KR20020063327A - Metal cathode and indirectly heated cathode assembly having the same - Google Patents

Abstract

PURPOSE: A metallic cathode and an indirectly heated cathode structure having the same are provided to improve an electrical characteristics of a metallic cathode by lowering a work function of the metallic cathode. CONSTITUTION: A sleeve(15) having a size about 1 mm is used as a support body. The sleeve(15) has a closed upper portion. A surface of an inside of the support is covered by alumina. A spiral heater(13) is inserted into an opened part of the sleeve(15). The spiral heater(13) is used as a heating source. An electron emission material of a metallic cathode(11) as an electron emission source is fixed on an outer surface of the closed upper portion of the sleeve(15). The metallic cathode(11) is formed by using an arc melting method or an induction melting method. The metallic cathode(11) is fixed to the sleeve(15) by using a welding method.

Description

Metal cathode and heat dissipating cathode structure having same {Metal cathode and indirectly heated cathode assembly having the same}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal cathode of an electron beam apparatus, and more particularly, to a thermoelectron emitting metal cathode for an electron beam apparatus having a high electron emission capability and a low operating temperature, which can be used for an electron beam apparatus such as a television CRT and an imaging tube, and a heat radiation type having the same. It relates to a cathode structure.

A conventional alkali metal carbonate layer having barium as a main component on a base metal containing nickel (Ni) as a main component and a trace amount of silicon (Si), magnesium (Mg) as a reducing agent in a conventional electron tube cathode, preferably Preferably, the so-called "oxide cathode" having an electron emitting material layer of oxide converted from a ternary carbonate composed of (Ba, Sr, Ca) CO ₃ , or a binary carbonate composed of (Ba, Sr) CO ₃ is widely used. . These oxide cathodes have the advantage of being able to be used at relatively low temperatures (700-800 ° C.) due to their low work function, but have a limit in electron emission capability, which makes it difficult to emit a current density of 1 A / cm 2 or more. Because the material is a semiconductor and the electrical resistance is high, if the electron emission density is increased, the material is evaporated or melted due to the self heating by Joule heat, thereby deteriorating the cathode, or the intermediate resistance layer is formed between the metal substrate and the oxide layer by long-term use. There is a disadvantage that the life is shortened.

In addition, since the oxide cathode is fragile and has low adhesion to the metal substrate to be mounted, the lifetime of the cathode ray device having this type of cathode is shortened. For example, if only one of the three oxide cathodes of a color receiver is damaged, the entire expensive device will fail.

For this reason, attempts have been made to apply high-performance metal cathodes to the cathode ray device without the disadvantages of the oxide cathode described above.

For example, a metal cathode based on lanthanum hexaboride (LaB ₆ ) is known to have higher strength and higher electron emission ability than an oxide cathode. Can emit. However, lanthanum hexaboride cathodes have been used only in some vacuum electronics, which can replace the cathode units because of their short lifetime. The short lifetime of the lanthanum hexaboride cathode is due to its high reactivity with the constituents of the heater, since lanthanum hexaboride forms many fragile compounds in contact with the constituents of the heater, eg tungsten. .

US Pat. No. 4,137,476 discloses a cathode in which another barrier layer is formed between lanthanum hexaboride and the body of the heater to eliminate this possibility of reaction. However, this method has a problem that due to its complicated structure, the production cost of the cathode is considerably increased, it is difficult to greatly improve the lifetime of the cathode, and it is difficult to apply to the CRT.

In addition, alloy emitters of platinum group elements such as Pt, Pd, and Ir and Ba have been used as cathodes of magnetron, traveling wave tube (TWT), backward wave tube (BWT), etc. The electrons were used as secondary electron emission cathodes which impinged on the material and emitted secondary electrons at that energy. In the alloy emitter of the platinum group element -Ba used as the secondary electron emission cathode in the conventional magnetron, the Ba content is 1 to 2% by weight and the lifespan is about 1000 hours, which makes it impossible to use it as a hot electron emission cathode for an electron tube.

Similarly, the hot electron emission cathode made of a binary alloy made of platinum and barium has better electron emission characteristics than the conventional oxide cathode, but since the operating temperature of the metal cathode requires a relatively high temperature of about 1200 ° C. A problem occurs.

Therefore, the technical problem to be achieved by the present invention is to reduce the work function of the metal cathode in order to solve the above problems the electron beam device hot electron emission metal cathode which can be used in electron beam devices such as large tube and high-definition electron tube excellent in life and electrical characteristics To provide.

Another object of the present invention is to provide a heat radiation type negative electrode structure having the metal cathode.

1 is a schematic cross-sectional view showing the structure of a heat radiation type negative electrode structure having a metal cathode according to the present invention.

2 shows the structure before rolling of the metal cathode according to the present invention.

Figure 3 shows the structure after the rolling of the metal cathode according to the present invention.

In order to achieve the above technical problem, the present invention has a dendrite structure having a particle diameter of 0.5 to 5 micrometers as an alloy containing 0.1 to 5 parts by weight of alkaline earth metal, and 95 to 99.9 parts by weight of group VIIIB elements, based on the total weight of the metal anode. A hot electron emitting metal cathode for an electron beam device is provided.

The alkaline earth metal is preferably barium.

It is preferable that the said Group VIIIB element is platinum or palladium.

The hot electron emission metal cathode for the electron beam device of the present invention may further include one or more transition metals selected from the group consisting of aluminum, copper, iron, molybdenum, tungsten, niobium, hafnium, rhenium, platinum group or rare earth metal.

In order to achieve another technical problem of the present invention, the present invention provides a heat radiation type negative electrode structure having the metal cathode.

Hereinafter, a metal negative electrode and a method of manufacturing the same according to the present invention will be described in detail.

In the case of purely platinum-only metal cathodes, the work function is very high as 5.3 eV, but when barium is added thereto, the work function is reduced to 2.2 eV, and thus it can be used as a hot cathode. This reduction in work function is known because the platinum-barium alloy forms a barium monoatomic layer on the surface to reduce the surface work function during cathode operation. Therefore, the electron-emitting mechanism of the platinum-barium alloy system has three steps as follows.

(1) The first step is to decompose Pt ₅ Ba in the alloy. In a Pt-Ba alloy system having a barium content of less than 16.66% by weight, barium exists in the form of a Pt ₅ Ba intermetallic compound, which decomposes during operation to give barium atoms.

(2) Step 2 is a step in which the decomposed barium diffuses to the metal cathode surface. This diffusion should continue to be rapid to improve the electrical properties, but short life due to the fast depletion of elements.

(3) Step 3 is to form an optimal barium monoatomic layer on the surface of the metal cathode. If the diffusion rate of the second stage is too slow, the monoatomic layer cannot be formed densely.

After all three steps, the work function of the surface of the metal cathode is reduced, and electron emission is possible even at a relatively low temperature. However, the conventional binary-based alloy composed of only platinum-barium can be operated only when the temperature is about 1200 ℃, such a problem such as heater disconnection and leakage current occurs when the operating temperature is high as described above.

Therefore, in the present invention, the metal cathode optimized by controlling the diffusion rate (or diffusion equilibrium) toward the surface of the element by the method of controlling the particle diameter of the tissue particles forming the alloy structure through the cooling rate control or heat treatment during alloy production Can be obtained.

The metal cathode may be manufactured in various shapes according to the purpose, but similarly to the conventional oxide cathode structure, the alumina inside the blocked metal tube, which is a support, is used as a support, using a sleeve 15 having a closed upper portion of about 1 mm as a support. The spiral heater 13, which is designed to completely block the furnace surface and prevent current leakage, is inserted and embedded at the open end of the sleeve 15 to be used as a heat source, and a metal cathode as an electron emission source on the outer surface of the blocked end ( It has a structure in which the electron-emitting material of 11) is fixed.

The metal cathode 11 is obtained by making an alloy in a molten state by a method such as arc melting or induction melting and cooling the same, and cutting the sleeve 15 into a size suitable for an application purpose. To be fixed by welding or the like.

In the production of the alloy used as the metal cathode, the fine internal structure of the alloy is determined according to the composition ratio, the heating temperature, the holding time, the cooling rate, and the like. Usually, the bonding state of the alloy depends on the cooling rate and the cooling rate. Tissue size is known to be affected.

Therefore, by further optimizing the production conditions of these alloys, as described above, the diffusion rate toward the surface of the element can be controlled. Thus, it is possible to manufacture a metal anode having better life and electrical properties than the conventional platinum-barium binary alloy.

Such metal cathodes can be compared by numerical values, such as the size of the work function, electrical characteristics (electron emission ability), operating temperature, etc., which are the limit energies capable of emitting electrons in a vacuum. The condition of the organization depends on the conditions.

Therefore, in the present invention, when an alloy containing an alkaline earth metal and a group VIIIB element is manufactured by the following method, an alloy having a dendrite structure having a particle diameter of 0.5 to 5 micrometers is obtained, and the alloy having such a structure has a long lifetime and It has been found that the electrical properties are excellent.

As the alkaline earth metal, barium is preferable, and the amount thereof is preferably used in an amount of 0.1 to 5% by weight based on the total weight of the metal cathode. When the amount is less than 0.1% by weight, the lifespan of the metal is lowered and the amount is 5% by weight. When it exceeds%, there is a problem that the hardness of the alloy becomes large and rolling becomes difficult.

Hereinafter, the method for producing a metal negative electrode according to the present invention will be described in detail taking a binary alloy as an example.

First, the group VIIIB element and the alkaline earth metal are placed in an arc furnace. Since Group VIIIB elements and alkaline earth metals have a large melting point difference, it is preferable to use an arc furnace that can melt the metal instantaneously.Alkaline earth metals are easy to evaporate, so they are 10 to 15% more than the contents of the final alloy. To adjust the content. Subsequently, the inside of the arc furnace is kept in a vacuum state and then an inert gas such as argon gas is injected. Thereafter, a voltage is applied to the arc furnace to melt the group VIIIB element and the alkaline earth metal in a short time. At this time, stir well with a metal rod such as tungsten to make the alloying well. In order to remove the impurity gas generated during the melting process, the vacuum is extracted and then the melting process is repeated in an inert atmosphere at the same pressure and cooled in the furnace to obtain an ingot.

In the obtained ingot, since the particle size of the dendrite structure is relatively large, rolling may be performed using a twin roller, a reversible two-stage rolling mill, or the like, or the particle size of the dendrite structure may be adjusted to 0.5 to 5 micrometers by a method such as heat treatment.

Since the Group VIIIB element and the alkaline earth metal have a large density difference during the manufacturing process of the metal cathode, it is difficult to obtain a uniform alloy made of these metals. Therefore, by repeatedly performing the melting process and the solidification process, a metal anode having improved chemical and microstructure uniformity can be obtained.

Subsequently, the alloy according to the present invention manufactured in an arc furnace is cut or molded to be suitable for the cathode structure of the electron tube and then mounted on the cathode structure.

The metal cathode for an electron tube according to the present invention may be used in a direct type cathode structure, but is preferably used in a heat radiation type cathode structure as shown in FIG. 1. That is, referring to FIG. 1, the metal cathode 11 of the present invention is preferably welded to the upper portion of the sleeve 15 in which the heater 13 is embedded and used as a hot electron emission material of the heat radiation type cathode structure.

The invention is described in more detail with reference to the following examples, which are not intended to limit the invention.

Example 1

3.5 g of Pt and 0.0875 g of Ba in powder form were placed in an arc furnace. Subsequently, the inside of the arc furnace was filled with 1 × 10 ⁻⁵ Torr of argon gas under vacuum, and a voltage was applied to the arc furnace to melt Pt and Ba and stir well with a tungsten rod. The impurity gas generated during the melting process was removed under reduced pressure and again adjusted to a pressure of 1 × 10 ⁻⁵ Torr using argon. The melting process was repeated eight times, and then cooled in a furnace to obtain an ingot. The obtained ingot was rolled at a compaction rate of about 70% using a twin roller to prepare a metal negative electrode having a desired structure.

The alloy was magnified at 500 times magnification using an electron microscope to confirm that there were no more than 10 dendrite structures per square centimeter, and the size was within the range of 0.5 to 5 microns.

Increasing the barium content in the metal negative electrode tends to increase the hardness of the alloy, making it difficult to roll, the hardness increases by rolling, but the scattering decreases as the structure becomes uniform. In the case of rolling at a compression rate of about 70%, the samples before and after 150 in Vickers hardness increased to about 250, and the surface roughness reduction effect can also be confirmed as shown in FIGS. 2 and 3. Fig. 2 shows the structure before rolling, and Fig. 3 shows the structure state after rolling.

Example 2

Ingot was prepared in the same manner as in Example 1 by weighing 3.5 g of Pt, 0.0875 g of Ba and 0.035 g of molybdenum in the form of powder.

Comparative example

Proceeding in the same manner as in Example 1, but without undergoing rolling to obtain a metal anode. Such a dendrite structure of the metal cathode can be confirmed that there is a non-uniform size and a large number of tissues having a particle diameter of more than 5 micrometers when magnified at 500 times magnification using an electron microscope.

Subsequently, the binary alloys prepared according to Examples 1, 2 and Comparative Examples were cut and welded to the upper portion of the heat dissipating cathode structure shown in FIG. 1, and the current density increase resulting from the decrease in the work function was measured under the same operating conditions. The measurement results are shown in Table 1 below.

Sample type Current density Example 1 2.1 Example 2 3.1 Comparative example 2.9

The metal cathode and the heat dissipating cathode structure having the same according to the present invention can be used in electron beam devices such as large tubes and high-definition electron tubes because of excellent life and electrical characteristics due to a reduction in work function.

Claims (5)

A thermoelectron emitting metal cathode for an electron beam device having a dendrite structure having a particle diameter of 0.5 to 5 micrometers as an alloy containing 0.1 to 5 parts by weight of alkaline earth metal and 95 to 99.9 parts by weight of a group VIIIB, based on the total content of the metal cathode. The metal negative electrode according to claim 1, wherein the alkaline earth metal is barium. The metal negative electrode according to claim 1, wherein the group VIIIB element is platinum or palladium. The metal negative electrode of claim 1, further comprising at least one transition metal selected from the group consisting of aluminum, copper, iron, molybdenum, tungsten, niobium, hafnium, rhenium, platinum groups or rare earth metals. A heat radiation type negative electrode structure comprising the metal cathode of any one of claims 1 to 4.