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Abstract  

A brief overview is given of recently obtained data on the surface structure and composition of various iron(III)-containing nickel hydroxide systems, as studied using transmission Mössbauer spectroscopy supplemented by atomic absorption, Auger electron and Fourier transform infrared spectroscopic data. The systems studied include coprecipitated binary Ni(II)–Fe(III) hydroxides in a wide range of compositions, ferric hydroxide precipitated on the surface of -Ni(OH)2 crystallites, ferric hydroxo complexes adsorbed onto nickel hydroxides from alkaline electrolytes and the products of their hydrolysis.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
Yu D. Perfiliev
,
V. S. Rusakov
,
L. A. Kulikov
,
A. A. Kamnev
, and
K. Alkhatib

Summary  

Resonant lines observed in source experiments are usually significantly broader thanthosein the corresponding absorber experiments. In order to explain this phenomenon, the model of a trapped electron has been proposed. Auger electrons emitted, for instance, after electron capture by 57Со or after the converted isomeric transition of119mSn, as well as secondary electrons, may be trapped in the vicinity of the nucleogenic ion. An asymmetric distribution of quadrupole splittings in the resulting emission Mössbauer spectra is thus a consequence of electron capture by lattice traps located at different distances from the daughter ion. Estimates of quadrupole splitting values, which may be causedby trapped electrons located at different distances from the nucleogenic atom, support the above mentioned model.

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Abstract  

Mössbauer, FTIR and XRD analyses showed that in aqueous medium in air in the presence of L-tryptophan (Trp) or indole-3-acetic acid (IAA) the ambient-temperature ageing of the precipitates formed from ferrous sulphate at pH7 gave composite phases with varying proportions of -FeOOH (a dominating crystalline phase), -FeOOH (both fine-grained, showing superparamagnetic behaviour at 298 K, and relatively better crystallized) and amorphous ferric hydroxide. The experimental data suggested a competition for adsorption sites at the oxyhydroxide surface in the suspension during phase transformations, as well as the transformation of -FeOOH (and/or amorphous ferric hydroxide) to -FeOOH via the dissolution-reprecipitation mechanism. The formation of certain ferric oxyhydroxide phases in the presence of Trp and IAA — released e.g., in the course of bacterial and plant metabolism — can contribute to the regulation of soil mineral composition.

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Summary  

This paper describes the Mössbauer investigations of iron(III) salts in aqueous solutions in the presence of indole-3-alkanoic acid ligands. The measurements showed two parallel reactions between the ligands and ferric ions: a complex formation and a redox process. The oxidation process takes place in the ligands, and a part of Fe3+is reduced to Fe2+.

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