Trivalent chromium-containing composition for use in corrosion resistant coatings on metal surfaces
First Claim
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1. A storage stable composition made by mixing together a first mass of water and at least the following components:
- (A) a second mass of a water-soluble source of fluorometallate anions to provide in the composition from about 1 to about 100 g/kg of the fluorometallate anion, each of said anions consisting of;
(i) at least four fluorine atoms; and
(ii) at least one atom of an element selected from the group consisting of titanium, zirconium, hafnium, silicon, aluminum, and boron, and, optionally, one or both of(iii) at least one ionizable hydrogen atom; and
(iv) at least one oxygen atom;
(B) a third mass in an amount of about 23 g/l to about 100 g/l of a water soluble source of chromium fluoride;
(C) an optional fourth mass of water-soluble source of fluorine anions;
(D) an optional fifth mass of a component of surfactant and/or water soluble thickener;
said composition being free of water-soluble organic corrosion inhibitor and water-soluble organic stabilizing agents, having a pH of at least 2.1 and no more than 4.4, being storage stable at ambient temperature for at least 2 weeks and capable of producing no more than 3 pits per panel after being exposed to 336 hour salt spray testing according to ASTM B-117.
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Abstract
A low sludge trivalent chromium based conversion coating bath is provided which forms corrosion resistant coatings on aluminum and aluminum alloys by immersion in aqueous solutions containing trivalent chromium ions and fluorometallate ions followed by optional rinsing. Trivalent chromium coated aluminum also serves as an effective base for paint primers.
126 Citations
24 Claims
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1. A storage stable composition made by mixing together a first mass of water and at least the following components:
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(A) a second mass of a water-soluble source of fluorometallate anions to provide in the composition from about 1 to about 100 g/kg of the fluorometallate anion, each of said anions consisting of; (i) at least four fluorine atoms; and (ii) at least one atom of an element selected from the group consisting of titanium, zirconium, hafnium, silicon, aluminum, and boron, and, optionally, one or both of (iii) at least one ionizable hydrogen atom; and (iv) at least one oxygen atom; (B) a third mass in an amount of about 23 g/l to about 100 g/l of a water soluble source of chromium fluoride; (C) an optional fourth mass of water-soluble source of fluorine anions; (D) an optional fifth mass of a component of surfactant and/or water soluble thickener; said composition being free of water-soluble organic corrosion inhibitor and water-soluble organic stabilizing agents, having a pH of at least 2.1 and no more than 4.4, being storage stable at ambient temperature for at least 2 weeks and capable of producing no more than 3 pits per panel after being exposed to 336 hour salt spray testing according to ASTM B-117. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A composition for coating a metal surface, said composition consisting of water and:
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(A) a component of fluorometallate anions, each of said anions consisting of; (i) at least four fluorine atoms; and (ii) at least one atom of an element selected from the group consisting of titanium, zirconium, hafnium, silicon, aluminum, and boron, and, optionally, one or both of (iii) at least one ionizable hydrogen atom; and (iv) at least one oxygen atom; (B) a component of water soluble chromium fluoride; (C) an optional component of water-soluble source of fluorine anions; (D) an optional component of surfactant; (E) and optional component of water soluble thickener; wherein the concentration of trivalent chromium is at least 6.0 g/l and said composition is substantially free of hexavalent chromium and has a pH of no more than 4.4 and is storage stable at ambient temperature for at least 2 weeks. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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21. A composition for coating a metal surface, said composition comprising water and:
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(A) a component of hexafluorozirconate anions present within a range from about 1 g/kg to about 4.5 g/kg; (B) a component of water soluble chromium fluoride present in an amount of about 5.0 g/l to about 50.0 g/l; and (C) fluorinated alkyl ester surfactant; wherein a ratio of trivalent chromium to zirconium is in a range of 12;
22, the composition being substantially free of hexavalent chromium and having a pH of at least 2.1 and no more than 4.4. - View Dependent Claims (22, 23, 24)
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Specification