Letter 1094

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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.

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 - Fl

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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