2,5-bis(n-methoxyphenyl)-1,3,4-oxadiazoles used as corrosion inhibitors in acidic media:: correlation between inhibition efficiency and chemical structure

The efficiency of 2,5-bis(n-methoxyphenyl)-1,3,4-oxadiazoles (n-MOX), as corrosion inhibitors for mild steel in 1 M HCl and 0.5 M H2SO4 have been determined by weight loss measurements and electrochemical studies. The results showed that these inhibitors revealed a good corrosion inhibition even at very low concentrations. Comparison of results among those obtained by the studied oxadiazoles showed that 2-MOX was the best inhibitor. It is found to behave better in 1 M HCl than in 0.5 M H2SO4, Polarisation curves indicate that 2-MOX is a mixed inhibitor in 1 M HCl, but in 0.5 M H2SO4, the inhibition mode of 2-MOX depends on the electrode potential and acts essentially as a cathodic inhibitor. The inhibition efficiency slightly increases with temperature in the range from 25 to 60 degreesC, the associated activation energy have been determined. The addition of 2-MOX leads to decrease this activation energy. The adsorption of 2-MOX on the mild steel surface in both acidic media follows a Langmuir isotherm model. Significant correlations are obtained between inhibition efficiency with the calculated chemical indexes, indicating that variation of inhibition with structure of the inhibitors may be explained in terms of electronic properties. (C) 2002 Elsevier Science Ltd. All rights reserved.