Kinetics of passivation of nickel-base alloys (Alloy 600 and Alloy 690) in high temperature water

Abstract

This chapter presents a study, which investigates the kinetics of passivation in high temperature and high pressure water of a Ni-16Cr-9Fe and a Ni-29Cr-l IFe (wt. %) alloys. The composition and the thickness of the surface oxide layers are measured for very short oxidation times (minutes) and longer oxidation times (up to 400 hours) and the thickness of the inner chromium oxide barrier layer is measured as a function of oxidation time. From the three kinetic laws that fit well the experimental data for the short oxidation times, only the logarithmic law is retained from the comparison of the extrapolated growth laws with the experimental data for long oxidation times. The logarithmic law is characteristic of an apparent mechanism of high charge field effect for the growth of the internal Cr2O3 layer. This approach reveals that it is possible to follow the kinetics of the growth of the inner Cr2O3 layer in the initial stages of passivation in high pressure, high temperature water.