Improved corrosion inhibition by heterocyclic compounds on mild steel in acid medium

A detailed comparative study on inhibitive behaviour against corrosion of mild steel in 1N H2SO4 IN HCl for the Schiff bases 2,6-diphenyl-3-methyl azinan-4-one (D3MA) (S1), 2,6-diphenyl-3-methyl azinan-4-one semicarbazone (D3MAS) (S2), 2,6-diphenyl azinan-4-one (DA) (S3) and 2,6-diphenylazinan-4-one semicarbazone (DAS) (S4) was investigated using gravimetric and potentiodynamic polarisation methods. The thermodynamic parameters for the mild steel corrosion and the synergistic behaviour of the inhibitors in the presence of anions and cations were determined and discussed. It was found that the adsorption of the inhibitors on the mild steel surface obeyed Langmuir adsorption isotherm. Electro chemical studies revealed that all the four inhibitors are of mixed type. We proved that the semicarbazones (Schiff bases S2b and S4) with additional O and N are more effective corrosion inhibitors than their parent keto-amines. As a whole from all the proposed studies it is proved that the explored Schiff's bases work as a very efficient corrosion inhibitor for mild steel in both the acidic medium.