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Title: Trivalent chromium electroplating baths and method
Claims: We claim: 1. A trivalent aqueous chromium plating solution comprising trivalent chromium ions in a concentration of at least 0.2 M, sulphate ions in a concentration of at least 0.3 M, a weak complexing agent for said trivalent chromium ions in a concentration of at least 0.1 M and selected from the group consisting of hypophosphite ions and glycine, fluoride ions in a concentration of at least 0.025 M, and chloride ions in a concentration of at least 0.1 M. 2. A trivalent chromium plating solution according to claim 1 wherein the weak complexing agent is in a concentration of from 0.25 to 3 M. 3. A trivalent chromium plating solution according to claim 2 containing ammonium ions in a concentration of from 1 to 7 M. 4. A trivalent chromium plating solution according to claim 3 containing ammonium ions in a concentration of at least 5 M. 5. A trivalent chromium plating solution according to claim 1 which contains additionally boric acid. 6. A trivalent chromium plating solution according to claim 1 which contains chloride ions in a concentration of from 0.1 to 5.0 M. 7. A trivalent chromium plating solution according to claim 6 containing chloride ions in a concentration of from 0.5 to 5.0 M, the molar ratio of chloride to sulphate being from 1:60 to 5:1. 8. A trivalent chromium plating solution according to claim 6 wherein said solution is substantially bromide-free. 9. A method for electrodepositing chromium on a substrate which comprises immersing said substrate as the cathode in an aqueous electrolyte solution comprising water, trivalent chromium ions in a concentration of at least 0.2 M, sulphate ions in a concentration of from 1 to 6 M, a weak complexing agent for said trivalent chromium ions in a concentration of at least 0.1 M and selected from the group consisting of hypophosphite ions and glycine, fluoride ions in a concentration of at least 0.025 and chloride ions in a concentration of at least 0.1 M, and passing an electric current through said solution thereby to deposit said trivalent chromium ions on said substrate. Other info: Inventors: Ward, John Joseph Bernard (Wantage, GB) Barnes, Clive (Wantage, GB) Application Number: 853326 Filing Date: 1977-11-21 Publication_date: 1978-08-15 Assignee: International Lead Zinc Research Organization, Inc. (New York, NY) Primary Class(es): 205/286 205/289, 205/290 Other Classes: US Patent Ref:
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