JP2011187376A - Discharge lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp which has stable diffusion of emitters and has a stable electrode strength. <P>SOLUTION: The discharge lamp includes a cathode 20 in which a sintered layer (sintered body) 24 consisting of a plurality of density gradient layers 26 is installed at the electrode tip part 23. The density gradient layer 26 is formed by compression inserting a mixed powder of an emitter powder such as barium oxide and a high melting-point metal powder such as tungsten into a recessed part 25 of the cathode 20 gradually and then, by SPS sintering integrally. The sintered body is inclined in each layer and its density is reduced continuously from the electrode tip side toward the electrode rear side. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a discharge lamp in which an electrode is disposed in an arc tube, and more particularly to a structure of an electrode tip portion and a manufacturing method thereof.

  A sintered body containing an emitter (electron emitting material) such as thorium oxide or barium oxide is embedded in the tip of the cathode of the discharge lamp in order to improve lamp startability. As a manufacturing method thereof, there is known a method in which a mixed powder of an emitter powder and a tungsten powder is inserted into a recess formed in an electrode tip portion and then sintered, instead of sintering first (Patent Document). 1).

  The method in which such powder is pressed into the tip and then integrally sintered with the electrode is performed for the purpose of suppressing emitter evaporation and easily manufacturing the cathode. When an integral sintering process with the electrode is performed, a swage process (forging process) is performed.

Japanese Patent No. 3269408 (see paragraphs [0018], [0019], etc.)

  In Patent Document 1, pressure insertion of a mixed powder in consideration of the density distribution of the sintered body is not performed. Therefore, a locally high density region is generated inside the sintered body, while a low density region is partially present, and the density change is severe. In general, the density becomes very high in the vicinity of the electrode tip surface, but the low density portions are irregularly scattered in the vicinity of the bottom surface of the recess.

  Therefore, the supply of the emitter is interrupted at the low density portion while the lamp is lit, and there is a possibility that the emitter cannot be supplied to the cathode tip for lubrication. Further, when the emitter is supplied excessively from the low density portion, the emitter diffusion is reduced and the life of the lamp is shortened.

  On the other hand, since the density distribution is not uniform as a whole, the electrode strength at the tip of the electrode is insufficient, and the electrode is easily deformed. Furthermore, as a result of the electrode tip becoming hot during lighting, the electrode tends to be thermally deformed at a high density portion, and the balance of electrode strength may be lost.

  Thus, for an electrode including an emitter, a stable emitter supply and an electrode structure having a stable strength are required.

  The discharge lamp of the present invention includes a discharge vessel and a pair of electrodes disposed in the discharge vessel, and at least one of the electrodes (for example, a cathode) has a sintered body containing an electron-emitting substance at the tip. For example, the electrode shape has a cylindrical body portion and a tip having a tapered surface, and is a structure along the electrode axis in a state where a part of the sintered body is partially exposed to face the other electrode. In order to increase the density of the electron radioactive substance at the tip, a flat surface may be formed at the tip of the electrode.

  In the present invention, the sintered body is inclined so that the density decreases from the electrode front end side toward the electrode rear end side. Here, the term “grading” means “integrated material that changes spatially from one function / characteristic to another function / characteristic continuously or stepwise” (“Technological development of functionally graded materials” ( Edited by Seiichi Uemura et al., CMC Publishing, published on October 31, 2003)), and the sintered body of the present invention has a continuous density gradient and has continuous characteristics (such as supply characteristics and strength of electron-emitting materials). It is configured to change.

  Unlike a conventional electrode structure, that is, an electrode structure with non-uniform density, or an electrode structure with a concentration gradient in which the concentration (ratio) of the electron-emitting material is increased on the rear end side of the electrode, in the present invention, The density continuously changes and has a density distribution that continuously decreases in the direction from the electrode front end side to the electrode rear end side.

  Since there are no sudden density changes in the sintered body, such as irregular low-density areas or high-density areas, the electron-emitting material (emitter) does not break off while the lamp is on. Stable supply. Further, since the sintered body has a continuous and stable density distribution structure, the strength of the electrode tip is maintained in a well-balanced manner.

  Considering the stable supply of the electron-emitting material, the temperature resistance performance of the electrode, and the like, the sintered body is, for example, an electron-emitting material made of an alkali-based oxide or the like and a crystal of a refractory metal such as tungsten. For the production of the sintered body, the powder containing the electron-emitting material is compressed and sintered integrally with the electrode, or the powder compressed body is first sintered and the sintered body is placed on the tip of the electrode. A method of burying is conceivable. In consideration of ensuring the continuous density change and ensuring the strength of the electrode structure, it is desirable to sinter the compression body integrally with the electrode.

  Therefore, it is preferable to sinter a powder compact containing an electron-emitting substance integrally with the electrode to form a sintered compact. For example, it is preferable to compress and insert a powder containing an electron-emitting material into the recess at the tip of the electrode, and then sinter and mold it integrally with the electrode.

  The sintered body may have a single layer structure in which the density is entirely graded, or may have a laminated structure including a plurality of layers. In order to stably supply the emitter and improve the strength of the electrode tip, it is desirable to employ a laminated structure in which a plurality of layers are stacked. In this case, the density of the sintered body decreases for each layer from the electrode front end side to the electrode rear end side.

  When the sintered body is constituted by a plurality of layers, a mixed powder of the electron-emitting material powder and the refractory metal powder may be laminated. In the case of sintering after compression, the mixed powder is compressed and inserted into the concave portion of the tip every predetermined thickness, and the laminated powder is sintered. At this time, the electron-emitting substance and the refractory metal are preferably distributed uniformly in each layer so as not to cause a concentration gradient in one of the substances.

  Alternatively, the sintered body may be configured by alternately laminating layers made of electron-emitting material powder and layers made of refractory metal powder. In consideration of improving the strength of the electrode tip, the thickness of the layer made of the refractory metal powder is relatively smaller as compared to the layer made of the electron-emitting material powder as the distance from the electrode tip side increases. do it. On the other hand, when the electron-emitting substance is concentrated on the tip, the thickness of the layer made of the refractory metal powder is made relatively larger as the distance from the electrode tip side becomes larger than the layer made of the electron-emitting substance powder. It is good.

  While the lamp is lit, the tip of the electrode becomes hot and easily deforms. In consideration of preventing distortion due to thermal expansion, it is desirable to provide a gap between the layers of the sintered body. As described above, when the powder is compressed and inserted for each layer, a gap can be formed between the layers.

In the case of a small short arc discharge lamp or the like, the diameter of the tip portion of the electrode becomes small, and it is necessary to effectively compress and insert the powder of the electron radioactive material. For example, when the diameter of the recess formed in the electrode tip is D and the thickness of each layer forming the sintered body provided in the recess is H, the thickness of the layer is set so as to satisfy the following formula: Is good.

H / D ≦ 3

  An electrode for a discharge lamp according to another aspect of the present invention has a tip end surface, and a sintered body containing an electron-emitting substance has a tapered tip portion embedded in a recess formed in the tip surface. However, it is characterized by being inclined so that the density continuously decreases from the electrode front end side toward the electrode rear end side.

  According to another aspect of the present invention, there is provided a method for producing an electrode, wherein at least one of a powder containing an electron-emitting substance, a powder containing a refractory metal, and a mixed powder thereof is formed at the tip of the electrode member. The electrode member is sintered in a state in which the powder is compressed and inserted into the recessed portion and the powder is compressed and inserted. At the time of compression insertion, a plurality of pressures are applied to the powder based on a predetermined compression force at predetermined time intervals so that the density of the powder sintered body continuously decreases from the electrode front end side toward the electrode rear end side. It is characterized by being repeated a number of times.

  The cathode tip is generally small in size and difficult to compress and insert powder. For example, in the case of a small short arc discharge lamp having a small electrode size and a short electrode interval (electrode interval: about 3 mm), the diameter of the recess formed at the electrode tip is very small (about 0.7 mm to 10 mm). . In the present invention, the density gradient of the sintered body is formed by repeatedly pressing the powder a plurality of times. As the powder, a mixed powder of an electron-emitting substance and a refractory metal may be sequentially compressed at a predetermined thickness so as to be laminated, or a powder of an electron-emitting substance and a powder of a refractory metal are separately compressed. However, they may be laminated.

  The compression force, time interval, and number of compressions may be determined according to the electrode size, powder particle size, and the like. For example, the predetermined compression force may be set to 151 MPa or more, the pressurization period may be set to 1 second or less, the predetermined time interval may be set to 0.1 to 3 seconds, and the number of pressurizations may be set to 20 or more. As a sintering method, for example, sintering may be performed by spark plasma sintering.

  According to the present invention, stable emitter diffusion and stable electrode strength can be provided.

It is a schematic sectional drawing of the short arc type discharge lamp which is 1st Embodiment. It is a fragmentary sectional view of the cathode along an electrode axis. It is cathode sectional drawing of the discharge lamp which is 2nd Embodiment. It is cathode sectional drawing of the discharge lamp which is 3rd Embodiment. It is cathode sectional drawing of the discharge lamp which is 4th Embodiment. It is cathode sectional drawing of the discharge lamp which is 5th Embodiment. FIG. 3 is a diagram showing the distribution of emitters and tungsten inside a sintered layer in Example 1. It is the figure which showed the microscope picture of the sintered layer. FIG. 9 is an enlarged photograph of FIG. 8 showing a high density portion and a low density portion of a sintered layer. It is the figure which showed the compression rate when changing the filling amount of the mixed powder at the time of compression processing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of a short arc type discharge lamp according to a first embodiment.

  The short arc type discharge lamp 10 includes an arc tube 12 made of transparent quartz glass, and a cathode 20 and an anode 30 are disposed in the arc tube 12 so as to face each other with a predetermined interval. On both sides of the arc tube 12, quartz glass sealing tubes 13 </ b> A and 13 </ b> B are connected to the arc tube 12 and are integrally formed. The arc tube 12 is filled with rare gas such as mercury and argon gas.

  Conductive electrode support rods 17A and 17B that support the cathode 20 and the anode 30 are disposed inside the sealing tubes 13A and 13B. The electrode support rods 17A and 17B are connected to conductive lead rods 15A and 15B through metal foils 16A and 16B, respectively. The sealing tubes 13A and 13B are welded to the metal foils 16A and 16B, respectively, whereby the arc tube 12 is sealed and both ends thereof are closed by the caps 19A and 19B.

  The lead bars 15A and 15B are connected to an external power source (not shown), and power is supplied to the cathode 20 and the anode 30 via the lead bars 15A and 15B. When a voltage is applied between the cathode 20 and the anode 30, an arc discharge is generated between the electrodes of the cathode 20 and the anode 30, and light is emitted toward the outside of the arc tube 12.

  FIG. 2 is a partial cross-sectional view of the cathode along the electrode axis.

  The cathode 20 is an electrode in which an electrode body 21 is integrally provided with a sintered body (hereinafter referred to as a sintered layer) including an emitter (electron-emitting substance). The electrode body 21 includes a cylindrical body portion 22 supported by the electrode support rod 17A on the rear end side away from the anode 30, and a conical tip portion 23 having a tapered surface 23T and a tip surface 23S facing the anode. The A bottomed cylindrical recess 25 is formed in the tip 23 along the electrode axis E from the tip surface 23S, and a sintered layer (sintered body) 24 is embedded in the recess 25. The upper end of the sintered layer 24 is exposed from the cathode 20 and constitutes a part of the tip surface 23S.

  The sintered layer 24 extending along the electrode axis E has a laminated structure composed of a plurality of layers. Each layer 26 is formed by sintering and molding a mixed powder obtained by mixing a powder of a high melting point metal such as tungsten (W) and an emitter powder containing an alkaline oxide such as barium oxide or thorium oxide. ing. The thickness of each layer 26 is substantially constant.

  In each layer 26 of the sintered layer 24, the sintered body is inclined from the electrode front end surface 23S toward the rear end side of the electrode body 21. More specifically, the density of each layer 26 continuously decreases along the electrode axis E, and the rate of change thereof has a constant distribution (hereinafter, each layer is referred to as a density gradient layer). The density gradient layer 26 has a crystal structure in which refractory metals and emitters are mixed almost uniformly. A minute gap QS exists between adjacent layers. When the lamp lighting is started, the emitter in the sintered layer 24 diffuses toward the tip surface 23S.

  A manufacturing process of such a cathode 20 will be described. First, the emitter powder and the high melting point powder are mixed using a meal ball or the like, the mixed powder is inserted into the recess 25 by a predetermined amount, and the compressed mixed powder layer is laminated step by step.

  In the compression treatment in each layer, one pressing force (compression force) on the mixed powder, one pressurization period, pressurization time interval, and the number of pressurization repetitions are determined, but the density of the mixed powder is continuous. It may be determined so as to change depending on the size, and is determined according to the size of the recess 25, the particle size of the refractory metal powder and the emitter powder and the like. For example, when the diameter of the recess 25 is approximately 0.7 mm to 10 mm, the compression force is 50 N (corresponding to 151 MPa when a pin having a diameter of 0.65 mm is used for compression) or more, and one compression period is 1 The compression time interval (frequency) can be set within a range of 0.1 to 3 seconds or less (for example, 0.1 second), and the number of compression iterations can be set to 20 or more.

  The thickness of the density gradient layer 26 is set to 2 mm or less in consideration of achieving a continuous change in density and reducing the total number of compression processes (number of laminations). After the compression process is performed for each layer, the sintering process is performed. As the sintering treatment, diffusion bonding such as arc discharge overheating, high-frequency heating, or discharge plasma sintering (SPS) is possible, and the sintering treatment is performed at a high temperature of 1000 ° C. or higher and in an inert gas atmosphere.

  As described above, according to the present embodiment, the discharge lamp 10 includes the cathode 20 in which the sintered layer 24 including the plurality of density gradient layers 26 is provided at the electrode tip portion 23. The sintered layer 24 is formed by compressively inserting a mixed powder of an emitter powder such as barium oxide and a refractory metal powder such as tungsten into the concave portion 25 of the cathode 20 and then SPS sintering integrally. . In each layer, the sintered body is inclined, and the density continuously decreases from the electrode front end side toward the electrode rear end side.

  Inclination of the sintered body, that is, the density gradient is almost constant, and the low density and high density regions are irregular and partially not scattered. Therefore, it is possible to suppress a decrease in emitter diffusion while the lamp is lit, and to prevent the supply of the emitter from being suddenly interrupted.

  In addition, because the sintered body is formed by laminating compressed layers that continuously change from high density to low density, the strength balance of the entire sintered layer is prevented from being biased, and the strength of the electrode tip is maintained in a balanced manner. The Such a configuration can prevent electrode deformation due to thermal expansion while the lamp is lit, and can stably maintain the balance of the strength of the electrode tip even at high temperatures. Further, the concentration gradient of the emitter or the refractory metal does not occur in each sintered layer, and the strength of the electrode tip is further stabilized by mixing both substances almost uniformly.

  Further, since a gap QS is generated between adjacent layers, the gap QS absorbs the expansion and prevents the sintered layer from being pushed out when the electrode tip portion thermally expands in the axial direction during lamp lighting. Can do. Further, the emitter can be prevented from overflowing excessively due to thermal expansion by the gap.

  The thickness of each sintered layer can be arbitrarily set under the condition that the mixed powder can be sufficiently compressed and inserted so that the density continuously changes. When the thickness of each layer is H and the diameter of the recess is D, the thickness is preferably determined so that the ratio H / D satisfies a relationship of 3 or less (H / D ≦ 3).

  Next, the discharge lamp which is 2nd Embodiment is demonstrated using FIG. In the second embodiment, the refractory metal powder constituting the emitter layer and the emitter powder are laminated separately. Other configurations are substantially the same as those in the first embodiment.

  FIG. 3 is a cross-sectional view of the cathode of the discharge lamp according to the second embodiment.

  The cathode 120 is an electrode in which a sintered layer 124 is integrally embedded in the cathode body 121. The sintered layer 124 has a structure in which layers 126A produced by sintering from a refractory metal powder such as tungsten and emitter layers 126B produced by sintering from an alkaline oxide powder such as barium oxide are alternately laminated. ing. Inside each layer, the metal density is inclined as in the first embodiment. That is, the density continuously decreases in the direction away from the electrode tip.

  The thickness of the refractory metal layer 126A in the electrode axis direction is larger than that of the emitter layer 126B. The thickness of the refractory metal layer 126A in the electrode axial direction and the thickness of the emitter layer 126B are constant.

  As a manufacturing process of the cathode 120, the high melting point metal powder is pressure-inserted into the recess as it is, and then the emitter powder is pressure-inserted thereon. By repeating the sintering process after repeating this process, the sintered layer shown in FIG. 3 is formed.

  Thus, by laminating and tilting each type of metal powder, diffusion of the emitter during lighting can be maintained and electrode deformation can be prevented.

  Next, the discharge lamp which is 3rd Embodiment is demonstrated using FIG. In the third embodiment, the thickness of the refractory metal layer changes. About another structure, it is the same as 2nd Embodiment.

  FIG. 4 is a cross-sectional view of the cathode of the discharge lamp according to the third embodiment. In the cathode 120 ', a sintered layer 124' is integrally formed with the cathode body 121 '. The sintered layer 124 'has a structure in which refractory metal layers 126A' and emitter layers 126B 'are alternately stacked.

  The thickness of the refractory metal layer 126A 'such as tungsten is larger as it is closer to the tip surface of the electrode. As a result, the strength increases near the electrode tip surface. On the other hand, since the proportion of the bottom of the emitter layer is large, the diffusion of the emitter at the start of the lamp tends to spread.

  Next, the discharge lamp which is 4th Embodiment is demonstrated using FIG. In the fourth embodiment, the refractory metal layer becomes thicker toward the bottom. About another structure, it is substantially the same as 3rd Embodiment.

  FIG. 5 is a cross-sectional view of the cathode of a discharge lamp according to the fourth embodiment. In the cathode 120 ″, a sintered layer 124 ″ is integrally formed with the cathode body 121 ″. The thickness of the refractory metal layer 126A ″ increases as the distance from the electrode tip surface increases. As a result, the proportion of the emitter layer 126 ″ increases in the vicinity of the tip, and the emitter is sufficiently supplied.

  Next, the discharge lamp which is 5th Embodiment is demonstrated using FIG. In the fifth embodiment, the sintered layer is formed by a single layer. About another structure, it is substantially the same as 1st Embodiment.

  FIG. 6 is a cross-sectional view of the cathode of the discharge lamp according to the fifth embodiment. An emitter sintered layer 224 is formed at the tip of the cathode 220. The sintered layer 224 is not a laminated structure but a single layer, and is produced by press-inserting a mixed powder of a refractory metal powder and an emitter powder into the electrode tip and sintering.

  In the emitter sintered layer 224, the refractory metal and the emitter are uniformly mixed, and the density continuously decreases as the distance from the electrode tip surface increases. Even with such an electrode structure, as in the first embodiment, stable supply of the emitter and prevention of electrode deformation can be realized.

  If the strength of the electrode can be ensured, the emitter powder may be compressed and sintered so as to be inclined first, and the sintered product may be embedded in the tip of the electrode. Moreover, you may use sintering methods other than SPS sintering. The emitter powder may be a powder made of a substance other than an alkaline oxide, or a refractory metal other than tungsten. The sintered body may have a crystal structure in which an emitter diffusion path is formed.

  The electrode tip may have a cone shape that does not form a tip surface. In addition to the cathode, a sintered body may be embedded in the anode or both electrodes. Furthermore, it is also possible to apply to a short arc type discharge lamp other than a small size.

  Hereinafter, the discharge lamp which is an Example is demonstrated using FIGS. 7-9. Here, a cathode in which the laminated sintered layer shown in the first embodiment was embedded was manufactured, and a lighting experiment was performed.

  The discharge lamp of the example is a small discharge lamp in which mercury and xenon having an electric power of 500 W are enclosed, and is defined as a gap of 3 mm, a sintered layer length of 3 mm, a sintered layer diameter of 1 mm, and a cathode and an anode diameter of 6 mm.

  For cathode production, emitter powder and tungsten powder were prepared and mixed. The tungsten powder is a mixture of 10 μm particle size, 4 μm particle size, and 1 μm particle size in 70% weight, 20% weight, and 10% weight, respectively. Emitter powder is powdered by mixing BaCO3, SrCO3, CaCO3, and WO3 at a ratio of 1.8 moles, 0.2 moles, 1.0 moles, and 1.0 moles, respectively, after firing at 1000 to 2000 ° C., followed by pulverization did. Both are mixed using a ball mill.

  The tungsten powder and the emitter powder stored in an inert gas atmosphere were mixed using a ball mill or the like at a ratio of 90% weight and 10% weight, respectively. Thereafter, the mixed powder was compressed and inserted into the recess formed in the tip surface of the cylindrical electrode member.

  In the compression stroke, the compression force of one time is set to 300 N (corresponding to 904 MPa when a pin having a diameter of 0.65 mm is used for compression), and is suppressed by a press machine for about 0.1 second at intervals of 1 second. Such pressurization is repeated about 100 times, and the density-graded layer of the mixed powder is laminated. The layers were laminated so that the thickness of each layer was about 0.5 mm.

  After the compression treatment, the sintering treatment was performed in the vicinity of 1000 ° C. for about 10 minutes under an inert gas atmosphere. Here, the sintering process was performed by a conventionally known discharge plasma sintering method.

  FIG. 7 is a diagram showing the distribution of emitters and tungsten in the sintered layer in the example. FIG. 8 is a view showing a micrograph of the sintered layer. FIG. 9 is an enlarged photograph of FIG. 8 showing a high density portion and a low density portion of the sintered layer.

  In the sintered layer shown in FIG. 8, the left side is the electrode tip surface side, and the mixed powder is compressed and inserted in order from the right side layer and fired. The higher the density, the higher the luminance. In each density gradient layer, a portion with high luminance exists on the electrode front end side, the luminance gradually decreases, and the luminance decreases on the electrode bottom side (rear end side). Therefore, it can be seen that the density continuously decreases from the electrode tip surface toward the bottom.

  FIG. 7 shows the occupation ratio of tungsten and emitter in the density gradient layer. The horizontal axis represents the gray scale (0 to 255) of the image. The vertical axis represents the total number of pixels at each luminance level and corresponds to the occupation ratio of the entire image. It can be seen that tungsten and emitters exist almost uniformly in the upper and lower portions of the density gradient layer. In addition, it can be confirmed that there are relatively many voids serving as diffusion paths of the emitter in the lower layer compared to the upper layer, and the density is lower in the lower layer.

  FIG. 9 shows an enlarged photograph of a portion that becomes a boundary between two adjacent layers. As shown in FIG. 9, it is confirmed that a gap is generated between the layers by the sintering process after the mixed powder is compressed and inserted.

  When the discharge lamp manufactured by the above manufacturing method was lit, deformation of the cathode tip was suppressed even after 1500 hours of lighting. Moreover, as a result of measuring light illuminance with a wavelength of 248 nm, it was possible to obtain a maintenance rate of 70%.

  On the other hand, in the case of a cathode in which the mixed powder is inserted at the tip of the electrode at a time, and the sintered body without inclination is formed by compressing only once, only a maintenance rate of 50% can be achieved after 1500 hours of lighting. There wasn't. When the internal structure of the electrode tip was examined with an electron micrograph (not shown here), the density of the sintered body at the electrode tip was unevenly distributed, and irregularly large voids were generated, resulting in rapid density changes. I understood it.

  The discharge lamp of Example 2 will be described with reference to FIG. Here, the compression ratio when the thickness of each layer of the sintered body layer was changed was measured.

  FIG. 10 is a diagram showing the compression rate when the filling amount of the mixed powder during the compression process is changed. The compression rate is determined from the thickness of the powder after compression insertion. FIG. 10 shows the compression ratio when the compression force is changed to 500N, 300N, and 100N. The size of the sintered layer is the same size as in Example 1, and the sintered layer length is 3 mm and the sintered layer diameter is 1 mm.

  As shown in FIG. 10, it was proved that the compressibility was relatively high when the thickness of the layer was 2.0 mm or less at each compressive force.

10 Short arc type discharge lamp 12 Arc tube (discharge vessel)
DESCRIPTION OF SYMBOLS 20 Cathode 21 Cathode main body 22 Body part 23 Cathode front-end | tip part 23S Cathode front end surface 24 Sintered layer (sintered body)
26 Density gradient layer (layer)
QS gap

Claims (15)

A discharge vessel;
A pair of electrodes disposed in the discharge vessel,
At least one of the electrodes has a sintered body containing an electron-emitting substance at the tip,
A discharge lamp characterized in that the sintered body is inclined so that the density continuously decreases from the electrode front end side toward the electrode rear end side.   2. The discharge lamp according to claim 1, wherein the sintered body is formed by sintering a powder compact including an electron-emitting substance integrally with the electrode. The sintered body has a laminated structure composed of a plurality of layers,
The discharge lamp according to claim 1, wherein the sintered body is inclined in each layer.   The discharge lamp according to claim 3, wherein each layer of the sintered body is a layer made of a mixed powder of an electron-emitting material powder and a refractory metal powder.   4. The discharge lamp according to claim 3, wherein the sintered body has a structure in which layers made of an electron-emitting material powder and layers made of a refractory metal powder are alternately laminated.   6. The discharge lamp according to claim 5, wherein the thickness of the layer made of the refractory metal powder becomes relatively smaller as the distance from the tip side of the electrode becomes smaller than the layer made of the electron-emitting material powder.   6. The discharge lamp according to claim 5, wherein the thickness of the layer made of the refractory metal powder becomes relatively larger as the distance from the electrode tip side becomes larger than the layer made of the electron-emitting material powder.   The discharge lamp according to any one of claims 1 to 7, wherein a gap is formed between the layers of the sintered body.   The discharge lamp according to claim 1, wherein the sintered body has a single-layer structure. The following formula is satisfied, where D is the diameter of the recess formed in the tip of the electrode, and H is the thickness of each layer of the sintered body provided in the recess. A discharge lamp according to claim 1.

H / D ≦ 3
  The discharge lamp according to claim 1, wherein the electrode has a flat surface at the tip. A body portion supported by an electrode support rod;
A tapered tip having a tip surface;
A sintered body containing an electron radioactive substance is provided in a recess formed in the tip surface,
An electrode for a discharge lamp, wherein the sintered body is inclined so that the density continuously decreases from the electrode front end side toward the electrode rear end side. At least one of a powder containing an electron radioactive substance, a powder containing a refractory metal, and a mixed powder thereof is compressed and inserted into a recess formed at the tip of the electrode member,
An electrode manufacturing method for sintering the electrode member in a state where the powder is compressed and inserted,
In compression insertion, a predetermined compressive force is applied to the powder based on one predetermined pressurization period so that the density of the sintered body of the powder continuously decreases from the electrode front end side to the electrode rear end side. A method for producing an electrode, wherein the pressure is repeated a plurality of times at predetermined time intervals.   The predetermined compression force is 151 MPa or more, the predetermined time interval is within a range of 0.1 to 3 seconds, the predetermined pressurization period is 1 second or less, and the predetermined number of times is 20 or more. The method for producing an electrode according to claim 13. The method for manufacturing an electrode according to claim 13, wherein the sintering is spark plasma sintering (SPS).