US2942990A - Metal plating by chemical reduction with borohydrides - Google Patents

Metal plating by chemical reduction with borohydrides Download PDF

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US2942990A
US2942990A US788715A US78871559A US2942990A US 2942990 A US2942990 A US 2942990A US 788715 A US788715 A US 788715A US 78871559 A US78871559 A US 78871559A US 2942990 A US2942990 A US 2942990A
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nickel
borohydride
cobalt
hydroxide
plating
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US788715A
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Edward A Sullivan
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Metal Hydrides Inc
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Metal Hydrides Inc
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/31—Coating with metals
    • C23C18/32—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron
    • C23C18/34—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents

Definitions

  • This invention relates to chemical deposition of nickel, cobalt and mixtures thereof upon metals, glass, ceramics and plastics by the reducing action of a borohydride in an'aqueous solution of a salt of nickel and/0r cobalt.
  • a process for chemical plating nickel and cobalt upon metallic surfaces has been proposed which involves the reducing action of hypophosphites in a solution of a nickel or cobalt salt, a temperature of 90 C. or more being used to start the reaction.
  • a process also has been proposed involving the reducing actions of hypophosphite and hydrazine, a noble metal catalyst being used to start the reaction.
  • the present invention is based upon the discovery that under certain conditions the water soluble alkali metal borohydrides, such as sodium borohydride, potassium borohydride and tetramethylammonium borohydride, are highly effective reducing agents for use in chemical plating of nickel and cobalt upon both metals and non-metals, such as glass, ceramics and plastics. It has been discovered that if the pH of the aqueous solution of the nickel and/or cobalt salt and the borohydride is adjusted to between about 12.0 and 13.0, the boride formation is suppressed and the reduction product is principally elemental metal. The pH of the solution is adjusted to between 12.0 and 13.0 by the'presence therein of an alkaline material, such as ammonium hydroxide.
  • an alkaline material such as ammonium hydroxide.
  • the precipitation of the hydroxide of nickel or cobalt is inhibited by conventional means, such as by the presence in the solution of an alkali metal salt of an organic carboxylic acid having at least two carboxyl groups, such as the alkali metal salt of citric, tartaric, adipic, succinic, malonic, oxalic, glutaric, pimelic or malic acid.
  • An effective amount of such inhibitor in terms of normality is at least equal to the normality of the nickel or cobalt salt.
  • the present invention therefore, provides a bath for plating by chemical deposition comprising an aqueous solution of a salt of nickel and/or cobalt having a pH between about 12.0 and 13.0, a Water soluble borohydride and a compound which inhibits the precipitation of nickel or cobalt hydroxide.
  • any water soluble salt of nickel or cobalt may be used, such as the sulfate, chloride, nitrate, acetate, formate, citrate or tartrate.
  • alkali metal hydroxides or quaternary ammonium hydroxides may be used, such as sodium hydroxide, potassium hydroxide or tetra- 2,942,990 Patented June 28, 1960 methylammonium hydroxide.
  • Any water soluble borohydride may be used, such as sodium borohydride', potassium borohydride or tetramethylammonium borohydride.
  • the plating bath of the invention is stable for a limited time at normal room temperature, it is preferred to prepare a separate aqueous solution of the borohydride having its pH adjusted to between 12.0 and 13.0 by the addition of an alkaline material if necessary and a second aqueous solution containing the salt of nickel and/or cobalt and having its pH adjusted to between 12.0 and 13.0 by the presence of ammonium hydroxide or other alkaline material and also containing a compound, such as sodium citrate, for inhibiting the precipitation of nickel and/or cobalt hydroxide.
  • the plating bath is made up when desired by combining aliquots of these two solutions in desired proportions.
  • the plating reaction may be started by heating the bath to a temperature of about 40 C.
  • the reaction normally is completed in 30 to 45 minutes, that is, when the borohydride is used up.
  • Adherence of the nickel or cobalt plate is especially good when the surface plated is an unglazed ceramic. Scraping of the surface with a knifeedge does not remove the plated metal.
  • the adherence of the plate is improved if the surface is first roughened with an abrasive, such as emery paper.
  • the invention is illustrated by the following examples.
  • the reaction was started by heating the plating bath to a temperature of 40 C. and heating was continued at a temperature in the range between 40 C. and 50 C. for a period of 30 to 45 minutes.
  • the base material was coated with an adherent, continuous plate of the plating metal.
  • the continuity of the -.plate on the non-metallic base materials of Examples 3-6 was tested by checking their electrical resistance with an ohmmeter. Resistivities of the order of 3 to 10 ohms were found.
  • the resulting plating bath was 0.123 N in nickel sulfate, 0.22 N in sodium citrate and 0.155 N in potassium borohydride and had a pH of 12.3, the molar ratio of BH; ions to nickel ions being 1.3.
  • the bath was used for plating nickel on copper.
  • Example 2 Five parts by volume of an aqueous solution 0.081 N in nickel acetate, 0.146 N in sodium citrate and 6.5 N in ammonium hydroxide were combined with one part by volume of an aqueous solution 0.93 N in potassium borohydride.
  • the resulting plating bath was 0.067 N in nickel acetate, 0.121 N in sodium citrate and 0.155 N in potassium borohydride and had a pH of 12.4, the molar ratio of BH, ions to nickel ions being 2.3.
  • the bath was used for plating nickel on mild steel.
  • Example 3 23 parts by volume of an aqueous solution 0.131 N in nickel chloride, 0.213 N in sodium citrate and 8.5 N
  • Example 4 Five parts by volume of an aqueous solution 0.046 N in cobalt acetate, 0.127 N in sodium tartrate and 6.9 N
  • Example 5 12.4, the molar ratio of BH; ions to nickel ions being 2.7.
  • the bath was used for plating nickel on Lucite.
  • Example 6 Five parts by volume of an aqueous solution 0.105 N 30 in cobalt nitrate, 0.213 N in sodium citrate and 8.2 N
  • a bath for plating by chemical deposition consisting essentially of an aqueous solution of a salt of a metal selected from the group consisting of nickel and cobalt in a concentration between about 0.02 and 0.15 normal, at borohydride selected from the group consisting of sodium borohydride, potassium borohydride and tetramethylammonium borohydride, an alkaline material selected from the group consisting of ammonium hydroxide, an alkali metal hydroxide and tetramethylammonium hydroxide in an amount sufficient to bring the pH of the solution to between about 12.0 and 13.0, and an agent adapted to inhibit precipitation of the hydroxide of said selected metal, said agent being selected from alkali metal salts of carboxylic acids having at least two carboxyl groups and being present in a concentration in. terms of normality at least equal to the normality of the salt of said selectedmetal.

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  • Chemical & Material Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemically Coating (AREA)

Description

United States Patent Metal Hydrides Incorporated, Beverly, Mass, a corporation of Massachusetts No Drawing. Filed .Ian. 26, 1959, Ser. No. 788,715
2 Claims. (Cl. 106-1) This invention relates to chemical deposition of nickel, cobalt and mixtures thereof upon metals, glass, ceramics and plastics by the reducing action of a borohydride in an'aqueous solution of a salt of nickel and/0r cobalt.
A process for chemical plating nickel and cobalt upon metallic surfaces has been proposed which involves the reducing action of hypophosphites in a solution of a nickel or cobalt salt, a temperature of 90 C. or more being used to start the reaction. A process also has been proposed involving the reducing actions of hypophosphite and hydrazine, a noble metal catalyst being used to start the reaction.
Sodium borohydride has been used extensively for effecting reductions of many compounds in aqueous solu tion. It is known that the alkali metal borohydrides reduce nickel salts but the reduction product is nickel boride. Thus, the United States patent to H. I. Schlesinger and H. C. Brown No. 2,461,661, column 5, lines 2 to 5, states: One characteristic reduction reaction of the alkali metal borohydrides is the reduction of nickel sulfate in solution to a black precipitate of nickel boride, Ni B.
The present invention is based upon the discovery that under certain conditions the water soluble alkali metal borohydrides, such as sodium borohydride, potassium borohydride and tetramethylammonium borohydride, are highly effective reducing agents for use in chemical plating of nickel and cobalt upon both metals and non-metals, such as glass, ceramics and plastics. It has been discovered that if the pH of the aqueous solution of the nickel and/or cobalt salt and the borohydride is adjusted to between about 12.0 and 13.0, the boride formation is suppressed and the reduction product is principally elemental metal. The pH of the solution is adjusted to between 12.0 and 13.0 by the'presence therein of an alkaline material, such as ammonium hydroxide. The precipitation of the hydroxide of nickel or cobalt is inhibited by conventional means, such as by the presence in the solution of an alkali metal salt of an organic carboxylic acid having at least two carboxyl groups, such as the alkali metal salt of citric, tartaric, adipic, succinic, malonic, oxalic, glutaric, pimelic or malic acid. An effective amount of such inhibitor in terms of normality is at least equal to the normality of the nickel or cobalt salt.
The present invention, therefore, provides a bath for plating by chemical deposition comprising an aqueous solution of a salt of nickel and/or cobalt having a pH between about 12.0 and 13.0, a Water soluble borohydride and a compound which inhibits the precipitation of nickel or cobalt hydroxide.
In the practice of the invention, any water soluble salt of nickel or cobalt may be used, such as the sulfate, chloride, nitrate, acetate, formate, citrate or tartrate. In place of ammonium hydroxide, alkali metal hydroxides or quaternary ammonium hydroxides may be used, such as sodium hydroxide, potassium hydroxide or tetra- 2,942,990 Patented June 28, 1960 methylammonium hydroxide. Any water soluble borohydride may be used, such as sodium borohydride', potassium borohydride or tetramethylammonium borohydride.
While the plating bath of the invention is stable for a limited time at normal room temperature, it is preferred to prepare a separate aqueous solution of the borohydride having its pH adjusted to between 12.0 and 13.0 by the addition of an alkaline material if necessary anda second aqueous solution containing the salt of nickel and/or cobalt and having its pH adjusted to between 12.0 and 13.0 by the presence of ammonium hydroxide or other alkaline material and also containing a compound, such as sodium citrate, for inhibiting the precipitation of nickel and/or cobalt hydroxide. The plating bath is made up when desired by combining aliquots of these two solutions in desired proportions. Satisfactory results have been obtained with a plating bath in which the concentration of the nickel or cobalt salt is between about 0.02- and 0.15 normal, the concentration of the borohydride being between about 0.05 to 0.60 normal but sufficient to effect substantially complete reduction of the nickel or cobalt salt.
In the use of the plating bath of the invention, the plating reaction may be started by heating the bath to a temperature of about 40 C. The reaction normally is completed in 30 to 45 minutes, that is, when the borohydride is used up. Adherence of the nickel or cobalt plate is especially good when the surface plated is an unglazed ceramic. Scraping of the surface with a knifeedge does not remove the plated metal. When plating smooth surfaces, such as other metals, glass or glazed ceramics, the adherence of the plate is improved if the surface is first roughened with an abrasive, such as emery paper.
The invention is illustrated by the following examples. In these examples the reaction was started by heating the plating bath to a temperature of 40 C. and heating was continued at a temperature in the range between 40 C. and 50 C. for a period of 30 to 45 minutes. In each example, the base material was coated with an adherent, continuous plate of the plating metal. The continuity of the -.plate on the non-metallic base materials of Examples 3-6 was tested by checking their electrical resistance with an ohmmeter. Resistivities of the order of 3 to 10 ohms were found.
Example Five parts by volume of an aqueous solution 0.148 N in nickel sulfate, 0.264 N in sodium citrate and 7.6 N in ammonium hydroxide were combined with one part by volume of an aqueous solution 0.93 N in potassium borohydride. The resulting plating bath was 0.123 N in nickel sulfate, 0.22 N in sodium citrate and 0.155 N in potassium borohydride and had a pH of 12.3, the molar ratio of BH; ions to nickel ions being 1.3. The bath was used for plating nickel on copper.
Example 2 Five parts by volume of an aqueous solution 0.081 N in nickel acetate, 0.146 N in sodium citrate and 6.5 N in ammonium hydroxide were combined with one part by volume of an aqueous solution 0.93 N in potassium borohydride. The resulting plating bath was 0.067 N in nickel acetate, 0.121 N in sodium citrate and 0.155 N in potassium borohydride and had a pH of 12.4, the molar ratio of BH, ions to nickel ions being 2.3. The bath was used for plating nickel on mild steel.
Example 3 23 parts by volume of an aqueous solution 0.131 N in nickel chloride, 0.213 N in sodium citrate and 8.5 N
in ammonium hydroxide were combined with one part by volume of an aqueous solution 4.44 N in sodium borohydride and containing about 40 percent by Weight of sodium hydroxide. The resulting plating bath was 0.125 N in nickel chloride, 0.206 N in sodium citrate and 0.185 N in sodium borohydride and had a 'pH of 12.8, the molar ratio of BH, ions to nickel ions being 1.5. The bath was used for plating nickel on unglazed ceramic.
Example 4 Five parts by volume of an aqueous solution 0.046 N in cobalt acetate, 0.127 N in sodium tartrate and 6.9 N
in ammonium hydroxide were combined with one part by volume of an aqueous solution 1.32 N in sodium borohydride and 6.8 N in ammonium hydroxide. The resulting plating bath was 0.038 N in cobalt acetate, 0.106 N in sodium tartrate and 0.22 N in sodium borohydride'and had a pH of 12.5, the molar ratio of EH ions to cobalt ions being 5.8. The bath was used for plating cobalt on glass.
Example 5 12.4, the molar ratio of BH; ions to nickel ions being 2.7. The bath was used for plating nickel on Lucite.
Example 6 Five parts by volume of an aqueous solution 0.105 N 30 in cobalt nitrate, 0.213 N in sodium citrate and 8.2 N
in ammonium hydroxide were combined with one part by volume of an aqueous solution 0.93 N in potassium borohydride. The resulting plating bath was 0.087 N in cobalt nitrate, 0.177 N in sodium citrate and 0.155 N in potassium borohydride and had a pH of 12.4, the molar ratio of EH ions to cobalt ions being 1.8. The bath was used for plating cobalt on unglazed ceramic.
I claim:
l. A bath for plating by chemical deposition consisting essentially of an aqueous solution of a salt of a metal selected from the group consisting of nickel and cobalt in a concentration between about 0.02 and 0.15 normal, at borohydride selected from the group consisting of sodium borohydride, potassium borohydride and tetramethylammonium borohydride, an alkaline material selected from the group consisting of ammonium hydroxide, an alkali metal hydroxide and tetramethylammonium hydroxide in an amount sufficient to bring the pH of the solution to between about 12.0 and 13.0, and an agent adapted to inhibit precipitation of the hydroxide of said selected metal, said agent being selected from alkali metal salts of carboxylic acids having at least two carboxyl groups and being present in a concentration in. terms of normality at least equal to the normality of the salt of said selectedmetal.
2. A plating bath as described by claim 1 wherein said salt of the selected metal is selected from the group consisting of sulfate, chloride, nitrate, acetate, formate, citrate and tartrate.
References Cited in the file of this patent UNITED STATES PATENTS 2,726,170 Warf et a1. Dec. 6, 1955 Notice ef Adverse Decisien in Interference In Interference No. 92,380 involving Patent No. 2,942,990, E. A. Sullivan, Metal plating by chemical reduction with borohydrides, final judgment adverse to the patentee was rendered Aug. 20, 1962, as to claims 1 and 2.
[Ofiicial Gazette September 18, 1962.]

Claims (1)

1. A BATH FOR PLATING BY CHEMICAL DEPOSITION CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF A SALT OF A METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL AND COBALT IN A CONCENTRATION BETWEEN ABOUT 0.02 AND 0.15 NORMAL, A BOROHYDRIDE SELECTED FROM THE GROUP CONSISTING OF SODIUM BOROHYDRIDE, POTASSIUM BOROHYDRIDE AND TETRAMETHYLAMMONIUM BOROHYDRIDE, AN ALKALINE MATERIAL SELECTED FROM THE GROUP CONSISTING OF AMMONIUM HYDROXIDE, AN ALKALI METAL HYDROXIDE AND TETRAMETHYLAMMONIUM HYDROXIDE IN AN AMOUNT SUFFICIENT TO BRING THE PH OF THE SOLUTION TO BETWEEN ABOUT 12.0 AND 13.0, AND AN AGENT ADAPTED TO INHIBIT PRECIPITATION OF THE HYDROXIDE OF SAID SELECTED METAL, SAID AGENT BEING SELECTED FROM ALKALI METAL SALTS OF CARBOXYLIC ACIDS HAVING AT LEAST TWO CARBOXYL GROUPS AND BEING PRESENT IN A CONCENTRATION IN TERMS OF NORMALITY AT LEAST EQUAL TO THE NORMALITY OF THE SALT OF SAID SELECTED METAL.
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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3096182A (en) * 1958-10-01 1963-07-02 Du Pont Chemical plating solution and process for plating therewith
US3140188A (en) * 1960-08-29 1964-07-07 Bayer Ag Bath compositions for chemical plating of metals containing boron nitrogen compounds nd an organic solubilizing compound
US3216834A (en) * 1960-10-05 1965-11-09 Engelhard Ind Inc Palladium decorating compositions
DE1239766B (en) * 1962-07-12 1967-05-03 Telefunken Patent Method for applying a firmly adhering nickel layer to a glossy carbon resistance layer applied to a ceramic carrier
US3338726A (en) * 1958-10-01 1967-08-29 Du Pont Chemical reduction plating process and bath
US3423214A (en) * 1965-06-30 1969-01-21 Ibm Magnetic cobalt and cobalt alloy plating bath and process
US3446657A (en) * 1964-06-18 1969-05-27 Ibm Coating method
US3637472A (en) * 1970-03-16 1972-01-25 Ventron Corp Chemical plating baths containing an alkali metal cyanoborohydride
US4157262A (en) * 1976-04-28 1979-06-05 Fuji Photo Film Co., Ltd. Intensification of photographic silver images by physical development and improvement in physical developer solution for use therein
FR2413194A1 (en) * 1977-12-28 1979-07-27 Cbs Sony Records Inc METHOD FOR MANUFACTURING RECORDING DISCS INCLUDING AN ENGRAVING

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2726170A (en) * 1954-09-07 1955-12-06 Superweld Corp Method of coating steel with nickel-boron

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2726170A (en) * 1954-09-07 1955-12-06 Superweld Corp Method of coating steel with nickel-boron

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3096182A (en) * 1958-10-01 1963-07-02 Du Pont Chemical plating solution and process for plating therewith
US3338726A (en) * 1958-10-01 1967-08-29 Du Pont Chemical reduction plating process and bath
US3140188A (en) * 1960-08-29 1964-07-07 Bayer Ag Bath compositions for chemical plating of metals containing boron nitrogen compounds nd an organic solubilizing compound
US3216834A (en) * 1960-10-05 1965-11-09 Engelhard Ind Inc Palladium decorating compositions
DE1239766B (en) * 1962-07-12 1967-05-03 Telefunken Patent Method for applying a firmly adhering nickel layer to a glossy carbon resistance layer applied to a ceramic carrier
US3446657A (en) * 1964-06-18 1969-05-27 Ibm Coating method
US3423214A (en) * 1965-06-30 1969-01-21 Ibm Magnetic cobalt and cobalt alloy plating bath and process
US3637472A (en) * 1970-03-16 1972-01-25 Ventron Corp Chemical plating baths containing an alkali metal cyanoborohydride
US4157262A (en) * 1976-04-28 1979-06-05 Fuji Photo Film Co., Ltd. Intensification of photographic silver images by physical development and improvement in physical developer solution for use therein
FR2413194A1 (en) * 1977-12-28 1979-07-27 Cbs Sony Records Inc METHOD FOR MANUFACTURING RECORDING DISCS INCLUDING AN ENGRAVING

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