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  for Metal Finishing since 1989
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Severe Corrosion Problem

We are searching for a coating/infusion that will withstand 5% Sulfuric acid mixed with cetyl trimethyl ammonium bromide. The item to be coated is a 5" dia. cylinder,8" depth, with a flat base welded to one end. Material is 316L S.Stl. There are two 1/2 " ports on the base and one 1/8" port on the side of the vessel.

The vessel is used in laboratory assays to determine fiber content in feeds. The acid solution is poured into the vessel at ambient temp. and a heating band raises the temp. to 100C with 22 psi. The heat cycle is 80 minutes and is repeated up to 8x/day. We would like a 3+ year life. We have tried phenolics, titanium nitride, gold, teflon, and chrome infusion, to name a few.

All coatings suffer from porosity problems which cause a super anode effect on the exposed metal. If anyone has suggestions we are interested. Thanks!

Peter Komarek
- Fairport New York
2000

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Peter, You may be taking the wrong approach to the problem in that the coatings you have tried are essentially barriers -- coatings that do not react as readily with the corrosive medium as the base metal. Accordingly, if there is a crack or pore in the coating you set up a galvanic cell.

An alternative is to consider a sacrificial coating, i.e., a coating that is more reactive than the base material, but forms a stable compound when reacted. This is basically what cadmium, zinc, and aluminum do to protect surfaces. You'll need to do some chemistry to come up with some potential materials. After you do, contact me and we can discuss the best way to deposit them.

Jim Treglio - scwineryreview.com
PVD Consultant & Wine Lover - San Diego,
California
2000

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Without coupon testing I would not want to suggest that any given material can withstand this solution, because it's a rather unusual exposure. However, gold does not have to be porous, and I would suggest you have stainless steel coupons gold plated by someone skilled in the art, perhaps to greater thickness than you've tried, and test the coupons under field conditions. There are several nitric acid and nitric fume based tests that should quickly reveal porosity in gold platings.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2000

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From your requirements, i.e., 5% sulfuric acid and cetyl trimethyl ammonium bromide, a logical question might be why not use borosilcate glass? Any scientific glassblower can make this vessel for you, and neither of the chemicals you mentioned will have any effect on it. Borosilicate glass will easily withstand the thermal cycling you outlined.

Drop us a line if you need the name of a glassblower. There are many other coatings which should be able to handle the environment you listed--the name of the game is 100% coverage.

Dale Woika
SCSC - Bellefonte, Pennsylvania
2000

Hi Peter, You can try with a non-porous thick coating, I suggest to try with ECTFE or ETFE. There are some manufacturers of those materials Ausimont (HALAR) Dupont (TFZEL), Withford (Dycor), Daikin, etc. You can contact with a teflon coater, they will help you.

Jordi Pujol
- Barcelona, Spain
2000