Semiconducting properties of surface oxides formed on austenitic stainless steel

Abstract

Using Mott-Schottky analysis technique, semiconducting properties of surface films formed on 316L stainless steel samples that were potentiodynamically polarized up to different ending potentials (Eending) in Ch3COONa and NaCI solutions were investigated. A frequency dependence of Mott-Schottky curves was shown between 1 kHz and 10 kHz frequencies. Also, on the surface films formed on samples potentiodynamically polarized to - 50 and +100 mV (vs. SCE) in NaCI solution, unusual behavior displaying deflection on the curves was observed at 1 kHz frequency. This might be related to pitting initiation. Donor densities in the surface films were calculated by determining the slopes between 1/C2 and the sweep potential during Mott-Schottky analysis. Higher donor densities were obtained in NaCI than in CH3COONa solution. Also, the compositions of the surface films were analyzed by time-of-flight secondary ion mass spectrometry. In this analysis, the depth profiles of chloride ions and oxygen ions in the surface films were determined, which are discussed as a function of the ending potential during potentiodynamic polarization.