US2180956A

US2180956A - Electric contacting element

Info

Publication number: US2180956A
Application number: US166371A
Authority: US
Inventors: Franz R Hensel
Original assignee: PR Mallory and Co Inc
Current assignee: Duracell Inc USA
Priority date: 1937-09-29
Filing date: 1937-09-29
Publication date: 1939-11-21
Anticipated expiration: 1956-11-21

Description

Patented Nov.'2l, 1939 UNITED STATES ELECTRIC CONTACTING ELEMENT Franz R. Hensel, Indianapolis, Ind., assignor to P, It. Mallory & (30., Inc., Indianapolis, Ind., a corporation of Delaware No Drawing.

1 Claim.

This invention relates to the production of electric contacting elements.

It is an object of this invention to provide a new contact element which will have a very high 5 melting point, combined with comparatively low electrical resistivity.

It is a further object of this invention to produce a contact material which will not dissociate at operating temperatures, and thus form layers of high contact and specific resistance.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the fea tures of construction, combinations of elements and arrangements of parts which will be exemplified in the constructions hereinafter set forth and the scope of the application of which will be indicated in the claim. a

In the prior art, compositions have been mentioned in which refractory metals and their compounds were impregnated with a lower melting point metal of the nature of silver and copper plus gold, or iron, nickel and cobalt, or a metal of the platinum or palladium group. Usually the metals selected are molybdenum or tungsten or their carbides. The metals tungsten and molybdenum, which are highly refractory, have the disadvantage that they oxidize at comparatively low temperature and certain forms of tungsten and molybdenum oxides produce very high contact resistance. As a matter of fact, they act as insulators. The carbides of these metals, which also have been tried, in many instances, have usually a very high specific resistance. The present invention contemplates electric contacting elements formed of metal compositions comprising as'essential ingredients thereof one or more metal compounds of metals selected from the fourth and fifth groups of the periodic system, namely, titanium, zirconium, hafnium, vanadium, columbium and tantalum combined with nitrogen and a low melting point metal selected from the group silver, copper and gold or an alloy of such metals. The metal compositions may also include substantial percentages of other refractory metals or refractory metal compounds such as metals of the tungsten group and other refractory compounds if desired.

An important advantage arising from the use of refractory nitrides listed above resides in their Application September 29, 1937, Serial No. 166,371

relatively high electrical conductivity whereby they are rendered advantageous for electrical purposes. As an example, the electrical resistivity of two of these compounds are here listed:

. Melting point Resistivity Compoum microhms/c. m. g gs gz Zirconium nitride 13.6 3255 Titanium nitride 21. 7 3220 It is quite remarkable that the nitrides of such metals as zirconium, hafnium and titanium show a much lower resistivity than the elements themselves. Pure zirconium, for instance, has a resistivity of 44.6 microhms c. m., while titanium has a resistivity of almost microhms c. m.

Tests have shown that the carbides of the sixth group of the periodic ystem, particularly the carbides of molybdenum and tungsten, are easily attacked by the air at elevated temperatures.

The compounds of the present invention are more resistive to an attack of oxidizing atmosphere at such elevated temperatures.

Any alloy of this nature may be employed to advantage for electric uses such aselectrical contacting elements. a

I have found that metal mixtures of the following combinations are particularly desirable? Per cent Borides and nitrides of elements selected from the group consisting of titanium, zirconium, hafnium, vanadium, columbium, tantalum either individually or in combination 50-99 Silver, copper or gold or alloys containing said elements as principal ingredients 150 the impregnation process.

will nottend to stick. Sticking is usually caused by the fusing together of small particles of the low melting point metal. However, by selecting the proper ratios of the refractory compounds with or without refractory metals of the nature of tungsten and molybdenum, a structure is produced which will completely separate the low melting point particles, so that in service they can not flow together if arcing occurs, and make contacts stick.

While it was necessary previously to use low percentages of refractory compounds in order to obtain a low specific resistance, with the new materials described herein, almost any percentage up to 99% of the refractory alloys may be used and still a good conductivity may be obtained without excessive over-heating.

The methods by which the above mentioned combinations are produced may vary. I may take, for instance, the powders of the refractory metal compounds and mix them with the powders of the metals of the tungsten group and the powders of the low melting point alloys. After an intimate mixture has been obtained, the powders can be pressed, either cold or at elevatd temperatures. After the pressing, the powders may be sintered, either below the melting point of the low melting point metal, or above. After the sintering operation, the material may be repressed and resintered and then swaged, rolled or forged to any desired shape or it may be used in the repressed condition.

Another possibility is to mix the powders of the refractory compounds and the refractory metals together, with or without the addition of a metal of the iron group. After pressing and sintering, or pressing, sintering, crushing, repressing and resintering, the low melting point constituent may be introduced into this mixture by means of capillary action at temperatures above the melting point of the low temperature constituent. Repressing and resintering, with or without further operations, may also be applied in this case. In certain instances it has been found advisable to combine the above mentioned manufacturing procedures by substituting various steps of the one procedure with certain steps of the second procedure.

There are also certain possibilities of varying It may, for instance,

be desirable to spray the low melting point constituent onto the pressed body of the sintered refractory material, and then heat same to absorb the sprayed-on layer of the low melting point material. Instead of spraying, other processes such as plating, may also be used.

By means of these methods, excellent metal compositions are obtained, the structure of which is homogeneous and the bodies of which may be easily prepared. Such bodies will also retain, over long periods of time, their original homogeneous structure.

Instead of using a pure nitride of the metal of the fourth or fifth group of the periodic system, I have found that I can use commercial grades of these materials which usually contain a certain percentage of impurities. As a matter of fact, in many cases, I have found it very desirable to have impurities present because they seem to improve the wetting characteristics and form a stronger union between the low melting point phases and the refractory metal compounds. Instead of using pure nitrides, therefore, I may use also, nitrides contaminated with a small percentage of carbon. Such nitrides are generally known as cyano nitrides.

Since certain changes in carrying out the above processes, and certain modifications in the composition, which embody the invention, may be made, without departing from its scope, it is intended that all matter contained in the above description, shall be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claim is intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which as a matter of language might be said to fall therebetween.

What is claimed is:

An electric contacting element formed of a metal composition consisting of 50 to 99% of at least one of the nitrides selected from the group consisting of nitridesof titanium, zirconium, hafnium, vanadium, columbium and tantalum, and l to 50% of lower melting point metal selected from the group consisting of silver, copper and gold and alloys consisting'predominantly of said metal.

FRANZ R. HENSEL.