LAUSR

The inhibitive effect of spironolactone drug (SPR) on C38 carbon steel corrosion in 10% hydrochloric acid solution was investigated using weight loss and two electrochemical techniques, namely electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP), in the temperature range between 30 and 60 °C. Spironolactone was found to act as an inhibitor for the acid corrosion of C38 carbon steel. Inhibition efficiency of the drug increased with an increase in concentration of SPR but decreased with increase in temperature. The maximum inhibition efficiencies obtained with 7.2 × 10–3 M SPR at 30 °C were 98.1%, 95.0% and 95.8% for weight loss, EIS and PDP technique, respectively. Anodic and cathodic polarization curves reveal that SPR is a mixed-type inhibitor. Impedance data show that charge transfer process controlled the mechanism of corrosion. The adsorption of SPR on the C38 steel surface was found to be spontaneous and obeyed Langmuir isotherm at all studied temperatures. The adsorption is a mixed adsorption involving both chemisorption and physisorption. The carbon steel surface was assessed using scanning electron microscopy (SEM), which also revealed the protective ability of the drug for C38 carbon steel in 10% HCl solution. Quantum chemical calculations in the framework of the density functional theory were undertaken to theoretically describe the adsorption and inhibition action of SPR on the C38 steel surface.