Interim report on task 1.2: near equilibrium processing requirements part 1 of 2 to Lawrence Livermore National Laboratory for contract b345772
The following ceramics were prepared for this study: the baseline ceramic, the baseline ceramic plus process impurities, a zirconolite-rich composition, a brannerite-rich composition, a composition designed to have {approx} 10% perovskite in addition to the normal baseline phases, and an {approx} 10% phosphate-doped batch. These samples were prepared by oxide (via wet or dry milling) and alkoxide-routes. The milling method has a direct effect on the samples. Incomplete milling leads to inhomogeneity in the microstructure. The main effect of incomplete milling is that unreacted actinide oxides remain in the microstructure, usually surrounded by brannerite. The phase composition also alters due to the actinide being tied up in the unreacted oxide, e.g., the pyrochlore has less actinide and additional phases, such as zirconolite may form. The approach to equilibrium is determined by a number of factors--the efficiency of the milling, the sintering time, the sintering temperature and the batch composition. The latter is very important, e.g., the zirconolite-rich batch has a slower approach to equilibrium than the baseline ceramic requiring higher sintering temperatures or longer sintering times. The addition of process impurities dramatically alters the approach to equilibrium. The additives produce a silicate liquid phase (at the sintering temperatures), which aids the dissolution and diffusion of the actinide oxide and densification such that even the relatively inhomogeneous dry milled oxide-route samples reach 90--95% of their equilibrium state on sintering at 1350 C for 4 hours. In terms of approach to equilibrium, the following summarizes the results. For 4 h at 1350 C samples: dry-milled oxide samples reach {approx} 50-80% of their equilibrium state, except for the baseline + additives batch which achieves {approx} 90-95% equilibrium. The wet-milled oxide route samples reach {approx} 90-100% equilibrium and alkoxide-route samples reach {approx} 95-100% equilibrium. The following refers to alkoxide or wet-milled oxide-routes. Sintering for 75 hours at 1350 C gives {approx} 98-100% equilibrium. Sintering at 1300 C gives {approx} 80-95% equilibrium. Sintering at 1400 C is more difficult to judge as the phase chemistry can change, but generally, the samples sintered for 4 hours at 1400 C are similar to the samples sintered for 75 hours at 1350 C. Generally, the compositions formed the phases expected. The exception was the batch with nominally {approx} 10% perovskite, which did not contain perovskite (except for the poorly milled Th/Udoped batch and in this case it was due to the Th being retained in large ThO{sub 2} grains).
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15007291
- Report Number(s):
- UCRL-CR-139074-PT-1; TRN: US200415%%73
- Resource Relation:
- Other Information: PBD: 5 Apr 1999
- Country of Publication:
- United States
- Language:
- English
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