Angle-resolved XPS analysis of molybdenum and tungsten in passive films on stainless steel PVD alloys

Passive films on physical vapour deposited alloys, based on 304L with additions of 20 at.% of molybdenum and tungsten, were studied with angle-resolved XPS. The samples were anodically polarized in a sulphate solution to potentials in the low and high passive region, respectively. In the low passive region, the Mo spectrum contained a strong contribution of Mo(IV) hydroxide. In the high passive region, higher fractions of hexavalent species were found; W(VI) gave a stronger contribution than Mo(VI), as can be understood by the lower solubility of the W(VI) salts. Contributions to tetravalent molybdenum were found to consist of oxide (MoO2) as well as oxyhydroxide compounds. For tungsten, the dominating tetravalent contribution was WO2- Copyright (C) 2002 John Wiley Sons, Ltd.