THE SYNERGISTIC INHIBITION EFFECT AND THERMODYNAMIC PROPERTIES OF 2-MERCAPTOBENZIMIDAZOLE AND SOME SELECTED CATIONS AS A MIXED INHIBITOR FOR PICKLING OF MILD-STEEL IN ACID-SOLUTION

The effect of some selected metal cations, viz., Na+, Al3+ and Zn2+ on the corrosion of mild steel in 1 M sulphuric acid solution containing a thiol called 2-mercaptobenzimidazol, has been studied by potentiody namic polarization technique, over the temperature range 30 to 50 degr ees C. The efficiency of mixed inhibitor was tested for different conc entrations of cations ranged from 10(-6) to 10(-3) M. It was found tha t the presence of metal cations together with the thiol in the corrosi ve medium increases the inhibition efficiency at all the concentration s and temperatures studied. The decrease in corrosion current was asso ciated with the positive shift in the corrosion potential, in the pres ence of investigated cations. This denotes that inhibition was found t o be predominantly anodic and following the Langmiur adsorption isothe rm over the wide concentration range of metal cations. The activation energy and thermodynamic parameters were calculated at different tempe ratures.