Metal finishing Q&As since 1989

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Zinc anode polarization

We have an alkaline non cyanide zinc plating line that uses hanging baskets for 2" diameter Zinc balls. The zinc balls polarize constantly and have to be taken out and cleaned in order to achieve good coating weight.What causes the polarization and what can we do to prevent polarization.

Mike Brown
- Antigo , Wisconsin
2003

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2003

You may be accurately assessing the situation, Mr. Brown, but maybe not. Zinc is soluble in caustic so that most platers have the opposite problem, i.e., zinc going into solution too readily. The primary reason most new alkaline non-cyanide zinc installations have "generation" tanks is to make it easier and more practical to limit the zinc content without having to constantly remove anode baskets or let them run dry.

Maybe if you could tell us the zinc and caustic concentration you are achieving, someone could offer some confirmation that your bath is in fact starved for zinc?

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

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2003

Yes, exactly what Ted said. High free caustic soda [affil links] promotes zinc solubility and throwing power., however, occasionally one of you platers get hold of titanium anode baskets which are required for ACID zinc but detrimental for Alkaline Zinc.

If you are using titanium baskets, they "anodize" when you turn on the current., and in just a few minutes current no longer passes and the zinc just sits there. When you turn off the rectifier the "anodic coating" dissolves and falls off., etc etc You must use steel baskets and do not drag in chlorides from the acid dip.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina