KR20020031590A - Metal cathode and indirectly heated cathode assembly having the same - Google Patents

Abstract

PURPOSE: A metal cathode and cathode structure having metal cathode is provided to easily manufacture small sized emitters, while improving electron emission capability and mechanical characteristics. CONSTITUTION: A metal cathode(13) comprises a cathode composed of a barium 0.5 to 10 weight percent, one or more from a tungsten and molybdenum 0.5 to 15.0 weight percent, and platinum; and a coating layer(12) formed of an iridium. The coating layer has a thickness of 1000 to 2000 angstrom. The iridium layer coated onto the cathode serves to decrease the work function of the cathode, without deteriorating the electron emission capability.

Description

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

The present invention relates to a metal cathode of an electron beam device, and more particularly, can be used in an electron beam device such as a television cathode ray tube, an imaging tube, etc., and has a hot electron emission metal cathode having excellent electron emission capability and improved life and mechanical properties, and the same. One heat dissipation type cathode structure.

A conventional alkali metal carbonate layer having a 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 without the disadvantages of the above-described oxide cathodes to cathode ray devices.

For example, a metal cathode based on lanthanum hexaboride (LaB ₆ ) is known to have a higher strength and higher electron emission ability than an oxide cathode. A single crystal cathode of hexaboride has a high current density of about 10 A / cm 2. Can emit. However, lanthanum hexaboride cathodes have been used only in some vacuum electronic devices that can be replaced by 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 significantly increases the cost of producing the negative electrode and makes it difficult to significantly improve the lifetime of the negative electrode.

Therefore, the technical problem to be achieved by the present invention is to provide a hot electron emitting metal cathode of an electron beam device not only excellent in the electron emitting ability, but also improved life and mechanical properties to solve the above problems.

Another technical problem to be achieved by 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.

<Description of Major Symbols in Drawing>

11 alloy layer 12 iridium coating layer

13 Metal cathode 14 Heater

15 ... sleeve

In order to achieve the above technical problem, the present invention provides an electron beam, wherein a coating layer made of iridium is formed on a cathode made of 0.5 to 10% by weight of barium, 0.5 to 15.0% by weight of one or more metals of tungsten and molybdenum, and the remaining amount of platinum. Provided is a hot electron emitting metal cathode for a device.

In the metal cathode of the present invention, the thickness of the iridium coating layer is preferably 1000 kPa to 20000 kPa.

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

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

The negative electrode of the present invention is characterized by lowering the work function of the negative electrode by preparing a negative electrode material by adding a predetermined amount of tungsten and / or molybdenum to an alloy made of platinum-barium, and coating iridium on the negative electrode material.

The metal cathode of the present invention contains 0.5 to 10.0% by weight of barium. If the content of the barium metal is less than 0.5% by weight, the lifetime of the negative electrode is shortened due to the lack of the active barium metal. If the content of the barium metal exceeds 10.0% by weight, a compound such as Pt ₂ Ba having low electron emission characteristics is formed on the surface of the negative electrode. There is this.

The anode alloy of the present invention comprises 0.5 to 15.0 wt% of tungsten and / or molybdenum. The content of tungsten and / or molybdenum is selected as long as the plasticity and electron-emitting ability of the alloy are not lowered. If the content is less than 0.5% by weight, the melting point of the alloy is lowered, so that the high temperature operation of the cathode is difficult and the content is 15.0. If the weight percentage is exceeded, there is a problem in that the electron-emitting ability and plasticity of the negative electrode are lowered.

In the metal cathode of the present invention, a coating layer made of iridium is formed on the cathode made of platinum-barium-tungsten and / or platinum-barium-molybdenum. The iridium layer coated on the negative electrode serves to reduce the work function of the negative electrode. It is preferable that the thickness of such iridium is 1000 kPa to 20000 kPa, and within this range, the work function of the cathode can be effectively reduced without lowering the electron-emitting ability.

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

First, Pt, Ba and tungsten and / or molybdenum are placed in an arc furnace. Since Pt and Ba have a large melting point difference, it is preferable to use an arc furnace that can melt the metal instantaneously. Since Ba is easy to evaporate, 10 to 15% of the content of the final alloy is added to control the content of Ba. do. Subsequently, the inside of the arc furnace is kept in a vacuum state and then an inert gas such as Ar gas is injected. A voltage is then applied to the arc furnace to melt Pt, Ba and tungsten and / or molybdenum in a short time. Since Pt and Ba have a large density difference, it is difficult to obtain a uniform alloy composed of these metals. Therefore, by repeatedly performing the melting process and the solidification process, it is possible to manufacture the alloy according to the present invention with improved chemical and microstructure uniformity.

Subsequently, a metal cathode according to the present invention is prepared by coating iridium on an alloy prepared in an arc using a vacuum deposition method or the like, and 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 13 of the present invention in which the iridium coating layer 12 is formed on an alloy 11 made of platinum-barium-tungsten and / or platinum-barium-molybdenum has a heater 14 embedded therein. It is preferable to use the hot electron emitting material of the heat radiation type cathode structure by welding the upper portion of the sleeve 15.

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

<Example 1>

First, 3.64 g Pt, 0.32 g Ba and 0.44 g molybdenum in powder or ingot form are placed in an arc furnace. Subsequently, Ar gas was injected after the inside of the arc furnace was kept in a vacuum state. Then, a voltage was applied to the arc furnace to melt the Pt, Ba and molybdenum metals, and to alloy the three metals well. The ingot thus obtained was repeated three times to melt the chemical and microstructure uniformity of the alloy. Finally, a ternary alloy consisting of 82.8 wt% Pt, 7.2 wt% Ba, and 10 wt% molybdenum was prepared.

Thus, the negative electrode according to the present invention was formed by forming an iridium coating layer having a thickness of 3000 kPa on the ternary alloy obtained by vacuum evaporation. The negative electrode was cut and welded to the upper portion of the heat radiation type negative electrode structure shown in FIG. The measurement results are shown in Table 1.

<Example 2>

Except for using tungsten 0.44g instead of molybdenum, according to the same method as in Example 1 was finally prepared a ternary alloy consisting of 82.8% by weight of Pt, 7.2% by weight of Ba and 10% by weight of tungsten.

Thus, the negative electrode according to the present invention was formed by forming an iridium coating layer having a thickness of 3000 kPa on the ternary alloy obtained by vacuum evaporation. The negative electrode was cut and welded to the upper portion of the heat radiation type negative electrode structure shown in FIG. The measurement results are shown in Table 1.

Comparative Example

3.64 g of Pt and 0.32 g of Ba in powder or ingot form are placed in an arc furnace. Subsequently, Ar gas was injected after the inside of the arc furnace was kept in a vacuum state. Then, a voltage was applied to the arc furnace to melt the Pt and Ba metals and to alloy the two metals well. The ingot was obtained by repeating the melting process three times to improve the chemical and microstructure uniformity of the alloy. Finally, a binary alloy composed of 91.9 wt% Pt and 8.1 wt% Ba was prepared.

The anode was manufactured from the binary alloy thus obtained, and the cathode was cut and welded to the upper portion of the heat radiation type cathode structure shown in FIG. 1, and then the operating temperature was measured. The measurement results are shown in Table 1 below.

Work function (eV) at 1100 ℃ Saturation Current Density at 1100 ℃ (A / ㎠) Example 1 1.7 10 Example 2 1.8 10 Comparative example 2.2 4

Referring to Table 1, the metal cathode according to the present invention having a metal and an iridium coating layer of any one or more of Pt and Ba, tungsten, and molybdenum has a low work function, electron emission characteristics, and the like, compared to a metal cathode composed of only Pt and Ba. It can be seen that it is very excellent.

The metal cathode according to the present invention is not only easy to manufacture a small size emitter having excellent plasticity, but also has a large electron emission ability, and particularly, has a long life, and thus is useful as a cathode material of an electron beam apparatus.

Claims (3)

A thermoelectron emitting metal cathode for an electron beam device, characterized in that a coating layer made of iridium is formed on a cathode made of 0.5 to 10% by weight of barium, 0.5 to 15.0% by weight of one or more metals of tungsten and molybdenum and the remaining amount of platinum. The hot electron emission metal cathode for electron beam device according to claim 1, wherein the iridium coating layer has a thickness of 1000 kPa to 20,000 kPa. A heat radiation type negative electrode structure, comprising the metal cathode of any one of claims 1 to 2.