INFLUENCE OF INCORPORATED ANIONS AND BOUND WATER ON THE FORMATION AND STABILITY OF ANODIC FILMS FORMED ON STAINLESS STEEL.

The nature of the anodic films formed on 304 stainless steel at plus 250 mV (vs. SCE) in deaerated solutions of 0. 5M H//2SO//4 and 0. 5M H//2SO//4 plus 0. 35M NaCl was determined by RHEED and variable angle XPS. Evidence is given of SO//4**2** minus and Cl** minus incorporation into the outer Fe-rich regions of the anodic film. In addition to Cr**3** plus species which make up the inner layer of the film, CrO//4**2** minus and/or Cr//2O//7**2** minus were observed by XPS in the outer layers. The mechanism of formation of the Cr**6** plus species in the solid-state and the influence of the incorporated anions on the passivation process are discussed.