$sup 3$He release characteristics of metal tritides and scandium--tritium solid solutions
Tritides of such metals as scandium, titanium, and erbium are useful materials for determining the effects of helium accumulation in metallic solids, for example, CTR first wall materials. Such effects include lattice strain and gross deformation, as reported elsewhere, which are related to $sup 3$He retention and ultimate release. Long term gas release studies have indicated that, during the early life of a metal ditritide, a large fraction of the $sup 3$He is retained in the solid. At more advanced ages (2 to 4 years, depending on the parent metal), the $sup 3$He release rate becomes comparable to the generation rate. Statistical analysis of the data indicates that the acceleration in $sup 3$He release rate depends on accumulated $sup 3$He concentration rather than strictly on age. $sup 3$He outgassing results are presented for thin films of ScT$sub 2$, TiT$sub 2$, and ErT$sub 2$, and the critical $sup 3$He concentrations are discussed in terms of a percolation model. Phase transformations which occur on tritide formation cast some doubt on the validity of extrapolating results obtained for metal tritides to predictions regarding the accumulation of helium in metals. Scandium is unique among the early transition and rare-earth metals in that the metal exhibits a very high room temperature tritium solubility (T/Sc = 0.4) with no phase transformation. Indeed, even the lattice parameters of the hcp scandium lattice are only minimally changed by tritium solution, and we have succeeded in obtaining single crystal ScT$sub 0$$.$$sub 3$ samples in two crystallographic orientations. Using a very sensitive technique, we have measured $sup 3$He emission from both these samples, as well as from fine-grained thin film scandium-tritium solid solution samples (ScT$sub 0$$.$$sub 3$$-$$sub 0$$.$$sub 4$). The fine-grained film samples release $sup 3$He at 2 to 3 percent of the generation rate, while the emission rate from the single-crystal samples is approximately 0.05 percent of the generation rate, indicating a strong grain size effect. (auth)
- Research Organization:
- Sandia Labs., Albuquerque, N.Mex. (USA)
- NSA Number:
- NSA-33-011724
- OSTI ID:
- 4151987
- Report Number(s):
- SAND--75-5443; CONF-750989--2
- Country of Publication:
- United States
- Language:
- English
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