Nickel acetate for sealing anodized aluminum

Nickel sealing is often used for dyed anodic oxides, since it is colorless. The corrosion resistance afforded by the process is generally not as good as boiling water or steam seal, unless the nickel acetate process is done at boiling temperature. Cobalt acetate may also be used. A practice found in Wernick, Pinner and Sheasby's "Surface Treatment and Finishing of Aluminum" is: 5 g/L nickel acetate, 1 g/L cobalt acetate, 8 g/L boric acid (in distilled water) for 15 to 20 min at 70 to 90°C and pH 5 to 6. Gary A. Nitowski, [email protected] You might want to review the following two references, which explain what occurs during sealing and provide information on seal bath make-up: "Sealing of Aluminum and its Alloys," Roy C. Spooner, Metal Finishing, December 1968, page 44, and "Sealing of Anodized Aluminum--A Review," Benjamin Yaffe, Metal Finishing, May 1990, page 41. In order to determine the nickel acetate concentration in a solution, I use the following method:

Reagents." EDTA (21.4 g/L = 0.0575 M) Ammonium Hydroxide Murexide (0.2 g Murexide to 100 g NaC1)

Procedure: Take a 2 ml sample in a 250-ml Erlenmeyer flask and 50 to 75 ml of water. Add 10 ml ammonium hydroxide. Add a pinch of Murexide and titrate with 0.0575 M EDTA to a

blue-purple endpoint.

Calculation: oz/gal Ni Acetate = mls EDTA x 0.678 Blair A. Smith, Organization: Hamilton Standard, [email protected] Nickel acetate works as a catalyst in the sealing process. Also, the nickel ions are incorporated into the pores on your coating, which is why the nickel acetate bath can seal anodized aluminum more quickly than water alone. The nickel ion basically blocks or fills up the opening to the pore. Also, nickel acetate will not leach the color out of your dyed parts, which makes it very effective in dyeing operations. Jerry Janssen, [email protected] ALUMINUM ANODES ANODIZING?

FOR HARDCOAT

We are installing an additional hard anodize line in one of our plants and want to know if it is okay to use aluminum cathodes in hard anodize. We know you can use them in normal Type II sulfuric. All of our other hardcoat tanks are stainless and thus the tank is the cathode. Any information would be greatly appreciated. David Kraft, Anacote Corporation High Technology Metal Finishing, [email protected]

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Circle 029 on reader informationcard METAL FINISHING

• March 1997

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