Thermal decomposition of co-precipitated oxide hydrates of zirconium and manganese

Abstract

The thermal decomposition of mixed ZrMn oxide hydrates containing 0–0.3 mol of manganese was examined by means of simultaneous TG and DTA. When heated, these mixed hydroxides decompose to an amorphous oxide phase and subsequently crystallize to a cubic phase. These changes are accompanied by a broad endothermic peak at around 165–180°C and an exothermic peak between 450 and 700°C. The temperature at which the crystallization occurs depends on the manganese content. A linear increase was observed between manganese content and crystallization (exothermic peak) temperature. The enthalpy of crystallization, however, showed a decreasing trend (from 28.7 to 12.1 kJ mol −1) with increasing manganese content within this range. Since no amorphous manganese oxide was formed when manganese oxide hydrate alone was heated, it is apparent that optimum concentrations of manganese (0.1–0.3 mol) in amorphous zirconia decrease the enthalpy of crystallization, thereby stabilizing zirconia in the cubic phase at low temperatures.