The influence of halide ion concentration on the effects of surface active inhibitors in strong electrolytes

Abstract

The effect of Cl −, Br − and I − on the efficiency of diphenyl amines, thiouiea and hydroxylamines in the corrosion of the low carbon steel alloys was investigated in aqueous solutions of H 2SO 4 and Na 2SO 4, at a total concentration between 10 −3 and 5M, in the pH range 0–6·5. The inhibitors efficiency was determined by the equation: p = Δ G — Δ G i Δ G ⋅ 100 where Δ G and Δ G t represent the loss of metal weight per surface unit during 24 h, in the presence or absence of inhibitors or halide ions respectively. It has been found that in the presence of halides the inhibitor efficiency increases with increasing halide concentration to an optimal value (maximum efficiency). Above this value, the increase of halide concentration decreases the inhibitor's efficiency. The optimal concentration of the halide which increases inhibitor's efficiency, decreases with the increase of the halide ion radius as follows Cl − > Br − > I − i.e. in the same order as that of the peaks on the halide concentration-inhibitor efficiency curve. The effect of the ratio between the halide and inhibitor concentrations on the efficiency of corrosion protection has been determined.