Effectiveness of O -bridged cationic gemini surfactants as corrosion inhibitors for stainless steel in 3 M HCl: Experimental and theoretical studies

Four novel cationic gemini surfactants with a spacer functionalised by an oxygen atom were synthesised, characterised using FTIR and ¹H NMR spectroscopy and tested as corrosion inhibitors for stainless steel in 3 M HCl solution. The corrosion inhibition efficiency was determined using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). The polarisation measurements showed that inhibitors act as mixed inhibitors. The results indicated that the highest inhibition efficiency was reached around the values of the critical micellar concentration (CMC) for individual inhibitors. The compound with twelve carbon atoms in the alkyl chains and hydroxyethyl groups linked to the positively charged nitrogen atoms appeared to be the most effective inhibitors showing 98% at concentration 3 mM. The efficiencies obtained from the EIS measurements were in good agreement with those obtained from the polarisation techniques. Following corrosion testing the surface of the stainless steel samples were studied by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The Density Functional Theory (DFT) was applied for theoretical studies of the inhibitors. Correlation between experimental and theoretical results was carried out and based upon Density Functional Theory (DFT) analysis.