X-Ray Photoelectron Study Of Oxides Formed On Ni Metal And Ni-Cr Alloy Surfaces Under Electrochemical Control At 25 Degrees C And 150 Degrees C

The oxide chemical composition on metallic Ni and NiCr alloy electrodes has been studied for changes in simulated reactor coolant solution chemistry, through a range of oxidizing potentials and pH settings at 25 degrees C and 150 degrees C. Even under strongly reducing conditions, the Ni surface has a 2-nm layer of oxide and hydroxide from which further oxides form, depending on the subsequent oxidative step. For basic (normal operating) pH conditions and under oxidation potentials near 0 volts (vs. SCE), a predominantly Ni(OH)(2) layer is formed that appears to remain relatively stable up to at least 48hours of oxidation at 150 degrees C. For the NiCr alloy, similar stability is imparted by a thin film of Cr(OH)(3)/ Cr2O3 and Ni(OH)(2)./NiO. Under milder oxidizing (but still basic) conditions, the surface is stabilized by a thin film that is mostly Ni(OH)(2)/NiO. Under neutral solution conditions, the same oxide/ hydroxide films do not seem to be as effective in stabilizing the surface. Copyright (c) 2017 John Wiley & Sons, Ltd.