Summary for alkaline zinc plating burning Discussion
Alkaline zinc plating burning is described as a coarse, granular or white-powder look in high-current-density areas such as edges and corners. In this thread, the parts were burning on the rack, with the bottom and side areas affected most, at 19–26 A/ft², 85°F, 1.2 oz/gal zinc metal, and 20 oz/gal caustic potash, using brightener and starter. The answer from KV says the practical fix is to raise the metal concentration to about 2 oz/gal while making sure the NaOH does not exceed the current level, and to maintain a metal:OH ratio of 1:10 to regain control. The discussion ties the defect to excessive current for the bath conditions rather than to temperature alone.
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The term ‘burning’ in electroplating refers to the parts getting a coarse, granular look, generally in high current density areas like edges and corners. It occurs when the current is too high for the situation, which causes excessive separation of the water in the plating solution into hydrogen and hydroxide and/or the plated deposit to occur so fat that it cannot form the correct crystal development.
Q. Parts came out from alkaline zinc tank burned at high current density areas, and the burn looks like white powder. The temp. in the tank is 85 deg F and the zinc metal concentration is 1.2 oz/gal and the caustic potash concentration is 20.0 oz/gal. We are using brightener and starter(refine rack). All parts are burning on the rack but the bottom and side parts are burning more. The current density we are plating at is 19 to 26 amps/sq. ft.
Popatbhai B. Patel
electroplating consultant – Roseville, Michigan
2003
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A. Dear Mr PP,
You need to up the Metal conc. to 2 oz/gal and also ensure that the NaOH does not exceed what you currently have. Maintain a metal:OH ratio of 1:10 and you will regain control.
Khozem Vahaanwala
Saify Ind
Bengaluru, Karnataka, India
Thanks very much for the knowledgable and confident response, KV.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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