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Abstract
The uptake and distribution of azelate ions on the surface of mild steel, inhibited in solutions of sodium azelate over the pH range of 5 to 7, has been studied by means of radio-tracer techniques. It has been shown that azelate ions become firmly bound to the inhibited surface and that the extent of uptake is dependent on solution pH, being greater during inhibition in slightly acidic solutions than in neutral solutions. The surface bound inhibitor was found to be contained in an insoluble, paniculate deposit, which is thought to be a ferric salt, formed anodically at sites of breakdown of the air-formed film.
A model has been put forward to explain the inhibitive rôle of azelate ions in terms of their effects on the several electrochemical reactions involved in film breakdown and repair in neutral and slightly acidic solutions.