US2061592A - Composition for and method of metal electroplating - Google Patents

Description

F. R. RAPIDS Nov. 24, 1936.

COMPOSITION FOR AND METHOD OF METAL ELECTROPLATING Filed March 2J.,

Patented Nov. 24, 1936 UNITED STATES PATENT OFFICE Felix R. Rapids, Chicago,v lll.

Application vMarch 21,

8 Claims.

This invention relates to a composition for and to amethod oi effecting the electrodeposition of metals. More particularly, the invention relates to a method whereby the electrodeposition of metals may be carried out as a brushing or similar operation without the use of stationary baths of an electrolyte.

This invention has for one of its objects to provide an aqueous solution of an electrolyte of suitable viscosity to adapt it for application by a brushing, wiping or similar operation to the work that is to be coated.

Another object of this invention is to provide a method whereby such a composition may be applied to the work by a brushing, wiping, or similar operation to effect the electrodeposition of a metal from the electrolyte, while simultaneously replenishing the metal content of the electrolyte by the passage of an electric current through an anode of the metal'.

A further object of this invention is to provide a method whereby an electrodeposition of a metal may be performed upon work outside of an electrolytic bath, so that stationary articles and structural elements, or the like, may be coated with a metal while in placeand without removal to a plating bath.

Other and further important objects of this invention will be apparent from the disclosures in the specification and the accompanying drawing.

This invention (in a preferred form) is illustrated in the drawing and hereinafter more fully described.

On the drawing:

Figure l is a longitudinal sectional view of a device of my invention, with parts in elevation and parts shown diagrammatically, illustrating the principles of this invention.

Figure 2 is an end elevational fragmentary view of the device with a container for the electrolyte composition, partly broken away and in section.

Figure 3 is a top plan view of the device, showing the method of application of the electrolyte composition to work to be metal coated.

As shown on the drawing:

The reference numeral I indicates generally a `brush of my invention for applying an electrolyte composition II to a piece of work I2. Although I have illustrated as an embodiment of my invention a special type of brush, it will be understood that various types of applicators, by means of which a brushing, wiping or coating operation may be carried out, may be used.

The brush IIl comprises a handle I3 of insulating material, such as wood, molded plastic, rubber, or the like, a brush proper of bristles I4, and a metal ierrule I encasing the upper ends of the bristles I4 and serving to attach the bristles to the handle I3. Said metal ferrule I5 is secured 1935, serial No. 12,210

(ci. :m4-1) to the handle I3 by suitable means, such as rivets I6. Said rivets I6 also serve to secure to the ferrule l5 a spring member I1 bowed outwardly from the handle I3 and carrying at its free extremity a contact button I8 backed by a thumb piece I9.

A contact member is secured in one face of the handle I3 in juxtaposition to the contact member I8 and is connected by means of a wire 2|, running through a hollow portion 22 lengthwise of the handle, to a source of current. such as a battery 23. A dry cell battery of one or more cells may suitably be used as a source of current, although for heavier work, it would probably be desirable to use a wet cell battery. The wire 2| is connected to the positive or anode side of the battery 23 and a wire 2Ia serves to connect the negative side of the battery to the work I2. As shown, the wire 2Ia is connected to a contact post 24 forming a part of a block 25 or the like which 20 within a suitable receptacle 26, provided with anv opening 21 through which the brush I4 may be inserted for dipping into the electrolyte II.

` The electrolyte may be an aqueous solution of any ionizable compound of the metal to be electrodeposited. In order to facilitate the application of ,the electrolyte by a brushing or wiping operation, it is preferable to provide a rather viscous solution of the electrolyte that will tend to adhere to the bristles of the brush I4 and provide a continuous path for the electric current between the ferrule I5 and the work I2. For this purpose, various thickening agents, such as starches, or mixtures of starches and proteins, gums, carbohydrates, sugars, petroleum jellies, and the like may be used. For instance, cornstarch may be incorporated into the electrolyte in an amount suflicientl to give the desired viscosity, 6% by weight or thereabouts of cornstarch having been found satisfactory for this purpose. However, from 21/2% upwards of starch, or an equivalent thickening agent, may be used, with about 12% of starch as an average. Preservatives, such as small percentages of nickel chloride, formaldehyde and the like may be added to prevent fermentation of the starch or other organic thickening agent.

Any viscosity of the electrolyte is suftlcient that will cause the electrolyte to adhere to the brushing element or applicator and work and thereby forms and maintains a continuous path for the electric current. Conslstencies up to a semi-solid or jell-like consistency maybe employed. The lower `limit of a suitable viscosity appears to be about 100 secs. at 62 F., Saybolt universal. This viscosity is more than twice that of usual plating bath electrolytes. Preferably a viscosity will be employed such that the electrolyte will not spread objectionably beyond the surface to be plated, but will be confined to the surfaces undergoing treatment.

The electrolyte itself may, in general, be any water, alkali or acid soluble compound of the metal that is to be plated. In general, any metal can be plated in accordance with my method, such as zinc, nickel, copper, lead, tin, cadmium, iron, chromium, or alloys of these or other metals. The concentration of the metal salt in the electrolyte may be varied from a few percent up to and above saturation.

The following specific examples are given of suitable electrolyte compositions, the percentages being expressed by weight:

Example 1.-Nickel plating formulae Per cent A. Nickel sulphate 22.64 Ammonium chloride '1.54 Sodium hydroxide 1.98 Starch 7.54 Water 60.30

B. Nickel chloride 26.66 Ammonium chloride 6.66 Starch 13:33 Water 53.35

C. Nickel sulphate 29.55 Nickel chloride 15.45 Ammonium chloride 2.17 Boric acid 1.00 Starch 8.90 Water 42.93

Example 2.-Znc plating formulae Per cent A. Zinc chloride 18.45 Aluminum chloride 2.45 Sodium chloride 14.72 Acetic ac'id 3.65 Starch 9.20 Gum arabic 7.36 Water 44.17

B. Zinc chloride 22.41 Aluminum chloride 2.95 Ammonium chloride 4.48 Sodium chloride 8.96 Starch 8.96 Water 52.24 C. Zinc chloride 19.35 Nickel chloride 0.38 Aluminum chloride 3.22 Sodium chloride 9.67 Starch 9.71 Water 57.67 Example 3.-Cadmium platina formulae Per cent A. Cadmium carbonate 11.14 Nickel chloride 1.02 Sodium hydroxide 2.77 Ammonium chloride 22.22 Sodium chloride 2.77 Starch 8.10 Glycerine 5.55 Water 46.43

B. Cadmium chloride 28.57 Nickel choride 0.90 Phosphoric acid 3.57 Sodium chloride 3.57 Starch 7.15 Water 56.24

Example 4.-Lead platina formulae Per cent A. Lead oxide (PbO) 13.11 Sodium hydroxide 25.22 Starch 6.55 Glycerine 2.67 Water- 52.45

B. Lead oxide (PbO) 17.64 Sodium chloride 5.82 Acetlc acid (36%) 47.20 Starch 5.82 Water 23.52

Example 5.-Irm platina formulae Per cent A. Ferrous chloride 27.58 Ammonium chloride 13.79 Oxalic acid 6.88 Sodium carbonate 3.44 Starch 6.88 Water 41.43

B. Ferrous chloride 14.54 Calcium chloride 18.06 Nickel chloride 2.00 Glycerine 1.96 Starch 14.54 Water 48.90

Example 6.Tin platina formulae Per cent A. Stannous chloride 9.52 *Chromic chloride 19.04 Starch 9.56 Gum arabic 4.76

Water 57.12

*Chromous chloride may be substituted for chromic chloride.

B. Stannous chloride 11.42 'Oxalic acid.;` 1.42 Phosphorlc acid 1.42 Starch 17.13

Water 68.61

*May be omitted.

Example 7.Copper platina formula Per cent Copper carbonate 2.49 Sodium cyanide 2.49 Sodium carbonate 1.24

Glycerine 2.49 Gum arabic 4.96

Starch 9.92 Water 76 41 'I'he foregoing formulae have been used successfully with voltages between 1.5 and 18 volts, current densitiesbetween 10 and400 amps. /sq. ft. and temperatures of between 40 and 180 F.

In the above formulae, many changes and substitutions may be made in the various ingredients, and some ingredients may be omitted, if desired. Sodium chloride, for instance, is added merely to give increased conductivity to the plating composition.

In Example 1C, the nickel chloride and ammonium chloride improve the qualities of the starch gel that is formed. Unless either a chloride or an alkali metal hydroxide is incorporated into the electrolyte composition, it is not generally possible to secure a satisfactory smooth gel-like quality in the composition.

In Example 3A. the ammonium chloride and sodium hydroxide function as aids in effecting the dissolution of the cadmium carbonate. In Example 3B, phosphoric acid acts as a brightener and cleanser. In Example 4B, the acetic acid serves to dissolve the lead oxide. Lead acetate could be used as the starting material, however.

Glycerine, or other hydroscopic substance, such as a water soluble glycol, glucose, dextrose, or other hygroscopic sugar, may be added to prevent the electrolyte from drying out.

In many instances, ingredients are added because they serve as brightening or cleansing agents, or because they bring about certain desirable results for some not clearly understood reason. Nickel serves as a brightening agent in formulae 3A and B. It is not necessary that the ingredients be wholly in solution in the aqueous composition, nor that any particular concentration, pH value or the like be used.

'I'he formulae given above indicate the latitude permitted in the choice of ingredients, concentrations, and the like. It should be understood, however, that any of the standard plating baths may be used with any suitable thickening agent for imparting the desired viscosity to the plating composition.

I have found that the voltage and current densities may be varied over a wider range than in the case of standard plating baths. This is probably due to the fact that higher concentrations of electrolytes are possible in my compositions. Consequently a faster rate of deposition can be realized.

The current density may be controlled by increasing or decreasing the amount of the Viscous electrolyte adhering to the brush, i. e. by controlling the cross sectional area of the conductor. The usual control devices, rheostats and like, may also be used.

Alloys of the various metals may be electrodeposited by suitable combinations of salts of the metals in the desired proportions. Alloys of nickel and iron may be plated in this way. Brass plating may be accomplished by using mixed cyanide salts of copper and zinc in the manner and proportions known to the art.

The electrolytes are preferably prepared by first dissolving the metallic salt in the water and then adding the starch, or other thickening agent, with stirring and heating. vIt is not necessary to apply heat, but if the mass is heated to boiling or thereabouts, the dispersion of the starch is facilitated.

Various cleansing agents may be incorporated into the electrolyte, such as abrasive agents like powdered pumice, or acids like hydrochloric. Insoluble materials can be kept in suspension because of the viscosity of the electrolyte. These cleansing agents serve to remove films or coatings of oxides, grease and the like from the work surface. However, where a bright, mirror-like surface is required, it will be found most satisfactory to start with a foundation surface that has already been prepared with the type of surface required, before carrying out the electroplating operation of this invention.

Another advantage of providing a relatively viscous electrolyte is that it eliminates, or reduces, the likelihood of spillage, leakage. etc., in shipment and during use.

In the plating operation, the metal forming the ferrule I5 constitutes an anode and may serve to supply metal to the electrolyte to replace the metal being electro deposited. Consequently, if zinc is to be electrodeposited, a zinc ferrule may be used, and if nickel, a nickel ferrule, and so on. As is well understood, the passage of an electrical current through the ferrule I5 and the electrolyte I I to the work I2 causes a deposition of the metal from the electrolyte II and a replenishing of the metallic ion by a dissolution of the metal of the ferrule I5 into the electrolyte.

It is not, however, necessary that the metal of the ferrule be the same as that to be electrodeposited, since the active electrolyte can always be replenished by repeated clippings of the brush or applicator into the electrolyte composition. Consequently, the anode may be lead, iron, tin, or any other suitable metal, regardless of the particular metal to be electrodeposited.

In carrying out the preferred method of my invention, the brush I 4 is dipped into the electrolyte II to a depth sufficient to provide a continuous film or coating of the electrolyte I I over the bristles I4 and into contact with the ferrule I5, as at 28. Because of the adherent or viscous nature of the electrolyte I I, a suicient quantity of the electrolyte will adhere to and remain on the brush proper I4 after the brush has been removed from the supply of electrolyte.

The brush I0 is then used in the usual manner for applying a paint or the like. Preferably, the surface to be plated is covered with a film or layer of the electrolyte first, before the current is applied. This makes for greater uniformity of results, since it gives the electrolyte time to thoroughly wet and cover the surface to be plated. While the electrolyte II is again being brushed over the surface of the work I2 (Fig. 3) contact is made manually between the contact points I8 and 20, so that a continuous flow of electricity passes through the circuit. From the positive side of the battery 23, this circuit includes the wire 2|, the spring member I'I, the ferrule I5, and the film or layer of electrolyte Il to the work I2. The 'negative side of the circuit includes the block 25 and the wire 2Ia.

The electrodeposition of the metal from this film 29 takes place simultaneously with the brushing action, if the current is on, so that by the time the entire surface of the work I2 has been gone over, a continuous film of the metal has also been electrodeposited on it. The thickness of the film will. of course, depend upon and may be controlled by controlling the length of time of contact during which the electrical circuit is closed, the current density, the concentration of the metallic ions in the electrolyte, the thickness of the layer of electrolyte applied, etc. The

brushing operation may be continued until the desired thickness of coating of the metal is obtained. At the finish of the plating step, the electrolyte composition may be wiped or washed off and the work surface washed.

The use of a fairly viscous electrolyte facilitates the electroplating operation in that it permits higher concentrations of the metallic salt than is usually possible in plating baths. There appear to be no critical limits of concentration, since plating can be successfully carried out using metal salt concentrations from as low as 1% or so up to the saturation point of the salt selected in the electrolyte composition.

Furthermore, the nature of my electrolyte seems to eliminate any difliculties arising from polarization. Whether this is due to absorption or adsorption of the hydrogen by the thickening agent, starch, or the like, has not been determined, but there appears to be some such action.

While it is not necessary in all cases to clean the surface of the work before applying the electrolyte, this is generally advisable. Any of the various well known methods for cleaning metal may be employed, as by scouring, pickling, sand blasting, or the like. The action of the bristles on the brush I4 also aids in providing a clean surface on the work to be coated. Similarly, where the work has an irregular surface, or a surface having relativelydeep contours. the application of the metal coating is facilitated by the flexibility of the bristles of the brush and the ability of the bristles to carry the electrolyte to all portions of the surface.

It will be understood that instead of having the battery separate from the brush, one or more dry cells may be attached to or secured in the handle of the brush to provide a self-contained unit. Instead of using bristles as the brushing agent, other fibers or metallic elements having a scrubbing, scouring or wiping action may be used. Wire bristles might, for instance, be employed.

A device such as has been described may likewise be used to strip a metal coating from a plated object. This can be accomplished merely by reversing the flow of the current and by using any electrolyte of suitable viscosity to complete the circuit between the work and the metal ferrule of the brush or applicator, In this case the metal ferrule I5 serves as thc cathode to receive the metal that is stripped from the work and carried by the flow of current into the electrolyte.

It is. of course, possible by a, simple galvanic action either to plate or strip by the use of a suitable electrolyte of my invention, without employing an electric current. In plating, a brush, spatula or trowel may be employed that is formed wholly or in part of a metal that is electronegative to the metal of the Work surface. Thus, if the work surface is iron or any melal below iron in the electromotive series, zinc or aluminum would preferably be used in the applicator, brush, spatula, trowel, or the like. If the electrolyte were nickel chloride, the action would be:

Per cent NHiCl 25 HCl 3-4 Starch 6 Balance water I am aware that many changes may be made and numerous details of construction may be varied through a wide range without departing from the principles of this invention, and I, therefore, do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

2. An electrolyte for use in the elcctrodeposltion of a metal, comprising an aqueous solution of jell-like consistency and containing an ionizable compound of the metal to be electrodeposited and starch but not over a few percent of a free acid by weight.

3. The method of electrodepositing a metal, which comprises applying to the work a coating of an aqueous solution of jell-like consistency and containing an ionizable compound of the metal to be electrodeposited and starch but not over a few percent of a free acid by weight, and passing an electric current through said solution to said work.

4. An electrolyte composition for use in the electroplating of metals, comprising an aqueous solution of an ionizable compound of the metal to be plated out and suicient starch to render said solution of jell-like consistency.

5. An electrolyte composition for use as such with a brushing element in the electrodeposition of a metal, which comprises an aqueous solution of such high viscosity as to adhere well to the brushing element as a. jell-like mass and containing dissolved therein a. thickening agent selected from the group consisting of carbohydrates, gums and proteins, and a metal compound capable of furnishing cations of the metal to be electrodeposited.

6. An electrolyte composition for use with a brushing element in the electrodeposition of nickel, which comprises an equeous solution of such high viscosity as to adhere well to the brushing element and containing dissolved therein starch and a nickel compound capable of furnishing nickel cations.

7. The method of electrodepositing a metal, which comprises brushing on to the Work a coating of an electrolyte composition, of such consistency as to be self adherent to the brushing element and to said work without spreading objectionably, said composition consisting of an aqueous solution of starch and a metal compound capable of furnishing cations of the metal to be electrodeposited, and passing an electric current through said composition coating to said work.

8. The method of electrodepositing a metal, which comprises brushing on to the Work a coating of an electrolyte composition of such consistency as to be self-adherent to the brushing element and to said work Without spreading objectionably, said composition consisting of an aqueous solution of a thickening agent selected from the group consisting of carbohydrates, gums and proteins, and a metal compound capable of furnishing cations of the; metal to be electrodeposited and passing an electric current through said composition coating to said work.

FELIX R. RAPIDS.

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