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How to do nickel acetate sealing


We currently warm seal anodized aluminium extrusions in water at approx. 100 C (212 degrees Fahrenheit). I understand that appropriate quantities of nickel acetate will help the sealing process. Could someone explain how it works? How much nickel acetate should we add? How can we check the concentration of nickel acetate?


Sanjay A. Bulchandani
- Bombay, India


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 temp. Cobalt acetate may also be used. A practice [mix] found in The Surface Treatment & Finishing of Aluminum and its Alloys by S. Wernick, R. Pinner, P.G. Sheasby is:

5 g/l nickel acetate, 1 g/l cobalt acetate, 8 g/l boric acid (in distilled water) for 15-20 min at 70-90 C and pH 5-6.

Gary A. Nitowski
Alcoa Center, Pennsylvania


You might want to review the following two references which explain what occurs during sealing and provide information on seal bath make-up:

1. "Sealing of Aluminum and its Alloys," Roy C. Spooner, Metal Finishing, December 1968, page 44.

2. "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, we use the following method:

EDTA (21.4 g/l = 0.0575 M)
Ammonium Hydroxide
Murexide (0.2 g Murexide to 100 g NaCl)

Take a 2 ml sample in a 250 ml Erlenmeyer flask and 50-75 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.

oz/gal Ni Acetate = mls EDTA x .678

Blair Smith
aerospace - Windsor Locks, Connecticut


Nickel acetate works as as 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
- Streamwood, Illinois

August 1, 2012

Q. We are currently using a Nickel Acetate Seal Bath. It is only nickel acetate and a desmut agent in the bath. I see that you say to use cobalt acetate as well as boric acid. Could you explain the advantages of using these chemicals in addition to nickel acetate?

It says in The Surface Treatment and Finishing of Aluminum and Its Alloys, on page 894 that there is little or no difference between the nickel and cobalt salts, but are frequently used together.

Also when controlling the concentration of nickel acetate in the bath, are you trying to control the amount of Nickel Ion in the bath? Or are you trying to control the amount of Nickel Acetate in the bath.

Thanks, any help is appreciated.

John Renbarger
- Boulder, Colorado, USA

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