A mechanism for the sintered density decrease of UO2-Gd2O3 pellets under an oxidizing atmosphere

A mixture of UO2 and Gd2O3 powders was pressed into compacts and sintered u nder various atmospheres ranging from reducing to oxidizing gases. The sint ered density of UO2-10 wt% Gd2O3 pellets decreases with increasing oxygen p otential of the sintering atmosphere. Dilatometry and X-ray diffraction stu dies indicate that the delay of densification takes place between 1300 degr eesC and 1500 degreesC, along with the formation of (U,Gd) O-2 A very large solubility of Gd2O3 in UOz relative to the reverse solubility might cause Gd ions to diffuse into UO2 so directionally that new pores are produced at the places of Gd2O3 particles. The new pores may be difficult to shrink an d thus lead to the density decrease under an oxidizing atmosphere but not u nder a reducing atmosphere, because a driving force for the shrinkage of ne w pores may be smaller under an oxidizing atmosphere than under a reducing atmosphere. (C) 2001 Elsevier Science B.V. All rights reserved.