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

• the present invention relates to chromium plating and more particularly relates to the use of novel catalysts in chromic acid baths for chromium plating.
• chromium plating became possible with the discovery that chromium could be electrodeposited from aqueous chromic acid baths containing small amounts of a sulfate ion as a catalyst.
• catalysts include borate ions, fluoride ions, chloride ions, etc.
• Silicofluoride and fiuoroborate ions have been disclosed to be catalysts. Silicofluoride (SiF has been successfully utilized whereas fluoroborate (BF4 is not commercially utilized.
• each catalyst has somewhat distinct characteristics. Alone or in specific combinations, they govern and/or affect the current efficiencies, the hardness of the deposit, the appearance of the deposit including color, filming, the covering and throwing power of the solution, the soundness of the deposit, etc. Often it has not been possible to obtain deposits having specific desirable characteristics, or to operate under specific desired process conditions, with the known catalyst. I have now discovered three new and useful catalysts.
• the invention also contemplates providing novel compositions of matter which when dissolved in water provide baths for chromium electrodeposition.
• fluoaluminate ions AIF fluotitanate ions
• TiF and fluozirconate ions ZrF are effective catalysts in aqueous chromic acid solutions for chromium electrodeposition. These catalysts are effective when used as the sole catalyst in chromic acid baths, or when used in combination with one or more other catalysts. When used in baths containng sulfate, they provide sui perior baths for chromium electrodeposition.
• Chromium plating baths are frequently designated as chromic acid baths.
• the chromic acid content of the bath is usually referred to as CrO (more accurately
• the bath may be made up by supplying CrO in the form of chromic anhydride or in the form of compounds containing cations which do not adversely affect the bath characteristics, including the chromates, dichromates, and polychromates of potassium, sodium, magnesium, and calcium.
• the C10 may also be added in the form of chromic acid and/or dichromic acid in solution. Where alkali metal cations are present, the bath should not be neutralized in excess of to the dichromate end-point.
• Ratio The weight ratio of CrO to total catalyst ions (herein referred to as Ratio) is of great importance. Chromium may be electrodeposited from baths having a Ratio of between about 50:1 to about 200:1. Under specific conditions, a lower than 50:1 or higher than 200:1 Ratio may be used, but this is dependent on the basis metal; CrO concentration; species, number and relative concentrations of catalyst ions used; temperature; desired properties of the electrodeposits and other factors.
• these novel catalysts are similar in their effect to sulfate, in others they are not.
• these novel catalysts are added in about 50 to 200% higher concentration (on a weight basis), depending on the particular plating conditions involved, than for sulfate for this purpose. This is an advantage since the optimum concentration limits for these novel catalyst ions are thereby made less critical than for sulfate.
• these novel catalysts when used alone have effects of the same general order of magnitude as sulfate.
• Chromium electrodeposition is affected by changes in concentration of CrO by the temperature, by the current density, by Ratio, by the type of catalyst present, by the proportion of each catalyst present when using more than one catalyst, by the presence of other cations in the bath, etc.
• the plating conditions and concentration ranges of bath components are those generally accepted in the art for chromium plating from sulfate catalyst or sulfate-silicofluoride catalyzed CrO baths. Detailed information concerning these conditions and bath components are set forth in the book, Chromium Plating by Morrisset et al., published by Robert Draper, Ltd. (1954).
• baths containing from about 50 g./l. to over 600 g./l. of CrO may be utilized in chromium electrodeposition
• the catalyst should be sulfate and that preferably at least 35% should be sulfate.
• the sulfate should not be more than 75% of the total catalyst to obtain the benefits of the dual catalyst system.
• the three novel catalyst ions, fiuoaluminate, fluotitanate, and fluozirconate are generally treated as a single group herein, each has a distinct characteristic which affects the electrodeposition process and which makes one or the other more favored under particular conditions. It has been found that the solubility of K ZrF in CrO decreases as the temperature is raised from 32 C. to 43 C. and then increases as the temperature is raised to 55 (3.; whereas the solubility of K TiF -H O increases as the temperature is raised from 32 C. to 43 C. and then decreases as the temperature is further raised to 55 C.
• the fiuoaluminate, fluotitanate, and fluozirconate anions may be added to the bath as salts, associated with such cations as sodium, potassium, calcium, strontium, ammonium, barium, etc. They may be formed in situ by the introduction into a chromic acid bath of elements and/or compounds which in the bath environment react to form the desired catalyst ion. Baths containing fiuoaluminate catalyst ions have been prepared by the introduction into a 400 g./l. CrO bath of a small amount of aluminum added as the hydroxide or aluminate and a small amount of sodium fluoride.
• Standard test samples were obtained by electro-depositing chromium under varied conditions on metal sheet. In the examples, sound deposits were obtained.
• the bath composition and the process conditions are given in the table below.
• An aqueous bath for chromium plating comprising between 50 and 600 g./l. chromic acid, sulfate ion, and at least one complex ion selected from the class consisting of fiuoaluminate, fluotitanate and fluozirconate ions, the Ratio of chromic acid to the total of the sulfate ion and the complex ion being between 50:1 to 2002 1.
• a process of electrodepositing sound chromium comprising passing an electric current between an anode and a cathode immersed in an aqueous bath comprising between 50 and 600 g./l. of chromic acid and at least one complex ion selected from the class consisting of fluoaluminate, fluotitanate and fluozirconate ions, the Ratio of chromic acid to said complex ion being between 50:1 to 200:1.
• a process of electrodepositing sound chromium comprising passing an electric current between an anode and a cathode immersed in an aqueous bath comprising between about 200 g./l. and about 450 g./l. of chromic acid, sulfate ion, and at least one complex ion selected from the class consisting of fiuoaluminate, fiuotitanate and fluozirconate ions, the Ratio of chromic acid to the total of the sulfate ion and the complex ion being between 50:1 to 200.1.
• An aqueous bath for chromium plating comprising between 50 and 600 -g./ l. of chromic acid and at least one 14.
• a composition of matter for making up and for maintaining aqueous chromic acid baths for chromium plating consisting essentially of chromic acid, and at least one salt of a complex anion selected from the class consisting of fiuoaluminate, fiuotitanate, and fiuozirconate ions, the weight ratio of chromic acid to the complex anion of the salt being between 50:1 to 200:1, said composition being characterized by dissolving in water to complex ion selected from the class consisting of fluoproduce a bath from which chromium is electrodeposited.

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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)
• Catalysts (AREA)
• Electroplating And Plating Baths Therefor (AREA)

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Citations (2)

• 1959
  • 1959-01-15 US US786923A patent/US2962428A/en not_active Expired - Lifetime
• 1960
  • 1960-01-12 DE DEM43958A patent/DE1120834B/de active Pending
  • 1960-01-13 GB GB1278/60A patent/GB932990A/en not_active Expired

Patent Citations (2)

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