Oxidation and thermo physical studies of non-stoichiometric thorium uranium oxides prepared by gel combustion method

Thorium uranium oxide powder with uranium concentrations 10, 20, 30, 40, 50 and 70 mol% was prepared by gel combustion method. The sintering behaviour of the powders studied by dilatometry indicated that samples containing uranium up to 30 mol% had similar shrinkage behaviour with single step sintering. However, samples containing 40, 50 and 70% uranium followed two step sintering process. Though the air calcined powder shows two phase system beyond 30% uranium containing samples, sintering results into single phase system for samples containing up to 50% of uranium. The temperature programmed reduction-oxidation experiments showed that compositions containing up to 50-mol% of uranium show single reducible species throughout the temperature range. X-ray photoelectron spectroscopic studies of these sintered pellets showed presence of uranium in 6(+) and 4(+) oxidation states in these oxides. The experimentally determined heat capacities of solid solutions were found to have higher values than that of computed using Neumann-Kopp's molar additivity rule.