JPH07169383A - Impregnated cathode and electron tube or electron beam applying apparatus using same - Google Patents

Abstract

PURPOSE:To provide an impregnated cathode for a cathode-ray tube with good reproducibility of electron emission properties at low temperture and provide a doped cathode for an electron beam applying apparatus with good reproducibility of electron emission peroperties at low temperature even under the low vacuum and intense ion impact environments. CONSTITUTION:An impregnated cathode for an electron beam applying apparatus which functions well even under the low vacuum and intense ion impact environments is prepared by mixing a base metal 22 powder, an electron emissive substance powder 24, and a rare earth-based substance powder 23 and sintering and uniting the mixture by hot isostatic pressing treatment. An impregnated cathode for a cathode-ray tube with excellent properties is obtained by coating the electron emissive surface of the impregnated cathode 25 with a coating film 26 of platinum-group metals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron tube such as a cathode ray tube, and an impregnated cathode used in an electron beam application apparatus such as an electron beam vapor deposition machine.

[0002]

2. Description of the Prior Art Cathode ray tubes for televisions and displays are always required to display brighter images for a longer period of time. Therefore, it is necessary to increase the current density of the cathode and at the same time extend the life. Although the impregnated cathode is suitable for this purpose, the impregnated cathode has a major drawback that the operating temperature is higher than that of the oxide cathode by 200 ° C. or more.

For this reason, efforts have always been made to reduce the operating temperature of impregnated cathodes. Here are some examples:

First, as a first example, a W powder and a Sc oxide powder were mixed and shaped, and then BaO was added to a porous substrate made by temporary sintering in hydrogen and main sintering in vacuum. Al ₂
There is an impregnated cathode made by a method of melt-impregnating an electron emitting material such as O ₃ and CaO in hydrogen. (Japanese Patent Publication No. 5-4772) As a second example, BaO, Al ₂ O ₃ ,
There is an impregnated cathode in which a CaO, Sc ₂ O ₃ compound is melt-impregnated.

As a third example, the surface of an impregnated cathode formed by impregnating a porous substrate with an electron-emitting substance (Ba,
There is an impregnated cathode coated with a Sc, O) composite compound layer. (JP-A-60-170136) As a fourth example, an impregnated cathode in which the surface of an impregnated cathode formed by impregnating a porous substrate with an electron emitting substance is coated with a thin film of a compound compound containing W and Sc oxides. There is. (Japanese Patent Application Laid-Open No. 61-13526) All of these are intended to lower the operating temperature by adding Sc atoms to the substrate, the electron emitting material or the surface, and are collectively referred to as scandate-impregnated cathodes.

On the other hand, apart from this, the cathode of an electron beam application apparatus such as an electron beam vapor deposition machine and an electron beam welding machine, which is used at a much lower degree of vacuum than a cathode ray tube, has an ion impact due to residual gas on the cathode ray tube. Is much larger than
W cathodes that are resistant to ion bombardment have been used in the past. However, the W cathode has a very high operating temperature (250 to 26
Therefore, the load on the heating power source is large, and the cathode peripheral member is unnecessarily heated, causing problems such as gas release, softening deformation, and deterioration of quality. Therefore W
A cathode that is strong against ion bombardment and has a low operating temperature is desired as an alternative to the cathode.

[0007]

However, the conventional scandate-impregnated cathode described above has the following drawbacks as a cathode of a cathode ray tube.

First, the type of the first example, in which the Sc oxide is mixed and sintered in the substrate, has a drawback that the electron emission distribution on the cathode surface is non-uniform. The reason for this is that when the porous substrate is sintered, it is heated to a high temperature of 2200 to 2500 ° C.
This is because the work function distribution on the surface becomes non-uniform as a result of a significant local reaction between the c oxide and W. Further, there is a drawback that activation is time-consuming because Sc atoms are slowly replenished from the substrate to the surface, and that the electron emission ability after ion bombardment is slowly recovered.

Next, in the second example, BaO, Al was added to the porous substrate.
The _{2 O 3, CaO, Sc 2} O 3 that the compound was melted _{impregnated, BaO, Al 2 O 3,} CaO, and substrate to a high temperature of from 1,700 to 1,900 ° C. to melt the Sc ₂ O ₃ compound wherein Since the compound locally reacts remarkably and the reaction product at that time is localized, the electron emission distribution on the cathode surface is similar to that of the first example in which Sc oxide is mixed and sintered in the substrate. It had the drawback of being non-uniform.

Further, in the case of the type in which the composite compound is coated on the surface as in the third and fourth examples, the production is remarkable due to the complicated structure of the coating layer, the characteristics are difficult to reproduce stably, and There is also a drawback that the Sc compound in the covering film is likely to become metallic Sc, and if so, the effect of reducing the operating temperature is lost.

When the above conventional scandate-impregnated cathode is used as a cathode of an electron beam application apparatus,
The electron beam application device has the following drawbacks different from the cathode ray tube because of the continuous strong ion bombardment, which is incomparable to the cathode ray tube.

BaO, Al ₂ was added to the first example of the type in which Sc oxide was mixed and sintered in the substrate, and the porous substrate of the second example.
Those obtained by melt-impregnating O ₃ , CaO, and Sc ₂ O ₃ compounds do not have the required electron beam intensity because the electron emission capability continues to be reduced due to continuous strong ion bombardment.

Further, in the case of the type in which the composite compound is coated on the surface as in the third and fourth examples, the coating layer is destroyed in a short time by the continuous strong ion bombardment, and the required electron beam intensity is still obtained. I will not be able to.

Therefore, the present invention has been proposed in view of the above problems of the prior art, and one of them is to provide an impregnated cathode capable of obtaining good electron emission characteristics at a low temperature and with good reproducibility for a cathode ray tube. Another object of the present invention is to provide an impregnated cathode for an electron beam application device, which can obtain good electron emission characteristics at low temperature and with good reproducibility even in an environment of low vacuum and severe ion bombardment. Another object of the present invention is to provide a high-quality electron tube, an electron beam application device, etc., which uses this impregnated cathode and has a long life and less variation in characteristics.

[0015]

The impregnated cathode of the present invention is one of a refractory metal powder, a powder of an electron emitting material containing a compound of Ba, a rare earth metal, a rare earth metal alloy, and an oxide of a rare earth metal. Hot isostatic pressing of a mixture of powders of rare earth materials consisting of at least one species and molding
sing) Processed and sintered.

Further, another constitution of the impregnated cathode of the present invention comprises a refractory metal powder, an electron emitting substance powder containing a compound of Ba, and at least one kind of rare earth metal, rare earth metal alloy and rare earth metal oxide. Hot isostatic pressing of a mixture of rare earth powders
c Pressing) treatment for sintering and integration, and a coating film made of a platinum group metal or a platinum group metal alloy is formed to form an electron emission surface. In particular, it is characterized in that the Ir coating film is 0.05 to 1.0 μm.

In the impregnated cathode, the refractory metal is W, Mo, Ta, Re, Ir, Os, or a mixture or alloy selected from the group thereof.

The electron emitting material containing a Ba compound may be a mixture of BaCO ₃ with at least one of CaCO ₃ , Al ₂ O ₃ and SrCO ₃ , or a mixture of CaO and CaO. , SrO, Al ₂ O ₃
It is characterized in that it is a mixture of one or more of them and BaO.

In the impregnated cathode, the rare earth metal is Sc, Y, Dy, La, Ce or a combination thereof, the rare earth metal alloy is an alloy of a refractory metal and the rare earth metal, and the rare earth metal oxide is the above. It is characterized by being an oxide of a rare earth metal.

In the impregnated cathode, the platinum group metal is Ir, Os, Ru, Rh, Pd, or a combination thereof, and the platinum group metal alloy is an alloy between the platinum group metals. And

In the impregnated cathode, the rare earth metal oxide is Sc ₂ O ₃ , and the added amount is 0.6.
It is characterized in that it is not less than wt% and not more than 8.2 wt%.

Furthermore, the present invention is characterized in that the various impregnated cathodes are used in an electron tube or an electron beam application device.

[0023]

By mixing a mixture of a high melting point metal powder, an electron emitting material containing a compound of Ba, and a Sc oxide powder with hot isostatic pressing (hot isostatic pressing) and sintering, The sintering temperature required from 2200 to 2500 ° C. or the melt impregnation temperature required from 1700 to 1900 ° C. can be lowered to 900 to 1400 ° C.
As a result, Sc oxide or S
It is possible to avoid the local reaction between the compound containing c-oxide and the refractory metal, and in addition to the effect of reducing the operating temperature, the non-uniformity of the electron emission distribution on the cathode surface is alleviated. An impregnated-type cathode is obtained in which the emissivity is not reduced.

At least one rare earth metal selected from the group consisting of rare earth metals, rare earth metal alloys and rare earth metal oxides is added to at least one of the base metal and the electron emitting material, and platinum group metal or platinum group metal is formed on the electron emitting surface. By forming the coating film made of an alloy, in addition to the effect of alleviating the non-uniformity of the electron emission distribution on the cathode surface, the work function of the electron emission surface is further reduced, so that the operating temperature can be further lowered. The latter effect is greater than when the above two means (one for the substrate and one for the electron emitting surface) are used alone. Further, since the two means are easy to manufacture, reproducibility of characteristics is good.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a flow chart of the manufacturing process of the impregnated cathode of the present invention.

First, BaCO ₃ , CaCO ₃ . Al ₂ O ₃
The respective powders of 1 are weighed so that the molar ratio becomes 4: 1: 1 and well mixed so that the dispersibility becomes good. (11) Next, the mixture is heated to about 1100 ° C. in the atmosphere to thermally decompose the carbonate and convert it into a compound containing barium calcium aluminate as a main component. Hereinafter, this compound is referred to as an electron emitting substance. (12) Next, the electron emitting material, W powder, and Sc ₂ O ₃ powder are mixed in an appropriate weight ratio, for example, electron emitting material 10, W100,
Weigh in a ratio of Sc ₂ O ₃ 2 (1.8 wt%) and mix well to obtain good dispersibility. (13) Next, the mixture is put into a rubber mold having an appropriate shape and size,
Cold isostatic pressing of about 2000 Kg / cm ² (Cold Static
Pressing) process converts the powder into a compact.
(14) Next, the above-mentioned molded body is put into a glass capsule, and alumina powder is filled in the space between the molded body and the glass capsule, and the inside is evacuated to about 10 ^-5 Torr and then sealed. (1
5) Next, the above-mentioned molded body containing glass capsules is hot isostatically pressed (Hot Isostatic Pressi) according to the heating / pressurizing schedule shown in FIG.
ng) process and sinter the compact at high temperature and high pressure. At this time, the atmosphere, temperature, pressure, and time are Ar gas, 900-
1400 ° C., 1000 to 2000 atm, and 1 to 180 minutes are suitable, but in this example, Ar gas and 10 respectively.
It was set to 00 ° C., 1500 atm, and 20 minutes. (16) Next, the sintered body is subjected to processing such as cutting, grinding and polishing,
An impregnated cathode pellet having a desired size and shape is obtained.
(17) At this stage, the impregnated cathode of Example 1 of the present invention was assembled in a diode to measure electron emission characteristics.

FIG. 2A shows a cross section of the impregnated cathode pellet 21 of the first embodiment of the present invention. As shown in FIG. 2A, the impregnated cathode pellet of the first embodiment of the present invention is a porous W substrate 22 in which Sc ₂ O ₃ 23 and an electron emitting substance 24 are dispersed and mixed and integrated. And the electron emission surface is 25.

In the impregnated cathode of the second embodiment of the present invention, the electron emission surface 25 of the cathode pellet was coated with Ir by the sputtering method (18 in FIG. 1), and then assembled in a dipole to measure the electron emission characteristics. The thickness of the Ir coating film is 0.0
5 to 1.0 μm is suitable, but 0.2 μm and 0.5 μm were used in this example. FIG. 2B shows a cross section of the impregnated cathode pellet 27 according to the second embodiment of the present invention. Figure 2
As shown in FIG. 2B, the impregnated cathode pellet of the second embodiment of the present invention has the Ir film 2 on the electron emission surface 25 of the impregnated cathode pellet of the first embodiment of the present invention shown in FIG. 2A.
6 is coated.

Similarly, the amounts of the electron emitting material and W are unchanged, and the amounts of Sc ₂ O ₃ are 0.5 wt% and 0.9 wt.
%, 3.5 wt%, 5.1 wt%, 6.7 wt%, 8.
An impregnated cathode pellet of 3 wt% was prepared and the electron emission characteristics were measured in the same manner.

Typical electron emission characteristics of the impregnated cathodes of the first and second embodiments of the present invention will be described with reference to FIG.

FIG. 3 is a comparison of the electron emission characteristics under high vacuum of the first and second embodiments of the present invention and various conventional impregnated cathodes by using the dipole characteristics. In FIG. 3, the horizontal axis represents the voltage applied between the cathode and the anode, and the vertical axis represents the cathode emission current. In FIG. 3, the higher the curve is on the left side, the better the characteristic.

In FIG. 3, a curve 31 is a conventional S-type impregnated cathode, that is, an impregnated cathode composed of W and an electron-emitting substance mainly containing barium calcium aluminate and having no coating film such as Ir on the surface. It is a polar characteristic. Curve 32 is a conventional M type impregnated cathode, that is, S
This is a diode characteristic of a mold-impregnated cathode whose surface is coated with an Ir film (thickness 0.2 μm). The curve 33 is the first example of the conventional product, that is, W powder and Sc oxide powder are mixed and molded, and then the powder is pre-sintered in hydrogen and main-sintered in vacuum. It is a dipole characteristic of an impregnated cathode produced by a method of melt-impregnating an electron emitting substance composed of Al ₂ O ₃ , CaO and the like in hydrogen. A curve 35 is the first embodiment of the present invention, that is, a mixture of W powder, an electron emitting substance, and Sc ₂ O ₃ powder is hot isostatically pressed (Hot Isostatic Pr).
essing) is a characteristic of the dipole of an impregnated cathode manufactured by a method of processing and sintering. The curve 34 represents the second embodiment of the present invention,
That is, it is the dipole characteristic of the impregnated cathode in which the electron emission surface of the impregnated cathode of the first embodiment of the present invention is coated with an Ir film (thickness 0.2 μm). The cathode temperature of the above-mentioned bipolar characteristics is 850 ° C. (luminance temperature).

As is apparent from FIG. 3, when the characteristics of various impregnated cathodes are compared, the S type (31), the conventional product first example (33), and the first embodiment of the present invention (35) ), M type (32), and the second embodiment (34) of the present invention.

As a result, the impregnated cathode of the second embodiment (34) of the present invention is a conventional product (for example, M type impregnated cathode 3).
It has better characteristics under high vacuum than 2) and is suitable for cathode ray tubes. On the other hand, the first embodiment (35) of the present invention seems to be slightly inferior to the M type (32) when used in a cathode ray tube, but when these are used in an electron beam application device, the M type (32) Since the coating film on the surface disappears in a short time due to ion bombardment and becomes an S type (31), it cannot be used in an electron beam application device such as an electron beam welding machine having a low degree of vacuum.
On the other hand, the impregnated cathode of the first embodiment (35) of the present invention is significantly resistant to ion bombardment, and thus can be used for a long time. In such applications, the first embodiment (3) of the present invention is used.
5) is superior to the M type (32). When the second embodiment (34) of the present invention is used in an electron beam application apparatus, the surface-coated Ir film disappears in a short time due to ion bombardment.
This impregnated cathode is most suitable for a high vacuum cathode ray tube because it becomes substantially the same as the embodiment (35).

The impregnated cathode of Example 1 (35) of the present invention was mounted on an electron beam welding machine, and characteristics were evaluated in an environment of low vacuum and high ion bombardment. As a result, it was confirmed that the electron emission ability equivalent to that of the conventional W cathode was obtained at a much lower temperature (about 1000 ° C.), and that it had the same durability against ion bombardment as the W cathode.

Next, referring to FIG. 4, a second embodiment of the present invention (3
The relationship between the Ir coating film thickness and the dipole characteristic in 4) will be described.

In FIG. 4, a curve 41 shows the characteristics of the dipole of the impregnated cathode whose surface is not coated with Ir. Curve 4
No. 2 shows the dipole characteristic of Ir film thickness of 0.2 μm, and curve 43 shows the dipole characteristic of Ir film thickness of 0.5 μm. In each case, the cathode temperature is 850 ° C. (brightness temperature).

As is apparent from FIG. 4, the dipole characteristics of the impregnated cathode of the present invention largely depend on the Ir film thickness, and the best value is around 0.2 μm at present.

Next, Sc in the impregnated cathode of the present invention
The relationship between the amount of ₂ O ₃ added and the electron emission characteristics will be described with reference to Table 1.

[0041]

[Table 1]

The symbols in Table 1 indicate the degree of electron emission characteristics, and were set in order of excellentness: ⊚>∘>Δ> X. In addition,
Among these symbols, Δ has characteristics equivalent to those of the conventional S-type impregnated cathode (FIGS. 3 and 31), and X has lower characteristics than the S-impregnated cathode (FIGS. 3 and 31).

Further, the levels of electron emission characteristics of Conventional Examples 1 and 2 are Δ to ◯.

From Table 1, the electron emission characteristics are improved as the amount of Sc ₂ O ₃ added is increased, but the electron emission characteristics are deteriorated when the amount added is further increased. It can be seen that the characteristics are inferior to the type cathode. Therefore, the optimum range of the amount of added Sc ₂ O ₃ is 0.6.
wt% or more and 8.2 wt% or less, especially 1.0 wt%
Above 5.0 wt% is desirable.

Although the refractory metal is W in the above embodiment, it is not limited to this and may be W, Mo, Ta, Re, Ir, Os, or a mixture or alloy thereof.

In the above embodiment, the electron emitting substance is Ba.
A mixture of CO ₃ , CaCO ₃ , and Al ₂ O ₃ is pre-calcined in the air, but not limited to this, CaCO ₃ , A
A mixture of one or more of 1 ₂ O ₃ and SrCO ₃ and BaCO ₃ may be used without preliminary calcination or after preliminary calcination. A mixture of BaO and one or more of CaO, Al ₂ O ₃ , and SrO may be used.

In the above embodiment, the rare earth material is Sc.
₂ O ₃ , but not limited to this, Sc, Y, Dy, La,
Ce or a combination thereof, a base metal and an alloy thereof, or an oxide thereof does not reach that of Sc ₂ O ₃ , but a similar effect can be obtained.

Further, in the above embodiment, the platinum group metal coating the electron emitting surface is Ir, but not limited to this, Ir, O
It may be s, Ru, Rh, Pd or a combination thereof or an alloy therebetween.

[0049]

As described above, in the impregnated cathode of the present invention, the refractory metal powder, the electron emitting material and the powder of the rare earth material are mixed, and then sintered by hot isostatic pressing. By doing so, it is possible to reduce the sintering temperature and suppress unnecessary reactions, and it is possible to reproducibly obtain favorable and stable electron emission characteristics that are particularly resistant to ion bombardment at a low vacuum degree.

Further, by forming a coating film made of a platinum group metal or a platinum group metal alloy on the impregnated cathode to form an electron emission surface, good and stable electron emission characteristics can be reproduced at a low temperature especially under a high vacuum. You can get good quality.

Further, by using the impregnated cathode of the present invention, it is possible to provide a long life and high quality electron tube and electron beam application device.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of an embodiment of an impregnated cathode of the present invention.

FIG. 2 is a first embodiment (a) of the impregnated cathode of the present invention.
And a pellet cross-sectional view of the second embodiment (b).

FIG. 3 is a comparison diagram of the dipole characteristics of the impregnated cathode of the present invention and various conventional impregnated cathodes.

FIG. 4 is a diagram showing the relationship between the surface Ir coating film thickness of the impregnated cathode of the present invention and the characteristics of a diode.

FIG. 5: Hot Isostatic Pres of the present invention
sing) A program showing an example of processing conditions.

[Explanation of symbols]

11 BaCO ₃ , CaCO ₃ , Al ₂ O ₃ Mixing Step 12 Pyrolysis Step 13 Electron Emitting Material, W Powder, Sc ₂ O ₃ Powder Mixing Step 14 Cold Forming Step 15 Encapsulation Step 16 Hot Isostatic Pressing ( Hot Isostatic Pressing) Treatment step 17 Cutting / machining step 18 Ir coating film forming step 21 Impregnated cathode of the present invention (first embodiment) 22 Porous W substrate 23 Sc ₂ O ₃ particles 24 Electron emitting material 25 Electron emission Surface 26 Ir coating film 27 Impregnated cathode of the present invention (second embodiment)

Claims (10)

[Claims] 1. A sintered body obtained by mixing and molding a refractory metal powder, a powder of an electron emitting substance containing a Ba compound, and a powder of a rare earth-based substance, and subjecting the mixture to hot isostatic pressing. An impregnated cathode in which the rare earth material is one or more of a rare earth metal, a rare earth metal alloy, and an oxide of a rare earth metal. 2. A platinum group metal is added to a sintered body obtained by mixing and molding a refractory metal powder, an electron emitting substance powder containing a Ba compound, and a rare earth substance powder, and subjecting the mixture to hot isostatic pressing. Alternatively, an impregnated cathode in which a coating film made of a platinum group metal alloy is formed to serve as an electron emission surface, and the rare earth-based substance is at least one selected from a rare earth metal, a rare earth metal alloy, and an oxide of a rare earth metal. 3. The refractory metal is W, Mo, Ta, Re,
The impregnated cathode according to claim 1 or 2, which is made of Ir, Os, a mixture selected from the group, or an alloy selected from these groups. 4. An electron emitting material containing the compound of Ba,
_3. A mixture of BaCO ₃ and at least one of CaCO ₃ , Al ₂ O ₃ and SrCO ₃ , or a mixture obtained by pre-calcining the mixture.
The impregnated cathode described. 5. An electron emitting material containing the compound of Ba,
The impregnated cathode according to claim 1 or 2, which is a mixture of one or more of CaO, SrO, and Al ₂ O ₃ and BaO. 6. The rare earth metal is Sc, Y, Dy, La,
3. The impregnating mold according to claim 1, wherein the rare earth metal alloy is Ce, or a combination of one or more selected from these groups, and the rare earth metal alloy is an alloy of a rare earth metal and a high melting point metal. Cathode. 7. The rare earth metal oxide is a Sc oxide, and the amount of addition thereof is 0.6 wt% or more and 8.2 wt% or less, according to claim 1 or 2. Impregnated cathode. 8. The platinum group metal is Ir, Os, Ru, R
The impregnated cathode according to claim 2, which is one or more selected from the group consisting of h and Pd. 9. The impregnated cathode according to claim 2, wherein the platinum group metal is Ir and the coating film thickness is 0.05 to 1.0 μm. 10. An electron tube or electron beam application apparatus, wherein an impregnated cathode selected from the impregnated cathodes according to claim 1 is used.