US2787589A - Chromium plating - Google Patents

Chromium plating Download PDF

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Publication number
US2787589A
US2787589A US449457A US44945754A US2787589A US 2787589 A US2787589 A US 2787589A US 449457 A US449457 A US 449457A US 44945754 A US44945754 A US 44945754A US 2787589 A US2787589 A US 2787589A
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United States
Prior art keywords
sulfate
silicofluoride
bath
dissolved
compounds
Prior art date
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Expired - Lifetime
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US449457A
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English (en)
Inventor
Jesse E Stareck
Dow Ronald
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Primerica Inc
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Metal and Thermit Corp
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Filing date
Publication date
Application filed by Metal and Thermit Corp filed Critical Metal and Thermit Corp
Priority to US449457A priority Critical patent/US2787589A/en
Priority to GB22187/55A priority patent/GB812338A/en
Priority to DEU3463A priority patent/DE1112366B/de
Priority to FR1129376D priority patent/FR1129376A/fr
Application granted granted Critical
Publication of US2787589A publication Critical patent/US2787589A/en
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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

Definitions

  • This invention relates to chromium plating using a chromic acid plating bath and particularly to a method for producing crack-free deposits of chromium.
  • the present invention has the. same purpose as the said cop'ending application and utilizes similar means for accomplishing the purpose except that the catalyst acid radical content of the bath solution isv not controlled by non-catalytic suppressor compounds.
  • the bath solution comprises chromic acid, and two soluble catalyst-supplying compounds, namely, a sulfate radical bearing compound and a silicofiuoride radical bearing compound.
  • the catalyst content is maintained by dissolving catalyst-supplying compounds in the bath as required.
  • Compounds of varying solubility may be used, including those readily soluble in the bath solution, those sparingly soluble therein, and those of intermediate solubility, all of which compounds are intended herein as: being soluble compounds.
  • Specific sulfate-supplying compounds include readily soluble compounds like sulfuric acid, sodium sulfate, potassium sulfate, chromium sulfate, sparingly soluble compounds like strontium sulfate and' compounds of intermediate solubility-such as calcium sulfate.
  • Specific silicofiuoride-supplying compounds include readily soluble compounds like hydrofiuosilicic acid and magnesium silicofiuoride, sparingly soluble compounds like potassium silicofiuoride, and compounds of intermediate solubility dissolved silicofluoride from 1.0 to 11.4 g./l., with the sum of the two catalysts lying in the range of 1.5 to
  • Non-catalytic suppressor compounds are kept out of the bath, so that the foregoing concentrations of dissolved catalysts are values not affected by suppressor compounds.
  • the sum of the dissolved sulfateand silicofluoride varies with the dissolved CrOs in the manner defined by the area ABCD of the-graph shown in the accompanyingdrawing.
  • the graph shows the variation of the chromic-acid concentration in grams per 2,787,589 Patented Apr. 1957 2 liter with the concentration, in grams per liter, of the; sum of dissolved sulfate and silicofluori'de.
  • the chromic acid varies from 200 to 900 g./l.
  • the catalyst content varies from a low of 1.5 g./l. to a high of 11.7 g./l.
  • the plate that is deposited is crack-free and has the other advantages described hereinafter.
  • the plate At catalyst concentrations that lie above the curve DC, the plate is cracked, and at catalyst concentrations below the curve AB, the plate is nodular and unsuitable.
  • the above described variation of the chromic acid with the sum of the sulfate and silicofluoride may also be shown by the following table, which also shows how the sulfate and silicofiuoride' concentrations may individually vary:
  • the sum of the dissolved sulfate. and silicofluoride is in the range of 1.9 to 7.6 g;./l.
  • the preferred concentration of dissolved sulfate may vary from 0.3 to 4.5- g./l. and that of dissolved, silicofluoride from 1 .5 to 6.3 g./l. with the preferred sum of the two catalysts lyingin the range of 1.9 to 7.6 g./l.
  • the preferred:- variation of the sum of the dissolved catalyst radicals with the C103 concentration therefore, is as defined by the area JKLM of the graph, and is also set forth in the following table:
  • the plating bath may be made up by adding a mixture of the ingredients to water and stirringuntil equilibrium is obtained.
  • the bath may also be maintained in this way.
  • the chromic acid content maybe supplied by adding chromic acid as such to the bath.
  • the catalyst acid radical content is maintained by dissolving catalyst-supplying compounds in the bath as required and in amounts equivalent to the amounts of catalyst radicals to be replaced.
  • readily soluble compounds are useful throughout the chromic acid range, either alone, as in the case of sulfuric and by drotluosilicic acids, or in combination with one or more other readily or less soluble compounds.
  • compounds of intermediate solubility may be used alone or in combination with other compounds.
  • the plating method comprises passing current in the r range of 0.5 to 8, preferably 1 to 3, amperes per square inch (a. s. i.) from an anode to an article cathode immersed in the bath
  • the bath is operated at a minimum temperature of F., it having been found that below this'temperature the plate that is produced is cracked.
  • the upper temperature may extend to the boiling point of the bath but preferably is about 180 F.
  • a preferred temperature range is to 160 F.
  • concentrations of dissolved CrOs, sulphate and silicofiuoride should be higher, and higher current densities are used.
  • the crack-free quality of the chromium plate produced by the present method is not only determinable visually but also by means of other tests, as set forth in said copending application.
  • the crack-free plate of the invention is characterized by having a hardness of about 425 to about 825, usually 550 to 700, Knoop.
  • the plate is relatively soft and ductile as compared with conventional chromium plate. It has a smooth texture, a satiny finish, and a dull, matte, white color. It is easy to polish or buff.
  • Example 1 A solid mixturewzis prepared comprising 900 parts of chromic acid, 15.5 parts of potassium silicofluoride, and 8.5 parts of strontium sulfate, all parts by weight. The mixture was added to water to form a solution having 900 g./l. of C103, 6.0 g./l. of silicofluoride, and 1.7 g./l. of sulfate. Two steel rods of diameter were plated in the solution at F. and a current density of 2 a. s. i., one of the rods being plated for 3 hours and the other for 14 hours. In each case a smooth dull crack- -free chromium plate was deposited. The thickness of the plate deposited during the 3 hour run was 0.9 mil, while the thickness of the plate during the 14 hour run was 4.2 mils.
  • Example 2 A plating solution was made up containing 750 g./l. of CrOz, 15.0 g./l. sodium silicofluoride, 7.5 g./l. strontium sulfate, and 1.0 g./l. of hydrofluosilicic acid.
  • the solution contained 12.2 g./l. of silicofiuoride and 2.5 g./l. of sulfate.
  • a dull smooth deposit of chromium was produced having a thickness of 0.95 mil and substantially free of cracks.
  • Another steel rod of the same size as the first one, was plated in the solution at 8 a. s. i. for one-half hour at F.
  • the deposit was smooth, dull, and dark gray, had a thickness of 0.20 mil, and was free of cracks.
  • Example 3 A solution was made up having 750.0 g./l. of CrOa,
  • Example 4 An aqueous solution was prepared by dissolving CrOs, sulfuric acid, and hydrofiuosilicic acid in water to form a solution having 350 g./l. of chromic acid, 1.8 g./l. of silicofluoride, and 1.1 g./l. of sulfate. A steel mandrel /8" in diameter and 4" long was plated in the solution at 150 F. and a current density of 3 a. s. i. for 3 hours, there being deposited a smooth, dull white crack-free chromium plate having a thickness of 2.8 mils.
  • Deposits of varying thicknesses may be plated, ranging for example from a thickness just suflicient to cover the pores of the basis metal to any desired thicker deposit for which a demand may exist.
  • the invention is useful for articles made of any of a variety of basis metals, such as plain carbon steels, alloy steels including stainless steel, iron, cast iron, Zinc and zinc alloys, nickel and nickel alloys, copper and copper alloys, aluminum and aluminum alloys, tin and tin alloys, lead and lead alloys, etc.
  • basis metal may be any metal, or an undercoat on a metal, that can be chromium plated.
  • a method of electrodepositing crack-free, chromium plate on an article of metal which comprises essentially: passing current in the range of 0.5 to 8 amperes per square inch from an anode to said article as a cathode immersed in an aqueous chromium plating bath at a temperature of 140 F. to the boiling point of the bath, said bath comprising essentially 200 to 900 g./l. CrOs, atleast one soluble sulfate-containing compound in an amount sufiicient to produce a concentration of 0.3 to 5.5 Y
  • dissolved sulfate 50F
  • said bath being free of compounds acting to suppress the concentrations of dissolved sulfate and silicofluoride, the sum of said dissolved sulfate and silicofluoride being in the range of 1.5 to 11.7 g./l., and said sum of dissolved sulfate and silicofluoride varying with the CrOs concentration in the manner defined by the area ABCD of the graph shown in the accompanying drawing.
  • a method according to claim 1 in which the metal article that is chromium plated is an article of plain carbon steel.
  • sulfate and silicofiuoride salts are salts of different alkali metals, said alkali metals being selected from the group consisting of sodium and potassium.
  • a method of electrodepositing crack-free, chromium plate on a metal article which comprises essentially:
  • said sulfate-containing compound is selected from the class consisting of sulfuric acid and soluble sulfate salts
  • said silicofluoride-containing compound is selected from the class consisting of hydrosilicofiuoric acid and soluble silicofiuoride salts.
  • sulfate and silicofiuoride salts are salts of different alkali metals, said alkali metals being selected from the group consisting of sodium and potassium.

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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)
US449457A 1954-08-12 1954-08-12 Chromium plating Expired - Lifetime US2787589A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US449457A US2787589A (en) 1954-08-12 1954-08-12 Chromium plating
GB22187/55A GB812338A (en) 1954-08-12 1955-08-02 Electrodeposition of chromium plate
DEU3463A DE1112366B (de) 1954-08-12 1955-08-11 Verfahren zur elektrolytischen Herstellung rissfreier Chromueberzuege auf Metallgegenstaenden
FR1129376D FR1129376A (fr) 1954-08-12 1955-08-11 Procédé de chromage par voie électrolytique

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US449457A US2787589A (en) 1954-08-12 1954-08-12 Chromium plating

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US2787589A true US2787589A (en) 1957-04-02

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US449457A Expired - Lifetime US2787589A (en) 1954-08-12 1954-08-12 Chromium plating

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US (1) US2787589A (fr)
DE (1) DE1112366B (fr)
FR (1) FR1129376A (fr)
GB (1) GB812338A (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3408272A (en) * 1963-07-24 1968-10-29 Canning & Co Ltd W Electrodeposition of chromium

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2916424A (en) * 1957-11-07 1959-12-08 Metal & Thermit Corp Process for chromium plating

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2640022A (en) * 1950-11-07 1953-05-26 United Chromium Inc Composition, bath, and process for chromium plating
US2640021A (en) * 1949-11-23 1953-05-26 United Chromium Inc Composition, bath, and process for chromium plating
US2686756A (en) * 1953-05-20 1954-08-17 United Chromium Inc Chromium plating

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2469015A (en) * 1943-02-20 1949-05-03 United Chromium Inc Method and compositions for producing surface conversion coatings on zinc
US2499231A (en) * 1944-08-25 1950-02-28 United Chromium Inc Method of producing surface conversion coatings on zinc

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2640021A (en) * 1949-11-23 1953-05-26 United Chromium Inc Composition, bath, and process for chromium plating
US2640022A (en) * 1950-11-07 1953-05-26 United Chromium Inc Composition, bath, and process for chromium plating
US2686756A (en) * 1953-05-20 1954-08-17 United Chromium Inc Chromium plating

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3408272A (en) * 1963-07-24 1968-10-29 Canning & Co Ltd W Electrodeposition of chromium

Also Published As

Publication number Publication date
DE1112366B (de) 1961-08-03
GB812338A (en) 1959-04-22
FR1129376A (fr) 1957-01-21

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