Expired streptomycin as corrosion inhibitor for carbon steel in acetic acid - sodium acetate buffer solution

Corrosion inhibition of carbon steel in buffer acid solutions by expired streptomycin was studied by weight loss method, linear polarization, electrochemical impedance spectroscopy, as well as scanning electron microscopy. It was found that streptomycin reduces the metal corrosion rate, and the inhibition efficiency increases proportionally with the drug content. A high efficiency has been obtained for 10–3 M amount of inhibitor. Tafel polarization results indicate that the drug is active especially on the cathodic side and less on the anodic dissolution of iron reaction, acting as a mixed type corrosion inhibitor. The double layer capacitance of the metal - buffer solution interface, polarization resistance and film formation on the carbon steel surface have been emphasized by electrochemical impedance measurements. The scanning electron micrographs of the carbon steel samples in blank solutions have revealed a severe corrosion on the samples surface, while in the presence of the expired drug, the surface has remained almost unaffected. Electrochemical behavior of streptomycin has been also investigated by cyclic voltammetry.