Need a chemical-resistant black coating for steel or aluminum

Letter 20010

Need a chemical-resistant black coating for steel or aluminum

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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. Harrison
diagnostics - Tarrytown, New York

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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

Editor's note:
   Mr. Probert is the
   author of Aluminum How-To / Aluminio El Como

First of two simultaneous responses +++

Black electroless nickel may work.

Todd Osmolski
Charlotte Plating, Inc.

Charlotte, NC USA

Second of two simultaneous responses +++

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
diagnostics - Tarrytown, New York

First of two simultaneous responses +++

There is no dye. They are electrodeposits that have been "poisoned" with other material 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

Second of two simultaneous responses +++

Black Chromium Electroplating is NOT a dye !!!

Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina

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Anoplate 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.

If you're interested in trying any of the above coatings, we have test coupons 1" x 4" available.

Milt Stevenson, Jr.
Anoplate Corp

Syracuse, NY, USA

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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

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You need multilayered interference black mirror.
It consist of SiO2, Cr,SiO2,Cr,SiO2,Cr,SiO2 layers.
Each layer of Cr have transmission in vis 30-40%.
Each layer of SiO2 need be L/4 thick for L (wave-length) 550nm.
It will be most chemical resistant coat.

Afanasev Konstantin
- Moscow, Russia

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