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Ted Mooney, P.E. RET
Pine Beach, NJ
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Need a chemical-resistant black coating for steel or aluminum
Q. I need a chemical-resistant, wear-resistant black coating for aluminum or steel. This is for an optical read head in an automatic urinalysis machine. Black Anodize is bleached out by the urine/reagent chemicals, Titanium Aluminum Nitride and Titanium Carbonitride on steel are attacked by the urine/reagents or by household bleach (a 10% bleach solution is used for cleaning). We are using black Delrin (which is very gradually bleached by the urine/reagents) but it is difficult to hold the required tolerances in this material - we would rather use metal. The coating must be black and anti-reflective for optical reasons.
John W. Harrisondiagnostics - Tarrytown, New York
2003
A. If there are no halogens present (no problem with hypochlorite), a wild guess would be "Black Chromium" over dull sulfamate nickel. Chromium vendors are listed on finishing.com and you might want to talk with one of their research people. There is not much Black Chrome done in job shops because the demand is low but I think it might work for you.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
A. Black electroless nickel may work.
Todd Osmolski- Charlotte, North Carolina, USA
Q. I thought that Black Chromium (and Black Nickel) were dyed coatings like Black Anodize. If they are, I would think that they would be subject to the same bleaching as Black Anodize.
John W. Harrison [returning]diagnostics - Tarrytown, New York
2003
A. There is no dye. They are electrodeposits that have been "poisoned" with other materials and produce a very thin black deposit. Black nickel is nice, but rather soft and when it is scratched or abraded, it has a normal sort of bright nickel look. Black chrome would probably work better, tho there are not many job shops that do it.
James Watts- Navarre, Florida
A. Black Chromium Electroplating is NOT a dye !
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
A. My company has supplied many firms in the optical and medical industries with black "optical" coatings including black nickel, black chrome and more recently electrolytically colored black anodize (no organic dyes to bleach). Black chrome with an electroless nickel underplate offers outstanding corrosion in many environs, however, yours is indeed unique.
Milt Stevenson, Jr.
Syracuse, New York
A. Hi John.
I agree with Robert and Todd and James that these coatings are probably good. I mostly agree with Milt, but I would note that the reason the black anodize gets bleached is probably related not only to the fact that the dye is bleachable, but probably also due to the fact that the anodizing is not remaining properly sealed because bleach attacks aluminum (it's not the chlorine, it's the fact that bleach is strongly alkaline). I would make the component out of steel rather than aluminum.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
A. We have discussed the conditions of your application with our engineers and they suggest that black titanium will fit your needs and will never be bleached.
Anna Berkovich
Russamer Lab
Pittsburgh, Pennsylvania
9th Edition, Vol. 5
"Surface Cleaning, Finishing & Coating"
on AbeBooks
or eBay or
Amazon
(affil links)
A. You need multilayered interference black mirror.
It consists of SiO2, Cr, SiO2, Cr, SiO2, Cr, SiO2 layers.
Each layer of Cr has transmission in vis 30-40%.
Each layer of SiO2 needs be 1/4 thick for L (wave-length) 550nm.
It will be most chemical resistant coat.
- Moscow, Russia
2005
A. Ceramic coating in matte black would be just fine for this application. It resists a 10 year controlled environment of 50/50 salt spray is almost completely chemical resistant and has wear resistance. This might be why the military coats most of their weapons in it. :)
Ryan Jones- gautier Mississippi usa
February 11, 2011
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