Abstract
Thermal decomposition of thorium oxalate hexahydrate, Th(C2O4)2⋅6H2O, has been studied by thermogravimetry (TG) and differential thermal analysis (DTA) in air and argon. The thermal decomposition took place in three steps. At temperatures below about 300°C. plateaus in TG and endothermic peaks in DTA indicated the appearance of dihydrate and monohydrate at the first two steps respectively. At higher temperatures monohydrate decomposed to the oxide at the third step. In argon the dehydration processes were essentially the same as those in air, but the decomposition to the oxide was sluggish. This might be due to the deposition of carbon caused by the disproportionation of primarily evolved CO. The decomposition to the oxide gave an endothermic peak in DTA in argon, but in air exothermic peaks due to the oxidation of CO and carbon were observed.
Hahn's emanation technique using thoron 54.5-second was applied to the studies of thermal decomposition. Three peaks were observed in the emanation curves and corresponded to the three steps as determined both in TG and DTA, .
In the electron microscope the oxalate particles were square platelets of a few microns, and the oxide appeared as the skeleton particles of the original oxalate.
