Investigation on the corrosion inhibiting property of modified cashew nutshell liquid

Abstract

The corrosion inhibiting property of modified cashew nutshell liquid (CNSL) in controlling corrosion of aluminium in 0.1 M HCl medium has been evaluated by gravimetry analysis. Gravimetry analysis was carried out at various inhibitor concentrations of 0.2, 0.4, 0.6, 0.8 and 1.0 g/L, at temperatures of 303, 313, 323 and 333 K and time intervals of 24, 48, 72, 96 and 120 h respectively. The pseudo first and second order kinetic model was used to study the kinetic contribution. Four adsorption isotherms, viz., Langmuir, Temkin, Freundlich and El-Awady, were used to study the adsorption mechanism. Thermodynamic parameters were also investigated. Gravimetry analysis reveals that the inhibition efficiency increases as the inhibitor concentration increases but decreased with increasing temperature and immersion time. Data from the kinetic study carried out, showed a pseudo-second order. Adsorption isotherm studies revealed that the Freundlich isotherm model best describes the adsorption of the inhibitor to the aluminium surface, The Gibbs free energy change was evaluated from the adsorption isotherm and the values (–10.14, –10.26, –10.49 and –10.80 kJ/mol) obtained were less than –20 kJ/mol indicating a physisorption mechanism and spontaneity. Values of activation energy obtained, Ea (19.10, 22.38, 23.70, 30.12, 60.43 and 48.44 kJ/mol), indicated that the physisorption mechanism operates, while the positive values of change in enthalpy of activation, ΔH, indicated an endothermic process. The CNSL–triethanolamine ether derivative proved to be a great corrosion inhibitor for aluminium corrosion in acidic environment.