US3753873A

US3753873A - Process for the electrodeposition of a colored nickel-tin alloy coating

Info

Publication number: US3753873A
Application number: US00087604A
Authority: US
Inventors: S Geffon; W Schwartz; L Cates
Original assignee: ENEQUIST CHEMICAL CO Inc
Current assignee: ENEQUIST CHEMICAL CO Inc; ENEQUIST CHEMICAL CO INC US
Priority date: 1970-11-06
Filing date: 1970-11-06
Publication date: 1973-08-21
Anticipated expiration: 1990-08-21

Abstract

ELECTROPLATING APPARATUS FOR PLATING AN ARTICLE IMMERSED IN AN ELECTROLYTIC BATH BY APPLYING A POSITIVE DC VOLTAGE TO AN ANODE IMMERSED IN THE ELECTRLYTIC BATH AND BY APPLYING A NEGIVE DC VOLTAGE TO THE ARTICLE, COMPRISES AN ELECTROLYTIC BATH CONTAINING AN AQUEOUS SOLUTION OF NICKEL IN A RANGE OF 5 TO 100 GGRAMS LITER AND PROVIDED BY ONE OF A GROUP CONSISTING OF NICKEL SULFATE, NICKEL SULFAMATE, NICKEL FLUOBORATE, NICKEEL CHLORIDE, NICKEL CARBONATE, NICKEL CYANIDE, NICKEL ACETATE, NICKEL ETHYLENE DIAMINE TETRA ACETIC ACID, NICKEL OXIDE AND NICKEL TARTATE, TIN IN A RANGE OF 5 TO 100 GRAMS PER LITER AND PROVIDED BY ONE OF A GROUP CONSISTING OF SODIUM STANATE, POTAS-

SIUM STANATE, STANNIC CHLORIDE, STANNOUS CHLORIDE, STANNIC SULFATE, STANNOUS SULFATE, STANNOIC FLUOBORATE AND STANNOUS FLUOBORATE, ALKALI CYANIDE IN A RANGE OF 5 TO 200 GRAMS PER LITER PROVIDED BY ONE OF A GROUP CONSISTIN OF SO DIUM CYANIDE AND POTASSIUM CYANIDE, AND AT LEAST ONE OF A GROUP CONSISTING OF COPPER, ZINC MOLYBDENUM, SELENIUM ARSENIC AN SULFUR IN A RANGE OF 0 TO 20 GRAMS PER LITER.

Description

L. H. CATES ET AL FROCESS FOR THE ELECTRODEPOSITLON OI" A COLORED NICKEL-TIN ALLOY COATING Original Filed Oct. 6, 1967 VOLTA/ffm? 22 D O THEIR ATTORNEY United States Patent O Int. Cl. C23f 5/38 U.S. Cl. 204-43 1 Claim ABSTRACT F THE DISCLOSURE Electroplating apparatus for plating an article irnmersed in an electrolytic bath by applying a positive DC voltage to an anode immersed in the electrolytic bath and by applying a negative DC voltage to the article, comprises an electrolytic bath containing an aqueous solution of nickel in a range of to 100 grams per liter and provided by one of a group consisting of nickel sulfate, nickel sulfamate, nickel uoborate, nickel chloride, nickel carbonate, nickel cyanide, nickel acetate, nickel ethylene diamine tetra acetic acid, nickel oxide and nickel tartrate, tin in a range of 5 to 100 grams per liter and provided by one of a group consisting of sodium stannate, potassium stannate, stannic chloride, stannous chloride, stannic sulfate, stannous sulfate, stannic uoborate and stannous tluoborate, alkali cyanide in a range of 5 to 200 grams per liter provided by one of a group consisting of sodium cyanide and potassium cyanide, and at least one of a group consisting of copper, zinc, molybdenum, selenium, arsenic and sulfur in a range of 0 to 2O grams per liter.

BACKGROUND OF THE INVENTION (A) Field of the invention This is a continuation of application Ser. No. 621,002, tiled Oct. 30, 1967, now abandoned, and relates to an alloy cyanide electroplating process. More particularly, the invention relates to an alkaline alloy cyanide electroplating process which produces a variety of colored deposits.

(B) Description of the prior art The electroplating of metals is a well known art, as evidenced by the McGraw-Hill Encyclopedia of Science and Technology, McGraw-Hill Book Company, Inc., vol. 4, 1960, pp. 528 to 535; Principles of Electroplating and Electroforming, by W. Blum and G. B. Hogaboom, third edition, 1949; Protective Coatings for Metals, by R. M. Burns and W. W. Bradley, third edition, A.C.S. Monograph 129, 1959; Electroplating Engineering Handbook, A. K. Graham, editor, 1955; Modern Electroplating, A. G. Gray, editor, 1953.

In electroplating, the cleaned article to be plated is connected as the cathode in a solution known as the electrolyte. Direct current is introduced through the anode, which usually consists of the metal to be deposited. Metal dissolves from the anode and deposits on the cathode. Under ideal conditions, the same weight of metal dissolves from the anode as is deposited on the cathode, and the overall composition of the bath remains constant. These conditions are never fully realized, and the bath composition changes and must be adjusted at intervals. If the anode eiciency exceeds the cathode eiliciency, the metal content of the solution increases and the pH of the solution increases, and vice versa.

The constituents of a plating bath include a soluble compound or compounds of the metal or metals to be deposited, together with other substances added in fairly ice large amounts to increase electrical conductivity, throwing power, or some other property. Small concentrations of certain addition agents or brighteners, are employed to yield smoother or brighter deposits. Acid plating baths are cheaper to prepare and maintain, but the alkaline baths, which consist principally of complex cyanides, have better throwing power and yield finer-grained deposits.

The throwing power represents the ability of a solution to produce coatings of uniform thickness on surfaces where the distances between various portions of the surface andthe anode differ.

The weight of metal deposited depends on the quantity of electricity, in coulombs or ampere hours, that is passed to the cathode. The average thickness of the coating depends upon the current density, expressed in amperes per square decimeter or per square foot, and the period of deposition. The uniformity of the coating thickness depends upon the shape of the of the article, its position with respect to the anodes and the throwing power of the solution.

The current density is an important factor in plating. To produce a given current density, it is necessary to apply a suitable potential, expressed in volts. The total bath potential includes: the decomposition potential; the IR drop, which depends upon the resistivity of the bath and the distance between the anodes and cathodes; the cathode polarization; and the anode polarization at the prevailing current densities.

Nickel is extensively applied in electroplating. It is more resistant to atmospheric corrosion than other metals except nobel metals such as gold, and is fairly hard and wear-resistant. Nickel is passive in air, and hence if nickel coatings could be made impervious initially they should remain so in service.

Most nickel plating is done in baths containing nickel sulfate, nickel chloride and boric acid. Organic and inorganic additions are made to produce bright deposits. By control of the bath composition, temperature and current density, it is possible to vary widely the physical properties of the nickel deposits.

To deposit adherent coatings it is necessary to have the surface of the basis metal clean, that is, free from all foreign substances such as grease, and compounds such as oxides or suldes. The two essential steps are cleaning and pickling.

Most plating operations are conducted with direct current at potentials of 6 to 12 volts. The plating tanks are usually made of steel, which requires no lining for alkaline solutions.

Small objects are plated in barrels, usually hexagonal prisms, with perforated plastic sides, that rotate on a horizontal axis in a tank containing the plating solution and anodes. The articles contact cathodic connections as they tumble during rotation of the barrel.

SUMMARY OF THE INVENTION The principal object of the present invention is to provide a new and improved colored alloy cyanide electroplating process. The electroplating process of the present invention provides an adherent coating having good corrosion resistance, excellent shelf-life and good wear and abrasion characteristics. The electroplating process of the present invention provides a deposit which may be black, blue-black, blue, brown or grey nish on all basis materials which accept an electroplate. The deposit provided by the electroplating process of the present invention is in any of a selected variety of nishes and retains the character of the surface plated. The deposit provided by the electroplating process of the present invention is uniform, adherent and easily controlled, and is produced in a single step. The electroplating process of the present invention plates an additional coating of metal, rather than removing metal, so that it provides an appreciable saving in the coloring of silver. The electroplating process ofthe present invention is applicable to barrel plating.

In accordance with the present invention, in electroplating apparatus for plating an article immersed in an electrolytic bath by applying a positive DC voltage to an anode immersed in the electrolytic bath and by applying a negative DC voltage to the article, an electrolytic bath comprises an aqueous alkaline cyanide solution of nickel in a range of 5 to 100 grams per liter, tin in a range of 5 to 100 grams per liter and alkali cyanide in a range of 5 to 200 grams per liter. The electrolytic bath further comprises at least one of a group comprising copper, zinc, molybdenum, selenium, arsenic and sulfur in a range of to 20 grams per liter. The nickel is provided by one of a group comprising nickel sulfate, nickel sulfamate, nickel fluoborate, nickel chloride, nickel carbonate, nickel cyanide, nickel acetate, nickel ethylene diamine tetra acetic acid, nickel oxide and nickel tartrate. The tin is provided by one of a group comprising sodium stannate, potassium stannate, stannic chloride, stannous chloride, stannic sulfate, stannous sulfate, stannic iluoborate and stannous uoborate. The alkali cyanide is provided by one of a group comprising sodium cyanide and potassium cyanide. The zinc, molybdenum, selenium, and etc., is provided from any of the water soluble salts of these elements.

In accordance with the present invention, an electroplating process for plating an article comprises immersing the article in an electrolytic bath comprising an aqueous alkaline cyanide solution of the aforedescribed composition. A positive DC voltage is applied to an anode immersed in the electrolytic bath. A negative DC voltage is applied to the article. The electrolytic bath is maintained at a determined temperature and a determined current density is provided for a determined period of time. The electrolytic bath is maintained at a temperature in a range of 110 to 190 P. and preferably in a range of 140 to 170 F. The current density is in a range of 2 to 250 amperes per square foot and preferably in a range of 5 to 100 amperes per square foot.

BRIEF DESCRIPTION OF 'IHE DRAWING In order that the present invention may be readily carried into effect, it will now be described with reference to the accompanying drawing, wherein the single figure is a top View, partly in section, of electroplating apparatus which may accomplish the electroplating process of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Any suitable electroplating apparatus known in the art may be utilized to accomplish the electroplating process of the present invention. Suitable electroplating apparatus may comprise, for example, that shown in the gure. The tank 11 may comprise steel, stainless steel or rubber-lined steel and houses the electrolyte or electrolytic bath 12, the anodes 13A and 13B immersed in the electrolyte and the cathodes 14 immersed in the electrolyte substantially half way between the anodes 13A and 13B.

The anodes 13A and 13B may be one or more in number and the cathodes 1'4 may be one or more in number. The anodes 13A and 13B may comprise steel, stainless steel, graphite, nickel or other suitable electrically conductive material, or the tank 11 may be made anodic.

A positive potential is applied to the anodes 13A via a lead 15A connected from the positive polarity terminal of a source 16 of DC voltage of suitable magnitude such as, for example, 6 to 12 volts, and a positive potential is applied to the anodes 13B via a lead 15B connected from said positive polarity terminal via the lead 15A. The DC voltage source 16 may comprise any suitable source of DC voltage such as, for example, a battery or transformer, rectifier circuit connected to an AC power supply line. A negative potential is applied from the DC source 16 to the cathodes 14 via a lead 17, a variable resistor or rheostat 18, an ammeter 19 and a lead 21. A voltmeter 22. is connected across the series circuit arrangement of the DC voltage source 16, the variable resistor 18 and the ammeter 19.

In accordance with the present invention, the electrolyte or electrolytic bath 12 is an aqueous alkaline cyanide solution comprising 5 to 100 grams per liter of nickel, 5 to 100 grams per liter of tin and 5 to 200 grams per liter of alkali cyanide. Other materials such as, for example, copper, zinc, molybdenum, selenium, arsenic or sulfur, may be added to the solution in amounts ranging from 0 to 20 grams per liter. Although the additional materials do not effect the color characteristics of the produced plated coating, they may modify the range, tone and uniformity of said coating.

The nickel is provided by any suitable nickel cornpound such as, for example, nickel sulfate, nickel sulfamate, nickel iduoborate, nickel chloride, nickel carbonate, nickel cyanide, nickel acetate, nickel ethylene diamine tetra acetic acid, nickel oxide, nickel tartrate, and so forth. The tin is provided by any suitable tin compound such as, for example, sodium stannate, potassium stannate, stannic chloride, stannous chloride, stannic sulfate, stannous sulfate, stannic uoborate, stannous uoborate, and so forth. The alkali cyanide is provided by any suitable alkali cyanide compound such as, for example, sodium cyanide, potassium cyanide, and so forth.

The electrical conductivity of the electrolytic bath 12 may be increased by the addition of carbonates, sulfates, chlorides, tartrates, acetates, borates, and so on. These materials are not essential to the basic operation of the process. Surface active materials, not essential to the basic operation of the process, may be added to the electrolytic bath to aid in rinsability.

The electrolytic bath 12 is maintained at a temperature in the range of to 190 F. and a current density in the range of 2 to 250 amperes per square foot. The preferred temperature range is to 170 F. and the preferred current density range is 5 to 100 amperes per square foot. The electrolytic bath 12 is heated by any suitable heating means such as, for example, steel heating coils, stainless steel thermopanels, steel immersion heaters or direct gas ltired heating apparatus. The electrolytic bath 12 may thus be heated, for example, by

immersion heaters

23A and 23B.

When the electroplating apparatus is 'operated at an electrolytic bath temperature of from 140 to 165 F. and a current density of from 5 to 60 amperes per square foot, a uniform grey or black coating is produced on any electrically conductive material connected as the cathode within 45 seconds. If the plating time is increased, thevthickness of the coating is increased accordingly. The plating time is preferably in the range of 45 to 120 seconds.

If the electroplating process of the present invention is undertaken at a slow plating speed, or low temperature and low current density for a short plating time, a brownish colored coating is produced. The initial brownish color is darkened to fblue or blue-black when the plating time is lengthened.

Brownish or bluish-black coatings are produced by varying the composition of the electrolytic bath 12. Brownish and bluish coatings are produced at lower concentrations of metal and/ or higher concentrations of alkali cyanide.

The color of the coating is also influenced by the brightness of the substrate or article to be plated. If the substrate is dull, the coating is grey or greyish-black. If the substrate is bright, the coating appears black. The limits `of the composition of the electrolytic bath are broad and the coating is a uniform grey, grey-black or black over wide temperature and current density ranges.

The electrolyte may be prepared as a solid composition of the proper chemical formulation and the electrolytic bath 12 may be prepared from the solid composition by adding water in a proper amount to dissolve said solid composition. The electrolyte may also be prepared as a concentrated liquid solution of the proper chemical formulation and the electrolytic bath 12 may be prepared from the concentrated liquid solution fby adding waterwin a proper amount. The electrolytic bath 12 may, ofcourse, be prepared by adding the proper chemicals in the proper concentrations to water.

While the invention has been described by means of a specific example and in a specic embodiment, we do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention. l

What we claim is:

1. A process for electrodepositing a selected black, blueblack, blue, brown or grey nish on a metal article, comprising the steps of immersing the article in an electrolytic bath comprising an aqueous alkaline cyanide solution of nickel of a group consisting of nickel sulfate, nickel sulfamate, nickel uoborate, nickel chloride, nickel carbonate, nickel cyanide, nickel acetate, nickel ethylene diamine tetra acetic acid, nickel oxide and nickel tartrate in a range of 5 to 100 grams per liters, tin of a a 6 group consisting of sodium stannate, potassium stannate, stannic chloride, stannous chloride, stannic sulfate, stannous sulfate, stannic fluoborate and stannous flulborate in a range of 5 to 100 grams per liter and alkali cyanide of a group consisting of sodium cyanide and potassium cyanide in a range of 5 to 200 grams per liter; applying a positive DC voltage to an anode immersed in the electrolytic bath; applying a negative DC voltage to a metal article; and maintaining the electrolytic bath at a determined temperature in a range of to 170 F. and providing a determined current density in a range of 5 to 100 amperes per square foot for a determined period of time.

References Cited Electrodeposition of Tin Alloys From Alkaline Stannate Baths, by Monk & Ellingham, Trans. of the Faraday Soc., No. 174, vol. 31, part 10, October 1935, pp. 1462- 1466.

Handbook of Chemistry and Physics, 32nd ed., The Chemical Rubber Publishing Oo., 1950, pp. 546-547.

JOHN H. MACK, Primary 'Examiner R. L. ANDREWS, Assistant Examiner