Electrochemical and gravimetric measurements of inhibition of aluminum corrosion by poly (methacrylic acid) in H2SO4 solution and synergistic effect of iodide ions

• Poly (methacrylic acid) moderately inhibited aluminum corrosion in H2SO4.
• Addition of I− ions enhanced inhibition efficiency significantly.
• The adsorption of PMAA alone and with I− ions follow El-Awady et al. isotherm model.
• The inhibitor behave as a mixed-type inhibitor.
• Results from surface analysis are in reasonable agreement.

The corrosion inhibition of Al in 0.5 M H2SO4 solution by poly (methacrylic acid) (PMAA) alone and in combination with iodide ions was studied at 303–333 K using gravimetric, electrochemical impedance spectroscopy, potentiodynamic polarization, scanning electron microscopy and water contact angle measurements techniques. Results obtained show that PMAA moderately inhibited the dissolution of Al in the corrosive medium. Addition of Iodide ions synergistically upgrades the inhibition efficiency of PMAA to a maximum value of 82.6%. From polarization results, PMAA and PMAA + KI can be classified as mixed-type corrosion inhibitor. Thermodynamic parameters namely Gibbs free energy of adsorption, activation energy and enthalpy of activation revealed that the adsorption processes of PMAA and PMAA + KI are endothermic reactions mainly by a physisorption mechanism and followed El-Awady et al. thermodynamic–kinetic adsorption isotherm.