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Passivation Effect Utilizing Electropolishing Methods (Pg. 2)
Thus, a 15x to 20x improvement can be expected in Electropolished parts versus conventionally passivated parts. The surface that remains after Electropolishing is the cleanest, most passive surface possible. In fact, the surface of Electropolished stainless steel will not even show normal fingerprints and handprints when simply wiped with a household window cleaner. Non-Electropolished stainless steel will show these same prints after as little as 36 hours. The prints will not clean off even using solvents.
Several factors contribute to the increased corrosion resistance of electropolished stainless steel. One of these is the removal of an amorphous, deformed surface called the Beilby layer. This layer, produced by mechanical finishing, is characterized by crystal fractures and other structural changes. Oxides, polishing compounds, and other materials become imbedded in the distorted crystal structure. These conditions allow the formation of surface corrosion cells. Electropolishing removes this layer and the corrosion producing compounds trapped in the Beilby layer.
Another factor is that the smoothing of the surface, previously described, greatly reduces the surface area of the part. This minimizes development of local corrosion sites. Electropolishing is the best method to remove sites. Disturbed layers can be removed completely regardless of their thickness while micro geometry is improved.
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References
1. L.J. Durney, Electroplating Engineering Handbook, Fourth Edition, Chapman & Hall, New York, 1996.
2. R.L. Davis, “Electropolishing: A User’s Guide”, http://www.ntaindustries.com/appnotes/electropolish/
3. Finishing.com, Inc., 503 Brick Blvd., Suite 106, Brick, N.J. 08723, http://www.finishing.com/ The principals of Finishing.com, Inc. are Ted Mooney, P.E. and Tom Pullizzi, CEF.
4. Electro Polishing Systems Inc., 5678 W. Brown Deer Rd., Brown Deer, WI., 53223. http://www.ep-systems.com/
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