Abstract
The effect of preparation — specific parameters such as energy input, thermal treatment, V2O5-content — on the kinetics of the anatase-rutile transformation, were investigated and their relative contributions analysed. The various degrees of transformation were determined by quantitative X-ray diffraction measurements and checked for various rate laws. The rate constants evaluated according to Avrami for the V2O5—WO3—TiO2 (anatase)-system were extrapolated from Arrhenius plots for temperature values corresponding to conditions in power plants. The experimental results yield information on the stabilities (exposition periods) of the anatase-modification which react sensitively towards changes in phase composition at the anatase phase boundary, thus reflecting activation and deactivation processes which have an effect on the kinetics of the anatase-rutile phase transformation. The kinetic behaviour determined according to Avrami for the V2O5—WO3—TiO2 (anatase)-system has not been found for the V2O5—MoO3—TiO2 (anatase)-system. A unique feature of MoO3-systems consists in the following: after passing through a kinetically controlled region they form stable phases which can no longer be influenced kinetically. The anatase content of such phases can be adjusted by maintaining specific preparation parameters.
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