Influence of trivalent ion dopants on the thermal decomposition kinetics of potassium bromate

Isothermal decomposition of potassium bromate (KBrO3) has been studied as a function of concentration of dopants, phosphate and aluminium by thermogravimetry (TG) in the temperatures range 668-683 K. The TG data were subjected to both model fitting and model free kinetic methods of analysis. The model fitting analysis shows that the decomposition of both pure and doped samples was best described by contracting cylinder equation, [1 (1 - alpha)(1/2) = kt] with two different rate constants k(1) (fort alpha = 0.15-0.45) and k(2) (for alpha = 0.5-0.95) such that k(1) < k(2). The rate law remained unaltered by doping. Both k(1) and k(2) increases with increase in dopant concentration. The diffusion of ions, K+ and BrO3-, is determining the rate in both stages. The formation of KBr-KBrO3 eutectic and consequent melting is observed in the stage 2 process of the decomposition. (C) 2011 Elsevier B.V. All rights reserved.