JPS5826766B2 - Hot cathode and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lanthanum hexaboride hot cathode and a method for producing the same.

Lanthanum hexaboride hot cathodes are attracting attention as an alternative to conventional tungsten hot cathodes.

Lanthanum hexaboride has a smaller work function than tungsten, and when used as a hot cathode, it can be used at low temperatures.
It has characteristics such as high brightness and long life.

However, at high temperatures, lanthanum hexaboride reacts violently with its supporting metals, which are refractory metals such as tungsten wire and tantalum wire, making it difficult to use lanthanum hexaboride as a hot cathode. Various solutions have been proposed.

For example, there is a method of interposing a barrier layer between lanthanum hexaboride and a supporting metal to prevent reaction.

This is achieved by stacking a layer made of lanthanum hexaboride, a barrier layer, and a refractory metal layer in this order, and then bonding them using a hot press method to form a multilayer chip. A supporting metal is bonded to the metal layer to form a lanthanum hexaboride hot cathode.

Since the chips are formed by hot press molding, the operation is complicated, and the yield rate is poor because cracks may occur due to the pressure applied when forming the chips. Since the barrier layer rarely reacts, it has poor bonding properties, and the lanthanum hexaboride portion may separate from the barrier layer and fall off during processing or use of the chip. I couldn't say it.

In addition, hot cathodes using single-crystal lanthanum hexaboride have a longer lifespan and higher brightness than conventional hot cathodes using polycrystalline sintered bodies of lanthanum hexaboride, and also have improved current stability. Because of its excellent atmospheric stability, the use of single crystal lanthanum hexaboride is expected to improve its performance as a hot cathode.

However, there are almost no examples of using single-crystal lanthanum hexaboride for hot cathodes, and there are still problems that need to be solved in the manufacturing and supporting methods of hot cathodes using single-crystal lanthanum hexaboride. left behind.

That is, the present inventors attempted to create the above-mentioned multilayer cathode structure by hot pressing using single crystal lanthanum boride, but the single crystal was small and had many cracks, making it impossible to manufacture a complete chip. There wasn't.

The present invention has solved these problems, and has an IV on the lower side of a lanthanum hexaboride chip, which is a single crystal or a sintered body.
By forming a metal diboride layer of Group A or Group Va by sintering and further forming a refractory metal layer on top of it by sintering, and bonding a support metal made of a refractory metal to the surface, a complicated process is possible. It is simple and has a high yield, and even if the lanthanum hexaboride chip and the barrier layer do not react sufficiently, the barrier layer is wrapped with a refractory metal and sintered, so the entire structure is firmly fixed. An object of the present invention is to provide an excellent lanthanum hexaboride hot cathode in which the lanthanum hexaboride chips do not peel off and fall off from the barrier layer as in the prior art, and a method for manufacturing the same.

That is, the first aspect of the present invention is to form a reaction barrier made of one or more metal diborides selected from group IVa or group Va metal diborides on the bottom surface and lower side surface of a single crystal or sintered lanthanum hexaboride chip. A hexaboride compound formed by forming a layer so as to be wrapped therein, further forming a refractory metal layer so as to wrap thereon, and joining a supporting metal made of a refractory metal onto the refractory metal layer. The second invention is a lanthanum hot cathode, in which a paste of a group IVa or group Va metal diboride is applied so as to cover the bottom and lower side surfaces of a single crystal or washed lanthanum hexaboride chip, and then A paste of a refractory metal is dried in a uniform manner so as to envelop it, and this is sintered and baked in an inert gas atmosphere to form the two layers of the reaction barrier layer made of the metal diboride and the refractory metal layer. This is a method for producing a lanthanum hexaboride hot cathode, which is characterized in that it is formed on the bottom and lower side surfaces of a lanthanum boride chip, and a supporting metal made of a refractory metal is bonded to the surface of the refractory metal layer.

The present invention will be further explained in detail below.

In the present invention, a barrier layer and then a refractory metal layer are sequentially laminated on the lower side surface of a hexaboride capacitor/chip, and a support metal made of a refractory metal is bonded and fixed to the surface of the barrier layer and then a refractory metal layer. In manufacturing, a paste made of refractory metal is applied and sintered to cover the reaction barrier layer and the lower side of the lanthanum hexaboride chip, and the surface is coated with a refractory metal. It is characterized by joining and fixing supporting metal.

In the present invention, the Va group or Va group metal diboride used as a barrier layer to prevent the reaction between lanthanum hexaboride and a refractory metal is zirconium diboride, titanium diboride, obium diboride, tantalum diboride, Refractory metal layer and 17
These are refractory metals such as tungsten, tantalum, niobium, molybdenum, and rhenium.

To apply these to the lower side of the lanthanum hexaboride chips, a paste is used that is a mixture of these powders and a binder (a mixture of glue and solvent).

There are no particular restrictions on the binder as long as it has a suitable viscosity and can be applied to lanthanum hexaboride chips, but specific examples include cellulose nitrate, cellulose acetate, etc., and organic solvents such as butanol, methanol, etc. be.

Such a paste is applied to the lower side surface of the lanthanum hexaboride chip so that the thickness of the reaction barrier layer and the refractory metal layer after sintering is at least 10 to 100 square meters.

The sintering method is simple, as it only requires one step if it is performed at a temperature of about 1700 to 1800°C after applying the paste that forms the reaction barrier layer and the refractory metal layer, but two-step sintering is also possible. be.

The product of the present invention can be obtained by bonding and fixing a supporting metal made of a refractory metal to the surface of the refractory metal layer on the lower side surface of the lanthanum hexaboride chip obtained as described above.

The present invention will be further explained below with reference to the drawings.

The drawings show an embodiment of the present invention, in which FIG. 1 is a sectional view of a hot cathode chip, and FIG. 2 is a perspective view of the hot cathode.

1. First, as a reaction barrier layer 2, a lVa group or Va group is applied to the lower side surface of a chip 1 made of a single crystal lanthanum hexaboride or a polycrystalline sintered body of lanthanum hexaboride, which has been processed as shown in FIG. A paste containing a powder mixed with one or more metal diborides is applied.

Furthermore, in order to bond with the supporting metal 4, a paste containing powder of 1 m or more of refractory metals is applied as a refractory metal layer 3, and then lanthanum hexaboride, a barrier layer, and a refractory metal layer 3 are applied. Sintering in an inert atmosphere that does not affect the metal layer yields a lanthanum hexaboride chip with a three-layer structure on the lower side of the chip.

A lanthanum hexaboride hot cathode is obtained by joining a lanthanum hexaboride chip and a supporting metal such as a tungsten wire or a tantalum wire by spot welding as shown in FIG.

According to the present invention, by using a polycrystalline sintered body of lanthanum hexaboride and a single crystal lanthanum hexaboride, a high yield can be obtained without taking complicated steps such as hot pressing, and moreover, lanthanum hexaboride can be used during use. An excellent hot cathode without problems such as chips peeling off and falling off can be obtained.

The present invention will be explained in more detail below by giving examples.

Example 1 A paste consisting of zirconium diboride powder, cellulose nitrate, and butanol to form a reaction barrier layer was coated to a thickness of about 60 microns on the lower side surface of a chip made of lanthanum hexaboride, and after thoroughly drying, Furthermore, a paste consisting of tungsten powder, cellulose nitrate, and butanol to form a refractory metal layer was applied thereon to a thickness of about 40 square meters.

This chip was heated at a temperature of 1800°C in an argon atmosphere for 1 time.
It was sintered and baked for 0 minutes.

The coating layer of the chip had no cracks at all.

A lanthanum hexaboride hot cathode was created by spot welding a tungsten wire as a supporting metal onto the refractory metal layer of the resulting lanthanum hexaboride chip with the three-layered structure on its sides.

When the obtained hot cathode was mounted on a scanning electron microscope, 2
It could be used for over 00 hours and oxidation was sufficiently prevented.

Example 2 On the lower side surface of a chip made of lanthanum hexaboride, a paste containing mixed powder of cellulose nitrate and butanol in a molar ratio of 1:1 of niobium diboride and titanium diboride to form a reaction barrier layer was applied twice. It was coated to a thickness of 50 microns and dried.

Next, 50% of tantalum powder, cellulose nitrate, and butanol or ranal paste to form a refractory metal layer are added on top of this.
It was applied to a micron thickness and dried.

This was sintered at a temperature of 1700° C. for 10 minutes in an argon atmosphere.

A tantalum wire was bonded onto the refractory metal layer of the obtained lanthanum hexaboride chip with a three-layer structure by spot welding to create a lanthanum hexaboride hot cathode.

The obtained product had the same effect as that of Example 1.

Example 3 A barrier layer and a refractory metal layer were provided on the lower side surface of a chip made of single crystal lanthanum hexaboride made by the floating zone method in the same manner as in Example 1.2. A hot cathode was created.

Even with an expensive material such as single-crystal lanthanum hexaboride, a hot cathode could be produced with good yield, and the same effects as in Examples 1 and 2 were obtained.

Comparative Example Zirconium diboride powder for forming a reaction barrier layer on a 25 m diameter sintered disk made of lanthanum hexaboride,
Approximately 10 g of paste consisting of cellulose nitrate and butanol
Coat it to a thickness of 0 microns, place a tungsten metal plate with a diameter of 25tz and a thickness of 0.5 m on top of it and dry it thoroughly.
Insert the sample into a graphite die that just fits, and heat it in a vacuum for 205 minutes.
Hot pressing was carried out at 0°C and a pressure of 250 kg/ca.

Since the molded body has a different thermal expansion coefficient depending on the material,
There were countless cracks, so when I cut it and processed it into chips, I was able to make 5 complete pieces.

A hot cathode was created by spot welding a tungsten metal layer and a tungsten wire, and when it was actually used as a hot cathode for a scanning electron microscope, the joint between the chip and barrier layer separated after 20 hours, making it unusable.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a sectional view of a hot cathode chip, and FIG. 2 is a needle perspective view of the hot cathode. Code, 1...Lanthanum hexaboride, 2...
- Reaction barrier layer, 3... Refractory metal layer, 4...
...Supporting metal.

Claims (1)

[Scope of Claims] 1. The bottom and lower side surfaces of a single crystal or sintered lanthanum hexaboride chip are covered by a reaction barrier layer made of one or more metal diborides of group A or group Va. A lanthanum hexaboride hot cathode comprising: a refractory metal layer formed over the refractory metal layer; and a supporting metal made of the refractory metal bonded to the refractory metal. 2 Apply a paste of Group A or Group Va metal diboride to cover the bottom and lower part of the single crystal or sintered lanthanum hexaboride chip, and then apply a paste of refractory metal to cover the top. After coating and drying, this is sintered and baked in an inert gas atmosphere to form two layers, the reaction barrier layer made of the metal diboride and the refractory metal layer, on the bottom and lower side surfaces of the lanthanum hexaboride chip. 1. A method for producing a lanthanum hexaboride hot cathode, comprising: bonding a support metal made of a fusible metal to the surface of the refractory metal layer.