Ion Transport Mechanisms in the Oxide Film Formed on 316L Stainless Steel Surfaces Studied by ToF-SIMS with 18O2 Isotopic Tracer

Luntao Wang,Philippe Marcus,Antoine Seyeux

doi:10.1149/1945-7111/ab9c87

Abstract

The composition and structure of the native and passive oxide films formed on 316 L stainless steel have been studied in situ by ToF-SIMS. High temperature re-oxidation experiments in isotopic 18O2 gas have also been done to assess the ion transport mechanisms in the native and passive oxide films. Duplex oxides with an inner Cr rich layer and an outer layer rich in Fe and Mo oxide have been observed on native and passive oxide films. Exposure of the oxide films to isotopic 18O2 tracer at 300 °C reveals that the outward cationic diffusion governs the inner oxide growth. The outer Mo-rich layer prevents the continued transport of Cr to the outermost surface. The passive film, due to its composition and structure, exhibits a markedly lower oxidation rate compared to native oxide films.

Highlights

In many industrial sectors, stainless steels (SS) have a wide range of applications due to their high corrosion resistance in severe environments.[1]
For the passive film (Fig.1(b)), while the 98Mo16O3- depth profile exhibits a similar trend as the one observed for the native oxide, indicating that oxidized molybdenum is located in the outer film, the 56Fe16O2- depth profile is slightly different. 56Fe16O2maximum intensity is still located in the outer oxide, but decreases slowly though the inner oxide film
When we look at the oxidation kinetics on passive films on 304L SS and 316L SS, we observe a lower oxidation rate for the 316 stainless steel, which can be assigned to the Mo-rich outer oxide layer, which acts as a barrier preventing Cr diffusion to the outer surface

Summary

Introduction

Stainless steels (SS) have a wide range of applications due to their high corrosion resistance in severe environments.[1]. Many studies have been carried out to characterize the composition and structure of the oxide film formed on SS surface in order to better understand the good corrosion resistance properties of the stainless steel.[2,3,4] The performance of the oxide films (including the native and passive films) has been tested in various conditions, such as aqueous, gaseous and high temperature environments.[5-7] Surface analysis, including X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), have demonstrated that the native oxide film formed on Fe-Cr based stainless steels generally shows a duplex structure, with an iron rich outer layer and a chromium rich inner layer.[8-12]. The passive film, formed electrochemically within the passive range in sulfuric acid, shows strong chromium enrichment compared to the native oxide film. This is attributed to the lower dissolution rate of chromium oxide compared to iron oxide in acidic media.[8, 11]

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