XANES Study of the Chemistry of Molybdenum in Artificial Corrosion Pits in 316L Stainless Steel

The chemistry of molybdenum species in artificial corrosion pits on 316L stainless steel was investigated using X-ray absorption spectroscopy (XANES). It was found that the K-edge spectra are consistent with the presence of an Mo(III) species. The presence of Mo(VI) polymolybdates as been proposed to explain the well-known beneficial effects of Mo in decreasing the susceptibility of stainless steel to localised corrosion, but no evidence of these species was found. High resolution measurements (with a spatial resolution of 3.5 μm in the vertical direction) through the dissolving metal interface did not detect the presence of any different Mo-containing species in the vicinity of the salt film. However, the spatial resolution was insufficient to detect the presence of submonolayer species on the dissolving metal surface that have been proposed to block active dissolution.