Abstract Newbouldia leavis (NL) andPepper fruit(PF) leaf extracts were investigated for their ability to impede corrosion of zinc in 0.5 M HCl by gravimetric and thermometric techniques. The results obtained showed that different concentrations of the (NL and PF) extracts hinder the corrosion of zinc in 0.5 M HCl. Inhibition efficiency of each extract varies with concentration, time of immersion and temperature. The values of activated energies were higher in the suppressed corrosion reaction of zinc than the values calculated for the blank. The thermodynamic study shows that the NL and PFleaf extracts adsorbed on the surface of zinc was spontaneous and follows Frumkin adsorption isotherm. Physical adsorption mechanism has been proposed for adsorption of these inhibitors on the surface of zinc metal.
Keywords Newbouldia leavis, Pepper fruit, Frumkin adsorption isotherm, zinc, thermometric.