Preparation of Alloys for ESCA Investigation

The surface compositions of stainless steels–Fe, Cr, Ni, Mo-alloys–after scraping in vacuum, mechanical polishing in air, electropolishing and ion etching have been studied by ESCA. The most representative surface composition is obtained after scraping the sample with a diamond tool in UHV. All other methods produce enrichment of some species on the surface. Mechanical polishing in air leads to a preferential oxidation of Fe and Cr and a concurrent accumulation of Mo and Ni atoms underneath the oxide. During electropolishing in perchloric acid Fe is selectively dissolved into the solution, while Cr and Mo are enriched in their metallic states in the surface region. (It is suggested that it is the enrichment of these alloy components which gives electropolished stainless steels their excellent corrosion properties.) Ion etching lowers the Cr and Ni content in the outermost layer of the metal by selective sputtering mechanism.