US3590197A - Electrical contacts containing gettering material - Google Patents

Abstract

An electrical contact for a vacuum interrupter consists of a binary alloy of 95 to 99 percent tungsten and 1 to 5 percent tantalum, which alloy when heated during contact arcing getters undesirable hydrogen which may be present in the interrupter.

Description

United States Patent [72] Inventor Henry J. Wesoloski Milton, Mass. 211 Appl. No. 772,347 [22] Filed Oct. 31, 1968 [45] Patented June 29, 1971 [73] Assignee Allis-Chalmers Manufacturing Company Milwaukee, Wis.

[54] ELECTRICAL CONTACTS CONTAINING GETTERING MATERIAL 2 Claims, 1 Drawing Fig.

[52] 11.8. C1 200/166 C, 200/144 B, 75/174, 75/176 [51] lnt.Cl 1101b 1/02, H0111 33/66 [50] Field otSearch 200/1442, 166C; 75/174, 176; 252/1816; 219/145, 146

[56] References Cited UNITED STATES PATENTS 2,321,910 6/1943 Hays 252/1816 X 2,785,285 3/1957 Bernard... 219/146 3,198,932 8/1965 Weatherly 219/145 3,270,172 8/1966 Chubb 200/144 (.2) 3,379,846 4/1968 Wood et a1. 200/144 (.2) FOREIGN PATENTS 693,827 9/1964 Canada 200/144 (.2)

1,201,164 12/1959 France 200/166 (C) 211,693 2/1968 U.S.S.R. 200/166 (C) OTHER REFERENCES TUNGSTEN AND ITS COMPOUNDS, by G. D. Rieck, copyright 1967 by Pergamon Press; p. 77; copy in scientific library of patent office. I

THE METAL TANTALUM, by Fansteel Metallurgical Corp., copyright 1951; p. 16; copy in Or. 110; class 75/174 Primary Examiner-Robert K. Schaefer Assistant ExaminerRobert A. Vanderhye Attorneys-Thomas F. Kirby, Robert B. Benson and Lee H.

Kaiser ABSTRACT: An electrical contact for a vacuum interrupter consists ofa binary alloy of 95 to 99 percent tungsten and 1 to 5 percent tantalum, which alloy when heated during contact arcing getters undesirable hydrogen which may be present in the interrupter.

SUMMARY OF THE INVENTION This invention relates generally to electrical contacts and particularly to contacts containing gettering material used in vacuum switches or similar interrupting devices hereinafter referred to as vacuum switches.

One type of vacuum switch comprises an evacuated envelope in which relatively movable tungsten contacts are enclosed. In normal operation, arcing which occurs upon contact separation is quickly extinguished. However, if impurities in the form of undesirable gases are present inside the envelope, then arcing is not readily extinguished and a risk of flashover between the contacts exists, particularly if alternating current is involved. One gaseous impurity often present is hydrogen which may evolve from several sources. For example, a monolayer of water on the surface of components or entrapped in component materials, particularly those which have been hydrogen fired or brazed during manufacture and assembly, may serve as a source of hydrogen. Steps to reduce the presence of undesirable hydrogen, such as bakeout and quality control in material selection, are not always completely successful. Furthermore, the high temperatures which exist inside the envelope during arcing causes evolution of hydrogen which may not have been completely released during manufacture and processing.

It is known that gettering materials can be employed inside the evacuated envelope of vacuum interrupters to getter hydrogen. However, such materials heretofore have been arranged as a separate component or as a surface plating on some other component. It is desirable, however, to provide improved gettering means.

In accordance with the present invention, a hydrogen-gettering material such as titanium or tantalum is alloyed with the tungsten material of which the contacts are made. Preferably, the alloy consists of 95 to 99 percent tungsten and 1 to 5 percent tantalum. During contact arcing when heating causes evolution of hydrogen, the gettering material is also heated and its gettering efficiency greatly increased.

OBJECTS It is an object of the present invention to provide improved gettering means for vacuum switches.

Another object is to provide such gettering means which are disposed at an optimum location within the vacuum switch.

Another object is to provide improved gettering means of the aforesaid character in which the gettering material selected has increased affinity for gettering hydrogen at elevated temperatures and is located at the position which is hottest.

Another object is to provide a gettering means of the aforesaid character wherein the gettering material is alloyed with the contact material.

Another object is to provide a tungsten vacuum switch contact which comprises tantalum as gettering materials.

Another object is to provide such a contact which comprises 95 to 99 percent tungsten and l to 5 percent tantalum.

Other objects and advantages of the invention will hereinafter appear.

DRAWINGS In the drawing, there is shown a vacuum switch which employs electrical contacts in accordance with the present invention.

DESCRIPTION OF THE INVENTION Referring to the drawing, there is shown a vacuum switch which comprises a bottle 1 made of insulating material and having metallic end plates 2 and 3 sealed thereto to define a chamber 4 within which a stationary contact rod 5 and a movable contact rod 6 are disposed. Rods 5 and 6 are preferably copper. A bellows 7 is secured to end plate 3 and contact rod 6 to permit axial movement of contact rod 6 to contact open and contact closed positions. Contact rods 5 and 6 are provided at their inner ends with contacts 8 and 9, respectively. A shield 10 is disposed on contact rod 5. Chamber 4 is understood to be evacuated to a pressure of at least l0 mm. of mercury.

In accordance with the present invention, either or both of contacts 8 and 9 are fabricated of an alloy consisting of tungsten and tantalum or tungsten and titanium. In a preferred embodiment, to 99 percent of the alloy is tungsten and l to 5 percent of the alloy is either titanium or tantalum. Alloys of tungsten-tantalum are commercially available, for example, from the Metals Division of the National Research Corporation. Alloys of tungsten-titanium can be fabricated by melting titanium into sintered tungsten in a manner similar to that in which copper is melted into sintered tungsten. If preferred, a tungsten contact could be coated with tantalum powder and the contact material and tantalum powder sintered together to provide the alloy primarily at the contact surfaces. On account of the high degassing temperature required for tantalum, tungsten is suitable as a base metal for tantalum powder. The tantalum or titanium in the contacts acts as a getter when arcing occurs as contacts 8 and 9 are separated while current is flowing therethrough.

As previously explained, hydrogen present in space 4 of the vacuum switch evolves from various sources primarily during arcing when the vacuum switch components are raised to extremely high temperatures. The presence of hydrogen in undesirable amounts make for a gassy" vacuum switch which tends to be unreliable.

Tantalum has an affinity for absorbing hydrogen very readily at the temperatures to which the tungsten-tantalum alloy contacts 8 and 9 or portions thereof would be raised when arcing occurs in vacuum switch 1. Specifically, tantalum absorbs up to 55 times its volume at red heat and up to 700 times its own volume at yellow heat. Carefully degassed tantalum sheets may absorb hydrogen to the extent of 740 times its volume provided that the temperature does not exceed 800 C. Optimum absorption occurs at about 600 C. In any event, the maximum gettering is secured by service wherein the contact or portions thereof operate at red to yellow heat.

It is to be noted that the vapor pressure of tantalum is almost equal to that of tungsten, therefore, these materials are compatible at the high temperatures to which they would be raised during arcing. Furthermore, tungsten has a melting point of 3,380 C, and tantalum has a melting point of about 2,996 C. 50 C. Tantalum can be brazed to itself and to other metals such as copper and tungsten if the braze material contains nickel and if the process is carried out in a vacuum at a pressure not higher than 10 torrs.

It is to be understood that titanium has properties similar to that of tantalum at least as regards the properties discussed herein which enable tantalum to be employed as a suitable hydrogen getter in an alloy.

The embodiments of the invention in which I claim an exclusive property or privilege are defined as follows:

1. An electrical contact consisting of a composition of tungsten and tantalum.

2. A contact according to claim 1 consisting of about 95 to 99 percent tungsten and about 1 to 5 percent tantalum.

Claims (2)

1. An electrical contact consisting of a composition of tungsten and tantalum.

2. A contact according to claim 1 consisting of about 95 to 99 percent tungsten and about 1 to 5 percent tantalum.

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