Thermal and kinetic analysis of uranium salts: Part III. Uranium(IV) oxalate hydrates

Abstract

Thermal decomposition of U(C 2 O 4 ) 2 · 6H 2 O was studied using TG method in nitrogen, air, and oxygen atmospheres. The decomposition proceeded in five stages. The first three stages were dehydration reactions and corresponded to removal of four, one, and one mole water, respectively. Anhydrous salt decomposed to oxide products in two stages. The decomposition products in nitrogen atmosphere were different from those in air and oxygen atmospheres. In nitrogen atmosphere UO 1.5 (CO 3 ) 0.5 was the first product and U 2 O 5 was the second product, while these in air and oxygen atmospheres were UO(CO 3 ) and UO 3 , respectively. The second decomposition products were not stable and converted to stable oxides (nitrogen: UO 2 , air-oxygen: U 3 O 8 ). The kinetics of each reaction was investigated with using Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa methods. These methods were combined with modeling equations for thermodynamic functions, the effective models were investigated and thermodynamic values were calculated. © 2013 Akadémiai Kiadó, Budapest, Hungary.