US3294654A - Metal plating process - Google Patents

Description

United States Patent 3,294,654 METAL PLATING PROCESS Vello Norman, Chapel Hill, N.C., Thomas P. Whaley, Glenview, Ill., and Hamilton B. Prestritlge, Houston, Tex., assignors to Ethyl Corporation, New York, N. a corporation of Virginia No Drawing. Filed July 28, 1965, Ser. No. 475,569 3 Claims. (Cl. 204-38) This application is a continuation-in-part of our copending application Serial Number 279,606, filed on May 10, 1963, and now abandoned, which copending application was a continuation-in-part of our prior copending US. application Serial Number 81,961, filed January 11, 1961, and now abandoned.

This invention relates to a process for electroplating metals upon a wide range of substrates, many of which have heretofore been non-electroplatable or electr0platable only with the utmost difficulty. More specifically, this invention relates to a novel dual plating process which produces highly desirable electroplated articles, some of which not only are new articles of manufacture but have been impossible to prepare by any previously known method.

Electroplating is a highly developed art which provides extremely cheap and commercially attractive techniques for producing objects plated with such desirable metals as chromium, nickel, zinc, copper and the like. But, a serious limitation upon electroplating is the fact that a whole myriad of materials cannot be electroplated at all, or with such difficulty as to render the process completely out of the realm of commercial feasibility. Such materials are plastics, glass, ceramics, refractories, paper, carbonaceous objects and even many metals, e.g., high purity molybdenum and tungsten which are essentially non-electroplatable. A process which would render such materials electroplatable in a cheap, simple, and commercially adaptable fashion would indisputably be a pioneering contribution which would result in a broad extension of the horizons of electroplating technology. For example, such a process would provide a simple and convenient technique for making highly effective seals between non-metallic and metallic mate rials for use in hermetically sealed electronic components, as for example, in the construction of electron tubes. Pressure-tight ceramic-to-metal seals could also be produced by the process. Carbon shapes could effectively be joined, as could plastics and glass, or glass and metals.

Thus a primary object of this invention is to provide a simple process for electroplating metals upon a wide spectrum of substrates-including heretofore non-electroplatable materials, such as glass and paper, and materials heretofore electroplatable only with the utmost difficulty, such as highly pure molybdenum and tungsten. Another important object is to provide highly novel and useful articles of manufacture, including articles wherein the base layer upon which the plates are deposited comprises a heretofore non-electroplatable material. These and other objects of this invention shall appear more fully hereinafter.

Basically, this invention is a process for producing an adherent metal coating upon an essentially non-electroplatable substrate which process is characterized by use of only two plating steps as follows:

(1) Heating said essentially non-electroplatable substrate to a temperature within the range of from about 100 C. to about 500 C. sufiicient to thermally decompose a plating compound hereinafter defined, and thereafter contacting said heated substrate with the .vapors of a heat-decomposable carbonand metalcontaining plating compound for a period of time sufficient to lay down on said substrate an essentially pure adherent metallic coating to serve as an electrically conducting intermediate layer, and

(2) Thereupon electrodepositing by electrolysis a final metal coating upon said intermediate adherent layer so as to form an adherent composite metal coating.

By two plating steps is meant that the process of this invention consists of only two separate and distinct plating steps and none other. It is to be understood of course that non-plating steps, such as surface preparation and treatment may be integrated into this process, however such is usually unnecessary. The coatings deposited by the first plating step, which coating constitutes the intermediate conducting layer, need not be inrpervious or thick to the extent that it seldom exceeds a thickness of 10 mils. In fact, a micromolecular coating, that is, one less than 0.1 mil, is preferred since a coating of such thickness is sufficient to impart very good adherence between the essentially non-electroplatable substrate and the final electroplated coating thus allowing extremely rapid production rates.

The intermediate coating is preferably a metallic coating selected from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, and aluminum, especially molybdenum and tungsten when working with the preferred substrates of this invention. Intermediate coatings containing these metals provide for the best subsequent electrodeposited coatings as effected by the second plating step of the process of this invention.

As brought out above the substrates to be employed in the instant invention are non-electroplatable or essentially non-electroplatable materials. Preferred substrates which are greatly enhanced by way of this invention are molybdenum and tungsten in their essentially non-electroplatable forms, such as the commercially available alloys Mo and 100 W. Thus, now for the first time such materials can be enhanced by the attendant advantages of electrodeposition. Therefore, a preferred embodiment of the present invention is a process for producing an adherent metal coating upon an essentially non-electroplatable metal selected from the group consisting of molybdenum, tungsten and alloys thereof, which process is characterized by use of only two plating steps as follows:

(1) Heating said essentially non-electroplatable metal substrate to a temperature within the range of from about 100 C. to about 500 C. suflicient to thermally decompose a plating compound hereinafter defined and thereafter contacting said heated substrate with the vapors of a heat-decomposable carbonand metal-containing plating compound for a period of time sufficient to lay down on said substrate an essentially pure adherent metallic coating to serve as an electrically conducting intermediate layer, and

(2) Thereupon electrodepositing by electrolysis a final metal coating upon said intermediate adherent layer so as to form an adherent composite metal coating. A surprising feature of this invention when working with the preferred substrates discussed above, is that the plating compounds employed in the first plating step can contain a metal constituent whichis non-electroplatable or essentially non-electroplatable, as long as it is a carboncontaining compound. Hence, an even more preferred embodiment of the instant invention is a process for producing an adherent metal coating upon an essentially nonelectroplatable metal selected from the group consisting of molybdenum, tungsten and alloys thereof, which procfollows:

(1) Heating said essentially non-electroplatable metal substrate to a temperature within the range of from about 100 C. to about 500 C. sufficient to thermally decompose a plating compound hereinafter defined and thereafter contacting said heated substrate with the vapors of a heat-decomposable carbonand metal-containing compound, said compound containing a metal which is essentially non-electroplatable, for a period of time sufficient to lay down on said substrate an essentially pure adherent metallic coating to serve as an electrically conducting intermediate layer, and

(2) thereupon depositing by electrolysis a final metal coating upon said intermediate adherent layer so as to form an adherent composite metal coating.

Another surprising feature of this invention when working with the preferred substrates is that a plating agent containing a metal constituent identical to that of the subsrate can be employed, even though that metal like the substrate is essentially non-electr-oplatable. Therefore, an especially preferred embodiment of the instant invention is a process for producing an inherent metal coating upon an essentially non-electroplatable metal selected from the group consisting of molybdenum and tungsten which process is characterized by use of only two plating steps as follows:

(1) Heating said essentially non-electroplatable metal substrate to a temperature within the range of from about 100 C. to about 500 C. suflicient to thermally decompose the plating compound hereinafter defined and thereafter contacting said heated substrate with the vapors of a heat-decomposable carbonand metal-containing plating compound selected from the group consisting of molybdenum and tungsten containing compounds for a period of time sufilcient to lay down on said substrate an essentially pure adherent metallic coating to serve as an electrically conducting intermediate layer, and

(2) Thereupon electrodepositing by electrolysis a final metal coating upon said intermediate adherent layer so as to form an adherent composite metal coating.

Thus, it can be seen that by way of the above process, an extremely unique article of manufacture can be prepared, viz. an essentially non-electroplatable molybdenum or tungsten substrate, an intermediate layer of the same metal, and a final coating of a selected electrodeposited metal. .This unique article of manufacture has certain significant properties. Since the intermediate layer is of the same metallic composition as that of the substrate, the composite coating upon subsequent treatment, such as diffusion, will comprise only two metallic constituents. It is to be understood of course, that plating compounds containing an essentially non-electroplatable metal constituent can be employed to effect an electrically conducted intermediate layer of other types of non-electroplatable or essentially non-electroplatable substrates, for example glass, ceramics, and the like.

Thus it can be seen that the subject invention does in fact drastically extend the scope of materials which can be electroplated. For the first time it is now possible to electroplate objects which heretofore could not be electroplated, or could be electroplated only with great difiiculty. Furthermore, generally improved electroplates can be produced by the process of this invention. Dramatically demonstrating the unique character of the process and compositions of the instant invention are the following experimental results.

Massive molybdenum-that is molybdenum metal in its natural state-is extremely difiicult to electroplate. However, when a massive molybdenum substrate was plated with an adherent molybdenum plate, produced by decomposition of molybdenum carbonyl in contact with the massive molybdenum by the first plating step of the process of this invention, the resulting molybdenum plate was thereupon easily electroplated with a metal, specifically copper. This electroplate had excellent and unusual adherence to the molybdenum plate. In contrast to these excellent results, when the same metal, namely copper, was electroplated directly upon the massive molybdenum, the resulting electroplate exhibited very poor adherence, and was easily rubbed off with a damp cloth.

Also massive tungsten was preplated with an adherent tungsten plate (by decomposition of tungsten carbonyl in contact with said massive tungsten by the first plating step of the process of this invention) and then electroplated with a metal (copper). The electroplate again was excellently adherent to the tungsten plate. The same metal (copper), when electroplated directly to massive tungsten, easily rubbed off with a damp cloth.

This clearly demonstrates that the plating of an intermediate metallic layer, such as molybdenum or tungsten, by the vapor phase decomposition of a metal-containing compound pursuant to the first plating step of the instant invention does in fact produce highly desirable objects which can be electroplated with ease. Furthermore, these easily applied electroplates exhibit an improved quality and extremely excellent adherence to the substrate upon which they are plated.

This invention will be further understood by reference to the following illustrative examples. In Examples I- VIH the following technique was employed.

Into a conventional heating chamber provided with means for high frequency induction heating and gas inlet and outlet means was placed the substrate (i.e., the base layer) to be plated by the first step of this process. The carbonand metal-containing plating agent (i.e., the metallic source for the metal plate) was placed in a standard vaporization chamber provided with heating means, said vaporization chamber being connected through an outlet port to the aforesaid combustion chamber inlet means. The object to be plated was heated to a temperature above the decomposition temperature of the carbonand metal-containing plating agent, the system was evacuated, and the plating agent was heated to an appropriate temperature where it possessed vapor pressure of up to about 10 millimeters (Hg). (In most instances the process is conducted at no lower than 0.01 mm. (Hg) pressure.) The vapors of the plating agent were pulled through the system as the vacuum pump operated, and they impinged on the heated object, decomposing and forming the desired plate. Generally no carrier gas was employed; however, in certain cases, a carrier gas can be employed if desired.

For the second plating step of the instant process, the resulting plated object was then placed into an electroplating bath (as the cathode thereof) wherein the anode was copper. The bath contained either CuCN-NaCN or an aqueous solution of copper sulfate (CuSO and H An electric current at a current density, at the cathode, of 20-50 amps/sq. ft. and a voltage of 1-6 volts was then passed through the system effecting electrodeposition of an excellent adherent copper plate upon the cathode. The bath temperature was 60-l50 F.

Example 1 Gas plating step:

Compound Mo(CO) Compound temp C. Substrate Massive Mo panel. Substrate temp 250 C. Pressure 1 mm. Hg. Result Bright coating. Electroplating step:

Electrolyte Cu(SO )-H SO Temp 60-120 F. Voltage 1-4 volts. Current density 20-50 amps/sq. ft. Anode Copper. Result Excellent, adherent copper plate on gas-plated Mo.

In Example I the decomposition of molybdenum carbonyl in contact with the massive molybdenum panel was controlled so that a portion of the panel was not covered with the gas-plated molybdenum. In other words, upon completion of the gas plating step a portion of the massive molybdenum panel remained uncoated. This was done in order to provide a direct comparison between an electroplate deposited on the gas-plated molybdenum coating and the identical electroplate deposited upon the uncoated massive molybdenum surface. Consequently, when the panel was subsequently electroplated with copper, the copper plate formed upon the bright gas-plated molybdenum coating was an excellent, adherent copper plate. However, the copper plate electroplated upon the uncoated massive molybdenum exhibited almost no adheren-cy, being easily wiped off with an ordinary cloth.

plate on gas-plated Mo.

As was the case in Example I, the decomposition of the tungsten carbonyl was controlled so that a portion of the massive tungsten wire remained uncoated. The copper electroplated upon the gas deposited tungsten coating was an excellent, adherent copper plate, whereas the copper deposited upon the uncoated portion of the massive tungsten wire exhibited very poor adherence.

The results of Examples I and II clearly demonstrate the I unique receptiveness of metallic coatings produced by decomposition of a carbonand metal-containing compound by the first plating step of this invention to electroplating. Moreover, Examples I and II illustrate an especially distinct advantage of the instant invention, viz. that whereas massive molybdenum or tungsten metal (i.e., in its natu ral crystalline state) can be electroplated only with great difficulty, by way of this unique two step process, they can be electroplated with the utmost ease. Furthermore, these easily applied ele-ctroplates exhibit an improved quality and excellent adherence to the substrate upon which plated.

The following examples employed the process of Examples I and H.

Example III Gas plating step:

Compound Dicyclopentadienyl titanium dichloride.

Compound temp. 150 C.

Substrate Copper.

Substrate temp 450 C.

Pressure 0.5 mm. Hg.

Result Light grey, dull coating.

Electroplating step:

Electrolyte CuCN-NaCN.

Temp. 120l50 Voltage 46 volts.

Current density 20 amps/sq. ft.

Anode Copper.

Result Excellent, adherent copper plate.

Example IV Gas plating step:

Compound Cyclopentadienyl vanadium tetracarbonyl. Compound temp 70 C. Substrate Steel. Substrate temp. 150 C. Pressure 2 mm. Hg. Result Dark grey, dull coating. Electroplating step:

Electrolyte CuCN-NaCN. Temp 150 F. Voltage 4-6 volts. Current density 20 amps/sq. ft. Anode Copper. Result Excellent, adherent copper plate. 7

Example V Gas plating step:

Compound Mesitylene chromium tricarbonyl. Compound temp. C. Substrate Mo. Substrate temp 350 C. Pressure 1 mm. Hg. Result Bright coating. Electroplating step:

Electrolyte CuCN-NaCN. Temp 120150 F. Voltage 4-6 volts. Current density 20 amps/sq. ft. Anode Copper. Result Excellent, adherent copper plate.

Example VI Gas plating step:

Compound Mo(CO) Compound temp 65 C. Substrate Aluminum. Substrate temp 200 C. Pressure 2 mm. Hg. Result Bright coating.

Electroplating step:

Electrolyte CuCN-NaCN. Temp. 120l50 F. Voltage 4-6 volts. Current density 20 amps/ sq. ft. Anode Copper. Result Excellent, adherent copper plate.

Example VII Gas plating step:

Compound Diethyl cadmium. Compound temp 25 C. Substrate Graphite. Substrate temp 300 C. Pressure 2-3 mm. Hg. Result 1 Light grey, dull coating. Electroplating step:

Electrolyte CuCN-NaCN. Temp. 120-150 F.

Voltage 4-6 volts. Current density 20 amps/ sq. ft. Anode Copper. Result Excellent, adherent copper plate.

7 Example VIII Gas plating step:

Compound W(CO) Compound temp 75 C. Substrate Magnesium. Substrate temp 225 C. Pressure 1 mm. Hg. Result Bright coating. Electroplating step:

Electrolyte CuCN-NaCN. Temp. 120-150" F. Voltage 4-6 volts. Current density 20 amps/ sq. ft. Anode Copper. Result Excellent, adherent copper plate.

As was the case in Examples I and II, the gas-plated coats produced in Examples III-VIII had excellent adherence to the substrate upon which they were deposited; furthermore, in all cases the electroplated copper exhibited excellent adherence to the gas-plated coatings. The diversity of substrates employed in the above examples demonstrates the wide scope of applicability of the subject dual plating or two step process.

In the above examples high frequency induction heating was employed. In Examples IX and X the use of a resistance heating method is illustrated. Hence, the first step employed in these examples is essentially the same as that employed in Examples I-VIII with the exception that the object to be plated is placed into a conventional heating chamber housed in a resistance furnace, as opposed to the former experiments where the heating chamber was provided with means for high frequency induction heating.

The electroplating or second step, except for Example X, utilizes a Watts bath wherein the anode is nickel and the gas-plated object is the cathode. The bath contains an aqueous solution of nickel sulfate (NiSOQ-nickel chloride (NiCl An electric current at a current density of 20-100 amps/sq. ft., is then passed through the system effecting electrodeposition of nickel upon the cathode. The bath temperature is maintained between 115-160 F.

Example IX Gas plating step:

Compound Dicyclopentadienyl nickel.

Compound temp. 170 C.

Substrate Ceramic tube.

Substrate temp. 450 C.

Pressure 0.2 mm. Hg.

Result Grey, dull coating. Electroplating step:

Electrolyte NiSO -NiCl Temp. 115-160 F.

Current density 20-100 amps/sq. ft.

Anode Nickel.

Result Adherent nickel plate.

Example X Gas plating step:

Compound .1 Ditertiarylbutylberyllium.

Compound temp. 80 C.

Substrate Steel.

Substrate temp. 350 C.

Pressure 0.2 mm. Hg.

Result Dull grey coating. Electroplating step:

Electrolyte Potassium fluoride complex of his (diethylberyllium) in diethylberyllium.

Temp. 185 F. Current density 5-10 amps/ sq. ft. Anode Platinum.

Result Shining beryllium coating.

In addition to the thermal decomposition techniques of this invention, other methods for decomposition can be employed, such as ultrasonic frequency or ultraviolet irradiation. The latter techniques would involve essentially the same procedure as employed in Examples 1- VIII with the exception that an ultrasonic generator is proximately positioned to the plating apparatus. The carbonand metal-containing compound is then heated to its decomposition threshold and thereafter the ultrasonic generator is utilized to effect final decomposition. Decomposition by ultraviolet irradiation would involve essentially the same method, with the exception that in place of the high frequency induction furnace there is utilized for heating a battery of ultraviolet and infrared lamps placed circumferentially around the outside of the heating chamber. The substrate to be heated is brought to a temperature just below the decomposition temperature of the carbonand metal-containing compound with the infrared heating and thereafter decomposition is elfected with ultraviolet rays. When coatings are produced employing the last-mentioned heating techniques, they are likewise readily electroplatable to form an excellent adherent electroplate.

The following example employs the process of Examples I-VIII with the exception that in place of the coppercontaining electrolytic bath employed in those examples, a rhodium-sulfuric acid bath is employed, utilizing a platinum anode.

Example XI Gas plating step:

Compound Dibenzene chromium.

Compound temp. 150 C.

Substrate Steel.

Substrate temp. 410 C.

Pressure 0.5 mm. Hg.

Result Bright coating. Electroplating step:

Electrolyte RhH SO Temp. IDS- F.

Current density 10-80 amps/ sq. ft.

Anode Pt.

Result Adherent rhodium plate.

The metals which comprise the metal constituents of the carbonand metal-containing compounds employed in the first plating step are in general any metals of Groups 11A through VA, IB through V113, and Group VIII (Periodic Chart of the Elements, Fisher Scientific Company, 1955). The carbonand metal-containing compounds employed in the first plating step include, for example, metal carbonyls, organic metal hydrides, organometallics, and the like.

The organometallics are preferably unsubstituted hydrocarbon metallics, having between about 1 to about 20 carbon atoms. These organometallics can be covalently bonded organometallics, such as the metal alkyls. For example: triethylaluminum, triisobutylaluminum, tetraethyllead, diethylmagnesium, diethyltin, ditertiarybutylberyllium, ethylaluminum sesquichloride, tetraethyltin,

tetraethylsilane, triethylborane, diethylzinc, triphenylaluminum, aluminum dimethyl hydride, diphenyl magnesium, magnesium methyl hydride, magnesium ethyl sulfide, aluminum trieicosyl, dimethyl aluminum chloride and the like. Furthermore, these organometallics can be organometallic chelates such as the acetyl acetones of copper, nickel, platinum, chromium and the like. Other types of organometallic compounds are also suitable, especially organometallic coordination compoundsparticularly transition metal coordination compoundssuch as: bis-cyclopentadienyl titanium, cyclopentadienyl manganese tricarbonyl, methyl cyclopentadienyl manganese tricarbonyl, bis-cyclopentadienyl zirconium dichloride, bis-cyclopentadienyl titanium dibromide, dibenzene chromium, bis-cyclopentadienyl ir-on, cyclopentadienyl cobalt dicarbonyl, bis-cyclo- 9 pentadienyl nickel carbonyl), dibenzene molybdenum, di benzene tungsten, dicumene tungsten, bis(cyclopentadienyl chromium carbonyl), bis(cyclopentadienyl chromium dinitrosyl), cyclopentadienyl titanium trichloride, methylcyclopentadienyl titanium t-ri'bromide, cyclopentadienyl zirconium trichloride, cyclopentadienyl hafnium trichloride, bis-cyclopentadienyl manganese, b-is-cyclopentadienyl nickel, and the like.

Especially preferred are coordination compounds such as the metal carbonyls which find particular applicability in the processes of this invention because of their economic advantages and general ready availability. Representative of these metal carbonyls are nickel tetracarbonyl, iron pentacarbonyl, chromium hexacarbonyl, molybdenum hexacarbonyl, tungsten hexacarbonyl, cobalt tricarbonyl nitrosyl, iron dicarbonyl dinitrosyl, cobalt tetracarbonyl hydride, iron tetracarbonyl dihydride, bis(manganese pentacarbonyl), vanadium carbonyl, and the like. Other carbonyl metal compounds can also be employed, as for example, carbonyl metal halides, carbonyl metal hydrides, and the like.

The following examples employing the procedure of Examples I-VIII further demonstrate various types of metal-containing plating agents which can be employed in the process of this invention.

Example XII Gas plating step:

Compound Tetraphenyllead.

Compound temp. 200 C.

Substrate Steel.

Substrate temp. 500 C.

Pressure 1 mm. Hg.

Result Dark, shiny coating. Electroplating step:

Electrolyte Cu(CN)-NaCN.

Temp. 120-l50 F.

Voltage 4-6 volts.

Current density 20 amps/ sq. ft. (not critical).

Anode Copper.

Result Adherent copper plate.

Example XIII Gas plating step:

Example XIV Gas plating step:

Compound Triisobutylamine complex of aluminum hydride. Compound temp. 70 C. Substrate Stainless steel.

Substrate temp. 200 C.

Pressure 0.5 mm. Hg.

Result Adherent, metallic coating. Electroplating step:

Electrolyte CuSO H SO Temp. 60-120 F.

Voltage 1-4 volts.

Current density Cathode, 20-50 amps/sq. ft.

Anode Copper.

Result Adherent copper plate.

10 Example XV Gas plating step:

Compound Dicumene chromium.

Compound temp. C.

Substrate Mild steel.

Substrate temp. 350 C.

Pressure 0.5 mm. Hg.

Result Bright coating. Electroplating step:

Electrolyte CuSO -H SO Temp. 60-120 F.

Voltage 1-4 volts.

Current density Cathode, 20-50 amps/sq. ft.

Anode Copper.

Result Adherent copper plate.

The substrates which are enhanced pursuant to the practice of this invention include non-electroplatable or essentially non-electroplatable materials. By essentially non- -electroplatable means that they can only be electroplated with great difliculty. Exemplary of materials that can be utilized in their non-electroplatable or essentially nonelectroplatable forms in the process of this invention are: glass, ceramics, mineral materials, plastics, paper, wood, cellulose products, aluminum, chromium, magnesium, molybdenum, tungsten, carbonaceous materials, and the like. The degree of electroplatability of the substrate is not a limiting factor to the extent that electroplatable substrates can be employed in the process of this invention since the initial coating effected by the first plating step imparts certain desirable physical properties to the substrate itself which oftentimes enables the application of superior electroplates than normally possible, that is, when electroplating without employing the first plating step of this invention. It is to be understood of course that the substrate must possess sufficient structural strength under the processing conditions employed herein.

In general, prior art technique for plating a metal upon an object by electrodeposition can be employed as the second plating step herein. For example, the nickel electroplate can consist of electrodeposited nickel obtained from plating baths of the conventional Watts type, or can consist of nickel deposited from an all-chloride or an all-sulfate bath, or can consist of bright or semi-bright nickel deposited from baths containing the usual brightners or levellers, or both, for enhancing the smoothness and appearance of a nickel electrodeposit. Satisfactory nickel deposits can be obtained from any of the known nickel plating baths of these types.

Cobalt layers can be electrodeposited from an acid bath containing cobalt sulfate, cobalt chloride and sodium borate, and cobalt-tungsten alloy layers from an alkaline bath containing cobalt chloride and sodium tungstate in appropriate proportions to give the desired proportions of cobalt and tungsten in the deposit, together with Rochelle salt (sodium potassium tartrate) and ammonium chloride. Satisfactory chromium electrodeposits can be obtained by the use of, for example, a standard chromic acid-sulfuric acid plating bath. An example of an electroplating bath for electrodepositing tin is a tin sulfate-sulfuric acidcresol sulfonic acid aqueous bath using anodes of Banka tin.

Beryllium can be deposited by employing an electrolytic bath comprising complex salts of organometallic beryllium compounds, such as the potassium fluoride complex of bis(diethylberyllium) dissolved in a suitable solvent, e.g., diethylberyllium.

Furthermore, copper, tin, zinc, silver, lead, iron and ferro-nickel electrodeposits can be produced using standard baths and operating conditions. Illustrative of such standard techniques are those described in Metal Finishing Guide Book Directory, 26th edition, 1958, Finishing Publications, Inc., Westwood, New Jersey, pages 299- 427.

It should be noted that when employing the carbonand metal-containing plating agents of this invention in the first plating step it is necessary to maintain enough vapor pressure below the decomposition temperature of the plating agent to enable the process to be conducted at an appreciable rate of plating. Too high vapor pressure results in poor substrate adherence. Thus, it is preferred to employ up to about mm. pressure during the plating operationpreferably 0.01 to 10 mm. pressure.

In practicing the first plating step, temperatures are very important in obtaining the desired product. Thus, although temperatures above the decomposition temperature of the carbonand metal-containing compound can in general be employed in the process of this invention, a preferred temperature generally exists for each plating agent. When this temperature is employed better plating results can be obtained. Although the plating compounds of the present invention vary insofar as their thermal stability is concerned, they can generally be decomposed within a temperature range of from about 100 C. to about 500 C. When plating the most preferred substrates employing the most preferred plating compounds, namely those selected from the group consisting of molybdenum and tungsten, a preferred temperature range whereby intermediate coatings effected by the first plating step are capable of conducting an electric current, is from about 200 C. to about 300 C., especially at about 250 C.

The thickness of the metal coats produced by the first plating step of this invention are preferably no greater than one mil and very frequently are less than 0.1 mil down to a micromolecular layer as long as it is sufficient to conduct electricity. For most applications 0.010.1 mil is sufficient. In no case has it been found necessary to employ an intermediate layer exceeding 10 mils.

The thickness of the electroplates produced by the second plating step of this invention generally ranges between about 0.01 to 50 mils depending upon the application requirements. In most cases, electroplates having a thickness of no greater than 1-2 mils is necessary.

In general, the first plating step of this invention is carried out in less than one hour. Contact times, that is the time during which the carbonand metal-containing plating agent is in contact with the substrate to be plated, range from as low as one to five seconds to as high as a few hours (generally no more than 2 hours).

What is claimed is:

1. A process for producing an adherent metal coating upon an essentially non-electroplatable metal selected from the group consisting of molybdenum, tungsten and alloys thereof, which process is characterized by use of only two'plating steps as follows:

(1) heating said essentially non-electroplatable metal substrate to a temperature within the range of from about C. to about 500 C. and thereafter contacting said heated substrate with a heat-decomposable compound selected from the group consisting of molybdenum carbonyl and tungsten carbonyl, for a period of time sufficient to lay down on said substrate an essentially pure adherent metallic coating to serve as an electrically conducting intermediate layer, and

(2) thereupon depositing by electrolysis a final metal coating upon said intermediate adherent layer so as to form an adherent compositemetal coating.

2. The process of claim 1 further defined in that said heat-decomposable compound is molybdenum hexacarbonyl.

3. The process of claim 1 further defined in that said heat-decomposable compound is tungsten hexacarbonyl.

References Cited by the Examiner UNITED STATES PATENTS 2,304,182 12/1942 Lang 204-38 2,333,534 11/1943 Lang 20438 2,475,601 7/1949 Fink 1l7-l07.2 3,225,071 12/1965 Crosby 260397.2

JOHN H. MACK, Primary Examiner.

W. VAN SISE, Assistant Examiner.

Claims (1)

1. A PROCESS FOR PRODUCING AN ADHERENT METAL COATING UPON AN ESSENTIALLY NON-ELECTROPLATABLE METAL SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM, TUNGSTEN AND ALLOYS THEREOF, WHICH PROCESS IF CHARACTERIZED BY USE OF ONLY TWO PLATING STEPS AS FOLLOWS: (1) HEATING SAID ESSENTIALLY NON-ELECTROPLATABLE METAL SUBSTRATE TO A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 100*C. TO ABOUT 500*C. AND THEREAFTER CONTACTING SAID HEATED SUBSTRATE WITH A HEAT-DECOMPOSABLE COMPOUND SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM CARBONYL AND TUNGSTEN CARBONYL, FOR A PERIOD OF TIME SUFFICIENT TO LAY DOWN ON SAID SUBSTRATE AS ESSENTIALLY PURE ADHERENT METALLIC COATING TO SERVE AS AN ELECTRICALLY CONDUCING INTERMEDIATE LAYER, AND (2) THEREUPON DEPOSITING BY ELECTROLYSIS A FINAL METAL COATING UPON SAID INTERMEDIATE ADHERENT LAYER SO AS TO FORM AN ADHERENT COMPOSITE METAL COATING.