The corrosion inhibition and mechanisms of pipemidic acid (8-ethyl-5-oxo-5,8-dihydro-2-(1- piperazinyl)pyrido[2,3-d]pyrimidine-6-carboxylic acid), levofloxacin [(±)-9-fluoro-2,3-dihydro-3- methyl-10-(4-methyl-1-piperazinyl)-7-oxo-7H-pyrido[1,2,3-de][1,4]benzoxazine-6-carboxylic acid] and ciprofloxacin [l-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinoline carboxylic acid) for mild steel in 0.5 mol/L H₂SO₄ was studied using weight loss experiment, potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) at 303 K. The results obtained from weight loss experiment showed the inhibition efficiency was significantly increased with the inhibitor concentration increasing. Electrochemical corrosion experiment revealed the inhibition process was related to the inhibitor molecules covering on the metal surface, which mainly inhibited cathode hydrogen evolution reaction. The inhibitor molecules on the mild steel surface obeyed Langmuir isothermal model and involved physical adsorption and chemical adsorption at 303 K. Scanning electron microscopy observations showed the three inhibitors played a significant protective effect on metal corrosion. All the test results concluded that ciprofloxacin inhibition performance was best under the same conditions.

Key words: corrosion, weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), adsorption