US2200855A - Electrical contact - Google Patents

Description

Patented May 14, 1940 PATENT FFiCE ELECTRICAL CONTACT Samuel Ruben, New Rochelle, N. Y.

No Drawing. Application May 2, 1939, Serial No. 271,347

Claims. (Cl. 200-166) This invention relates to electrical contacts, specifically to silver or copper base contacts.

The art discloses silver contacts containing a relatively high melting point oxide, such as lead oxide or thallium oxide, added to reduce arcing and tendency to stick. Such oxides after sintering of the contact have usually remained in the contact as localized particles, the distribution depending upon initial grain size and. extent of intermixing prior to pressing.

I have found that silver or silver composition contacts such as mixtures or alloys of silver with copper, molybdenum, etc., it mixed in powdered form with a small quantity of antimony trioxide, pressed and sintered into shape, produce a new and superior product for a large number of electrical applications. The antimony trioxide which melts in the neighborhood of 656 C., provides a dense contact structure due to grain boundary cementation. When the pressed, mixed materials are brought up to the melting point of the antimony trioxide an extremely uniform grain structure is produced as distinguished from mechanical mixtures of the prior art where 2i! relatively high melting point oxides have been added to the particles of silver. In the latter case, the distribution is entirely dependent upon the relative grain size of the metal particles and extent of mixing prior to pressing. The result- 30 ing structure is quite different, however, in contacts of the present invention. At a temperature of. about 650 0., below the normal sintering temperature of the silver particles, the antimony' trioxide will flow between the granule boundaries 8' and produce a thin film 'of oxide throughout the contact structure, as distinguished from a contact structure in which particles of oxide are distributed throughout the contact.

I have also noted that antimony trioxlde apa pears to have a dissolving action upon both silver and copper oxides. This probably accounts to some extent for the improved bonding of the metal particles and'the homogeneous structure of the contacts of this invention as compared to other contacts of metal and non-metal mixtures. The contacts may be made of pure powdered silver and powdered antimony trioxide. The" mixture is ball milled to insure complete intermixing and contacts are pressed therefrom into discsof the desired shape. The discs are heated to a temperature of about 675 C. so as to allow melting of the antimony trioxide and are then rapidly cooled to avoid volatilization of the oxide.

The useful range of antimony trioxide is from .l% to and the preferred limits are from about 1 to about 10%. A contact adaptable for a great many electrical applications is one consisting of. 95% silver and 5% antimony trioxide.

While silver has the preferred contact resistance properties I have found that contacts made with copper powder and employing antimony trioxide as a bonding material have less tendency to stick and are than usual copper, contacts and less tendency to oxidize.

The antimony trioxide is the only oxide of antimony which I have found suitable for the purposes of this invention. The other oxides of antimony do not possess characteristics which permit its use or which afford desirable results in electrical contacts.

While the invention is specifically directed to contacts of silver or copper containing a relatively small proportion of antimony'trioxide it is recognized that other elements may be added to the silver or copper, 'or' that the silver and copper may be alloyed, in order to reduce the cost or the contact, and that the term silver base or copper base contact when used herein will cover compositions of silver and copper with other metals.

What is claimed is: a

1. An electrical contact composed of a contact material characterized by the addition of a relatively small amount of antimony trioxide.

2. An electrical contact of the group consisting of silver and copper base contacts containing from .1 to 25% antimony trioxide.

3. A silver base electrical contact containing from .1 to 25% antimony trioxide.

4. A copper base electrical contact containing from 1. to 25% antimony trioxide.

5. A silver base electrical contact containing from about 1% to about 10% antimony trioxide.

SAMUEL RUBEN.