APPLICATION OF AC-IMPEDANCE METHOD TO EVA LUATION OF THE CORROSION-RESISTANCE OF ALLOYS IN A SIMULATED WASTE INCINERATION ENVIRONMENT

Electrochemical impedance measurements of 31 alloys have been carried out in NaCl-KCl-Na2SO4-K2SO4-ZnSO4 melts under air containing H2O and HCl at 723, 773 and 873 K. Regarding relatively good corrosion resista nt alloys, the interface of alloy/molten salt can be represented by an equivalent circuit model consisting of a charge transfer resistance, double layer capacitance solution resistance and finite diffusion impe dance. Meanwhile, the impedance characteristics of poor corrosion resi stant alloys can be explained by a transmission line equivalent circui t model in which the current distribution inside pores of thick porous oxide layers formed on the surface is considered. A good correlation was established between the reciprocal of impedance at 10 mHz and the corrosion rates calculated from mass loss after immersion tests. The A C impedance method was shown to be useful as rapid corrosion test for evaluating the corrosion performance of alloys in molten salt environm ents.