Effect of oxygen on the compatibility of tantalum and potassium

Static capsule tests were used to study the effect of oxygen in each phase on the compatibility of tantalum and potassium at 600, 800, and 1000 C (1112, 1472, and 1832 F). As the oxygen concentration of the potassium was increased, the amounts of tantalum in potassium after test also increased. The results indicate the formation of an unidentified ternary oxide phase (probably at the tantalum-potassium interface) that is either nonadherent or dissolved when the potassium is dissolved for chemical analysis. On the other hand, when the tantalum specimens contained oxygen above a certain threshold concentration that depends on test conditions, potassium penetrated the tantalum, and both intergranular and transgranular attack occurred. The threshold levels for intergranular attack at 600, 800, and 1000 C were determined to be 500, 700, and 1000 ppm of oxygen, respectively. Again the explanation involves the formation of a ternary oxide phase.