JP7193676B1 - discharge lamp - Google Patents

Abstract

Kind Code: A1 A discharge lamp is provided in which a coating is applied to the surface of an electrode so that the coating function can be effectively exhibited during lamp operation. A discharge lamp (10) has a coating layer (44) formed on the surface of a body (34) of an electrode (30). It has a concentration distribution such that the amount of tungsten particles adhered along the electrode axis C increases toward the tip of the electrode. [Selection drawing] Fig. 2

Description

The present invention relates to discharge lamps, such as short arc discharge lamps, and in particular to coatings on electrode surfaces.

When the discharge lamp is lit, the tip of the electrode reaches a high temperature, and the electrode material such as tungsten melts and evaporates, blackening the discharge tube, and lowering the illumination of the lamp. In order to prevent overheating of the electrode, including the electrode tip, for example, the side surface of the electrode body is formed with a threaded groove to increase the surface area, and tungsten powder is sintered on the groove to form a heat dissipation layer ( See Patent Document 1).

Also, a discharge lamp is known in which a heat radiating member is sintered to an electrode main body (see Patent Document 2). Here, a hollow cylindrical heat dissipation member made of a ceramic material having a higher thermal conductivity than the electrode main body is sintered to the electrode main body, and heat is dissipated from the side surface of the electrode, thereby suppressing an increase in electrode temperature.

JP-A-2000-306546 JP 2008-186790 A

During lamp operation, electrode overheating evaporates a portion of the electrode material (such as tungsten), and a portion of the vapor adheres to the electrode surface. This is the same even if the electrode surface is formed on the surface of a heat radiating member made of a ceramic material. Adhesion of such an electrode material to the electrode surface leads to deterioration of the heat dissipation function of the ceramic material.

Therefore, there is a need to provide a discharge lamp that can effectively dissipate heat from the electrode surfaces during lamp operation.

A discharge lamp, which is one aspect of the present invention, comprises a discharge tube and a pair of electrodes arranged opposite to each other in the discharge tube, wherein at least one of the electrodes contains a coating layer containing ceramics and having tungsten adhered to the layer surface. is formed on at least a part of the electrode body surface, and in the coating layer, the amount of tungsten adhering to a portion near the electrode tip side is the same as the amount of tungsten adhering to a portion near the electrode support rod side Relatively more than quantity.

The coating layer can be formed at various positions, and for example, the coating layer can be formed on the surface of the electrode body so as to straddle the central portion of the electrode in the axial direction. In this case, the amount of tungsten attached to the layer surface closer to the tip of the electrode than the central portion in the axial direction is greater than the amount of tungsten attached to the layer surface closer to the electrode support rod than the central portion in the axial direction. It can be configured to have more.

Various modes are possible for the method of providing a difference in the amount of deposited tungsten between the electrode tip side and the electrode support rod side, and it is possible to have a defined concentration distribution. For example, in the coating layer, it is possible to determine the deposition amount of tungsten so as to have a gradation in which the deposition amount of tungsten gradually increases from the electrode supporting rod side toward the electrode tip side.

The coating layer includes a single coating layer containing one or more ceramics as a material and a plurality of coating layers. In addition, with respect to a plurality of coating layers, each layer includes one ceramic as a material, or a plurality of ceramics.

The configuration of multiple coating layers can vary, for example, one coating layer (e.g. bottom layer) contains ceramics and electrode material (tungsten, molybdenum, etc.) while another coating layer (e.g. bottom layer) contains The coating layer to be formed) can be configured to contain only the ceramic component or components other than the ceramic and the electrode material. Alternatively, it is also possible to configure a plurality of coating layers with different components on the electrode front end side and the electrode rear end side along the lamp axial direction.

The ceramics contained in the coating layer may consist of at least one of nitrides, oxides, borides, carbides and silicides. That is, it can be made of one of nitrides, oxides, borides, carbides, and silicides, or two or more ceramics.

For example, the ceramics can be composed of at least one of silicon nitride, aluminum nitride, zirconium nitride, aluminum oxide, zirconium oxide, zirconium carbide, silicon carbide, tantalum silicide, and zirconium boride.

The coating layer can be chromatic. For example, a chromatic color can be obtained by adjusting the atomic concentration ratio of nitrogen to zirconium in zirconium nitride in the range of 0.2<N/Zr<0.9.

Advantageous Effects of Invention According to the present invention, it is possible to provide a discharge lamp that can effectively exhibit a heat dissipation function during lamp lighting.

1 is a schematic plan view of a discharge lamp according to this embodiment; FIG. FIG. 4 is a schematic plan view partially showing an electrode of the present embodiment; 4 is a graph showing illuminance maintenance ratios of Examples and Comparative Examples.

The short-arc discharge lamp 10 is a large-sized discharge lamp capable of outputting high-intensity light, and includes a substantially spherical discharge tube (arc tube) 12 made of transparent quartz glass. A pair of electrodes 20 and 30 are arranged facing each other (coaxially). On both sides of the discharge tube 12, quartz glass sealing tubes 13A and 13B are connected to the discharge tube 12 and integrally formed. A discharge space DS in the discharge tube 12 is filled with mercury and a rare gas such as halogen or argon gas.

Electrode 20, which is a cathode, is supported by electrode support rod 17A. The sealing tube 13A includes a glass tube (not shown) through which the electrode support rod 17A is inserted, a lead rod 15A connected to an external power source, a metal foil 16A connecting the electrode support rod 17A and the lead rod 15A, and the like. Sealed. Similarly, for the electrode 30, which is the anode, mount parts such as a glass tube (not shown) through which the electrode support rod 17B is inserted, the metal foil 16B, and the lead rod 15B are sealed. In addition, caps 19A and 19B are attached to the ends of the sealing tubes 13A and 13B, respectively.

When a voltage is applied to the pair of electrodes 20 , 30 , arc discharge is generated between the electrodes 20 , 30 and light is emitted outside the discharge tube 12 . Here, power of 1 kW or more is applied. Light emitted from the discharge tube 12 is guided in a predetermined direction by a reflecting mirror (not shown).

FIG. 2 is a schematic plan view partially showing the electrode (anode) 30. FIG. The electrode (cathode) 20 can also have a similar structure.

The electrode 30 has an electrode distal end surface 32T and is composed of a tapered portion (hereinafter referred to as a distal tapered portion) 32 and a columnar portion (hereinafter referred to as a trunk portion) 34 connected to the electrode support rod 17B. . The electrode 30 can be made of tungsten, molybdenum, or alloys thereof. Here, the electrode 30 is constructed integrally.

A coating layer 44 is formed on the side surface 34S of the body portion 34 . Here, the coating layer 44 is formed over the entire body portion 34, that is, from the electrode tip side end portion 34E1 of the body portion 34 to the electrode support rod side end portion (not shown in FIG. 2). In addition, in FIG. 2, the coated portion is indicated by oblique lines.

The coating layer 44 is configured as a coating layer containing ceramics having thermal performance (including heat resistance and heat dissipation). In particular, a high melting point of 2000° C. or higher is preferable, and ceramics include nitrides such as zirconium nitride (ZrN), silicon nitride (Si3N4), aluminum nitride (AlN), aluminum oxide (Al2O3), and zirconium oxide (ZrO2). oxides such as zirconium carbide (ZrC), carbides such as silicon carbide (SiC), silicides such as tantalum silicide (TaSi), or borides such as zirconium boride (ZrB). , or a combination of at least two or more thereof.

Here, the coating layer 44 includes ceramics made of zirconium nitride or zirconium carbide, or both. The coating layer 44 may contain the same metal as the electrode 30, such as tungsten or molybdenum.

Due to the properties of zirconium nitride, coating layer 44 is visible as colored side areas. That is, it is identified as a color different from that of the electrode base. Therefore, it becomes easy to check the color unevenness and the state of the film from the appearance, and it becomes possible to inspect whether the coating layer 44 is properly formed without measuring the emissivity and performing lighting experiments.

For example, if the atomic concentration ratio of nitrogen to zirconium in zirconium nitride is in the range of 0.2<N/Zr<0.9, the coating layer 44 is formed in a brownish chromatic color. The atomic number concentration ratio can be clarified by measuring and analyzing the surface of the body portion 34 using, for example, energy dispersive X-ray spectroscopy (EDS).

On the surface of the coating layer 44 (hereinafter referred to as layer surface), particles of tungsten (refer to symbol W) are adhered. Here, they are interspersed (interspersed) over the entire layer surface of the coating layer 44 . Furthermore, regarding the deposition of tungsten particles on the layer surface of the coating layer 44, the deposition amount gradually increases along the electrode axis C from the electrode support rod side end portion of the body portion 34 toward the electrode tip end portion 34E1. is configured to be

In other words, the concentration of scattered (scattered) tungsten along the electrode axis C becomes higher as it approaches the electrode tip end 34E1 from the electrode support rod side end, forming a concentration distribution close to gradation. ing. In FIG. 2, the difference in the adhesion amount (concentration) of the tungsten particles is schematically shown by enlarged portions (reference numerals A1 and A2).

By providing the coating layer 44 in which the adhesion amount of tungsten particles is gradually increased toward the tip end of the electrode, it is possible to suppress deterioration of the heat dissipation function of the coating layer 44 during lamp operation. This will be explained below.

The anode 30 of the short arc discharge lamp 10 is configured to contain tungsten as an electrode material, as described above. As a result, the temperature of the electrode 30 increases during lamp operation, and tungsten, which is a component of the electrode 30, partially evaporates. The evaporated tungsten moves along the convection of the gas (see symbol F) in the discharge tube 12 and some of it adheres to the layer surface of the coating layer 44 .

On the other hand, the tungsten particles adhered to the coating layer 44 are a different substance from tungsten, which is the material of the electrode. Therefore, even the tungsten particles previously attached to the surface of the coating layer 44 so as to have a concentration distribution are partially evaporated due to the temperature rise of the electrode 30 due to the lighting of the lamp. A part of the evaporated tungsten adheres to the layer surface of the coating layer 44 .

Here, whether the tungsten particles adhering to the surface of the coating layer 44 undergo crystal growth depends on whether the entire system is thermodynamically stable. A critical nucleus at the boundary between stabilization and non-stabilization becomes a stable nucleus, and it is necessary to follow the crystal growth. The frequency of occurrence of tungsten, which becomes a stable nucleus from critical nuclei, is closely related to crystal growth.

As described above, the layer surface of the coating layer 44 is configured such that the closer to the tip side of the electrode, the greater the adhesion amount of the tungsten particles. Therefore, the amount of tungsten that evaporates from the electrode 30 is also greater the closer it is to the tip of the electrode. That is, the concentration of tungsten near the layer surface of the coating layer 44 is high. The higher the tungsten concentration, the higher the probability that tungsten stable nuclei reaching the layer surface of the coating layer 44 will be formed. This means that there are more stable nuclei on the layer surface of the coating layer 44 closer to the tip side of the electrode.

As the number of stable nuclei formed on the layer surface of the coating layer 44 increases, the probability that the tungsten particles attracted to and adsorbed to the layer surface will evaporate again and leave the layer surface will decrease and settle on the layer surface. As a result, the crystal growth becomes faster, the growth becomes active, and the tungsten concentration becomes high. The density distribution of the deposited tungsten along the electrode axis C is substantially the same density distribution as before the lamp is turned on, that is, a density distribution with gradation.

The closer to the electrode support rod side of the electrode 30, the less the amount of tungsten particles attached. Therefore, the coating layer 44 exerts its heat dissipation function, and a decrease in emissivity is suppressed. On the other hand, the closer to the electrode tip side of the electrode 30, the greater the amount of tungsten particles attached, which prevents the evaporated tungsten from adhering to the inner wall of the discharge tube 12 and blackening as the gas flows in the discharge tube 12. produce a restraining effect.

As described above, in the discharge lamp 10 of the present embodiment, the coating layer 44 is formed on the surface of the body portion 34 of the electrode 30, and the tungsten particles are attached to the surface of the coating layer 44 so as to be scattered and scattered. there is It has a concentration distribution such that the amount of tungsten particles adhered along the electrode axis C increases toward the tip of the electrode.

Although the coating layer 44 is formed on the entire surface of the body portion 34 of the electrode 30 in this embodiment, the coating layer 44 may be formed on a part of the surface. Considering that gas convection occurs when the short arc discharge lamp 10 is arranged straight (along the vertical direction), the central portion of the body portion 34 of the electrode 30 along the electrode axis C A coating layer 44 may be formed across CL. On the other hand, the coating layer 44 may be formed closer to the tip of the electrode than the central portion CL.

In addition to the configuration in which tungsten is deposited on the layer surface of the coating layer 44 so as to have a concentration distribution like a gradation, other variations are possible. In the surface region where the layer surface of the coating layer 44 is formed, the amount of tungsten deposited at a location relatively close to the electrode tip side is increased so that the amount of tungsten deposited at a location relatively close to the electrode support rod side is increased. do it. For example, a configuration is possible in which the amount of tungsten deposited near the central portion CL is larger than that near the electrode supporting rod side. The particle size does not have to be constant, and can be, for example, between about 0.1 and 20 μm. For example, a configuration may be adopted in which tungsten having a larger grain size is deposited closer to the tip of the electrode along the electrode axis C, and tungsten having a smaller grain size is deposited closer to the electrode supporting rod.

The electrode 30 of such a discharge lamp can be manufactured as follows.

First, an electrode having a columnar body portion and a tapered portion on the distal end side is molded. Next, a coating layer is formed by application. Any method can be used to attach the tungsten particles to the layer surface. For example, tungsten is deposited by dispersing tungsten powder in a solvent and spraying it. The concentration distribution can be adjusted by changing the amount of tungsten and spraying in stages. In addition, a method of sprinkling tungsten powder, a method of dipping in a solvent with a different tungsten concentration, and the like are possible.

A coating layer of another component may be overlaid on the coating layer 44 to form a multiple-layer coating layer. For example, the lower layer made of zirconium nitride may contain tungsten particles or molybdenum particles, while the surface layer made of zirconium nitride may not contain tungsten particles or molybdenum particles. A coating layer made of zirconium nitride may be formed on a coating layer made of zirconium carbide to form a plurality of layers made of different materials. It is also possible to configure one of the multiple layers to contain ceramics.

It is possible to form the electrode 30 by joining the member having the tip end side tapered portion 32 and the member having the body portion 34 by solid phase bonding such as diffusion bonding. It is also possible to join via an intermediate member.

A heat dissipation structure may be provided on the side surface 34S of the body portion 34 or the tapered portion side surface 32S. The heat dissipating structure has a higher emissivity than the base surface, that is, the surface that does not have a special heat dissipating structure, and has the function of enhancing heat dissipation. The heat dissipation structure is, for example, configured by forming grooves along the circumferential direction (around the electrode axis) at a predetermined pitch, and the grooves can be formed, for example, by laser or cutting. Alternatively, it may be composed of grooves along the axial direction of the electrode. Also, a heat dissipation structure other than the groove may be employed.

For example, the end of the coating layer 44 is positioned at a predetermined distance along the direction of the lamp axis C from the electrode tip end 34E1 of the body 34, and heat is dissipated between that end and the electrode tip end 34E1. It is possible to avoid forming the coating layer 44 while forming the structure. It is possible to prevent peeling of the coating layer 44 due to the heat of the arc discharge. Note that the value of the predetermined distance is determined according to the size of the electrode, the value of the rated power, and the like.

Hereinafter, the heat dissipation performance of the electrode having the coating layer formed thereon will be described using examples.

The discharge lamp of the example is a short arc discharge lamp having an electrode (anode) having a configuration corresponding to that of the above embodiment. Configured. A coating layer is formed on a part of the side surface of the body of the electrode.

The coating layer is formed by dissolving zirconium nitride powder in a solvent containing ethyl cellulose, coating it on the side surface of the body, drying it, and then heat-treating it. Tungsten particles are deposited over the coating layer by the method described above.

A comparative experiment was conducted between the above-described embodiment and the discharge lamp of the comparative example. The electrode shape of the discharge lamp of the comparative example is substantially the same as that of the electrode of the example. On the other hand, in the comparative example, an electrode without a coating layer was used in order to confirm the heat dissipation function of the coating layer of the example.

FIG. 3 is a graph showing the illuminance maintenance rate of the example and the comparative example. The discharge lamp was lit for 600 hours, and the blackened state of the discharge tube was visually observed. After 600 hours from the start of lighting, the illuminance maintenance rate was 69% in the comparative example and 76% in the example. From this, it was confirmed that blackening could be suppressed more in the example than in the comparative example.

The fact that effective blackening suppression was achieved in the electrodes of the examples suggests that the tungsten deposited on the surface of the coating layer does not actively contribute to the blackening phenomenon, and electrode materials other than the coating layer This indicates that the evaporation of tungsten from the coating layer was suppressed, that is, the heat dissipation function of the coating layer was effectively exhibited. The fact that such a result was obtained in the electrode of the comparative example in which no coating layer was formed indicates that even when compared with the electrode in which only the coating layer was formed and no tungsten was deposited as in this example, It can be said that the electrode of 1 is more effective with respect to the radiating function.

10 discharge lamp 30 electrode (anode)
44 coating layer

Claims (5)

a discharge tube;
A pair of electrodes arranged oppositely in the discharge tube,
In at least one electrode, a coating layer containing ceramics and having tungsten adhered to the layer surface is formed on at least a part of the surface of the electrode body,
In the coating layer, the amount of tungsten adhering to a portion near the electrode tip side is relatively larger than the amount of tungsten adhering to a portion near the electrode support rod side Discharge characterized by that lamp. The coating layer is formed on the surface of the electrode body so as to straddle the central portion of the electrode in the axial direction,
that the amount of tungsten adhering to the layer surface closer to the tip of the electrode than the central portion in the axial direction is greater than the amount of tungsten adhering to the surface of the layer closer to the electrode support rod than the central portion in the axial direction; 2. A discharge lamp as claimed in claim 1. 2. The discharge lamp according to claim 1, wherein the amount of tungsten deposited on said coating layer gradually increases from the side of the electrode support rod toward the tip of the electrode. 4. A discharge lamp as claimed in any one of claims 1 to 3, characterized in that the coating layer is chromatic. 4. The discharge lamp according to any one of claims 1 to 3, wherein said ceramics comprises at least one of nitrides, oxides, borides, carbides and silicides.

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