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topic 314

Will aluminum withstand caustic environment?

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(1996)

We have a customer who has a corrosive environment that contains 26-degree Baumé Ammonium Hydroxide at a nominal temperature of 155 degrees F.

He currently is using a finished enclosure of galvanized steel that is not giving him satisfactory service. What he wants to know is if an anodized aluminum finish will withstand this corrosive environment. His alternative is a stainless steel substrate.

Will anodized aluminum withstand this environment?

Thanks,

Joe Hillock
anodizing shop - Philadelphia, Pennsylvania

Surface Treatment & Finishing of Aluminium and Its Alloys
Wernick, Pinner & Sheasby

I don't quite understand, Joe. Is this enclosure actually a container for the ammonia water, or is the enclosure merely in a room where vapors from the process are present? Is it the room that is 155 deg., or is it the liquid?

Aluminum is unacceptable for caustic immersion service (it doesn't even hold up long in a dishwasher), so with or without an anodized surface I wouldn't consider it. But anhydrous ammonia has only a moderate effect on aluminum, so if it's only dry vapors, anodized aluminum would probably be okay. Now, if the case is halfway in between, with splashing or very high humidity, you are back into a questionable area, but personally I don't think it would be a very good application for an anodized finish.

Note that this is only a projection from book knowledge--so if anybody out there has 'hands-on' knowledge, please chime in!

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



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