Thermal decomposition kinetics. Part XI. Mechanism of thermal decomposition of calcium oxalate monohydrate from a thermogravimetric study — the effects of heating rate and sample mass on kinetic parameters from mechanistic equations

Abstract

The mechanisms of the first two stages of the thermal decomposition of calcium oxalate monohydrate ▪ have been established from non-isothermal thermogravimetric studies. For both stages, the rate-controlling processes are phase boundary reactions; the dehydration step assumes spherical symmetry whereas the decomposition step follows cylindrical symmetry. The kinetic parameters calculated from mechanistic equations show the same trend as those from mechanism-non-invoking equations. Thus, for the decomposition of CaC 2O 4 the kinetic parameters are not appreciably affected by heating rate or sample mass. For the dehydration step they show a systematic decrease with increase in either heating rate or sample mass. The best fit correlations can be expressed as follows E(or, log A) = (Constant/Heating rate) + Constant, (at fixed sample mass) E(or, log A) = (Constant) × (Mass) 2 − (Constant) × (Mass) + Constant, (at fixed heating rate)