The role of dissolved oxygen in the corrosion of niobium and tantalum by liquid sodium

Abstract

The corrosion of niobium and tantalum in liquid sodium is strongly influenced by the quantity of dissolved oxygen in the liquid metal. The oxides Na₃TaO₄ and Na₃NbO₄ have been identified on the surface of tantalum and niobium after immersion in liquid sodium containing dissolved oxygen at temperatures in excess of 300°. The oxides were identified by their X-ray powder diffraction patterns which were recorded through a matrix of sodium. Measurement of the lattice constant of the underlying transition element enabled the extent of oxygen solid solution to be calculated. The formation of an oxide, together with oxygen in solid solution, enables a mechanism of corrosion for niobium and tantalum in the presence of liquid sodium to be established.