摘要:

AbstractTwo dimensional film formation on smooth surfaces has been investigated theoretically. The commonly used exponential law for nucleation and its limiting cases in connection with the Avrami theorem are examined critically.A new model for describing nucleation on surfaces on the basis of the classical nucleation theory is proposed. This model takes into account the time‐dependent supersaturation caused by the simultaneous processes of adsorption of molecules from the bulk to the surface and the real phase transition. The model was proofed experimentally by the investigation of condensation of 5‐bromocytosine on mercury electrodes in aqueous Na2SO4‐electrolyte solution. On the basis of the new model the experimental results can be for the first time explained consist

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000402

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractTetrahedral and octahedral palladium clusters with an entrapped proton, [Pd4H]+and [Pd6H]+, were considered as models of electron‐deficient palladium species encaged in a zeolite matrix. Density functional studies employing a gradient‐corrected exchange‐correlation potential have been carried out on the bare and protonated Pd4and Pd6clusters as well as on their complexes with a CO molecule adsorbed at the three‐fold hollow position. In line with the experimental data it is found that the protonation of palladium clusters leads to a reduced CO adsorption energy and an increased vibrational frequency of the adsorbed CO. The protonation energies of the clusters Pd4and Pd6were calculated to 9.4 eV and 9.9 eV, respectively. These large values are comparable to the proton affinity of such a strong base as NH3(calc. 9.2 eV) and support the hypothesis that, as a result of the interaction of the guest metal particles with zeolitic protons, electron‐deficient [PdnHx]x+species a

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000403

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe vaporization of the solid alloys of the Ti‐Al system has been extensively studied for the complete composition range of the system by using Knudsen effusion mass spectrometry at temperatures between 1113 and 1664 K. 19 alloy samples of different compositions covering the complete composition range were investigated and their Ti and Al partial pressures determined. Thermodynamic activities and chemical potentials of Ti and Al as well as Gibbs energies were evaluated for a temperature of 1473 K. Two independent methods were used for the determination of the Ti activities yielding consistent results. The large temperature range of the partial pressure measurement for three alloys in the homogeneity range of the TiAl phase rendered possible the determination of partial and integral thermodynamic functions (ΔH, ΔG) for the formation of this phase. The data obtained are discus

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000404

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractExperiments on thermal demixing of β‐Ag2+δS (high‐temperature phase) are reported. By means of a nonisothermal solid state galvanic cell, the redistribution of the metal excessδin an external temperature gradient has been investigated in the temperature range 200°C

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000405

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

Abstract1H and127I NMR, differential thermal analysis (DTA), differential scanning calorimetry (DSC), electrical conductivity, and powder and single crystal X‐ray diffractions were studied for trimethylethylammonium iodide. Three solid phases, named I, II, and III, were obtained above 410 K, between 336 and 410 K, and below 336 K, respectively. Powder X‐ray patterns showed that Phase I and II have a NaCl‐type cubic structure (a= 10.00(1) Å,Z= 4) and a tetragonal structure (a= 8.430(5),c= 6.216(4) Å,Z= 2), respectively. The structure of Phase III was determined to be orthorhombic (Pnam (#62),a= 11.294(4),b= 10.729(2),c= 7.158(6) Å,Z= 4) by single crystal X‐ray diffraction. In Phase III, the C3reorientation of CH3groups and the C3reorientation of the whole (CH3)3N group in the cation were observed by1H NMR. In Phase II, the cation is expected to perform the quasi‐isotropic reorientation. In Phase I, the cation was found to carry out the isotropic reorientation, while the spherical anion the translational self‐diffusion, as evidenced by1H and127I NMR, and electrical conductivity. Phase II and I are, therefore, dynamically disordered phases; especially, Phase I is highly disordered. From the dynamical behaviour of the cation and anion, and thermal properties, Phase I can be classified into an ionic plastic phase with a NaCl

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000406

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe diffusion of subliming ZnSe in argon and helium gas has been investigated by a modified entrainment method with a flowing gas at a reduced pressure between 70 and 100 mbar. From the weight loss measurements an effective diffusion coefficient results for the (Zn+0.5 Se2, Ar) system as 0.0828 (T/273)1.47cm2/s and for the (Zn+0.5 Se2, He) system as 0.177 (T/273)1.88cm2/s between 1140 and 1280 K. With a simplified gas collision theory, rigid sphere diameters are estimated as 4.11×10−8cm for Zn and 5.97 × 10−8cm fo

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000407

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractSteady‐state photolysis of oxalylfluoride (FC(O)C(O)F) together with FTIR‐spectroscopy has been used to investigate the reactions of FCO and FC(O)OO radicals in the presence of O2and NO2. Formation of FCO radicals has been identified as the main photodissociation process of oxalylfluoride atλ= 254 nm. However, a quantum yield of ø = 0.11±0.02 was attributed to the direct formation of CF2O and CO in this process. In the presence of O2, the products of reactions of FC(O)Ox(x= 0, 1, 2) radicals were bis‐fluoroformylperoxide (FC(O)OOC(O)F) and bis‐fluoroformyltrioxide (FC(O)OOOC(O)F), as well as CF2O, CO and CO2. Addition of NO2to the reaction system led to the formation of fluoroformylperoxynitrate (FC(O)OONO2). The rate constant for the thermal decomposition of fluoroformylperoxynitrate in the temperature range 275–307 K was measured to bek(T) = 3.5 × 1016exp (‐13 900+1700−2600/T) s−1. For bis‐fluoroformyltrioxide, a rate constant for thermal decomposition of 6.0×10−4s−1was measured at temperatures around 250 K. The thermal stability of bisfluoroformyltrioxide and fluoroformylperoxynitrate is discussed in terms of a comparison with the stab

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000408

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe reactions of HOBr with atomic chlorine (1), with oxygen (2) and with hydroxyl radicals (3) have been investigated at 300 K using the discharge flow technique with mass‐spectrometric detection. The rate constants based on HOBr consumption have been determined to bek1= (8.0±0.4)·10−11andk2= (3.1±0.2)·10−11. For the reaction with OH radicalsk3<5×10−13was obtained. All rate constants are given in units cm3molecule−1s−1.The reactions of HOBr with Cl and with O are shown to proceed via bromine abstraction with formation of BrCl and BrO, respectively. The predominant channel in the reaction of OH with BrCl was identified to be step (4a) OH+BrCl → HOBr+Cl (4a) Based on the present kinetic investigation the heat of formation for HOBr atT= 300 K was evaluated to be ΔH0f(HOBr) =

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000409

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe gas‐phase reaction of NO3radicals with 1,3‐cyclohexadiene, α‐terpinene, and α‐phellandrene has been studied in a flow system at 298 K in the pressure range 8

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000410

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe electron transfer reactions of the cis‐tetraamminediaquocobalt(III) complex with hexacyanoferrate(II) and octacyanomolibdate(IV) in four different water‐cosolvent binary mixtures have been investigated. ketand KIPvalues have been experimentally determined and discussed within the framework of current theories on electron transfer reactions and ionic association. For this purpose, the standard formal potentials of hexacyanoferrate(II) and octacyanomolibdate(IV) were also determined.Comparison of the second order rate constants (k12‐ketKIP) to predictions of the Marcus Cross‐relation gives some indication of the adiabaticity of the processes inves

ISSN:0005-9021    

DOI:10.1002/bbpc.19961000411

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY