Inhibition of the pitting corrosion of 304 stainless steel in 0.5Â M hydrochloric acid solution by heptamolybdate ions

The corrosion inhibition effect of heptamolybdate ions on 304 stainless steel in 0.5 M hydrochloric acid solution at 298 K was investigated using gravimetric, electrochemical and optical microscopy methods. Increasing inhibitor concentration led to significant reduction in the corrosion rate of stainless steel, with inhibitor efficiency values above 90%. The adsorption of the inhibitor onto the steel surface is described using the Langmuir adsorption isotherm. The value of the free energy of adsorption determined at 298 K (ΔG° = −31.1 kJ mol−1) characterizes the adsorption process of heptamolybdate ions on the surface of the metal.