Abstract
In situ X-ray photoelectron spectroscopy real-time measurements and angular-dependent high resolution core level analysis were used for the first time to investigate the Cr enrichment and oxide growth mechanisms on a model 304 austenitic stainless steel surface in the very initial stages of oxidation leading to pre-passivation. The oxidation kinetics was followed for increasing oxygen exposure and temperature, revealing an early nucleation regime (for exposure <10 L) leading to the formation of a strongly Cr-enriched Cr3+/Fe3+ mixed layer followed by an oxide growth regime where preferential iron oxidation takes over and mitigate the initial chromium enrichment.
Highlights
Stainless steels (FeCr-based alloys) are widely used because of their high corrosion resistance resulting from the formation of a continuous and protective surface oxide layer, the passive film
Most studies [16,17,18,19,20,21,22] on the initial oxidation of pure iron and Fe-based alloys have been carried out with a surface science approach in ultra-high vacuum (UHV) conditions, because it provides a maximal control of surface state and oxidation conditions which are key factors to surface reactivity and growth mechanism studies of ultra-thin oxide films
At room temperature (RT), the calculated thickness is stable at 1.6–1.7 nm after the 6 L exposure, in agreement with the saturation observed in the oxygen uptake (Fig. 2 and 4) and with 1.8–2 nm thickness reported for the native oxide film formed on the same austenitic stainless steel surface [23]
Summary
Stainless steels (FeCr-based alloys) are widely used because of their high corrosion resistance resulting from the formation of a continuous and protective surface oxide layer, the passive film. Numerous surface analytical studies have shown that the passive film is only a few nanometers thick and markedly enriched in Cr(III) oxide/hydroxide species [1,2,3,4,5,6,7,8,9,10,11,12,13] It has been suggested from nanometer scale studies on austenitic stainless steels that. The study was performed by in situ XPS on a (100)-oriented Fe-18Cr-13Ni single crystal (a model of the most common 304 grade of austenitic stainless steel) during the initial stages of oxygen exposure (< 100 L) at RT, 150◦C and 250◦C. The work is aimed at providing new comprehensive knowledge for the surface treatments of Fe-Cr-Ni alloys for improved resistance to initiation of localized corrosion of stainless steel
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