Thermal and kinetic analysis of uranium salts: Part 1. Uranium (VI) oxalate hydrates

The thermal decomposition kinetics of UO 2 C 2 O 4 ·3H 2 O were studied by TG method in a flowing nitrogen, air, and oxygen atmospheres. It is found that UO 2 C 2 O 4 ·3H 2 O decomposes to uranium oxides in four stages in all atmosphere. The first two stages are the same in the whole atmosphere that correspond to dehydration reactions. The last two stages correspond to decomposition reactions. Final decomposition products are determined with X-Ray powder diffraction method. Decomposition mechanisms are different in nitrogen atmosphere from air and oxygen atmosphere. The activation energies of all reactions were calculated by model-free (KAS and FWO) methods. For investigation of reaction models, 13 kinetic model equations were tested and correct models, giving the highest linear regression, lowest standard deviation, and agreement of activation energy value to those obtained from KAS and FWO equations were found. The optimized value of activation energy and Arrhenius factor were calculated with the best model equation. Using these values, thermodynamic functions (ΔH * , ΔS * , and ΔG * ) were calculated. © 2011 Akadémiai Kiadó, Budapest, Hungary