations in bond distances bond angles force constants to amend the bond strengths and to gain some insight into the structural reorganizations within the molecules as well as in the changes in hybridization and resonance energies in and between the bonds transferred.Nevertheless the measured atomization energies are not very dependent upon the actual structure because the numerical values of the free energy functions do not vary much with structure. The atomization energies would however differ from the reported values if some vibration frequencies were much lower than assumed or if internal rotations were present. Perhaps an argument in favour of the Cz,structure of P203 with an oxygen bridge is the apparent ease with which this molecule dimerizes to P406 which then R. N. Zare Ber. Bunsenges to be published. 'S. B. Hartley W. S. Holmes J.K. Jacques M. F. Mole and J. C. McCoubrey Quart. Rev. 1963 17,204. 168 GENERAL DISCUSSION appears as a re-evaporation product. This dimerization is somewhat more readily visualized with the C, than with the C,structure. Referring to Margrave’s question similar arguments can not be used for P205 since this molecule was under the experimental conditions less abundant than P4O10 and since no re-evaporation of P4010 could be detected. There can however be little doubt on the basis of the appearance potential 13 eV compared to 23 eV when P4OI0is the major component of the vapourY1 that P,05 is here a parent ion and not a fragment of P4010. Dr. Milton Farber (Space Sciences Inc. Monrovia California) said We have recently completed an effusion-mass spectrometer study of the reaction of elemental chlorine with beryllium metal in the temperature range 1415-1592 IS.* After establishing electron ionization intensity curves for the species involved and operating at 1-2 eV above their appearance potentials to ensure against fragmentation a second-law Van’t Hoff calculation of the Be+ intensities yielded a value of 77.0+2 kcal/mol for the heat of sublimation of Be.This is in agreement with the well- established value of 78 kcal/mol for the AHs298K of Be(c). A second-law value of 10.0k4 kcal was obtained for the AH at an average temperature of 1504 K employing the intensity data for the isomolecular reaction Be(g)+BeCl,(g) = 2BeCl(g). (1) After application of suitable cross-sections and electron multiplier corrections a third-law AHf298Kof 4.0+1 kcal/mol was obtained for BeCl.The second- and third-law values agreed within 1.7 kcal/mol and yielded an average value of 103.4 kcal/mol for the dissociation energy of BeCl(g). This value agrees within 1 kcal with the previous molecular flow effusion experiment the transport experiments of Gross and Lewin and the spectroscopic measurements of Novikov and Tunitskii. However it is in wide disagreement with the value of 91 kcal/mol reported by Hilden- brand and Theard. Their study involved the reaction of gaseous HC1 with a mixture of solid Be and A1 metals in a Knudsen cell. Their reported bond energy was based on average third-law values for the reactions involving the various A1 and Be com- pounds produced; we made a second-law least-squares calculation of their data for reaction (l) obtaining 29 5 16 kcal/mol indicating extremely widely scattered data.Further a second-law least-squares plot of their Be+ intensity resulted in a value of 63 39 kcal/mol. Since complete agreement exists among the three experimental studies described the widely scattered data obtained by Hildenbrand and Theard should be discounted. Dr. P. Gross (FulmerRes. Inst. Ltd) (partly communicated) In reply to Farber the cell in the experiments of Hildenbrand and Theard (HT) contained beryllium and aluminium in concentrations which were not the same at all temperatures. It is therefore not a valid criticism of the experiments that a second-law plot based on the intensities of the metal lines or on the equilibrium constants derived from them is unsatisfactory.We have derived the equilibrium constants of reaction (1s) from HT values for (lg) by multiplying them by the vapour pressures of solid beryllium at each tempera- ture. Subjecting HT (F.R.I. Report R.l63/SR/8 of which we sent copies to Farber and Hildenbrand in August 1971) to second-law analysis as is done for the other D. W. Muenow 0. M. Uy and J. L. Margrave J. Inorg. Nucl. Chem. 1970,32,3459. * M. Farber and R. D. Srivastava J.C.S. Farachy I to be published. GENERAL DISCUSSION values in table 2 gave Al = 23.22x lo3 26A1 = 3.62 x lo3,B1= 7.78 26B1 = 2.72 Fl= 170 lo5& 1500 = 9.3 x AH,298= 112.2kcal 26AHr = & 16.64 kcal. Fisher’s F value and the uncertainty intervals show the second-law analysis to be satisfactory.The HT second-law enthalpy of reaction agrees well with their third- law value but also with our own second-law enthalpy. Had we chosen to adopt our second-law heat we would no longer have had a big discrepancy between the HT heat and ours. However we consider second-law evaluation of our enthalpy of reaction much less reliable than the third-law one first because the uncertainty interval is very wide (it includes our own third-law value) and secondly the second-law empirical entropy of reaction (49.3 17.6 cal mol-1 K-l) which is coupled with the second-law enthalpy is 12.3 cal mol-l K-l greater than the calculated one. The high heat of reaction and a reaction entropy compatible with the theoretical value leads to a transport which is much lower than that actually observed. The problem of explaining the discrepancy is not resolved but becomes much less relevant by the agreement between the transport measurements and Farber’s new so far unpublished mass-spectroscopic investigations ; for further discussion we must await publication. At present I should be grateful if he would inform us whether he could with certainty avoid interference by fragmentation.

ISSN:0301-5696    

DOI:10.1039/FS9730800165

出版商:RSC    

年代:1973

数据来源: RSC