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Letter 1094
Additives for DI Water Seal after
Anodizing
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We are looking for information on additives for deionized water
seal (following sulfuric acid anodizing), in order to suppress
sealing bloom or smut. We have heard that there is a formulation
containing an alkali salt of a polycarboxylic acid which has been
used. Any information on this or any other type of DI water seal
additive would be greatly appreciated.
Steve Starr
Treffers Precision, Inc.
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Additives to the DI hot water seal do help prevent smut or bloom
and give a better seal.
My question would be why bother with it. You will spend a lot of
time, which is money, and may never equal the dedicated research that
chemical companies have done to save possibly a dollar a day for an
average size anodizer.
I would stick to a company that Aluminum is their main business.
The first two that come to my mind are Novamax and Clarient.
James Watts
- Navarre, Florida
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Sealing smut usually forms when the sealing tank becomes alkaline
rather than slightly acidic. Unfortunately this is also an area which
produces a very good hydrothermal seal due to the excess of OH- ions.
Additives usually suppress the smut by dispersion of the precipitate.
Albright & Wilson has such an additive called "Speedseal" for
conventional hot DI water sealing. The advantage is the excess
hydroxyls speed up the seal time.
Better rinsing may help the problem since about 95% of the sealing
smut problems come from sulfides from the anodize bath
Lee C. Branch
Albright & Wilson Americas
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