Stability additive for trivalent chrome conversion coating bath solutions
AssigneeUnited Technologies Corporation
InventorsXia Tang, Promila Bhatia, Joseph John Parkos, Jr., Gary M. Lomasney, Mark Jaworowski
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Abstract
An acidic aqueous solution containing a water soluble trivalent chromium compound is provided with a solution stability additive for reducing precipitation of trivalent chromium over time. The concentration of the solution stability additive varies based on the complexing capability of the additive. Suitable additives for use as solution stability additives in accordance with the present invention are selected from the group consisting of acetic acid, glycolic acid, and mixtures thereof.
Claims21
An acidic aqueous solution which is free of hexavalent chromium comprises a water soluble trivalent chromium compound, a water soluble fluoride compound, an alkaline reagent, and a solution stability additive for reducing the precipitation of trivalent chromium over time, wherein the solution stability additive is present in an amount of between 1×10−4 M/l to 1×10−2 M/l with respect to the total acidic aqueous solution.
An acidic aqueous solution which is free of hexavalent chromium comprises a water soluble trivalent chromium compound, wherein the trivalent chromium compound is present in the solution in an amount of between 0.2 g/liter to 5 g/liter, the fluoride compound is present in an amount of between 0.2 g/liter to 5 g/liter, and the alkaline reagent is present in an amount to maintain the pH of the solution between 3.0 to 5.0 a water soluble fluoride compound, an alkaline reagent, and a solution stability additive for reducing the precipitation of trivalent chromium over time.
A process for preparing a corrosion-resistant trivalent chromium coating on aluminum and aluminum alloy substrates comprises treating the substrates non-electrolytically with an acidic aqueous solution, which is free of hexavalent chromium, comprising a water soluble trivalent chromium compound, a water soluble fluoride compound, an alkaline reagent, and a solution stability additive for reducing the precipitation of trivalent chrome precipitates over time.
Dependencies are inferred from the claim text.