Newbouldia laevis Leaves Extract as Tenable Eco-Friendly Corrosion Inhibitor for Aluminium Alloy AA7075-T7351 in 1 M HCl Corrosive Environment: Gravimetric, Electrochemical and Thermodynamic Studies

Abstract

The corrosion inhibition evaluation of aluminium alloy AA7075-T7351 in 1.0 M HCl environment, by biologically active and water soluble luteolin 7—glucoside and phenolic polymeric compounds in Newbouldia laevis (NBL) extracts—as organic corrosion inhibitors of aluminium—have been investigated using gravimetric, electrochemical and thermodynamic techniques respectively, at room temperature (25 ± 1 °C), and at elevated temperatures of 40, 50, 60 and 65 °C. Gravimetric results showed that optimal inhibition efficiency ( $$\zeta$$ ), at room temperature (298 ± 1 K) and 338 K are 86.1% and 67.5% respectively for the maximum concentration of 0.6 g/L. This suggests that NBL extract was affected by temperature and accomplished the inhibiting episode through an electrostatic pull of the polymeric components of the NBL extract onto AA7075-T7351 coupons or physical adsorption, that obeyed Langmuir, Freundlich and Temkin adsorption isotherms, in increasing order; Temkin, Freundlich and Langmuir. Adsorption coefficient, $$K_{\text{ads}}$$ , and Gibb’s free energy of adsorption, $$\Delta {\text{G}}_{\text{ads}}^{0}$$ , values obtained from Temkin isotherms were high and proved that adsorption of NBL on AA7075-T7351 surfaces were strong and spontaneous. Potentiodynamic polarization and electrochemical impedance spectroscopy results showed that NBL is a mixed-type corrosion inhibitor of AA7075-T7351 in 1 M HCl environment, which was achieved through the blockage/obstruction/reduction of charge flow by the polymeric barrier on the aluminium alloy’s surface. Increases in the linear part of the Bode plot slopes with increase in NBL concentrations further indicated the existence of a protective layer on the AA7075-T7351 surface.