4-Hydroxyl-N′-[(3-Hydroxy-4-Methoxyphenyl) Methylidene] Benzohydrazide] as Corrosion Inhibitor for Carbon Steel in Dilute H₂SO₄

The effect of an aromatic hydrazide derivative 4-hydroxyl-N′-[(3-hydroxy-4-methoxyphenyl) methylidene] benzohydrazide] (HMBH) as inhibitor for the corrosion of carbon steel in 0.5 M H₂SO₄ solution was investigated in the temperature range of 303 K to 323 K using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). The concentration of HMBH used was in the range of 0.1 to 1 mM. Inhibition efficiency (% IE) increased with increase in concentration of HMBH and decreased with increase in temperature. Maximum % IE obtained was around 71 with 1 × 10^-3 M HMBH in 0.5 M H₂SO₄ at 303 K. The Tafel polarization results indicate that HMBH acted as a mixed type of inhibitor. The results of evaluation of thermodynamic and activation parameters suggest the mixed adsorption of HMBH took place by physisorption, and it obeyed Freundlich’s isotherm. Scanning electron microscope (SEM) and atomic force spectroscopy (AFM) images were also recorded to supplement the results of electrochemical studies, and mechanism for corrosion inhibition was suggested.