Thermal and kinetic analysis of uranium salts

In this study the thermal decomposition kinetics of uranyl acetate dehydrate [UO2(CH3COO)2·2H2O] were studied by thermogravimetry method in flowing nitrogen, air, and oxygen atmospheres. Decomposition process involved two stages for completion in all atmosphere conditions. The first stage corresponded to the removal of two moles of crystal water. The decomposition reaction mechanism of the second stage in nitrogen atmosphere was different from that in air and oxygen atmospheres. Final decomposition products were determined with X-ray powder diffraction method. According to these data, UO2 is the final product in nitrogen atmosphere, whereas U3O8 is the final product in air and oxygen atmospheres. The calculations of activation energies of all reactions were realized by means of model-free and modeling methods. Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods were selected for model-free calculations. For investigation of reaction models, 13 kinetic model equations were tested. The model, which gave the highest linear regression, the lowest standard deviation, and an activation energy value which was close to those obtained from KAS and FWO equations, was selected as the appropriate model. The optimized value of activation energy and Arrhenius factor were calculated using the selected model equation. Using these values, thermodynamic functions (ΔH*, ΔS*, and ΔG*) were calculated.