Electropolishing, also known as electrochemical polishing, anodic polishing, or electrolytic polishing (especially in the metallography field), is an electrochemical process that removes material from a metallic workpiece, reducing the surface roughness by levelling micro-peaks and valleys, improving the surface finish.
It is used to polish, passivate, and deburr metal parts. It is often described as the reverse of electroplating. It may be used in lieu of abrasive fine polishing in microstructural preparation.
Mechanism
Typically, the work-piece is immersed in a temperature-controlled bath of electrolyte and serves as the anode; it is connected to the positive terminal of a DC power supply, the negative terminal being attached to the cathode. A current passes from the anode, where metal on the surface is oxidised and dissolved in the electrolyte, to the cathode.
At the cathode, a reduction reaction occurs, which normally produces hydrogen. Electrolytes used for electropolishing are most often concentrated acid solutions having a high viscosity, such as mixtures of sulfuric acid and phosphoric acid. Other electropolishing electrolytes reported in the literature include mixtures of perchloric acid with acetic anhydride (which has caused fatal explosions), and methanolic solutions of sulfuric acid.