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Problem in cyanide zinc plating

We have cyanide zinc plating bath with metal 20g/Lm NaOH 60g/L and NaCN 60g/L, since last week we had no problem, but for last one week during plating we get ammonia ⇦ this on eBay or Amazon [affil links] smell and the parts at bottom gets Dull plating(only on bottom surface of part top it is ok) and some sticky material flots on the bath during plating, why it is so please give suggestion.

Thanks

Shetty Shetty
chemist - Bangalore, Karnataka, India
March 4, 2008

There are lots possibilities, but please concider the following. NaOH concentration seems too low. In a consequence, zinc anodes stopped working correctly, current efficiency decreased (probably someone tried to increase total current to keep paramethers), there's a lot of gases in the bath, it smells ammonia (oxidation!), some brighteners float at the surface as a sticky oil and the bath is more and more decomposed. Of course some other reasons are also conciderable.

Janusz LABEDZ
- Warsaw, Poland
April 1, 2008