US2684937A - Brass plating - Google Patents

Brass plating Download PDF

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Publication number
US2684937A
US2684937A US207704A US20770451A US2684937A US 2684937 A US2684937 A US 2684937A US 207704 A US207704 A US 207704A US 20770451 A US20770451 A US 20770451A US 2684937 A US2684937 A US 2684937A
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United States
Prior art keywords
cyanide
bath
zinc
copper
per gallon
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Expired - Lifetime
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US207704A
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English (en)
Inventor
Leon R Westbrook
Edward J Roehl
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Pittsburgh Steel Co
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Pittsburgh Steel Co
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Priority to US207704A priority Critical patent/US2684937A/en
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Publication of US2684937A publication Critical patent/US2684937A/en
Priority to BE643297A priority patent/BE643297A/xx
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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
    • C25D3/56—Electroplating: Baths therefor from solutions of alloys
    • C25D3/58—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of copper

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  • This invention relates to the electroplating of brass from cyanide solutions and has for its object electrodepositing brass at very fast rates from high concentration solutions of high efficiency at high current densities and high temperatures, particularly on continuous steel strip.
  • brass is meant the common alloy comprising about 80% (range 65-8570) copper, balance zinc, and generally referred to as yellow brass.
  • More specific objects of the invention include the maintenance of high electrode efticiencies, and substantially constant bath composition and operating conditions with a minimum of control.
  • Still another object of the invention is providing an improved dry mix which may be utilized for the preparation of brass plating solutions.
  • a brass plating bath comprising an aqueous solution of sodium cyanide, copper cyanide, sodium hydroxide and zinc oxide with a very small proportion of zinc to copper.
  • the proportion of sodium cyanide to copper cyanide may be relatively small, preferably a mol ratio of about 2 to 1, and the sodium hydroxide concentration is relatively very high.
  • Fig. l is a graph of deposit composition plotted for two different temperatures, the vertical coordinate representing percent copper in the deposit and the horizontal coordinate representing cathode current density in amperes per square foot.
  • Fig. 3 is a graph of cathode efficiency plotted against excess sodium cyanide concentration for different cathode current densities.
  • Fig. 4 is a graph of deposit composition plotted against excess sodium cyanide concentration
  • Fig. 5 is a graph of anode voltage plotted against anode current density for dii'rerent temperatures.
  • brass has been commercially plated from an aqueous solution containing copper cyanide, zinc cyanide and sodium cyanide. These are the essential ingredients, besides which the solution usually contains Various amounts of sodium carbonate and a little ammonia, either added as such or resulting from the decomposition of cyanide.
  • aqueous solution containing copper cyanide, zinc cyanide and sodium cyanide.
  • sodium carbonate a little ammonia, either added as such or resulting from the decomposition of cyanide.
  • the copper-zinc concentration ratio is approximately the same as in the deposit, usually from 2:1 to 4:1.
  • Sodium hydroxide is seldom present and, if it is, the concentration is very low, oi the order of about one ounce per gallon or less.
  • the higher the concentration of free sodium cyanide the easier it is to get good color brass deposits, but unfortunately the einciency of metal deposition decreases rapidly with increase in free cyanide concentration, and this eiiect is magniied with increase in cathode current density.
  • the eiiciency of metal deposition is commonly referred to as cathode metal current efliciency.
  • Another suggested remedy is to provide two or three times as much anode surface as cathode so that the anode current density will of necessity be one-half or one-third that of the cathode. This is all very Well on paper, but in practice it is often impossible to meet these conditions.
  • the continuous plating of strip steel for example, when a continuous strip of steel moves over or between anode beds it is practically impossible to deviate very far from a 1:1 anode and cathode surface ratio.
  • Our new bath formulation based on a radically new concept of composition and operation.
  • a typical bath formulation, with preferred ranges and practical operating limits would be:
  • our preferred bath formulation may be prepared by dissolving in water the following chemicals in the order named:
  • the solution may also be prepared from a dry mix instead of dissolving ingredients successively as we have just explained.
  • the dry mix may consist of ingredients in the following proportions: 14.5 ounces sodium cyanide, l2 ounces copper cyanide, 8 ounces sodium hydroxide and 0.7 ounce zinc oxide.
  • An equivalent dry mix can be made by mixing the following ingredients in the proportions shown:
  • the preferred composition bath can then be made ing, or treatment with 0.05 oz./gal. of sodium sulde followed by several hours standing then charcoal treatment and filtration.
  • Such purification treatments are highly recommended because of the presence of impurities in commercial copper cyanide, zinc cyanide and lsine oxide.
  • the molal ratio of NaCN to CuCN is essentially 2:1, no NaCN being required for the zinc content, which is preferably in the form of sodium zincate (Zinc oxide dissolved in sodium hydroxide).
  • the caustic soda or sodium hydroxide concentration is relatively very high-several ounces per gallon instead of around one or less, or none.
  • the concentration of sodium hydroxide is not significant within the range of about 6-10 ounces per gallon. These relatively high concentrations are very desirable from the standpoint of providing high bath conductivity and high electrode eiciencies.
  • the copper-zinc ratio is exceptionally high, normally of the order of around :1 instead of around 3:1 as in present day commercial baths.
  • the principal control is the zinc concentration in the bath. ln practical operation this factor holds surprisingly constant. This is because the deposit composition holds relatively constant over a wide range of operating conditions, remaining usually within the approximate range of 'l5-80% Cu, the cathode metal current efliciency remains high over a wide range of operating conditions, and the anodes do not polarize at anode current densities below 'I0-100 amperes per square foot, depending on bath composition and temperature. Thus, by holding the average anode composition essentially the same as the deposit composition, that is of copper content between 'l5-80%, the bath composition is automatically kept relatively constant. Thus, the absence of anode polarization permits anode and cathode eiliciencies to approach equality.
  • the bath then acts as a relatively constant composition carrier of metal. Agitation helps maintain bath equilibrium, as does movement of the cathode, as in continuous steel strip plating for example. 1f the zinc concentration of the bath wanders, it may be adjusted by adding anodes higher or lower in cinc content as required. Variation, if any, is at such a slow rate that routine control analysis of either bath or deposit ⁇ /vill provide information regarding trends that can be used as a basis for such adjustments as may be found necessary.
  • the bath operates best at around 185 F. or through a range of 16E-200 F.
  • the higher operating temperatures are accompanied by high erliciences, high bath conductivity, less anode polarization, and wider permissible operating limits in zinc concentration.
  • the bath temperature is raised from F. to 200 F'., a gradual improvement in uniformity of operating conditions and deposit appearance and composition under variations in current density are noted, and the rate of these improvements is accelerated with rise in temperature.
  • the practical operating temperature may be selected to best suit the conditions encountered in any installation.
  • Fig. 1 represents the variation of deposit coinposition with cathode current density at tempel'- atures between 150 F. and 200 F.
  • the curves in this graph are based on a bath composition as follows; 14.5 ounces sodium cyanide, l2 ounces copper cyanide, 0.7 ounce Zinc oxide, 8.0 ounces sodium hydroxide, excess sodium cyanide 0.5 to 1.2 ounces per gallon.
  • the two curves in Fig. 1 are plotted for bath temperatures of 200 F. and 150 F., respectively, the upper curve being for the higher temperature.
  • the curves show that between 25 and 150 amperes per square foot cathode current density and between 15G-200 F. the cathode composition averages around 50% Cu, varying only from about 'Z5-83% Cu.
  • Fig. 2 depicts the relationships between cathode current density and cathode metal current eiTlciency at various temperatures. It shows that between -200o F. and between 20-120 amperes per square foot cathode current density, the cathode metal current eiiiciency averages better than 90%, varying between about 'T8-98%. It is particularly noteworthy that high cathode metal current eiciency is maintained at high current densities and high bath temperatures, i. e., it is above 90% at 10.0 amperes per square foot at bath temperatures above 180 F. rlhis is particularly important in providing rapid plating rates and maintaining constancy of bath composition. It will be noted that the line representing relationships at 150 F.
  • Fig. 3 represents the relationship between excess sodium cyanide (over a 2:1 ratio of NaCN/CuCN), and cathode metal current efiiciency at various cathode current densities and at 165 F.
  • Fig. 3 is based on a bath composition of copper cyanide 12 ounces per gallon, zinc oxide 0.7 ounce per gallon, sodium hydroxide 8 ounces per gallon, with the excess sodium cyanide being varied as shown by the curves.
  • the curves are plotted for four different cathode current densities 27, 57, 86 and 120 amperes per square foot respectively, the uppermost curve being for the lowest current density.
  • Fig. 3 represents the relationship between excess sodium cyanide (over a 2:1 ratio of NaCN/CuCN), and cathode metal current efiiciency at various cathode current densities and at 165 F.
  • Fig. 3 is based on a bath composition of copper cyanide 12 ounces per gallon, zinc oxide
  • Fig. 4 consists of two curves bounding an area showing the relationship between percentage copper in the deposit and excess sodium cyanide in ounces per gallon in the bath over a range of zinc concentrations of 0.5-1.0 ounce per gallon of zinc oxide at 165 F., with the bath composition as follows; 12 ounces per gallon of sodium cyanide, 8 ounces per gallon of sodium hydroxide, 0.5 to 1.0 ounce per gallon of zinc oxide, utilizing a cathode current density of 120 amperes per square foot.
  • the cross-hatched area between the upper and lower curves falling within the range of Gil-85% copper in the deposit represents the good color range.
  • Fig. a emphasizes the wide range of bath composition over which yellow brass deposits f satisfactory color and composition can be obtained.
  • Fig. consists of curves at four different temperatures, 150 F., 165 F., 180 F. and 200 F.,
  • Figs. 1 and 5 emphasize the outstanding features of our invention, particularly the fact that it provides relatively high concentration baths that operate at high temperatures, high current densities, at high eiciencies and without anode polarization under these conditions.
  • Our new bath formulation produces yellow brass deposits of good color and relatively constant composition under a wide variety of operating conditions, and maintains itself well within optimum operational limits with a minimum of control.
  • our new bath is a high speed plating bath, comparable in operating speed, efficiency and econ- @my with modern baths for plating other common metals such as copper, nickel, cadmium. zinc, tin, etc.
  • Our new bath for the first time, puts brass plating on a par with these other metals commercially.
  • alkali metal is used in the claims to signify either or both of the common alkali metals sodium and potassium.
  • a yellow brass plating bath comprising in aqueous solution, sodium cyanide, copper cyanide, sodium hydroxide and a cyanide soluble rinc compound, the sodium hydroxide being present in concentration exceeding 3 ozs. per gallon and the zinc being maintained in low concentration, such that the ratio of copper to zinc in solution lies between 35:1 and 10:1.
  • a yellow brass plating bath comprising in aqueous solution, sodium cyanide, copper cyanide, sodium hydroxide and a cyanide soluble zinc compound, the sodium hydroxide being present in concentration exceeding 3 ounces per gallon and the zinc being maintained in low concentration, such that the ratio of copper to zinc solution is approximately :1.
  • a yellow brass plating bath comprising in aqueous solution approximately 9 to 22 ounces per gallon sodium cyanide, 8 to 16 ounces per gallon copper cyanide, 3 to 16 ounces per gallon sodium hydroxide, 0.2 to 1.4 ounces per gallon zinc oxide.
  • a yellow brass plating bath comprising in aqueous solution approximately 12 to 18 ounces per gallon sodium cyanide, 10 to 14 ounces per gallon copper cyanide, 6 to l0 ounces per gallon sodium hydroxide, 0.4 to 1.2 ounces per gallon zinc oxide.
  • a yellow brass plating bath comprising in aqueous solution approximately 14.5 ounces per gallon of sodium cyanide, 12 ounces per gallon of copper cyanide, 8 ounces per gallon sodium hydroxide, 0.7 ounce per gallon zinc oxide.
  • a process for the electrodeposition of yel- 10W brass comprising depositing brass 10 from an aqueous solution containing sodium cyanide, copper cyanide, sodium hydroxide and a cyanide soluble zinc compound, the sodium hydroxide being present in concentration exceeding 3 ozs. per gallon and the Zinc being maintained in low concentration, such that the ratio of copper to zinc in solution lies between 35:1 and 10:1.
  • step 7 comprising depositing brass from an aqueous solution containing sodium cyanide, copper cyanide, sodium hydroxide and a cyanide soluble zinc compound, the sodium hydroxide being present in concentration exceeding 3 ounces per gallon and the zinc being maintained in low concentration, such that the ratio of copper to zinc in solution is approximately 15:1.
  • a process for the electrodeposition of yellow brass comprising depositing brass from an aqueous solution containing approximately 12 to 18 ounces per gallon sodium cyanide, l0 to 14 ounces per gallon copper cyanide, 6 to 10 ounces per gallon sodium hydroxide, 0.4 to 1.2 ounces per gallon zinc oxide and maintaining the solution at a temperature between approximately 150 F. and 200 F.
  • a dry mix composition which, when dissolved in water to yield 1 gallon of solution, may be used to form a yellow brass plating bath, the proportions of ingredients in said composition being approximately within the ranges of 9 to 22 ounces of sodium cyanide, 8 to 16 ounces of copper cyanide, 3 to 16 ounces of sodium hydroxide, 0.2 to 1.4 ounces of zinc oxide per gallon of resultant solution.
  • a dry mix composition which, when dissolved in water to yield 1 gallon of solution, may
  • proportions of ingredients in said composition being approximately Within the ranges of 12 to 18 ounces of sodium cyanide, 10 to 14 ounces of copper cyanide, 6 to 10 ounces of sodium hydroxide, 0.4 to 1.2 ounces of zinc oxide per gallon of resultant solution.
  • a dry mix composition which, when dissolved in water to yield 1 gallon of solution, may be used to form a yellow brass plating bath, the proportions of ingredients in said composition being approximately within the ranges of 14.5 ounces oi sodium cyanide, 12 ounces of copper cyanide, 8 ounces of sodium hydroxide, 0.7 ounces of zinc oxide per gallon of resultant solution.
  • a dry mix composition which, when dissolved in water in proportion to give approximately 35 ounces of dry mix composition per gallon of resultant solution, may be used to form a yellow brass plating bath, the ingredients in 1l said composition being approximately in the proportions of sodium cyanide 40%, copper cyanide 34%, Zinc cyanide 3%, sodium hydroxide 23%.
  • a dry mix composition which may be dissolved in water in the approximate proportion of 27 ounces of dry mix per gallon of resultant solution along with sodium hydroxide in the proportion of 8 ounces per gallon of resultant solution to produce a yellow brass plating bath, said dry mix comprising a mixture of chemicals in the following approximate proportions: sodium cyanide 52.0%, copper cyanide 44.5%, zinc cyanide 3.5%.
  • a process for the electro-deposition of yellow brass comprising depositing brass from an aqueous solution containing alkali metal and copper cyanides, alkali metal hydroxide in concentration exceeding 3 ounces per gallon and a bath soluble zinc compound, maintaining the zinc in sufiiciently low concentration so that the ratio of copper to Zinc in solution lies between 35-1 and 10-1, heating the solution sufficiently to maintain its temperature between about 150 F. and 200 F., and maintaining the cathode current density between about 25 and 150 amperes per square foot.
  • a process for the electro-deposition oi yellow brass the steps substantially as herein set forth comprising depositing brass from an aqueous solution containing alkali metal and copper cyanides, alkali metal hydroxide in concentration exceeding 3 ounces per gallon and a bath soluble zinc compound, maintaining the zinc in sufficiently low concentration so that the ratio of copper to Zinc in solution lies between 35-1 and 10-1, heating the solution sufficiently to maintain its temperature between about 150 F. and 200 F., and maintaining the cathode current density between about 25 and 150 amperes per square foot, while operating with anode current densities between 25 and 100 amperes per square foot.
  • a process for the electro-deposition of yellow brass comprising depositing brass from an aqueous solution containing alkali metal and copper cyanides, alkali metal hydroxide in concentration exceeding 3 ounces per gallon and a bath soluble Zinc compound, maintaining the zinc in sufficiently low concentration so that the ratio of copper to zinc in solution is approximately 15-1, heating the solution sufficiently to maintain its temperature between about F. and 200 F., and maintaining the cathode current density between about 25 and 150 amperes per square foot.
  • steps substantially as herein set forth comprising depositing brass from an aqueous solution containing alkali metal and copper cyanides, alkali metal hydroxide in concentration exceeding 3 ounces per gallon and a bath soluble zinc compound, maintaining the Zinc in sufficiently low concentration so that the ratio of copper to zinc in solution is approximately 15-1, heating the solution suiiiciently to maintain its temperature between about 150 F. and 200 F., and maintaining the cathode current density between about 25 and 150 amperes per square foot, while operating with anode current densities between 25 and 100 amperes per square foot.

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  • Chemical & Material Sciences (AREA)
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  • Chemical Kinetics & Catalysis (AREA)
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  • Organic Chemistry (AREA)
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US207704A 1951-01-25 1951-01-25 Brass plating Expired - Lifetime US2684937A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3930965A (en) * 1974-03-18 1976-01-06 Mcgean Chemical Company, Inc. Zinc-copper alloy electroplating baths

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1366316A (en) * 1971-01-25 1974-09-11 Rank Xerox Ltd Method and apparatus for electroforming

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2181773A (en) * 1937-01-12 1939-11-28 Du Pont Brass plating

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2181773A (en) * 1937-01-12 1939-11-28 Du Pont Brass plating

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3930965A (en) * 1974-03-18 1976-01-06 Mcgean Chemical Company, Inc. Zinc-copper alloy electroplating baths

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