Corrosion Inhibition of Steel in Phosphoric Acid by Phenacyldimethyl Sulfonium Bromide and some of its p-Substituted Derivatives

Corrosion inhibition of mild steel in 0.67 M H3PO4 by phenacyl dimethylsulfonium bromide and six of its p-substituted derivatives was studied using different chemical, electrochemical and scanning electron microscopy techniques. The order of increasing inhibition efficiency was correlated with its p-substituted through Hammett relation. Potentiodynamic polarization curves indicated that the compounds acted primarily as mixed-type inhibitors. Electrochemical impedance spectroscopy showed that the steel dissolution is controlled by charge-transfer mechanism. The kinetic-thermodynamic model of adsorption isotherm described the experimental findings. Number of active sites, binding constant and change of free energy were computed for all studied compounds. Depending on the inhibitor, it was found that each organic molecule replaced one or two adsorbed water molecules from the steel surface. The adsorption center was suggested to be the pi electrons of the phenyl ring, and a flat configuration adsorption of the molecule may occur.