The corrosion inhibition effects of iodide ion and its synergistic effect with methyl violet (MV) oncarbon steel in 1.0 mol/L phosphoric acid solution have been investigated using potentiodynamicpolarization, electrochemical impedance spectroscopy and weight loss measurements. The resultsshow that there is an excellent synergistic effect between iodide ion and MV for carbon steel corrosioninhibition in 1.0 mol/L H3PO4. The electrochemical studies reveal that single iodide ion orcombination of iodide ion and MV acts as a mixed-type inhibitor and the corrosion reaction iscontrolled by charge transfer process. Adsorption of iodide ion on the steel surface obeys Langmuiradsorption isotherm in the absence or presence of MV. The values of Kads, ΔGoads, ΔHa, ΔSa and Eawere obtained and discussed. The adsorption of inhibitor molecules on the steel surface is aspontaneous process containing a mixed physical and chemical adsorption mechanism.
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