Non-isothermal studies for the decomposition course of CdC 2O 4–ZnC 2O 4 mixture in air

Abstract

The thermal decomposition of cadmium–zinc oxalate (1:1 mol ratios) mixture in air was investigated by non-isothermal thermogravimetric analysis. Intermediates and the final products were characterized by X-ray diffraction and scanning electron microscopy techniques. TG showed that the mixture dehydrated in two steps and decomposed exothermically to CdO–ZnO mixture at 390 °C in a further two steps. The observed increase in the intensity of the X-ray diffraction lines by raising the calcination temperature from 400 to 800 °C is attributed to the grain growth of CdO–ZnO mixture as revealed from SEM experiments. The kinetics of the oxalate decomposition steps was performed using the various reaction interface models and differential techniques of computational analysis of non-isothermal data. The activation parameters, calculated using the integral composite method, showed that the reactions were best described by the random nucleation model characteristic of solid state nucleation growth mechanism. The results of activation parameters for the different decomposition steps are compared and discussed.