Ceramics-Silikáty 19, (3) 203 - 210 (1975)

The study deals with dimensional changes taking place during the sintering of uranium dioxide spheres made by reduction at 600 °C in H₂ + Ar atmosphere of uranium trioxide xerogels which have been prepared by the sol-gel technique. Extensive sintering of the material tarts at a relatively low temperature of about 800 °C and densities ≥ 95 % TD are attained at about 1150 °C. Further raising of temperature results in oversintering, involving a considerable volume expansion at temperatures of up to 1500 °C. The study of dimensional changes was supplemented by a study of the internal structure using the scanning microscope; a suitable method for the preparation of fracture surfaces was developed for this purpose. The structure of sintered spheres is not homogeneous throughout the whole sphere, as a reduced grain growth has been observed in the subsurface layer; this inhibited grain growth is an inherent property of the pre-reduced material, and the respective differences are kept up throughout the entire sintering process.