Experimental and theoretical tools for corrosion inhibition study of mild steel in aqueous hydrochloric acid solution by new indanones derivatives

The anti-corrosive behavior of 2-(4-methylbenzylidene)-3-oxo-2,3-dihydro-1H-indene-1-carboxylic acid (MIC), 2-(hydroxymethylene)-3,3-dimethyl-3-oxo-2,3-dihydro-1H-indene-1-one (HIO) and 2-benzylidene-3-oxo-2,3-dihydro-1H-indene-1-carboxylic acid (BIC) on mild steel in 1 M HCl was studied using gravimetric, electrochemical measurements (Potentiodynamic polarization and impedance spectroscopy), surface analysis and theoretical studies. The obtained results showed that these compounds possess good inhibiting properties for mild steel corrosion in 1 M HCl solution. The inhibition efficiency increased with inhibitor concentration and reached 92%, 87% and 90% at the optimum concentration of MIC, HIO and BIC respectively. Accordingly, the inhibition was assumed to occur via adsorption of inhibitor molecules on metal surface. Langmuir isotherm was used to approximate the adsorption process of the studied Indanone derivatives. Moreover, the analysis of polarization curves shows that MIC exhibits a mixed-type behavior, while HIO and BIC behave as mixed-type inhibitors with an anodic predominance. Impedance data are analyzed in terms of the modified Randles equivalent circuit with single relaxation time constant characteristic of charge transfer process. DFT calculations indicated correlation between molecular structure of studied inhibitors and the corresponding inhibition efficiencies.