Corrosion behaviour of carbon steel in polyvinyl alcohol

Purpose - To evaluate the inhibition efficiency (IE) of polyvinyl alcohol (PVA) in controlling the corrosion of carbon steel immersed in neutral aqueous solutions containing 60ppm of Cl-, in the absence and presence of Zn2+. To investigate the influence of sodium sulphite (Na2SO3), sodium dodecyl sulphate (SDS), pH and duration of immersion on the IE of PVA-Zn2+ system. To analyse the protective film formed on the metal surface. Design/methodology/approach - The IE has been evaluated by weight loss method. The protective film was analysed by FTIR and fluorescence spectra. Findings - A formulation consisting of 100 ppm of PVA and 75 pprn of Zn2+ offered 81 per cent IE to carbon steel immersed in a solution containing 60 pprn of Cl-. A synergistic effect on inhibition of a combination of PVA and Zn2+ was observed during the tests. The protective film consisted of the Fe2+ -PVA complex and Zn(OH)(2). It was found to be UV-fluorescent. When SDS was added to the PVA-Zn2+ system, the mixture showed maximum IE at the critical micelle concentration (200 ppm) of SDS (an anionic surfactant). The oxygen-scavenging effect of Na2SO3 increased as the concentration of Na2SO3 was increased, At lower concentrations of Na2SO3, the transport of the inhibitors played a more major role than did the removal of dissolved oxygen. As the pH value was increased, the IE of the PVA-Zn2+ system decreased. As the duration of immersion was increased, the IE was observed to decrease. Research limitations/implications - Electrochemical studies such as polarization and AC impedance spectra will enlighten more on the mechanistic aspects of corrosion inhibition. Practical implications - If this study is carried out at high temperature under simulated conditions, the findings may find applications in cooling water systems. Originality/value - The role of transport of inhibitors towards the metal surface from the bulk of the solution, formation of micelles by surfactants, removal of dissolved oxygen by oxygen scavenger, competition between formation of insoluble iron-inhibitor complex on metal surface and formation of soluble iron chloride in influencing the inhibitive property has been investigated. The protective film was analysed by FTIR spectra and fluorescence spectra.