Nonisothermal decomposition of CdC2O4–FeC2O4 mixtures in air

DTA–TG, XRD, and 57Fe Mössbauer spectral measurements were used to study the thermal decomposition reactions of the system CdC2O4–FeC2O4 (1:2 mole ratio) in air. The results showed that the thermal oxidative decomposition of each metal oxalate in the mixture occurs in one TG step and that oxide spinel is formed at 800°C. Mössbauer spectra of samples showed that the iron(III) oxide formed in the early stages of the decomposition at 250°C is mainly fine-grained and as the temperature is increased, well-crystalline hematite is formed. Above 250°C, the Mössbauer spectrum showed the typical six-line pattern of magnetically oriented Fe(III) oxide, but at 800°C, the spectrum showed quadrupole interaction characteristic of CdFe2O4 spinel. Kinetic analysis of the nonisothermal data according to the integral composite method showed that the oxidation and decomposition of FeC2O4 to Fe2O3 and CO2 and of CdC2O4 to CdO and CO2 are best described by the three-dimensional phase boundary (R3) model. The activation parameters for both decomposition steps were calculated and discussed.