Electrochemical study of the corrosion of metals in molten fluorides

Abstract

Resistance to corrosion of the structural materials is a key factor for nuclear applications that use molten fluorides. Low chromium, nickel-base alloys are regarded as the most suitable metallic materials. In a first approach, corrosion of some pure metallic constituents Ni, Mo, W and Fe, was studied by electrochemical techniques. Linear voltammetry was applied in LiF-NaF and LiF-AlF3, in the temperature range 900-1100°C. The relative stability of the metals in LiF-NaF is established. To determine the corrosion current density, three methods are presented, two based on the Tafel extrapolation method and the third one being the polarization resistance method. Results regarding corrosion rates are compared. Two corrosion behaviors are observed: on the one side, Ni, Mo and W and on the other side Fe. The difference might come either from different corrosion mechanisms or from a different number of exchanged electrons. The corrosion rate increases with temperature following the Arrhenius law. However, further experiments are needed in order to identify the key parameters that influence the corrosion in the different melts.