Effect of Zinc Addition on Cobalt Ion Accumulation into the Corrosion Surface of Type 304 Stainless Steel in High-Temperature Water Containing Dissolved Hydrogen

Abstract

The effect of zinc addition on the corrosion and the cobalt accumulation on type 304 stainless steel exposed to water at 561K has been investigated. The exposure tests were carried out at three different zinc concentrations 0, 0.2 and 0.8μM, and also using three different types of zinc compounds ZnO, ZnSO₄, and Zn(NO₃)₂. The structure and elemental depth distributions of the corrosion surface were analyzed by EPMA, XRD and GDS. The zinc addition suppressed the amount of corrosion and the cobalt accumulation. These effects were related to the zinc concentration, however, no significant change was observed with the zinc constitution. The cobalt accumulation suppression by the zinc addition is due to two separate factors; first, the reduction in amount of corrosion film, and secondly, the suppression of the cobalt concentration increase with time in the corrosion film.