Observation of oxide particles below the apparent oxygen solubility limit in tantalum

The apparent solubility of O in polycrystalline Ta as determined by the x-ray diffraction lattice parameter technique is approximately 1.63 at. percent at 8200C. However, oxide particles were identified in samples containing as low as 0.5 at. percent O. These particles were present at the grain boundaries and within the grains. The number of oxide particles increased with increasing O concentration in Ta. The presence of oxide particles suggests that the true solubility in the polycrystalline Ta metal is probably lower than that reported in the literature. (U.S.)