US3920527A - Self-regulating plating bath and method for electrodepositing chromium - Google Patents

Self-regulating plating bath and method for electrodepositing chromium Download PDF

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Publication number
US3920527A
US3920527A US792970*A US79297069A US3920527A US 3920527 A US3920527 A US 3920527A US 79297069 A US79297069 A US 79297069A US 3920527 A US3920527 A US 3920527A
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Prior art keywords
chromium
acid
electrolyte
chromium trioxide
weight
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Expired - Lifetime
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US792970*A
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English (en)
Inventor
Manfred Dettke
Manfred Roosen
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Bayer Pharma AG
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Schering AG
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Priority claimed from DE19681696088 external-priority patent/DE1696088C3/de
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    • 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
    • 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

Definitions

  • Fie'l 148/6 2 lysts such as boric acid, hydrofluoric acid, fluosilicic acid, fluotitanic acid or fluoboric acid or their soluble salts maintains a constant effective catalyst concentra-
  • Fie'l 148/6 2 lysts such as boric acid, hydrofluoric acid, fluosilicic acid, fluotitanic acid or fluoboric acid or their soluble salts maintains a constant effective catalyst concentra-
  • Bright chromium metal is deposited electrolytically on a cathode from an aqueous solution of chromium trioxide (chromic acid) when the solution contains known catalytic ions of sulfuric or fluosilicic acid in a precise ratio to the chromic acid present. Because of the criticality of the catalyst concentration, such conventional chromium plating baths must be analyzed frequently and adjusted to the required composition to maintain adequate current efficiency, covering power,
  • a chromium plating bath containing hexavalent chromium ions as a source of chromium can be made self-regulating as to its activator or catalyst content by the use of lead sulfate in conjunction with a secondary activator which may be an acid from the group consisting of boric acid, hydrofluoric acid, fluoboric acid, fluosilicic acid and fluotitanic acid, or a soluble salt of such an acid.
  • the chromium plating baths of the invention are effective over a wide range of chromic acid concentrations, the preferred range being from 150 g to 550 g CrO per liter, and acceptable results are also obtained at values of chromium trioxide concentration slightly, but not substantially, above and below this range.
  • Best covering power and a most stable catalyst concentration are achieved when the bath further contains ions of dichromic acid, most conveniently derived from sodium or potassium dichromate in an amount of 10 to 40%, based on the chromium trioxide present and expressed as alkali metal dichromate.
  • the optimum ratio of alkali metal dichromate to chromium trioxide is between approximately 4 l and 5 1, that is, 20 to 25% alkali metal dichromate, based on the chromium trioxide.
  • the addition of the dichromate brings about a substantial improvement of the electrodeposit at high current densities and improves the covering power.
  • the lead sulfate addition may amount to approximately 0.5 to of the chromium trioxide dissolved in the plating bath, best result usually being obtained with 0.5 to 5.5% lead sulfate. 2.6% Lead sulfate produces desirable results under most operating conditions.
  • the chromium electrodeposits of the invention are distinguished by unusually good covering power and by high brightness free from haze over a wide range of cathode current densities. Even when built up to relatively high thickness values, the chromium electrodeposits produced by the method of the invention have at least a satin sheen. Regardless of thickness, the coatings are smooth and free from dendrites, and thereby far superior to otherwise similar coatings produced from the conventional electrolytes using sulfuric aciid as the catalyst or activator.
  • Lead sulfate in the chromium electroplating baths of the invention is compatible with a wide range of secondary activators or catalysts which are stable under all operating conditions, and do not form decomposition products capable of being codeposited with the chromium metal to interfere with the quality of the deposit.
  • the secondary catalysts of the invention are acids, namely boric acid, hydrofluoric acid, fluosilicic acid, fluoboric acid, or fluotitanic acid, and salts of these acids which are soluble in the electrolyte to furnish anions of the acids.
  • the amounts of the secondary catalysts are too small to make the nature of their cationic moiety (hydrogen or alkali metal ions) relevant to the success of the method.
  • the secondary activators are effective in minute amounts. As little as 0.05% based on the CrO in the electrolyte produces practically significant improvements, but the effects of even smaller amounts can be detected. No critical upper limit of secondary activator concentration could be established, but nothing useful is achieved by increasing the amounts of activator above the preferred concentration range which is l to 5% for fluosilicic acid, 0.2 to 5% for boric acid, 0.1 to 3% for fluotitanic acid, 0.1 to 2% for hydrofluoric acid, and 0.1 to 3% for fluoboric acid.
  • the soluble salts are effective as the free acids in equirnolecular amounts, the sodium and potassium salts being generally most readily available.
  • the chromium plating baths of the invention are free from organic compounds.
  • the amount of solid phase present in contact with the electrolyte is extremely small, and equilibrium between the solid phase and the supernatant liquid is quickly established.
  • the agitation of the bath resulting from thermal convection and the insertion and removal of objects to be plated is normally sufficient to maintain equilibrium.
  • the chromium plating baths of the invention are operated effectively at temperatures from approximately 25 to 60C and at cathode current densities from 5 to amps, per dm
  • the cathode current efficiency is affected by the temperature, cathode current density, and electrolyte temperature as shown on the graphs of cathode current efficiency (per cent) v. chromium trioxide concentration (g/l) in the attached drawing.
  • the four curves of FIG. 1 respectively relate to cathode current densities cf 30, 20, 15 and 10 amps./dm at an electrolyte temperature of 30C.
  • FIG. 2 has four curves relating to the same current density values as in FIG. 1, but measured for an electrolyte temperature of 40C.
  • the four curves of FIG. 3 were determined at 55C and at current densities of 70, 60, 30 and 15 amps. per dm respectively.
  • the curves of FIGS. 1 and 2 reflect typical conditions for decorative chromium plating whereas the curves of FIG. 3 apply mainly to hard chromium plating.
  • the method of the invention permits a chromium electrodeposit having microcracks to be produced in the bath itself, and the number of cracks per centimeter to be determined in advance, at least approximately, by suitable selection of plating conditions.
  • chromium electrodeposits having microcracks have better corrosion resistance than continuous chromium coatings because of the lack of ductility of chromium. Mechanical stresses may cause a continuous electrodeposit to crack through its entire thickness so that local cells may be formed between the exposed base metal and the electrodeposit. The anode current density in such cells can be very high, and the corrosion correspondingly rapid.
  • the properties of the chromium layer produced by the method of this invention can be controlled by selecting the chromic acid concentration.
  • a grid of microcracks extending over the entire chromium surface is obtained if the chromic acid concentration is between 200 and approximately 400 g/l. Within this concentration range, the number of cracks per centimeter decreases with rising temperature and with rising chromic acid concentration if the temperature is between 30 and 40C, the current density between 5 and 30 amps. per (1111 and the plating time between 12 and 15 minutes.
  • the chromium plating baths of the invention produce chromium electrodeposits characterized by a much finer grid of microcracks, approximately 1500 cracks per centimeter. Intermediate values of crack density can be obtained by suitable modification of process variables.
  • EXAMPLE 1 An electrolyte suitable for producing mirror bright decorative chromium electrodeposits at 30-50C, preferably 38-40C, at 5-25 amps./dm was prepared by dispersing the following materials in water:
  • Chromium trioxide C10: 350 g/l 100.0%
  • EXAMPLE 2 An electrolyte which produces hard chromium plates at high deposition rates with good current efficiencies under the conditions of Example 1, particularly in the higher range of cathode current densities was prepared from the following ingredients:
  • the electrolyte When operated at 48 C and 15 20 amps. per dm the electrolyte produced chromium electrodeposits which had 400 to 600 cracks per centimeter at a thickness of at least 2.0 to 2.5 microns.
  • EXAMPLE 5 A chromium base layer was deposited from the electrolyte described in Example 1, and was then covered by a surface layer of chromium from an electrolyte of the following composition at 45 C and 10 7 20 amps./dm in 4 8 minutes:
  • the surface layer had approximately 400 600 cracks per centimeter, the width of each crack being uniform and 0.1 0.2 microns.
  • a chromium deposit one millimeter thick was formed in 12 14 hours. It showed several superimposed, uniform grids of cracks.
  • EXAMPLE 7 An electrolyte suitable for forming thin chromium plates having microcracks was prepared from:
  • the electrolyte of Example 7 could also be used for producing a surface deposit of cracked chromium on a chromium base formed from the electrolyte of Example l.
  • the chromium electrodeposits of the invention are metallic in appearance at all cathode current densities not substantially lower than 1.8 amps. per dm and this lower limit is raised only insignificantly at the highest deposition temperatures mentioned above.
  • the nickel surface exposed by the stripping operation may be chromium plated anew without the preparatory steps necessary with the usual chromium electrolytes, such as polishing or deposition of a fresh nickel layer.
  • the chromium plating baths of the invention can be operated with uniform results over extended periods without requiring adjustment of their composition.
  • a method for forming a microcracked chromium electrodeposit which comprises making an electrically conductive object the cathode in a self-regulating acidic aqueous chromium electroplating electrolyte comprising between 200 and 400 grams per liter of chromium trioxide, lead sulfate in amounts of from 0.5 to 10 percent by weight based on the concentration of chromium trioxide, and an effective amount of a sec- 6 ric acid, and fluotitanic acid, said effective amount being sufficient to contribute to the production of a microcracked chromium deposit, at a temperature of 25C. to 60C. and at a cathode current density of 5 to 70 amps. per square decimeter.
  • a self-regulating acidic aqueous chromium electroplating electrolyte for depositing a amicrocracked layer of chromium comprising from about 150 to about 550 grams per liter of chromium trioxide, lead sulfate in amounts of from 0.5 to 10 percent by weight based on the concentration of chromium trioxide, and at least 0.05 weight percent based on the weight of chromium trioxide of a secondary activator selected from the group consisting of the anions of hydrofluoric acid, fluosilicic acid, fluoboric acid and fluotitanic acid.
  • a self-regulating acidic aqueous chromium electroplating electrolyte for depositing a microcracked layer of chromium comprising from about 150 to about 550 grams per liter of chromium trioxide, lead sulfate in amounts of from 0.5 to 10 percent by weight based on the concentration of chromium trioxide, and from 0.2 to 5 weight percent based on the weight of chromium trioxide of boric acid as a secondary activator.
  • activator is ondary activator selected from the group consisting of 40 from 0.1 to 2 weight percent boric acid.

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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)
US792970*A 1968-02-03 1969-01-22 Self-regulating plating bath and method for electrodepositing chromium Expired - Lifetime US3920527A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DESC041927 1968-02-03
DE19681696088 DE1696088C3 (de) 1968-02-03 1968-02-03 Selbstregulierendes galvanisches Chrombad

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US3920527A true US3920527A (en) 1975-11-18

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FR (1) FR1597909A (zh)
GB (1) GB1259515A (zh)
NL (1) NL161205C (zh)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080060945A1 (en) * 2004-04-21 2008-03-13 Rudolf Linde Production of a Structured Hard Chromium Layer and Production of a Coating
US20080293634A1 (en) * 2006-07-07 2008-11-27 Harding Joseph W C-met receptor regulation by angiotensin iv (at4) receptor ligands
US20100112376A1 (en) * 2002-11-29 2010-05-06 Federal-Mogul Burscheid Gmbh Production of structured hard chrome layers
US20110115167A1 (en) * 2008-04-04 2011-05-19 Federal-Mogul Burscheid Gmbh Structured chrome solid particle layer and method for the production thereof
CN110487954A (zh) * 2019-08-01 2019-11-22 广东致远新材料有限公司 一种硫酸根的检测方法

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1590170A (en) * 1925-09-10 1926-06-22 Chromium Products Corp Process of plating with chromium
US2050478A (en) * 1935-08-10 1936-08-11 Wickenhiser Christian Electrolytic bath for depositing chromium
US2952590A (en) * 1959-08-14 1960-09-13 Metal & Thermit Corp Process for chromium plating
US3408272A (en) * 1963-07-24 1968-10-29 Canning & Co Ltd W Electrodeposition of chromium
US3461048A (en) * 1959-05-28 1969-08-12 M & T Chemicals Inc Method of electrodepositing duplex microcrack chromium

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB718630A (en) * 1952-03-03 1954-11-17 Floricel Arquimedes Rojas Method and means for the electro-deposition of chromium
GB946958A (en) * 1961-07-26 1964-01-15 Nat Res Dev A method of and an apparatus for the electrolytic production of chromium of a high degree of purity

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1590170A (en) * 1925-09-10 1926-06-22 Chromium Products Corp Process of plating with chromium
US2050478A (en) * 1935-08-10 1936-08-11 Wickenhiser Christian Electrolytic bath for depositing chromium
US3461048A (en) * 1959-05-28 1969-08-12 M & T Chemicals Inc Method of electrodepositing duplex microcrack chromium
US2952590A (en) * 1959-08-14 1960-09-13 Metal & Thermit Corp Process for chromium plating
US3408272A (en) * 1963-07-24 1968-10-29 Canning & Co Ltd W Electrodeposition of chromium

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100112376A1 (en) * 2002-11-29 2010-05-06 Federal-Mogul Burscheid Gmbh Production of structured hard chrome layers
US8277953B2 (en) 2002-11-29 2012-10-02 Federal-Mogul Burscheid Gmbh Production of structured hard chrome layers
US20080060945A1 (en) * 2004-04-21 2008-03-13 Rudolf Linde Production of a Structured Hard Chromium Layer and Production of a Coating
US8110087B2 (en) * 2004-04-21 2012-02-07 Federal-Mogul Burscheid Gmbh Production of a structured hard chromium layer and production of a coating
US20080293634A1 (en) * 2006-07-07 2008-11-27 Harding Joseph W C-met receptor regulation by angiotensin iv (at4) receptor ligands
US20110115167A1 (en) * 2008-04-04 2011-05-19 Federal-Mogul Burscheid Gmbh Structured chrome solid particle layer and method for the production thereof
US8337687B2 (en) 2008-04-04 2012-12-25 Federal-Mogul Burscheid Gmbh Structured chrome solid particle layer and method for the production thereof
CN110487954A (zh) * 2019-08-01 2019-11-22 广东致远新材料有限公司 一种硫酸根的检测方法

Also Published As

Publication number Publication date
FR1597909A (zh) 1970-06-29
NL161205B (nl) 1979-08-15
GB1259515A (zh) 1972-01-05
DE1696088B2 (de) 1976-01-08
NL161205C (nl) 1980-01-15
NL6901641A (zh) 1969-08-05
DE1696088A1 (de) 1971-11-18

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