Ion Transport Mechanisms in the Oxide Film Formed on 316L Stainless Steel Surfaces Studied by ToF-SIMS with 18 O 2 Isotopic Tracer

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 18 O 2 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 18 O 2 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.