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Electroplating Manganese on Cobalt for Conversion Coating Applications

October 18, 2011

First off, I am already indebted to you folks because most of my questions were answered via a search of the site. However I have a couple left, one practical and one more abstract.

I am working with the degradation of solid oxide fuel cells for my graduate work, and a key way they usually fail is the interconnects, which electrically connect individual cells together, corrode away. This kills both the conductivity, and poisons the catalyst. To fix this coatings are generally applied, and in true academic fashion this is often performed using completely non-industrial methods. However, more recently people have begun to look at coatings that can actually be performed in a job shop. More specifically electroplated CoMn coatings that convert to a dense, conductive oxide.

I'd like to study the transition between the electroplated metallic coating and the converted oxide coating. To do that I need to electroplate Co and Mn. Electroplating the alloy seems to be tied up in patents, so my intention is to plate the layers, and use a reducing furnace to diffuse the metals together and then begin investigating the conversion process.

My practical problem is this: I cannot get the manganese to stick, cobalt was no problem. But try as I might, no manganese will stick to the cobalt layer. The recipe I used is below. I know that manganese is a tough one, but is there a book I should get, a recipe to try, or any other direction to go?

Recipe:
150 g/l ammonium sulphate [on eBay or Amazon]
200 g/l Manganese sulphate
Sulfuric acid added to pH 3
Balance Distilled water

Temp: ~25-30 C
Current density: 30mA/cm up to 250 mA/cm

My abstract question is this: What does "activation" do in the electroplating process. As I understand it, the surface must be cleaned, the surface oxide must be removed, and then there is a mystery step of "activation." What exactly is happening here.

Thanks in advance, I can answer any more questions if necessary.

Micah Casteel
Graduate Student - Troy, New York, USA

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Look on page 469 of "Modern Electroplating" edited by Lowenheim [adv: this book on AbeBooks, eBay, Amazon] .
This page is from the 3rd edition.
It has a reference among others for plating nickel-manganese alloy.
Cobalt and nickel are nearly identical so you can substitute cobalt for nickel interchangeably.
It is a source book for plating references.

James Watts
- Navarre, Florida
October 19, 2011

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I have looked at Modern Electroplating, and the recipes they give are based from the ones in Brenner's book "Electrodeposition of Alloys" which I have also looked through. The key differences I found were the that the NiMn baths were run at a neutral pH and the CoMn baths tended to be at a very low pH. However, Brenner discussed that most of these baths do not work very well.

After spending a great deal of time working through Brenners book, and others I have been able to get CoMn to codeposit, using a sulphate/citrate based solution similar to those shown in Brenners book, acetic acid [on eBay or Amazon] for pH control, and a carbon electrode. At this point I'm working to improve the composition control and reduce the amount of hydroxide and oxides present in the coating. Metallic Co seems to plate out nicely whereas the codeposited metal often includes a large amount of oxides. Hopefully, better pH control, better solution mixing, and current control will fix these problems. Thanks for the all help I appreciate it

Micah Casteel
- Troy, New York, USA
November 1, 2011