Enhanced oxidation–dissolution theory of electropolishing

Abstract Electropolishing is the electrolytic metal finishing process currently widely used in several high tech applications such as cardiovascular and orthopaedic body implants, pharmaceutical and semiconductor installations, superconductive niobium cavities, among others. The process provides a very clean, smooth, Beilby layer free, corrosion resistant surface. Currently, almost any metal, alloy and intermetallic compound can be electropolished, but in spite of that, we still do not have a single commonly accepted electropolishing theory. To make it even more complicated, the electropolishing process is constantly modified by addition of other physical agents and/or forces such as a magnetic field – magnetoelectropolishing, ultrasounds, or by changing the existing process parameters such as switching from direct to pulse current. The existing electropolishing theories differ in many ways from each other but possess one common ingredient, namely the viscous layer. The aim of this work is to show that the viscous layer is not an indispensible prerequisite to achieve a satisfactory electropolishing finish in every metal–electrolyte system. A supplement to the most broadly accepted electropolishing solid film theory by Hoar, namely the enhanced oxidation–dissolution equilibrium theory, is proposed.