Thermophysical studies on the binary system UO2(NO3)2·6H2O – Sr(NO3)2

Thermoanalytical (TG-DTA-EGA) and X-ray diffraction measurements have been used to study the reaction between uranyl nitrate hexahydrate and strontium nitrate. The results confirmed the absence of a direct interaction between the two compounds. The presence of strontium nitrate, however, ensured that the extent of hydrolysis and polymerisation of uranyl nitrate hexahydrate during its dehydration and decomposition to UO3 is significantly reduced. DTA curves recorded in both heating and cooling modes gave evidence to the occurrence of a reaction between molten strontium nitrate and uranium trioxide to form nitrato-complexes of uranium and strontium. X-ray diffraction data on reaction residues obtained at different temperatures and cooled to room temperature also showed evidence for the formation of such complexes. The results obtained indicated an increase in thermal stability of these nitrato-complexes with increase in Sr/U ratio. The complex with an Sr/U ratio of 2.0 is stable up to 660 °C and the complex with Sr/U ratio of 4.0 is stable up to 680 °C. These complexes decompose at higher temperatures to give strontium uranates.