Abstract
The initial-stage sintering mechanism of hyperstoichiometric urania prepared by sol-gel process was determined in relation to temperature during constant rate heating (CRH). The urania powder used in this experiment was prepared by crushing in Ar atmosphere the micro- spheric gel of UO2 obtained by sol-gel process, and reducing the resulting powder by heating in H2 for 1 hr at 500°C. The results obtained from densification measurements indicated that the initial-stage sintering proceeded in two phases governed by different shrinkage mechanisms, as follows. 1. The sintering up to 675°C would be due to a mechanism such as rearrangement of grains and/or plastic flow. 2. Sintering from 750° to 800°C was interpreted as being controlled by uranium volume diffusion. The estimated diffusion coefficient D = 1.42×10−6 exp(-52,500/RT) cm2/sec. This value agreed in order of magnitude with the uranium diffusion coefficients measured by other workers for hyperstoichiometric urania.
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