DE1254256B - Cathode for an electron tube - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

HOIj

German class: 21g-13/04

Number: 1254 256

File number: S 88398 VIII c / 21 g

Filing date: November 23, 1963

Opened on: November 16, 1967

The invention relates to a cathode for an electron tube, especially for magnetrons, with an emission-suppressing coating made of metal on places not intended for emission, this coating also has a getter function.

It is known to have components of transmitter tubes, but not the cathode, with a porous coating of Ti, ¹ Zr, Hg, Th, V, Nb, Ta or U, mixtures or alloys or compounds (for example carbides or hydrides) of these metals, in particular Zirconium, to be coated.

It is also known to use anodes of electrical discharge tubes to improve the heat dissipation on the areas radiating outwards with a porous layer of metals that bind gas at operating temperature, such as. B. zirconium or tantalum, too Mistake.

These known porous coatings are unable to perform any useful emission-inhibiting function; they only act as a getter against gases, such as. B. oxygen or nitrogen.

In the case of evacuated electron-emitting cathodes, however, it may be crucial to check the electron emission to a desired cathode area to ensure proper operation of the tube for the duration. It is at certain types of such tubes, for example in the case of magnetrons, are known to provide annular flanges, of which one is arranged laterally at each end of the cathode emission surface in order to be used as End shielding to serve and an exit of electrons in the longitudinal direction from the cathode-anode interaction space in the end areas flanking the anode. The internal structure of the tube is such that the outer edge each end shield is near a magnetic pole piece.

Both during the rest and during the working hours of the tube there is a migration of electron-emitting Substances from the cathode emission surface to the adjacent end shields take place, creating areas of unwanted emission will. When changing the operating state of the tube, for example when switching from the Idle state in full load operation or the change in the pulse lengths or the operating cycle the areas with unwanted emission at the end shields periods more undesirable Work instability.

Because the distance between the end shield and the pole piece is small and between these components largely different electrical working potential cathode for an electron tube

Applicant:

Litton Industries, Inc.,

Beverly Hills, Calif. (V. St. A.)

Representative:

Dipl.-Ing. H. Görtz, patent attorney,

Frankfurt / M., Schneckenhofstr. 27

Named as inventor:
Joseph Avery Smith,
Robert James Foreman,
Williamsport, Pa. (V. St. A.)

Claimed priority:
V. St. v. America 23 November 1962
(239 453)

tial are present, the unwanted emission in this area, which interacts in conjunction with the magnetic and electrical fields of the device, forms an electron beam which passes between the end shield and the adjacent pole piece. This undesirable and harmful condition, also known as the high energy hollow beam, can lead to arcing and severe erosion of the steel pole piece, creating metal splashes and harmful gases. These in turn encourage aimless arcing and lead to a reduction in the cavity Q, which further reduces the performance and reliability of the tube.

To eliminate the unwanted emission and its consequences, attempts have been made with a number of Fabrics and coatings for the end shields and corresponding arrangements carried out, however the resulting disadvantages ■ often compensated for the intended advantages.

A magnetron is known in which a certain part of the cathode is covered with a layer of zirconium is provided, which suppresses the emission. However, pure zirconium proved unsatisfactory, because it is at a temperature below the normal manufacturing and working temperature of the Tube a transformation of the crystalline structure,

709 688/323

namely a phase change, experiences. As a result, zirconium end shields have had substantial mechanical deformation. When applying non-alloy zirconium as a coating, the adhesion was insufficient. The peeling of zirconium particles upon handling made plain zirconium unsuitable and useless for this purpose. In addition, the porous zirconium sintered layer had a poorer emission suppression ability.

It is therefore an object of the present invention to remedy the aforementioned disadvantages in the case of cathodes avoid or belittle and create a cathode in which certain areas are alloyed are covered, which advantageously forms a smooth, non-porous surface and which does not experiences noticeable deterioration when exposed to elevated temperatures.

The alloy layer should have a good coverage depth and adhesive strength and in a simple manner can be handled without damaging the surface. In addition, it should both reduce emissions as well as having getter properties.

These tasks are performed on a cathode with an emission-suppressing coating Metal, which is not intended for emission at a cathode, in particular for magnetrons, is applied, solved according to the invention in that the coating consists of a dense, pore-free layer a zirconium alloy.

According to a preferred embodiment of the invention, the dense, pore-free coating consists of an alloy of zirconium with nickel.

The coating advantageously consists of a zirconium containing 83 to 96 percent by weight Nickel alloy, which is arranged on a base made of molybdenum.

To produce the cathodes according to the invention, a powdery mixture of metallic materials is used Zirconium with the other alloy component on the base and heated to over the melting point of the alloy.

The alloy material thus formed is excellent in oxide reducing power and good Getter properties, covers the areas concerned well, alloys itself to the surface of the heat-resistant Metal base well and learns from the manufacturing and operating temperatures of the tube no disturbing deformation.

When using the non-porous cover layers according to the invention on the non-electron emission Certain places on cathodes succeed in increasing the formation of hollow electron beams Energy, which leads to the creation of arcs within the electron tube with their undesirable Consequences can lead to suppress safely. The covering effect of the alloy layers exceeds for example that of porous zirconium sintered layers is considerable. The invention In addition, layers have a far better resistance to mechanical and thermal Influences and optimal adhesion to the metal base.

Advantages and possible uses of the invention emerge from the following description of a Embodiment in conjunction with the drawing, which is an enlarged plan view of a part the cathode and the adjacent tube parts shows.

The cathode carrier 11 consists of a cylindrical hollow body 13 made of a heat-resistant Metal, for example molybdenum, which can withstand the high working temperatures. The cathode support 11 can be aligned with respect to the anode 15 and to the steel magnetic pole pieces 17 and 17 'which are provided with longitudinal bores 19 and 19 'in order to facilitate the holding of the cathode carrier 11. A sleeve-shaped supply cathode 21 from a

ίο Tungsten sintered body containing an electron emission substance, for example barium aluminate, is impregnated, is located on the hollow body 13 at a distance from the anode 15. An insulated tungsten heater 23 of conventional design is within the cathode support 11 attached to heat the cathode 21 and thermionic electron emission from the cathode to facilitate. An annular flange or end shield 25, also made of molybdenum or tungsten, is in one piece on the hollow body 13

ao designed to form a barrier against electrons leaving the interaction space 48 and Try to enter the adjacent end space 50. All electrons outside the interaction space mean a loss of current that reduces the performance of the tube.

A similar protective device is provided by a further annular flange or an end shield 27 formed similar to the flange 25, which is attached in one piece to a molybdenum sleeve 29. The inside diameter the sleeve 29 is slightly larger than the outer diameter of the hollow body 13, so that the sleeve fits with a sliding fit on the hollow body and can apply to the cathode 21, whereupon the Sleeve 29 attached to the hollow body 13, for example by welding, soldering or similar measures will. This second annular flange or end shield 27 acts similarly to that previously described Shield 25 in that he or she forms a barrier for electrons to enter end space 52 ' Looking for.

A coating of a zirconium-nickel mixture is applied to the end shielding sleeve 29 and baked under vacuum before the sleeve 29 is attached to the hollow body 13. This process is described in more detail below, but it should already be mentioned that during this process, at which temperatures between 1500 and 1700 ^° C. occur, the Zr-Ni mixture melts and wets the molybdenum sleeve

So the sleeve is alloyed and on this a smooth one, not forms a porous surface layer made of a zirconium alloy 31. Evaporates during the heat treatment excess nickel, which increases the melting point of the resulting zirconium alloy layer Temperatures well above 1200 ° C is increased, which is the highest temperature to which the cathode support is heated during the manufacturing or subsequent working conditions of the tube will.

In the completed cathode assembly 11, the zirconium alloy layer 31 begins at one concentric edge 35 on the annular flange 27, which is approximately in the middle of the point facing the cathode 21 Surface of the flange 27 lies. The alloy layer 31, which extends over the outer edge 28 of the Flange 27 extends, covers the remaining part of the flange and extends on the sleeve 29 up to an edge 37 near the end of the sleeve.

Between the concentric edge 35 and the cathode 21 there is a free sleeve area 39, which is uncovered by the zirconium alloy. This free surface forms a barrier that prevents migration from zirconium to the cathode emission surface.

A corresponding zirconium alloy layer 40 is on a certain surface area of the Hollow body 13 applied, which at a concentric edge 41 on the annular flange 25 in similar Way begins approximately in the middle of the surface of the flange 25 facing the cathode 21. This alloy layer extends over the outer edge 26 of the flange 25 and covers the remainder of the flange and then continues along the hollow body 13 to an edge 43 which is inside the bore 19 of the magnetic pole piece 17 is located. Between the concentric edge 41 and the cathode 21 is a Bare surface area 45 is provided, which is similar to the above-mentioned free sleeve area 39 is not covered with the zirconium alloy.

The importance of the zirconium-nickel alloy can be explained in more detail in the following manner will. The outer edge 26 and 28 of the molybdenum shielding flanges 25 and 27 are spaced apart adjacent to the surfaces 18 and 18 'of the steel magnetic pole pieces 17 and 17'. When the tube is working the full pulse voltage lies between the pole piece surface 18 and the flange outer edge 26; the the same applies to the pole piece surface 18 ′ and the flange outer edge 28. In addition, there is this A permanent magnetic field of considerable amplitude that runs parallel to the electric field. If there are scattering electrons in the end spaces, support, as mentioned above, these two fields form a high-energy electron beam, creating this area the tube is made particularly vulnerable to harmful arcing. While cathode activation at approximately 1170 ° C and under the following operating conditions where the cathode is at a temperature of 900 to 990 ° C, there is a migration of Barium, barium oxide and other emissions from the surface of the cathode to neighboring ones Surfaces, for example the adjacent end shield instead. Certain areas of the end shield and the hollow body adjacent to the cathode 21 are in a corresponding manner with a Layer of alloy material 31 and 40 covered, which has emission suppressing and gettering properties Has.

As mentioned above, sintering on pure zirconium powder does not give satisfactory results Results that the adhesion is poor and the emission suppressing ability is proportionate is low. In addition, end shields made of pure solid zirconium undergo transformation of the crystalline structure at a temperature of 862 ° C, resulting in significant surface deterioration leads. It has been found that alloying nickel with zirconium does not adversely affect the surface entry.

In the preferred embodiment, zirconium is due to its emission suppression and Getter properties are desirable as the main component of the alloy. In combination with nickel, the resulting alloy improved surface coverage and bonding properties. It has been found that when a Zr-Ni mixture is applied and alloyed onto the molybdenum carrier parts 13 and 29 diffuses from the surface molybdenum into the zirconium-nickel alloy and at the Interface forms a ternary Zr-Ni-Mo alloy. While the necessary for each individual case Conditions for forming the Zr-Ni-Mo alloy at the interface have not been studied in detail

ίο, it has been found that the desired alloy formation depends on the Zr-Ni mixture used occurs in the temperature range from 1500 to 1700 ° C. By increasing the weight percentage of nickel in the Zr-Ni mixture towards the eutectic composition (17% Ni) the temperature required for alloy formation can be reduced to allow rapid alloy formation for the most varied of embodiments of the hollow body 13 within a temperature range

ao to make it easier for the cathode structure in question is not harmful.

In order to achieve the desired Zr-Ni-Mo alloy, it has been found that the proportion of Zirconium in the Zr-Ni mixture can be varied between 83 and 96 percent by weight. This weight percentage range of the Zr-Ni mixture represents the proportions for which the most advantageous alloying results can be achieved. The specified Limit values are by no means critical for success or failure, but only represent values above and below which also usable, albeit less optimal results are achieved will. It is advisable to keep the zirconium content as high as possible, but it increases as it increases of the zirconium content also indicates the required alloy temperature, and it becomes a poorer one Surface coverage observed. Experience has shown that ratios in the above range lead to the desired results. The eutectic temperature for the Zr-Ni composition with 83 percent by weight zirconium and 17 percent by weight nickel is 961 ° C. At the top End of the range preferably used when the zirconium content is increased above 96%, the alloy temperature rises to over 1600 ° C and thus approaches the critical temperature, in which the molybdenum carrier parts become brittle, which can be undesirable in certain applications.

The zirconium content of the Zr-Ni-Mo alloy shows the reducing power inherent in zirconium on. Barium and barium oxide migrating from the cathode 21 come into contact with the Zr-Ni-Mo material. The barium oxide undergoes a very rapid reduction during which the zirconium oxide is formed and Barium is released and evaporated from the Zr-Ni-Mo surface. That formed in this way Zirconium oxide is a very stable compound even at the highest temperatures that occur during activation and operation of the tube. This prevents it from switching off unwanted electron emission from migrating emission precipitates the formation of the above-described high-energy hollow jet, and the operational stability and performance of the tube are vastly improved.

Zirconium also excels as an effective high temperature getter element and, like all, tends chemical getter substances to deterioration

in the formation of oxides, nitrides, etc. on its surface. As a result, according to the working temperatures from 1150 to 1170 ° C during activation and evacuation of the tube its surface gettering capacity largely reduced. However, there is an excess of subsurface alloyed zirconium on end shield flanges 25 and 27 adjacent the magnetic pole surfaces 18 and 18 'where arcing occurs in magnetrons in general, the occurrence ruptures of an arch the surface compounds on the alloy material 31 and 40 and lay thereunder a new surface made of active zirconium free. The arcing creates a small amount metallic zirconium evaporates, which is not only released with those released during the arc formation Gases, but also combined with the gas originally responsible for initiating the arc was. Such regenerative gettering or pumping action is constant within the tube available, depending on how there is a need for this during continued operation. This saved Getter capability leads to the maintenance of desired gas levels within the tube, whereby the life expectancy of high-performance magnetrons is noticeably increased.

An additional advantage of the alloy layer results from its surface properties. So is the surface is slightly darkened and as a result has an improved heat radiation capacity. This fact is advantageous in the case of high-performance high-frequency magnetrons in order to dissipate To support heat due to the back impact of particles on the cathode.

The process of applying and alloying the Zr-Ni mixture with the molybdenum sleeve 29 and the molybdenum hollow body 13 takes place in each of the parts concerned before the assembly of the overall combination.

The process begins with the formation of the Zr-Ni material. The zirconium forming the mixture and nickel powder each have particle sizes in the range of 2 to 4 microns. You will be in only small Quantities of 4 or 5 g dry mixed, since zirconium is highly reactive to oxygen and therefore spontaneous combustion can occur. As a precaution, wet mixing should be used for larger ones Recommended quantities. In addition, zirconium hydride powder can be used instead of pure zirconium powder for safety can be used in a mixture.

The mixture of zirconium and nickel powder is in a volatile organic binder, suspended for example a nitrocellulose lacquer. A solvent such as amyl acetate is used added to dilute the mixture to a consistency that is convenient for application and achievement the desired coverage and adhesion. As a result of the volatility of the amyl acetate, various Liquid consistencies can be achieved. It was found that a viscosity of the suspension of about 100 cP is very satisfactory for easy application of the mixture to the support members is. If the suspension is too viscous, the layer may peel off during the vacuum heat treatment appear.

The method of applying the Zr-Ni mixture is not critical, provided that only that is desired Area of the support part is well covered with a layer of Zr-Ni material of suitable thickness. try found that to ensure good coverage the finished alloy had a minimum thickness of Should be 0.05 mm. The layer thickness desired for a satisfactory coverage can be achieved by building up two or more individually processed layers. A defined maximum strength is not given, since a complete surface coverage meets the essential requirements. The inner clearances and dimensions of the respective version must be taken into account accordingly will. The application is expediently carried out using a device which Can rotate support parts while the Zr-Ni suspension in a fine compressed air spray or by means of applied with a brush. The rotation to apply the Zr-Ni metal to the concerned Parts is made easier by using the chuck of a lathe, which is the end piece 47 of the shielding sleeve 29 and the shaft part 49 of the hollow body 13 is detected.

In the alloying process, the shielding sleeve 29 is applied to the end of the hollow body 13, and the two coated parts are subjected to a temperature treatment at the same time. The alloy is carried out in a vacuum oven at a pressure of not more than 5 × 10 ^-5 mm Hg.

As such, the alloy takes place very rapidly over a period of 10 seconds at one temperature between 1500 and 1700 ° C. The exact temperature depends on the composition of the Zr-Ni mixture which is to be alloyed with the molybdenum surfaces to which the suspension is applied became. Since the recrystallization of molybdenum follows a time-temperature relationship, it is expedient to make the alloy of the Zr-Ni layer on the molybdenum surface quickly before the Molybdenum experiences embrittlement.

As mentioned above, the weight proportions of zirconium and nickel in the alloy can be within the Above given range can be varied to the alloying with respect to the size and mass of the concerned To lighten the cathode without significantly affecting the benefits of the zirconium content he follows. This enables the processing temperatures to be varied while remaining constant Time factor.

During the high temperature vacuum treatment The Zr-Ni suspension is chemically degraded for a short period of time, followed by that of amyl acetate and nitrocellulose existing binders are volatilized. Part of the nickel content is from the Alloy surface evaporated. During the exact nickel content of the alloy layer ultimately obtained is not known exactly, it is evident from experience in processing that one is so The higher the nickel content of the alloy, the greater the amount of nickel that evaporates. Because the high temperature treatment is short lived, it can be assumed that most of the evaporated nickel will come from the outer layers of the alloy surface originates. While nickel is the preferred metal additive for zirconium, various other finely divided or powdered transition metals can be used similarly in appropriate ratio combinations with zirconium under suitable ones Temperature conditions are used. For this purpose, the zirconium should be

i 254

ίο

Neter way to be alloyed material a metal, which at the operating temperature of the cathode a has favorable vapor pressure and a smaller amount of which has a lowering of the melting point caused by zirconium in the range of 1500 to 1700 ° C. In addition to nickel, suitable transition metals include Cobalt, vanadium, titanium, chromium, manganese, molybdenum and tungsten. Some examples of zirconium alloy combinations are:

Parts by weight Alloy mixture Eutectic of temperature Powder mixture Zirconium-titanium ⁰ C 50:50 Zirconium-vanadium 1610 70:30 Zirconium-chromium 1230 82:18 Zirconium-manganese 1300 77.5: 22.5 Zirconium-molybdenum 1135 69:31 Zirconium-tungsten 1520 82:18 1650

A cathode suitable for use in a magnetron has been described in detail and in which a layer of alloy material having reducing and gettering capabilities is provided. This Material is alloyed in one piece with the relevant areas of the cathode and is characterized by excellent Adhesion, good coverage, and excellent emission suppression and gettering capabilities the end. This results in a very considerable improvement in the stability of the tube operation and an extension the service life. It has been found that leakage current and gas content within the tube during operations have been significantly reduced, resulting in significant improvements in overall functionality and performance of the tube have been achieved. Tubes that have undergone a rejuvenation process, that was required by the wear and tear or arcing in operation have a considerable Experience extension of service life.

The invention is equally applicable to traveling wave tubes, backward wave oscillators, and klystrons and similar tubes can be used in which it is of interest that certain areas under electrodes working at high temperatures have emission suppression and gettering capabilities, to improve performance. The desired alloy mixture is applied as a coating applied to certain areas of the electrodes made of heat-resistant metal and for the purpose Alloy heat treated as described above in a vacuum.

Claims (5)

Patent claims: 1. Cathode for an electron tube, especially for magnetrons, with an emission suppressive metal coating on non-emission areas, thereby characterized in that the coating consists of a dense, pore-free layer of a zirconium alloy consists. 2. Cathode according to claim 1, characterized in that the coating is made of an alloy consists of zirconium with nickel. 3. Cathode according to claim 2, characterized in that the coating consists of a 83 to 96 weight percent zirconium-containing nickel alloy consists. 4. Cathode according to claims 1 to 3, characterized in that the coating on a Base made of molybdenum is arranged. 5. A method for the production of cathodes according to any one of claims 1 to 4, characterized in that that a powdery mixture of metallic zirconium with the other alloy component on the base applies and heated to above the melting point of the alloy. Considered publications:
German Patent Nos. 725 521, 745 134;
French patent specification no. 1 201 868. 1 sheet of drawings 709 688/323 11.67 © Bundesdruckerei Berlin