UO<sub>2</sub>焼結ペレットの微細構造

Abstract

Microstructure of outer and fractured surface of sintered uranium dioxide pellet was investigated using an electron microscope.The technique of carbon atomic replica was adopted for the preparation of samples for electron microscopic observation. The structure of outer and fractured surfaces changes markedly, as expected, during the progress of sintering. Especially, the degree of sintering, sintering conditions and minute additives are sensitivelly and informatively reflected in the shape and microstructure of pores on fractured surfaces.Pores in pellets well sintered in hydrogen are remarkably bounded by well developed facets, some of them show a perfect cubic holohedral symmetry. Their facets are indexed as {111}, {100}, {110} and higher indices nearly parallel to {110}. Facets indexed as {110} consist of repeated steps having much smaller facets {111}.Contrary to the above, pores in pellets sintered in vacuo and in earlier stage pellets sintered in hydrogen show rounded and sometimes spherical shape. Crystalline anisotropy is supposed to be masked by strong surface migration or diffusion. Small facets bounded by concentric steps, however, are often observed on the wall of rounded and spherical pores. Their facets are indexed as {111}, {100} and {110}. Although Padden observed just {110}, it appears less frequently than others. Much smaller facets nearly parallel to {111} or {110} but slightly deflected to [100] directions are sometimes observed.Small amounts of alumina or titania as additives affect differently to the shape of pores and the mode of precipitation on pore walls. The former tends to develop facets on pores, while the latter to keep the pores spherical.