On the origin of exothermic DSC peak prior to glycine-nitrate gel combustion during ThO2 synthesis

Abstract Nature of interaction between Th 4+ , glycine, and nitrate ions and associated thermo chemical-changes prior to glycine-nitrate gel combustion for the synthesis of ThO 2 powder have been investigated by DSC and XRD techniques, combined with FT-IR and Raman spectroscopic measurements. Combustion of dried gel is preceded by a distinct exothermic process; origin of which has been probed by systematic analysis of DSC thermograms. Mono- and multi-nuclear complexes of thorium with glycine exist in the gel before combustion and their relative concentrations depend on the starting stoichiometry, heat treatment temperature and extent of water content. Depending on the rate at which water gets removed from the gel, complexes mentioned above undergo rapid or slow aggregation to form amorphous or crystalline molecular solids. Observed additional exothermic peak in DSC thermogram prior to combustion of the gel confirms the formation of such molecular solids.