# US 4,392,922 A · Trivalent chromium electrolyte and process employing vanadium reducing agent > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,392,922 A - Document ID: US4392922A - Status: Granted - Kind: A - Application number: 06/205,406 - Filed: 1980-11-10 - Granted: 1983-07-12 - Earliest claimed: 1980-11-10 - Assignees: Occidental Chemical Corporation - Inventors: Thaddeus W. Tomaszewski - Web page: https://patentgrep.com/patent/US4392922A ## CPC - C25D 21/18: of electrolytes (C25D21/22 takes precedence) - C25D 3/06: from solutions of trivalent chromium - Y10S 204/13: Purification and treatment of electroplating baths and plating wastes - C25D: PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR - Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS ## Abstract An aqueous acidic trivalent chromium electrolyte and process for electrodepositing chromium platings comprising an electrolyte containing trivalent chromium ions, a complexing agent, halide ions, ammonium ions and a reducing agent comprising vanadium ions present in an amount effective to maintain the concentration of hexavalent chromium ions formed in the bath at a level at which satisfactory chromium electrodeposits are obtained. ## Claims ### Claim 1 An aqueous acidic trivalent chromium electrolyte containing trivalent chromium ions, a complexing agent for maintaining the trivalent chromium ions in solution, halide ions, ammonium ions, hydrogen ions to provide a pH on the acid side, and a reducing agent comprising vanadiums ions present in at least an amount effective to maintain the concentration of hexavalent chromium ions at a level which is not in excess of 0.4 grams/liter. ### Claim 2 (depends on 1) The electrolyte defined in claim 1 in which said trivalent chromium ions are present in an amount of about 0.2 to 0.8 molar. ### Claim 3 (depends on 1) The electrolyte as defined in claim 1 in which said trivalent chromium ions are present in an amount of about 0.4 to about 0.6 molar. ### Claim 4 (depends on 1) The electrolyte as defined in claim 1 in which said complexing agent is present in a molar ratio of complexing agent to chromium ions of from about 1:1 to about 3:1. ### Claim 5 (depends on 1) The electrolyte as defined in claim 1 in which said complexing agent is present in a molar ratio of complexing agent to chromium ions of from about 1.5:1 to about 2:1. ### Claim 6 (depends on 1) The electrolyte as defined in claim 1 in which said vanadium ions are present in an amount of about 0.015 to about 6.3 g/l. ### Claim 7 (depends on 1) The electrolyte as defined in claim 1 in which said vanadium ions are present in an amount of about 0.2 to about 1 g/l. ### Claim 8 (depends on 1) The electrolyte as defined in claim 1 in which said ammonium ions are present in an amount to provide a molar ratio of ammonium ions to chromium ions ranging from about 2.0:1 to about 11:1. ### Claim 9 (depends on 1) The electrolyte as defined in claim 1 in which said ammonium ions are present in an amount to provide a molar ratio of ammonium ions to chromium ions ranging from about 3:1 to about 7:1. ### Claim 10 (depends on 1) The electrolyte as defined in claim 1 in which said halide ions are present in an amount to provide a molar ratio of halide ions to chromium ions of from about 0.8:1 to about 10:1. ### Claim 11 (depends on 1) The electrolyte as defined in claim 1 in which said halide ions are present in an amount to provide a molar ratio of halide ions to chromium ions of from about 2:1 to about 4:1. ### Claim 12 (depends on 10, 11) The electrolyte as defined in claim 10 or 11 wherein said halide ions comprise chloride ions, bromide ions, and mixtures thereof present in an amount of at least about 15 g/l. ### Claim 13 (depends on 1) The electrolyte as defined in claim 1 further containing conductivity salts. ### Claim 14 (depends on 13) The electrolyte as defined in claim 13 in which said conductivity salts are present in an amount up to about 300 g/l. ### Claim 15 (depends on 1) The electrolyte as defined in claim 1 further containing borate ions. ### Claim 16 (depends on 15) The electrolyte as defined in claim 15 in which said borate ions are present in an amount of at least about 10 g/l. ### Claim 17 (depends on 15) The electrolyte as defined in claim 15 in which said borate ions are present in an amount up to about 60 g/l. ### Claim 18 (depends on 1) The electrolyte as defined in claim 1 further containing a buffering agent in an amount of about 0.15 molar up to bath solubility. ### Claim 19 (depends on 18) The electrolyte as defined in claim 18 in which said buffering agent is present in an amount of about 0.45 to about 0.75 molar. ### Claim 20 (depends on 1) The electrolyte as defined in claim 1 further including a buffering agent comprising boric acid and the alkali metal and ammonium salts thereof as well as mixtures thereof. ### Claim 21 (depends on 1) The electrolyte as defined in claim 1 further containing a surfactant. ### Claim 22 (depends on 21) The electrolyte as defined in claim 21 in which said surfactant is present in an amount of about 0.05 to about 1 g/l. ### Claim 23 (depends on 1) The electrolyte as defined in claim 1 in which said hydrogen ions are present to provide a pH of about 2.5 to about 5.5. ### Claim 24 (depends on 1) The electrolyte as defined in claim 1 in which said hydrogen ions are present in an amount to provide a pH of about 3.5 to about 4.0. ### Claim 25 (depends on 1) The electrolyte as defined in claim 1 in which said trivalent chromium ions are present in an amount of about 0.2 to about 0.8 molar, said complexing agent is present in a molar ratio of complexing agent to chromium ions of about 1:1 to about 3:1, said halide ions are present in a molar ratio of halide ions to chromium ions of about 0.8:1 to about 10:1, said ammonium ions are present in a molar ratio of ammonium ions to chromium ions of about 2.0:1 to about 11:1, said hydrogen ions are present in an amount to provide a pH of about 2.5 to about 5.5, and said vanadium ions are present in an amount of about 0.015 to about 6.3 g/l. ### Claim 26 (depends on 1) The electrolyte as defined in claim 1 in which said trivalent chromium ions are present in an amount of about 0.4 to about 0.6 molar, said complexing agent is present in a molar ratio of complexing agent to chromium ions of about 1.5:1 to about 2:1, said halide ions are selected from the group consisting of chloride, bromide and mixtures thereof present in an amount to provide a molar ratio of halide ions to chromium ions of about 2:1 to about 4:1, said ammonium ions are present in an amount to provide a molar ratio of ammonium ions to chromium ions of about 3:1 to about 7:1, said hydrogen ions are present to provide a pH of about 3.5 to about 4.0 and said vanadium ions are present in an amount of about 0.2 to about 1 g/l. ### Claim 27 (depends on 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26) A process for electroplating a chromium deposit on an electrically conductive substrate comprising the steps of immersing the substrate in an aqueous acidic trivalent chromium electrolyte as defined in claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 or 26, applying a cathodic charge to said substrate to effect a progressive deposition of a chromium electrodeposit thereon, and continuing the electrodeposition of said chromium electrodeposit until the desired thickness is obtained. ### Claim 28 The process for rejuvenating an aqueous acidic trivalent chromium electrolyte which has been impaired in effectiveness due to the contamination by excessive quantities of hexavalent chromium, said electrolyte containing trivalent chromium ions, a complexing agent for maintaining the trivalent chromium ions in solution, halide ions, ammonium ions and hydrogen ions to provide a pH on the acid side, said process comprising the steps of adding to said electrolyte a reducing agent comprising vanadiums ions in at least an amount sufficient to reduce the concentration of hexavalent chromium ions to a level which is not in excess of 0.4 grams/liter. ### Claim 29 (depends on 28) The process as defined in claim 28 in which said vanadium ions added are of a valence of 4.sup.+. ### Claim 30 (depends on 28) The process as defined in claim 28 in which said vanadium ions are added in an amount of about 0.015 to about 6.3 g/l. ### Claim 31 (depends on 28) The process as defined in claim 28 in which said vanadium ions are added in an amount of about 0.2 to about 1 g/l. ### Claim 32 (depends on 28) The process as defined in claim 28 in which said vanadium ions are added in an amount to reduce the hexavalent chromium ion concentration to a level below about 100 ppm. ### Claim 33 (depends on 28) The process as defined in claim 28 in which said vanadium ions are added in an amount to reduce the hexavalent chromium ion concentration to a level below about 50 ppm. ### Claim 34 (depends on 28) The process as defined in claim 28 in which said vanadium ions are introduced in the form of electrolyte soluble and compatible vanadium salts. ### Claim 35 (depends on 28) The process as defined in claim 28 including the further step of electrolyzing the electrolyte following the addition of said vanadium ions at a moderate current density to accelerate reduction of said hexavalent chromium ions by said vanadium ions.