Investigation of the inhibitive effect of substituted oxadiazoles on the corrosion of mild steel in HC1 medium

The influence of 2,5-bis(4-nitrophenyl)-1,3,4-oxadiazole (PNOX) and 2,5-bis(4-aminophenyl)-1,3,4-oxadiazole (PAOX) on the corrosion of mild steel in hydrochloric acid was studied in relation to the concentration of oxadiazoles using various electrochemical techniques and weight loss measurements. The results showed that PAOX inhibited the corrosion of mild steel in 1 M HCl whereas PNOX accelerated it. PAOX suppressed both cathodic and anodic processes of steel corrosion in 1 M HCl by its chemisorption on the surface via sharing electrons between nitrogen or oxygen and iron atoms. PAOX was adsorbed on the mild steel surface according to a Langmuir isotherm adsorption model. The electronic properties of PNOX and PAOX obtained by using the AM1 semi-empirical quantum chemical approach, were correlated with their experimental efficiencies. (C) 2001 Elsevier Science Ltd. All rights reserved.