ACID CORROSION INHIBITION OF NICKEL BY 2-(TRIPHENOSPHORANYLIDENE) SUCCINIC ANHYDRIDE

The corrosion inhibition of nickel in acid solutions by 2-(triphenyl phosphoranylidene) succinic anhydride (2TPSA) has been investigated using DC and AC techniques. The percentage inhibition was up to 85 percent at a concentration of 400-mu-M of 2TPSA. The inhibitor used was found (1) to shift the corrosion potential to less negative values and (2) to decrease the anodic dissolution of nickel and hydrogen evolution reaction. The effect, however, was more pronounced on the anodic rather than on the cathodic process. The passivation current density (i(p)) and the capacitance of the double layer (C(d)) were also affected by 2TPSA. Experimental findings reported in this paper show that at the critical concentration of 25-mu-M of 2TPSA, these parameters attain their lowest values and that subsequent increases of inhibitor concentration do not lead to any significative change of either i(p) or C(d). Inhibition efficiency results obtained from DC (corrosion current and polarization resistance) and AC (charge transfer resistance) were in good agreement. Moreover, the experimental data fit the Flory-Huggins and the Dhar-Flory-Huggins adsorption isotherms with x = 3. This result indicates that each organic molecule replaces three adsorbed water molecules on the nickel surface. In addition, the size of the adsorbed 2TPSA molecule was approximately 37.5 angstrom 2.