CHEMICAL TREATMENT WITH CERIUM TO IMPROVE THE CREVICE CORROSION-RESISTANCE OF AUSTENITIC STAINLESS-STEELS

The effect of cerium ion implantation in improving the localized corrosion resistance of stainless steels was demonstrated earlier. The work has now been extended to study the effect of cerium salt solution treatment. Rotating disc assemblies were employed to study the cathodic electrode process and its inhibition by cerium salt treatment on austenitic stainless steels in a simulated seawater solution. The reduction of oxygen and protons on both untreated steels is shown to be controlled by the mass transport processes in solution. Cerium treatment effectively inhibits the cathodic reduction of oxygen which is controlled primarily by charge transfer at the electrode. The overvoltage for cathodic reduction of protons increases after the cerium treatment and the electrode reaction is controlled by both the mass transport process in solution and the charge transfer on the electrode. As a result of inhibition of the electrode processes, cerium improves the localized corrosion resistance, and in particular the crevice corrosion resistance, of stainless steels. This is supported by results obtained from electrochemical measurements and crevice corrosion tests both in the laboratory and at a seawater test site.