XPS study of oxides formed on nickel-base alloys in high-temperature and high-pressure water

The aim of this work is to characterize the oxidation behaviour of different nickel-base alloys exposed to high-temperature and high-pressure water for short oxidation times. The behaviour of Alloy 600 (74% Ni, 16% Cr, 9% Fe), Alloy 690 (60% Ni, 30% Cr, 9% Fe) and Alloy 800 (47% Fe, 32% Ni, 21% Cr) exposed to simulated, pressurised water reactor primary water at 325degreesC has been compared. From the combination of chemical and structural data obtained by XPS, nuclear reaction analysis and scanning electron microscopy, the chemical composition and the morphology of the oxide formed on the surfaces have been determined. All alloys present a duplex oxide layer composed of Fe-rich crystals in the external layer and an inner Cr-rich layer that is compact and continuous. The oxide thicknesses were 4-20 nm for Alloy 600 exposed for 0-400 h, 4-40 nm for Alloy 690 exposed for 0-400 h and 4-150 nm for Alloy 800 exposed for 0 to 150 h. The kinetics of oxidation of these samples most probably fit a logarithmic growth equation. Copyright (C) 2002 John Wiley Sons, Ltd.