Effect of semiconducting metal oxide additives on the kinetics of thermal decomposition of sodium oxalate under isothermal conditions

摘要

The effect of semiconducting metal oxide (CuO and TiO_2) additives on the kinetics of thermal decomposition of sodium oxalate (Na_2C_2O_4) to sodium carbonate has been studied at five different temperatures in the range 783-803 K under isothermal conditions by thermogravimetry (TG). Irrespective of whether p- or n-type, the metal oxides show an increase in the rates of both stages of decomposition up to an oxide concentration of 1 wt% and then decreases (at higher concentrations). The TG data were subjected to model fitting kinetic methods of analysis. The rate law for the decomposition of Na_2C_2O_4 (Prout-Tompkins and contracting cylinder models respectively for the acceleratory and decay stages) remained unaffected by the additives. Similar effects were observed with pre-compressed metal oxide additives on the thermal decomposition of Na_2C_2O_4. The results support the diffusion controlled mechanism proposed earlier for the isothermal decomposition of sodium oxalate.