Synergistic action of vinyl triphenyl phosphonium bromide with various anions on corrosion of steel

The effect of mixtures of vinyl triphenyl phosphonium bromide containing various anions on the corrosion rate of steel in 0.5M H2SO4 has been investigated The inhibition mechanism has been studied by conducting electrochemical polarisation measurements. The inhibitor acts by covering the cathodic area of the metal surface through adsorption of the phosphorus atom. A synergistic effect has been observed for KBr, KI, and RSCN with vinyl triphenyl phosphonium bromide. Thus, an improvement in inhibition was obtained by using mixtures compared with that given by individual components. A probable mechanism for this process is suggested. The degree of surface coverage of iron in acid solution containing 10(-5) M inhibitor was determined for various concentrations of Br-, I-, and SCN-. The inhibiting effectiveness was in the order KI > KSCN > KBr. Protection of 93.8% was given by a mixture of 10(-5) M inhibitor + 10(-2) M KI. It was observed that the protection efficiency was sharply enhanced in the presence of 10(-3) M KI with very low concentrations (10(-5) M-10(-4) M) of the inhibitor. (C) 2000 IoM Communications Ltd.