Thermal decomposition of hafnyl oxalate and ammonium/magnesium hafnyl oxalate

Abstract

Conditions for the preparation of stoichiometric hafnyl oxalate, HfOC 2O 4·3.5H 2O, ammonium hafnyl oxalate, (NH 4) 2HfO(C 2O 4) 2·3H 2O and magnesium hafnyl oxalate, MgHfO(C 2O 4) 2·7H 2O have been standardised. The thermal decomposition of these oxalates has been investigated employing thermogravimetric (TG), differential thermal analysis (DTA), infrared spectral and chemical analysis techniques. The decomposition proceeds through three major steps, viz. the dehydration of the hydrated oxalate, the decomposition of the anhydrous oxalate to the carbonate and, finally, the decomposition of the carbonate to the oxide. Pure hafnium oxide, HfO 2, is the end product in the thermal decomposition of simple hafnyl oxalate and ammonium hafnyl oxalate, while for magnesium hafnyl oxalate, MgHfO 3 is isolated as the final decomposition product.