Inhibition of Cast Iron Corrosion in Acid, Base, and Neutral Media Using Schiff Base Derivatives.

Three Schiff bases, 2-acetylpyridine thiosemicarbazone ( I), 2-acetylpyridine-(4-methylthiosemicarbazone) ( I), and 2-acetylpyridine-(4-phenylthiosemicarbazone) ( I) were tested against corrosion of cast iron in aqueous solutions of HCl, NaOH, NHCl, and NaCl by means of a mass loss method and electrochemical measurements. The inhibition efficiency is directly proportional to inhibitor concentration, while it decreases with prolonged immersion time and at low temperatures. In order to study the effect of an additive, synergism of KI was also studied. The adsorption of Schiff bases in corrosive media obeys Langmuir's isotherm, both in the presence and absence of KI. The UV-Vis, FT-IR, WAXD and SEM analyses were carried out to support the mechanism of corrosion inhibition. The ΔG values reveal that the inhibition was mainly due to physisorption of the inhibitor molecules on the surface of cast iron. The electrochemical polarization results showed the predominantly cathodic nature of the inhibitors. [ABSTRACT FROM AUTHOR]