Effect of Henna Leaves on the Corrosion Inhibition of Tin in Acidic and Alkaline Media

Abstract

The corrosion inhibition behaviour of Henna leaves on Tin in 1.0 M HCl and 1.0 M NaOH was investigated using weight loss technique at temperatures ranges, 25-50°C. The maximum inhibition efficiency was found to be 95.45 at optimum inhibitor concentration. The presence of the compound adsorbed on the tin coupons was verified by spectroscopic measurements of the surface before and after corrosion tests. The leaves extract of <i>Lawsonia inermis</i> was found to be more effective in alkaline solution. It also confirmed that the inhibition efficiency decreased with increased in temperature but increased with increasing inhibitor concentrations. The Activation energy, Gibbs free energy were found to be 28.131, 29.589 kJmol^-1; -3.280, -3.245 kJmol^-1 in acidic and alkaline media respectively. The adsorption was found to obey Freundlich isotherm with linear coefficient (R²) and equilibrium parameter K_ads to be 0.972, 0.957; 0.06, 0.05 for both systems in acidic and alkaline media respectively. Physical adsorption mechanism is proposed from the trend of ∆G_ads. The negative values of ∆G_ads shows the spontaneity of the inhibition process. The increase in the activation energy of the inhibition processes with values of 80kJ/mol support the mechanism of physical adsorption process. <i>Lawsonia inermis</i> leaves extract has proved to be more excellent inhibitor for tin in NaOH alkaline.