Discharge lamp

Abstract

The present invention provides a discharge lamp in which a coating is applied to the electrode surface, allowing the coating function to be effectively performed while the lamp is lit. [Solution] A coating layer 44 containing ceramics is formed on the surface of the body portion 34 of the electrode 30. The ceramics consist of zirconium nitride (ZrN), and the atomic concentration (%) of nitrogen (N) is relatively lower than the atomic concentration (%) of zirconium (Zr).

Description

Technical Field

[0001] The present invention relates to a discharge lamp such as a short arc discharge lamp, and particularly to a coating on the electrode surface.

Background Art

[0002] During lighting of a discharge lamp, the tip of the electrode becomes hot, and electrode materials such as tungsten melt and evaporate, causing the discharge tube to blacken and resulting in a decrease in lamp illuminance. To prevent overheating of the electrode including the tip of the electrode, for example, the surface area of the side surface of the electrode body is increased with a screw-shaped groove, and tungsten powder is sintered on the groove to form a heat dissipation layer (see Patent Document 1).

[0003] Also, a coating method is known in which a film containing ceramics is formed on the electrode surface and tungsten particles are attached to a part of the outer surface of the film (see Patent Document 2). In this method, a solvent of zirconium oxide is applied to the electrode surface and heat-treated to form a ceramic film, and tungsten particles are attached at a predetermined coating rate by vacuum evaporation.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As has been known to those skilled in the art for quite some time, when a discharge lamp is constructed using electrodes made of tungsten, some of the tungsten electrode material evaporates due to overheating of the electrodes when the lamp is lit, and some of the evaporated material adheres to the electrode surface. This occurs even if the electrode surface is partially coated or otherwise protected.

[0006] Therefore, even if the coating ratio of tungsten particles attached during lamp manufacturing is adjusted, the extent to which some of the tungsten evaporated from the electrode material adheres to the electrode surface varies depending on the structure of the discharge tube including the discharge space, the size of the electrodes, and the rated power value, and the measurement time from the start of operation (the coating effect is not determined by the initially set coating ratio). Excessive adhesion to the electrode surface can conversely reduce the coating function such as heat dissipation, potentially leading to illuminance fluctuations (reduction in illuminance).

[0007] Therefore, there is a need to provide a discharge lamp in which a coating is applied to the electrode surface that can effectively exert its coating function while the lamp is lit. [Means for solving the problem]

[0008] A discharge lamp according to one aspect of the present invention comprises a discharge tube and a pair of electrodes arranged opposite each other within the discharge tube, wherein a coating layer containing ceramics is formed on the surface of at least one of the electrodes. The shape and structure of the electrodes vary; for example, the electrode comprises a columnar electrode body connected to an electrode support rod.

[0009] In this context, "coating layer" includes both a single-layer coating layer containing one or more ceramics as material, and multiple coating layers. Furthermore, in the case of multiple coating layers, each layer may contain either one or multiple ceramics as material.

[0010] The configuration of multiple coating layers can vary. For example, one coating layer (e.g., the bottom layer) may contain ceramics and electrode material (tungsten, molybdenum, etc.), while other coating layers (e.g., coating layers formed on top of the bottom layer) may contain only ceramic components, or components other than ceramics and electrode material. Alternatively, it is possible to configure multiple coating layers with different compositions along the lamp axis, at the electrode tip and rear end.

[0011] The ceramics of the present invention consist of at least one of nitrides, oxides, borides, carbides, and silicides. That is, they consist of one ceramic made of nitrides, oxides, borides, carbides, or silicides, or two or more ceramics.

[0012] Furthermore, in the coating layer, the atomic number concentrations (%) of nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) are lower than the atomic number concentrations (%) of the elements that chemically bond with nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) in the nitrides, oxides, borides, carbides, and silicides, respectively. For example, the atomic number concentrations (%) are measured on the surface of the coating layer using energy-dispersive X-ray spectroscopy (EDS).

[0013] If the ceramics consist of nitrides, oxides, borides, carbides, or silicides, their atomic concentration (%) is configured to satisfy the above conditions. Furthermore, if the ceramics consist of two or more of the nitrides, oxides, borides, carbides, or silicides, the atomic concentration (%) of each ceramic is configured to satisfy the above conditions, or the most dominant ceramic in the coating layer is configured to satisfy the above conditions.

[0014] Furthermore, if multiple coating layers are formed, all coating layers are configured to satisfy the above conditions. Alternatively, a specific coating layer (for example, the outermost coating layer) is configured to satisfy the above conditions.

[0015] Thus, the statement "In the coating layer, the atomic concentrations (%) of nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) are lower than the atomic concentrations (%) of the elements that chemically bond with each of these elements" is defined as explained above. Furthermore, this includes not only configurations where these atomic concentrations (%) are satisfied in all or any part of the coating layer, but also configurations where they are satisfied in part. For example, it is possible to define a configuration where the above conditions are satisfied in multiple locations across the section from the electrode tip end to the electrode support rod end of the coating layer, or a coating layer where it can be judged that the above conditions are satisfied in approximately the entire area of ​​the coating layer.

[0016] Various materials can be used as types of ceramics. For example, the ceramic can be composed of at least one of the following: silicon nitride, aluminum nitride, zirconium nitride, aluminum oxide, zirconium oxide, zirconium carbide, silicon carbide, tantalum silicide, and zirconium boride. For example, the ceramic is made of nitride, and the atomic concentration (%) of nitrogen (N) in the coating layer is lower than the atomic concentration (%) of the elements that chemically bond with the nitrogen (N) in the nitride.

[0017] The above-mentioned conditions for atomic concentration (%) (differences in atomic concentration (%)) may be slight or significant. For example, in a coating layer, the ratio of the atomic concentration of at least one of nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) to the atomic concentration of at least one element that chemically bonds with nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) in nitrides, oxides, borides, carbides, and silicides can be configured to be in the range of 0.2 to 0.9.

[0018] On the other hand, another aspect of the present invention, provided from the perspective of functional ceramics, is a discharge lamp comprising a discharge tube and a pair of electrodes arranged opposite each other within the discharge tube, wherein a coating layer containing ceramics is formed on the electrode surface of at least one of the electrodes. The ceramics consist of functional ceramics having at least thermal properties, and in the coating layer, the atomic number concentration (%) of elements with relatively high electronegativity of the functional ceramics is lower than the atomic number concentration (%) of elements with relatively low electronegativity of the functional ceramics.

[0019] The coating layer is defined as described above. Furthermore, "functional ceramics" are defined in the same way as "nitrides, oxides, borides, carbides, and silicides" as described above. That is, they consist of one functional ceramic material, or at least two or more functional ceramic materials. Nitrides, oxides, borides, carbides, and silicides are included in the "functional ceramics" of this invention.

[0020] The location of the coating layer on the electrode can vary; it can be formed on part or all of the surface of the electrode body. For example, the coating layer can be formed on at least part of a groove formed around the circumference of the electrode body. In this case, the emissivity of the coating layer can be configured to be greater than that of the groove.

[0021] For example, it is possible to form a coating layer such that the emissivity of the combination of the groove and the coating layer is 0.8 or more when represented by the following formula. ε = 1 / (1 + (L / S)×(1 / ε0 - 1)) Here, L represents the axial length of the groove formation region, S represents the total cross-sectional length, and ε0 represents the emissivity of the coating layer. Also, L / S is determined to be 0.9 or less.

[0022] Another aspect of the manufacturing method of the electrode for a discharge lamp according to the present invention is to mold an electrode having a columnar body portion and a tip-side tapered portion, put powder of particles composed of at least any one of nitrides, oxides, borides, carbides, and silicides into a solvent, apply the solvent to the side surface of the body portion, and perform heat treatment to form a coating layer containing ceramics. It is a manufacturing method of an electrode for a discharge lamp, and a coating layer containing ceramics is formed so that the atomic concentration (%) of nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) is lower than the atomic concentration (%) of the elements that chemically bond to each of nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si). Regarding the "coating layer" and the configuration of "the atomic concentration (%) of nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) being lower than the atomic concentration (%) of the elements that chemically bond to each of nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si)", it is based on the above-described definitions.

[0023] For example, it is possible to form a groove along the circumferential direction of the electrode on the side surface of the body portion and form a coating layer having an emissivity greater than the emissivity of the groove on the groove by coating. For example, the coating layer has a configuration in which a plurality of coating layers are laminated.

Advantages of the Invention

[0024] According to the present invention, it is possible to provide a discharge lamp in which a coating that can effectively exhibit a coating function is applied to the electrode surface during lamp lighting.

Brief Description of the Drawings

[0025] [Figure 1] This is a schematic plan view of the discharge lamp according to the present embodiment. [Figure 2] This is a schematic plan view of the electrode of the present embodiment. [Figure 3] This is a diagram showing a table of the correlation between the shape of the groove and the emissivity of the coating layer. [Figure 4] This is a schematic view showing the shape of the groove. [Figure 5] This is a graph showing the relative temperatures in the electrodes of the examples and comparative examples.

Mode for Carrying Out the Invention

[0026] The short arc type discharge lamp 10 is a large-sized discharge lamp capable of outputting high-intensity light, and includes a substantially spherical discharge tube (light-emitting tube) 12 made of transparent quartz glass. Inside the discharge tube 12, a pair of electrodes 20 and 30 made of tungsten are arranged opposite (coaxial) to each other. On both sides of the discharge tube 12, sealing tubes 13A and 13B made of quartz glass are connected to the discharge tube 12 and integrally formed. In the discharge space DS inside the discharge tube 12, mercury and rare gases such as halogen and argon gas are enclosed.

[0027] The electrode 20, which is the cathode, is supported by an electrode support rod 17A. In the sealing tube 13A, 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 are sealed. Similarly, for the electrode 30, which is the anode, mount components such as a glass tube (not shown) through which the electrode support rod 17B is inserted, a metal foil 16B, and a lead rod 15B are sealed. Also, caps 19A and 19B are respectively attached to the ends of the sealing tubes 13A and 13B.

[0028] When a voltage is applied to the pair of electrodes 20 and 30, an arc discharge occurs between the electrodes 20 and 30, and light is emitted outwards from the discharge tube 12. At this point, a power of 1 kW or more is applied. The light emitted from the discharge tube 12 is guided in a predetermined direction by a reflector (not shown).

[0029] Figure 2 is a schematic plan view of the electrode (anode) 30. The electrode (cathode) 20 can also be constructed with a similar structure.

[0030] The electrode 30 has an electrode tip surface 32T and is composed of a tapered portion (hereinafter referred to as the tip-side tapered portion) 32 and a columnar portion (hereinafter referred to as the body portion) 34 that connects to the electrode support rod 17B. Here, the electrode 30 is constructed integrally, but it is possible to construct the electrode 30 by joining the member having the tip-side tapered portion 32 and the member having the body portion 34 by solid-state bonding such as diffusion bonding. It is also possible to join them via an intermediate member. The electrode 30 can be made of tungsten, molybdenum, or an alloy thereof.

[0031] A heat dissipation structure 40 is provided on the side surface 34S of the fuselage section 34 (see the shaded area in Figure 2). The heat dissipation structure 40 has a higher emissivity than the base surface 33, i.e., a surface that does not employ a special heat dissipation structure, and thus enhances heat dissipation. As shown in the enlarged section of the side surface 34S (see reference numeral B) in Figure 2, the heat dissipation structure 40 is configured in which grooves 42 are formed at a predetermined pitch along the circumferential direction (around the electrode axis). The grooves 42 can be formed, for example, by laser or cutting.

[0032] Furthermore, a coating layer 44 (shaded area in Figure 2) is formed on the side surface 34S of the body portion 34, which is provided with the heat dissipation structure 40 (groove 42). Here, the end 44E1 of the coating layer 44 is defined as a position a predetermined distance T away from the electrode tip end 34E1 of the body portion 34 along the direction of the lamp axis C, and the coating layer 44 is formed from that end 44E1 to the electrode support rod end 34E2 of the body portion 34. Between the end 44E1 of the coating layer 44 and the electrode tip end 34E1 of the body portion 34, the heat dissipation structure 40 (groove 42) is formed, while the coating layer 44 is not formed. The value of the predetermined distance T is determined according to the size of the electrode, the rated power value, etc.

[0033] The coating layer 44 is composed of a coating layer containing ceramics with thermal properties (including heat resistance and heat dissipation). It is particularly preferable that the ceramics have a high melting point of 2000°C or higher. The ceramics can be composed of nitrides such as zirconium nitride, silicon nitride, and aluminum nitride; oxides such as aluminum oxide and zirconium oxide; carbides such as zirconium carbide and silicon carbide; silicides such as tantalum silicide; or borides such as zirconium boride. Alternatively, it can be composed of at least two of these combinations. In this example, the coating layer 44 contains ceramics made of zirconium nitride. Furthermore, the coating layer 44 may also contain the same metal as the electrode 30, such as tungsten or molybdenum.

[0034] In the coating layer 44 containing ceramics made of zirconium nitride, the atomic concentration (%) of the element Zr (zirconium) is set to be higher than the atomic concentration (%) of the element N (nitrogen). Here, this zirconium-rich state in the coating layer 44 extends throughout along the lamp axis C.

[0035] Further, the coating layer 44 is formed such that the ratio of the atomic concentration of nitrogen to the atomic concentration of zirconium in zirconium nitride is in the range of 0.2 < N / Zr < 0.9. For example, it is set in the range of 0.4 < N / Zr < 0.9. The atomic concentration and the atomic concentration ratio can be determined by measuring and analyzing the surface of the body portion 34 using, for example, energy dispersive X-ray spectroscopy (EDS).

[0036] As described above, by forming ceramics in which the atomic concentration (%) of nitrogen (N) is relatively lower than the atomic concentration (%) of zirconium (Zr), the coating layer 44 made of ceramics with excellent thermal performance is formed.

[0037] That is, during lamp lighting, when the electrode 30 becomes high temperature, in a part of zirconium nitride, nitrogen is separated and released from the coating layer 44. However, the separated and released nitrogen easily recombines with zirconium that is relatively abundant on the surface of the body portion 34 and functions as ceramics again.

[0038] Therefore, the coating layer 44 can exhibit thermal performance over a long period of time, and an electrode structure with a high emissivity can be obtained. Further, by setting the ratio of the atomic concentration of nitrogen to the atomic concentration of zirconium in zirconium nitride in the range of 0.2 < N / Zr < 0.9, the function of the coating layer 44 can be further exerted while maintaining a zirconium-rich state.

[0039] On the other hand, the coating layer 44 is not formed over the entire formation region of the heat dissipation structure 40 (grooves 42) of the body portion 34, and the coating layer 44 is not formed in a part on the electrode tip side. That is, the coating layer 44 is formed with the electrode support rod side as an end portion (end portion 44E1) rather than the electrode tip side end portion 34E1 of the body portion 34. Thereby, it is possible to suppress the coating layer 44 from peeling off due to the heat of arc discharge and adhering to the discharge tube 12, which causes a decrease in illuminance.

[0040] Furthermore, due to the characteristics of zirconium nitride, after the formation process of the coating layer 44 described below, the coating layer 44 is visually recognized as a colored side region. That is, it is identified as a color different from that of the electrode substrate 33. Therefore, it becomes easy to confirm color unevenness and the film condition from the appearance, and it is possible to inspect whether the coating layer 44 is properly formed without performing emissivity measurement and lighting experiments.

[0041] In particular, if the ratio of the atomic number concentrations of nitrogen and zirconium is in the range of 0.2 < N / Zr < 0.9, the coating layer 44 is formed as a colored tea-like color. For example, when the atomic number concentration of nitrogen is low, the coating layer 44 becomes a black-based color and does not become a colored one. Therefore, it can be determined that an appropriate coating layer is not formed from the appearance. The same effect occurs for other ceramics in which coloration appears due to coating formation.

[0042] The coating layer 44 may be formed so as to overlap with the entire formation region of the heat dissipation structure 40 (groove 42) configured in the body portion 34. Also, in the tip-side tapered portion 32 and / or the body portion 34, the coating layer may be formed in a portion where the groove 42 is not formed.

[0043] On the other hand, a coating layer of a different component may be stacked on the coating layer 44 to form a plurality of coating layers. For example, tungsten or molybdenum may be contained in the lower layer made of zirconium nitride, and the composition may be changed to a plurality of layers such that tungsten or molybdenum is not contained in the surface layer also made of zirconium nitride, or a coating layer made of zirconium nitride may be formed on a coating layer made of zirconium carbide to form a plurality of layers of different materials. It is also possible to configure one of the plurality of coating layers to contain ceramics.

[0044] Furthermore, when forming a coating layer 44 that includes ceramics made of nitrides such as silicon nitride and aluminum nitride, oxides such as aluminum oxide and zirconium oxide, carbides such as zirconium carbide and silicon carbide, silicides such as tantalum silicide, or borides such as zirconium boride, the ceramics should be constructed such that, similar to zirconium nitride, the atomic concentration of elements with relatively high electronegativity is lower than the atomic concentration of elements with relatively low electronegativity. This principle can also be applied to functional ceramics that have at least thermal properties, even if they are not listed, by similarly determining the atomic concentration and atomic concentration ratio.

[0045] For example, in nitrides, oxides, borides, carbides, or silicides, ceramics can be constructed in which the atomic concentrations of nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) are lower than the atomic concentrations of the elements that chemically bond with each of these elements (for example, Al in the case of aluminum oxide). Alternatively, ceramics can be constructed in which the ratio of the atomic concentrations of nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) to the atomic concentrations of the elements that chemically bond with each of these elements is set to a range of 0.2 to 0.9.

[0046] Furthermore, the coating layer 44 containing ceramics is not limited to being formed so as to satisfy the above atomic concentration and atomic concentration ratio over the entire lamp axis C of the coating layer 44. For example, it may be a part of the coating region (e.g., more than half of the region) that satisfies at least the atomic concentration condition among the above atomic concentration and atomic concentration ratio, and it is sufficient that at least the above atomic concentration condition is satisfied at any point in the circumferential direction along the lamp axis C, for example, if the condition is satisfied in a proportion of more than half in that circumferential direction. Alternatively, the degree of concentration of the atomic concentration may be configured to change gradually along the direction of the lamp axis C.

[0047] The configuration and function of the coating layer 44 have been described above. As will be explained below, the combination of the heat dissipation structure 40 (grooves 42) and the coating layer 44 provides a more effective heat dissipation function.

[0048] As shown in Figure 2, the height of the top 42P of the groove 42 covered with the coating layer 44, that is, the distance from the lamp axis (electrode axis) C to the top 42P (layer surface), is located closer to the electrode center than the side surface 34S of the body 34. By having the top 42P of the groove 42 recessed relative to the side surface 34S of the body 34, peeling or thinning of the coating due to arcs and flares can be effectively suppressed.

[0049] The coating layer 44 functions to further enhance the heat dissipation function of the heat dissipation structure 40 (grooves 42), and here has a higher emissivity than the grooves 42. The heat dissipation structure 40 composed of grooves 42 and the coating layer 44, which have two heat dissipation functions (hereinafter, this side portion will be called the heat dissipation function portion J), are formed on a part of the side surface 34S of the body portion 34. The emissivity ε of the surface on which the grooves are formed can be approximately expressed by the following equation (1). ε=1 / (1+(L / S)×(1 / ε0-1)) ···(1) However, L represents the axial length (along the side surface 34S) of the groove formation region, and S represents the total length (total cross-sectional length) along the groove in the groove cross-sectional view (see Figure 4). The emissivity ε of the heat dissipation function part J is derived by replacing the material-specific emissivity ε0 with the emissivity of the coating layer 44 (represented as εcoat in Figure 3) (represented as εgroove+coat in Figure 3). However, since the coating layer 44 is very thin compared to the size (depth) of the groove, its thickness can be ignored.

[0050] By applying the above equation (1) to derive the emissivity of the combined groove 42 and coating layer 44, the shape of the groove 42 and the components of the coating layer 44 can be appropriately combined to effectively (cooperatively) improve the heat dissipation (emissivity) of the fuselage 34. In particular, by setting the emissivity of the coating layer 44 higher than that of the groove 42, a heat dissipation function section J can be configured in which the heat dissipation function of the coating layer 44 is the primary function and the heat dissipation function of the groove 42 is secondary.

[0051] Depending on the L / S value of the groove 42, if the wrong coating layer 44 is selected, an emissivity not significantly different from that of the coating layer 44 may be obtained, resulting in insufficient heat dissipation. However, by referring to the table in Figure 3, various groove shapes (L / S values) can be used. Even with respect to this, the emissivity εgroove+coat can be maintained at a high level.

[0052] In the body portion 34 provided with such a heat dissipation function J, the tapered side surface (surface) 32S of the tip-side tapered portion 32 is provided with a heat dissipation structure (uncoated heat dissipation structure) 50 in which only grooves are formed and no coating layer is formed on top of them. However, the heat dissipation structure 50 on the tapered side surface 32S may be covered with a coating layer.

[0053] The electrodes 30 of such a discharge lamp can be manufactured as follows.

[0054] First, an electrode having a columnar body and a tapered tip is formed, and grooves are created along the circumferential direction on the side of the body by processing such as laser or cutting. Next, a coating layer is formed on top of the grooves by coating. At this time, as shown in Figure 2, the coating layer is formed so that the end is at a predetermined distance T from the tip end of the electrode on the body. Note that if it is determined that the effect of arc discharge is small depending on the power of the discharge lamp, this predetermined distance T may be shortened or eliminated. Furthermore, the powder of the material constituting the ceramics described above is placed in a solvent and coated so as to satisfy the atomic concentration and atomic concentration ratio described above. This is then heat-treated in a heating device such as a vacuum furnace. The atomic concentration and atomic concentration ratio may be adjusted by setting the heat treatment time and the atmosphere of the furnace (degree of vacuum and type of gas).

[0055] Furthermore, by setting the emissivity of the coating layer higher than that of the grooves, a heat dissipation function with high emissivity can be constructed. Homogeneous coating methods such as spraying, vapor deposition, sputtering, and CVD can be employed. The applied coating may also be sintered by laser.

[0056] In this embodiment, the heat dissipation structure is formed by grooves along the circumferential direction, but it may also be formed by grooves along the electrode axis direction. Furthermore, a heat dissipation structure other than grooves may be adopted. For example, a textured surface created by sandblasting or a blackening inhibitor can be used as the heat dissipation structure. If the main objective is to suppress blackening, a blackening inhibitor can be used, and if improved heat dissipation is desired, grooves can be used. If low cost is desired, a textured surface can be used. The heat dissipation structure should be determined according to the lamp output, electrode shape, electrode material, ease of processing such as cutting, etc. Furthermore, sandblasting can be performed over the grooves to further improve the adhesion of the coating layer. In addition, electrodes may be manufactured with the coating layer formed on the side of the body without forming grooves.

[0057] As mentioned above, in the case of zirconium nitride, the coating layer is chromatic. That is, a coating layer is formed on the electrode that is visible as a color (a colored color) containing all three elements: hue, which indicates the difference in color; lightness, which indicates the brightness or darkness of the color; and saturation, which indicates the degree of color change. If the technical challenge is to confirm and verify the appropriate formation of the coating layer on the electrode surface, it is possible to provide a discharge lamp equipped with an electrode having a coating layer containing zirconium nitride, regardless of the nitrogen (N) and zirconium (Zr) atomic concentration (%) conditions of zirconium nitride as described above.

[0058] In other words, a discharge lamp can be provided comprising a discharge tube and a pair of electrodes arranged opposite each other within the discharge tube, wherein a coating layer containing ceramics is formed on the surface of at least one of the electrodes, and the ceramics are made of ceramics whose chromatic color is visible when the coating layer is formed. It may consist of at least ceramics with thermal properties (e.g., zirconium nitride or zirconium carbide), or in the case of multiple ceramics, it may be configured to include such ceramics. The coating layer may consist of a single layer or multiple laminated coating layers. [Examples]

[0059] The thermal performance of electrodes with a coated layer will be described below using examples.

[0060] The discharge lamp of the embodiment is a short-arc type discharge lamp equipped with an electrode (anode) with a configuration corresponding to the above embodiment, and the electrode has a body length of 57 mm and a diameter of 35 mm along the lamp axis. A groove is formed along the entire side surface of the electrode body, while a coating layer is formed on a part of the side surface of the body, with the end being at a predetermined distance from the electrode tip end of the body.

[0061] The coating layer is formed by dissolving zirconium nitride powder in a solvent containing ethylcellulose, applying it to the side of the fuselage, drying it, and then heat-treating it. The atomic concentration of the coating layer was measured and analyzed by energy-dispersive X-ray spectroscopy (EDS). Here, the atomic concentration was measured at predetermined distances (specifically, 10 mm, 20 mm, and 40 mm) from the electrode support rod end of the fuselage.

[0062] Energy-dispersive X-ray spectroscopy (EDS) analysis revealed that the atomic number concentrations (%) of Zr:N at the 10mm, 20mm, and 40mm points were 62.6:35.0, 56.3:41.2, and 56.7:29.1, respectively. The atomic number concentration ratio (N / Zr) at the 10mm, 20mm, and 40mm points was 56.0%, 73.1%, and 51.4%, respectively.

[0063] A comparative experiment was conducted between the above-described example and a discharge lamp equipped with an electrode having a coating layer that did not meet the required atomic number concentration (%) as a comparative example. The electrode of the comparative example had a coating layer made of zirconium carbide formed by the same manufacturing method as in the example. The electrode shape was substantially the same as that of the electrode in the example. Analysis by energy-dispersive X-ray spectroscopy (EDS) revealed that the atomic number concentration (%) of Zr:C in the electrode of the comparative example was 38.34:60.76, 38.09:54.76, and 33.02:52.4 at 10 mm, 20 mm, and 40 mm, respectively.

[0064] The electrode temperature at the initial stage of illumination (0 hours) and after 600 hours were measured for the coated electrode region of both the example and comparative example, and the temperature change was confirmed. Figure 5 is a graph showing the temperature change of the electrodes of the example and comparative example.

[0065] In the graph in Figure 5, the vertical axis represents the relative temperature with the temperature at a predetermined location in the coating layer set to 100, and the horizontal axis represents the temperature measurement location of the electrode. Here, a portion of the coating layer was defined as the measurement area, and the temperature at the electrode tip side of that area was set to 100, with the measured temperature up to the electrode support rod side being graphed as the relative temperature. The lines labeled T1A and T1B represent the relative temperature of the electrode in the example at the initial stage of illumination and after 600 hours, respectively. The lines labeled T0A and T0B represent the relative temperature of the electrode in the comparative example at the initial stage of illumination and after 600 hours, respectively.

[0066] As shown in Figure 5, in the case of the electrode in the example, there was little change in relative temperature when comparing the initial state after ignition with the state after 600 hours, confirming that the coating layer was maintained over a long period of time. On the other hand, in the case of the electrode in the comparative example, the relative temperature after 600 hours was higher across the entire measurement area compared to the initial state after ignition. In the case of the electrode in the comparative example, it was confirmed that the coating function had deteriorated and the coating layer was not maintained. [Explanation of Symbols]

[0067] 10 Discharge Lamps 30 electrodes 40 Heat dissipation structure 42 Groove 44 Coating layer

Claims

1. Discharge tube and, The discharge tube comprises a pair of electrodes arranged opposite to each other, In at least one electrode, a coating layer containing ceramics is formed on the electrode surface. The aforementioned ceramics consist of at least one of nitrides, oxides, borides, carbides, and silicides. A discharge lamp characterized in that, in the coating layer, the atomic number concentration (%) of at least one of nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) is lower than the atomic number concentration (%) of at least one of the elements that chemically bond with nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) in the nitride, oxide, boride, carbide, or silicide.

2. The discharge lamp according to claim 1, characterized in that the ratio of the atomic number concentration (%) of at least one of nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) to the atomic number concentration (%) of at least one element that chemically bonds with nitrogen (N), oxygen (O), boron (B), carbon (C), and silicon (Si) in the nitride, oxide, boride, carbide, and silicide is in the range of 0.2 to 0.

9.

3. Discharge tube and, The discharge tube comprises a pair of electrodes arranged opposite to each other, In at least one electrode, a coating layer containing ceramics is formed on the electrode surface. The aforementioned ceramics consist of functional ceramics having at least thermal properties. A discharge lamp characterized in that, in the coating layer, the atomic number concentration (%) of elements with relatively high electronegativity in the functional ceramics is lower than the atomic number concentration (%) of elements with relatively low electronegativity in the functional ceramics.

4. The discharge lamp according to claim 1, characterized in that the coating layer has a configuration in which multiple coating layers are stacked.

5. The aforementioned ceramics consist of nitrides, The discharge lamp according to claim 1, characterized in that the atomic number concentration (%) of nitrogen (N) in the coating layer is lower than the atomic number concentration (%) of the element that chemically bonds with the nitrogen (N) of the nitride.

6. The discharge lamp according to claim 1, characterized in that the atomic number concentration (%) is the concentration measured on the surface of the coating layer using energy-dispersive X-ray spectroscopy (EDS).

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