OXIDATION OF TANTALUM AT HIGH TEMPERATURES - GEOMETRICAL EFFECTS

Tantalum specimens in the form of short tubes have been oxidised at 825 ° and 930 °C in oxygen at a pressure of approximately 400 torr. The external diameters of all the specimens were the same, and the internal diameter was varied. The oxidation rate of the inner surface decreased with decreasing radius of curvature, but the rate on the outer (convex) surface was approximately the same as that on the inner (concave) surface for the thinner-walled tubes. During oxidation the metal tubes dilated because of the stresses generated at the oxidising surfaces. The results suggest that the major source of this stress is in the adherent part of the oxide scale rather than in the surface layers of metal affected by solution of oxygen. © 1968.