Abstract
The effects of dichromate, molybdate, tungstate, nitrate, and nitrite ions on the composition and thickness of the passive films formed on the surface of 304 stainless steel in H3PO4-Cl− solutions have been determined by Auger electron spectroscopy. Correlations between the properties of the passive films and the inhibitive action of the oxyanions are deduced. It is shown that in the presence of nitrate and nitrite, the most effective species, the surface film contains high concentrations of iron oxide and approximately equal amounts of chromium and nickel, in addition to considerable nitrogen. The results could also explain why the inhibitive efficiencies of chromate and molybdate decrease with in, creasing anion concentration in solution.
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