Indian Journal of Chemical Technology, Vol.19, No.3, 173-179, 2012
Anisidine isomers as corrosion inhibitor for oil well casing steel in hydrochloric acid
The present study deals with the evaluation of effectiveness of the ortho anisidine (OAD), meta anisidine (MAD) and para anisidine (PAD) as corrosion inhibitors for N80 steel in 15% HCl solution by weight loss method and potentiodynamic polarization method. The protective ability of the compounds has been verified at different temperatures (303 - 383 K) and exposure periods (6 - 24 h). PAD shows maximum inhibition (88.3%). Potentiodynamic polarization studies reveal that the tested inhibitors act as mixed type inhibitor; OAD and PAD act preferentially on cathodic areas and MAD preferentially on anodic areas. The red shift of N-H and C-O bond frequencies of the metal surface products after the 6 h immersion test indicate the donation of electron pair through N atom and involvement of phenyl ring into the surface adsorption. SEM study reveals formation of semi globular inhibitor products on the metal surface. The comparison of the protection efficiencies of these isomers according to their relative electron density on the reaction centre and projected molecular area of the inhibitor molecules have also been done. An adsorption model of the inhibitor molecules on the metal surface on the basis of Tafel parameters, thermodynamic parameters and infrared spectra has been proposed.