US2432893A - Electrodeposition of nickeltungsten alloys - Google Patents

Description

Patented Dec. 16, 1947 ELECTRODEPOSITION OF NICKEL- TUNGSTEN ALEQYS' Matthew Leslie Holt, Madison, Wis., and Morris.

L. Nielsen, Anniston, Ala.,, assignors to. P. R- Mallory & (30., Inc., Indianapolis. Incl, a cor.-

porati'on of- Delaware No Drawing. Application July 13, 1943, Serial No. 4945498 2; Claims. 1-

Thisinvention relates to the elect-rodeposition of nickel-tungsten alloys.

An object of the invention is to improve the electrodeposition. of nickel-tungsten alloys, and. the methods andcompositions used therefor.

Other objects of. the-invention will. be apparent from the description and claims.

Av great deal of interest in theelectrodeposition of tungsten and tungsten alloysha-sbeen in evidence. in recent years. but apparently none of the methods tried have been found suitable.- for commercial practice; Most. of the efforts have been: directed to the production of alloys having high: tungsten: content and: many special baths have been proposed. for: this purpose;

It was applicants" belief that. a: nickel electrodeposit containing small percentages of tungsten would show advantages over pure nickel for many commercial applications and would also have utility in many cases where pure tungsten or high tungsten alloys have heretofore been thought necessary.

It would not ordinarily be supposed that nickel plating baths could be modified. by the addition of soluble tungstates without deleterious eifect. In fact such tungstates have a marked effect on such baths in lowering the cathode current efficiency and usually prevent electrodeposition. of metal or result in a deposit which is non-metallic in character. This is perhaps due to the formation of a tungstate-film on thecathode, preventing the deposition of metal, or permittingv only a deposit which is non-metallic in appearance.

We have found. however, that" under certain conditions. anickelplating; bath, such as a; Watts. type hath, can be: modified: by the addition. of tungstates, such as sodium tungstate, and the solution electrolyzed to obtain smooth, adherent metallic deposits of nickel-tungsten alloys on the cathode.

One suitable nickel-tungsten plating bath contained:

Grams per liter Nickel sulfate (NiSO4.6H2O) 250 Nickel chloride (NiC12.6H2O) 21 Boric acid (H3303) 30 Sodium tungstate (Na2WO4.2HzO) 4 The sodium tungstate was added to the nickel plating bath from a stock solution containing '71.? grams per liter of Na2WO4.2HzO which is equivalent to 2 grams of tungsten per 50 ml. When this tungstate solution was added directly to the nickel plating bath, a precipitate formed. This precipitate, perhaps a basic nickel tungstate, dissolved on addition of. a small amount of sulfuric acid. and thorough. stirring. Instead of permitting the precipitate to. form, it seemed best to have a. predetermined. excess of the acid present before adding the sodium tungstate solution. The volume. of H280; required was indicated by an experimentally determined buffer curveplotted in terms of pH of the nickel plating bath and volume of added acid. Then an excess of 2 ml. of 6N H2804 was added for each 2' grams of tungsten equivalent to be added to the bath. The sodium. tungstate solution was then added" and as long. asthe. pH was below 5.4; no precipitate remained in. the bath.' The bath was finally made up to a volume of one liter andthe pH more carefully adjusted tov the desired value. This completed bath was stable at temperatures. as high as C.

The pH of the bath. was adjusted to about 3 and plating was-carried out at a tiemp'eratur'e between 40 anddll." C. andia cathode current density between 0.5 and 1.0 ampere per square decimeter.

The anode was of nickel.

The cathode basisv metal"v was copper although brass, iron, steel, nickeLor any oithe other commonv basis metalsv either plain or with" a preliminary flash. orplated. coating of copper may be used.

the resulting electrod'eposit was. a nickeltungsten alloy containing ab.out.4% tungsten. It formed a smooth, adherent, metallic deposit which took a. high polish when buffed. The deposit had a higher corrosion resistance than pure nickel deposits.

The conditions and compositions of the baths may be. varied. to. obtain different proportions of tungsten in the alloy deposit. Deposits containin from a trace up to 20% or more of tungsten can be obtained.

The amount of tungsten in the bath will generally be between 0.2 and 16 grams per liter and is added as sodium tungstate or other soluble tungstates, such as potassium tungstate, or ammonium tungstate. Usually 1 to 2 grams of tungsten per liter is preferred.

The pH of the bath should be maintained between 2 and 5.4, the preferred acidity being pH3, although where higher percentages of tungsten are desired in the electrodeposited metal the upper part of the pH range given is more effective. The higher pH values also aid in increasing the current efficiency.

Good deposits are best obtained at elevated temperatures, the range between 40 C. and 70 C.

3 being most suitable. The higher temperatures increase the current efficiency,

Cathode current densities between 0.1 ampere and 5 amperes per square decimeter are preferred, although still higher densities may be used. Current density has little effect on current efficiency or on percentage of tungsten in the alloy deposit.

It is to be understood that in the present specification and claims the term Watts nickel-plating bath is used to denote a nickel-plating bath of the type described by Oliver P. Watts in Transactions of the American Electrochemical Society, 1916, vol, 29, page 395 and ff. and consisting of an aqueous solution of nickel sulfate, nickel chloride and boric acid in the above described concentrations.

The nickel-tungsten alloy plate can be used in places where straight nickel plating fails to give proper corrosion resistance. It may also be used as a substitute for chromium plating on hardware, automobile parts and accessories and other uses. This has the advantage of requirin less plating operations. In chromium plating it is necessary to plate iron or steel parts with copper, nickel and then chromium. With our process the parts may be plated with copper and then with the nickel-tungsten alloy.

What is claimed is:

1. A modified Watts bath for nickel-tungsten alloy plating consisting of an aqueous solution containing about 250 grams per liter of nickel sulfate, about 21 grams per liter of nickel chloride, about 30 grams per liter of boric acid, and about 4 grams per liter of sodium tungstate, said bath having a pH of about 3.

2. A modified Watts bath for nickel-tungsten alioy plating consisting of an aqueous solution containing nickel sulfate, nickel chloride, boric acid, and about 1 to 2 grams per liter of a soluble tungstate, said bath having a pH of about 3.

3. A modified Watts bath for nickel-tungsten alloy plating consisting of an aqueous solution containing nickel sulfate, nickel chloride, boric acid, and sufiicient sodium tungstate to provide a concentration of about 1 to 2 grams per liter of tungsten, said bath having a pH of about 3.

4. In the art of electrodepositing a nickeltungsten alloy, the step of passing a current between a cathode and a nickel anode through a modified Watts bath consisting of an aqueous solution containing nickel sulfate, nickel chloride, boric acid, and sufficient sodium tungstate to provide a concentration of about 1 to 2 grams per liter of tungsten, said bath having a pH of about 3.

5. In the art of electrodepositing a nickeltungsten alloy, the step of passing a current between a cathode and a nickel anode through a modified Watts bath consisting of an aqueous solution containing nickel sulfate, nickel chloride, boric acid, and about 1 to 2 grams per liter of a soluble tungstate, said bath having a pH of about 3.

6. In the art of electrodepositing a nickeltungsten alloy, the step of passing a current between a cathode and a nickel anode through a modified Watts bath consisting of an aqueous solution containing about 250 grams per liter of nickel sulfate, about 21 grams per liter of nickel chloride, about 30 grams per liter of boric acid, and about 4 grams per liter of sodium tungstate, said bath having a pH of about 3.

7. In the art of electrodepositing a nickeltungsten alloy, the steps which consist in passing current between an anode and a cathode through a modified Watts bath containing nickel sulfate, nickel chloride, boric acid, and a soluble tungstate, maintaining the tungstate content of the bath at such a value as to provide a tungsten concentration Within the range of 0.2 to 16.0 grams per liter, operating the bath at a pH within the range of 2.0 to 5.4, and controlling the tungsten concentration and pH so as to produce a metallic deposit.

8. In the art of electrodepositing a nickel tungsten alloy, the steps which consist in passing current between an anode and a cathode through a modfied Watts bath containing nickel sulfate, nickel chloride, boric acid, and sodium tungstate, maintaining the sodium tungstate content of the bath at such a value as to provide a tungsten concentration within the range of 0.2 to 16.0 grams per liter, operating the bath at a pH Within the range of 2.0 to 5.4, and controlling the tungsten concentration and pH so as to produce a metallic deposit.

M. LESLIE HOLT. MORRIS L. NIELSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Armstrong et al May 30, 1939 OTHER REFERENCES Number