Anodic Corrosion of High Nickel Alloys in Sulfuric Acid Solution

Abstract

Various experimental techniques, such as the potentiostatic and the potentiokinetic polarization charachteristics measurements, the colorimetric analyses of dissolved alloy constituents and the electron microscopic observation, were adopted to study the anodic corrosion of high nickel alloys in 1N sulfuric acid. Hastelloy B, which was the lowest in chromium content among five sorts of alloys used, showed no indication of passivation but poor corrosion resistance in the potential range investigated. Other four alloys passivated at the potential around 200mV vs. S. C. E., and the higher chromium content resulted in less passivatiog current in general tendency. These observations led the conclusion that chromium played essential role in the passivation of the alloys. In the potential range around 600mV vs. S. C. E., selective dissolution of moybdenum was observed with two sorts of alloys, namely Hastelloy C was the most remarkable in this behaviour and Hastelloy X less but slight. Localized attack was found surrounding the deposit of chromium carbide. The control of chromium depletion due to the decrease of carbon content or the increase of chromium content in alloy seemed to be effective in prevention of such selective attack of molybdenum.