Frequency response studies for the plasma electrolytic oxidation process

This paper introduces a methodology for obtaining a fundamental characteristic of the plasma electrolytic process — that is the frequency response (magnitude and phase angle). A methodology is developed for plasma electrolytic oxidation (PEO) of aluminium; however, it can be applied to any plasma electrolytic process. For PEO the frequency response was evaluated as a complex impedance of the electrolyser. It was found that the impedance magnitude decreases with frequency growth from 10 3–10 4 to 10–10 2 Ω and the phase angle decreases from 0 to − 70 − 80°. This fact appears to be consistent with a hypothesis of active–capacitive load behaviour for the PEO process. Evolution of the frequency response during PEO is consistent with that of the surface state; therefore, it can be used for process diagnostics and control. Frequency response adds a new dimension to the investigation of plasma assisted electrochemical processes. Major benefits of this approach are expected in the field of the process automation and the development of new pulsed plasma electrolytic technologies.