4-(2-pyridylazo-)-resorcinol as effective corrosion inhibitor for mild steel in 0·5M sulphuric acid

The efficiency of 4-(2-pyridylazo-)-resorcinol (PAR) as corrosion inhibitor for mild steel in H₂SO₄ was investigated by electrochemical methods such as steady state galvanostatic and potentiostatic polarisation measurements. The dissolution parameters such as corrosion currents, passive current, flade potential, open circuit potential, cathodic and anodic Tafel slopes and efficiencies were determined. Potentiodynamic polarisation was used to assess the ability of heterocyclic organic inhibitor/PAR to provide an effective barrier to corrosion in acidic environments. Electrochemical measurements showed that the heterocyclic compound investigated has a fairly good inhibiting properties. The absorption and corrosion rates based on heat of adsorption and activation energies are calculated from Langmuir's adsorption isotherm. The inhibition efficiency range of 84–93% is obtained for a concentration range of 10⁻⁷–10⁻¹ mol L⁻¹. Passivating parameters revealed that this inhibitor is strongly passivating. Scanning electronic microscopy observations and quantum chemical calculations along with the electrochemical data suggested that the ability of PAR to act as a physical barrier was more important in providing corrosion protection of mild steel surface against acidic environments.