摘要:

AbstractA formal analysis is given treating the phenomenon of internal and external oxidation of oxide solid solutions. Theoretically, two situations can arise if those oxides are brought in an environment of higher oxygen potential. (1) Demixing and subsequently the formation of an outer layer of the reaction product occurs. (2) The reaction product forms internally; the two‐phase front advances into the interior of the solid solution. Some analogies with the phenomenon of internal alloy oxidation are discussed. Normally, a parabolic reaction kinetics prevails. Depending on the composition of, and the transport coefficients in the solid solution, a change from an internal to an external reaction may occur, and a criterion for this change is deduced. Internal oxidation (and reduction) is a means to disperse a second phase into an oxide matrix. This process may alter electrical, chemical and mechanical properties of the solid in question and thus could be of interest for materials science as well as geochemistr

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870702

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

年代:1983

数据来源: WILEY

摘要:

AbstractIn tetragonal ZnP2paramagnetic Mn2+substitutes for the Zn2+ions that are all equivalent. The hyperfine structure constantAof the paramagnetic Mn2+centre was determined to 53(2) · 10−4cm−1. Measurements of the optical activity revealed a characteristic twinning of the red, plate‐like crystals. In monoclinic ZnP2two different Mn2+centres could be detected in accordance with two different Zn sites. A site assignment was possible by considering a pseudo‐orthorhombic unit. The same assignment was obtained by comparing the orientations of the centres' axes with calculated directions of the axes of crystal field tensors. The agreement of theAvalues of the two different centres in monoclinic ZnP2among themselves and with theAvalue in tetragonal ZnP2supports a structure without Zn‐Zn bonds for the monoclinic mo

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870703

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

年代:1983

数据来源: WILEY

摘要:

AbstractSrCl2cristallizes in the fluorite structure and shows, like all materials with this structure, anomal properties with regard to thermodynamic as well as to transport phenomena. In a temperature region starting about 200 K below the melting point (1146 K) a pronounced maximum ofCpis found, which is to be identified with a Schottky anomaly. Most significant are the increasing values of ionic conductivity with rising temperature. They mostly exceed those of a typical ionic melt. The degree of the “molten” anion lattice and the distinct places of the defect ions are not clarified until now. The temperature of transition at the maximum of the expansion coefficient value atT= 1000 K has been determined by dilatometric measurements. The existence of predominant Frenkel‐disorder has been demonstrated by comparing X‐ray and dilatometric measurements. The ratio of ionic radii relative to the configuration in the fluorite structure has been determined from lattice parameter and the crystal structure.The enthalpy of formation of Frenkel disorder has been calculated from dilatometric measurements to ΔHf= (248 ±

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870704

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

年代:1983

数据来源: WILEY

摘要:

AbstractCorrect diffusion measurements using electrochemical methods must be carried out under careful consideration of the boundary conditions. — It is shown that the diffusion of recombined H‐atoms from the metal surface into the electrolyte does not seem to be the main reason for a loss of hydrogen concentration, but the presence of oxidizing species (generally oxygen), solved in the electrolyte, which lead to an enhanced electrochemical oxidation of hydrogen. In order to avoid this source of systematic errors, deaerated H2SO4was used for measuring time lag curves of hydrogen diffusion in palladium. Measured time lag curves, obtained by the current pulse method, agree very well with theoretical curves, evaluated from the solution of Fick's second law. — When determining diffusion coefficients by measuring the break‐through time one has to take into account the ratio of the amount of hydrogen, discharged on the entry side of the diffusion foil, to the content of hydrogen within the sample from prechargi

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870705

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

年代:1983

数据来源: WILEY

摘要:

AbstractThe measurements of35Cl NQR spectra and X‐ray powder diffraction patterns were carried out in a series of the complexes of trimethylsulfonium hexachlorometallates(IV), (triMS)2MCl6(M = Pt, Se, Te, Sn). For (triMS)2TeCl6and (triMS)2SnCl6,1H NMR second moments were determined at various temperatures between 77 K and 370 K. The temperature dependence of1H NMR spin‐lattice relaxation times was observed for (triMS)2PtCl6, (triMS)2TeCl6, and (triMS)3SnCl6. From X‐ray powder patterns, it was found that the complexes studied are isomorphous with each other and form cubic crystals belonging to the space group T h6‐Pa3. The unit cell dimensions were determined. A single35Cl NQR line was observed for all of the complexes in agreement with the crystal symmetry. From1H NMR studies, two kinds of motions of (triMS)⊕, namely, the intracationic CH3group reorientation and the reorientation of the whole cation about its C3axis, were observed separately in the above three complexes. The activation energies of these motions were evaluated and compared with those of trimethylammonium ions in hexahalometallate(IV) complexes previous

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870706

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

年代:1983

数据来源: WILEY

摘要:

Abstract14N nuclear quadrupole resonance was observed in acetamide, CH3CONH2, and chloroacetamide, CH2ClCONH2, by pulse technique. The resonance frequencies in both compounds increase with raising from 80 K to 340 K. In acetamide the activation energy was calculated to be 17.6 kJ · mol−1in the temperature range from 260 K to 320 K and 48.1 kJ · mol−1above 320 K. The former is thought to be attributed to the reorientation of the amino group and the latter, to the torsional motion of molecule. In the case of chloroacetamide the echo signal is too weak to obtain the correctT1value, but the relaxation mechanism seems to be similar to that of acetamide. The positive temperature dependence of resonance frequencies is due to the hydrogen

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870707

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

年代:1983

数据来源: WILEY

摘要:

AbstractLine shapes of the17O n.m.r. of the solvent water have been measured in solutions containing small amounts of HCl or NaOH and various inorganic and organic salts. Proton life times τ in the water molecule have been derived from these spectra. The life time in the neutral electrolyte solutions, the maximum life time, the rate constants for the proton exchange catalized by H+and OH−ions, and the pH value at which the maximum r occurs are reported. Correlations with the well‐known structure forming and structure breaking properties of ions are discussed. The results are also compared with the electrical extraconductivity observed in these solut

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870708

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

年代:1983

数据来源: WILEY

摘要:

AbstractIntegrated band strengths for rovibrational absorption in the frequency range of the CF‐chromophore (800 to 1300 cm−1) have been obtained from vapour phase IR‐spectra of twelve fluoroalkanes containing one or more CF groups. It is found that the chromophore band strength is about 1.7 (pm)2for each CF group with some minor variations due to neighbouring substituents at the CF carbon atom. These variations can be accounted for by a simple, empirical equation. The results are discussed in relation to the chromophore principle in IR‐photochemistry. The frequency distribution of the chromophore absorption for primary, secondary, and tertiary alkyl fluorides is considered. The primary CF‐chromophore (R ‐ CH2‐ F) is suggested to be a particularly useful general chromophore for CO2‐laser pumping. The foundations of the group additivity for chromophore band strengths and some further applications are di

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870709

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

年代:1983

数据来源: WILEY

摘要:

AbstractBy means of time resolved ESR spectroscopy in the microsecond time scale the H atom addition to different vinyl monomers was investigated. The H atoms produced by pulse radiolysis of aqueous solutions show a strong recombination CIDEP effect which also allows the recombination rate constant of H atoms to be determined. By analysis of ESR time profiles with the modified Bloch equations the relaxation timesT1,T2, the polarization factors and the chemical rate constants with scavengers were obtained. Besides the H atom addition rate constants to different vinyl monomers the structure of the monomer radical was determined for acrylic acid.

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870710

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

年代:1983

数据来源: WILEY

摘要:

AbstractMeasurements of sound attenuation and velocity in the homogeneous phase near the critical mixing point of isobutyric acid and water have been carried out. The data are obtained by a pulse transmission technique at seven frequencies between 9 and 45 MHz in a temperature range between 26.29°C and 40 °C. The experimental results are analysed in terms of a theory of critical ultrasonic absorption proposed by Bhattacharjee and Ferrell which contains no adjustable parameters. All the values of these parameters are known for the investigated system from independent experiments. The frequency dependence of the absorption coefficient of ultrasound at the critical temperature is in good agreement with this theory which takes into account only sound absorption by local concentration fluctuations. The absorption data obtained at temperatures away from the critical temperature do not scale when plotted as function of a reduced frequency given by the theory. This clearly indicates an additional mechanism causing absorption of ultrasound. This additional sound absorption can be represented by a single temperature dependent relaxation process. It is assumed that this process is due to an unspecified chemical reaction. The temperature dependence of the relaxation time follows a power law of the form τr∝︁ (T‐Tc)−awith 1 ≤a≤ 1.25. This result seems to support the idea of Gitterman. Procaccia and Hentschel that chemical reactions slow down near the

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870711

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

年代:1983

数据来源: WILEY