Corrosion behaviour of stainless steel alloys in molten (Na,K)NO3 eutectic mixture

In the present article it is aimed to study the corrosion (oxidation) behaviour of two types of stainless steel alloys, ferritic (15.03% Cr) and austenitic (20.45% Cr, 8.37% Ni), in molten (Na, K)NO3 mixture at different temperatures ranging from 400-600 C. In this investigation the technique of potential-time and current-time under the open-circuit conditions is employed. The variation of potential with time at different temperatures was explained in terms of propagation and thickening of oxide film with a rate which depends on the temperature. It is assumed that the oxide film thickens according to a solid state mechanism under high field strength. The activation energy of the corrosion process was estimated using Arrhenius plots. The calculated values are found to be 21.36 KJ/mol for the ferritic stainless steel alloy and 23.3 KJ/mol for the austenitic one. The low value of activation energy signifies diffusion controlled process occurring in the oxide matrix. The corrosion products formed on the surface of stainless steel alloys are identified by X-ray diffraction analysis. Also the melt is chemically analysed to detect the amount of Fe, Cr and Ni in the melt after the completion of experiment. (orig.)