The purpose of the present investigation was to determine the effect of SO₂ gas dissolved in water containing Cl^- ion on the pitting corrosion of austenitic stainless steel. Inhibiting effect of NO₃^- ion and NO₂^- ion was also studied. 18-8 stainless steel is passivated by water containing dissolved SO₂ owing to the oxidizing power of HSO₃^- ion, but it is more susceptible to pitting corrosion in water containing both Cl^- ion and dissolved SO₂ than in water containing Cl^- ion and sulphuric acid owing to the less protective effect of HSO₃^- ion than SO₄^2- ion for pitting corrosion. Nitrite added to above solution passivates 18-8 stainless steel, but inhibits less effectively pitting corrosion than nitrate. Nitrate, on the other hand, inhibits effectively pitting corrosion, but not passivates 18-8 stainles steel.

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Influence of temperature on intermolecular association of an inhibitor N, N-dimethyl-cetyl-amine with proton donors and on chemisorption of the inhibitor on steel surface were studied. Presence of the intermolecular association was determined by infrared spectra of the proton donors dissolved in carbon tetrachloride solution of the inhibitor at various temperature. Weight losses of mild steel test coupons prefilmed with the inhibitor in the solution with and without the proton donors at various temperature were measured by dipping in uninhibited 5% HCl aqueous solution.
Inhibition efficiencies of the intermolecularly associated inhibitors were lower than those of the unassociated, since an unshared electron-pair which was necessary for chemisorption of the inhibitor on metal surfaces was blocked by hydrogen-bonding. Elevation of temperature was effective for dissociation of these intermolecularly associated inhibitors. Inhibition efficiencies of the associated inhibitors were, therefore, more increasing than those of the unassociated ones with elevation of the filming temperatures. Warming of filming solution was more effective on increase of inhibition efficiencies of the associated inhibitors at their low concentration than those of high concentration because hydrogen bond could more easily be dissociated.
Adsorption of amine-hydrochloride of which unshared electron-pair was occupied with proton was further studied by measurements of inhibition efficiencies of test coupons pre-filmed in some solvents at various temperature.

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