The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Plating Solution Additives

Greetings!

I'm an electrical engineer who's been dabbling in electrochemistry for several years now. Lately my interests have started migrating to electrowinning and electrorefining - needless to say, I am rapidly discovering this is completely out of my league.

If you fine folks would indulge me for a second, I have a question regarding plating solutions. I understand that many additives are present in these solutions, things like guar gum, glues and other goodies. Being somebody who isn't satisfied with "just because" to answer why they're there, I'm curious as to what role they serve in the solution and why they are so important. Are there certain categories of additives? Like oxygen scavengers, anti-coagulants, etc?

I'm sure this is a whole art and science itself... is there some really good textbook or online resource that would help me wrap my head around some of this?

Thanks!

Chris Martens
Engineer out of my league - Calgary, Alberta, Canada
April 25, 2011

---

April 26, 2011

Hi, Chris. Perhaps the simplest and most obvious addition agents are the surfactants, like sodium lauryl sulphate, which can help plating in a few ways. First by reducing the wastage of dragout; secondly by helping to dislodge hydrogen bubbles that tend to form on the parts as plating proceeds and some of the electricity reduces hydrogen ions from solution; thirdly by reducing the environmental hazard of certain plating solutions (like chrome) being carried into the air like ginger ale bubbles.

Another important class is the grain refiners. If large crystals of plated metal grow during the plating process, there will be porosity where these large crystals meet, and there will be little brightness. The grain refiners force more and smaller crystals to grow.

Another class of additives might be "levelers", whose purpose is to discourage metal deposition in high current density area so that a deposit of more even thickness can be obtained.

Nickel plating is a good process to look at when studying this subject, since it benefits from all sorts of different addition agents and enormous work has been done in developing them over the decades. The ASM Metals Handbook, Vol. 5, has a good discussion of addition agents in the Nickel Plating chapter, although it is restricted to generic addition agents whereas most bright nickel plating is done with proprietaries these days.

Regards,

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

Interesting! Thank you!

Chris Martens
- Calgary, Alberta, Canada
May 6, 2011