Corrosion product of the tantalum-interstitial oxygen-potassium system at 1800 °F (982 °C)

Abstract

The isolation and identification of the corrosion product formed by the exposure of oxygen-doped tantalum to potassium are described. The corrosion of tantalum by liquid potassium appears to be quantitatively dependent on the oxygen impurity content and to occur by the formation of a ternary oxide. When tantalum containing oxygen in the range 1600–3800 p.p.m. is exposed to potassium at 1800 °F (982 °C), depletion of oxygen from tantalum occurs and the hygroscopic potassium tantalate, K 3TaO 4 is isolated as the reaction product. Indications are that under the test conditions, the dissolution of tantalum is quantitatively governed by the equation: 3 K + Ta + 4 O ( Ta) → K 3 TaO 4( K) These results imply that the total amount of “oxygen-effect” corrosion can be predicted when the total amount of interstitial oxygen in tantalum is known ( i.e., oxygen in solution in the metal initially, plus oxygen that enters the metal from the environment during the life of the system). Since oxygen-effect corrosion is the most serious type of corrosion encountered by tantalum alloys in contact with potassium at elevated temperatures, the present results are significant for the design and operation of advanced space power systems.