JPS5826768B2 - Manufacturing method of impregnated cathode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an impregnated cathode, and particularly to a method for manufacturing an impregnated cathode that is most suitable for use in small cathodes such as CRT cathodes.

Conventionally, the manufacturing method of an impregnated cathode requires a sintered body that is much larger than the required amount of the cathode shape (for example, 20 x 20 x 500 m7).
M) is melted and impregnated with copper or plastic to facilitate machining, machined into a predetermined cathode shape, and then the copper or plastic is removed by heating or dissolving with acid in a vacuum. It was manufactured by melting and impregnating a processed body of -t with an electron radioactive substance.

This is because, when υ company's high melting point metal powder is directly sintered into the cathode shape, the sintering at the edges is not uniform, and the shrinkage rate varies depending on the location, resulting in dimensional deformation.

This conventional manufacturing method is shown in FIG.

First, in step 1, a high melting point metal powder with an appropriate particle size distribution is prepared.

Next, in step 2, the metal powder prepared in step 1 is molded into an appropriate shape by a method such as mechanical pressing, isostatic pressing, or casting.

After molding in step 2, sintering is performed in step 3 by direct current application, in a furnace, hot press, or the like.

After the molded body is sintered, the sintered body is then immersed in molten copper in step 4 to impregnate the pores of the porous body with copper.

Once impregnated with copper, in step 5 it is processed into a predetermined cathode shape by ordinary machining such as a lathe.

After processing into a predetermined cathode shape, in step 6, in order to facilitate machining, the copper impregnated in step 4 is removed by heating in a vacuum, so-called decopper removal.

In addition to heating in a vacuum, there are other methods for removing copper, but since the copper cannot be completely removed, it is common to remove the copper by heating in a vacuum afterwards.

Once the copper has been removed, the amount of micropores in the sintered body is measured in step 7 to determine whether the sintered body is good or bad.

Next, in step 8, a mixture of oxides mainly containing barium oxide or a mixture containing carbonate, which is a raw material thereof, is applied to the decoppered sintered body, and melted in a reducing atmosphere or vacuum to form a sintered body. Impregnate the micropores with an electron radioactive substance.

After the impregnation with the electron radioactive material is completed, in step 9, excess electron radioactive material adhering to the surface of the sintered body is removed.

Conventionally, an impregnated cathode has been manufactured through the above steps.

However, this manufacturing method involves a large number of steps and involves machining, resulting in a large amount of wasted material and a very low material yield.

In addition, conventional manufacturing methods waste expensive oxygen-free copper, are not suitable for mass production, are not sufficiently sintered at the edges, and have different porosity depending on the location, resulting in wasted material.

For example, if the electric sintering method is used, approximately 176 mm of each end portion cannot be used, and the porosity of the center portion is also reduced.

Therefore, the cathode becomes expensive, and an impregnated cathode that can obtain a high current density cannot be used for a CRT cathode that requires an inexpensive cathode, such as a cathode for a television's cathode ray tube. This prevents the development of separated images on the screen, and even Currently, there are restrictions on the transmission of images.

An object of the present invention is to provide a method for manufacturing an impregnated cathode that eliminates the above-mentioned drawbacks and can be mass-produced at low cost.

The present invention will be explained below based on illustrated embodiments.

FIG. 2 shows the steps of the method for manufacturing an impregnated cathode according to the present invention.

In step A, a high melting point metal powder having a particle size of 10 μm or less, an average particle size of 4 to 7 μm, and a particle size distribution in which particles of 2 μm or less are 3% or less by weight is prepared.

This is because if the particle size is larger than the above or there are many small particles, sintering will not be done uniformly, and the desired porosity may not be obtained due to insufficient or excessive porosity, and may also cause deformation. It is from.

To explain in more detail, particles with small diameters are easily sintered, and if the relationship between temperature and time is not very strictly controlled, sintering will proceed too much, resulting in problems such as uneven porosity, and vice versa. If the particle size is too large, it will be difficult to sinter and the humidity will have to be raised more than necessary.In addition, it will be difficult to raise the temperature very high, and it will be difficult to maintain the sintering furnace. This also has the drawback that the porosity is not constant.

When these fine particles and large particles are mixed, the temperature
Needless to say, no matter how the time conditions are controlled, the sintering conditions for fine particles and large particles are different and it is impossible to obtain a uniform sintered body.

For example, tungsten powder with an average particle size of 2μ and an average particle size of 6μ
Figure 3 shows the variation in porosity as a result of sintering under conditions such that the porosity was 25% with the tungsten powder.

In this case, tungsten powder with a small particle size is easier to sinter than one with a large particle size, and if the tungsten powder is sintered too much, the porosity decreases, so we changed the sintering conditions. The particles were sintered at a lower sintering temperature than those for larger particles, and under approximately the same sintering time.

The figure a shows the average particle size of 2μ, and the figure shows the mean particle size of 6μ.
As is clear from the figure, those with an average particle size of 2μ have a greater variation in porosity than those with an average particle size of 6μ.

Therefore, it is necessary to select particles that are almost uniform, and to obtain a sintered body with relatively gentle sintering conditions and a constant porosity, we experimentally determined the particle size range. This is the above numerical range.

After the preparation of the high melting point metal powder in step A, step B
0.5 to 2.0 by mechanical press, hydrostatic pressure, etc. O1
After sintering, taking into account shrinkage during sintering at a pressure of /crri, it is shaped into the shape of the cathode.

Further, by using a large number of molds such as molds, a large number of molds can be molded at the same time, and mass production is possible.

Once molded in step B, sintering is then performed in step C.

Sintering is performed on the shaped material at 2000°C to 2600°C in a reducing atmosphere or in a vacuum.

According to this sintering method carried out at 2000°C to 2600°C, a desired porosity can be obtained by selecting the particle size distribution of the raw material powder.

After obtaining a sintered body with the desired porosity in step C, in the next step, an electron-radioactive substance made of an oxide mixed powder mainly containing barium oxide or a carbonate mixture as its raw material is added to the sintered body. It is melted and impregnated in a reducing atmosphere or in a vacuum.

Next, in step E, excess electron radioactive material on the surface of the sintered body is removed.

Therefore, according to this embodiment.

In the sintering process, in the conventional sintering method using an electric current method,
Although the temperature can be raised sufficiently, the sintering at both ends of the formed material is insufficient, resulting in a low material yield and uneven sintering degree. It is possible to eliminate disadvantages such as low porosity, insufficient sintering, and high porosity.

That is, according to this embodiment, by carefully selecting high melting point metal powder and sintering it in a furnace at an appropriate temperature, the entire compact of high melting point metal powder can be sufficiently sintered.

In addition, the material yield was high and the degree of sintering was uniform.

Furthermore, it is possible to obtain a porosity in the range of 20% to 30%, which is optimal for use as an impregnated cathode.

Furthermore, according to this embodiment, the copper impregnation process, machining process, porosity measurement process, and copper removal process of the conventional manufacturing method can be omitted, and mass production is possible. Never waste it.

As explained above, according to the present invention, the number of steps is significantly reduced, mass production is possible, there is no wastage of raw materials, and the material yield is significantly improved, so it can be manufactured at low cost and the quality is stable. do.

Therefore, it can be used for cathodes for CRTs such as cathodes for cathode ray tubes in televisions, which require inexpensive cathodes, and can provide high resolution for televisions, etc., making it possible to achieve clearer colors, improved image quality, and larger screens. , its application fields are extremely wide.

[Brief explanation of drawings]

Figure 1 is a flowchart of the conventional manufacturing method, Figure 2 is a process flowchart of an example according to the present invention, and Figure 3 is the result of sintering with conditions set so that the porosity is 25%. FIG. 3 is a diagram showing variations in porosity. A... Metal powder preparation process, B... Molding process, C.
...Sintering process, D...Electron radioactive substance impregnation process, E
...Removal process of surplus electron radioactive materials.

Claims (1)

[Claims] 1. In a method for producing an impregnated cathode in which a porous body of a high melting point metal such as tungsten or molybdenum is melted and impregnated with an electron radioactive substance, the particle size is 10 μm or less and the average particle size is 4 to 7 μm;
and a step of preparing a high melting point metal powder containing 3% by weight or less of particles with a particle size of 2μ or less;
A step of molding into a desired cathode shape at a pressure of t/cvz, and a step of molding the molded material in a reducing atmosphere or vacuum for 2000
A method for producing an impregnated cathode, comprising the steps of firing at a temperature of .degree. C. to 2,600.degree. C., and directly melting and impregnating the sintered body formed in the step with an electron emissive material.