Experimental and Computational Chemistry Studies on the Inhibition Efficiency of Phthalic Acid (PHA) for the Corrosion of Aluminum in Hydrochloric and Tetraoxosulphate (VI) Acids

Abstract

In this work, phthalic acid is investigated for its corrosion inhibition properties (for aluminum in solutions of HCl and H₂SO₄) through experimental and computational chemistry methods. The experimental approach was achieved by using gravimetric (weight loss), linear and potentiodynamic polarization techniques as well as two spectroscopic techniques (Fourier transformed infra red and scanning electron microscopy). The theoretical approach incorporated the computation of semi empirical parameters and Fukui functions. Data obtained from weight loss were in strong agreement with those obtained from polarization methods. They generally pointed to the conclusion that phthalic acid inhibited the corrosion of aluminum better in solution of HCl than in solution of H₂SO₄. The inhibition efficiency of the inhibitor increases with increase in concentration but with increasing period of contact and temperature, the inhibition efficiency notably decreased. Confirmation of a physical adsorption mechanism was established by observed low values of activation energy and free energy of adsorption as well as the trend of decrease in inhibition efficiency with temperature. Frumkin and El awardy et al. adsorption isotherms best fitted the adsorption characteristics of phthalic acid on aluminium (in both HCl and H₂SO₄ media). The isotherms revealed that the inhibitor occupies more than one adsorption site and exhibited attractive behavior. Calculated quantum chemical parameters were within the range reported for good corrosion inhibitors while Fukui function, Huckel charge, HOMO–LUMO graphs and FTIR analyses indicated that phthalic acid is adsorbed on aluminum surface via the carboxylic oxygen atom.