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White patches in electropolishing

August 13, 2008

After electro polishing we getting white patches on the surface finish.
Before electro polish we do buff the material and electro cleaning.
please help and give some idea.

Ponnuswamy Krishnan
supplier - Malaysia

August 15, 2008

Hi,
Which metal are you electropolishing?

If it's aluminium the patches may be due to a residual oxide film or etching during transfer from electropolishing bath to rinse.

If it is oxide then it should be removed by dipping in a deoxidiser. Dilute sodium hydroxide will do, but do not over do it or you will get etching! A deoxidiser should always be used even if the electropolished Al looks OK as you may get white patches after anodizing. They are caused by a double oxide layer: the residual oxide on top of the anodizing.

If it is transfer etch, then shorten the transfer time or lower the temperature of the polishing bath.

harry_parkes
Harry Parkes
- Birmingham, UK

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