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Constant current platinum plating -- why does voltage vary?

Q. We have a Platinum Plating line at our shop. I have read, and think I understand that plating at a too high current/voltage can cause loss of plating efficiency and low yield.

We have current regulating Rectifiers, so the current is always maintained the same by adjusting voltage. What I have noticed is that some runs are using a higher voltage than usual to maintain the current that is set. I have attributed this to corrosion/oxide build up on our fixtures hanging on the cathode bar.

My question is would a higher voltage but still maintaining the same current still cause this same issue? Electrolysis of water inhibiting the plating reaction?

Thanks!

Garrett D.
Engineer - Greer, South Carolina
July 3, 2024


A. Hi Garrett.

To avoid my confusing other readers, I should start by noting that voltage and current are locked together by Ohms Law, A = V/R, so you can only control one, and the other will go where it goes depending upon R.

Yes, a poor connection increases resistance, thereby increasing voltage if you are holding current constant. But what might possibly also be happening is the load size is smaller, meaning the resistance is greater (because the current is passing through a smaller area of solution), meaning more voltage is necessary to maintain your constant current value. And that can cause the current density on that smaller load to be too high, causing excessive electrolysis of the water as well as "burning" of the plating.
Luck & Regards,

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




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