SOME ASPECTS OF THE FABRICATION TECHNOLOGY OF BERYLLIUM AND BERYLLIA
Cold-compacting and sintering, hot-compacting, and slip-casting have been investigated as methods for the fabrication of beryllium oxide powders prepared by decomposition of the hydroxide. The thermal decomposition of beryllium hydroxide obeys a unimolecular law with an activation energy of 14.7 kcal/mole. Decomposition is not complete below 500 deg C. As the temperature of calcination of the hydroxide increases above 500 deg C, the surface area and activity of the powder decrease. For calcination temperatures in the range 500 to 900 deg C the powder produced has a surface area of approximately 100 m/sup 2// g. Such powder cold-compacts poorly, and low sintered densities result ( approximates 2.0 g/cm/sup 3/). Addition of a fluxing agent such as lime enables densities of approximates 2.6 g/cm/sup 3/ to be attained. These very active powders hot-compact readily to approximates 2.8 g/cm/sup 3/ at 1400 deg C. The oxide produced using calcination temperatures of 1000 to 1200 deg C is less active, having a surface area of approximates 16 m/sup 2//g. Its cold- compacting and sintering behavior is better than that of the more active material, and densities of 2.7 g/cm/sup 3/ are obtained. The hot-compacting properties deteriorate with the decreased activity. This type of oxide powder can be used to give slip-cast ware of very high green strength, but of relatively poor sintering properties. Further increase of calcination temperature (> 1400 deg C) diminishes the surface area to below 5 m/sup 2//g. The cold-compacting and sintering behavior of these powders is poor but can be improved by lime additions; their poor hot-compacting behavior can be improved by powder comminution. The corrosion of beryllium in wet and dry carbon dioxide at atmospheric pressure has been investigated for the temperature range 500 to 700 deg C. At 500 deg C the corrosion rate in both wet and dry gas is negligible; at 600 deg C the corrosion film is protective in the dry, but not in the wet gas; at 650 deg C and 700 deg C the surface film is no longer protective even in the dry gas. Comparison of the corrosion behavior in dry oxygen and dry carbon-dioxide suggests that beryllium carbide formation may become significant at 650 deg C and render the oxide film non-protective. Of the various types of fabricated beryllium available those showing the smallest departure from isotropy with regard to mechanical properties are probably most suitable for use as a canning material for uranium. Two methods of canning uranium in beryllium have been developed which avoid the necessity of a can closure by fusion welding. The sheath forging process is an integral canning technique in which the can is formed by consolidating beryllium powder around a uranium core. Consolidation is achieved by hot forging the powder and core within a steel can at about 1000 deg C. In the second method end closure is obtained during coextrusion of uranium within beryllium in the range 400 to 500 deg C. The thermal-cycling behavior of these two types of element is described. (auth)
- Research Organization:
- Atomic Energy Research Establishment, Harwell, Berks, Eng.
- NSA Number:
- NSA-13-006782
- OSTI ID:
- 4282599
- Report Number(s):
- A/CONF.15/P/319
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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