Some Organic Additives as Corrosion Inhibitors for Zinc in Acetic Acid Media

The inhibition effect of some dialkylene dithiophosphate derivatives namely mercapto-2-thiono-5,5-dimethyl-1,3,2-dioxaphosphorinane OCH2CMe2CH2OPS2H (A);2-mercapto-2-thiono- 5,5-2,2diethylene-1,3,2-dioxaphosphorinane. OCH2CEt2CH2 -OPS2H(B) and 2-mercapto-2- thiono-4,5,5-tetramethyl-1, 3,2 dioxaphospholane, OCMe2CMe2OPS2H(C) on the corrosion of zinc in 2M CH3COOH solution has been investigated using weight loss, pH measurement and electrochemical measurements. The percentage inhibition efficiency was found to increase with increasing concentration of inhibitor and with decreasing temperature. The adsorption of these inhibitors on the zinc surface obeys Langmuir isotherm. Some activated thermodynamic parameters were calculated. The variation of the open circuit potential of zinc electrode with time in 2M CH3COOH shows that E̥c is shifted with time in the cathodic direction, i.e. to more negative values before return to the positive direction and the attainment of quaisteady states. But the addition of these organic inhibitors, the potential is shifted initially to more positive values then returned to negative values with time by increasing concentration of the additive extracts is recorded in comparison with blank. The variations of conductivity with time for different concentrations of these organic inhibitors revealed an inversely relationship. Morphological investigations of zinc surface before and after corrosion in 2M acetic acid solution containing different concentrations of these organic inhibitors A, B and C were remarked and illustrated.