KR20020063394A - 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 characteristics of electron emission and enlarge a lifetime of a metallic cathode by forming an osmium coating layer or an osmium-ruthenium alloy coating layer on a cathode including barium, one of tungsten and rhenium, and platinum. CONSTITUTION: A metallic cathode(13) is formed by depositing an osmium coating layer or an osmium-ruthenium alloy coating layer(12) on an alloy(11) including barium-tungsten or rhenium-platinum. The metallic cathode(13) is fixed on an upper portion of a sleeve(15) including a heater(14) by using a welding method. The ruthenium of the osmium-ruthenium alloy coating layer(12) is less than 50 weight percent. The osmium coating layer or the osmium-ruthenium alloy coating layer(12) has thickness of 100 to 10000 angstrom.

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, a heat electron emission metal cathode having an excellent electron emission capability and an improved lifetime, which can be used in an electron beam apparatus such as a television CRT and an imaging tube, and a heat radiation type including 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 significantly increases the cost of producing the negative electrode and makes it difficult to significantly improve the lifetime of the negative electrode.

Accordingly, the technical problem to be achieved by the present invention is to provide a hot electron emitting metal cathode of an electron beam device having an excellent electron emission capability and an improved lifetime in order 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.

2 is a graph showing a change in current density according to the ruthenium content change of the metal anode prepared according to the present invention.

In order to achieve the above technical problem, the present invention provides a coating layer formed of an osmium or osmium-ruthenium alloy on a cathode composed of 0.5 to 10.0 wt% of barium, 0.5 to 15.0 wt% of at least one metal of tungsten and rhenium, and a balance of platinum. A hot electron emitting metal cathode for an electron beam device is provided.

In the metal cathode according to the present invention, the osmium-ruthenium alloy preferably has a ruthenium content of 50% by weight or less.

In the metal cathode according to the present invention, the thickness of the osmium or osmium-ruthenium alloy coating layer is preferably 100 kPa to 10000 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 prepared by adding a predetermined amount of tungsten and / or rhenium to an alloy of platinum-barium to prepare a negative electrode material, and coating an alloy of an osmium monomaterial or an osmium-ruthenium layer on top of the negative electrode material. It is characterized by lowering the function.

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 cathode is shortened due to the lack of the active barium metal. If the content of the barium metal is more than 10.0% by weight, a compound such as Pt ₂ Ba having low electron emission characteristics is formed on the surface of the cathode. have.

The alloy for the negative electrode of the present invention comprises 0.5 to 15.0% by weight of tungsten and / or rhenium. The content of tungsten and / or rhenium 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, making it difficult to operate the cathode at a high temperature and the content is 15.0%. If it exceeds%, there is a problem that the electron-emitting ability and plasticity of the negative electrode is lowered.

The metal cathode of the present invention is characterized by forming a coating layer made of osmium or osmium-ruthenium alloy on the cathode made of barium-tungsten and / or rhenium-platinum. The osmium or osmium-ruthenium alloy layer coated on the cathode serves to reduce the work function of the cathode. It is preferable that such an osmium-ruthenium alloy has a ruthenium content of 50% by weight or less, more preferably about 25% by weight.

In addition, the thickness of the osmium or osmium-ruthenium alloy layer is preferably 100 kPa to 10000 kPa, more preferably 300 kPa to 5000 kPa. 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 which concerns on this invention is demonstrated in detail, for example.

First, Pt, Ba and tungsten and / or rhenium 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 rhenium 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 produce an alloy according to the present invention with improved chemical and microstructure uniformity.

Subsequently, the metal cathode according to the present invention is prepared by coating an osmium or osmium-ruthenium alloy on an alloy prepared in an arc by vacuum deposition or the like, and cutting or shaping it to be suitable for the cathode structure of the electron tube, and then attaching it to the cathode structure. do.

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 an osmium or osmium-ruthenium alloy coating layer 12 is formed on an alloy 11 made of barium-tungsten and / or rhenium-platinum has a heater 14. It is preferable to use the hot electron emitting material of the heat dissipating cathode structure by welding the upper portion of the built-in sleeve 15.

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to the following examples.

<Example 1>

First, 178 g Pt, 16 g Ba and 6 g tungsten in powder 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 tungsten 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 including 89 wt% Pt, 8 wt% Ba, and 3 wt% tungsten was prepared.

The negative electrode according to the present invention was formed by forming an osmium-ruthenium alloy coating layer having a thickness of 3000Å and a ruthenium content of 25% by weight using a vacuum deposition method on the obtained ternary alloy, and then performing heat treatment at about 1,000 ° C. under hydrogen or nitrogen atmosphere. Was prepared.

Subsequently, the prepared negative electrode was cut and welded to the upper portion of the heat dissipating negative electrode structure shown in FIG. 1, and then the change in current density was measured. The measurement results are shown in the graph of FIG. 2.

<Example 2>

A negative electrode was prepared in the same manner as in Example 1 except that an osmium-ruthenium alloy coating layer having a ruthenium content of 10% by weight was formed.

Subsequently, the prepared negative electrode was cut and welded to the upper portion of the heat dissipating negative electrode structure shown in FIG. 1, and then the change in current density was measured. The measurement results are shown in the graph of FIG. 2.

<Example 3>

A negative electrode was prepared in the same manner as in Example 1 except that an osmium-ruthenium alloy coating layer having a ruthenium content of 40 wt% was formed.

Subsequently, the prepared negative electrode was cut and welded to the upper portion of the heat dissipating negative electrode structure shown in FIG. 1, and then the change in current density was measured. The measurement results are shown in the graph of FIG. 2.

Comparative Example 1

A negative electrode made of a ternary alloy was prepared in the same manner as in Example 1 except that the osmium-ruthenium alloy coating layer was not formed.

Subsequently, the prepared negative electrode was cut and welded to the upper portion of the heat dissipating negative electrode structure shown in FIG. 1, and then the change in current density was measured. The measurement results are shown in the graph of FIG. 2.

Referring to the graph of Figure 2, it can be seen that the metal cathode according to the present invention has a high current density compared to the conventional metal cathode that does not form an osmium-ruthenium alloy coating layer has excellent electron emission characteristics.

The metal cathode according to the present invention can lower the work function to lower the operating temperature, increase the electron emission ability, and has a long life, and thus is useful as a cathode material of the electron beam apparatus.

Claims (4)

Barium 0.5-10.0% by weight, at least one metal of tungsten and rhenium 0.5-15.0% by weight and the remaining amount of platinum on the cathode consisting of a coating layer made of osmium or osmium-ruthenium alloy is hot electron emission metal for electron beam device cathode. The hot electron emission metal cathode for an electron beam device according to claim 1, wherein the osmium-ruthenium alloy has a ruthenium content of 50 wt% or less. The hot electron emission metal cathode for an electron beam apparatus according to claim 1, wherein the osmium or osmium-ruthenium alloy coating layer has a thickness of 100 kPa to 10000 kPa. A heat dissipating negative electrode structure comprising the metal negative electrode of any one of claims 1 to 3.