Letter 27089

Electroplating Hard Material [UK] 

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I am a researcher in Microsystems and am looking for a material which is hard and conductive which can be electroplated. PArticularly I would be interested in tungsten if it is possible. Can anyone offer any input on this? Also if anyone knows how to increase the stress in nickel electroplating the info would be greatly received.

Michael Cooke
R&D - Durham, UK

Electroplating is not the only coating technology available, but no, tungsten cannot be electroplated. Chromium is probably one of the hardest electroplateable materials but maybe you already considered that. Composite plating with diamond or other particles may be useful to you. Rhodium is very hard, but extraordinarily expensive and perhaps not thick enough. Chlorides should drive the stress in nickel electroplating through the roof.

Please tell us what you are trying to do.

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

Stress in nickel can be induced by almost anything, but one surefire way of doing it is to add chloride. Sulphamate nickle has been designed to offer los stress deposits, but you can always use high sulphate and/or high chloride baths.

For hard materals, probably the hardest is hard chromium, although you can also get hard electroless nickel with a high phosphorus content. You certainly cannot electrodeposit pure tungsten, (although there are some claims you can) but you can deposit binary systems using tungsten and (say) chromium or other metals. If you want to deposit pure tungsten, try vacuum technology; this will also let you put down tungsten nitride, which has a hardness well in excess of 2,000Hv. Perhaps you would like to tell a bit more about what you are doing?

Trevor Crichton R&D practical scientist - UK

I think that he is looking for sodium tungstanate, which is added to nickel plating solutions to increase the hardness. Twenty years ago, there were several articles and formulas in print. I am fairly sure that it is still being used in some brush plating solutions, with a very limited build up possible--IE: a cap coat.

James Watts
- FL

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