Electrochemical Impedance of Neutral Base Oils

Abstract

Solvent neutral 100 (SN-100), SN-150, SN-500, and SN-650 base oils have been investigated by electrochemical impedance spectroscopy (EIS). The investigation has been followed in the frequency range of 100 kHz to 1 mHz. The results indicate that in all cases upon decrease of frequency, the impedance (Z) will be raised up. Also obtained data designates that at each applied frequency, Z values vary in the order: SN-100 < SN-150 < SN-500 < SN-650. In all cases, plots of phase angle versus log of frequency are nearly peak shaped. Based on the composition of base oils, the possible reasons for the different observations has been discussed. The equivalent circuit consists of a parallel constant phase element and polarized resistance (R ct ), in series with solution resistance (R s ). Linear correlation has been observed between R ct and viscosity at 40 or 100 • C, as well as log R ct and viscosity index or specific gravity.