Effect of alternately changing the dissolved Ni ion concentration on the oxidation of 304 stainless steel in oxygenated high temperature water

Characteristics of oxide films formed on 304 stainless steel under alternately changing Ni2+ concentrations in oxygenated high temperature water were examined. Oxides preformed under low Ni2+ concentration evolve from hematite to spinel after subsequent immersion under high Ni2+ concentration. Meanwhile, Ni content in the surface layer of oxide rises up while Fe content drops. Oxide films preformed under high Ni2+ concentration show little change in phase composition after subsequent immersion under low Ni2+ concentration. Fe contents in surface layer rise up while the change of Ni contents depends on the original phase composition and whether residual Ni2+ is present.

► Hematite preformed under low Ni2+ level evolves into spinel under high Ni2+ level.
► Oxide films maintain in phase composition when Ni2+ level changes from high to low.
► Oxide film preformed under high Ni2+ level could consume trace Ni2+ in solution.