Letter 15085

Stopping an Electroless Metal Deposition [Tennessee] 

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My company produces polymers that use some metals including cobalt, titanium, antimony and manganese, as well as, phosphorus as catalysts. The processing temperature is usually above 180 C and the equipment we use to make the polymer is 304L/316L stainless steels. The polymer is in a non-oxygen containing environment when molten. Our problem is the build-up of cobalt, manganese and antimony phosphides, phosphites or phosphates on the inside of the equipment. This creates many problems as the thin coatings spall off - contamination of the product being #1. It causes greater consumption of the catalyst metals and clean out of equipment becomes quite a pain. Finally, it can play havoc on the reaction rates within the system. I really feel that we have created an enormous electroless metal plating process with the stainless steel equipment acting as a nice catalytic surface. I am looking for any suggestions in stopping this plating reaction.

Thanks.

Robert J. Sinko
- Kingsport, TN, USA

In the early days of electroless nickel plating, the tanks were made of stainless, and had the difficulty you mention. So platers switched to polypropylene tanks, which were fine until plateout began, then it became uncontrollable. More recently (the last 5-10 years), platers have switched back to stainless tanks but with an impressed current to stop the unwanted catalytic action. You can buy these cathodic protection units commercially from many plating equipment suppliers and distributors.

Or maybe they're 'anodic protection units'. Drives me crazy trying to remember which you call them :-)

Ted Mooney, P.E.  finishing.com Brick, NJ

Robert,

I dont know if I understood your question , but what you are describing is the formation of metallic salts. If this is the case its not an electroless reaction. For a reaction to be considered plating, (either electrolyitc or electroless) you must reduce the salts to the "0" valence state or metallic state. Please give more details to better help you.

Guillermo Marrufo
Monterrey, NL, Mexico

We have taken scrapings from the inside of the equipment. Elemental analysis shows high peaks for manganese and phosphorus using optical emission spectroscopy and electron dispersive spectroscopy. There were other trace amounts of catalyst metals. Some had high carbon peaks and some results had very little carbon peaks. Since the earlier posting of this inquiry, we have performed more testing. With the larger, more colorful sample amounts we tried to perform x-ray diffraction but no matches to manganese phosphate. It is quite likely that the manganese and phosphorus is tied up in the organic polymer. However, some of the thinner deposits are shiny and metallic looking but there isn't enough sample to run XRD.

Robert Sinko
- Kingsport, TN

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