Abstract
The action of sodium benzoate as a corrosion inhibitor for mild steel in neutral aqueous solution has been studied in relation to the surface preparation of the steel, the presence of aggressive salts in the solution, and temperature.
The minimum concentration of benzoate required for protection of mild steel in distilled water is considerably affected by the surface preparation of the metal, grit-blasted surfaces requiring about 100 times the concentration of benzoate that is required for abraded surfaces. In solutions containing aggressive anions, a linear relation exists between the logarithm of the benzoate concentration and the logarithm of the maximumconcentration of aggressive anion that will permit inhibition. In solutions of low benzoate concentration the order of aggressiveness of anions is sulphate > chloride > nitrate; the order changes with increase in benzoate concentration. Corrosion in non-inhibiting benzoate/sulphate solutions is of a uniform nature, in benzoate/chloride solutions it is uniform with a tendency to local attack at some concentrations, and in benzoate/nitrate solutions it is usually localised. A 10-fold increase inbenzoate requirement for inhibition of abraded mild steel in distilled water is found between 5° and 40° little change from 40° to 80°, and a further large, rather indeterminate, increase above about 80°.
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