Studies on Anionic Gemini Surfactants as Corrosion Inhibitors on AZ31 Magnesium Alloy

Abstract

The magnesium alloys are considered to be the best structural materials, because of their advantageous strength to weight ratio. But, the limitation in their real field applications lies in the fact that magnesium alloys are highly susceptible for corrosion. Hence understanding the corrosion of AZ31 alloy and developing the measures to combat the same are crucial. In the present studies, the corrosion behaviour of AZ31 alloy was investigated by electrochemical methods in sodium chloride and sodium sulphate media of different concentrations at different temperatures and followed by its inhibition studies. The corrosion rate was monitored by potentiodynamic polarization technique and electrochemical impedance spectroscopy along with SEM-EDX, and XPS. The synthesized inhibitors were subjected to theoretical studies as well. The blank corrosion studies were performed at various medium concentrations, pH and temperatures. The results revealed a trend of higher corrosion rate associated with higher medium concentration, lower pH and higher temperature. Five different long chain anionic Gemini surfactants namely, DB, DH, DO, DC and DD were synthesized and tested as corrosion inhibitors for AZ31 alloy. The calculated activation and thermodynamic parameters have been recorded in the thesis. The inhibitors were predominantly physisorbed with partial chemisorption. The adsorption of the surfactant on the surface of AZ31 alloy obeyed Langmuir adsorption isotherm. The studied surfactants were found to function as mixed-type inhibitors. The surfactants were more efficient at lower temperatures. The efficiencies of the surfactants decreased in the order: DD>DC>DO>DH>DB and this has been accredited to the reduction of chain length. The proposed mechanism attributed the cathodic inhibition to the blockage of the reaction spots by chemisorbed acetates. The anodic inhibition resulted from the compaction of porous film by precipitated magnesium- inhibitor salts.