Summary for plating an alloy Discussion
Plating an alloy is not the same as plating single metals, because the actual deposition behavior depends on concentration and chemistry, not just standard reduction potentials. In this thread, Matt Chambers asked whether platinum and lead would co-deposit according to their standard potentials, or whether platinum could plate alone while leaving lead behind. Ted Mooney explained that the Nernst equation is the right tool for quantitative analysis because it accounts for concentration as well as standard reduction potential. His practical answer was that, in the example given, platinum would plate by itself. He added that to plate alloy coatings, it is generally necessary to complex the metal with the more positive reduction potential so those ions are effectively tied up, allowing the other metal a chance to deposit. The discussion therefore points to selective deposition being possible, and to bath chemistry as the key control.
I have a need to know whether the electrochemistry of plating an alloy is different than plating single metals, specifically whether both metals will still plate at their same standard reduction potential. For example, if I wanted to plate an alloy of platinum and lead (reduction potentials +1.118 and -0.126 vs. standard hydrogen electrode respectively) would any of the lead plate out at a potential more positive than -0.126? That is, are there some voltages that the platinum would plate by itself and leave the lead behind or would the platinum always carry at least some of the lead along with it when it came out of solution?
Matt Chambers
Researcher – Goleta, California
December 7, 2009
Hi, Matt. For quantitative data look into the Nernst Equation, which takes concentration as well as standard reduction potentials into account. But the short answer is that the platinum would plate by itself in your case.
To plate alloy coatings it is generally necessary to complex the metal which has the more positive reduction potential to”tie up” those ions and give the other metal a chance to deposit.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
December 7, 2009
Q. Looking at old books concerning the manufacture of “Imitation Alloys”, does anyone know if the alloys can be electrodeposited on steel. My interest is in the making of Imitation Platinum in ingot form and then using the platinum in coating a piece of steel.
How would I go about this?
Dwayne Weber
– Chicago, Illinois
January 20, 2012
Hi, Dwayne. Almost nothing is totally impossible, but many ideas present barriers so formidable as to be discouraging.
The reason that batteries work is because different metals can have radically different electrochemical potentials. To simultaneously plate two metals is therefore difficult and requires special chemistry; there are only a couple of tri-metal alloys that have been successfully plated (white bronze probably being the most common). If you can tell us the composition of the alloy in question people may be able to advise whether they think you have a fighting chance; but if you do, it will require specialized chemistry, not plating out of simple metallic salts. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
January , 2012