THE ROLE OF ALLOYED ELEMENTS AND ADSORBED IMPURITIES IN PASSIVATION OF METAL-SURFACES

Recent advances in understanding the nature of passive films formed on well-defined metal surfaces are reviewed. Results obtained by angle-resolved photoelectron spectroscopy on passivated single crystal surfaces are described. The major effects of alloyed elements such as chromium and molybdenum on the thickness, the composition, and the in-depth distribution of the species in the passive films are presented. The action of strongly adsorbed impurities such as sulphur on dissolution and passivation of metals and alloys and the associated mechanisms are reviewed. The surface reactions governing passivation/depassivation phenomena in the presence of adsorbed impurities (S) and alloyed elements (Mo) are presented. The results presented have direct implications in corrosion and protection of metallic materials.