Corrosion behaviour of steel in solutions containing mixed inhibitive and aggressive ions

The action of sodium benzoate, sodium chromate and sodium nitrite in relation to the presence of sodium chloride, sodium nitrate, sodium sulphate and sodium sulphide has been studied by means of visual observation as well as potential measurements. It has been found that the critical concentration of the inhibitor for protection in distilled water could tolerate a range of concentration of the aggressive anion. The linear double logarithmic relationship between the concentration of an inhibitive anion and the maximum tolerated concentration of an aggressive anion is only beyond a certain critical concentration of the aggressive anion. The results are interpreted in terms of competitive adsorption between the inhibitor and aggressive ions on the bare metallic parts.