INHIBITOR SELECTION BASED ON NICHOLS PLOT IN CORROSION STUDIES

Ali Hassanzadeh,^a Asghar Zeini-Isfahani,^a,* Karim Movassaghi,^a and Habib Ashassi-Sorkhabi^b

^aDepartment of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran

^bElectrochemistry Research Laboratory, Department of Physical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran

Abstract

Inhibition effects have been studied on carbon steel in solutions containing different amines. These compounds were dissolved in some petroleum/water corrosive mixtures containing acetic acid and NaCl. Corrosion inhibition afforded by propylamine (PA), iso-propylamine (i-PA), butylamine (BA), tert-butylamine (t-BA), hexylamine (HA), ethylenediamine (EDA), diethanolamine (DEA), 3-amino-1-propanol (3-AP), 2-dimethylethanolamine (2-DEA), cyclohexylamine (CHA), N-methylcyclohexylamine (N-MCA) and dicyclohexylamine (DCHA), have been investigated by electrochemical impedance spectroscopy (EIS) with a carbon steel rotating disc electrode at 25 ºC. In the previous works, the corrosion inhibition behavior of aliphatic and cyclic substituents amines has not been compared. The aim of this work is to introduce a simple graphical approach for comparison of corrosion inhibition behavior of the above mentioned amine compounds. The complex plane and Bode plots were used for this study but these graphical methods were not adequate to understand the effect of inhibition behavior due to small structural changes in the amines. Therefore, a logarithm of impedance magnitude versus phase angle (Nichols) plot of EIS data was used for this purpose and the results showed that this graphical method provides a good interpretation of corrosion inhibition behavior. Finally, a guideline to select the best inhibitor for carbon steel protection in petroleum/water system was drawn.

Keywords: electrochemical impedance spectroscopy, corrosion inhibitor, Nichols plot, Bode plot, amines