Sintering and morphology of interconnected porosity in UO$sub 2$ powder compacts
Uranium dioxide powder compacts of approximately 46% green density were sintered in flowing hydrogen at temperatures between 1500 and 1700 deg C. On annealing, the compacts readily formed an interconnected system of pores stabilized by grain boundaries. The volume of open porosity decreased with an activation energy of 4.6 J mol/sup -1/ at a rate controlled by grain growth. The grainboundary migration removed the restraint on the porosity allowing shrinkage to commence. The compact surface area decreased with a higher activation energy of 6.0 J mol/sup -1/. The mechanism proposed for the diminishing area was the smoothing of the faceted powder grains. Nucleation of atomic layers on the facets was shown to account for the high activation energy. The equilibrium shapes that may be adopted by interconnected porosity were calculated using a model in which simpler geometry was substituted for the real anticlastic surface curvature. The model demonstrated the stabilizing effect of increasing grain- boundary energy and the formation of closed pores. (auth)
- Research Organization:
- Berkeley Nuclear Labs., Eng.
- NSA Number:
- NSA-29-021330
- OSTI ID:
- 4327479
- Journal Information:
- J. Mater. Sci., v. 8, no. 12, pp. 1717-1724, Journal Name: J. Mater. Sci., v. 8, no. 12, pp. 1717-1724; ISSN JMTSA
- Country of Publication:
- United Kingdom
- Language:
- English
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