Thin electrolyte layer thickness effect on corrosion behaviour of invar in sulphate solutions

Abstract

In the present work electrochemical studies were carried out with disc electrodes of Fe–36Ni alloy in sulphate solution at pH 1·5, using linear voltammetry (LV) and electrochemical impedance spectroscopy (EIS) techniques, comparing the results with those of pure iron and pure nickel. The alloy shows a reduced corrosion when compared to pure iron, following the classical binary alloy behaviour where iron is preferentially dissolved (dealloyed) resulting in a nickel rich surface. The corrosion of Fe–36Ni alloy was further investigated under a thin electrolyte layer, where it was of interest to study the potential distribution as well as the variation of the electrochemical impedance as a function of the electrolyte film thickness. In this geometry, the corrosion current density, estimated from the low frequency (10 mHz) intercept of the EIS plot, decreases as the electrolyte thickness decreases below 500 μm, but does not change significantly while ϵ is >500 μm.