US3270232A

US3270232A - Gaseous discharge device with shield for directly heated cathode

Info

Publication number: US3270232A
Application number: US123024A
Authority: US
Inventors: Jr Ward E Bailey; William J Kearns
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1961-07-10
Filing date: 1961-07-10
Publication date: 1966-08-30
Anticipated expiration: 1983-08-30

Description

g- 30, 1966 w. E. BAILEY, JR.- ETAL 3,

GASEOUS DISCHARGE DEVICE WITH SHIELD FOR DIRECTLY HEATED CATHODE Filed July 10, 1961 I TANTALUM TAN/UM INVENTORIS:

WARD E. BAILEY,JR. WlLLlAM J. KEARNS,

BY, TH IR ATTORNE United States Patent 3,270,232 GASEOUS DISCHARGE DEVICE WITH SHIELD FOR DIRECTLY HEATED CATHODE Ward E. Bailey, lira, Pittsfield, Mass., and William J. Kearns, Scotia, N.Y., assignors to General Electric Company, a corporation of New York Filed July 10, 1961, Ser. No. 123,024 7 Claims. (Cl. 313-38) This invention relates to gaseous electric discharge devices and pertains more particularly to a new and improved ceramic and metal thermionic cathode gas diode.

In many circuit applications, such, for example, as power generator circuits, it is desirable to employ a gaseous rectifier diode. Additionally, it is often desirable to employ such circuits in equipment, such as high speed vehicles, wherein the circuits, including the diode, are normally subjected to substantial mechanical shock and vibration as well as wide circumambient temperature ranges including substantially high temperatures.

In applications of the above-discussed types it is desirable that the diode be adapted for withstanding, over an extended operating tube life, the normally encountered conditions of shock and vibration. Additionally, it is desirable that the devices be adapted for operating over the whole of the normal ambient temperature range with stable electrical characteristics including a substantially low forward potential drop, and substantially constant tube potential drop each conducting cycle and for all values of tube current. It is also desirable that the diodes be adapted for operating with constant filament power over the entire normal ambient temperature range thus obviating the need for filament derating.

Further, in constructing electric discharge devices of the presently considered types it has been found desirable to fabricate certain different parts of certain different materials in order to take advantage of various desirable properties thereof, such, for example, as high refractoriness and effectiveness as a base for an emissive material. However, at elevated temperatures some of such different materials are generally chemically incompatible in the sense that they tend readily to alloy and adversely affect the structures in which they are employed. Therefore, it is desirable to provide arrangements which will allow the use of such different materials in close association but without the danger of adverse effects and subsequent tube inoperability resulting from the usual incompatibility of the materials.

Disclosed and claimed in copending US. application S.N. 123,023 of W. J. Kearns, filed concurrently herewith and assigned to the same assignee as the present invention, and now US. Patent 3,204,140, is a ceramic and metal thermionic cathode gas diode and method of manufacturing same adapted for affording the above-discussed desiderata. The present invention contemplates the provision of a modified form of diode adapted for affording the above-discussed desiderata and for ensuring against adverse effects resulting from chemical incompatibility of certain materials employed in the manufacture of the devices. More specifically, the present invention contemplates the provision of an improved ceramic and metal thermionic cathode gaseous diode which is in an alternative form of device for attaining the functions of the device disclosed and claimed in the above-mentioned copending Kearns application and which comprises a highly mechanically damped electrode system and thus is particularly adapted for withstanding substantial mechanical shock and vibration. Additionally, the present invention, as does the above-mentioned Kearns invention; contemplates structure effective for providing a device adapted for operating with the above-discussed electrical operat- Patented August 30, 1966 'ice ing characteristics over the whole of a circumambient temperature from about 65 C. to about +400 C. The present invention also contemplates an electrode arrangement having nickel-containing elements effectively isolated from certain titanium elements which can be adversely affected thereby.

Accordingly, a primary object of the present invention is to provide a new and improved ceramic and metal thermionic cathode gaseous rectifier device.

Another object of the invention is to provide a new and improved ceramic gaseous electric discharge device adapted for substantially uniform operating characteristics over a substantially wide normal operating temperature range including relatively high temperatures.

Another object of the invention is to provide a new and improved ceramic and metal gaseous electric discharge device adapted for operating with substantially uniform electrical operating characteristics at. relatively high circumambient temperatures and without the need for any cathode derating.

Another object of the invention is to provide a ceramic discharge device system including both titanium and nickel parts and improved means for avoiding adverse effects on the titanium parts by the presence of nickel in the device.

Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of the invention there is provided a ceramic and metal gaseous discharge device including an envelope'comprising a pair of cylindrical ceramic insulators, and a titanium washer-like member buttsealed between the opposed ends of the insulator and a titanium disk-like member butt-sealed to the outer end of each insulator to complete the envelope. The disk-like member at one end of the envelope comprises a planar anode while the disk-like member at the other end and the washer-like member constitute contacts of a directly heated nickelate cathode. The cathode is a nickelate-impregnated nickel wire mesh ribbon-like construction formed generally in the shape of an S and extending parallel to the longitudinal axis of the envelope. The annular cathode contact member includes an inner rim portion disposed interiorly of the tube envelope. One end of the cathode is secured to a discrete support rod which extends parallel to the axis of the tube envelope and is supported by and electrically connected to the inner rim por tion of the annular contact member. The other end of the cathode is secured to a second discrete support rod which includes a stepped section disposing the major length of the rod on the longitudinal axis of the envelope. This rod is electrically secured to the lower disk-like member. The support rods are formed of a material which is non-alloying at the operating temperature with the titanium in the tube structure. Also carried on the inner rim of the annular contact member is a refractory metal shield surrounding the cathode and extending concentrically in the envelope in close proximity to the cathode and effective for providing uniformity of temperature of the cathode throughout the axial length thereof.

For a better understanding of the invention reference may be had to the accompanying drawing wherein:

FIGURE 1 is an enlarged elevational sectional view of a gaseous discharge device with preferred materials constructed according to the present invention; and

FIGURE 2 is a transverse sectional view taken along the lines 2-2 in FIGURE 1 and looking .in the direction of the arrows.

Referring to FIGURE 1, there is illustrated a gaseous discharge device comprising an embodiment of the present invention and generally designated 10. The device includes a ceramic and metal envelope 11 which contains an inert gas, such as Xenon, at approximately 100 microns of pressure and comprises coaxially arranged upper and lower cylindrical ceramic insulators or

wall sections

12 and 13, respectively, and upper and lower metal end caps or disk-like

members

14 and 15, respectively. Each of the

end caps

14 and 15 includes on its inner side an annular shoulder 16 which is dimensioned to extend into the corresponding end of the respective

ceramic wall section

12 or 13. This arrangement serves to facilitate assembly of the tube envelope sections and to insure concentricity thereof. Also included in the envelope structure is an annular of washerlike contact and electrode support member 17 which is interposed between the opposed ends of the

insulators

12 and 13. Each side of the member 17 is formed to include a shoulder 16 for extending into the opposite ends of the

ceramic sections

12 and 13. This feature also is adapted for facilitating stacking of the parts and assembly of the tube as well as concentricity of the parts in the finished envelope.

The

metal members

14, 15 and 17 are preferably formed of titanium. However, the present invention is operative if zirconium replaces the titanium in whole or in part. The

insulators

12 and 13 are formed of a suitable ceramic which is adapted for matching the thermal expansion of titanium and thus facilitates bonding thereto and subsequent use of the device at varying temperatures without adversely affecting the ceramic of the bonds between the ceramic and metail members. A group of ceramics found to be suitable are generally known in the art and available under the denomination Forsterites. One such Forsterite is disclosed and claimed in US. Patent No. 2,912,340 of A. G. Pincus issued November 10, 1959, and assigned to the same assignee as the present invention. Another ceramic which is particularly suitable for use in constructing the present device is the Forsterite-Spinel disclosed and claimed in copending U.S. application S.N. 831,510 of R. H. Bristow, filed August 4, 1959, now Patent No. 3,060,040, and assigned to the same assignee as the present invention.

The ceramic and metal members are suitably joined by butt-seals indicated by the heavy dark lines 18 to complete the envelope structure 11 by metallic bonds which are preferably formed by the method disclosed and claimed in U.S. Patent No. 2,857,663 of J. E. Beggs issued October 28, 1959, and also assigned to the same assignee as the present invention. It is understood that in some applications other sealing techniques are equally applicable such, for example, as any one of the several generally known methods requiring premetalizing of the ceramic and the use therewith of a solder material to effect bonds between the metallized ceramic surfaces and another member. However, the bonding material employed preferably should be characterized by low oxygen permeability and a low evaporation rate. Thus, for example, solders containing silver would be undesirable because of oxygen permeation especially at elevated temperatures. Thus, the seals are preferably silver-free. This feature, however, does not constitute part of the present invention but is disclosed and claimed in the above-mentioned copending Kearns application. Gold-containing solders would be of marginal utility because of their high evaporation rate during the sealing process which would tend to cause deposition of conductive material on the insulator walls. The abovementioned sealing technique disclosed in the Beggs patent and which involves the use of titanium has been found particularly effective in the manufacture of the tube illustrated.

In the completed envelope 11 the upper disk-like member 14 serves as a planar anode, the lower member 15 serves both as a cathode support element and a cathode contact member. The annular contact member 17 also serves the dual functions of cathode support and cathode contact. Additionally, the member 17 includes an inner rim portion 18 which serves several functions, one of which is to provide partial support for a cathode structure generally designated 20 which will now be described in detail.

The cathode structure 20 is of the directly-heated type and comprises a nickel wire mesh element 21 in the form of a substantially wide ribbon and impregnated with nickelate. The nickelate cathode is employed due to its normal high operating temperature which permits substantial elevation of the temperature of the envelope without adversely affecting operation of the cathode or requirement of filament derating. This concept is also disclosed and claimed in the copending Kearns application. The mesh 21 is in generally sheet or ribbon form so as to have substantial width and thereby serve as a copious and relatively rigid source of electrons. Additionally, and as seen in FIGURE 2, the mesh is generally S-shaped with the center thereof on the axis of the envelope 11. One end of the S-shaped cathode mesh is suitably secured to a discrete refractory metal filament support rod 22. The rod 22 is eccentric and parallel relative to the axis of the envelope and includes a transversely extending foot portion 23 electrically secured, as by welding, to the rim portion 19 of the contact member 17. The other end of the cathode mesh 21 is suitably secured to a second discrete refractory metal filament support rod 24. The rod 24 includes an inwardly extending stepped section 25 which disposes the lower section of the rod on the axis of the tube envelope. A foot portion 26 of the rod 24 is welded to the lower end cap 15 and thus is electrically secured thereto.

In the described cathode support structure the rods '23 and 24 are formed of tantalum or any other highly refractory material which is not readily alloyable with titanium. Thus, the nickel-containing cathode is isolated and prevented from alloying with the titanium of which the contact members '15 and 17 are formed. Additionally, the support rod mounting arrangement and the relatively wide ribbon-like and S-shaped cathode provides for a highly-damped directly-heated cathode system adapted for withstanding substantial mechanical shock and vibration. In fact, the disclosed structure has been found effective for withstanding mechanical shock of 50 gs and vibrations of 20 gs throughout the range of from 10 to 2000 c.p.s. across the operating ambient temperature range of from 65 C. to +400 C.

In the just-described arrangement the inner rim portion 19 of the annular contact member 17 serve-s additionally as means for shielding the ceramic insulator 13 from deposition thereon of conductive material. Specifically, the central aperture in the annular contact member 17 is so dimensioned that the inner rim 19 extends substantially inwardly and thus shields the lower ceramicto-metal bonds from any conductive material that may be sputtered from the cathode.

The upper insulator .12 is shielded from deposition thereon of conductive material by a refractory metal tubular shield 27 which can advantageously be formed of molybdenum. The shield 27 is preferably cylindrical and is secured concentrically in the envelope to the upper surface of the inner rim portions 18 of the member 17 by a plurality of circumferentially spaced tabs 28 Welded between the shield 27 and the member 17. The upper end of the shield 27 extends in close proximity to the anode :14 and thus shields substantially all of the upper insulator from deposition of sputtered material originating from the cathode which is spaced inwardly from the outer end of the shield.

Additionally, the shield 27 extends in close proximity to the cathode mesh 21 along the whole axial length of the mesh. Thus, the shield 27 serves to maintain a substantially uniform temperature and emissivity throughout the axial length of the cathode.

In order to facilitate connecting the described device in a circuit, the various contact elements are each provided with a radially protruding apertured tab or terminal 29. Additionally, the cathode contact 15 is formed with an integral threaded nut 30 which includes opposed flattened land surfaces 31 for accommodating a wrench and enabling the device to be affixed to a support surface carrying a threaded mounting stud (not shown). Thus, the device may be mounted rigidly and easily on, for example, the chassis of a piece of equipment and will provide for desirable high heat transfer from the tube to the relatively more dissipative chassis.

The described tube structure is preferably manufactured according to the method disclosed and claimed in the above-referenced copending Kearns application.

While a specific embodiment of the invention has been shown and described it is not desired that the invention be limited to the particular forms shown and described, and it is intended by the appended claims to cover all modifications within the spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A ceramic and metal gaseous discharge device comprising an envelope including a pair of coaxial ceramic insulators, a pair of disk-like contact members sealed across the outer ends of said insulators, one of said disk-like members comprising an anode and the other a cathode contact, an annular contact member sealed between said insulators and including an inner rim portion disposed concentrically in said envelope, a tubular open-ended metallic shield supported on said inner rim portion of said annular member and extending concentrically in said envelope to a point adjacent said anode, a directly heated cathode disposed in said shield, a discrete first lead supporting one side of said cathode and mounted on and conductively connected to said rim portion of said annular contact member, and a discrete second lead supporting the other side of said cathode and extending through said annular contact member and mounted on the inner surface of the disk-like member comprising a cathode contact.

2. A ceramic and metal gaseous discharge device according to claim 1, wherein said cathode comprises a wire mesh impregnated with an electron emissive material and extends parallel to the longitudinal axis of said envelope.

3. A ceramic and metal gaseous discharge device according to claim '1, wherein said cathode is in sheet form, is generally S-shaped and extends parallel to the longitudinal axis of said envelope.

4. A gaseous discharge device according to claim 1, wherein said cathode is in general sheet form and generally S-shaped with the center thereof lying on the axis of said envelope, one of said support rods is eccentrically disposed and is secured electrically to said rim portion of said annular contact member, and the major portion of the other of the said support rods lies on the axis of said envelope and is secured electrically to said disk-like member comprising a cathode contact.

5. A ceramic and metal gaseous discharge device according to claim 1, wherein said cathode is a nickel wire mesh impregnated with nickelate.

6. A ceramic and metal gaseous discharge device according to claim 1, wherein said contact members are substantially titanium and said cathode contains nickel and is supported on rods of a metal which is substantially non-alloying with titanium at the operating temperature of said device.

7. A ceramic and metal gaseous discharge device comprising an envelope including a pair of coaxial ceramic insulators, a pair of titanium disk-like contact elements sealed across the upper ends of said insuiators, one of said disk-like elements constituting an anode and the other a cathode contact, a titanium annular contact member sealed between said insulators and including a substantial inner rim portion disposed .interiorly of said envelope, a directly-heated cathode contained in said envelope and of a substantially wide nickel wire mesh ribbon which is impregnated with nickelate, is generally S-sh-aped and extends parallel to the axis of the said envelope with the center thereof on said axis, an eccentrically located discrete first support rod having one end of said cathode electrically secured thereto and being electrically secured to said rim portion of said annular contact member, a discrete second support rod having the major portion thereof extending along the axis of said envelope and having the ends thereof electrically secured to the other end of said cathode and said cathode contact, said support rods comprising a metal which is substantially non-alloying with titanium at the operating temperature of said device, and a tubular open-ended refractory metal shield mounted concentrically about said cathode in close proximity thereto and supported on said inner rim portion of said annular contact member, said shield extending in close proximity to said cathode throughout the axial length of said cathode and said shield cooperating with said anode in defining a void space therebetween.

References Cited by the Examiner UNITED STATES PATENTS 1/1949 Smith 3l3-205 X 8/1960 Riley et al. 313-497 X C. R. CAMPBELL, D. E. SRAGOW,

Assistant Examiners.