GB2226573A

GB2226573A - Dispenser cathode

Info

Publication number: GB2226573A
Application number: GB8924407A
Authority: GB
Inventors: Kyung-Cheon Shon
Original assignee: Samsung Electron Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1988-11-19
Filing date: 1989-10-30
Publication date: 1990-07-04
Anticipated expiration: 2009-10-30
Also published as: GB8924407D0; GB2226573B; KR910003699B1; JPH02244536A

Abstract

A manufacturing method for a dispenser cathode is disclosed which comprises a step of immersing, in an aqueous solution containing an aluminum compound, a powder mixture made by mixing metal powder selected from among Mo, Ta and W or powder of alloys of at least two or more metals selected from among the carbonates of Sr, Ba and Ca; or immersing in said solution a pellet formed into a required shape from the former metal powder mixture whereby the aluminum ingredient in said aqueous solution is impregnated into said powder mixture or the pellet. According to the present method, a heat treatment at a temperature of over 1700 DEG C is not required unlike the case of conventional methods, and therefore, the decrease of the electron releasing efficiency due to the adverse reactions generated at the high temperature heat treatment can be avoided.

Description

MANUFACTURING METHOD FOR DISPENSER CATHODE Field of the Invention The present invention relates to a manufacturing method for a dispenser cathode, and particularly to a manufacturing method for a dispenser cathode in which the decrease of the electron releasing efficiency due to a high temperature heat treatment can be restrained.

Background of the Invention The general dispenser cathode as shown in Figure 1 comprises a porous pellet 3 containing barium-calcium aluminate as the cathode material, a cup 2 for storing the pellet 3, and a sleeve 1 for storing a heater 4. Among these components, the pellet 3 which is an important component is manufactured by sintering a high melting point metal powder such as tungsten(W), and has to undergo a high temperature heat treatment because the material itself is a high melting point heat resistant metal. There are many different methods for manufacturing the pellet, and one of them is carried out in such a manner that a mixture of BaCO3 , CaC03 , and A12 CO3 as the cathode material, or barium-calcium aluminate obtained by baking the above.

mixture is impregnated into a porous pellet made of a heat resistant metal such as tungsten. Another method is carried out such that a mixture prepared by mixing a heat resistant metal powder such as tungsten, molybdenum, or tantalum with a cathode material in a proper ratio is fabricated through compression into the required shape, and is sintered.(Refer to U.S.Pat. No. 4,737,679; 4,400,648) In such conventional methods, a baking process has to be carried out at a temperature of over 1700C , but according to these methods, the electron releasing efficiency is greatly lowered due to the adverse reaCtion generated by the high temperature treatment.The reason is that Al2 03 , e.g., alumina which is very high in its own melting point and the reaction temperature related to other materials is used as the cathode material, and as long as A12 03 is used as the cathode material, the high temperature baking process causing the thermal adverse effect can not be excluded.

Summarv of the Invention Therefore, it is the object of the present invention to provide a manufacturing method for a dispenser cathode in which the decrease of the electron releasing efficiency in the cathode material accruable due to a high temperature heat treatment can be restrained.

To accomplish the above object, the manufacturing method for a dispenser cathode according to the present invention comprises: a step of immersing, in a aqueous solution containing an aluminum compound, powder mixture made by mixing metal powder selected from among Mo, Ta and W or powder of alloys of at least two or more metal selected from among the carbonates of Sr, Ba and Ca; or immersing in said solution the pellet formed into required shape with the former metal powder mixture so as for the aluminum ingredient in said aqueous solution to be impregnated into said powder mixture or the pellet.

Brief DescriDtion of the Drawings The above object and other advantages of the present invention will become more apparent by describing the preferred embodiment of the present invention with reference to the attached drawing in which: Figure 1 is a sectional view of the general dispenser cathode.

Description of the Dreferred embodiments Examole 1 NaCO 3 is dissolved in a solution containing a mixture of SrNO3 , BaNO3 and CaNO3 so tht Sr, Ba and Ca are let to be commonly deposited in the form of carbonates. Then the deposited carbonates are recovered and dried to mix them with the metal powders of Mo, Ta and W, and the above mixture is press-formed into a pellet having the required shape. Meanwhile, an aluminum compound is dissolved in a proper medium, and the pellet is immersed in the solution to conduct a impregnation. Thereafter, the pellet is baked at a temperature of 1200 - 130or to remove CO2 , thereby completing the manufacturing of the pellet.

ExamDle 2 NaCo3 is dissolved in a solution containing SrNO3 BaNO 3 and CaNO, so tht Sr, Ba and Ca are let to be commonly deposited in the form of carbonates through chemical reactions. Then the deposited carbonates are recovered and dried, and then the dried carbonates are mixed with the metal powders of Mo, Ta and W. And the mixture is press-formed into a pellet having the required shape.

Thereafter, the pellet is baked at a temperature of 1200 13000C to remove C0z , the pellet is immersed into an aqueous solution containing an dissolved aluminum compound to conduct a impregnation, and the pellet is taken out and dried. As the following process, the pellet is subjected to a reduction treatment under a hydrogen atmosphere at a temperature of slightly over 1200 - 1300C -in order to remove the residue oxygen atoms.

Example 3 NaNO 3 is dissolved in a solution containing SrNO, BaND3 and CaNO3 so that Sr, Ba and Ca are let to be commonly deposited in the form of carbonates through chemical reactions, then the deposited carbonates are recovered and dried, the dried carbonates are mixed with the metal powders of Mo, Ta and W, the resultant mixture is put into an aqueous solution containing an aluminum compound in order to impregnate the mixture, and the impregnated mixture is recovered and dried. The dried mixture is put into a pellet having the required shape, and the fabricated pellet is subjected to baking and reducing processes, thereby completing the manufacturing of the pellet.

The pellet 3 manufactured based on the above described processes is inserted into a cup 2 which is secured at the portion of the leading end of a sleeve 1 as shown in Figure 1, and the pellet 3 is fixea by a resistance welding or a laser welding.

According to the manufacturing method of the present invention as described above, a heat treatment at a temperature of over 1700"C is not required unlike in the case of the conventional methods, but all the required baking and reducing processes can be conducted at a temperature of no more than 1200-1300'C . Accordingly, the decrease of the electron releasing efficiency due to the adverse reactions generated at the high temperature heat treatment can be avoided, thereby improving the electron releasing efficiency, and making it possible to produce a high performance cathode.

Claims

CLAIMS:

1. A manufacturing method for a dispenser cathode comprising a step of immersing, in an aqueous solution containing an aluminium compound, powder mixture made by mixing metal powder selected from among Mo, Ta and W or powder of alloys of at least two or more metals selected from among the carbonates of Sr, Ba and Ca; or immersing in said solution the pellet formed into required shape with the former metal powder mixture so as for the aluminium ingredient in said aqueous solution to be impregnated into said powder mixture or the pellet.

2. A method of manufacturing a porous pellet for a dispenser cathode, comprising making a powder mixture containing a first powder carbonate constituent selected from the carbonates of Sr, Ba and Ca, and a second powder metal constituent selected from Mo, Ta and W, and forming a pellet from the powder mixture, wherein the powder mixture is impregnated with an aqueous solution of an aluminium compound either before or after said formation thereof into said pellet.

3. A method according to claim 2 wherein the mixture is impregnated after formation into said pellet, and said pellet is baked after impregnation to remove C02.

4. A method according to claim 2 wherein the mixture is impregnated after formation into said pellet and after baking of the pellet to remove CO2.

5. A method according tq claim 2 wherein the mixture is impregnated before formation into said pellet.

6. A method of making a porous pellet for a dispenser cathode substantially as hereinbefore described with reference to examples 1, 2 or 3 described herein.

7. A porous pellet for a dispenser cathode, made by a method according to any preceding claim.

8. A dispenser cathode including a porous pellet according to claim 7.

9. A dispenser cathode according to claim 8 and substantially as hereinbefore described with reference to the accompanying Fig. 1.