Electrochemical behavior and corrosion inhibition of Zinc electrode in solutions of (NH_4)_2SO_4 containing Ce(IV) ions

摘要

The corrosion behavior of Zn in (NH_4)_2SO_4 solutions in absence and in the presence of Ce(IV) ions and the effect of adding two different surfactants as corrosion inhibitors were studied using potentiodynamic, potentiostatic and cyclic voltammetry techniques complemented with scanning electron microscopy and electron dispersion X-ray analysis (SEM/EDX). In (NH_4)_2SO_4 solutions, the E/I curves indicated active/passive transition peak in the anodic region which become more active by increasing sulfate ion concentration. Increasing the scan rate has no effect on the corrosion rate while the combined effect of sulfate and Ce(IV) ions accelerate the corrosion rate than that caused by (NH_4)_2SO_4 alone. This complemented by potentiostatic polarization technique which indicated that the stability of the oxide film is affected by the applied potentials. The addition of sodium salt of N-(2-hydroxy-3- sulfopropyl)-5- stearyl -1,3,4-triazole-2-thione (17T-HSP) and potassium salt of N-(carboxymethyl)-5- stearyl -1,3,4-triazole-2-thione (17T-CM) lead in all cases to inhibition of the corrosion process but with low values. Surfactant 17T-CM inhibits the anodic reaction only, while 17T-HSP depressing both the anodic and cathodic reactions. The difference in molecular structure contributes to the different adsorption mechanism. Langmuir and Freundlich adsorption isotherms were tested for fitting the experimental data of the studied compounds.