Electrochemical Surface Treatment for Tailored Porous Structures

Abstract

Plasma electrolytic oxidation (PEO) was used to establish a porous metal oxide layer on various titanium and zirconium workpieces in the form of wires, porous tubes, and 3D-printed structures. The ultimate goal of the work was to create a layer with the desired characteristics over a catalyst support or metal membrane structures to improve the performance of the targeted high-temperature catalytic conversion or separation applications. In doing so, it was ensured that the PEO-treated layer could provide the desired morphology, thickness, and porosity needed for the final processing step, which is usually a conventional coating method. This addresses the limitations of ceramic structures, including their mechanical resistance, thermal resistance, and conductivity, and their potential for being functionalized and utilized for high-temperature applications. The entire experimental run was carried out using a 2 kilowatt (maximum output) AC-power source with a maximum current limit of 6.5 Ampere while applying a constant potential (potentiostatic) and monitoring the current fluctuation. Depending on the surface areas of the PEO-treated samples, the applied potential ranged from 200 V to 260 V. The surface features of the fresh and PEO-treated composites, including their morphology and phases, were studied using conventional characterization techniques such as SEM, EDX, and XRD. The time required to observe the spark discharge was shortened by tuning the PEO parameters, such as gradually increasing the applied potential. This, in turn, allowed for longer surface treatment and, eventually, more control over the surface texture. The EDX analysis of the elemental composition of the PEO-treated surface indicated that the contribution of the electrolyte-deposited components increases when increasing the voltage and is accompanied by an increase in the extent of oxidation. The titanium samples displayed relatively intense discharges, especially in comparison to the Zirconium wires. The PEO-treated samples were coated via standard wet-coating techniques.