US3256458A

US3256458A - Electrode structure

Info

Publication number: US3256458A
Application number: US322108A
Authority: US
Inventors: Jarasse Lucien; Joiret Jacques
Original assignee: CSF Compagnie Generale de Telegraphie sans Fil SA
Current assignee: Thales SA
Priority date: 1962-11-22
Filing date: 1963-11-07
Publication date: 1966-06-14
Anticipated expiration: 1983-06-14
Also published as: GB1016067A; FR1349286A

Description

June 14, 1966 JARASSE ET AL ELECTRODE S TRUCTURE Filed Nov. 7, 1963 INVENTORS l-JARASSEe/JJO/fifr BY 7QJQ2. 8M? ATTORN Y United States Patent Ofiice 3,256,458 Patented June 14, 1966 7 Claims. a. 313-106) The present invention relates to electrode structures for electron tubes, and more particularly to electrode structures devoid of parasitic thermo-ionic emission for use in electron tubes exposed to high temperatures.

It is known that when certain electrodes of electronic tubes, either diodes or polyodes, carried during a portion of the operating cycle at a negative potential with respect to the cathode, attain suificient temperatures, for example, above 300 C., a parasitic phenomenon due to the thermoionic emission of these electrodes appears disturbing the operation of the tube in an unacceptable manner.

Objects of the present invention are to provide improved electrodes, in particular for'tubes subjected to technological treatments at high temperature, for example of the order of 1,000 C., or which attain elevated temperatures in the operation thereof, in which this thermoionic parasitic emission is very strongly reduced, if not completely suppressed.

One well known means for suppressing thermal emission consists in coating the electrodes with an anti-emissive substance such as gold, platinum or titanium, for example, by way of electrolytic deposit.

Nevertheless, in the known tubes of the prior art, this coating has been applied to relatively massive or solid electrodes, with the quantity of material in the electrolytic deposit being negligible as compared to the quantity of material making up the electrode.

When it is necessary for these tubes to be operated at elevated temperatures, or when they are subjected in the course of the manufacture thereof to operative cycles at elevated temperatures, a diffusion of the aforesaid coating into the relatively thick support metal occurs. This means that the coating actually disappears by reason of the negligible ratio of the quantities of materials mentioned hereinabove. The surface then loses its initial anti-emissive properties, moreover, the superposition of several layers of electrolytic deposits wherein an intermediary serves as a barrier between the support and the anti-emissive deposit is only an onerous and little effective solution thereto.

According to the present invention, an electrode displaying no parasitic thermo-ionic emission in tubes subjected to high temperautres has been developed and is characterized by the fact that it is supported by a ceramic wall and that it is constituted by the combination of a sintered metal layer, known for its capacity to form a conductive refractory surface, and a coating of anti-emissive metal, known per so. In this combination, the thicknesses of the coating and of the sintered layer are in a ratio that is not negligible, for example, 1:10.

Since, in accordance with the present invention, the quantity of material in the coating is no longer negligible with respect to that in the metal support, the diffusion of a portion of the coating into the sub-adjacent metallized layer does not penetrate any further than the surface of the ceramic material and leaves a suflicient quantity of coating metal remaining on the surface of the sintered layer in order to preserve the anti-emissive properties thereof. Additionally, a fraction of the coating metal enters into combination by way of compound formation with the constituent elements of the base layer producing ultimately a refractory layer that is stable and which possesses anti-emissive properties at high temperatures.

Accordingly, it is an object of the present invention to provide a process for the manufacture of an electrode structure which is capable of withstanding high temperatures without losing its anti-emissive qualities and to an electrode structure produced by such a process having the desired lasting anti-emissive properties.

Still another object of the present invention resides in the provision of an electrode structure capable of operating at high temperatures without the emission of electrons which is simple, effective, and avoids the shortcomings and drawbacks encountered with the prior art structures.

A further object of the present invention resides in the provision of an electrode structure capable of retaining its anti-emissive characteristics even under high operating temperatures which may be readily manufactured in an inexpensive manner.

A still further object of the present invention resides in the provision of an electrode structure of the type described hereinabove which is provided with an anti-emissive layer that is capable of performing fully satisfactorily for its intended purposes notwithstanding exposure of the electrode structure to high temperatures and very high inverse voltages.

These and other objects, features and advantages will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, in the single figure thereof, one embodiment of an electrode structure obtained in accordance with the process of the present invention.

A process for the realization of such an electrode will be described hereinafter as a non-limiting example, applied to the anode of a very high-voltage diode having a cermaic envelope, intended for operation in a hot surrounding or environment, for example, of 350 C., whereby the anode may attain or exceed 500 C.

An electrode is made by forming a sintered conductive metal layer on a ceramic supporting surface, obtained by sintering in a hydrogen atmosphere at 1,550 O, a layer having a molybdenum base, or a molybdenum and titanium base, or a molybdenum, manganese and iron base, etc. The thickness of the layer thus formed is of some tens of microns.

On this conductive refractory surface there is deposited by electrolytic means or any other suitable known way, a substance having the desired anti-emissive properties such as, for example, gold. The thickness of the thusly obtained deposite is of the order of microns.

The ceramic piece thus treated is thereupon reheated under vacuum at a high temperature of the order of 1,000" C.

One obtains thereby finally a stable refractory layer wherein thermal emission under inverse voltages of the diode is reduced, and in the case of operation at anode temperatures of the order of 500 C., as experiments have indicated, to a ratio of 10- to 10- relative to tubes not treated in accordance with the present invention.

Referring now to the single figure of the drawing which represents a partial cross sectional view through an electrode structure in accordance with the present invention, reference numeral 1 designates therein the sintered layer applied onto a ceramic support 2. The sintered layer 1 is coated with a deposit of anti-emissive metal 3 and the assembly thus constituted forms the electrode having no parasitic thermal emission for a tube subjected to high temperatures.

While we have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto, but is susceptible of numerous changes and modifications within the spirit and scope of the present invention as known to a person skilled in the art, and we therefore do not Wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1. An electrode structure for an electron tube adapted to be exposed to high temperatures while retaining its anti-emissive properties, comprising a ceramic support, a sintered layer of a metal having the property of forming a conductive refractory surface coating said support, and a layer of a metal coating said refractory surface and having the property of substantially suppressing emission of electrons from said refractory surface upon heating thereof.

2. The electrode structure of claim 1, wherein said sintered layer is constituted by metals selected from the group consisting of molybdenum, a combination of molybdenum and titanium and a combination of molybdenum, manganese and iron.

3. The electrode structure of claim 1, wherein said layer of a metal coating said refractory surface is selected from the group consisting of gold, platinum and titanium.

4. An electrode structure for an electron tube adapted to be exposed to high temperatures while retaining its anti-emissive properties, comprising a ceramic support, a sintered layer of a metal having the property of forming a conductive refractory surface coating said support, and a layer of a metal coating said refractory surface and having the property of substantially suppressing emission of electrons from said refractory surface upon heating thereof, the ratio of thickness of the said respective emis' sion-suppressing and sintered layers being about 1:10.

5. An electrode structure for an electron tube adapted to be exposed to high temperatures while retaining its anti-emissive properties, comprising a ceramic support, a sintered layer of a metal having the property of forming a conductive refractory surface coating said support, and

4, a layer of a metal coating said refractory surface and having the property of substantially suppressing emission of electrons from said refractory surface upon heating thereof, said ceramic support forming a part of the enclosure of the tube.

6. An electrode structure for an electron tube adapted to be exposed to high temperatures while retaining its anti-emissive properties, comprising a ceramic support, a sintered layer of a metal selected from the group consisting of molybdenum, titanium, manganese, iron and alloys thereof having the property of forming a conductive refractory surface coating said support, and a layer of a metal consisting essentially of gold coating said refractory surface and having the property of substantially suppressing emission of electrons from said refractory surface upon heating thereof.

7. An electron tube adapted to be exposed to high temperatures, comprising enclosure means, and an electrode structure retaining its'anti-emissive properties, said electrode structure including a ceramic support forming part of said enclosure means, a sintered layer of a metal having the property of forming a conductive refractory surface coating said support, and a layer of a metal coating said refractory surface and having the property of substantially suppressing emission of electrons from said refractory surface at high temperatures.

References Cited by the Examiner UNITED STATES PATENTS 2,497,111 2/ 1950 Williams 313-355 X 2,527,513 10/1951 Arditi et a1. 313106 2,576,129 11/1951 Levin 313-106 2,647,218 7/ 1953 Sorg et a1 31329l X 2,754,445 7/1956 Sorg 313-291 X JOHN W. HUCKERT, Primary Examiner. DAVID J. GALVIN, Examiner.

A. J. JAMES, Assistant Examiner.

Claims

6. AN ELECTRODE STRUCTURE FOR AN ELECTRON TUBE ADAPTED TO BE EXPOSED TO HIGH TEMPERATURES WHILE RETAINING ITS ANTI-EMISSIVE PROPERTIES, COMPRISING A CERAMIC SUPPORT, A SINTERED LAYER OF A METAL SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM, TITANIUM, MANGANESE, IRON AND ALLOYS THEREOF HAVING THE PROPERTY OF FORMING A CONDUCTIVE REFRACTORY SURFACE COATING SAID SUPPORT, AND A LAYER OF A METAL CONSISTING ESSENTIALLY OF GOLD COATING SAID REFRACTORY SURFACE AND HAVING THE PROPERTY OF SUBSTANTITLALY SUPPRESSING EMISSION OF ELECTRONS FROM SAID REFRACTORY SURFACE UPON HEATING THEREOF.