DE1255207B - Matrix or layer cathode for glow cathode tubes - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

HOxj

German KL: 21 g - 13/04

Number: 1255 207

File number: W 37408 VIII c / 21 g

Filing date: August 19, 1964

Open date: November 30, 1967

The invention relates to a matrix or layer cathode for hot cathode tubes with finely divided Particles of an oxide or carbonate of at least one alkaline earth metal, which with a Metal film are coated.

There are currently three main types of commercially available cathodes. The most common and oldest The cathode type is the layered cathode, which has a base with an alkaline earth oxide, mostly containing barium oxide is coated. The second type of cathode is a porous pressed tungsten sintered body, one so-called matrix, which is impregnated with barium aluminate, is provided. The third type of cathode is the nickel matrix cathode, which is made up of a mixture that is pressed and fired to form a shaped body Nickel powder and an alkaline earth oxide is formed.

In general, each of these three cathode types has its own advantages and disadvantages, which determine their use in the individual case. For example, a layered cathode delivers a significantly higher current density than any of the matrix cathode types under comparable conditions. On the other hand, the matrix cathodes form a reservoir of active material which is used for the continuous refreshment of the active, emitting surface layer during the operating time. Accordingly, it is considered advantageous to use matrix cathodes in cases where they are exposed to high loads, e.g. When there is a high degree of backbombardment, or in cases where destruction of the relatively thin oxide layer of the first cathode type may occur, for example when maintaining a direct current emission greater than about 0.4 amps. / Cm ² .

The so-called storage cathodes are built up using a mixture of compounds, such as barium carbonate, which in turn releases carbon dioxide during manufacture to form the active oxide, e.g. B. barium oxide, break through. These connections are made with Metal particles, generally with tungsten or molybdenum particles, mixed. The disadvantage of The usual arrangement is that the carbon dioxide reacts with the tungsten during breakthrough and forms an undesirable reaction product which is evident in the subsequent migration of the emissive Material obstructed to the surface.

Two approaches to solving this problem are known. After the first, the in this sense not inert tungsten matrix material is replaced by inert material, e.g. B. Nickel, which is no such undesirable reaction product during the breakdown of the matrix or layered cathode for
Hot cathode tubes

Applicant:

Western Electric Company Incorporated,

New York, N.Y. (V. St. A.)

Representative:

Dipl.-Ing. H. Fecht, patent attorney,

Wiesbaden, Hohenlohestr. 21

Named as inventor:

Dean William Mason, Warren Township, NJ;
Charles Michael Pleass, Bernardsville, NJ
(V. St. A.)

Claimed priority:
V. St. v. America 19 September 1963
(310 040)

Forms carbonic acid. It was found, however, that the later migration of the emitting Material is undesirably small. The latter is in turn made by using an overlying porous Metal layer overcome. Thus, according to this approach, there is no coating at all for the particles of the emitting material used. According to the second approach, a non-inert matrix metal, z. B. tungsten used, and the reaction between the emitting substance containing Particles and the matrix are prevented by means of a metal coating on the particles. This coating is designed to be a physical touch (and consequently a chemical reaction during breakthrough) with the matrix metal to prevent. The coating accordingly consists of inert metals, e.g. B. made of a metal of the platinum group. After the carbonate or some other connection to the Formation of the emitting substance has decomposed, this metal coating dissolves in the matrix metal and is accordingly no longer present as a coating in the finished cathode. So you can see that the coating the particle here only serves to react with a non-inert matrix metal, e.g. B. tungsten, to prevent; the coating would therefore never come together

709 690/397

3 4

with an inert matrix metal, ζ. B. nickel, form compounds. Especially for this purpose

as in this case the harmful suitable metals are tungsten, molybdenum, nickel

Reaction through the choice of this inert matrix and cobalt,

metal is prevented. Coating or coating the particles

In contrast, the invention cathodes 5 can be made with the help of any conventional coating or plating electrode type mentioned are produced, the process can be accomplished, for. B. by authorities Current densities at lower operating temperatures in the dry or wet process or drum fittings compared to the previously known cladding.

having methods. The invention is illustrated for this cathode in FIG. 1 is a dry fluidized bed system

characterized in that the one for the finely divided io is shown schematically as one of the various

Particles provided metal film at least from possibilities for coating the powdery

one of the metals nickel, tungsten, molybdenum or substance can be used. A wetting

Cobalt is made of. The stainless steel column 11 is fitted with a glass column 12

Connected by the cover selected according to the invention with the aid of a polyethylene compound 13, metals, thermally unstable compounds are obtained, 15 At the lower end of the column 11 is a porous one, made of the migratory stainless steel made sintered frit 14 a material do not affect, rather even favor, soldered, which weighs the entire cross section of the column 11 from the resulting increase in vitality. A glass frit 15 of the same porosity as that Durable and improved emissivity to frit 14 is in column 12 at the top of the same is close. The coated particles can be melted down to ao, so that a loss of powder through the for the production of a cathode taken from stock for whirling or wetting will. : Gas flow is avoided. The column 11 is

In the following, the invention is heated on the basis of the drawing by heating windings 16, so that hereby

tion described; it shows the heat required to decompose the metal

Fig. 1 is a schematic view of a wetting connection during the coating process.

or vortex system that is produced in a type of manufacture. A line 17 is connected to the column 12

is used to manufacture a cathode, a drying tube 18 is connected through which the gas

F i g. 2 a schematic view of a wetting-shaped product of the process before it is applied to the system, that are burned down in a different way of production to the aisle of the system, passed through Making a cathode can be used 30. A wash bottle 20 is attached to the column 11

F i g. 3 shows a cross section through a cathode connected via a line 19. The wash bottle

structure, contains a metal compound 21, which is thermally

Figure 3A shows a cross section through a with metal decomposed during the process. The system is

coated, thermally emissive active particle, by a flow meter 22 located at the entrance of the

F i g. 4 is a diagram of the voltage system arranged, completed by which the

Current characteristic curve of a fluidizing gas with the aid of a plasma jet from a source (not shown)

sprayed cathode at: a cathode temperature occurs. A bypass 23 and valves 24, 25 and

from 750 ° C after 720 hours of operation to the Dar- 26 are used to control the process,

position of the space charge breakthrough, whereby the

Current in milliamps on the ordinate in the power of 40 netes fluidizing gas, z. B. hydrogen, nitrogen

two thirds and the voltage on the abscissa in or argon - depending on the nature of the to

Volt is applied, and coating powdery substance - that

F i g. 5 is a graphical representation of the voltage system input, after which it is fed by the

Current characteristic curve of a flow meter 22 recorded with the aid of air with the valves 25 closed

sprayed cathode at cathode temperature 45 and 26 and with valve 24 open over the bypass

of 750 ⁰ C after 315 hours of operation for representation 23 and the line 19 flows into the column 11, the

of the space charge breakthrough, again on the with the help of the heating windings 16 to bake out the

Ordinate is the current in milliamps and in the system power over a suitable period of time

two thirds and the voltage on the abscissa in is heated. After that, the thermo-emissive

Volt is applied. 50 active material previously in a ball mill

The embodiments described below. the required particle size, which in general

refer to the coated cathode (layer - between 1 and 5 microns, has been crushed,

cathode), but it should be noted that other entered the system and the wetting or

Matrix cathodes from the cathode material introduced after the vortex. The gas used for this

Invention can be produced. 55 can be hydrogen or any of the other above

The first step of the technique according to the invention will be described gas. Then the on

is the coating of discrete particles of a thermo- system outlet ignited exiting gas flow,

emissive active material with a thin being this burning off during the whole process

Metal film. Usually the particulate has taken place. Then the hydrogen is

Material an alkaline earth oxide or an alkaline earth carbonate. 60 device23 by closing the valve 24 and through

These materials are the usual emissive openings of the valves 25 and 26 to the wash bottle 20

Substances and are generally diverted during manufacture so that the gas can pass through them

Sprayed-on oxide cathodes and matrix cathodes and then enters the column 11, in which

used. the metal compound 21 at the elevated temperature

Suitable coating materials can decompose from the 65 with the formation of elemental metal, which the

those materials are selected that are encased with the thermally emissive active particles.

Cathode function are compatible and in one The metal-coated particles are subsequently

practical temperature range thermally unstable removed from the system. and will be

position of a cathode element in stock.

Another technique for coating the particles of material is the method shown in FIG. 2 shown Device used. The system shown is commonly called wet-wetting or Wet vortex system called. In this system, pillars 11 and 12 are shown in FIG. 1 replaced by a vertebral column 30, which contains an inert liquid 31, in which a distributed, thermo-emissive active material of the type described above is suspended. The column 30 is with the help of a Constant temperature bath 32 heated. A suitable stirring device 33, usually a magnetic stirrer, ensures the necessary movement of the powdery substance during the coating process.

Some examples are described below:

Example I.

30th

This example describes the manufacture of a cathode using nickel-coated alkaline earth oxides (jointly precipitated barium strontium carbonate) with the help of a plasma jet on a solid Base, consisting of an active alloy, are sprayed on.

Jointly precipitated barium-strontium-peroxide was placed in a boat made of nickel, a passive material of high purity. The boat was then ^{heated in a quartz tube furnace under vacuum to 900 °} C. for a few hours. This resulted in the decomposition of the peroxides into the oxides in accordance with equation (1) below. At the end of the heating process, the pressure was about 10 ^-3 mm of mercury.

2 (BaSr) O ₂

200 ⁰ C

2 (BaSr) O + O ₂₁ (1)

The crude product was then placed in a Pyrex ball mill given, in which aluminum oxide balls were contained, and ground for about 36 hours, whereby a fine barium strontium oxide powder with a maximum grain size of less than 37 microns was obtained. The resulting fine powder was then placed in a pre-cleaned and baked spinal column, as shown in Fig. 1, filled. The vortex was created by feeding one Introduced hydrogen stream, which in the washing 5 <> bottle 20 has been saturated with nickel carbonyl at room temperature. Coating of the particles was made obtained by heating the spinal column to a temperature of 100 ° C for 20 hours. At this temperature the nickel carbonyl decomposes with simultaneous coating of the barium strontium oxide particles with a nickel film. The coated particles were 14 weight percent nickel and 86 percent by weight barium strontium oxide.

Two cathode buttons (machined wires) made of a 0.1% zirconium-nickel alloy with a diameter of 2.16 mm were selected and the end faces of the same were sandblasted with aluminum oxide and subjected to a cleaning procedure customary for oxide cathode supports. The cleaning process involved placing the caps in a nickel-zirconium boat and subjecting them to conventional evaporation for the purpose of degreasing. The caps were then blown dry with low-pressure nitrogen and washed under the action of ultrasound. Thereafter, the washed caps were showered with deionized water and dried for 15 minutes in a drying oven at 110 ⁰ C for 20 minutes oxidized at 400 ⁰ C in air and 30 minutes is reduced in wet hydrogen at 1050 ⁰ C. The cleaned buttons were then fixed in a clamping device and sprayed with the nickel-coated barium-strontium oxide particles with the aid of a plasma jet until a layer thickness of 0.076 mm was obtained. The plasma jet spraying was done in the following way:

The coated particles were sprayed on with the aid of a direct current arc plasma gun, at the hydrogen was passed through a high power direct current arc and ionized and as a result, a high-energy plasma flow was achieved from the arc, in which the recombination The energy generated by the ions was converted into thermal energy of the gas atoms. The introduction the powdery substance in this area of high energy brings the individual particles to Melt. The melted particles were then sprayed onto a base, the cathode buttons, where they clumped together and formed a dense coating.

One of the buttons thus obtained was then baked in hydrogen in hydrogen for 15 minutes at 800 ° C. and subsequently embossed with a pressure of 7.8 t / cm ² . The button was then placed in a molybdenum heating tube and ^{burned for 15 minutes at 1000 °} C. in hydrogen for the purpose of sintering.

The other cathode button was immediately placed in the molybdenum heating tube and as above described, sintered.

In Fig. 3 shows a cathode element which, in accordance with the above-described Technk has been made. A base 41 has nickel together with an activator on which a coating 42 of metal-coated, thermally emissive active powder 43 is applied. A Particle43 is shown enlarged in FIG. 3A.

The ready-to-use cathode elements produced in this way were usually fixed in a tube and fused to a vacuum system in which a vacuum of 10 ~ ⁷ mm mercury could be obtained and in which the structure was baked out at 400 ° C. for 16 hours. ^{The cathode was then heated to 1050 °} C. for 5 minutes by applying voltage to the heating element. Thereafter, voltage was applied to the anode until a cathode current of 1 Amp./cm ^{2 was} obtained. The tube was then melted from the vacuum system. The finished cathode was then placed on a life test bench and its operating characteristics were observed.

The data of the F i g. 4 were obtained with tubes manufactured according to Example I on a service life test stand at an anode voltage of 200 volts. After 720 hours of operation the DC current was added to each tube as a function of the anode voltage at 75O ⁰ C was measured. The data obtained were then recorded with the current to the power of two thirds in milliamperes on the ordinate and the voltage on the abscissa.

It should be noted that the space conduction-limited emission of the two prepared according to Example I. Cathode is around 15 milliamps at 750 ° C (the same curve applies to both). This value the comparison with a maximum space-charge-limited emission of 10 milliamperes at normal Nickel matrix cathodes represent a significant advance in cathode manufacturing technology.

Example II

This example describes the manufacture of a cathode element in which nickel plated Alkaline earth carbonates (barium-strontium) with HiUe was sprayed by air onto a solid base consisting of an active alloy.

80 g of SrCO ₃ , 72 g of BaCO ₃ and 200 cm ^{3 of} amyl acetate were ground in a ball mill with flint stones for 64 hours, so that a fine suspension of carbonate powder in amyl acetate was formed. The resulting suspension was then introduced into a spinal column 30 as shown in FIG. The spinal column was immersed in an oil bath 33 at a constant temperature. A vortex was brought about by introducing a nickel-carbonyl vapor-containing hydrogen stream into the vortex column. In coating the particles of the suspension 22 hours was 33 heated to a temperature between 80 and 90 ⁰ C temperature for by means of the oil bath. At these temperatures, the carbonate decomposes and the carbonate particles are coated with a thin nickel film.

The apparatus would then be opened and the carbonates separated from the amyl acetate by filtering as well as in Air dried at 110 ° C.

100 g of the coated or coated carbonates were then mixed with 75 ml of amyl acetate and 82 ecm of a Nitrocellulose binder solution mixed to form a carbonate mixture.

A cathode button from a 0, l ° / ₀ solution of zirconium-nickel alloy has a diameter of 2.16 mm with selected and purified according to the purification procedure described in Example I. The carbonate mixture was then sprayed onto the cathode with a conventional air brush to form a 0.0127 mm thick layer. The sprayed-on cathode was then ^{burned at 250 °} C. in oxygen to burn off the binder.

The cathode produced in this way was fixed in a tube with the aid of conventional methods and fused to a vacuum system in which a vacuum of 10 ~ 'mm of mercury could be obtained. The tube system was baked at 400 ° C. overnight. After baking, voltage was applied to the cathode heating element to increase the cathode temperature to 800 ° C. This process served to degas the cathode. The degassing was carried out for 100 minutes or until the pressure became 4 x 10 -4 mm of mercury. The temperature was then increased ^{to 950 ° C. for about 5 minutes.} Subsequently, the temperature of 85O ⁰ C was lowered and applied to the anode voltage to a cathode current of 0.5 Amp./cm ²

ίο was received. The tube was then melted placed in a service life test stand and aged.

The in the F i g. 5 reproduced data

obtained with a cathode produced according to Example II in a lifetime test start at 150 volts anode voltage. After 315 hours of operation the DC current was measured as a function of the anode voltage at 750 ⁰ C. The data obtained were then plotted with the current in milliamps to the power of two thirds on the ordinate and the

ao tension on the abscissa.

It should be noted that the space charge limited emission cathode prepared according to Example II is about 48 milliamps at 750 ⁰ C. This value can be compared with a maximum space-charge-limited emission current of 17 milliamperes for conventional matrix cathodes.

The material of the base preferably consists of nickel and an activator material and / or a nickel alloy and an activator.

Claims (4)

Patent claims: 1. Matrix or layer cathode for hot cathode tubes with finely divided particles of a Oxide or carbonate of at least one alkaline earth metal coated with a metal film, characterized in that the metal film consists of at least one of the metals Nickel, tungsten, molybdenum or cobalt. 2. Cathode according to claim 1, characterized in that the coated particles on a consisting of nickel and an activator and / or a nickel alloy and an activator Base to form a layer cathode are applied. 3. A cathode according to claim 2, characterized in that the backing is a 0, l ° / _o strength zirconium-nickel alloy. 4. Cathode according to one of claims 1 to 3, characterized in that the particles from Barium Strontium Oxide and are coated with nickel. Considered publications:
French Patent No. 1,284,384. 1 sheet of drawings