US2443651A

US2443651A - Process of electroplating on tungsten

Info

Publication number: US2443651A
Application number: US566775A
Authority: US
Inventors: Joseph J Cannizzaro
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1944-12-05
Filing date: 1944-12-05
Publication date: 1948-06-22
Anticipated expiration: 1965-06-22

Description

Patented June 22, 1948 PROCESS OF ELECTBOPLATING ON TUNGSTEN Joseph J. Cannizzaro, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh,'Pa., a corporation of Pennsylvania Q No Drawing. Application December 5, 1944,

Serial No. 566,775 7 v 3 Claims.

1 This invention relates to the plating of a metal upon tungsten members, and more particularly to the electroplating of a metal on various hing-- sten members in the form of wire, sheets and the like. i

Previously the electroplating of metals on tungsten has not been satisfactory from the standpoint of an adherent bond between the metal and the tungsten. Tungsten wire, in particular, has not been electroplated heretofore satisfactorily with other metals. Even with the best of care, in the prior art practice an electroplated coating of metal deposited on tungsten wire can be readily stripped off in the form of a tubular sheath. This indicates that the bond between the electroplated metal and the tungsten is ineffective for producing a strongly united composite member.

For many applications, it is desirable to produce a tenaciously adherent electroplated coating of some metal on tungsten sheets, wires and other bodies of the tungsten. For example, it may be desirable to soft solder a tungsten wire or the like to a base composed of copper or other metal. Tungsten, however, is not considered to be soft solderable. However, an electroplated coating of nickel on the tungsten will permit effective soft soldering to be accomplished. Numerous other applications are facilitated if an electroplated coating of some metal, such as nickel, copper, tin or the like, can be electroplated on the tungsten with a good adherent bond being present.

The object of this invention is to provide an adherent electroplated coating of a metal on tungsten members.

A further object of the invention is to pro vide for etching tungsten members to facilitate electroplating thereon of adherent coatings of metals.

Other objects of the invention will in part be obvious and will in part be apparent hereafter.

It has been discovered that tungsten may be electroetched to provide for a clean surface having such characteristics that metals may be electroplated thereon to produce tenaciously adherent coatings. Briefly, the electroetching process consists in applying to the tungsten member an aqueous solution containing from 5% to 50% hydrofluoric acid and while the tung sten member is in contact with the aqueous solution of hydrofluoric acid applying alternating current at a voltage of the order of 5 volts. The current is conducted to the'solution through a second electrode composed of platinum, graphite or other relatively inert material. The etch ing is accomplished at room temperature though the solution may be heated, if desired. The operation may be accomplished rapidly, generally a period of time of one or two minutes being suflicient. V

As anexample of the practice of the invention, a tungsten wire was connected to alternating current at 5 volts and immersed in a bath containing 24% hydrofluoric acid solution, the other electrode in this case being ofplatinum. After one minute at room temperature, the tungsten wire was found to be etched to a clean bright state suitable for electroplating a metal thereon. The etched wire was immediately transferred to a conventional nickel plating solution containing nickel chloride and sulfate salts. A direct current of milliamperes at 6 volts was applied to the etched tungsten wire while in the plating solution. In one minute, a thin coating of nickel was plated upon the tungsten wire.

The nickel plated tungsten wire was bent sharply several times and otherwise mechanically deformed without any observable loosening or cracking of the nickel plated coating. By comparison, a, tungsten wire not subjected to the electroetch of this invention but cleaned by dipping in a mineral acid and then electroplated in the same nickel solution acquired a relatively non-adherent nickel coating. Upon bending the latter wire, the nickel plated coating sleeved and could be readily removed from the wire.

The electroetched tungsten may be plated in any of the conventional plating solutions such, for example, as copper, tin, zinc, chromium, cadmium and the like. It is desirable to commence plating of the electroetched tungsten wire as soon as possible after removal from the etching bath in order to prevent the reoxidation of the cleaned tungsten surfaces. The thickness of plating may be varied to suit requirements. Since the bond between the clean tungsten and electroplated metal is extremely adherent the plated member may be subjected to various treatment without failure. The electroplated tungsten members may be mechanically processed by bending, swaging, twisting or other desired treat-- ment. Likewise the electroplated tungsten members may be heated in order to accomplish soldering or to produce any predetermined condition in the composite member.

The nickel plated tungsten wire whose making was above described in detail was satisfactorily bent to predetermined shapeand soldered to a copper base member for use in producing a crystal probe. The tungsten wire could not be satisfactorily welded or hard soldered to the base member, since overheating would take place and the tungsten wire would be unsatisfactory for its intendedpurpose,

Since certain "changes may be made in the above invention and different embodiments of the invention may be made without departing. from the scope thereof, it is intended that all matter contained in the above disclosure shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In the process of electroplating a metal. on a tungsten member, the steps comprising applying to the tungsten member a hydrofluoric acid solution, passing an alternating current at 5 volts through the tungsten member in the presence of the hydrofluoric acid solution for from one to two minutes to etch the surface, removing the etched tungsten member from the hydrofluoric acid solution and electroplating a metal on the treated tungstenmem-ber.

2. In the process of electroplating a metal on a tungsten member, the steps comprising applying. to the tungsten member an aqueous solution. having from 5% to 50% hydrofluoric acid, passing an alternating currentat 5 volts through the tungsten member while it is in contact with the aqueous solution for a period of time to etch the surface of the member, removing the tungsten member from the aqueous solution and electroplating a metal on the treated member.

3. In the process of plating nickel on a tungsten member, the steps comprising, applying to the tungsten. member an aqueous solution having from 5'% to- 50% hydrofluoric acid, passing an alternating current at 5 volts through the tungsten member while it is in contact with the aqueous solution for a period of from one to two minutes to etch the member, removing the tungsten member from the aqueous solution, applying to the tungsten member a plating solution from which nickel may be electro-deposited, passing a direct current through the member and the plating solution to plate nickel on the tungsten member.

JOSEPH J. CANNIZZARO.

REFERENCES CITED The following referencesare of record in the file of" this patent:

UNITED STATES PATENTS OTHER REFERENCES Websters New International Dictionary, 22nd ed. 1940,.pages 171-5 and 1716.