Trivalent chromate conversion coating
AssigneePavco, Inc.
InventorsLeonard L. Diaddario, Jr., Michael Marzano
Life of this patent
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Abstract
In a preferred embodiment of the present invention, a conversion coating composition comprising chromium (III) ions, cobalt (II) ions, and nitric acid is provided. The coating composition is substantially free of chromium (VI) ions and substantially free of an oxidizing agent. The present trivalent chromium based conversion coating provides corrosion protection equal to or greater than most hexavalent chromium conversion coatings.
Claims24
A conversion coating bath including a coating composition comprising:
- chromium (III) ions,
- cobalt (II) ions, and
- nitrate ions,
- wherein said composition is acidic, includes a ratio of nitrate ions to the combination of chromium (III) and cobalt (II) ions of less than 1.5:1, is substantially free of chromium (VI) ions, and is substantially free of oxidizing agents other than said nitrate ions.
An acidic conversion coating bath composition comprising:
- 0.020 to 0.075 mole/L chromium (III) ions,
- 0.010 to 0.035 mole/L cobalt (II) ions,
- a film polisher agent, and
- about 0.010 to 0.045 mole/L nitrate ions,
- said composition including a ratio of nitrate ions to the combination of chromium (III) and cobalt (II) ions of less than 1.5:1, being substantially free of chromium (VI) ions and substantially free of oxidizing agents other than said nitrate ions.
A concentrate for forming a conversion coating bath comprising:
- chromium (III),
- cobalt (II), and
- nitric acid,
- wherein said concentrate is acidic, is substantially free of chromium (VI) ions, is substantially free of oxidizing agents other than said nitric acid, and includes less than a 1.5 to 1 ratio of nitric acid to chromium (III) plus cobalt (II).
A method for applying a conversion coating onto an article comprising the steps of:
- plating the article with zinc, and
- exposing the article to an acidic conversion coating composition comprising water, chromium (III) ions, cobalt (II) ions, fluoride ions, and nitrate ions, said conversion coating being substantially free of chromium (VI) ions and substantially free of oxidizing agents other than said nitrate ions, and including a ratio of nitrate ions to chromium (III) and cobalt (II) ions of less than 1.5:1.
A method for applying a colored conversion coating onto an article comprising the steps of:
- plating the article with zinc,
- exposing the article to an acidic conversion coating composition comprising water, chromium (III) ions, cobalt (II) ions, fluoride ions, and nitrate ions, said conversion coating having a ratio of nitrate ions to the combination of chromium (III) and cobalt (II) ions of less than 1.5:1, and being substantially free of chromium (VI) ions and substantially free of oxidizing agents other than said nitrate ions,
- rinsing the article
- exposing the article to a dye solution, and
- rinsing the article.
Dependencies are inferred from the claim text.