JP2002110089A - Electrode, discharge lamp and optical device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deformation and wear of an electrode of a high pressure discharge lamp or the like due to a mechanical strength of an electrode material itself or an increase in an electrode temperature, and to suppress rapid scattering of an electron-emitting substance. . By using such an electrode,
Increase the luminous flux maintenance rate and lamp life of the discharge lamp. SOLUTION: The electrode is made of a tungsten material containing at least one oxide selected from a rare earth oxide and a composite oxide containing a rare earth element, and has a desired electrode shape. The material and the like are made of a spark plasma sintered body. By using such an electrode as the cathode 4, for example, the high-pressure discharge lamp 11 is formed. An electrode made of a tungsten material or the like can be applied to the anode 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode using a high melting point metal material such as a tungsten material, and a discharge lamp and an optical device using the same.

[0002]

2. Description of the Related Art High-pressure discharge lamps such as metal halide lamps, xenon lamps, and high-pressure mercury lamps are widely used as light sources for optical devices such as movie theater projectors, semiconductor exposure devices, laser devices, and liquid crystal projectors.
Generally, tungsten (W) is used for the electrodes of such a high-pressure discharge lamp. Specifically, a tungsten alloy to which an electron-emitting substance such as thorium oxide is added is used for the cathode, and doped tungsten (K, Si, Al) having excellent deformation resistance at high temperatures is used for the anode.
Tungsten or the like doped) is used.

[0003] A conventional tungsten electrode is manufactured by combining a sintering method based on an ordinary powder metallurgy method with rolling including wire drawing. That is, a tungsten material is produced by a usual sintering method using a doped tungsten powder or a tungsten alloy powder having a desired composition as a raw material powder. After forging, rolling, etc. on such a tungsten material,
By performing wire drawing, a tungsten electrode having a desired electrode shape is obtained (see, for example, JP-A-2000-106131).

In the conventional method for manufacturing a tungsten electrode as described above, it is difficult to increase the density of the tungsten material, and in addition, the tungsten crystal grains become elongated by wire drawing, and the mechanical strength is reduced. Therefore, there is a problem that the electrode which becomes high in temperature during the operation of the lamp is easily deformed or consumed.

Further, in the conventional tungsten electrode, abnormal growth of recrystallized grains due to lighting heat tends to proceed, and electrons such as thorium oxide pass through a grain boundary which has become large due to the abnormal growth of the recrystallized grains. There is a problem that the radioactive dope material is rapidly deposited on the electrode surface, and the precipitate is scattered to the surroundings, so that the electrode temperature rises and the electrode is liable to be consumed or deformed. The rapid scattering of thorium oxide and the like also causes a reduction in the luminous flux maintenance factor of the high-pressure discharge lamp and blackening of the lamp.

[0006] With the recent miniaturization and high load of discharge lamps, the above-mentioned deformation and wear of the electrodes, a reduction in the luminous flux maintenance ratio, blackening of the lamp, and the like are more likely to occur. I have. Further, the temperature of the electrode is easily increased by sealing the discharge lamp, which also contributes to deformation and wear of the electrode.

[0007]

As described above, in the conventional high-pressure discharge lamp, the deformation and consumption of the electrode are caused by the electrode material manufactured by combining the usual sintering method and wire drawing. There is a problem that such is easy to occur. further,
Due to such deformation and consumption of the electrode, and rapid precipitation and scattering of the doping material, there is a problem that the luminous flux maintenance ratio is reduced and the lamp is blackened.

On the other hand, regarding electrode materials (particularly, cathode electrode materials), the use of radioactive substances such as thorium and its compounds has been banned due to recent environmental problems.
Therefore, as an electrode material for the cathode, a tungsten alloy using a rare earth oxide such as yttrium oxide, lanthanum oxide, or cerium oxide as an electron-emitting substance instead of thorium oxide is considered to be promising.

However, similar problems also occur in an electrode made of a tungsten alloy containing a rare-earth oxide or the like, when it is manufactured by applying a manufacturing method combining a conventional sintering method and a wire drawing process. Is concerned. Therefore, there is a need for a technique capable of suppressing deformation and wear of an electrode made of a tungsten alloy containing a rare-earth oxide and the like, and a reduction in the luminous flux maintenance factor and blackening of a lamp due to these.

The present invention has been made to address such problems, and when used as an electrode of a discharge lamp, deformation or wear due to the mechanical strength of the electrode material itself or an increase in the electrode temperature. It is another object of the present invention to provide an electrode capable of suppressing the rapid scattering of an electron-emitting substance, and to improve the luminous flux maintenance rate by using such an electrode, and to improve the lamp by blackening. An object of the present invention is to provide a discharge lamp in which a reduction in life is suppressed and an optical device using such a discharge lamp.

[0011]

According to a first aspect of the present invention, there is provided an electrode comprising a refractory metal containing at least one oxide selected from a rare earth oxide and a composite oxide containing a rare earth element. An electrode made of a material and having a desired electrode shape, wherein the high melting point metal material having the electrode shape is formed by a discharge plasma sintering method.

According to the spark plasma sintering method, an electrode material having a shape close to the final shape of the electrode can be produced at a relatively low temperature and a high density. Therefore, a high-melting metal material such as a tungsten material having a desired electrode shape, that is, a high-melting metal material containing a rare-earth oxide or a composite oxide containing a rare-earth element, without subjecting the electrode material to wire drawing or the like. Electrodes can be obtained. The electrode obtained in this way has high density and also has granular and fine crystal grains, so that the mechanical strength of the electrode itself can be increased. Therefore, when the electrode of the present invention is used, for example, as an electrode for a discharge lamp, it is possible to suppress deformation, wear, and the like.

Further, since the crystal grains are prevented from being coarsened due to, for example, lighting heat based on the graining or miniaturization of the electrode crystal grains, a rare earth oxide or a composite oxide containing a rare earth element as a doping material is used. It is possible to suppress rapid precipitation and scattering of. This contributes, for example, to the improvement of the luminous flux maintenance rate of the discharge lamp and the suppression of blackening, and also works effectively to reduce the temperature rise of the electrode, so that deformation and wear caused by the rise in the electrode temperature are also suppressed. can do.

The electrode of the present invention is particularly suitable as an electrode for a discharge lamp. Further, for example, as recited in claim 2, the high melting point metal material is made of tungsten material, and tungsten material _{Y 2 O 3, La 2 O} 3, CeO 2, HfO 2, and A _x B _y O _z ( Here, A is at least one element selected from Hf and Sr, and B is Y, La and Ce.
At least one element selected from the group consisting of x, y and z
Represents an arbitrary integer), and preferably contains at least one oxide selected from the group consisting of: Further, as described in claim 3, the tungsten material preferably contains the above-mentioned oxide in a range of 1 to 4% by mass.

According to a sixth aspect of the present invention, there is provided a discharge lamp including a glass bulb and a pair of electrodes opposed to each other in the glass bulb. Is characterized by comprising the above-mentioned electrode of the present invention. According to another aspect of the present invention, there is provided a discharge lamp including a glass bulb, and a cathode and an anode disposed in the glass bulb so as to face each other. It is characterized by comprising the electrode of the present invention containing as a radioactive substance.

According to such a discharge lamp of the present invention,
Based on the above-described characteristics of the electrodes, it is possible to improve the luminous flux maintenance ratio and to suppress a decrease in lamp life due to blackening. The discharge lamp of the present invention is particularly effective for a high-pressure discharge lamp such as a metal halide lamp, a xenon lamp, and a high-pressure mercury lamp. However, the present invention is also applicable to a general lighting discharge lamp and the like.

According to a ninth aspect of the present invention, there is provided an optical apparatus comprising: a light source; and an optical system for irradiating an object to be processed with light emitted from the light source. And a high-pressure discharge lamp to which the discharge lamp of the present invention is applied. Specific examples of the optical device of the present invention include a movie theater projection device, a semiconductor exposure device, a laser device, and a liquid crystal projector.

[0018]

Embodiments of the present invention will be described below.

The electrode of the present invention is made of a high melting point metal material containing at least one oxide selected from rare earth oxides and composite oxides containing rare earth elements. As the refractory metal material, it is particularly preferable to use a tungsten material, but the material is not necessarily limited thereto, and a molybdenum material or the like may be used depending on the use of the electrode. Hereinafter, a case where a tungsten material is used as a typical example of the high melting point metal material will be mainly described.

The rare earth oxide and the composite oxide containing a rare earth element in the high melting point metal material are not particularly limited, and various rare earth element oxides,
Alternatively, composite oxides of various rare earth elements and transition metal elements can be used, and metal oxides having other electron emission characteristics can also be used.

When the electrode of the present invention is used as a cathode of a discharge lamp, for example, a rare earth oxide or a composite oxide containing a rare earth element contained in a tungsten material functions as an electron-emitting substance. In such a case, as a rare earth oxide, Y ₂ O ₃ (2.0 eV) having a small work function,
At least one selected from La ₂ O ₃ (2.8 eV) and CeO ₂ (3.21 eV) is preferably used.

The same applies to composite oxides containing rare earth elements.
HfO with small work function _Two(2.81eV) or Sr
Complex acid of O (1.27 to 1.4 eV) and the above rare earth oxide
Compound, such as HfLa_TwoO_FiveIt is preferable to use
No. That is, as a composite oxide containing a rare earth element,
A_xB_yO_z(Where A is selected from Hf and Sr
At least one element, B is from Y, La and Ce
X, y and z represent at least one selected element.
Is preferable.) Also this
HfO instead of_TwoMay be used.

When the electrode of the present invention is used as an anode of a discharge lamp, for example, a rare earth oxide or a composite oxide containing a rare earth element contained in a tungsten material functions as a damage preventing material for the anode. . According to a tungsten material containing a rare earth oxide or a composite oxide containing a rare earth element, damage to the tip of the anode due to long-time operation of the lamp can be suppressed as compared with conventional doped tungsten or the like.

When the electrode of the present invention is applied to an anode, the rare earth oxide or the composite oxide containing a rare earth element may be an oxide of various rare earth elements or a composite oxide of various rare earth elements and a transition metal element. However, it is particularly preferable to use Y ₂ O ₃ which is excellent in preventing damage to the anode.

The amount of the rare earth oxide or the composite oxide containing a rare earth element to be contained in the tungsten material or the like is appropriately set according to the intended use of the electrode. It is preferable to contain it in the range of 4% by mass. When the content of the rare earth oxide or the composite oxide is less than 1% by mass, the effect of the addition may not be sufficiently obtained. In particular, when the electrode of the present invention is used as a cathode, the content of the rare earth oxide or the composite oxide is 1% by mass.
If it is less than 3, the electron emission characteristics required for the cathode of the discharge lamp may not be sufficiently satisfied.

On the other hand, if the content of the rare earth oxide or composite oxide exceeds 4% by mass, their distribution becomes non-uniform. For example, when used for a cathode, an electron-emitting substance is rapidly deposited on the electrode surface. When the precipitates are scattered around, there is a possibility that the electrode temperature will increase and the electrodes will be consumed or deformed accordingly. These cause a reduction in the luminous flux maintenance rate of the discharge lamp and blackening of the lamp.

The electrode of the present invention is obtained by subjecting a tungsten powder containing the above-mentioned rare earth oxide or a composite oxide containing a rare earth element to a spark plasma sintering method (SPS method: Spar method).
k Plasma Sintering) to approximate electrode shape. That is, the electrode of the present invention has a high melting point metal material such as a tungsten material made of a discharge plasma sintered body.

The spark plasma sintering method uses a green compact (compact).
Pulse electric energy directly into the particle gap of
This is a method of sintering green compacts (compacts) at high density by effectively utilizing high-temperature energy of discharge plasma (high-temperature plasma) generated by spark discharge phenomenon for thermal diffusion, electric field diffusion, and the like. According to the spark plasma sintering method, a normal pressure sintering method, a hot press method, a hot isostatic sintering method (HIP
Method), a high-density sintered body can be obtained in a temperature range lower by about 200 to 500 ° C. and in a relatively short time as compared with a normal sintering method. Further, an electrode material having a shape close to the final shape of the electrode can be produced from the sintering principle.

Specifically, first, a tungsten powder (mixed powder) containing the above-mentioned rare earth oxide or a composite oxide containing a rare earth element at a predetermined composition ratio is prepared by, for example, using a carbon die and a pair of upper and lower punches. Into a mold
After a vacuum atmosphere in the apparatus, a power supply is connected and energized while applying pressure to the upper and lower punches. The tungsten powder (compact) filled in the mold is heated to a predetermined sintering temperature by discharge plasma generated by energization. By maintaining the pressure application state at the sintering temperature for a certain period of time, a high-density sintered body (electrode material) having a relative density of, for example, 94% or more can be obtained.

The mixed powder used as a sintering raw material is a mixture of a tungsten powder and a powder of a rare earth oxide or a composite oxide at a predetermined composition ratio, or a method of doping a rare earth oxide or a composite oxide (for example, Tungsten powder added by a solution doping method in which the oxide is added as a nitric acid solution of an oxide can be used. At this time, it is preferable that the rare earth oxide or the composite oxide is added so that the average particle diameter is 2 μm or less. Further, the sintering temperature is preferably in the range of 1550 to 1900 ° C. The sintering time is preferably about 0.2 to 1 hour.

According to the above-described discharge plasma sintering method, an electrode material having a shape close to the final shape of the electrode can be obtained as a high-density sintered body. It is possible to produce a high-density tungsten sintered body having a desired electrode shape, that is, an electrode suitable for use in a discharge lamp or the like, by merely performing a basic cutting process or the like.

An electrode (such as a high-density tungsten sintered body) obtained by a discharge plasma sintering method can obtain a desired density and shape without performing wire drawing as in a conventional electrode. Therefore, as shown in FIG. 1, the microstructure of the sintered body becomes an aggregate of granular W crystal grains A, and the density of the W crystal grains A can be increased while maintaining a fine state. It is possible. On the other hand, the conventional electrode subjected to the wire drawing has an elongated shape (needle-shaped crystal grains) in which the W crystal grains B extend in the axial direction, as shown in FIG.

In addition to increasing the density of the electrode (such as a discharge plasma sintered body of tungsten) (for example, having a relative density of 94% or more), the electrode has a fine and fine W crystal grain A. In addition, since the mechanical strength of the electrode itself can be increased, it is possible to suppress deformation and wear of the electrode for the discharge lamp. Further, since the coarsening of the W crystal grains A due to the lighting heat is suppressed based on the granulation or miniaturization of the W crystal grains A, the rapid precipitation and scattering of rare earth oxides and composite oxides are suppressed. Becomes possible. This contributes to the improvement of the luminous flux maintenance rate of the discharge lamp and the suppression of blackening, and also works effectively to reduce the temperature rise of the electrode. It greatly contributes.

As described above, an electrode made of a discharge plasma sintered body such as a tungsten material containing a rare earth oxide or a composite oxide is formed based on the sintering conditions, the shape and the grain size of the W crystal grains, and the processing steps. Thus, for example, deformation and consumption due to lighting heat or the like can be significantly suppressed. Further, rapid scattering of rare earth oxides or composite oxides contained in a tungsten material or the like can be suppressed. With these, for example, it is possible to improve the luminous flux maintenance factor of the discharge lamp, and it is possible to suppress a reduction in the life of the discharge lamp due to blackening.

Although the case where the electrode of the present invention is used as a cathode of a discharge lamp has been mainly described, the mechanical strength and damage resistance of the electrode of the present invention can be improved even when the electrode of the present invention is used as an anode. Based on the function of suppressing a rise in temperature, for example, damage to the tip of the anode due to long-time operation of the lamp can be reduced. This also makes it possible to achieve a longer life of the discharge lamp.

The electrode of the present invention is a metal halide lamp,
As described above, it is suitable for an electrode of a high-pressure discharge lamp such as a xenon lamp or a high-pressure mercury lamp, particularly a cathode, but is also applicable to an anode. Further, the electrode of the present invention is applicable not only to electrodes of a DC discharge lamp such as a high-pressure discharge lamp, but also to electrodes of an AC discharge lamp such as a general lighting discharge lamp.

Next, an embodiment of the discharge lamp of the present invention will be described.

FIG. 3 is a diagram showing a schematic structure of an embodiment in which the discharge lamp of the present invention is applied to a high-pressure discharge lamp such as a metal halide lamp, a xenon lamp, and an ultra-high pressure mercury lamp. In FIG. 1, reference numeral 1 denotes a bulb made of quartz glass or the like. This bulb 1 has a spherical or elliptical spherical discharge space 1a and a pair of branch pipes 1 communicating therewith.
b, 1b. The first and second electrode shafts 2 and 3 are housed in the branch pipes 1b and 1b, respectively.

The first electrode shaft 2 is made of a tungsten rod, and its tip is shaped into a conical shape to form the cathode 4. Such a cathode 4 comprises the electrode of the present invention. That is, the cathode 4 is constituted by an electrode formed of a discharge plasma sintered body of a tungsten material containing a rare-earth oxide or a composite oxide containing a rare-earth element as an electron-emitting substance.

The second electrode shaft 3 is made of a tungsten rod or the like, and an anode 5 is mounted on the tip thereof. The anode 5 is disposed to face the cathode 4 in the discharge space 1a of the bulb 1, and forms a pair of electrodes together with the cathode 4. The anode 5 may be composed of the electrode of the present invention, or may be composed of a conventional doped tungsten, for example, doped tungsten containing at least one selected from K, Si and Al in a range of 0.001 to 0.01% by mass. It is also possible. Also for the electrode made of doped tungsten, it is preferable to apply a high-density sintered body produced by spark plasma sintering.

The above-mentioned first and second electrode shafts 2, 3
The base ends thereof are sealed and fixed in the branch pipe 1 b of the bulb 1 via a quartz glass cylindrical member 6. A metal foil, for example, a molybdenum foil 7 is electrically connected to the first and second electrode shafts 2 and 3, and an external lead rod 8 is further electrically connected to these.

The branch terminal 1b of the bulb 1 is provided with a cathode terminal 9 and an anode terminal 10, respectively. The discharge space 1a of the sealed bulb 1 is filled with a discharge medium made of mercury and a rare gas such as argon or xenon, and these constitute a high-pressure discharge lamp 11.

As described above, according to the high-pressure discharge lamp 11 using the electrode of the present invention as the cathode 4, deformation and wear of the electrode and rapid scattering of the electron-emitting substance can be suppressed. It is possible to improve the luminous flux maintenance rate and extend the life. Such discharge lamps of the present invention include metal halide lamps, xenon lamps,
Although it is suitable for a high-pressure discharge lamp such as an ultra-high pressure mercury lamp, it is also applicable to a discharge lamp (fluorescent lamp) for general lighting. It is particularly effective for short arc type high pressure discharge lamps.

Next, an embodiment of the optical device of the present invention will be described. The optical device of the present invention includes a high-pressure discharge lamp to which the present invention is applied as a light source, and an optical system that irradiates the object to be processed with light emitted from the light source,
Specific examples are movie theater projection equipment, semiconductor exposure equipment,
Examples include a laser device and a liquid crystal projector. The high-pressure discharge lamp used as the light source is appropriately selected according to the type and use of the optical device.

FIG. 4 shows a semiconductor exposure apparatus as one embodiment of the optical apparatus of the present invention. In the figure, reference numeral 21 denotes a high-pressure discharge lamp to which the present invention described above is applied, and ultraviolet rays (for example, g
Is reflected by the elliptical mirror 22 and the specular reflection mirror 23, and then condensed by the aspheric lens 24 and the condenser lens 25. The condensed ultraviolet light passes through a regular reflection mirror 26 and a condenser lens 27, passes through a photomask 28, further passes through a reduction projection lens 29, and is irradiated on a semiconductor wafer 30. Thereby, the semiconductor wafer 3
0 is exposed in a predetermined pattern.

[0046]

Next, specific examples of the present invention will be described.

Example 1 and Comparative Example 1 First, tungsten powders having an average particle diameter of 1 μm and 2 μm were prepared, respectively, and La ₂ O ₃ was added by 2% by mass by applying a solution doping method (using a nitric acid solution). did. These La ₂
Tungsten powder containing O ₃ was set in a discharge plasma sintering apparatus, and each was subjected to discharge plasma sintering under the sintering conditions shown in Table 1 to produce electrode materials having a shape close to a desired electrode shape. Spark plasma sintering was performed in a vacuum atmosphere on the order of 1 Pa.

Each of these electrode materials was cut into a final shape to obtain a cathode for a high-pressure discharge lamp. Table 1 shows the relative density and crystal grain shape of each tungsten electrode obtained in this manner. Using these cathodes, a 250 W ultra-high pressure mercury lamp was assembled,
After the lamp was turned on for 00 hours, the degree of deformation of the electrode (cathode) and the luminous flux retention were measured and evaluated. Table 1 also shows the results. The lamp luminous flux maintenance ratio is the maintenance ratio of the i-line illuminance after lighting for 2000 hours.

The comparative example 1 in the table is provided for comparison with the present invention, and the conventional normal pressure sintering method (3000 ° C. ×
1 hour) and a rolling process including a wire drawing process. For each of these electrodes (cathodes), the relative density of the electrodes and the shape of the crystal grains were measured. Furthermore, using each of these cathodes, a 250 W ultra-high pressure mercury lamp was assembled, and the degree of deformation of the electrode (cathode) and the luminous flux maintenance rate after 2,000 hours of operation of the lamp were measured and evaluated.

[0050]

[Table 1] As is clear from Table 1, the ultrahigh-pressure mercury lamp using each tungsten electrode of Example 1 has a smaller degree of deformation of the electrode (cathode) and the luminous flux than the one using the tungsten electrode of Comparative Example 1. It can be seen that the retention rate is excellent.
This greatly contributes to extending the life of the high-pressure discharge lamp.

Example 2 In Example 1 described above, L was used as an electron-emitting substance.
Instead of a ₂ O ₃ , Y ₂ O ₃ , CeO ₂ , HfO ₂ , HfLa
Except for using ₂ O ₅ , a cathode for a high-pressure discharge lamp was produced in the same manner as in Example 1. The characteristics of each of these electrodes were measured and evaluated in the same manner as in Example 1. As a result, it was confirmed that good results were obtained as in Example 1.

Example 3 An anode for a high-pressure discharge lamp was manufactured in the same manner as in Example 2 except that the tungsten electrode containing Y ₂ O ₃ of Example 2 was manufactured according to the shape of the anode. When an ultra-high pressure mercury lamp was manufactured using this tungsten anode, it was confirmed that a long life could be achieved.

[0053]

As described above, according to the electrode of the present invention, even when it is used as an electrode of a high-pressure discharge lamp, for example, deformation and wear can be suppressed, and at the same time, rapid scattering of an electron-emitting substance can be achieved. Can be suppressed. Therefore, according to the discharge lamp of the present invention using such an electrode, it is possible to improve the luminous flux maintenance factor and to suppress a reduction in lamp life due to blackening. That is, it is possible to extend the life of the discharge lamp.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an example of the shape of crystal grains constituting an electrode of the present invention.

FIG. 2 is a diagram schematically showing an example of the shape of crystal grains constituting a conventional discharge lamp electrode.

FIG. 3 is a sectional view showing a schematic structure of one embodiment of a high-pressure discharge lamp to which the discharge lamp of the present invention is applied.

FIG. 4 is a diagram illustrating a configuration example of a semiconductor exposure apparatus as one embodiment of the optical device of the present invention.

[Description of Signs] 1... Bulb 2, 3... Electrode shaft 4... Cathode 5... Anode 11 and 21.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuhiro Iwato 4-3-1 Higashishinagawa, Shinagawa-ku, Tokyo F-term in Toshiba Lighting & Technology Corporation (reference) 5C015 JJ05 JJ06 KK02

Claims (9)

[Claims] 1. An electrode made of a high melting point metal material containing at least one oxide selected from a rare earth oxide and a composite oxide containing a rare earth element, and having a desired electrode shape, wherein the electrode shape is An electrode characterized in that the high-melting point metal material having the following is formed by a spark plasma sintering method. 2. The high melting point metal material is made of a tungsten material, and the tungsten material is made of Y ₂ O ₃ , La ₂ O ₃ , C
eO _2, HfO _2, and A _x B _y O _z (However, A is Hf
And B represents at least one element selected from Y, La and Ce, and x, y and z represent any integers. The electrode according to claim 1, comprising: 3. The tungsten material according to claim 1, wherein the oxide is
2. The composition according to claim 1, wherein the content is in the range of 4 to 4% by mass.
Or the electrode according to claim 2. 4. The electrode according to claim 1, wherein the tungsten material has granular crystal grains. 5. The electrode according to claim 1, wherein the tungsten material has a relative density of 94% or more. 6. A discharge lamp comprising a glass bulb and a pair of electrodes opposed to each other in the glass bulb, wherein at least one of the pair of electrodes is at least one of the electrodes.
A discharge lamp comprising the electrode according to any one of the preceding claims. 7. A discharge lamp comprising a glass bulb, and a cathode and an anode disposed in the glass bulb so as to face each other, wherein the cathode contains the oxide as an electron-emitting substance. A discharge lamp comprising the electrode according to claim 1. 8. The discharge lamp according to claim 6, wherein the discharge lamp is a high-pressure discharge lamp. 9. An optical device comprising: a light source; and an optical system for irradiating the object with light emitted from the light source, wherein the light source includes the high-pressure discharge lamp according to claim 8. Optical device.