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  • Author or Editor: B. Prochowska-Klisch x
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Abstract  

The kinetics of the thermal decomposition of Co3O4 has been examined in the 1123–1200 K temperature and 2.66–20.73 kPa oxygen pressure range. The kinetics of this process has been deseribed in terms of a mixed-control model of reaction. The values of activation energies of diffusion and chemical reaction as well as the observed activation energy have been given. The strong dependence of the decomposition rate on temperature and oxygen pressure has been explained.

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Abstract  

A detailed analysis is presented of the applicability of several dependences commonly used for the determination of activation energies from non-isothermal measurements. Reactions proceeding according to different kinetic equations are simulated and the validity of the activation energy values obtained is discussed. The general conclusion is drawn that none of the examined dependences should be used to determine the activation energy. For a rough estimation of activation energy, the Kissinger equation can be applied according to Ockham's razor.

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Abstract  

It has been found that the modified Zhuravlev equation, [(1−α)−1/3−1]2=ktn, which describes the kinetics of oxidation of V2O4 and V6O13 in the temperature range 820–900 K and in the oxygen pressure range 1.0–20 kPa, can be derived via the assumption that the changes in the observed activation energy result from the changing contributions of the two diffusion processes controlling the reaction rate. The values of the observed activation energy are in the range 160–175 kJ mol−1 for V2O4 and 188–201 kJ mol−1 for V6O13 in the scope of the experimental oxygen pressures and temperatures and conversion degrees of 0.1–0.9.

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Journal of Thermal Analysis and Calorimetry
Authors: R. Gajerski, A. Maŀeki, B. Prochowska-Klisch, and M. Weirzbicka

Abstract  

The powders of Ni−P alloys containing 13% of phosphorus were obtained by precipitation from the solution. The oxidation of Ni−P alloys in polythermal conditions was studied. It was found that oxidation of Ni−P alloys goes through stages and that intermediate products of the oxidation are: Ni2P and Ni2P2O7. The final products of oxidation process are NiO and Ni3(PO4)2. The sequence of chemical reactions describing the oxidation of Ni−P alloys was proposed.

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Journal of Thermal Analysis and Calorimetry
Authors: A. Małecki, A. Małecka, R. Gajerski, B. Prochowska-Klisch, and A. Podgórecka

The mechanism of thermal decomposition of Co(NO3)2 · 2H2O was found to involve stages in which Co(NO3)3 and Co2O3 · H2O are formed both of which decompose to Co3O4. During the process, the total cobalt enters the +3 oxidation state, which is consistent with the results reported by Mehandjiev [2].

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Journal of Thermal Analysis and Calorimetry
Authors: A. Małecki, R. Gajerski, S. Łabuś, B. Prochowska-Klisch, and K. Wojciechowski

Abstract  

A series of six nitrates(V) hydrates of 4d-metals as well as mercury and cadmium thermal decomposition was examined by DTA, TG and EGA techniques. It was found that thermal decomposition of d-metals nitrate(V) hydrates proceeds in three stages: partial dehydration, oxo-nitrates and hydroxide nitrates formation and metal oxides formation. General chemical equations for all decomposition stages were proposed. It was found that dehydration of hydrated salts is accompanied by partial decomposition of nitrate(V) groups.

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