Comparative study of thermal decomposition of the sol–gel products of U and Ce by external and internal gelation processes

The synthesis of U0.7Ce0.3O2+x was carried out using external gelation (with urea/NH3 solution) and internal gelation (with urea/hexamethylene tetramine). The compounds formed were characterized using thermal analytical techniques in Ar, vacuum and air, X-ray powder diffraction and effluent gas analysis by mass spectrometry. The compound formed through external gelation was found to form UO3 as an intermediate product (identified by O2 loss to form U3O8) whereas the compound formed through internal gelation resulted in single-phase UO2, which could be sintered into homogeneous pellets with 97% th.d. in Ar + 2% H2 atmosphere at temperatures as low as 1100 °C.