US3092749A - Electron discharge device - Google Patents

Description

June 4, 1963 w. 'r. MILLIIS 3,092,749

ELECTRON DISCHARGE DEVICE Filed April 15, 1960 HIGH TENSILE STRENGTH MATERIAL FIG. 2

INVENTOR. WALTER T. MILLIS United States The invention relates to electron discharge devices and more particularly, to electron discharge devices of the type having a heated electron emissive surface.

In electron discharge devices or tubes of the type having heated electron emissive surfaces or cathodes, difficulty may be encountered during tube operation from undesired primary emission of electrons emanating from surfaces other than the cathodes, such as, for example, a grid. During the use of a tube, electron emissive material of a cathode may evaporate and become deposited on other internal tube structures. At the high operating temperatures that may be encountered during electron discharge device or tube operation, the cathode material that may be deposited on the various internal tube structures may act as a primary emitter of electrons.

To reduce the undesired electron emission from the deposited material on these structures, the operating temperatures of the structure surfaces may be reduced. Several methods have been proposed for reducing internal tube structure temperatures; however, the methods now in use generally have several disadvantages. For example, it has been the practice that alloys such as chrome copper be utilized in various grids as supports since such material is an excellent thermal conductor. Although the structure temperature may be reduced by the utilization of such a material, the material itself fails metallurgically, that is, it is too soft to be capable of manufacture in small Wire sizes as required for some tube element structures such as grid wires. The use of tungsten or molybdenum, unplated, or plated with gold or silver, has been used as grid lateral wire, but is undesirable for manufacture because of cost and inherent difiiculty of fabrication. When unplated, these materials form oxides at relatively low temperatures, which oxides are volatile and tend upon evaporation to deposit on the cathode causing destructive cathode poisoning. Further, gold and silver plating have high vapor pressures at normal tube operating and processing temperatures and thus tend to cause inter-element leakage, together with an increase in primary emission during the life of the discharge device or tube as the platings evaporate. Several other suggestions have been made to reduce internal tube structure temperature, and all suggestions have had serious shortcomings either in the performance of the tube constructed with these materials orin the capability of the materials to be produced in small sizes suitable for the various internal structures.

It is therefore an object of the invention to provide an electron discharge device having improved operating characteristics.

It is another object of the invention to provide a material suitable for use in the formation of structural elements of an electron discharge device.

It is another object of the invention to provide a material having a high thermal conductivity and a high tensile strength at the operating and processing temperatures of electron discharge devices.

It is still another object of the invention to provide an improved material useful in electron discharge device internal structures and that is capable of being produced in extremely small sizes.

It is a further object of the invention to provide a durable, dependable and relatively inexpensive grid electrode material for use in electron discharge devices.

Briefly stated, in accordance with one aspect of the invention, the various internal structures of an electron discharge device, such as a grid electrode, are constructed of a laminar material having a core of high thermal conductivity material clad with a coating or plating of high tensile strength metal. The proper relationship between tensile strength and thermal conductivity may be provided by controlling the relative percentage of core-tocladding cross-sectional areas.

The invention both as to its organization and operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 shows a partial fragmentary view of an electron discharge device incorporating the teachings of the invention.

FIG. 2 is a cross-sectional view of the grid wire shown in FIG. 1.

Referring to FIG. 1, an electron discharge device is shown in a partial fragmentary view. An envelope 1 is provided with a pair of insulating support members 2. Support members 2 secure a tubular plate elec rode 3 in a fixed relation to a cathode electrode 4 and a grid electrode structure 5. The grid structure 5 may be formed by securing a helically wound grid wire 6 on a pair of spaced vertical grid support rods 7. The cathode 4 may be coated with a suitable electron emissive material which, when heated, will readily emit electrons. To provide a heat source, the cathode 4 may include a filament 8 which is adapted to be connected to a suitable source of potential (not shown).

It is well known that during the operation of an electron discharge device such as shown in FIG. 1, the electron emissive material coated on the cathode will to some extent evaporate and become deposited on various other internal structures of the tube. For example, the emissive material may become deposited on the grid wires 6. =It will be apparent to those skilled in the art that any internal structure such as the grid wires 6 having emissive material deposited thereon may become a source of primary emission if the structure attains the required temperature. To alleviate such difiiculties, it is desirable that the temperature of the affected surface, in this case the grid, be kept as low as possible.

Referring to FIG. 2, an enlarged cross-section of one of the grid wires of FIG. 1 is shown constructed in accordance with the teachings of the invention. A core 10 of high thermal conductivity material, such as copper, is utilized to provide the required high thermal conductivity for rapidly carrying away the heat and thus reduc ing the temperature of the grid. The core 10 is clad or plated with a suitable material 11 having high tensile strength at elevated temperatures to provide the strength necessary to maintain the shape of the grid electrode structure at operating temperatures and also to enable the grid electrode to be manufactured by high-speed winding as found in modern techniques without breaking. The cladding material 11 is preferably of a material having a relatively high tensile strength and an ability to be cold worked. Exmples of such suitable cladding materials are: Inconel, Inconel 702, Inconel 713, Udimet 500, and Nichrome V. The trade-named materials stated above as examples, according to standard handbooks of metallurgy, have the following percentage compositions by weight:

3 Inconel: Percent Chromium 13.518. Iron 6.5-9. Nickel Balance. Inconel 702:

Chromium 14-47. Aluminum 2.75-3.75. Titanium 0.25-1.0. Iron 1.0. Nickel Balance. Inconel 713:

Chromium 11-14.

Molybdenum 3.5-5.5. Titanium 0.25-1.25.

Aluminum 5.5-6.5. Iron 5.0. Nickel Balance. Udimet 500:

Chromium 17.5.

Nickel 53.0. Molybdenum 4.0. Cobalt 16.0. Titanium 3.0. Aluminum 2.5. Nichrome V:

Chromium 18-22. Nickel Balance.

These materials are further characterized in that they possess a relatively high resistance to oxidation at the normal operating and processing temperatures of the electron discharge devices in which the grid is incorporated.

The relative percentage of cross-sectional area of the high thermal conductivity core and the high tensile 7 temperature of operation of the grids with clad Wire sizes as small as 2 /2 mils. Generally, it is necessary to increase the proportion of high tensile strength material as the size of the clad Wire decreases to enable the clad wire to withstand the relatively high 'tensile stress during.

winding operation and to maintain its form at the high operating temperature. A relative cross-sectional area of 20% copper and 80% Inconel has been found to have excellent thermal conductivity and adequate tensile strength in overall Wire sizes of from about 1 mil to the merely indicative of the many advantages to be gained through the use of the invention. It will be understood by those familiar with the art that structures having high thermal conductivity cores and having a high tensile strength cladding thereon may be utilized in other parts of tube structures, such as the grid electrode supports 7 FIG. 1), and will be equally advantageous in any circumstance where deposition of emissive material causes undesired primary emission from surfaces within an electron discharge device. 7

While I have shown and described specific embodiments of my invention, 1 do not desire my invention to be limited to the particular forms shown and described, and I intend by the appended claims to cover all modifications Within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is: V

1. A grid electrode for an electron discharge device having a thermionic cathode and an anode supported in an evacuated envelope and in mutually spaced relation thereto, means supporting the grid electrode between said cathode and said anode in close proximity to said cathode so that the grid is subject to being rendered electron-emissive during operation of the device, said grid electrode comprising a plurality of lateral wires mounted on said supporting means, said wires comprising a core of copper material and a cladding of high-tensile strength material completely encasing said core, the relative crosssectional areas of said core and said cladding being in the range of about 4 to about 7 to elTect cooling of said grid below electronemissive temperatures and simultaneously to provide sufiicient structural strength of said grid to withstand tensile stresses exerted thereon during fabrication and operation of the device.

2. The grid electrode as defined in claim 1, further characterized in that said core material, at the temperature of fabrication and operation of the device, is normally subject to the formation of oxides of copper, said cladding operating to minimize the formation of such oxides, thereby to avoid adversely afiecting the vacuum condition within said envelope. 7

3. The grid electrode as defined in claim 1, wherein said core material, at the temperatures of fabrication-and operation of said device,-is normally subject to evaporation and sublimation resulting in undesired electrically conductive deposits on insulative surfaces of said device, said cladding operating to prevent such evaporation and the consequent formation of such deposits.

References Cited in the file of this vpatent UNITED STATES PATENTS 2,282,097 Taylor May 5, 1942 2,417,459 Eitel Mar. 18, 1947 2,568,705 Beck Sept. 25, 1951 2,691,116 Allwine Oct. 5, 1954 2,875,363 Nunan Feb. 24, 1959 2,904,717 Kerstetter Sept. 15, 1959

Claims (1)

1. A GRID ELECTRODE FOR AN ELECTRON DISCHARGE DEVICEHAVING A THERMIONIC CATHODE AND AN ANODE SUPPORTED IN AN EVACULATED ENVELOPE AND IN MUTUALLY SPACED RELATION THERETO, MEANS SUPPORTING THE GRID ELECTRODE BETWEEN SAID CATHODE AND SAID ANODE IN CLOSE PROXIMITY TO SAID CATHODE SO THAT THE GRID IS SUBJECT TO BEING RENDERED ELECTRON-EMISSIVE DURING OPERATION OF THE DEVICE, SAID GRID ELECTRODE COMPRISING A PLURALITY OF LATERAL WIRES MOUNTED ON SAID SUPPORTING MEANS, SAID WIRES COMPRISING A CORE OF COPPER MATERIAL AND A CLADDING OF HIGH-TENSILE STRENGTH MATERIAL COMPLETELY ENCASING SAID CORE, THE RELATIVE CROSSSECTIONAL AREARS OF SAID CORE AND SAID CLADDING BEING IN THE RANGE OG ABOUT 1/4 TO ABOUT 3/2 TO EFFECT COOLING OF SAID GRID BELOW ELECTRON-EMISSIVE TEMPERATURES AND SIMULTANEOUSLY TO PROVIDE SUFFICIENT STRUCTURAL STRENGTH OF SAID GRID TO WITHSTAND TENSILE STRESSES EXERTED THEREON DURING FABRICATION AND OPERATION OF THE DEVICE.

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