Influence of Cr and Mo on the passivation of stainless steel 430 (18Cr) and 444 (18Cr-2Mo): In situ XANES study

Abstract

We have studied the influence of metal elements on the passivation of stainless steel (SS) 430 (18Cr) and 444 (18Cr(2)Mo) by real time X-ray absorption near edge spectroscopy. We developed an electro-chemical cell that is suitable for in situ electro-chemistry experiments. The behavior of Fe, Cr and Mo elements of SS 430 and 444 was studied in passive region reaction in a borate buffer solution (pH 7.0). We found that the Cr203/Fe,03 ratio gradually decreased with passivation time due to the oxidation of Cr2O3 to CrO42-, indicating weakening of passivity. In the meanwhile, the amount of Mo at passive films increased with passivation time. The improvement of passivity in the SS 444 is mainly attributed to the substitution of Cr oxide by Mo oxide in the passive film. (C) 2002 Elsevier Science B.V. All rights reserved.