A Thermoanalytical Study of the Solid State Reactions in the K2CO3-MxOy Systems. Evidence for a kinetic compensation effect

Abstract

This paper presents the results obtained in the investigation of the reactions of potassium carbonate with some transition metals oxides (TiO2 , V2 O5 , Cr2 O3 , MnO2 , Fe2 O3 ). The reactions were carried out under non-isothermal conditions, and thermogravimetric analysis was used to monitor the transformation degree a. Experimental data indicated that the reaction of potassium carbonate and iron(III) oxide occurs in one stage, whereas the reactions of the oxides of titanium, vanadium, chromium and manganese are more complex, involving two-stage processes. Activation energies and pre-exponential factors were determined for all the processes taking place in the investigated systems. For the second stage of the reaction of K2 CO3 with Cr2 O3 , and V2 O5 the obtained values of activation energy were 59.2 and 512 kJ mol−1 respectively. Based on the values of activation energy and pre-exponential factor, the existence of a kinetic compensation effect was postulated for the three homologous series of reactions.