The use of in the x-ray photo-electron spectroscopy analyses of passive layers on stainless steel

The repassivation of a commercial grade 18% Cr 8% Ni austenitic stainless steel in low temperature, neutral, de-oxygenated water was studied by XPS, obtaining composition profiles by argon ion milling. Evaluation of the technique revealed negligible effect of sample transfer through air from the spectrometer to the corrosion cell, but photo-electron attenuation and reduction in peak definition resulted from organic carbon pick-up both from water and spectrometer vacuum. The passive layers contained chromium-rich and iron-rich areas. The Cr³⁺, Fe²⁺ and Fe³⁺ cations are incorporated in layers containing both OH^- and O^2- ions. The unreacted nickel of the alloy showed an attenuation of the 2p _{3 2} signal with exposure which presented a unique opportunity to calculate film thickness. Increases in refreshment rate (1, 3 and 6 ml/h) at 313 K and 353 K respectively increased the film thickness (1.5-3.0 nm); possibly due to increased carbon accreation, incorporating hydrogen-bonded water into the film. The outer 33% of the film revealed (Fe²⁺ + Fe³⁺)/(Cr³⁺) corresponding to alloy proportions, suggesting no overall selective oxidation or dissolution.