Potentiostatic Study on the Anodic Behaviour of Iron-Nickel Alloys

Abstract

The anodic behaviour of annealed iron-nickel alloys of nickel content ranging from 0 to 100% was investigated in deaerated sulphuric acid solution at 25°C by means of electrochemical techniques. The semi-conductor type potentiostat was used for polarization measurement. Data concerning the relationship between the composition of alloys and the various properties such as corrosion potential, passivation potential, Flade potential, passivation current density, anodic current density at the passive state and the trans-passive state were presented. It was found that the anodic behaviour of iron-nickel alloys was very much different from that of iron-chromium alloys (previous report), the difference being summarized as follows: (1) In contrast with iron-chromium alloy, no negative loop was observed in the anodic polarization curves of any of the iron-nickel alloys studied. (2) Anodic current densities at the passive state, or passivity-maintaining current densities, of the iron-nickel alloys are far greater than that of the iron-chromium alloys, but in the trans-passive region anodic current densities are small for the former compared with that for the latter. (3) The Flade potential for alloys of nickel content more than 30% appears to be varied depending upon whether the initial potential for the decay trace is set in the passive region or in the trans-passive region. This phenomenon was not observed in the iron-chromium alloys.