ELECTROPOLISHING PROCESS & BENEFITS
The process of electropolishing is the controlled anodic dissolution of metals (alloys, intermetallic compounds, etc.) which remarkably improves surface properties of metals.
To establish optimum conditions for electropolishing a particular metal or alloy, a V-I curve is plotted and a plateau of current densities is established. The current densities plateau mainly exists just below the oxygen evolution regime. However, for many metals, alloys, etc., the best electropolishing results are obtained beyond this plateau under oxygen evolution conditions. The best example is most often industrially used electropolishing process for electropolishing austenitic stainless steels, which are carried out under oxygen evolution regime
ELECTROBRIGHT takes great care in ensuring that each component treated by electropolishing maintains its integrity.
According to the Theory of Jacquet (viscous film theory), the dissolution products accumulate near the anode (electropolished surface) and form a visous layer that increases the resistance of the system and limits the current. This viscous layer over peaks is much thinner than over depressions. Consequently, the current density over peaks is higher than over depressions, which results in the fact that peaks dissolved faster and the leveling effect is observed.
The remarkable improvement in corrosion resistance of electropolished surfaces are caused by several interconnected events occurring during the electropolishing process:
- Removal of deformed Beilby layer, which consists of inclusion of martensitic phase (Fig. 1), foreign material, preexisting oxides, etc., created by forming, machining, mechanical polishing, etc.
- Creating new corrosion resistant outer layer that is enriched in chromium oxide due to selective dissolution of ferromagnetic elements (Fe, Ni)
- Improving the surface smoothness by dissolving the surface picks preferentially to the surface depression
- Equipotentializing gain boundaries
Improved cleanability of electropolished surfaces is the result of two interconnecting parameters:
- Improvement of surface smoothness and profile
- Lowering the water contact angle (making the surface more wettable). Standard electropolishing reduces water contact angle about 12%
Bacterial Attachment and Early Biofilm Formation Reducibility
Many studies have been done by the US Department of Agriculture (J.W. Arnold et al., ‘”Surface Finishes on Stainless Steel Reduce Bacterial Attachment and Early Biofilm Formation: Scanning Electron and Atomic Force Microscopy Study) indicates that electropolished surfaces are less susceptible to bacterial attachment and early biofilm formation. This feature of electropolishing is of great importance for pharmaceutical, biotech, food and beverage industries.
Bio and Hemocompatibility Improvement
Electropolishing process is widely used for treatment of body implants and medical devices. The study by Tepe G. at.al., “Thrombogenicity of various endovascular stents types an in vitro evaluation” J Vasc Inter Radiol. 2002 Oct, 13 (10): 1029-35 shown that electropolishing clearly reduced the thrombogenicity of the stents.
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Electropolishing Special & Exotic Metals
Figure 1 - X-ray diffraction patterns of 316LSS
Figure 1a: Mechanically polished
Figure 1b: Electropolished
Martensite phase has been removed by electropolishing process.
Sharp profile before electropolishing
Rounded profile after electropolishing