JP2000067811A - Impregnated negative electrode for discharge tube and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize stabilization and a long service life of the light output by lowering the work function of an electron emission surface, furthering equalization thereof and performing activation. SOLUTION: At least one kind of metal out of iridium, ruthenium, rhenium and osmium is spattered to deposit on, applied to or infiltrated into the electron emission surface of a negative electrode base material 4 composed by impregnating an infiltrating material into porous tungsten or the like, and then, an iridium-tungsten alloy layer 8, for instance, is formed in a film thickness of 0.1-10 μm on the electron emission surface by annealing the negative electrode base material 4 at 1000-2400 deg.C. The annealing is performed in the saturated vapor pressure of the infiltrating material in order to restrain evaporation of the infiltrating material. The electron emission surface can be activated by removing an adsorptive substance of the electron emission surface, and the formation of a Ba-O dipole layer by means of sputtering or the like and annealing to the negative electrode base material 4 on which the alloy layer 8 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impregnated cathode for use in a discharge tube, and more particularly to a cathode capable of promoting a reduction in work function and homogenization of an electron emission surface, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, tungsten cathodes, tungsten cathodes containing thoria, and impregnated cathodes have been widely used as cathodes for discharge tubes. The former two tungsten cathodes and the tungsten cathode containing thoria rely on thermionic emission for most of the current during discharge, and secure the necessary emitted electrons by raising the temperature to near the melting point of the cathode base material. I have. Therefore, the maximum temperature of the cathode is 3000
-3500 ° C., and the cathode voltage drop during discharge becomes relatively large. However, at temperatures above 3000 ° C., the cathode tip is melted or evaporated. In addition, an increase in the cathode voltage drop causes an increase in the cathode temperature and spattering of the cathode base material due to collision of sealing gas ions (for example, a xenon lamp) generated by ionization.

[0003] Therefore, in these cathodes, the shape of the cathode tip deteriorates in about 1700 hours, and the life of the cathode itself becomes the life of the discharge tube. On the other hand, since the light output can be stabilized by sharpening the tip of this kind of cathode, the tips of the tungsten cathode and the tungsten cathode containing thoria are sharpened to about 20 degrees.

[0004] The latter impregnated cathode is formed by pressing, molding and sintering tungsten powder or vacuum-treating copper-impregnated tungsten into porous tungsten having a porosity of 15 to 25%, and adding alumina to alumina. It is impregnated with barium and calcium. This impregnated cathode, compared to the former two tungsten cathode and triangular tungsten,
High thermoelectron emission characteristics and γ action (2 due to ion collision)
Secondary electron emission), and the cathode voltage drop during discharge is relatively relaxed.

Accordingly, the maximum temperature of the impregnated cathode is 3000
C. or less, and almost no spattering due to the enclosed gas ions occurs. According to the discharge tube using this impregnated cathode, the tip shape is less deteriorated and a long-life discharge tube can be obtained. For example, a high-pressure arc lamp of 150 W class currently has a life of about 2500 hours, which is relatively longer than that of the tungsten cathode or the like.

[0006]

However, the cause of the life of the discharge tube using the above-mentioned conventional impregnated cathode is that the evaporated material of the impregnating material adheres to the glass tube wall and lowers the light transmittance. This is a decrease in luminance, and is not a life due to deterioration of the cathode shape itself such as the former two cathodes. Therefore, if the amount of evaporation of the impregnating material is reduced, the life of the discharge tube using the impregnated cathode can be extended.

The most effective means for achieving this is to reduce the cathode temperature by improving the thermoelectron emission capability and the γ action of the cathode to reduce the cathode voltage drop. That is, the thermoelectron emission ability and the γ action can be improved by sputter depositing at least one metal of iridium, ruthenium, rhenium, and osmium on the electron emission surface of the cathode.

However, in this method, an alloy layer of the above-mentioned sputtered metal and the cathode base material is formed in a self-forming manner only in a portion where the temperature is increased during discharge lighting, and the electron emission surface of the cathode becomes non-uniform. For this reason, the temperature of the cathode partially rises excessively, and the amount of evaporation of the impregnating material (or the cathode base material) increases, resulting in a short life, and the luminescent spot fluctuates, thereby deteriorating the stability of light output. was there. In addition, in the case of this impregnated cathode, it is difficult to sharpen the tip of the cathode as in the case of the above-mentioned tungsten cathode and tungsten cathode containing thoria, since the base material is porous, and the light output by sharpening the tip shape is reduced. Stabilization has limitations.

Further, in the impregnated type cathode, molecules such as water vapor, hydroxyl groups, and oxides are adsorbed on the electron emission surface.
Initial characteristics including the stability of light output are unstable, and an aging step that requires a certain period of time is indispensable to bring out the original characteristics.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to reduce the work function of an electron emission surface, promote homogenization and activate the light emission surface, stabilize the light output, and prolong the lifetime. It is an object of the present invention to provide an impregnated cathode for a discharge tube and a method for manufacturing the same.

[0011]

In order to achieve the above object, an impregnated cathode for a discharge tube according to the invention of claim 1 is an impregnated cathode using porous tungsten or porous molybdenum as a cathode substrate. An alloy layer of at least one metal of iridium, ruthenium, rhenium and osmium and the above-mentioned cathode substrate is formed on the electron emission surface of the cathode substrate. The method for producing an impregnated cathode for a discharge tube according to the invention of claim 2 is characterized in that, among the iridium, ruthenium, rhenium, and osmium, the electron emission surface of the impregnated cathode for a discharge tube using porous tungsten or porous molybdenum as a cathode substrate. At least one kind of metal is sputter-deposited, and the cathode member after the sputter deposition is 1000 to 24
An annealing treatment is performed at 00 ° C. to form an alloy layer of the cathode base material and each of the above metals on the electron emission surface in a thickness of 0.1 to 10 μm. The method for producing an impregnated cathode for a discharge tube according to the invention according to claim 3 is characterized in that iridium, ruthenium,
At least one metal selected from the group consisting of rhenium and osmium is applied or impregnated.
Annealing treatment is performed at 000 to 2400 ° C. to form an alloy layer of the cathode substrate and each metal on the electron emission surface. The invention according to claim 4 is characterized in that the annealing treatment is performed in a saturated vapor pressure of the impregnated material in order to suppress evaporation of the impregnated material for the cathode base material.

The invention according to claim 5 is characterized in that the electron emission surface of an impregnated cathode for a discharge tube using porous tungsten or porous molybdenum as a cathode substrate is activated. Here, an activation treatment can be performed on the electron emission surface of the cathode after forming an alloy layer of the cathode base material and each of the metals. According to a sixth aspect of the present invention, in the activation treatment, the electron emission surface is sputtered in an inert gas plasma, and thereafter, the sputtering is performed in a vacuum or in an inert gas.
It is characterized by performing an annealing treatment at 0 to 1200 ° C. The invention according to claim 7 is that, in the activation treatment, while applying an annealing treatment at 1050 to 1200 ° C. in a vacuum or an inert gas, a high voltage for obtaining an electrolysis effect of the adsorbed substance is applied. Features.

According to the above-mentioned manufacturing method, at least one kind of metal layer of iridium, ruthenium, rhenium, and osmium is formed on the surface of a cathode base material made of, for example, tungsten by sputter deposition, coating, or impregnation. By the annealing treatment, an alloy layer of the metal and the tungsten of the cathode substrate is uniformly formed. That is, by using an alloy layer of iridium, ruthenium, rhenium, and osmium, a decrease in work function can be promoted, and a uniform alloy layer can be formed by annealing to achieve a uniform electron emission surface. Can be.

Further, the electron emission surface of the impregnated cathode or the impregnated cathode having the above-mentioned alloy layer formed thereon is subjected to an activation treatment so that adsorbed molecules such as water vapor, hydroxyl groups, oxides and the like adhered to the surface. Is removed, the migration of barium (Ba) as the impregnating material is promoted, and a Ba-O dipole layer is formed on the electron emission surface. Thereby, high thermionic emission characteristics and γ action can be obtained.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows two structures of an impregnated cathode for a discharge tube according to an embodiment, in which an alloy layer is formed on the cathode surface (electron emission surface). . As shown in FIG. 1A, the impregnated cathode substrate 1A
Is made of, for example, porous tungsten or porous molybdenum molded into a cylindrical shape having a conical tip. The porous substrate is impregnated with barium calcium aluminate, and a molybdenum lead 2A is provided on the rear end side. It is attached. Then, an alloy layer 3A of at least one metal of iridium, ruthenium, rhenium, and osmium and tungsten or molybdenum as a cathode material is formed on the surface of the cathode substrate 1A, that is, the electron emission surface.

In the case of a discharge tube cathode having another configuration shown in FIG. 1B, the same cathode base material 1B as described above is fixed in a state of being partially embedded in the tip of the molybdenum lead 2B. An alloy layer 3B of iridium and tungsten (similar to the above-mentioned alloy layer 3A) is formed on the cathode base 1B.

FIG. 2 shows a first example (manufacturing process) of a manufacturing method for forming the impregnated cathode shown in FIG. 1 described above. This first example is a method of performing sputter deposition and annealing. It is. In the first example, as shown in FIG. 2A, a cathode base material 4 to which a molybdenum lead 2 is fixed is used as a mother cathode, and the cathode base material 4 is made of porous tungsten as described with reference to FIG. Alternatively, porous molybdenum is impregnated with barium calcium aluminate. this is,
For example, tungsten powder is pressed, molded and sintered, or copper impregnated tungsten is subjected to vacuum treatment to produce a cathode substrate 4 made of porous tungsten having a porosity of 20%. Impregnate with impregnating material.

In the sputter deposition step shown in FIG. 2B, first, as shown, an argon (Ar) atmosphere 5 is formed.
In the sputtering chamber 6 of (−10 ⁻³ Torr), the cathode base material 4 is disposed so as to face an iridium (may be ruthenium, rhenium, or osmium) target 7. Voltage,
A positive voltage is applied to the cathode substrate 4 to perform sputter deposition.
As a result, as shown in FIG. 2C, an iridium layer 8 having a thickness of about 0.1 to 10 μm is deposited and formed on the surface of the cathode substrate 4.

Next, the process proceeds to the annealing step shown in FIG. 2D. Here, a hydrogen gas (H ₂ ) atmosphere 10
The sealed container 12 made of molybdenum is placed in an annealing furnace 11 having The container 12 has an impregnating material atmosphere 14 formed by disposing an impregnating material (barium / calcium aluminate) 13 therein. In the impregnating material atmosphere 14, the above-described cathode base material is placed via a molybdenum sample stand 15. 4
Is arranged. The cathode substrate 4 is used for the annealing furnace 1
1 is heated to, for example, 1800 ° C., and an annealing process is performed for about 20 minutes. The temperature of this annealing treatment can be set in a range from 1000 ° C. at which the formation of the alloy layer starts, to 2400 ° C. near the melting point of the alloy layer.

According to such an annealing process, as shown in FIG. 2E, the surface of the electron emission surface of the cathode base material 4 is made of iridium having a thickness of about 0.1 to 10 μm.
The tungsten alloy (Ir ₃ W alloy) layer 17 is formed uniformly. In addition, by performing the annealing process in the impregnated material atmosphere 14, the decrease in the impregnated material is favorably suppressed.

That is, at the above temperature, the barium calcium aluminate as the impregnating material 13 is easily melted or evaporated, and the amount in the cathode base material 4 during the annealing process is reduced and deteriorated. Therefore, the impregnating material 13 is placed under the sample base 15 made of molybdenum so as not to come into direct contact with the cathode substrate 4, and the inside of the closed container 12 is set to a saturated vapor pressure atmosphere of barium calcium aluminate (14). As a result, the reduction of the impregnating material from the cathode base material 4 in the thermal equilibrium state can be considerably suppressed.

FIG. 3 shows a second example of a method for manufacturing an impregnated cathode. In this second example, a cathode base material coated or impregnated with fine metal powder is annealed.
In this second example, as shown in FIG.
A binder solution 19 to which iridium fine powder having a particle size of 1 μm or less is added is placed in the inside 8, and the cathode substrate 4 as a mother cathode is immersed in the binder solution 19. Then, FIG.
As shown in (B), the container 18 in which the cathode base material 4 is immersed is put into an acrylic container 20 as it is, and vacuum impregnation in which pressure reduction and leak (atmospheric pressure) are repeated is executed.

After that, when the cathode base material 4 is taken out from the binder solution 19, the iridium fine powder is fixed on the surface and below the surface of the cathode base material 4 as shown in FIG.
An impregnated layer is formed. Next, the cathode substrate 4 is annealed by an annealing furnace 11 shown in FIG.

This annealing treatment is exactly the same as the annealing treatment of the second example, and the hydrogen gas 10 in the annealing furnace 11 is used.
A closed container 12 made of molybdenum is disposed in the container 12.
In the barium / calcium aluminate atmosphere 14 set in the above, for example, 1800 ° C. (1
(In the range of 000 ° C. to 2400 ° C.) for about 20 minutes.

This also suppresses the decrease of the impregnating material and does not deteriorate the cathode base material 4, and as shown in FIG. -10
μm thick iridium-tungsten alloy (Ir ₃ W
Alloy) layer 23 is formed homogeneously. In the case of the second example, the above-described process can be repeated any number of times, and the coating, impregnation, and annealing treatments are repeatedly performed, thereby increasing the thickness of the alloy layer 23 compared to the second example. Can be achieved. This increase in film thickness can achieve a longer life.

Next, the activation process of the impregnated cathode will be described with reference to FIGS. FIG. 4 shows a third example of a process of performing an activation process by sputtering and annealing.
As shown in FIG. 4A, in the sputtering chamber 6 in an argon (Ar) atmosphere 5, the impregnated cathode base material 24 on which the alloy layer is formed in the second example or the second example is molybdenum. The anode 25 is arranged to face the anode 25. The cathode substrate 24 may be an impregnated cathode substrate on which no alloy layer is formed.

Then, a high voltage is applied to the sputtering chamber 6 (a positive voltage is applied to the anode 25,
4, a negative voltage is applied to perform sputtering, and the electron emission surface of the cathode base material 24 is cut by about 100 ° in argon plasma.
Expose a clean tungsten surface. That is, argon ions collide with the electron emission surface, and adsorbed molecules such as water vapor, hydroxyl groups, and oxides present on the surface are removed.

Next, as shown in FIG. 4B, the inside of the annealing furnace 11 is made an inert gas atmosphere (or vacuum) 26, and the cathode base material 25 is placed in the inert gas atmosphere 26 to Annealing is performed for 30 minutes at a temperature of 1200C to 1200C. According to this annealing treatment, the migration of barium in the barium / calcium aluminate impregnated in the cathode base material 24 is promoted, and a Ba-O dipole layer is formed on the electron emission surface. As a result, FIG.
The cathode 28 shown in (C), that is, the cathode 28 in which the electron emission surface is activated can be obtained.

FIG. 5 shows the steps of a fourth example in which an annealing treatment and an activation treatment are performed by electrolysis. In this fifth example, as shown in FIG. In 11, an impregnated type cathode base material having an alloy layer formed thereon (or a cathode base material having no alloy layer formed thereon) 24 is disposed to face a molybdenum anode 25. In the annealing furnace 11, the inside is an atmosphere 30 of a vacuum or an inert gas of 10 ⁻⁷ Torr or more, and annealing is performed at a temperature of 1050 to 1200 ° C. , 1-2 kV for about 30 minutes.

According to the treatment in the annealing furnace 11, the cathode base material 24 is produced by thermionic electrons or residual gas ions under the vacuum 30, and by the discharge action in the inert gas atmosphere 30.
Adsorbed molecules such as water vapor, hydroxyl groups and oxides on the surface layer are electrically decomposed. At the same time, the migration of barium in the cathode base material 24 is promoted, and Ba-O
A dipole layer will be formed, which results in FIG.
The cathode 31 shown in (B), that is, the cathode 31 in which the electron emission surface is activated can be obtained.

The temperature of the annealing treatment in the third and fourth examples is preferably 1050 ° C. or higher at which barium migration is possible, and
If the temperature exceeds 200 ° C., the scattering of barium becomes remarkable and the cathode base material 24 is deteriorated.
It is preferable to set the temperature in the range of 200 ° C.

In the above example, the case where the present invention is applied to the cathode base material 24 on which the alloy layer is formed has been described. However, this activation treatment is similarly applied to the impregnated cathode base material on which the alloy layer is not formed. By applying, the effect of activating the electron emission surface can be exhibited. According to such an activation process, there is an advantage that the aging step which has been performed conventionally is not required.

The impregnated cathode shown in FIG. 1, the impregnated cathodes produced by the manufacturing methods of the first and second examples, and the activated and impregnated cathodes of the third and fourth examples are discharged. The discharge tube is manufactured by being incorporated in a glass tube for a tube, and containing the discharge gas in the glass tube.

[0034]

As described above, according to the first aspect of the present invention, iridium or the like and the cathode substrate are provided on the electron emission surface of the cathode substrate in which porous tungsten or porous molybdenum is impregnated with an impregnating material. An alloy layer with the material is formed, and this is used as the cathode for the discharge tube.This promotes the reduction and homogenization of the work function of the electron emission surface of the cathode for the discharge tube, and a long-life discharge that greatly stabilizes the light output. It becomes possible to obtain a tube.

According to the second aspect of the present invention, iridium, ruthenium, rhenium,
At least one kind of metal of osmium is sputter-deposited, and the cathode member after the sputter-deposition is 1000-2.
Annealing treatment was performed at 400 ° C., and an alloy layer of the above-mentioned cathode base material and each of the above-mentioned metals was formed on the above-mentioned electron emission surface in a thickness of 0.1 to 10 μm to produce an impregnated cathode for a discharge tube. And the homogenization of the alloy layer is promoted, and a high thermoelectron emission ability and a gamma action can be obtained, and it is possible to greatly stabilize the light output and extend the life. According to the third aspect of the invention, the metal such as iridium is applied or impregnated, and the cathode member after the application or impregnation is annealed to form the alloy layer on the electron emission surface. The same effect as in the case of No. 2 can be obtained, and in this case, in particular, the effect can be further enhanced by forming the thick film alloy layer.

According to the fourth aspect of the present invention, since the annealing treatment is performed in the saturated vapor pressure of the impregnating material of the cathode base material, evaporation of the impregnating material can be suppressed and deterioration of the cathode can be prevented. .

According to the fifth to seventh aspects of the present invention, since the electron emission surface of the impregnated cathode for a discharge tube is activated, the adsorbed substance is removed and the Ba-O dipole layer is removed. Are formed, high thermoelectron emission capability and a gamma action can be obtained, and the light output can be stabilized.

[Brief description of the drawings]

FIG. 1 is a view showing two exemplary embodiments (FIGS. (A) and (B)) of an impregnated cathode for discharge tubes according to the present invention.

FIG. 2 is a view showing a process of a first example of a method for manufacturing an impregnated cathode for a discharge tube according to an embodiment of the present invention.

FIG. 3 is a view showing a process of a second example of the method for manufacturing the impregnated cathode for a discharge tube according to the embodiment of the present invention.

FIG. 4 is a view showing a step (activation processing step) of a third example of the method for manufacturing the impregnated cathode for a discharge tube according to the embodiment of the present invention.

FIG. 5 is a view showing a step (activation treatment step) of a fourth example of the method for producing an impregnated cathode for a discharge tube according to the embodiment of the present invention.

[Explanation of symbols]

1A, 1B, 4, 24 ... Cathode substrate, 2A, 2B, 2 ... Molybdenum lead, 3A, 3B, 17, 23 ... Iridium-tungsten alloy layer, 6 ... Sputtering chamber, 11 ... Annealing furnace, 7 ... Iridium target , 13 ... impregnating material (barium calcium aluminate), 25 ... molybdenum anode.

Continued on the front page (72) Inventor Jun Inoue 2-1-1 Fukuoka, Kamifukuoka-shi, Saitama New Nippon Radio Co., Ltd. Kawagoe Works (72) Inventor Fumio Takamura 2-1-1 Fukuoka, Kamifukuoka-shi, Saitama No. Shin Nihon Radio Co., Ltd. Kawagoe Works F-term (reference) 5C015 JJ05

Claims (7)

[Claims] 1. An impregnated cathode for a discharge tube using porous tungsten or porous molybdenum as a cathode substrate, wherein at least one metal selected from the group consisting of iridium, ruthenium, rhenium and osmium is provided on the electron emission surface of the cathode substrate. An impregnated cathode for a discharge tube, comprising an alloy layer formed with the cathode base material. 2. At least one metal selected from the group consisting of iridium, ruthenium, rhenium and osmium is sputter-deposited on the electron emission surface of a discharge tube impregnated cathode having porous tungsten or porous molybdenum as a cathode substrate. The cathode member after sputtering deposition is 1000 to 2400 ° C.
Annealing in the above, the alloy layer of the above-mentioned cathode base material and each of the above metals 0.1 to 10μ
A method for manufacturing an impregnated cathode for a discharge tube, wherein the cathode has a thickness of m. 3. An iridium, ruthenium, rhenium, or osmium metal is applied or impregnated on an electron emission surface of a discharge tube impregnated cathode having porous tungsten or porous molybdenum as a cathode substrate, After applying or impregnating the cathode member, the cathode member is heated to 1000 to 2400 ° C.
A method of manufacturing an impregnated cathode for a discharge tube, wherein an alloy layer of the cathode substrate and each of the metals is formed on the electron emission surface. 4. The method according to claim 2, wherein the annealing is performed at a saturated vapor pressure of the impregnating material in order to suppress evaporation of the impregnating material for the cathode substrate.
A method for producing the impregnated cathode for a discharge tube according to the above. 5. A method for producing an impregnated cathode for a discharge tube, wherein the electron emission surface of the impregnated cathode for a discharge tube using porous tungsten or porous molybdenum as a cathode substrate is activated. 6. The activation process, wherein the electron emission surface is sputtered in an inert gas plasma, and thereafter, an annealing process is performed at 1,050 to 1,200 ° C. in a vacuum or an inert gas. A method for producing an impregnated cathode for a discharge tube according to claim 5. 7. The activation process is characterized in that a high voltage for obtaining an electrolysis effect of an adsorbed substance is applied while performing an annealing process at 1,050 to 1,200 ° C. in a vacuum or an inert gas. A method for producing an impregnated cathode for a discharge tube according to claim 5.