Non-linear impedance analysis of industrial lubricants

This paper examines the application of higher harmonic non-linear electrochemical impedance spectroscopy (NLEIS) for analysis of electrochemical properties of industrial lubricants. NLEIS is a powerful new technique, which provides higher resolution than traditional linear impedance for distinguishing specific mechanisms governing electrode response. High-amplitude NLEIS showed the potential to deliver kinetic parameters not available from small amplitude, fundamental harmonic impedance measurement. Simulation of experimental NLEIS results and evaluation of the 1st (fundamental), 2nd, and 3rd order harmonics impedance data was performed using Mathematica™ software. Results from this simulation study were compared with experimental data leading to a better interpretation and quantification of charge transfer, adsorption and diffusion processes affecting the low-frequency impedance response. This information was utilized in development of more accurate equivalent circuit impedance model for a typical industrial lubricant represented by a combination of bulk solution and interfacial resistances, capacitances, and CPE parameters.