Synergistic influence of iodide ions on the inhibition of corrosion of C-steel in sulphuric acid by some aliphatic amines

The synergistic influence caused by iodide ions on the inhibition of corrosion of C-steel in 1 M H2SO4 in the presence of some aliphatic amines has been studied using weight loss, potentiodynamic polarization, linear polarization and a.c. impedance techniques. Aliphatic amines used inhibit the corrosion of C-steel and the inhibition efficiency increases by increasing the concentration of the additives and also by addition of iodide ions. The adsorption of these compounds is found to obey Frumkin's adsorption isotherm. The increase in surface coverage in the presence of iodide ions indicates that iodide ions enhance the adsorption of these aliphatic amines on the metal surface. Defines and evaluates synergism parameter (S-theta). Values of the parameter which are more than unity indicate the fact that the enhanced inhibition efficiency in the presence of iodide ions is only due to synergism and there is a definite contribution from the inhibitors molecules, which are adsorbed by coulombic interaction on the metal surface, where iodide ions are already adsorbed and thus reduces the corrosion rate. (C) 2004 Elsevier Ltd. All rights reserved.