US3127537A

US3127537A - Cathode mount and alloy therefor

Info

Publication number: US3127537A
Application number: US11045A
Authority: US
Inventors: Carel W Horsting
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1960-02-25
Filing date: 1960-02-25
Publication date: 1964-03-31
Anticipated expiration: 1981-03-31
Also published as: CH395351A; NL261666A; DE1212223B; ES265177A1; GB961404A

Description

March 3l, 1964 c. w. HoRsTlNG CATHODE MOUNT AND ALLOY THEREF'OR Filed Feb. 25, 1960 INVENTOR. Carel lU. Horsh'ng BY i 4 1MM uneasy 3,127,537 CATHDE MUNT AND ALLOY THEREFR Carel W. Horsting, Caidweil, NJ., assigner to Radio Corporation of America, a corporation of Delaware Filed Feb. 25, 1969, Ser. No. 11,045 7 Claims. (Ci. 313-346) This invention relates to cathode mounts and particularly to such mounts including an indirectly heated cathode supported at one end thereof in cantilever fashion and to an alloy for the core body of the cathode having relatively high hot strength and contributing to desired emission from the cathode.

In one class of electron tubes, such as the so-called Pencil type, a cathode mount comprises a sleeve type cathode supported at one end thereof in cantilever manner on one end of a first tubular support made of a material characterized by relatively low heat conductivity such as an alley commercially known as Kovar. The other end portion of the tubular support is fixed to a second tubular support which is in turn fixed to a tubular terminal portion of the tube.

Several problems are associated with a cathode mount of this kind. One of the problems arises as a consequencc of the composition to which the first tubular support has been restricted heretofore by the consideration of low heat conductivity. Low heat conductivity of the irst support referred to, is desirable for reducing heat drain from the cathode and thereby economizing in heater power. Kovar has been favored heretofore for use as the material of the first tubular support aforementioned because of its relatively low heat conductivity and high hot strength. However, Kovar includes an appreciable amount of volatile constituents which are harmful to tube operation. Gne form in which such harm is evidenced is in the evaporation of these constituents, which form a coating or lm on the inner wall of the tube envelope, thereby giving rise to an adverse operating condition called bulb loading.

Another problem inherent in the mount structure described, involves the number of parts required for the structure. Such number of parts not only involve a complex and costly manufacturing procedure, but each part, such as the cathode and first tubular support, has a different structure, requiring different methods of manufacture. For example, Pencil tube constructions heretofore have included a seamless cathode to provide uniform emission around the cathode, and a first tubular support having a welded seam of double thickness of the material of the support. The making of the second tubular support referred to and the fixing of one end thereof to an end of the cathode, have heretofore required about forty welds. It has been impractical to make the second tubular sup- `port in the form of seamless tubing, because of the foillike thinness thereof, found desirable to supplement the low heat conducting character of the material of the support, for reducing heat drain from the cathode.

Another problem area involving cathodes and supports therefor heretofore employed in Pencil type tubes, relates to the space relation of the cathode to the next adjacent grid electrode. In the Pencil tube all electrodes are cylindrical, so that expansions and contractions thereof occur without substantially changing initially established spacings therebetween. For best operation of tubes of this type at ultra-high frequencies, it is desirable that the initially established spacing between the electrodes be uniform around the several electrodes. This requires that the electrodes be disposed in an exact co axial relation. However, a difficulty has appeared in maintaining the original co-axial line-up of the tube elements. This difficulty arises as a result of the seam required in the structure of the tubular support aforementates tent tioned, engaging the cathode. Such seam, due to its local double material thickness, causes an asymmetric thermal distribution, which tends to result in warping of the support cylinder upon prolonged tube use and especially upon frequent on and otf-switching of the tube. The double thickness also tends to induce distortion due to the fact that a triple material thickness appears at the locations where the seamed support is welded to the cathode and second support.

Another problem arises as a consequence of the cantilever disposition of a cathode mount in some tube types, such as the Pencil tube. This problem involves the top-heavy character of the mount structure. This topheavy character is due to the materials heretofore available for use in the compositions of the cathode and its support. Because of the relatively low strength of conventional cathode sleeve material, the wall thickness of the cathode sleeve heretofore has been two mils, in order to provide sufficient strength. The Kovar support p0rtion of the cathode mount, however, has heretofore been restricted to a thickness of one-half mil for reasons of thermal insulation of the cathode sleeve. These requirements in respect of material thickness have resulted in a relatively large mass, i.e. a sleeve of two mil thickness at the free end of the cantilever structure, supported by a relatively small mass, i.e., Kovar sleeve of one-half mil thickness. The resultant top-heavy character of the cathode mount is unfavorable with respect to mechanical stability thereof when an electron tube in which it is used, is subjected to vibration and shock.

lt is an object of the invention to provide a cathode mount that avoids the problems enumerated heretofore. To this end, further objects are:

(l) To provide a cathode mount in which a sleeve type cathode and its support constitute an integral structure;

(2) To provide an integral cathode and support structure wherein the material thereof contributes to good emission, has a relatively high hot strength, and is characterized by relatively poor heat conductivity;

(3) To provide a cathode mount having a structure for facilitating maintenance of an exact co-axial disposition of a cylindrical cathode with respect to a next adjacent cylindrical electrode;

(4) To provide a cathode mount having a structure and composition contributing to facility in manufacture and in assembling the mount in an electron tube; and

(5) To provide an integral cathode and support structure adapted to be supported in cantilever fashion with freedom from top heaviness and thereby adapted to withstand appreciably severe vibrations and shocks with no adverse effects on the operation of an electron tube in which it is incorporated.

These and other objects and advantages which will be apparent as the description proceeds, are realized in an electron tube constituting one embodiment of the invention and presented as an example only, of the invention. In such embodiment a cathode of the slee-ve type and a tubular support therefor, constitute an integral seamless structure. The structure referred to has a composition which may vary within certain ranges to be described, but in its best form includes the following materials in the approximate relative `amounts by weight indicated: 40% cobalt, 10% tungsten, 5% molybdenum, 0.2% aluminum, 0.1% carbon, 0.08% magnesium and the balance nickel. ln addition to these materials, the composition referred to may include impurities, in such small amounts that the removal thereof is diicult and commercially impractical. This material possesses the advantageous properties of contributing to good electron emission, relatively high hot strength permitting reduced thinness of the cathode, and relatively poor heat conductivity.

A seamless tubular structure made of this material is advantageously suited for use in a Pencil tube, wherein the structure is supported only in one end portion of an elongated envelope and has an active cathode portion in the other end portion of the envelope, The seamless character of the support facilitates maintaining the cathode in exact co-axial relation with respect to a next adjacent electrode.

For a more detailed considerati-on of an embodiment of the invention, reference is now made to the accompanying drawing, wherein,

FIG. 1 shows an elevation partly in section of a Pencil type tube in which the invention is incorporated; and

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1.

The Pencil tube structure shown in FIG. l, includes an elongated envelope having a cylindrical anode 12 supported in one end portion of the envelope formed by a tub-ular structure 14 and constituting lthe anode terminal of the tube. A cylindrical cathode 16 including an integral tubular portion 18, is supported in the other end portion of the envelope, on a tubular support 20 tixedly engaging the inner wall of a tubular structure 22 serving as the cathode terminal of the tube. A cylindrical grid 24 is `fixed at one end to an annular wall 26 defining an opening 28 through a metal disc 30. The disc 30 is sealed across a glass or ceramic portion of the tube envelope formed by two relatively

short tubes

32, 34. The terminal portion 14 is closed by au exhaust tubulation 36 suitably pinched off to effect a vacuum tight closure. The terminal portion 22 is closed in vacuum tight manner at the lower end thereof as viewed in FIG. l, by a suitable stem, not shown. Two of the four prongs 38 are connected to a heater 40, and the remaining two prongs 38 are connected to a getter (not shown) within the terminal portion 2-2. The prongs are adapted to be connected to suitable energizing circuits, for energizing the heater 40 and flashing the getter.

The cathode y16 and tubular support 1S integral therewith, constitute a seamless tube of uniform diameter and thickness throughout their lengths. Consequently, by the use of suitable jigs, not shown, the anode 12, grid 24 and cathode 16 may be yoriented in an exact co-axial relation and xed while in such orientation.

Furthermore, the integral character of the cathode and its tubular support, assures freedom from tilting of the cathode 16 with respect to the grid 24 during tube operation. Such tilting, which would be occasioned by a non-symmetrical cross-section of the tubular support 18 resulting from a seamed construction, -is avoided by the cross-sectional symmetry of the suppor-t as shown in FIG. 2. Further contribution to freedom from tilting is provided by a symmetric .array of spot welds 42 between the lower free end of support 18 and the tubular support 20. Instead of spot welding, a continuous weld around the periphery of the lower end `of support 18 may be made. In either case, the welded engagement between the suppor-t 18 and support 20 is free from any -component tending to tilt the integral cathode and

support structure

16, 18.

In the tube construction shown in FIG. 1, it is essential to dispose the active lcathode portion `16 at a region remote from tubular member 20 on which it is supported. It is not feasible to extend the support 20 upwardly rto engage the cathode because of the obstruction to such extension provided by grid-supporting disc 30. Such-obstruction occurs since the opening 2S in the disc is obviously smaller than the transverse dimensions of the support 20. AFor like reasons it is not feasible to locate the active portion of the cathode below disc 30, as viewed in FIG. l, since the anode cannot be extended downwardly through the disc. Consequently, it is necessary to supply a supporting means between the cathode 16 and the support 20.

Such supporting means 11S according to the inventron, is integral with the cathode 16. The integral structure 16, 1S, Aformed `of seam-:less tubing, is relatively long. It extends from the support 20 -in terminal portion 22 of the tube envelope, through opening 2S yin disc 30, and into the anode 12 in terminal portion I14. The cathode portion 16 of the integral structure referred to, is coated with a suitable electron emitting material 44, such as a mixture of the oxides of barium, strontium and calcium. The support portion 18 of the structure is free from such coating.

The utilization of `a common composition for the cathode 16 and its integral support l18 requires that the composition possess a number or" properties not heretofore found in any one composition. Among these properties are a relatively high hot strength to per-mit the support portion 18 to meet the relatively `severe support demands placed upon it by virtue of the cantilever mounting of the cathode portion 16; ability to contribute to good electron emission from the coating 44; relatively poor heat conductivity to reduce the amount of heat loss from the cathode portion 16 by conduction to the support 20 through the support portion 18 of the integral cathode and support structure; and absence of constituents which volatilize from the cathode support and into the tube envelope, and give rise to lan objectionable condition of tube operation known as bulb loading.

In providing a common composition for the electrode 16 and its support 13, according to the invention, it has been necessary to provide a novel combination of materials. Heretofore, no combination of materials was known that possessed all of the desirable properties described in the foregoing.

In its best form, the alloy according to the invention, includes in approximate amounts, 40% cobalt, 10% tungsten, 5% molybdenum, 0.2% aluminum, 0.1% carbon, 0.08% magnesium and 44.62% nickel, all by weight. In this form, the alloy has contributed to best performance of a cathode mount of the type shown in FIG. l.

As the amounts of the several materials are varied within an acceptable range to be described, no appreciable change in the effectiveness of the alloy, in the respects mentioned, has been observed.

This is believed to be due to the fact that each material contributes in a greater or lesser degree to the several advantages of good emission with freedom from an objectionable high resistance interface, structural strength, low heat conductivity and lack of bulb loading.7

This contribution, in connection with some of the materials may assume a passive form insofar as certain of the advantages referred to, are concerned, and an active form in connection with other of the advantages. Thus, the combination of molybdenum and tungsten, according to the invention, permits the use of aluminum without any appreciable peeling of the emission coating. In the past, when aluminum has been used in the amount according to the invention, serious incidents of coating peeling have occurred, particularly in connection with indirectly heated cathodes. Applicant has also found that magnesium can be used in the alloy in an amount heretofore considered objectionable. Thus, magnesium in the amount tolerated by the invention, normally would be expected to give rise to excessive vaporization thereof due to its fugitive character, with resulting adverse effects on tube operation.

Applicant has further found that the amounts of tungsten and molybdenum which contribute to the foregoing desirable coactions with aluminum and magnesium, are suihciently small to permit inclusion in the alloy of an appreciable amount of cobalt for further contributing to the strength of a structure made of the alloy, and to low heat conductivity thereof. Cobalt, however, adversely affects the workability of the alloy. Where the alloy is to be used in a seamless tubing structure, such Workablity must be sutiiciently high to permit normal tube drawing operations. According to the invention, therefore, the amount of cobalt is limited to an amount of from 30 to 60% by Weight of alloy. The balance of the alloy consists of nickel and a relatively small amount of carbon, both of which contribute to the aforementioned desirable Workability thereof.

The ranges in terms of weight, in which the materials aforementioned may be present in the alloy of the invention Without seriously impairing the advantages above pointed out, is as follows:

Cobalt 30 to 60% Aluminum 0.01 to 2.0% Tungsten 2 to 25 Molybdenum 2 to 25% Carbon 0.01 to 0.25% Magnesium 0.01 to 0.10% Nickel remainder Applicant has found that the operating life of Pencil type tubes incorporating a cathode mount including the integral cathode and support structure of the invention and consisting of the novel alloy described herein, is more than ve times the operating life of Pencil type tubes incorporating prior cathode mounts and alloys. For example, in one Pencil type tube, the increase in maximum attainable life was from two hundred hours to twenty-tive hundred hours. This increase in life is realized as a consequence of the contribution of applican s invention of long continued electron emission, structural stability of the cathode mount, and freedom from a condition of tube operation known as bulb loading resulting from excessive evaporation of cathode constituents such as nickel and magnesium. ln addition to the advantages of contributing to good emission from the coating 44 on the cathode 16, high structural strength required for the cantilever mounting of the cathode and support structure, and reduced heat drain from the cathode, the alloy of the invention is characterized by advantages in Welding to the support 20, and certain advantages accruing as a consequence of a combination of the high structural strength of the alloy and its low heat conductivity. In connection With the latter it is pertinent to point out that Whereas the prior separate Kovar support for the cathode was limited to a thickness of about 0.5 mil for a desired low heat conduction therethrough, the support portion 18 of applicants integral structure may have a thickness of about 1.1 mil Without increasing its heat conduction above that of the prior structure. Furthermore, the same thickness of 1.1 mil may characterize the cathode portion 16 of the integral structure shown in FIG. 1, Without resulting in deformation thereof. Due to the low strength of prior cathode structures, the cathode material thereof has required a thickness of about 2 mils to prevent such deformation. The reduced thickness of the cathode according to the invention not only contributes to a faster heat up time of the cathode in that it avoids the thermal lag incidental to cathodes having the thicker sleeve material, but in addition, the free end portion of the structure is given a reduced mass so that it is less influenced by impact shock. This is particularly important in view of the cantilever construction of the cathode assembly. Applicant found it fortuitous that a common thickness for both a cathode and the support thereof, Was feasible with good results. Such common thickness permits increased thickness of the cathode support portion 16 for improved support of the cathode, and reduced thickness of the cathode material for eliminating a top heavy condition and reducing thermal lag therein, as aforementioned. The common thickness referred to also contributes to advantage in fabricating the integral structure.

What is claimed is:

1. A cathode comprising a core having a coating thereon of emitting material, said core comprising an alloy consisting by Weight and exclusive of diilicultly removable impurities, of from 30 to 60% cobalt, 0.01 to 2.0% aluminum, 2 to 25% tungsten, 2 to 25% molybdenum, 0.01 to 0.25% carbon, 0.01 to 0.10% magnesium and the remainder nickel, said alloy having relatively high hot strength, poor heat conductivity, and good effect on emission from said coating, for improved operation of said cathode.

2. A core material for an indirectly heated cathode characterized by relatively high hot strength, poor heat conductivity and contributing to good electron emission, said material consisting by Weight essentially of 40% cobalt, 10% tungsten, 5% molybdenum, 0.2% aluminum, 0.1% carbon, 0.08% magnesium and the remainder nickel.

3. A cathode mount comprising a tubular sheet metal structure having a coating thereon of emitting material, and means engaging one end portion of said structure for support thereof, said structure being made of a predetermined material and said sheet metal having a predetermined thickness for contributing to reduced heat losses by conduction from said cathode to said support means, said material comprising an alloy consisting essentially by weight of from 30 to 60% cobalt, 0.01 to 2.0% aluminum, 2 to 25% tungsten, 2 to 25 molybdenum, 0.01 to 0.25% carbon, 0.01 to 0.10% magnesium and the remainder nickel, said thickness being about 1.1 mils.

4. A core for an indirectly heated cathode comprising an elongated tubular structure, said core being made of a material having a relatively high hot strength and relatively poor heat conductivity at a predetermined thickness thereof, said material consisting of by Weight in addition to diiiicultly removable traces of impurities, about 40% cobalt, about 10% tungsten, about 5% molybdenum, about 0.2% aluminum, about 0.1% carbon, about 0.08% magnesium and the remainder nickel, said thickness being about 1.1 mils.

5. In a cathode mount, an integral structure comprising a tubular cathode and a tubular support therefor, the material of said integral structure having a uniform thickness throughout its length, said material consisting of by weight, in addition to traces of ditlicultly removable impurities, about 40% cobalt, about 10% tungsten, about 5% molybdenum, about 0.2% aluminum, about 0.1% carbon, about 0.08% magnesium, and the remainder nickel, said material contributing to high hot strength and poor heat conductivity of said support, and good electron emission from said cathode.

6. An electron tube having a cathode core body which is formed of an alloy consisting by Weight, excluding impurities which are diicult to remove, of from 30 to 60% cobalt, 2 to 25 tungsten, 2 to 25% molybdenum, 0.1 to 2.0% aluminum, 0.01 to 0.25% carbon, 0.01 to 0.10% magnesium, and the remainder nickel.

7. An electrode support having a body formed of an alloy consisting by Weight, exclusive of impurities which are diiicult to remove, of from 30 to 60% cobalt, 2 to 25% tungsten, 2 to 25% molybdenum, 0.01 to 2.0% aluminum, 0.01 to 0.25% carbon, 0.01 to 0.10% magnesium, and the remainder nickel.

References Cited in the file of this patent UNITED STATES PATENTS 1,921,619 Kayko Aug. 8, 1933 2,445,993 Beggs July 27, 1948 2,543,841 Foley Mar. 6, 1951 2,726,346 Busby Dec. 6, 1955 2,743,175 Talbot Apr. 24, 1956 2,899,592 Coppola Aug. 11, 1959 2,945,295 Feaster July 19, 1960 UNITED i. STATE-S l"P'ATEM OFFICE CET1F1CME- QF `(;0BRE(:'1101\1 Patent No. 3,12%537.l E l 'E E Y March 31, 1964 Crli w., Horsning It s hereby certified, that error appears in the above numbered patent requiring correction and that theesaid Letters Patent should read as corrected below Signed and sealed this 17th day of November 1964,

LEAL) nest;

RNEST W. SWIDERI EDWARD J. BRENNER ttesting Officer s Commissioner of Patents

Claims

1. A CATHODE COMPRISING A CORE HAVING A COATING THEREON OF EMITTING MATERIAL, SAID CORE COMPRISING AN ALLOY CONSISTING BY WEIGHT AND EXCLUSIVE OF DIFFICULTY REMOVABLE IMPURITIES, OF FROM 30 TO 60% COBALT, 0.01 TO 2.0% ALUMINUM, 2 TO 25% TUNGSTEN, 2 TO 25% MOLYBDENUM, 0.01 TO 0.25% CARBON, 0.01 TO 0.10% MAGNESIUM AND THE REMAINDER NICKEL, SAID ALLOY HAVING RELATIVELY HIGH HOT STRENGTH, POOR HEAT CONDUCTIVITY AND GOOD EFFECT ON EMISSION FROM SAID COATING, FOR IMPROVED OPERATION OF SAID CATHODE.