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Coating solution for metal surfaces

  • US 4,273,592 A
  • Filed: 12/26/1979
  • Issued: 06/16/1981
  • Est. Priority Date: 12/26/1979
  • Status: Expired due to Term
First Claim
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1. An aluminum surface having a uniformly colorless and clear coating which is free of boron and phosphate and is capable of turning light golden brown to purple in color when heated at a temperature of 900°

  • F. for 5 minutes, but which resists blackening for at least 5 minutes when heated in water having a temperature within the range of about 140°

    F. to about 170°

    F., said coated aluminum surface having been obtained by contacting such aluminum surface with an acidic aqueous coating solution having a pH within the range of about 3.0 to about 5.0 and consisting essentially of at least about 0.5×

    10-3 moles/liter of zirconium or hafnium or a mixture thereof, at least about 0.025×

    10-3 moles/liter of a polyhydroxy compound having no more than 7 carbon atoms, and at least sufficient fluoride to combine with and form a soluble complex with all of the zirconium and hafnium present in the solution, wherein said polyhydroxy compound is selected from the group consisting of gluconic acid, a salt of gluconic acid, sorbitol, mannitol, dextrose, ethylene glycol, glycerine, and glucoheptonate.

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