Effect of halide ions on the corrosion inhibition of mild steel in acidic medium using polyvinyl alcohol

Purpose - To investigate the effect of halide ions on the corrosion inhibition of mild steel using polyvinyl alcohol (PVA) in H2SO4 at 30-60 degrees C and to study the mechanism of action. Design/methodology/approach - The corrosion rates were determined using the gravimetric (weight loss) and gasometric (hydrogen evolution) techniques. The results obtained in the absence and presence of PVA, halides, PVA - halides combination were used to calculate the inhibition efficiency (%, degree of surface coverage and to propose the mechanism of inhibition and type of adsorption. Findings - Results obtained showed that inhibition efficiency (% increased with the increase in concentration of PVA, on the addition of halides and with the increase in temperature. Phenomenon of chemical adsorption was proposed and PVA was found to obey Langmuir Flory-Huggins and Freundlich adsorption isotherms. The synergism parameter, S-1, evaluated was found to be greater than unity and the values of E-a, Delta H degrees, Delta S degrees and Delta G degrees obtained revealed that the adsorption process was spontaneous. Research limitations/implications - Electrochemical studies such as polarization and AC impedance spectra will enlighten more on the mechanistic aspects of the corrosion inhibition and more polymers need to be evaluated as corrosion inhibitors. Practical implications - PVA can be used as corrosion inhibitor and the addition of halides to PVA improves the inhibition efficiency considerably. Originality/value - This paper provides new information on the effects of halides on the corrosion inhibition using PVA as an inhibitor for mild steel in acidic medium. Such a study had not been reported elsewhere.