抄録
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°C 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.
