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, NY, USA

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, NC, USA Editor's note:        Mr. Probert is the    author of Aluminum How-To

Black electroless nickel may work.

Todd Osmolski Charlotte Plating, Inc. Charlotte, NC USA

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, NY, USA

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

Black Chromium Electroplating is NOT a dye !!!

Robert H Probert Robert H Probert Technical Services Garner, NC, USA

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

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

You need multilaered interferens blak miror.
It consist of SiO2, Cr,SiO2,Cr,SiO2,Cr,SiO2 laers.
Each laer of Cr have transmition in vis 30-40%.
Each laer of SiO2 need be L/4 thik for L (wave-length)550nm.
It will be moust chemikal resistant coat.

Afanasev Konstantin
- Moscow, Russia

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