ISSN:0005-9021    

DOI:10.1002/bbpc.199000053

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

年代:1990

数据来源: WILEY

ISSN:0005-9021    

DOI:10.1002/bbpc.199000054

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn the electrostatic processing of crude potash salt, a mixture of mainly KCl, NaCl and MgSO4· H2O, the single salt particles gain an electric charge component‐selectively on contact with each other. This enables the components to be separated in an electric field. The component‐selective stimulation of contact charging can be achieved using a technology developed over many years, where small amounts of certain monocarboxylic acids are added to the salt mixture, while the relative humidity of the ambient air is maintained at some definite value. – Recently a model has been proposed to elucidate the mechanism of stimulated contact charging. It has been applied in the case of NaCl. H2O molecules bonded in surface‐cation‐vacancies of the crystal have an important role in this model, which will be extended in the present work to the case of the stimulated contact charging of kieserite. This enables the interpretation of empirical diagrams characterising the electrostatic salt separation to be made for the first time. Conversely, this may be regarded as a convincing verification of the mo

ISSN:0005-9021    

DOI:10.1002/bbpc.199000055

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe photocatalytic activities of titanium dioxide for the reduction of silver ions and the oxidation of isopropanol were evaluated by using titanium dioxide with the various amount of surface hydroxyl groups per unit surface area. The photocatalytic activities increased with increasing concentration of the surface hydroxyl groups on the catalyst and then decreased from an inflection point. The mechanism was discussed from the stand point of the surface hydroxyl radical formation and their interaction.

ISSN:0005-9021    

DOI:10.1002/bbpc.199000056

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe corrosion behaviour of iron was investigated in aqueous borate buffer solutions with and without additions of sodium chloride and in quaternary salt brine at temperatures between 150°C and 300°C. A magnetite film grows according to the parabolic rate law. The parabolic rate constant is independent of the pH‐value, increases with the electrode potential and with the chloride concentration, and attains a maximum at about 250°C. The parabolic rate constants are compared to literature data and theoretical calculations. – After some time the corrosion rate drops to a steady state value, if the chloride concentration is not too high and the electrode potential not too positive. The steady state corrosion rate increases with the temperature according to an activation enthalpy of 41 kJ/mol and remains less than 10 μA/cm2up to 300°C. Above some critical electrode potential becoming more negative with the concentration of chloride, a local corrosion is observed producing flat pits covered by thick oxide layers. At the very high chloride concentration of the quaternary salt brine the whole surface becomes activated and corrosion proceeds rather

ISSN:0005-9021    

DOI:10.1002/bbpc.199000057

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

年代:1990

数据来源: WILEY

摘要:

AbstractRadiolytic reduction of AgClO4solutions containing a polyanion leads to the formation of long‐lived oligomeric silver clusters which are stabilized on the polymer chains. Under suitable conditions, the accompanying formation of colloidal silver consisting of metallic particles is strongly suppressed and cluster concentrations of several 10−4M can be produced. In the presence of polyacrylate, the clusters are particularly long‐lived; they have absorption bands at 300 nm, 340 nm, and 370 nm. The bands of the latter two clusters are red‐shifted as compared to the bands of the unstabilized clusters or clusters stabilized by polyphosphate. The Ag24+cluster, which is formed in the initial stages of Ag+reduction, absorbs at 275 and 480 nm in the presence of polyacrylate. – The various clusters react at different rates with electron acceptors, such as oxygen, carbon tetrachloride and nitromethane. The clusters also react with complexing agents, such as ammonia, cyanide and hydrogen sulfide anions, to form larger particles of silver and/or larger complexed clusters. The great reactivity of the clusters towards nucleophilic reagents is explained by the high coordinative unsaturation of the silver atoms in the clusters. This also explains the stabilization of the clusters by the anion groups of the polymers used. – These reactivity studies were also complemented by investigating the reactions of larger silver particles, which already have metallic properties, with complexing agents. The oxidative corrosion of such particles is strongly accelerated by the complexing agents. A mechanism for the catalysis of the oxidative corrosion is presented, in which the principle steps are the complexation of silver atoms on the surface with simultaneous electron transfer into the metal interior (“pre‐complexation” or “pre‐oxidation” of surface atoms) followed by pick‐up o

ISSN:0005-9021    

DOI:10.1002/bbpc.199000058

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe solubility of hydrogen in Pd – Ti and Pd – Zr solid solution alloys containing up to 6.0 at.% Ti and Zr has been measured at temperatures between 273 K and 433 K and hydrogen pressures up to 1000 Torr. The relative partial molar enthalpy, ΔH0H, at infinite dilution for Pd – Ti alloys shows a minor minimum around 4 at.% Ti, in spite of the Pd lattice contraction on Ti substitution. For Pd – Zr alloys the ΔH0Hvalues increase in exothermicity regularly with Zr content. The relative partial molar entropy, ΔS0H, at infinite dilution in both alloy series decreases with the solute contents. The apparent H‐H attractive interactions,g1, in Pd – Ti(Zr) alloys decrease with alloying metal content, and the trend of theg1value with Ti content is dissimilar to those found for other lattice contracted alloys. The stability of the β‐phase hydride in Pd – Ti alloys decreases with Ti content and the β‐phase hydride in Pd – Zr alloys also becomes less stable with Zr content, albeit by a small amount, despite being a lattice expanded alloy system. Solvus compositions at the αmaxphase boundary in both Pd – Ti and Pd – Zr alloys are almost equal at the same alloying compositions of each alloy series, although increasing with alloyin

ISSN:0005-9021    

DOI:10.1002/bbpc.199000059

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe aryl coupling reaction of halobenzenes over alumina‐supported copper catalysts has been studied by FTIR spectroscopy. Time‐dependent changes in the spectra were recorded after stepwise addition of bromobenzene to the carrier gas stream. The coupling product, biphenyl, as produced by the copper‐catalyzed “Ullmann type I” reaction, as well as phenol and phenolate species, have been observed. It was found that the thermal pretreatment of the supported catalyst has a pronounced influence on the rate of the catalytic bromobenzene conversion, and on the distribution of side products observed. Novel approaches to inhibit the catalytic dehydrogenation of aryl halides by ethanolamine addition to the catalyst have been studied for the investigated model reaction. The inhibitory action is due to both site blocking and irreversible deactivation of the copper surface due to nitride

ISSN:0005-9021    

DOI:10.1002/bbpc.199000060

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

年代:1990

数据来源: WILEY

摘要:

AbstractUltrasonic attenuation data (frequency range 10 MHz

ISSN:0005-9021    

DOI:10.1002/bbpc.199000061

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

年代:1990

数据来源: WILEY

摘要:

AbstractWörterDielectric measurements have been performed on oriented samples of a nematic mixture with a glass‐transition temperature of about 285 K in a frequency range between 0.1 and 106Hz and on unoriented, quenched samples of this mixture from 156 K up to 300 K. Rotations around the short and long molecular axis gave a Vogel‐Fulcher‐Tammann‐behaviour; the seperate rotation of polar end‐groups caused the appearance of a high‐frequency‐Arrhenius‐like mechanism which was observable at very

ISSN:0005-9021    

DOI:10.1002/bbpc.199000062

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

年代:1990

数据来源: WILEY