Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium

Definitions

• this invention relates to novel compositions and to a process for electroplating chromium plate onto a basis metal which comprises passing current from an anode to a cathode at least a portion of which contains a conductive metal layer through an aqueous acidic chromium-plating solution substantially free of nitric acid and other oxidative catalysts containing 1. at least one chromium compound providing hexavalent chromium ions for electroplating chromium; and
• chromium electroplate having a thickness of at least 1X10 mm.
• PROCESS FORELECTROPLATING CHROMIUM AND ELECTROLYTES THEREFOR This invention relates to novel compositions and to novel processes for the electrodeposition of chromium from an aqueous acidic chromium-plating bath.
• chromium may be plated onto various basis metals from aqueous bath solutions.
• aqueous bath solutions it has been found that the use of certain catalysts such as silicofluoride ions and-sulfate ions provide improved chromium electrodeposits especially insocalled low current density areas.
• catalysts such as silicofluoride ions and-sulfate ions provide improved chromium electrodeposits especially insocalled low current density areas.
• the effect of such catalyst systems has been found to vary with the concentration of the chromic acid and the ratio of the catalysts to the total chromic acid'content.
• the concentration of the chromium-plating bath continually varies during operation due to the removal of chromium in the form of deposited metal and due-to the addition of impurities arising from the electrodes as well as decomposition products, it has been difficult to control and maintain the proper catalyst and chromic acid concentrations throughout the life of a typical aqueous acidic chromium-electroplating bath.
• a further object of the invention is to provide stabilized chromium-plating bath compositions which have good throwing power and extended useful life.
• Other object of the invention will be apparent to those skilled in the art upon inspection of the following detailed description of the invention.
• this invention relates to novel compositions and to a process for electroplating chromium plate onto a basis metal which comprises passing current from an anode to a cathode at least a portion of which contains a conductive metal layer through an aqueous acidic chromium-plating solution substantially free of nitric acid and other oxidative catalysts containing 1. at least one chromium compound providing hexavalent chromium ions for electroplating chromium; and
• cerous ions in combination with fluoride ions and sulfate ions as catalysts for a time sufficient to deposit a chromium electroplate having a thickness of at least I Xl' mm.
• the chromium electroplating bath compositions of the invention may contain about 100-600 g./l. of chromic acid (expressed as CrO and preferably about 200-350 g./l. of chromic acid.
• the fluoride ions may be added to the chromium electroplating bath in the form of compounds such as sodium silicofluoride (Na SiF fluosilicic acid (H SiF strontium silicofluoride (SrSiF ammonium silicofluoride [(Nl-l Sif magnesium silicofluoride (MgSif calcium silicofluoride (CaSiF etc.
• fluoride compounds which may be used in the bath according to the invention include sodium fluoride, potassium fluoride, calcium fluoride, hydrofluoric acid, ceric fluoride, cerous fluoride, etc.
• fluoride ions including complex fluoride ions
• fluoaluminates fluoborates, fluotitanates, and fluozirconates.
• the sulfate ions may be added to the chromium-electroplating bath in the form of suitable sulfate compounds such as strontium sulfate (S180 sulfuric acid (H S0 lithium sulfate (Li SO ammonium sulfate [(NH.,) 80 calcium sulfate (CaSo etc.
• suitable sulfate compounds such as strontium sulfate (S180 sulfuric acid (H S0 lithium sulfate (Li SO ammonium sulfate [(NH.,) 80 calcium sulfate (CaSo etc.
• the chromium electroplating process may use temperatures of 30-I0 C. with a chromic acid bath containing 100-600 gJl. of chromic'acid (as CrO).
• CrO chromic'acid
• the ratio of chromic acid to sulfate ion (Cr0 :SO may be maintained at l00-500: l ically l50-300:l and preferably about 200:1.
• Cerous ions may be added to the bath in the form of salts such as cerium carbonate, cerium fluoride, cerium sulfate, etc.
• cerium fluoride CeF
• the chromium plating bath composition containing -600 g./l. of Cr0 may be saturated with can, Such saturation is provided to obtain self-regulation of the catalyst content of the bath.
• CeF Cerous salts including complex fluoride salts
• CeF or other cerous salts including complex fluoride salts
• a chromic acid solution which contains excess undissolved cerium fluoride (CeF Excess cerous ion concentrations derived from other cerium salts maybe utilized to suppress and further control the fluoride ion concentration.
• chromic acid concentration of less than 100-600 g./l. may be used, the preferred range is 100-600 g./l/, and the most preferred range is 200-400 g./l.
• the chromic acid:fluoride ratio remains relatively constant leading to uniformity of operation
• the concentration of the fluoride ion may be further suppressed by the use of an excess of cerous ion as supplied, for example, by cerous carbonate or soluble cerous oxide.
• the cerous ion-containing baths must be essentially free of substantial quantities of oxidative catalysts (such as nitric acid, perchloric acid, etc.) to prevent excessive oxidation of the cerous ion to the eerie ion on electrolysis. Because the solubility of ceric fluoride is substantially greater than the solubility of cerous fluoride, the presence of ceric ions in the bath compositions of the invention is undesirable.
• oxidative catalysts such as nitric acid, perchloric acid, etc.
• control solution showed the slight darkening expected from the formation of trivalent chromium by electrolysis.
• the experimental solution containing the nitric acid was virtually black thus indicating that much trivalent chromium and tetravalent cerium had been formed.
• the oxidation tivity is not directly proportional to the total fluoride because the complex fluorides may modify this activity.
• the unexpected stability of operation ofthe plating baths of the invention may be illustrated by the use of an aqueous bath was confirmed by analyzing the solutions for fluoride.
• the 5 made up originally to contain 300 g./l. chromic acid, 6.6 g./l. control solution contained 0.36 g./l. of fluoride. This was the strontium sulfate, 5.8 g./l. strontium chromate, and 3.5 cerous amount expected from the equilibrium solubility of cerous fluoride.
• the bath was allowed to equilibrate at 46 C. for fluoride.
• the experimental solution contained considerably three days with preelectrolysis of 4 amp-hr./liter (4 AH/L). more fluoride, 6.68 g./l.
• the aqueous acid chromium plating bath compositions of the invention may be employed TABLE at temperatures of about 3070 C. to prepare improved chromium plated articles by passing current from an anode to l5 Example m Hum k '6 a basis metal cathode through said aqueous acidic chromium (4.l AH/l.) ($51 :i-i/Ll plating solution at a temperature of 3070 C. for a time sufflcient to deposit a chromium electroplate having a thickness of Crq1 300 265 at least l l0 mm.
• the baths Standard test stl'lps m a Hull Cell Chrolmum coveroage are characterized by excellent stability and uniformity of the was measured by Platlng at 2 amperesfor 3 minutes a! 46 fluoride: sulfate ratios in the presence of chromic acid which is T coverage resllhs m ofchromlum measured fr Om the saturated with cerous fluoride. The ratios have been found to fi current denslty end of the test panels are Show" In table remain fairly uniform over wide concentrations of chromic TABLE III The following examples are submitted for the purpose of 11- lustration only and are not to be construed as limiting the Scope of the mvenuon in any I Example No. Days AH/LITER Coverage (mm.)
• an excess of cerous ion may be utilized to reduce or suppress the concentration of the fluoride ion as desired.
• Table I also illustrates that use of the complex fluoride provides a greater total fluoride content than the simple fluoride. It is to be noted that the catalytic acover long periods of use and show that the oxidation of cerous ion to ceric ion apparently does not occur even after electrolysis for extended time periods as long as the bath is free of nitric ion or other catalytic oxidative ions.
• a process for electroplating chromium plate onto a basis metal which comprises passing current from an anode to a cathode at least a portion of which contains a conductive metal layer through an aqueous acidic chromium plating solution substantially free of nitric acid or other oxidative catalyst containing 1. at least one chromium compound providing hexavalent chromium ions for electroplating chromium; and
• a composition for electroplating chromium plate onto a basis metal which is substantially free of oxidative catalyst which comprises 1. at least one chromium compound providing hexavalent chromium ions on aqueous media for electroplating chromium; and

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Catalysts (AREA)

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• 1969
  • 1969-10-06 US US864170A patent/US3634211A/en not_active Expired - Lifetime
• 1970
  • 1970-09-10 GB GB4337770A patent/GB1322939A/en not_active Expired
  • 1970-09-22 ZA ZA706489A patent/ZA706489B/xx unknown
  • 1970-09-28 JP JP45084917A patent/JPS4911539B1/ja active Pending
  • 1970-09-29 ES ES384095A patent/ES384095A1/es not_active Expired
  • 1970-10-01 CA CA094,545A patent/CA975709A/en not_active Expired
  • 1970-10-02 SE SE13382/70A patent/SE368723B/xx unknown
  • 1970-10-05 NL NLAANVRAGE7014597,A patent/NL171074C/xx not_active IP Right Cessation
  • 1970-10-05 FR FR7035891A patent/FR2064156B1/fr not_active Expired
  • 1970-10-06 DE DE2049038A patent/DE2049038C3/de not_active Expired

Patent Citations (1)

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