Corrosion Inhibition Studies of GA9 Magnesium Alloy in Chloride and Sulphate Media

Abstract

The corrosion behaviour of GA9 magnesium alloy in two different media, namely, sodium chloride and sodium sulphate in different concentrations and temperatures have been studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The effect of pH of the medium on the corrosion behaviour of GA9 magnesium alloy have also been studied in both the media. The results revealed a trend of higher corrosion rate associated with higher medium concentration, lower pH and higher temperature. The corrosion rate in the sodium chloride medium was higher than that in the sodium sulphate medium. Four different alkyl sulfonates namely sodium dodecylbenzenesulfonate (SDBS), sodium 4-n-octylbenzenesulfonate (SOBS), sodium 2,4-dimethylbenzenesulfonate (SDMBS) and sodium benzenesulfonate (SBS) were tested as corrosion inhibitors for GA9. The results pertaining to the corrosion inhibition studies of four inhibitors in two different media at different temperatures in the presence of varying concentrations of inhibitors are reported in the thesis. The inhibition efficiencies of all the four inhibitors decrease with the increase in temperature and increase in the concentration of the media. Activation parameters for the corrosion of the alloy and thermodynamic parameters for the adsorption of the inhibitors have been calculated and have been documented in the thesis. The sulfonates predominately physisorbed and adsorption was in accordance with Langmuir adsorption isotherm. The studied sulfonates were found to function as mixed type inhibitors. The sulfonates were more efficient at lower temperatures in both the media. Inhibition efficiency is in the order SDBS > SOBS >SDMBS > SBS. Proposed mechanism attributed the cathodic inhibition to the blockage of the reaction spots by chemisorbed sulphonates. The anodic inhibition resulted from the compaction of the porous film by precipitated magnesium sulfonates.