KR20020034751A - Metal cathode and indirectly heated cathode assembly having the same - Google Patents

Abstract

PURPOSE: A metal cathode and a heat-sink type cathode structure having the same are provided to enhance capacity of electron emission and lengthen a lifetime of the metal cathode by improving a structure of metal cathode. CONSTITUTION: A metal cathode(11) for electron tube is used in a heat-sink type cathode structure. The metal cathode(11) is formed on an upper portion of a sleeve(15) by using a welding method. A heater(13) is mounted in the sleeve(15). The metal cathode(11) is used as a thermion emission material of the heat-sink type cathode structure. The metal cathode(11) is formed with barium of 3 to 20 wt%, one or more high melting point metal of 0.01 to 20 wt% selected from a group including niobium, osmium, molybdenum, tantalum, tungsten, and rhenium, and platinum of the remaining wt%.

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 device, and more particularly, to a heat electron emission metal cathode for an electron beam device having a high electron emission capability and an improved lifetime, which can be used for an electron beam device such as a television CRT and an imaging tube, and a heat dissipating cathode having the same. It is about a 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.

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 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. .

U.S. Patent 4137476 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 an electron beam device hot electron emission metal cathode which can be used for electron beam devices such as large tube and high-definition electron tube to have a large electron emission ability and a long life 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 cathode structure having a metal cathode according to the present invention,

2 is a graph showing the electron emission capability of the alloy according to an embodiment of the present invention.

In order to achieve the above technical problem, the present invention includes 3 to 20% by weight of barium, 0.01 to 20% by weight of one or more high melting point metals selected from the group consisting of niobium, osmium, molybdenum, tantalum, tungsten and rhenium, and the balance of platinum. Provided is a hot electron emission metal cathode for an electron beam device.

The metal anode of the present invention may further include any one or more rare earth metals selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, and samarium.

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.

Platinum group elements such as Pt, Pd, and Ir and alloy emitters of Ba have been used as cathodes of magnetron, traveling wave tube (TWT), backward wave tube (BWT), etc. Was used as the secondary electron emission cathode, which impinged on the material and released 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.

In the present invention, the former is made of an alloy comprising from 3 to 20% by weight of barium, 0.01 to 20% by weight of at least one high melting point metal selected from the group consisting of niobium, osmium, molybdenum, tantalum, tungsten and rhenium and the balance of platinum It is characterized by the use of a metal cathode as a hot electron emitter for electron tubes with a large emitting capacity, uniformity, and improved lifetime.

The hot electron emission cathode made of a binary alloy composed of platinum and barium has better electron emission characteristics than the conventional oxide cathode. However, since the operating temperature of the metal cathode is relatively high, the crystal growth of the emitter is excessive, resulting in a limitation in the lifetime characteristics. It becomes visible.

Therefore, in the present invention, the content of platinum and barium is adjusted to be suitable for the thermoelectron emitting cathode of an electron beam device such as an electron tube, and at the same time, the electron emission characteristics are improved by adding a high melting point metal which can prevent crystal growth of these binary alloys. It was intended to make it uniform and to increase the lifetime of the cathode.

In the metal negative electrode of the present invention, if the content of Ba is less than 3% by weight, the lifetime characteristics of the negative electrode are lowered, and if it exceeds 20% by weight, there is a problem that slump and the like occur.

In the metal cathode of the present invention, niobium, osmium, molybdenum, tantalum, tungsten, rhenium, etc. may be added as the high melting point metal to be added. If the content of the high melting point metal is less than 0.05% by weight, the effect of improving the life characteristics of the negative electrode is insignificant, and if it exceeds 20% by weight, the main phase is changed in the crystal structure of the metal, there is a problem that the initial characteristics are reduced. More preferred content of the high melting point metal is 0.5 to 20% by weight.

One or more rare earth metals selected from the group consisting of lanthanum, cerium, praseodymium, neodymium and samarium may be further added to the metal anode according to the present invention.

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

First, Pt, Ba and high melting point metals 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. Then, a voltage is applied to the arc furnace to melt Pt, Ba and the high melting point metal in a short time. At this time, stir well with a metal rod such as tungsten to ensure good alloying of the three metals. 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 ternary alloy prepared in the arc furnace is cut or molded to suit 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 having the heater 13 embedded therein and used as a heat 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>

First, 10 g of powder Pt, 1.0 g of Ba and 1 g of molybdenum 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 Mo metals. Thus obtained ingot was repeated three times the melting process to prepare a ternary alloy to improve the chemical and microstructure uniformity of the alloy.

Example 2

A ternary alloy was prepared in the same manner as in Example 1 except that 10 g of powder Pt, 1.3 g of Ba, and 0.3 g of tungsten were placed in an arc furnace.

Example 3

A quaternary alloy was prepared in the same manner as in Example 1 except that 10 g of powder Pt, 1.0 g of Ba, 0.15 g of molybdenum, and 0.07 g of cerium were placed in an arc furnace.

Subsequently, the three-membered alloy and the four-membered alloy prepared according to the embodiment were cut and welded to the upper portion of the heat radiation type negative electrode structure shown in FIG. 1, and then the electron emission capability of the negative electrode was measured according to the applied voltage. Indicated.

Referring to Figure 2, it can be seen that the cathode (Examples 1 to 3) of the ternary alloy and the quaternary alloy having the content of the present invention has a very large electron emission ability.

The metal cathode according to the present invention and the heat dissipating cathode structure having the same are operated at a temperature of about 1200 ° C. similar to the impregnated cathode, and thus can be applied without changing the conventional cathode manufacturing process. . In addition, unlike the conventional carbonate cathode, the metal anode of the present invention has good process applicability, and is excellent in stability against external factors such as vacuum degree or gas in the CRT, and thus may be usefully used in large tubes and high-definition electronic tubes.

Claims (3)

3-20 wt% barium, 0.01-20 wt% of one or more high melting point metals selected from the group consisting of niobium, osmium, molybdenum, tantalum, tungsten and rhenium and the balance of platinum for an electron beam device Metal cathode. The hot electron emission metal cathode of claim 1, further comprising any one or more rare earth metals selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, and samarium. A heat radiation type negative electrode structure, comprising the metal cathode of any one of claims 1 to 2.