KR970009775B1 - Manufacture of impregnated type cathode - Google Patents

Abstract

A method of a cathode which is used for a cathode ray tube is disclosed. The method comprises the steps of: heating a composite of tungsten W and In2O3 to form a pellet; forming a cathode base by combining the pellet with a melted composite of BAO, CaO, and Al2O3; and coating the cathode base with an element such as Os, Ru, Ir, Re or like.

Description

Manufacturing method of impregnated cathode

1 is an impregnated cathode structure.

2 is a manufacturing process diagram of the present invention.

3 is a graph showing the evaporation effect of Ba.

4 is a graph showing the saturation current density.

* Explanation of symbols for main parts of the drawings

1: Cathode itself 2: Cathode cup

3: cathode sleeve 6: coating layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impregnated cathode, and more particularly, to a method of manufacturing an impregnated cathode suitable for electron emission characteristics of an impregnated cathode used in an electron tube such as a CRT, in low temperature operation, and to increase its service life under high current density.

Impregnated cathodes have been used in oscilloscopes, imaging tubes, space transmitters, etc. that require high current densities, but the need for impregnated cathodes, which are cathodes for high current densities, has increased due to the trend toward larger and higher resolution CRTs used in monitors and TVs. 1 shows a structure of a general impregnated cathode, and barium ceramics (BaO, CaO, Al ₂ O), which are electromagnetic radiation materials in a sintered compact, which is a porous pellet prepared by compressing and sintering a heat resistant material such as tungsten (W). to ₃ the molar ratio of 4: 1: 1 or 5: 3: 2 mixture) is also melted in a vacuum or hydrogen atmosphere at about 1600 ℃ such as a needle-like cathode gas (1), tantalum (Ta) or molybdenum (Mo) It is inserted into the inside of the negative electrode cup (2), which is a heat-resistant metal, and laser welded the side.

In addition, a cylindrical negative electrode sleeve 3 made of a heat-resistant metal (metal such as Ta or Mo) is attached and fixed to the outer surface of the negative electrode cup 2, and the negative electrode sleeve 3 is made of a heat-resistant metal (Ta or Mo). Using three straps for the cathode holder 4, one end of the strap is welded to the bottom of the cathode sleeve 3 and the other end of the strap to the top of the cathode holder 4.

A cathode heating heater 5 is inserted into the cathode sleeve 3, and rare earths such as osmium (Os), ruthenium (Ru), iridium (Ir), and rhenium (Re), which are platinum group elements, are inserted on the cathode gas (1). The coating layer 6 made of metal is formed by the sputtering method.

In such a structure, when a current is applied to the heater 5, heat generated in the heater is conducted to the cathode gas 3 after the cathode sleeve 3 and the cathode cup 2, thereby melting inside the porous pellet of the anode gas 1. The mixed oxide, which is an impregnated electron radiating material, reacts with W, which is the main component of the negative electrode gas 1, to form Ba / BaO. The generated Ba / BaO diffuses over the negative electrode gas to form a monoatomic layer on the upper part of the negative electrode gas. Contributes to radiation.

While the impregnated cathode of the cathode gas structure made of such mixed oxide has high electron emission capability, the operating temperature is high at 1050∼1200 ℃, and there are problems such as evaporation of Ba, an electron-emitting material, or a heating heater that cannot withstand long time use. The surface of the cathode gas (1) is coated with a platinum group element such as Os, Ru, Ir, Re, or a rare earth element such as rhenium (Re), and the concentration of Ba is increased on the surface of the cathode gas by the coating effect. The work function is lowered and the operating temperature is lowered by about 100 ~ 150 ℃.

However, the operating temperature is still high at 950-1100 ° C., which causes thermal deformation due to high heat in the electrode parts of the electron gun and the negative electrode housing, thus adversely affecting the characteristics.

In addition, in order to operate at a high temperature, the capacity of the heater must be increased, which has been a problem such as shortening the lifetime of the heater or being unable to guarantee reliability.

The present invention has been made to solve the problems of the conventional impregnated cathode, the operating temperature of the cathode is capable of low temperature operation of 850 ~ 950 ℃ and low temperature operation under high current density and has a long life and excellent reliability It is an object to provide a needle-shaped cathode.

In order to achieve the above object, the present invention provides an impregnated cathode prepared by melting and impregnating an electron-emitting material such as barium, calcium, aluminate into a porous pellet, and mixing In ₂ O ₃ with tungsten powder when preparing an impregnated cathode gas. Obtaining a pellet having a porous body by heating the same in a hydrogen atmosphere and a vacuum atmosphere; and obtaining a cathode gas by melting and impregnating BaO, CaO, and Al ₂ O ₃ into the pellet pores, and a platinum group on the cathode gas. The impregnated cathode is obtained by coating the element or the rare earth element.

In this configuration, the size of tungsten powder is suitably about 3 to 8 μm, and BaO: CaO: Al ₂ O ₃ impregnated in the pellet pores is mixed in a molar ratio of 4: 1: 1 or 5: 3: 2. It was done.

2 is a manufacturing process diagram of the present invention will be described in detail accordingly.

First, when preparing a porous tungsten anode gas, 1 to 5 μm by weight of In ₂ O ₃ powder is uniformly mixed with tungsten (W) powder having a particle diameter of ₃ to ₈ μm, followed by extrusion molding and pre-sintering in a reducing (hydrogen) atmosphere. Final sintering in vacuum produces a porous pellet having a porosity of 20-30%.

BaCO ₃ , CaCO ₃ , and Al ₂ O ₃ , which are electron-emitting materials, are finally oriented at a molar ratio of BaO: CaO: Al ₂ O ₃ = 4: 1: 1, and then mixed so that carbonates are evenly mixed with each other. The barium ceramics are prepared by heat treatment at 占 폚.

The pulverized and mixed barium ceramic powder is then placed on top of the prepared porous tungsten pellets and melt impregnated at 1600 ° C. in vacuum.

In this way, the coating layer 6 is formed by coating iridium (Ir), osmium (Os), ruthenium (Ru), or the like on the impregnated cathode gas by sputtering.

Insert and weld the negative electrode gas produced as described above to the negative electrode cup 2 made of Mo or Ta as shown in FIG. 1, fix the negative electrode cup to the negative electrode sleeve 3 by laser welding, and heat the negative electrode inside the negative electrode sleeve. Insert the heater 5 to complete the impregnated cathode. In the impregnated cathode as described above, barium, calcium, aluminate and tungsten (W) in the cathode gas react with each other by heating of the heater, and W is combined with oxygen of barium oxide to form free Ba atoms.

The glass Ba diffuses to the surface through the pore wall of the porous metal gas composed of W and In, and at this surface, the barium (Ba), indium (In) and oxygen (O) combine to form a single molecule of Ba-In-O. The monomolecular layer emits hot electrons even at low temperatures because it serves to lower the work function.

Indium oxide (In ₂ O ₃ ) is a volatile material at about 850 ° C. The temperature when barium, calcium, aluminate and tungsten react to produce free Ba / BaO, which contributes to electron emission during the activation process of the cathode. In other words, it reduces the activation temperature and at the same time O ₃ itself is a good reactive material at high temperature, and thus acts as an activation accelerator to shorten the activation time.

Therefore, the dispenser cathode according to the present invention has an activation temperature lowered by about 100 to 200 ° C. and an activation time of about 1 hour.

However, the amount of the amount of dispersion of the In ₂ O ₃ dispersed In ₂ O when 1% by weight, less than ₃ too small to In ₂ O ₃ without the effect of the added dispersion, In ₂ O ₃ dispersion amount is formed on the electron emission surface, if 5% or more by weight Excessive oxygen (O) molecules are bonded to the monomolecular layer, that is, Ba-Ib-O, thereby reducing the dipole effect of the monomolecular layer, thereby suppressing electron emission, which is undesirable.

As described above, the In-based impregnated cathode has a higher Ba (or BaO) density on the surface than the conventional impregnated cathode, and a monolayer of Ba-In-O is formed on the surface of the composite porous metal gas. Since the electric dipole moment is large, the Ba evaporation ratio is low and the density with the electric dipole is high, as shown in Figs. 3 and 4, the work function can be made low, and it is formed on the composite porous metal substrate made of Ir Os / Ru. The thin film layer increases the surface residence time of Ba (or BaO) on the surface of the composite porous metal substrate.

In other words, the increase in the residence time of Ba (or BaO) by a thin film layer such as Ir or Os / Ru increases the electric dipole density of Ba-In-O, thereby lowering the work function.

Claims (3)

Mixing tungsten (W) powder with indium oxide (In ₂ O ₃ ) and heating it in a reducing atmosphere and vacuum atmosphere to obtain pellets having pores, and BaO, CaO, Al ₂ O ₃ in the pellet pores. A method of manufacturing an impregnated cathode, comprising melting and impregnating to obtain a cathode gas (1) and coating a platinum group element or a rare earth element on the cathode gas (1). The method of claim 1, wherein the indium oxide (In ₂ O ₃ ) is 1 to 5% by weight. The method of claim 1, wherein BaO, CaO, Al ₂ O ₃ is mixed at a molar ratio of 4: 1: 1 or 5: 3: 2.