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  for Metal Finishing since 1989
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Condition of cyanide zinc solution and blackening

 

Dear sir,

When I started zinc plating in zinc cyanide solution the anode plate (Zinc Metal) become a black color. I checked my solution composition, but that was right. The problem is that this black layer came onto my anode plate and my solution became dirty too. I electroplate on lower current density 40 amp/ft and on my small articles comes some granules and unsmooth.

Thanks,

Mohammed Asad
- Karachi, Pakistan

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Mr. Asad, you have not given us a solution analysis or other way to narrow in on the problem. But are we having a language misunderstanding or do you actually use "plates" (sheets) of zinc as your anodes? If you do, it sounds to me like you are having a quality control problem with the anodes. You need high purity anode material for electroplating, not just any old zinc-containing product :-)

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
 

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Black anodes normally mean a high zinc: low cyanide ratio, so I suggest you recheck your analysis.

The correct colour film on your Cyanide zinc anodes should be chocolate colour with bright gold patches here and there if your zinc to cyanide ratio is 1 : 3.

Irrespective of yr zinc and Cy concs. mantain Caustic conc @ 65 - 75 gms /lit.

If your tank is plain steel unlined , then you may have dissolved rust in your solution, it does not come from anode film. Unless as Mr Mooney presumes that you may be using other than 99.95 % zinc anodes.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India