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 h ydrochloric acid was studied in relation to the concentration of oxadiazole s using various electrochemical techniques and weight loss measurements. Th e results showed that PAOX inhibited the corrosion of mild steel in 1 M HCl whereas PNOX accelerated it. PAOX suppressed both cathodic and anodic proc esses 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 adso rbed 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 exper imental efficiencies. (C) 2001 Elsevier Science Ltd. All rights reserved.