摘要:

AbstractPassivation behaviour of zinc electrodes in 4–10 M H2SO4and some hydrogensulphates and alkylammonium salts with anions containing S–VI in the concentration range 0.5–5 M were studied under galvanostatic conditions. After a transition time τ, voltage increased steeply, indicating the onset of passivation. The productj· √τ is found to be roughly constant. This is explained in terms of an accumulation of zinc ions in front of the electrode up to the point, where the concentration reaches saturation. From the Sand constant, a diffusion coefficient was calculated in the right order, depending on the electrolyte composition. The passive layer is assumed to be the corresponding zinc salt. Only at 30–100 V, dielectric break down occurs under potentiostatic conditions. Open circuit potential in the passive region attains in short times (ms) the active potential again. From this it is concluded that the thickness of the zinc salt layer must be ext

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950111

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

年代:1991

数据来源: WILEY

摘要:

AbstractTwo thermodynamic models of stepwise hydration of solutes in aqueous solutions are merged: one for 1:1 electrolytes and a another one for hydrophilic nonelectrolytes. The theory is compared with measurements for six systems taken from the literature. Except for: H2O + HCl + glycerol, the agreement is satisfactory.

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950112

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

年代:1991

数据来源: WILEY

摘要:

AbstractA recently formulated Debye‐Hückel theory for aqueous solutions of hydrated, singly charged ions is extended to solutions with reciprocal electrolyte pairs: MX, MY, NX and NY. The results are analyzed with respect to the square‐cross rule for the excess Gibbs energy of hydrogen and alkali halogenides. The parameters for the model are taken from a fit to the activity coefficients of the respective binary solutions. The DH 2 variation of the new model theory is in good agreement with the square‐cros

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950113

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

年代:1991

数据来源: WILEY

摘要:

AbstractComparative study of the role of solvent effects of aqueous methyl cellosolve and tetrahydrofuran solvent systems on the alkaline decomposition of tetraphenylphosphonium bromide was carried out. The reaction rate increases remarkably as the medium changes from purely aqueous to a water‐organic cosolvent reaction mixture. The relative changes in the solvation states of both reactants and transition state as the structural properties of the two solvent binaries change were shown to be the direct reasons for the difference in the effects on rate and activation energie

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950114

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe fluorescence properties of surface modified quantum‐sized CdS colloids were investigated by means of static and time‐resolved low temperature fluorescence spectroscopy. All samples investigated had high fluorescence quantum yields already at room temperature and exhibited either exclusively excitonic or a mixture of excitonic and trapped fluorescence. Mechanisms are presented which explain both the static and time‐resolved behaviour of both the excitonic and trapped fluorescence. The excitonic fluorescence is described as delayed fluorescence occuring by detrapping of electrons. Extremely shallow traps having trap depths of a few meV are disc

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950115

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

年代:1991

数据来源: WILEY

摘要:

AbstractAt a certain surfactant concentration called “critical” or “hemimicelle” concentration a spontaneous aggregation takes place of surfactant molecules adsorbed onto polar surfaces. In spite of many works which have been published, the nature of that surface aggregation is still not understood well. The aim of this paper is to explore to which extent the concept of 2D condensation can explain the observed features of that surface aggregation. To that purpose the recent theoretical approach by Koopal is generalized to take the surface heterogeneity into account. This is because the surface heterogeneity is believed to be an important factor affecting the surface aggregation. Some striking similarities between the observed features of surface aggregation and the theoretical predictions based on the concept of 2D condensation are found. That concept, however, cannot at the present stage of the theory explain yet the finite tangent of the linear sections in the experimental isotherms corresponding to the surface aggr

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950116

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

年代:1991

数据来源: WILEY

摘要:

AbstractSubmolayer concentrations of (strongly electropositively polarized) Na and K on the Au(100) surface create three new acctonitrile (CH3CN) and benzonitrile (C6H5CN) binding states (the γ‐states) on the high‐temperature side of the corresponding molecular thermal desorption spectra (β‐state) observed for the clean, unpromoted Au surface. The additional states appear with both alkali metals and nitriles, whereby they are energetically about equally spaced (ΔT≈ 30 K with K, and ΔT≈ 50 K with Na) and sequentially populated, indicating a more general electrostatic modification of the nitrile's adsorptive bonding in the vicinity of an adsorbed alkali atom. The triplet of TD states is tentatively interpreted as being caused by a subsequent filling of a coordination shell formed by the nitriles around each individual alkali metal atom. Similar energetics involved in the formation of gas‐phase and surface cluster complexes of the kind Meδ+{N  C–CH3}δ

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950117

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe oscillations of the current which take place during the anodic dissolution of silicon in fluoride electrolytes have been investigated. These oscillations occur only upon a perturbation in the electrode potential, and are associated with a fluctuation of the thickness of an oxide layer on the electrode surface. In the corresponding potential range, the experimental data strongly support the picture of a surface consisting of a juxtaposition of small self‐oscillating areas. These areas are decorrelated from each other in the steady state, but are synchronized by a potential perturbation, giving rise to macroscopic oscillation

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950118

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

年代:1991

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950119

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

年代:1991

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.19910950121

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

年代:1991

数据来源: WILEY