Effect of molybdenum and tungsten polyoxometalates on the composition of surface layers and electrochemical behavior of stainless steel in sulfuric acid

• L. P. Kazansky, Yu. E. Pronin, E. M. Sokolova and S. S. Veselyi

A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskii pr. 31, Moscow, 119071 Russian Federation

Abstract: The composition and thickness of the surface layers formed on ferrite steel at various applied potentials in pure 1 N H2SO4 and in the presence of polyoxometalate (POM) anions (PMo₁₂O₄₀^3-, Mo₈O₂₆^4-, and PW₁₂O₄₀^3-) have been studied by XPS. Noticeable changes in cationic composition are observed near the passivation potential. At anodic potentials the surface oxide layer is enriched by chromium oxide. The thickness of this layer does not exceed 2–3 nm. If polymolybdate or polytungstate anions are added to sulfuric acid, they are located mostly in the uppermost oxide layer. The anodic currents decrease notably with an increase in POM concentration. At the passivation potential the oxide layer thickness exceeds 3–4 nm and it is substantially enriched by molybdenum. On the samples kept for 1 h in 1 N H2SO4, a protective layer is formed in the presence of POM and an after-affect is achieved. This layer remains stable upon transfer into pure 1 N H2SO4, especially in the case of PMo₁₂O₄₀^3-. The stronger protective properties of PMo₁₂O₄₀^3- are assumed to be due to its redox properties.

Keywords: stainless steel, passivation, surface layers, molybdenum and tungsten polyoxometalates, XPS study

Int. J. Corros. Scale Inhib., 2013, 2, no. 1, 67-81 PDF (980 K)
doi: 10.17675/2305-6894-2013-2-1-067-081

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