Non-Isothermal Decomposition Kinetics of Hafnium and Zirconyl Hydrogentellurates

The thermal characteristics of zirconyl and hafnium hydrogentellurates, ZrO(HTeO4)2 x 4H2O (ZrOTe) and Hf(HTeO4)4 x 8H2O (HfTe), were investigated via non-isothermal decomposition kinetics in this paper for the first time. Important kinetic parameters such as activation energy (EA), pre-exponential factor (A) and g(alpha) function were determined using Coats-Redfern integral method. The latter was verified by means of z(alpha) master plots. In addition, plausible decomposition mechanisms for the title compounds were offered. Based on the EA values, less thermal stability for ZrOTe (633.69 kJ/mol) with respect to HfTe (872.24 kJ/mol) was observed. Thermodynamic functions (Delta S not equal, Delta H not equal, and Delta G not equal) of the activated complexes generated during the thermal decomposition steps were studied as well. A high positive Delta H not equal value (855.70 kJ/mol) for the thermal decomposition of HfTe indicated formation of high-ordered activated complexes. In contrast, lower Delta H not equal (612.50 kJ/mol) for ZrOTe suggested easier formation the transition states in that case.