Letter 2063

Blackening Copper

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I have a copper panel that is kept at liquid nitrogen temperature when used in a vacuum system. One of it's purposes is for heat removal. There are indications that copper is a very good reflector of infrared radiation and thus a poor absorber. I am looking to increase the absorbsion of IR possibly by blackening the copper. I have heard that this can be done electrolytically. Is this true? Can it also be done by wiping liquid over the surface much like blueing steel (ie. does it come in a bottle or do I have to send out the whole panel?)?

I also have some concerns about whether the 'blackened copper' will cause great problems in a production vacuum system like outgassing, flaking, etc.

Any other comments are always appreciated.

John Davis
- Berthoud, CO, USA

John,

Try an immersion blackening liquid with copper panels: 1.6 - 1.9 g/L liverof sulfur or liquid polysulfide solution at around 25 C for 50 to 80 seconds. As long as you optimized the conditions to get the color you want, you can blacken your parts.

Good luck!

Ling

L. Hao

Dear John ,

The solution offered by Ling is correct for blackening copper , however I suspect that because it is a simple conversion coating there might be problems with the adhesion , if you are looking for a coating that is black and adherent , then I would be looking towards Black Chrome Plating , provided the panels are not subjected to a lot of flexing and that the temperature can be GRADUALLY decreased then it may work

best regards

John Tenison - Woods
- Victoria Australia

What substance is produced when granular copper and sulfur are heated in a test tube? Thanks, Trisha

Trisha Fade
Albany, NY

Why do I get the feeling that this is your homework question, Trisha, that you would know the answer to if you had read the assigned chapter? It would depend on the atmosphere in which you did this. In a vacuum you could produce nothing but sulphides of copper.

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

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