Electropolishing

The Basics of the Electropolish Process

Electropolishing is an electrochemical process by which surface material is removed by anodic dissolution. Sometimes referred to as "reverse plating", electropolishing actually removes surface material, beginning with the high points within the microscopic surface texture. By removing these points, the electropolishing process will improve the surface finish, leaving a smoother and more reflective surface.

Electropolishing is accomplished by creating an electrochemical cell in which the material to be polished is the anode. A cathode is formed to mirror the geometry of the work-surface and the two are submerged in a heated electrolyte bath. When a DC current is applied, the electrical charge forces metal ions to be dissolved from the work-surface.

A cathode will have been assembled to mirror the geometry of the work-surface. When a DC current is applied, the electrical charge forces metal ions to be dissolved from the work-surface. The key to the electropolishing process is the difference in current density across the surface. Within the microscopic surface profile, the current density is greater at the high points and lesser at the low points. The rate of the electropolishing reaction is directly proportional to the current density. The increased current density at the raised points forces the metal to dissolve faster at these points and thus tends to level the surface material. After the electropolishing treatment, the work-piece is passed through a series of steps to neutralize, rinse, clean and dry the surfaces.

Electropolishing has many applications in the metal finishing industry because of its simplicity and it can be applied to objects of complex shape. Typical examples are electropolished stainless steel drums of washing machines and stainless steel surgical devices. Electropolishing is also commonly applied to the preparation of thin metal samples for transmission electron microscopy because electropolishing does not cause mechanical deformation of surface layers usually observed when mechanical polishing is used. Anodic dissolution under electropolishing conditions deburrs metal objects due to increased current density on corners and burrs. Ultra high vacuum (UHV) components are typically electropolished in order to have a smoother surface for improved vacuum pressures, outgassing rates, and pumping speed