US2344552A

US2344552A - Electric discharge device

Info

Publication number: US2344552A
Application number: US429866A
Authority: US
Inventors: Knochel William John; Cherry Sidney John
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1942-02-07
Filing date: 1942-02-07
Publication date: 1944-03-21
Anticipated expiration: 1961-03-21

Description

M r h. 21,1944. w. J. KNQCHEL M. 2 34 5 2 ELECTRIC DISCHARGE DEVICE Filed Feb. 7, 1942 INVENTQRS W.J'. KNOC'l/fl- J- J- C'f/E BY Wm ATTORNEY Patented Mar. 21, 1944 UNITED STATES PATENT OFFICE ELECTRIC DISCHARGE DEVICE Pennsylvania Application February 7, 1942, Serial No. 429,866

4 Claims.

This invention relates to high vacuo incandescent filament electron discharge devices and more particularly to such devices wherein the filament is mounted upon a support means arranged to expand and contract with the expansion and contraction of the filament during each heating and cooling cycle.

In such devices, the high vacuo and relatively high temperatures normally encountered .during operation of the device makes it exceedingly difficult to provide an expandable and contractible filament support means which is freely operative over an extended time period. The essential reason for this difiiculty appears to reside in the circumstance that the coemcient of friction between clean and dcgasified metal surfaces such as are normally present in high vacuo devices is many times that of the same metal surfaces in air. It appears that surface metal oxides are essential to a low coefiicient of friction between two contacting metal surfaces and as surface metal oxides are not tolerable in high vacuo electron discharge devices, it is essential to provide in such devices wherein a sliding contact between substantially clean metal surfaces is provided, some means for lowering the coefiicient of friction between the said metal surfaces.

One of the objects of the present invention is to provide a means for lowering the coefficient of friction between two slidably engaging metal surfaces.

Another object is to provide a substitute for surface metal oxides on slidably engaging metal surfaces in expandable and contractible filament supporting means in high vacuo electron discharge devices.

Still another object is to provide an improved expandable and contractible filament mount assembly for high vacuo electrical discharge devices of the type known in the art as a triode vacuum tube.

Other objects and advantages will be apparent as the invention is more fully hereinafter disclosed.

In accordance with these objects we have discovered that the normally high coefficient of friction between slidably engaging substantially clean and degasified metal surfaces in high vacuo may be materially lowered by surfacing at least one of the surfaces with a thermally stable intermetallic compound having a relatively low vapor pressure in high vacuo, such as the sulfide, selenide and telluride compounds of the highly refractory metals tungsten and molybdenum, or

with the thermally stable amorphous carbide compounds of the metals tungsten, molybdenum, boron and silicon.

The sulfide and telluride compounds of tungsten and molybdenum are recognized lubricants for use in high vacuo devices as has heretofore been disclosed in U. S. application Serial No. 381,673, filed March 4, 1941, by P. H. Brace, issued April 28, 1942, as Patent 2,280,386, and assigned to the same assignee as the present application, and in which patent is described the adaptation of these compounds as a lubricant in the lubrication of roller bearings in high vacuo.

In the present invention, the sulfide, selenide and telluride compounds as well as the amorphous carbide compounds mentioned are employed as a surfacing material for substantially clean and degasified metal surfaces sustained in sliding relation to each other in an evacuated device in replacement of or in substitution for, the usual oxide film layer normally present thereon and removed therefrom in the cleaning and degasifying process, during the manufacture and assembly of the device, thereby to lower the coefficient of friction therebetween.

As one specific embodiment of the present invention, but not as a limitation of the same, the adaptation of the invention in the production of an expandable and contractible filament support means will be described. Reference now should be made to the drawing, wherein- Fig. 1 is a side elevational view of an expandable and contractible filament support means adapted for use in an electrical discharge device iofbthe type known in the art as a triode vacuum Fig. 2 is an enlarged sectional view of the same, showing the improvement made therein by the present invention;

Fig. 3 is a view along plane 3-3 of Fig. 1;

Fig. 4 is a view along plane 4-4 of Fig. 1; and

Fig. 5 is an enlarged view partly in section of the improvement of the present invention.

In the specific embodiment illustrated in the drawing, a plurality of filament lengths f] are sustained in substantially parallel spaced relation about the periphery of disc members 011-112. The lower said disc member dz consists of two sections (12' and d2 sustained in substantially the same plane transverse to the filament axis in a fixed position by leading-in support wires m and we passing through press 1).

The upper disc member (ii is sustained in substantial parallel spaced relation to lower disc member 022 by tubular member t slidably mounted on support rod 1* sustained in press s with its axis in substantially parallel spaced relation to the filament axes and at the approximate center of discs di and 022. The bottom end of tubular member is provided with an annular collar 0 resting on spring means 3 operative to urge tubular member t upwardly, thereby maintaining each of the filaments in tension and in substantial parallelism irrespective of variations in length incident to variations in filament temperature. In practice, the filament mount shown is included as usual in an evacuated envelope sealed to the mount at the annular flange b on the press p.

The several metal parts comprising the filament and its mounting means, prior to assembly, are baked in a readily removable gas, such as hydrogen, to thoroughly deoxidize the same and to saturate the metal with the said gas. Following sealing-in and exhaust the metal parts are thoroughly degasified by heat treatment to relatively high temperatures under a continuously maintained exhaust at high vacuum. This treatment normally results in the complete removal of all surface metal oxides on the slidably engaging surfaces of tubular member if and support rod 'r. In the prior art, this assembly and process has both required and resulted in excessive clearance between member t and support rod 1' of necessity to obtain the desired sliding relation between the parts, since any contact therebetween will result in the sticking together of the two contacting metal surfaces thereof due to the relatively high coefiicient of friction between the oxide-free and degasified metal surfaces. This relatively large spacing between the contacting surfaces of tubular member t and supporting rod r is undesirable and detrimental as it introduces transverse rocking of the filament mount and unequal tension on the filaments ff thereby throwing the filaments ff out of the desired parallelism in which they are mounted.

We have found that by the application of relatively thin surface coating of one of the intermetallic compounds hereinabove identified to either one or to both of the slidably engaging metal surfaces of tubular member if and supporting rod 1', the two said surfaces may be brought together in relatively close spaced relation to overcome the defect of the assembly hereinabove pointed out without the disadvantages of the parts sticking together as heretofore experienced.

As an example, supporting rod 1 which is usually comprised of tungsten or molybdenum, after having been subjected to the usual heat treatment in hydrogen to thoroughly deoxidize the same and to saturate the metal with hydrogen is surfaced with a relatively thin coating it of finely divided molybdenum sulfide, in suitable manner, of which painting, spraying, dipping, and tumbling are examples.

The metal surface of rod 1*, following the hydrogen heat treatment is normally relatively rough, due to the reduction to metal of the surface metal oxides on the surface thereof. It appears necessary only to provide a sufficient thickness of the molybdenum sulfide to provide a separating film thickness of material equivalent to a surface layer of metal oxide. Larger thicknesses of the material may be provided, if desired. In this respect, the film layer of molybdenum sulfide functions as a separating medium and not as a lubricant as in the above identified patent to P. H. Brace.

Alternatively, the film layer H] of molybdenum sulfide may be applied to the inner tubular surface of tubular support member t, which usually is comprised of nickel.

Also alternatively, finely divided amorphous boron carbide may be substituted for molybdenum sulfide as film layer l!) without departure from the present invention, and in this substitution the difference of the functioning of the material it) from the material employed as a lubricant in the practice of the Brave invention is effectively demonstrated.

Where the temperatures of vacuum heattreatment of the filament assembly to effectively degasify the several metal parts thereof is materially above about GOO-700 C. or where the temperature attained by the tubular support member if and rod 1' during normal operation of the device incorporating the same is materially above about 600 C., it is preferable to employ the amorphous carbide of one of the refractory metals, tungsten, molybdenum, silicon and boron as a separating film It between the slidably engaging metal surfaces of member t and rod 1. These mentioned materials are not detrimentally affected by heating to such relatively high temperatures and are thermally stable at these temperatures in high vacuo. On the other hand, however, the sulfide, telluride and selenide compounds of tungsten and molybdenum are thermally dissociable in high vacuo at temperatures approximating about 800-1000 C., with liberation of sulfur, tellurium and selenium vapors which interfere with the normal operation of the electron discharge device.

Where previous heat-treatment of the metal parts t and r in hydrogen is not practiced, the surface of the metal part to be surfaced with the separating medium of the present invention may be roughened to the extent required to provide a retaining surface for the separating material without departure from the present invention.

From the above description of the present invention and from the description of the specific embodiment given, it is believed apparent that the present invention is of wide utility in the art of electron discharge devices of the high vacuo type, and all such modifications and adaptations of the same are contemplated as may fall within the scope of the accompanying claims.

We claim:

1. A high vacuo electron discharge device enclosing metal parts having slidably engaging metal surfaces, means for materially lowering the coefficient of friction between the said slidably engaging metal surfaces, said means comprising a relatively thin film layer of an inter-metallic compound of the group consisting of the sulfide, selenide and telluride compounds of one of the metals tungsten and molydenum and the amorphous carbide compound of one of the metals tungsten, molybdenum, silicon and boron, the said film being disposed upon the surface of at least one of said slidably engaging metal surfaces.

2. A filament support means including a spring urged metallic tubular member slidably sustained on a metal rod having a diameter closely approximating the inside diameter of the said tubular member, means to lower the coefiicient of friction between the slidably contacting metal surfaces, said means consisting of a. loosely adherent film layer of a compound of the group including the sulfide, selenide and telluride compounds of the metals tungsten and molybdenum and the amorphous carbide compounds of the metals tungsten, molybdenum, silicon and boron, the said film layer being on at least one of the said slidably contacting metal surfaces.

3. A filament support means including a spring urged metallic tubular member slidably sustained on a metal rod having a diameter closely approximating the inside diameter of the said tubular member, means to lower the coefficient of friction between the slidably contacting metal surfaces, said means consisting of a loosely adherent film layer of a compound of molybdenum sulfide and the amorphous carbide compounds of the metals tungsten, molybdenum, silicon and boron, the said film layer being on at least one of the said slidably contacting metal surfaces.

4. A filament support means including a spring urged metallic tubular member slidably sustained on a metal rod having a diameter closely approximating the inside diameter of the said tubular member, means to lower the coeflicient of friction between the slidably contacting metal surfaces, said means consisting of a loosely adherent film layer of a compound of the group including the sulfide, selenide and telluride compounds of the metals tungsten and molybdenum and amorphous boron carbide, the said film layer being on at least one of the said slidably contacting metal surfaces.

WILLIAM JOHN KNOCHEL. SIDNEY JOHN CHERRY.