Study of thermal decomposition and characterization of uranium compounds by thermogravimetry and differential calorimetry

The thermal behaviour of different types of ammonium diuranates, produced in the pilot plants of Instituto de Pesquisas Energeticas e Nucleares (Sao Paulo, Brazil), is studied. It was observed that: the contents of absorption and crystallization waters, as well as the content of absorption ammonia vary as a function of drying conditions; the contents of occluded ammonium nitrate vary according to the washing step; ammonia contents vary as a function of pH and of the original solution - greater ammonia concentrations are observed when diuranates are precipitate in uranyl nitrate solutions at higher pH's (9.0). Thermal instability of the intermediate compound varies as a function of the type of the occluded ion, NO-3 or SO sup(=)4. The thermoanalytical curves show that the diuranates obtained by continuous precipitation have a more reproducible chemical composition than those obtained by batch precipitation. (C.L.B.)