US2916424A - Process for chromium plating - Google Patents

Process for chromium plating Download PDF

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Publication number
US2916424A
US2916424A US695146A US69514657A US2916424A US 2916424 A US2916424 A US 2916424A US 695146 A US695146 A US 695146A US 69514657 A US69514657 A US 69514657A US 2916424 A US2916424 A US 2916424A
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United States
Prior art keywords
chromium
bright
concentration
sulfate
bath
Prior art date
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Expired - Lifetime
Application number
US695146A
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English (en)
Inventor
Jesse E Stareck
Jr Edgar J Seyb
Johnson Andy Albert
William H Rowan
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Primerica Inc
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Metal and Thermit Corp
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Publication date
Application filed by Metal and Thermit Corp filed Critical Metal and Thermit Corp
Priority to US695146A priority Critical patent/US2916424A/en
Priority to DEM39468A priority patent/DE1122344B/de
Priority to GB35742/58A priority patent/GB849790A/en
Priority to FR778667A priority patent/FR1215179A/fr
Application granted granted Critical
Publication of US2916424A publication Critical patent/US2916424A/en
Anticipated expiration legal-status Critical
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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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S428/00—Stock material or miscellaneous articles
    • Y10S428/922—Static electricity metal bleed-off metallic stock
    • Y10S428/923—Physical dimension
    • Y10S428/924—Composite
    • Y10S428/926—Thickness of individual layer specified
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S428/00—Stock material or miscellaneous articles
    • Y10S428/922—Static electricity metal bleed-off metallic stock
    • Y10S428/9335—Product by special process
    • Y10S428/934—Electrical process
    • Y10S428/935—Electroplating
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12771—Transition metal-base component
    • Y10T428/12806—Refractory [Group IVB, VB, or VIB] metal-base component
    • Y10T428/12826—Group VIB metal-base component
    • Y10T428/12847—Cr-base component
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12993—Surface feature [e.g., rough, mirror]

Definitions

  • the present invention relates to a novel process for electrodepositing chromium, and more particularly, to a 1 process for electrodepositing bright crack-free chromium plate.
  • Chromium is widely used as a decorative and protective surface finish.
  • Decorative chromium plate is usually .of too small a thickness, in order of 0.00001 inch to be of .substantial value for protecting the basis metal. When deposited in greater thicknesses, the plate contains a network of hair-like cracks extending through the chromium to the basis metal, destroying the plates protective value.
  • Chromium deposits in the order of 0.00005 inch, 0.0001 inch and greater, which are bright and crack-free as plated, are desirable for providing decorative chromium plates having good corrosion resistance. It has been found that for a given thickness of deposit; e.g., 0.00005 inch, 0.0001 inch and greater, the corrosion resistance of crack-free deposits is far superior to the corrosion resistance of deposits having a crack pattern, even including those deposits of sufiicient thickness that the cracks are healed.
  • the art has not known how toobtain thick, bright crack-free chromium deposits and it appeared that it would be impossible to obtain them.
  • the known conditions for obtaining bright decorative deposits are, on the whole, the opposite of the conditions necessary to obtain crack-free deposits.
  • the term bright in describing bright crack-free chromium electrodeposits, as used herein, is limited to surfaces which have suificient reflectivity to render a well defined and recognizable image.
  • the bright range of deposits is divided into two subdivisions-deposits referred to as mirror-bright and deposits referred to as bright.
  • the mirror-bright deposits are those which have the re- U 2,916,424 Patented Dec. 8, 1959 2 flectivity ordinarily associated witha good mirror.
  • the bright deposits have a lesser degree of reflectivity than a good mirror, but suflicient reflectivity to render a well defined and recognizable image.
  • These bright deposits are sufliciently bright as plated to be acceptable decorative finishes. Their degree of brightness may be improved by a bufiing operation to achieve mirror brightness.
  • Ratio The amount of catalyst ion that may be present in an operative bath isrelated to the CrQ concentration. It is specified as the ratio of the weight of CrO to the. weight of all the catalyst ions ,(herein referred to as Ratio).
  • Ratio The range of Ratios within which it is possible to obtain bright crack-free chromium plating is between :1 to 150: 1, dependent upon the CrOQ concentration and the temperature]
  • the temperature must be maintained above 112 F. and below F. With temperatures above about 119 F. and below 140 F., it is possible to obtain bright crackfree chromium electrodeposits utilizing any Ratio between 80:1 and :1. As the temperature is lowered the tendency to crack increasesmarkedly.
  • baths having lower catalyst concentrations must be employed. Baths with very low catalyst concentrations, as noted by Ratios as high as 150:1, may be utilized at temperatures as low as 112 F. As the temperature is raised, the tendency to electrodeposit bright chromium decreases. Dull deposits are obtained at high temperatures. The upper temperature limit for obtaining bright chromium for the conditions specified is 140 F. The temperature and Ratios at which bright crack-free chromium may be obtained are also related to the CrO concentration of the bath. Baths containing from about g./l. to about 540 g./l. are utilized. The tendency for the electrodeposition of chromium in a less bright condition increases as the CrO concentration is increased.
  • the catalyst is a mixture sulfate ions and silicofluoride ions. Of the total catalyst present, a minimum of 20% is sulfate and preferable at least 35% should be sulfate.
  • the sulfate should not be-more than 85% of the total catalyst and preferably not more than 75%
  • bright crack-free chromium can be lectrodeposited at temperatures between 112 F. and 11-9 F., by utilizing a high Ratio.
  • a Ratio of about 115:1 is the limiting Ratio, whereas the limiting Ratio at 112 F. is 150:1.
  • Electrodeposition of bright crack-free chromium between the temperaturesof 117' F. and 135 F. is preferred. Within this range of temperatures'it is preferred to utilize CrO concentrations between about 250 g./l. and about 425 g./l.; the relationship between the three variables being that defined by the enclosed areas of the curve in Fig. 2. In the large enclosed area ABC, all Ratios between 80:1 and 150:1 may be used. In the area segment ABD the preferred range of Ratios is progressively more narrow with the limiting preferred range at line ADB being 115:1 to 150:1.
  • Maximum thicknesses of bright crack-free chromium are deposited when plating within the rectangular area ABCD of Fig. 1, at Ratios between about 105:1 and 135:1, utilizing baths having a CrO concentration between about 275 g./l. and 400 g./l. and plating at temperatures between about 125 F. and 138 F.
  • Chloride ion in the bath promotes the formation of cracks.
  • Baths containing more than 0.05 g./l. of chloride ion cannot be used to electrodeposit bright crackfree chromium to a thickness of 0.00005 inch. Less than this amount may be tolerated when electrodeposition is carried out, for a given temperature and C'rO concentration, at a Ratio selected from the high end of those allowable under the conditions specified. If it is desired to operate at a low Ratio (high catalyst ion content) selected from the allowable range, it is necessary to compensate for the presence of chloride by subtracting from the allowable catalyst ion content about fourteen times the amount of chloride ion present. When less than 0.005 g./l. of chloride is present, it may be ignored. It is preferable to operate with baths containing not more than 0.02 g./l. of chloride ion.
  • Chromium plating baths are frequently designated as chromic acid baths.
  • the chromic acid content of the bath is referred to asCrO (more accurately designated chromic anhydride).
  • 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. Such compounds include the chromates, dichromates, and polychromates of potassium, sodium, magnesium and calci-
  • the CrO 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 neutr'ali'ze'd in excess of 80% to the dichromate end-point.
  • Sulfate ions may be added in the form of sulfuric acid,- or as sulfate salt(s) with a cation that does not ad-' versely affect bath characteristics, such as potassium, sodium, calcium, strontium, magnesium, chromium, etc.
  • silicofluoride ions may be added in the form of fluosilicic acid, or as silicofluoride salt(s) with a cation that does not adversely affect bath characteristics, such as potassium, sodium, magnesium, chromium, etc.
  • the amount of sulfate and of silicofluoride added to the bath, and maintained in the bath, must be such that their sum results in a Ratio that conforms to the limits set herein.
  • the desired catalyst ion concentration may be attained by adding soluble salts and controlling concentration by analysis.
  • Baths having suitable sulfate ion and/ or silicofluoride ion characteristics may be made-up by adding to the bath a sulfate compound and/or a silicofluoride compound in excess of their solubility in the bath, where the compounds selected have solubility characteristics in the bath so that the resultant total ion concentration is within the limits specified herein.
  • a relatively insoluble sulfate compound e.g.
  • strontium sulfate present in excess of its solubility in the bath, a more soluble sulfate compound such as sulfuric acid or sodium and/or potassium sulfate to adjust the sulfate concentration upward to that desired, within the limits specified herein.
  • Baths having lower sulfate concentrations may be prepared by adding the sulfate in the form of a relatively insoluble compound; e.g., strontium sulfate, in excess of its solubility in the bath and also adding a more soluble compound having a common cation with the sulfate compound and having an anion that is non-catalytic and that does not adversely alfect the bath characteristics; e.g.
  • the silicofluoride ion content may be varied and still controlled by the proper choice of compounds.
  • Potassium silicofluoride is relatively insoluble and when present 'in excess of its solubility may result in a bath having a proper ratio when taken in conjunction with sulfate ion.
  • potassium silicofluoride should be used in conjunction with another more soluble potassium compound, such as potassium chromate or dichromate, potassium carbonate, etc.
  • chromic acid baths prepared and maintained from compositions in which the silico fluoride is added as K SiF in an amount in excess of its solubility in the bath, the silicofluoride concentration being further lowered by the inclusion of a soluble potassium compound, such as potassium dichromate.
  • a soluble potassium compound such as potassium dichromate.
  • the sulfate ion concentration may be lowered by the addition of a soluble strontium compound such as strontium chromate.
  • Bright crack-free electrodeposits are obtained under the conditions of this invention using suitable current densities.
  • the current densities vary between 0.5 a.s.i. (amperes per square inch) and 6 a.s.i., depending primarily on the plating temperature. These current densities are conventional and are described in Chromium Plating by Morisset et al., published by Robert Draper Ltd., 1954, pages 351-363 and particularly page 354.
  • a standard Hull cell was used to determine the thickness to which bright chromium plate can be electrodeposited without cracking.
  • the cell is a box with an anode perpendicular to the sides and an inclined cathode.
  • the current density on the cathode varies inversely with the distance from the near end where the current density is highest and the electrodeposit is thickest.
  • the chromium plated cathode was examined for cracks and for brightness, and a thickness measurement made at the region where the crack pattern begins and/or where the plate is no longer bright.
  • Bright crack-free chromium was electrodeposited from all the baths listed below ,(defined by their CrO sulfate ion and silicofiuoride ion concentrations) at the specified conditions to the thickness, in all cases, of at least 0.00005 inch.
  • Articles made ofany of a variety of basis metals such as plain carbon steels, alloy steels including stainless steel, iron, copper and copper alloys, nickel and nickel alloys, zinc and zinc alloys, etc., may be plated with bright crack-free chromium.
  • the basis metal may be any metal, or an undercoat on: a metal, that can be chromium plated.
  • the basis metal does affect the thickness of chromium which may be plated bright and crack-free to a certain extent. This is illustrated by the slightly greater thickness of bright crack-free chromium which can be deposited directly on steel than can be deposited directly on copper under the same process and bath conditions. The greater thickness attainable under the same conditions on the steel is attributed to the greater hardness of the basis metal and the support it is thus able to give the electrodeposit.
  • a process for electrodepositing bright crack-free chromium to a thickness of at least 0.00005 inch on a metal cathode comprising passing current from an anode to said cathode immersed in an aqueous chromium plating bath at a temperature between 112 F. and 140 F., said bath containing less than 0.05 g./l. of chloride ion and comprising essentially between 180 g./l. and 540 -g./l. of CrO a total catalyst ion concentration of between 1.2 g./l. and 6.3 g./l.
  • Ratio of sulfate and silicofiuoride ions, the Ratio of 00;, concentration to total catalyst ion concentration being between :1 and 150:1, the sulfate ion content being between 20% and of the total catalyst concentration, the CIO;, concentration, Ratio and temperature having a relationship defined by the areas enclosed by the curves in Fig. l.
  • a process for electrodepositing bright crack-free chromium to a thickness of at least 0.00005 inch on a metal cathode comprising passing current from an anode to said cathode immersed in an aqueous chromium plating bath at a temperature between 117 F. and 135 F., said bath containing less than 0.02 g./l. of chloride ion and comprising essentially between 250 g./1. and 425 g./l.
  • a process for electrodepositing bright crack-free chromium to a thickness of at least 0.00005 inch on a metal cathode comprising passing current from an anode to said cathode immersed in an aqueous chromium plating bath at a temperature between F. and 138 F., said bath containing less than 0.02 g./l. of chloride ion and comprising essentially between 275 g./l. and 400 g./l.
  • a process for electrodepositing bright crack-free chromium to a thickness of at least 0.00005 inch on a metal cathode comprising passing current from an anode to said cathode immersed in an aqueous chromium plating bath at a temperature between 119 F. and 140 F., said bath containing less than 0.02 g./l. of chloride ion and comprising essentially between 190 g./l. and 50S g./l.

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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)
  • Glass Compositions (AREA)
  • Electroplating Methods And Accessories (AREA)
US695146A 1957-11-07 1957-11-07 Process for chromium plating Expired - Lifetime US2916424A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US695146A US2916424A (en) 1957-11-07 1957-11-07 Process for chromium plating
DEM39468A DE1122344B (de) 1957-11-07 1958-10-31 Verfahren zum elektrolytischen Abscheiden von glaenzenden rissfreien Chromueberzuegen
GB35742/58A GB849790A (en) 1957-11-07 1958-11-06 Improvements in or relating to electro-depositing chromium
FR778667A FR1215179A (fr) 1957-11-07 1958-11-07 Procédé de chromage par dépôt électrolytique

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US695146A US2916424A (en) 1957-11-07 1957-11-07 Process for chromium plating

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2952590A (en) * 1959-08-14 1960-09-13 Metal & Thermit Corp Process for chromium plating
US3108933A (en) * 1961-02-28 1963-10-29 M & T Chemicals Inc Process and composition for chromium plating
US3157585A (en) * 1959-12-18 1964-11-17 Gen Motors Corp Chromium plating
US3188186A (en) * 1959-12-18 1965-06-08 Gen Motors Corp Chromium plating
US3461048A (en) * 1959-05-28 1969-08-12 M & T Chemicals Inc Method of electrodepositing duplex microcrack chromium

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA945107A (en) * 1969-05-20 1974-04-09 Hyman Chessin Process for bulk electroplating

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2686756A (en) * 1953-05-20 1954-08-17 United Chromium Inc Chromium plating
US2800438A (en) * 1955-07-26 1957-07-23 Metal & Thermit Corp Chromium plating
US2800443A (en) * 1955-07-26 1957-07-23 Metal & Thermit Corp Method of chromium plating

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2787589A (en) * 1954-08-12 1957-04-02 Metal & Thermit Corp Chromium plating
US2787588A (en) * 1954-08-12 1957-04-02 Metal & Thermit Corp Chromium plating

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2686756A (en) * 1953-05-20 1954-08-17 United Chromium Inc Chromium plating
US2800438A (en) * 1955-07-26 1957-07-23 Metal & Thermit Corp Chromium plating
US2800443A (en) * 1955-07-26 1957-07-23 Metal & Thermit Corp Method of chromium plating

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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
US3157585A (en) * 1959-12-18 1964-11-17 Gen Motors Corp Chromium plating
US3188186A (en) * 1959-12-18 1965-06-08 Gen Motors Corp Chromium plating
US3108933A (en) * 1961-02-28 1963-10-29 M & T Chemicals Inc Process and composition for chromium plating

Also Published As

Publication number Publication date
FR1215179A (fr) 1960-04-15
DE1122344B (de) 1962-01-18
GB849790A (en) 1960-09-28

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