US3811939A - Method for the manufacture of heterogeneous penetration compound metal - Google Patents

Abstract

In a protective gas atmosphere, at least one metal of high vapor pressure (diffusion metal) is admitted as an alloying component through diffusion into the impregnating metal of lower melting point such as silver or copper contained in the pores of the frame metal, such as tungsten, rhenium or molybdenum. The diffusion temperature is chosen so that the impregnating metal exists in the liquid phase at least after the diffusion of the diffusion metals. The diffusion takes place, preferably, at 20 to 240*C above the melting temperature of the impregnating metal or the alloy formed between the impregnating metal and the diffusion metal. As the diffusion metal is used at least one of the metals bismuth, cadmium, gallium, indium, lead, tin and tellurium.

Description

finite States Patent 1191 Hassler et a1.

Siemens Aktiengesellschaft, M1L11911213I11 ansilit en sn, Germany Filed: Dec. 28, 1971 Appl. No.: 213,205

Assignee:

Foreign Application Priority Data Jan. 13, 1971 u.s.c1...-. 117/227, 117/99, 117/131,

117/230 Int. Cl B4411 1/02 Field of Search 117/227, 131, 230, 99

References Cited UNITED STATES PATENTS 9/1958 Hoyer 117/227 Germany 2101414 May 21, 1974 2,671,955 3/1954 Grubel et a1 117/131 2,813,808. 11/1957 Hoyer 117/131 2,706,759 4/1955 Williamson 117/227 3,290,170 12/1966 Houston 117/227 Primary ExaminerCameron K. Weiffenbach Attorney, Agent, or Firm-l-lerbert L. Lerner [5 7] ABSTRACT In a protective gas atmosphere, at least one metal of high vapor pressure (diffusion metal) is admitted as an alloying component through diffusion into the'impregnating metal of lower melting point such as silver or copper contained in the pores of the frame metal, such as tungsten, rhenium or molybdenum. The diffusion temperature is chosen so that the impregnating metal exists in the liquid phase at least after the diffusion of the diffusion metals. The diffusion takes place, preferably, at 20 to 240C above the melting temperature of the impregnating metal or the alloy formed between the impregnating metal and the diffusion metal. As the diffusion metal is used at least one of the metals bismuth, cadmium, gallium, indium, lead, tin and tellurium.

6 Claims, N0 Drawings METHOD FOR THE MANUFACTURE OF IIETEROGENEOUS PENETRATION COMPOUND METAL SPECIFICATION The present invention concerns a method for the manufacture of a heterogeneous penetration compound metal especially for use as contact material for vacuum circuit breakers, in which the pores ofa porous sintering skeleton of a high-melting, burn-off resistant metal (skeleton metal) such as tungsten, rhenium or molybdenum or of an alloy of these metals, are filled with a lower melting metal (impregnating metal) of high electric conductivity, such as silver and copper, or with a lower melting alloy of these metals.

ln contact materials which are used in vacuum circuit breakers, the requirement exists for extremely low gas content and gas producing impurities. Such contact materials should, in addition, exhibit particularly low weld-ability and little burn-off due to evaporation in an arc, in order to obtain long life and low contact resistance. The latter requirement regarding low contact resistance can easily be met in a vacuum circuit'breaker due to the fact that the chemical and physical substances which are active in the atmosphere are absent,

in contrast to air circuitbreakers, and no foreign layers are generated at the contact surfaces of compounds of the contact metals and oxygen or sulfur, respectively. Furthermore, there exists a requirement for a low chopping effect, i.e., in switching small currents the arc should not be interrupted so that voltage spikes which might lead to breakdowns, are caused by the induction effect. In order to obtain this anti-chopping effect, components which have high vapor pressure under the conditions in the arc, are added to the basic contact material, whereby a constriction of the arc due to current forces (pinch effect) is avoided.

The known contact materials of copper or copper alloys exhibit relatively high weldability and great burnoff particularly when used in vacuum circuit breakers.

to l,500C, if a metal with high vapor pressure is used for achieving the anti-chopping effect, it is difficult to maintain a desired defined content of the metal.

It is an objective of the invention to provide a method for a manufacture of the above-named contact materials, avoiding the described difficulties regarding maintenance of a defined content of an effective component of a metal with high vapor pressure.

We resolve this problem by adding at least one metal or a metal alloy of higher vapor pressure than that of the liquid copper (diffusion metal) as the alloying component by diffusion, in a protective gas atmosphere, which has low solubility in the diffusion metal and the impregnating metal, into the lower-melting impregnating metal located in the pores of the skeleton (frame) metal wherein the compound material of the skeleton material and impregnating metal has already been degassed in a preceding operation in a high vacuum. The diffusion temperature is chosen so that the impregnating metal exists in the liquid phase at least after the diffusion metal is diffused in.

The diffusion of the diffusion metal into the impregnating metal, filling the pores of the high melting component, takes place in the liquid state of the impregnating and diffusion metal. The diffusion temperature is preferably 20 to 240C above the melting temperature of the impregnating metal or the alloy which is formed between the impregnating metal and the diffusion metal. If silver is used as impregnating metal, the diffusion temperatures of 1,000 to l,200C are preferably used. If copper is used as the impregnating metal, diffusion temperatures between 1,100 and l,300 are used.

Particularly suited as diffusion metals are at least one of the metals bismuth, cadmium, gallium, indium, lead, tin and tellurium.

As a surprising effect, it has been found in the diffusion process that bismuth in copper as the impregnating metal which is situated in the pores of the sintered skeleton of molybdenum or tungsten, reaches a depth of penetration of 5 mm at temperatures of l',200C after about 15 minutes. After the diffusion treatment, the bismuth content in the copper impregnated region is practically uniform within the space of the pores of the high melting component. According to this diffusion method, it is possible to distribute the diffusion metal in the impregnationmetal with high vapor pressure in a defined,'desired concentration. For vacuum circut breakers, it has been found particularly successful to use WCuBi contact materials with copper contents of Example 1 A contact'blank of WCu 20 with 80 g W and 20 g Cu is placed in a 35 mm diameter graphite crucible. 0.3 to L0 g of bismuth or tellurium was added as the diffusion metal. The graphite crucible was subsequently heated to a temperature between l,l00 and 1,200C. The diffusion took place in a protective gas atmosphere of argon or nitrogen and was completed after about 10 minutes. Subsequently, the graphite crucible was cooled.

Example 2 In a variant of the method, an alloy, for instance of 10 g of Cu.. As a diffusion metal, 5 g of a prealloyed CuBi 4 to 12 or CuTe 4 to 12 was, for instance, added. The quantity and concentration of the prealloyed material was so determined that a final concentration of 0.3 to 1.0 percent by weight is obtained. Subsequently, the crucible was heated to a temperature of 1,000 to l,100C. The diffusion took place under a protective gas atmosphere of argon or nitrogen and was completed after about minutes. Subsequently, the graphite crucible was cooled.

What is claimed is:

1. In the manufacture of an electrical contact comprising forming a composite structure constituted of a porous sintered body selected from the group consisting of tungsten, rhenium, molybdenum and a high melting alloy thereof, filling the pores of the sintered body with an impregnating metal selected from the group consisting of copper, silver and a low melting alloy thereof and degassing the structure in a high vacuum, wherein the improvement comprises subsequent to the degassing step, contacting the exposed surfaces of the impregnating metal with a diffusion metal selected from the group consisting of bismuth, cadmium, gallium, indium, lead tin, tellurium and an alloy thereof in a protective gas atmosphere which has low solubility in both the impregnating metal and the diffusion metal, and heating the structure to a temperature of from to 240C above the melting point of the impregnating metal or of the alloy to be formed between the impregnating metal and the diffusion metal for a period of time sufficient to diffuse the diffusion metal into the impregnating metal.

2. Th method of claim 1, wherein the impregnating metal is silver and the temperature to which the structure is heated is from 1,000 to 1,200(I.

3. The method of claim 1, wherein the impregnating metal is copper and the temperature to which the structure is heated is from l,l00 to 1,300C.

4. The method of claim 1, wherein bismuth is diffused into copper at a temperature of 1,200C for 15 minutes.

5. The method of claim 1, wherein the diffusion metal is an alloy selected from the group consisting of copper-bismuth and coppentellurium.

6. The method of claim 1, wherein the protective atmosphere is. selected from the group consisting of argon and nitrogen.

Claims (5)

1. 2. Th method of claim 1, wherein the impregnating metal is silver and the temperature to which the structure is heated is from 1,000* to 1,200*C.
2. 3. The method of claim 1, wherein the impregnating metal is copper and the temperature to which the structure is heated is from 1,100* to 1,300*C.
3. 4. The method of claim 1, wherein bismuth is diffused into copper at a temperature of 1,200*C for 15 minutes.
4. 5. The method of claim 1, wherein the diffusion metal is an alloy selected from the group consisting of copper-bismuth and copper-tellurium.
5. 6. The method of claim 1, wherein the protective atmosphere is selected from the group consisting of argon and nitrogen.