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

The apparent solubility of oxygen in poly crystalline tantalum as determined by the X-ray diffraction lattice parameter technique is about 1.63 at. pct at 820°C. However, oxide particles were identified in samples containing as low as 0.5 at. pct oxygen. These par-ticles were present at the grain boundaries and within the grains. The number of oxide particles increased with increasing oxygen concentration in tantalum. The presence of oxide particles suggests that the true solubility in the poly crystalline tantalum metal is probably lower than that reported in the literature.