2,5-Bis(n-Pyridyl)-1,3,4-Oxadiazoles as Corrosion Inhibitors for Mild Steel in Acidic Media

The effect of new corrosion inhibitors—namely, 2,5-bis(n-pyridyl)-1,3,4-oxadiazoles (n-POX)—on the corrosion of mild steel in 1 M hydrochloric acid (HCl) and 0.5 M sulfuric acid (H₂SO₄) was investigated using weight loss measurements and electrochemical techniques such as polarization curves and electrochemical impedance spectroscopy. Results obtained revealed that these compounds were very good inhibitors and behaved better in 1 M HCl than in 0.5 M H₂SO₄. Potentiodynamic polarization studies showed that n-POX are mixed-type inhibitors in 1 M HCl and anodic-type inhibitors in 0.5 M H₂SO₄. n-POX acted on the cathodic reaction without changing the mechanism of the hydrogen evolution reaction. The ability of the n-POX to inhibit the corrosion of mild steel was dependent on the position of the nitrogen atom on the pyridyl substituent. Surface analysis also were carried out to establish the mechanism of corrosion inhibition of mild steel in acidic solutions. The adsorption of n-POX on the mild steel surface in both acidic media followed a Langmuir adsorption isotherm.