US2560979A - Chemical deposition of metallic films - Google Patents

Description

Patented July 17, 1951 CHEMICAL DEPOSITION OF METALLIC FILMS Leopold Pessel, Philadelphia,

Pa., assignor to Radio Corporation oi America, a corporation of Delaware No Drawing. Application July 30, 1948, Serial No. 41,721

11 Claims. 117130) This invention relates to the chemical deposition of metallic films on metal surfaces by simple immersion without the use of electrical current.

More particularly, the invention relates to improvements in the chemical deposition of metallic films in general, using a depositing solution which includes pentanedione-2,4.

The chemical deposition of a metal upon another metal anodi-c thereto is very old in the chemical art. It is a general principle that a metal will replace from solution any other metal below it in the well-known .electromotive series. In general, however, the deposit of metal so formed is soft and spongy and usually may easily be rubbed off. In the past, in order to get a hard, brilliant coating of metal on another metal, it has usually been necessary to deposit the metal electrolytically.

The essence of the present invention lies in the discovery that when a certain organic chemical, namely; pentanedione-2,4, is included in a solution of a metallic salt, the metal will not only deposit more readily on baser metals but will form deposits which, in hardness and brightness, compare favorably with those produced by electrodepo'sition.

One object of the present invention is to provide an improved method of depositing metals chemically on other metals without the use of an electric current.

Another object of the invention is to provide improved compositions for the chemical deposition of metals.

Another object is to provide improved compositions for chemical deposition of metals, which compositions include pentanedione-2,4.

Another object of the present invention is to provide improved compositions for chemically depositing metals on baser metals, which compositions contain pentanedione-2,4, Water and a mutual solvent for pentanedione-2,4 and Water.

Still another object of the present invention is to provide improved compositions for chemically depositing a metal on another metal anodic thereto, which compositions contain pentanedime-2,4, water and an acid.

These and other objects will be more readily apparent and the invention will be better understood from the following specification.

In general, the objects of the present invention are accomplished by first providing a solution comprising pentanedione-2,4, at least a small amount of water, and a soluble metal compound. Next, the base metal to be coated is preferably immersed in the above solution and allowed to remain until a coating of desired thickness is formed. Preferably, the metal which is to be deposited should be cathodic toward the base metal upon which deposition is to occur, al-

though examples have been found in which, this so requirement is not necessary. The metal compound which is in solution forms a complex salt with the pentanedione-2,4. In some cases, it appears that the deposition which occurs is due simply to the preference of the pentanedione-2,4 radical for one metal over another one, resulting in the deposition of the latter as a film on the surface of the immersed metallic body.

Although it is preferred to immerse the base metal being coated in a solution of the metal which is being deposited, the base metal may be subjected to the action of the metal being deposited in other ways. For example, a plate of the base metal may simply be covered on one side. :with a layer of thesolution or the solution may be sprayed over the surface of the base metal.

One of the necessary requirements for proper deposition of a metallic film, according to the invention, is the presence of at least a small amount of water. Without water, if a film is deposited at all, deposition occurs at an extremely slow rate. The presence of as little as 0.5 percent by volume of water causes a very noticeable acceleration of film formation, which becomes increasingly more pronounced as the percentage of water increases. Most metals are deposited at. room temperature in a matter of seconds if 1 to 2 percent by volume of water is present. The amount of water may be increased up to its maximum miscibility with pentanedione-2,4 without separating into two phases. Still more water may then be added by including a mutual solvent for pentanedione-2,4 and water, such as diacetone alcohol. At room temperatures, and using a mutual solvent, as much as 25 parts by volume of water may be mixed with 50 parts of pentanedione-2,4. This proportion may be increased by raising the temperature. A preferred solvent mixture contains 50 volume percent pentanedione-2,4, 25 volume percent water and .25 volume percent diacetone alcohol. Other mutual solvents such as acetone and gamma valero lactone may also be employed in somewhat smaller amounts.

Examples of the manner in which the present invention may be practised in the case of specific metals will now be given:

EXAMPLE I Deposition of copper on iron or steel An aqueous solution containing 7 percent by weight of cupric sulfate is added to from 10 to 30 percent by volume of pentanedione-2,4. In this solution is immersed a previously cleaned piece of iron or steel. A hard, brilliant copper film forms on the base metal in a matter of seconds. The adhesion is so good that it is almost impossible to remove the coating by rubbing.

- per hydroxide until vent mixture is not I ratio is l gram of copper voi! solvent mixture. A piece mersed in this mixture'becomes coated withinroom temperature, with a. Y brilliant film of metallic copper having such adhesion that it cannot be rubbed on. The density and superior adhesion of this film'is" such an excellent stop-of!" to -prevent carbon penetration in carburizing operations. Another application is in the copperto seconds, at

above examples is solely 'tion of the componen "film, particularly 7 of when the same method'is carried out without adding pentanedione 2,4,- the red copperdeposit which is formedis not only-dullbut is spongy and shows pooradhesion to ExAMPnEn Deposition. o .ama 5,,,,, u

the metal surface.

Another preferred method of preparing a solution, for thedeposition oi copper. comprises shaking a mixture I v pentanedione-zA, v volume percent water and 25 volume percent diacetone alcohol with cop saturated with the copper compound.- Although the proportion of copper at all criticaL'one preferred of iron or steel imthat it may serve as plating of powdered iron cores used in the radio industry.

The function of the diacetone alcohol in the that 01' maintaining a homogeneous solution of water and pentanedione-2,4 at room temperature without separa- Any other solvent mutually compatible with water and pentanedione- 2,4 may be used or such solvent may be left out entirely if the water content in the mixture is to be kept low.

' The film-forming ability of the above-described copper compounds may be accelerated by additions of moderate amounts of acids. Excessive acid additions cause deterioration of the its adhesive properties. Thus, additions of concentrated formic acid up -to 20 percent, accelerated film' formation without affecting adhesion ofthe metal films. Additions beyond 20, percent containing 1 50 volume. percent hydroxide to thesolhydroxide to 20 cc.-

the solution is thoroughly i on steel or zinc.

ausedthe progressive deterioration of adhesion of the film to the base.

YAddition of concentrated hydrochloric acid up to 5 percent by volume I 'film formation. Additions beyond 5 percent by caused acceleration. of

volume caused progressive inhibition offilrn deposition.' The eil'ect of other acids was similar, except that the maximum volume addition compatible with good film properties acid.

Although, in the previously described examples, iron or-steel was specified as the base, copper may be deposited. also] on other metal surfaces in accordance with, the present invention.

Some examples. of other metals are zinc, lead, lead-tin alloys, aluminum, iron alloys contain-j ing nickel,- silicon, manganese, etc. vflhe'base" metal may be any metal' to which copper is cathodic,

It is also possible todeposit flms'oi many other metals, it being necessary only that, in general, the metal to be depositedbe cathodic to the base metal upon which the deposition is to occur.

Examples of the deposition of other metals follow:

EXAMPLE III Deposition of silver on copper A mixture comprising pntanedione-ZA,

varied with the adherent filmpt metallic. silver;

. volume percent, and.

rated with silver oxide. A' sheetoi copp immersed in this solution with a shiny,

. fle i lf Me l To a mixture'icontaininz pehtanedione-ZQ, 90 water, 10 volume- :percent, weight oi-palladium chloimmersed in this, soluis'added 1 percent by ride. A sheet of copper ,tion iscoated with' ,a.shiny adherentfilm of palladium metal.

7 Deposition offacid'on steelyetc. I To a mixture containing penta'nedione-ZA, 50 volume :percent, water," ,25 volume. percent, and diacetone alcohol, 25 volume percent, ,isadded 5 volume} percent oi a saturated-aqueous acid gold chloride solution. .A gold of; good quality is deposited. on any of the, variousmetals more active thangold. immersed in this solution. Forexample. a shiny gold film is deposited A gold film oi somewhat less shiny appearance is obtained on immersing silver. A gold film may also be deposited on aluminum by adjusting the pH of the solution to about 6 by the addition-of an alkali such as ammonia. The film whi h is deposited on aluminum is dark at first but may be buffed to the characteristic shiny gold color. Its adhesion is very good.

EXAMPLE VI Deposition of nickel on steel A solution of pentanedione-2,4, 50 volume percent, water, 25 volume percent, and diacetone alcohol, 25 volume percent, was saturated with nickel hydroxide. A thin film of nickel is deposited on cold-rolled SAE 1010 steel immersed in the solution.

- Deposition s lbismutni 0 7i. 5 and steel containing pentanedione-2A, 50 volume percent, water, 255volume percent,"and diacetone alcohol, 25 vol e rated with bismuth oxide. of bismuth metal were obtained by immersing'pieces of various other metals, such as zinc and steel, in this solution. EXAMPLE VIII Deposition of lead on zinc The same solvent mixture in Example VII was saturated with lead oxide '(PbO). From this solution, films of metallic lead were obtained onpieces oi immersed metal, suchas "Deposition of ctuimium on'einc,

The same solvent mixture used in Example VII was saturated with cadmium oxide. Ex-

tremely thin films of cadmium were deposited trom this solution on other metals such as zinc.

EXAMPLE x Deposition of platinum on copper and steel To the same solvent mixture used in Example VII, 10 volume percent of a 5' percent aqueous percent, was satuplatinum chloride solution was added. A sheet of copper immersed in this solution was coated with a shiny film of platinum, which, although somewhat dark in color, showed excellent adhesion. This film formed very slowly, requiring several hours at room temperature. A similar film of platinum was also obtained on steel.

EXAMPLE XI Deposition of selenium on copper, etc.

Solutions made according to the present invention may also be used to precipitate a film of metallic selenium on some immersed metals. As one example, a 1 percent (by weight) solution of HzSeOa was added to the solvent mixture containing pentanedione-2,4, 50 volume percent. water, 25 volume percent, and diacetone alcohol, 25 volume percent. A copper or brass sheet, immersed in this solution, at room temperature, is rapidly coated with a film of selenium which is first purple, then blue, and, lastly. gray. The film is of brilliant smoothness and shows excellent adhesion. A sheet of iron or carbon steel, such as annealed spring steel, immersed in this solution, becomes also coated with a black, shiny, adherent film of selenium, but the formation in this case is much slower, requiring 4 to 6 hours, at room temperature. A strip of zinc immersed in solution becomes rapidly coated with a brown, smooth, adherent film of selenium. On magnesium, a reddish-brown film of selenium is obtained. The formation of a selenium film on steel may be brought about more rapidly by first copper plating the steel, as described in Examples I or II, and then immersing the plated steel in a seleniumcontaining solution which includes pentanedione- 2,4. A rapid conversion of the copper film into a selenium film takes place. Metals coated with selenium, in this manner, may be used in apparatus such as rectifiers, photoelectric cells, etc. Instead of selenious acid, a solution of selenium oxychloride, or some other soluble compound of selenium may be used.

EXAMPLE XII Deposition of tellurium on zinc or steel A saturated potassium tellurate solution in water was prepared and acidified with concentrated hydrochloric acid to a pH of 4. 10 percent by volume or the resulting solution was added to the solvent mixture described in Example VII. Pieces of zinc or steel, immersed in this solution. were rapidly coated with films of tellurium.

The above examples are intended to be merely illustrative of the many possible combinations of film and base material which may be carried out by utilizing the present invention. As is the case with chemical reactions in general, the reactions occurring in the above described examples may be accelerated by increasing the temperature or by agitation of the solution, or by adjustment of the pH, all in accordance with the principles well known in this art. It has beentound that the complex salt which is formed between the metal and the pentanedione-2,4, especially in the presence of water or acids, provides an improved method of plating immersed metal surfaces with smooth, often brilliant and well-adhering films of metal, without the use of electrical current. even in those cases where the precipitation of the corresponding metal, without the use of pentanedione-2,4, ordinarily results in a loose, sponsy deposit with poor adhesion.

I claim as my invention:

1. In a process 01' chemically depositing a film of metal on a body of another metal anodic thereto by subjecting said body to a solution of a win-- ble compound of said metal to be deposited until said film has assumed a desired thickness, the improvement consisting in utilizing as the solvent portion of said solution a mixture comprising pentanedione-2,4 and water, said water being present in said mixture in a proportion between 0.5 volume percent and the upper limit of miscibility with said pentanedione-2,4.

2. A process according to claim I in which said solvent portion also includes a mutual solvent for pentanedione-2,4 and water.

3. A process according to claim 1 in which said solvent portion also includes a relatively small volume percentage 01' an acid.

4. A process according to claim metal to be deposited is copper.

5. A process according to claim 1 in which the metal to be deposited is silver.

6. A process according to claim 1 in which the metal to be deposited is selenium.

7. A process according to claim 1 in which said metal body consists essentially or iron. I

8. A process according to claim 1 in which said metal body consists essentially of an iron-carbon alloy.

9. A process according to claim 1 in which said metal body comprises copper.

10. A composition for chemically depositing a metal on another metal anodic thereto comprising pentanedione-2,4, water and a soluble compound of the metal to be deposited, the water being present in a proportion between 0.5 volume percent and the upper limit of miscibility with maturedime-2,4.

11. A composition according to claim 10 ineluding also a minor percentage of acid.

LliOPOID REFERENCES CITED The following references are oi record in the tile 0! this patent: I

' UNITED STATE8 PATIN'I'B Number Name Date 2,351,974 Kollmar June 20. 1044 2,430,520 Marboe Nov. 11, 1047 l in which th