Tungsten-containing materials and DC discharge lamp electrodes

Abstract

A material containing tungsten, wherein the amount of oxygen generated at 2100℃ to 2300℃ detected by oxygen analysis according to the oxygen separator method exceeds 1 ppm and is 20 ppm or less, and contains potassium of 5 ppm or more and 30 ppm or less.

Description

Technology Field

[0001] The present invention relates to a material comprising tungsten. The present application claims priority based on Japanese patent application No. 2022-067481, filed on April 15, 2022. All contents of said Japanese patent application are incorporated herein by reference. Background Technology

[0002] Conventionally, materials containing tungsten are disclosed, for example, in Japanese Patent Publication No. 2003-027111 (Patent Document 1), Japanese Patent Publication No. 2007-169789 (Patent No. 5265867) (Patent Document 2), and Japanese Patent Publication No. 2005-183355 (Patent No. 4167199) (Patent Document 3). Prior art literature

[0003] Patent Document 1: Japanese Patent Publication No. 2003-027111 Patent Document 2: Japanese Patent Publication No. 2007-169789 Patent Document 3: Japanese Patent Publication No. 2005-183355

[0004] A material containing tungsten has an oxygen generation amount at 2100℃ to 2300℃ detected by oxygen analysis according to the oxygen separator method that is greater than 1 ppm and less than or equal to 20 ppm, and contains potassium of 5 ppm or more and 30 ppm or less. Brief explanation of the drawing

[0005] Figure 1 is a graph showing the relationship between output and temperature in an oxygen separator used in an embodiment. Specific details for implementing the invention

[0006] [Problems to be solved by the present disclosure]

[0007] In conventional tungsten-containing materials, there was a problem that the illuminance retention rate was low when used as an electrode for a discharge lamp.

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0009] (1) Contents of the present disclosure

[0010] Japanese Patent Publication No. 2007-169789 (Patent Document 2) discloses a method for manufacturing a component or semi-finished product from a group of materials including molybdenum, molybdenum alloy, tungsten, and tungsten alloy, having an average relative density greater than 98.55%, a relative core density greater than 98.3%, and an average number of grains greater than 100 grains / mm² in a direction perpendicular to the direction of deformation by processing in a deformed state by processing, characterized by including the following process.

[0011] A process for preparing a powder having a particle size of 0.5 to 10 μm by measurement according to the Fischer method. A process for pressurizing the powder under a pressure of 100 to 500 MPa.

[0012] A process of sintering at a temperature of (0.55~0.92)×solidus line temperature and making the relative density (D) 90% < D < 98.5%, and a process of hot isotropic press processing without using a mold at a temperature of (0.40~0.65)×solidus line temperature and under a pressure of 50~300 MPa.

[0013] A process of forming such that the degree of form (ψ) is 15% < ψ < 90% by radial forging or rolling.

[0014] Japanese Patent Publication No. 2003-027111 (Patent Document 1) discloses a method for manufacturing a high melting point metal material by obtaining a high melting point metal material by plastically processing an ingot containing an alloy comprising at least one of Mo and W or at least one of them within a temperature range of 700°C to 1700°C so that the cross-section becomes non-circular.

[0015] Japanese Patent Publication No. 2005-183355 (Patent Document 3) discloses a tungsten electrode characterized by containing less than 5 ppm of Si, 5 to 20 ppm of K, and 5 to 20 ppm of Al, with the remainder substantially containing tungsten, and having a diameter of 15 mm or more. It discloses a tungsten for discharge lamps having a density of 19,100 kg / m³ or more, and an aspect ratio of crystal grain size of 2 to 20 parts with an area greater than 50%.

[0016] Tungsten is one of the high-melting-point materials (melting point about 3,400°C), and taking advantage of this characteristic, it is used as a high-temperature furnace component, filament, discharge lamp, etc.

[0017] In particular, when used in discharge lamps, it is said that a temperature load exceeding 2,500°C is applied, and as a material capable of withstanding this, tungsten with added potassium is often used as an electrode.

[0018] In discharge lamps using potassium-doped tungsten, the electrode tip may be consumed and scattered by the discharge during use, causing impurities to scatter or adhere to the inner surface of the lamp glass, known as blackening. In addition, deformation of the tip causes the light source to flicker due to the discharge, resulting in a loss of the stability required as a light source, and if used for exposing electronic component circuits, the lamp reaches the end of its lifespan.

[0019] By adding potassium to tungsten, the recrystallization characteristics of the tungsten material are improved, and the growth of crystal grains at the electrode tip during discharge lamp ignition is also suppressed.

[0020] Prior art patent documents 1 and 2 have achieved an improvement in lamp life by using the above technology to enhance the characteristics of a discharge lamp, such as by controlling the amount of K added to tungsten or improving the specific gravity, thereby refining the recrystallized grains during electrode use.

[0021] In the present disclosure, it was discovered that the factor causing the decrease in the light intensity retention rate due to blackening of the lamp lies in oxygen generated in a specific temperature range within the tungsten material, and the deformation and consumption / scattering of tungsten were improved by reducing the amount of oxygen.

[0022] Although tungsten material is used as the anode of a DC discharge lamp used for semiconductor lithography and lighting, the anode, which is heated to a high temperature by receiving electrons, has an oxygen contained in the material that reacts with tungsten during the lamp's discharge and volatilizes / scattering as a low-melting point oxide, causing the inner glass of the lamp to blacken, which causes a decrease in light bundle and degrades the quality as a point light source required for lithography power supply due to deformation, resulting in a short lifespan.

[0023] Conventional tungsten materials, when used as lamps, sometimes caused the inside of the lamp glass to blacken due to the scattering of tungsten and other impurities caused by oxygen components, making them unusable for stable use.

[0024] In the present disclosure, a material containing tungsten was used by adopting new manufacturing conditions to control the amount of oxygen, preferably potassium, and crystal grain size contained in the material.

[0025] By doing so, blackening of the discharge lamp can be suppressed to maintain a light beam for a long period, thereby contributing to a long lifespan. The tungsten material of the present disclosure can be applied not only to electrodes of discharge lamps but also to furnace components used at high temperatures, such as nuclear fusion reactors, where high-strength materials that dislike oxygen emission are required.

[0026] The tungsten-containing material of the present disclosure has an oxygen generation amount at 2100°C to 2300°C detected by oxygen analysis according to the oxygen separator method that is greater than 1 ppm and less than or equal to 20 ppm, and contains potassium of 5 ppm or more and 30 ppm or less.

[0027] (2) Measurement of oxygen release

[0028] If the amount of oxygen generated exceeds 20 ppm, it causes blackening of the lamp glass during use, leading to a shortened lifespan of the lamp. More preferably, the amount of oxygen generated is 10 ppm or less.

[0029] The method for measuring oxygen content is as follows.

[0030] The weight of the material being measured is 0.10 g to 1.00 g, and the material is sampled from the center of the material containing tungsten.

[0031] The measurement was evaluated by using the amount of oxygen detected in the designated temperature range (2100℃~2300℃) by the oxygen separator function as the amount of oxygen released at 2100℃~2300℃.

[0032] The analysis conditions and parameters are as follows.

[0033] [condition]

[0034] Oxygen, Nitrogen, and Hydrogen Analyzer manufactured by LECO Japan Kodo Kaisha, Model: ON836

[0035] Carrier gas: Helium gas

[0036] Flux: Nickel particles

[0037] Crucible: Standard crucible

[0038] Analysis Method: Non-dispersive infrared absorption method

[0039] [Parameter]

[0040] Standardized sample: YY-001-114-00(0.119%)

[0041] Analysis Mode: Automatic

[0042] Analysis Delay: 45 seconds

[0043] Integration Delay: 2 seconds

[0044] Comparator: Not in use

[0045] End line: 2 seconds

[0046] Integration time: 500 seconds

[0047] Analysis power: The temperature was increased from 100 W to 6000 W over 400 seconds.

[0048] Figure 1 is a graph showing the relationship between output and temperature in an oxygen separator used in an embodiment. The test temperature is 2500°C according to the correspondence table between power value and temperature shown in Figure 1.

[0049] (3) Method for measuring composition, average crystal particle size and density

[0050] The potassium content added to the tungsten material needs to be between 5 ppm and 30 ppm. Potassium functions as a grain growth inhibitor for the electrode. If the content is less than 5 ppm, there is no grain growth inhibition effect, and if it exceeds 30 ppm, it affects the reduction of the discharge lamp's lifespan. Due to the aforementioned potassium, the crystal grain size during the recrystallization of the tungsten material becomes 200 μm or less. Regarding the measurement of the crystal grain size, it was performed on the RD plane (a plane perpendicular to the rolling direction). Specifically, a magnified photograph at 200x magnification was taken at an arbitrary position near the center, and a certain length (1000 μm) within that field of view was set as the numerator. The number of crystal grain boundaries crossing that certain length was set as the denominator. The crystal grain size within that field of view was determined using the intercept method, where the value of the numerator / denominator is the crystal grain size within that field of view. A total of 6 fields of view (per sample) were measured, and the average value of these crystal grain sizes was taken as the crystal grain size.

[0051] The method for measuring potassium content is as follows.

[0052] The mass of the measurement material is 0.40 g, and the material sampled from the center of the tungsten material is used.

[0053] As a sample pretreatment prior to measurement, acid washing using an acid (HNO3:HF:water = 1:1:1 (volume ratio)) is performed for 5 minutes. Afterward, water washing is performed for 15 minutes. After performing water washing for 15 minutes, the dried sample is placed in a platinum dish, 1 cm³ of nitric acid and 1 cm³ of hydrofluoric acid are added and heated to decompose it, and the solution is evaporated to dry to form tungsten oxide. Then, 10 volume% of lithium carbonate is added to heat and dissolve the oxide, and the solution diluted to 50 cm³ is used as the measurement sample solution.

[0054] The measuring instrument used was a Flame atomic absorption spectrophotometer, model: ContrAA300, manufactured by Analytic Jena, Inc. Japan. The composition was measured in accordance with JISH1403:2001 (Analysis method for tungsten materials). The analysis method was based on atomic absorption.

[0055] Materials containing tungsten may contain calcium, silicon, aluminum, magnesium, and potassium. The total content of these non-tungsten compositions is 30 ppm or more and 300 ppm or less. These measurement methods are carried out in accordance with JISH 1403: 2001 (Methods for analyzing tungsten materials).

[0056] The density of a material containing tungsten is measured by using Archimedes' principle to measure the mass in air and water, respectively, and then calculating the density by determining the volume from both.

[0057] Preferably, the crystal grain size of the tungsten-containing material is 200 μm or less. If the crystal grain boundary is 200 μm or less, the illuminance retention rate is highest when used as a DC discharge lamp.

[0058] Preferably, the density of the material containing tungsten is 19.1 g / cm³ or higher.

[0059] Preferably, a material containing tungsten is used for discharge lamp electrodes.

[0060] Preferably, the discharge lamp electrode is a direct current discharge lamp electrode.

[0061] Examples

[0062] A. Manufacture of tungsten-containing material (rod)

[0063] (A-1) Tungsten Sintered Body Manufacturing Process

[0064] [Preparation of Raw Materials]

[0065] Potassium was added to the tungsten raw material in the same manner as general potassium-added tungsten for lighting, and potassium-containing tungsten powder was obtained by hydrogen reduction. The amount of potassium added to the potassium-containing tungsten powder was adjusted by performing acid washing in an intermediate process as needed. The FSSS particle size of the potassium-containing tungsten powder according to the Fischer method is 2.2 to 2.4 μm.

[0066] [Heat Treatment]

[0067] Since some oxygen still remained in this powder, heat treatment was further performed in a batch-type electric furnace in a hydrogen atmosphere at 700°C for 10 hours. Afterward, the powder was cooled to room temperature in hydrogen to obtain low-oxygen and potassium-containing tungsten powder.

[0068] While the oxygen content in conventional tungsten powder is 600 to 900 ppm, the oxygen content of the low-oxygen potassium-containing tungsten powder through this heat treatment becomes 150 to 250 ppm.

[0069] [Pressing and Sintering]

[0070] This powder was stored so as not to be exposed to oxygen in the atmosphere, fed into a rubber mold for a hydrostatic press, and a press body was produced by applying a pressure of 180 MPa using a hydrostatic press. In addition, a molded body was produced by molding this press body.

[0071] This molded body was first sintered at 1,500°C for 10 hours in an argon atmosphere using a hot isostatic pressing (HIP) device. This first sintered body was sintered at 2,300°C for 30 hours in a hydrogen atmosphere using a batch sintering furnace to obtain a tungsten sintered body (a material containing tungsten).

[0072] The size of the sintered body at this time was 100 mm in diameter × 500 mm in length. The density after sintering was 18.3 g / cm³.

[0073] The silicon content in the sintered body was less than 5 ppm.

[0074] As a result of various tests, the FSSS particle size is preferably 1 μm or more and 10 μm or less.

[0075] If the particle size exceeds 10 μm, there is a concern that the specific gravity of the sintered body will decrease and the density will not rise to a level sufficient to withstand plastic processing. Furthermore, "concern" indicates that there is a slight possibility of this happening, and does not mean that it will happen with a high probability.

[0076] If the particle size is less than 1 μm, the density during pressing does not increase, and there is a risk that the specific gravity will decrease after sintering.

[0077] If the density of the sintered body is 17.5 g / cm³ or higher, there are no restrictions on the sintering method, but 18.0 g / cm³ or higher is preferred.

[0078] In addition to a vacuum atmosphere, an inert atmosphere such as argon or a hydrogen atmosphere may be selected as the sintering atmosphere. When the density after sintering is 17.5 g / cm³ or higher, multiple combinations of sintering atmospheres are possible (e.g., a hydrogen atmosphere up to 1,200°C, a vacuum atmosphere from 1,200°C to 2,000°C, etc.), and the sintering temperature and sintering time may also be selected arbitrarily. It is preferable to heat treat at a sintering temperature of 2,300°C or higher.

[0079] (A-2) Processing Process

[0080] This tungsten sintered body was heated in hydrogen at 1,800°C in a furnace, and then forged using a die with a forging machine. The diameter was forged to 80 mm in the first process, 70 mm in the second process, 60 mm in the third process, and 50 mm in the fourth process. At this time, heating was added for each heat. The material forged to 50 mm was then heated at a furnace temperature of 1,800°C and processed by swaging (rotary swaging) until it reached a diameter of 40 to 15 mm. At this time, processing was performed while sampling at arbitrary sizes.

[0081] The heating atmosphere during forging may be in an argon or hydrogen atmosphere in addition to a nitrogen atmosphere.

[0082] The heating temperature during forging is preferably between 1,600°C and 1,800°C. If the temperature exceeds 1,800°C, the lifespan of the heating furnace is shortened, so productivity is not excellent.

[0083] A total processing rate of 65% or higher is desirable. However, regarding the processing rate, it is preferable if the final specific gravity exceeds 19.1; if it is lower than this, the specific gravity may not be satisfied. Furthermore, the closer the specific gravity exceeds 19.1 and approaches the theoretical specific gravity of tungsten, the better.

[0084] By the above process, tungsten-containing materials (tungsten rods) of sample numbers 1 to 12 were produced.

[0085]

[0086] Sample No. 13 is manufactured by the method described in (A-1) and (A-2) above and is a sample with a low potassium content. In this case, the crystal grain size is large, and Sample No. 14 is manufactured by the method described in (A-1) and (A-2) above and is a sample with low specific gravity. Sample No. 15 is manufactured by the method described in (A-1) and (A-2) above and is a sample with low specific gravity and slightly large particles. Sample No. 16 is manufactured by the method described in (A-1) (provided that [heat treatment] is not performed) and (A-2) above and is a sample containing potassium. Sample No. 17 is manufactured by the method described in (A-1) (provided that [heat treatment] is not performed) and (A-2) above and is a sample not containing potassium. Sample number 18 is a sample containing a large amount of potassium, prepared by the method shown in (A-1) (however, [heat treatment] is not performed) and (A-2) above.

[0087] B. Evaluation Results

[0088] For measuring the lifespan of the discharge lamp, a 1 kW DC discharge lamp was manufactured and evaluated based on its illuminance retention rate. For the discharge lamp, tungsten materials of sample numbers 1 to 15, manufactured in the process of “A. Manufacture of Tungsten Rod”, were processed into a 30 mm electrode and used as the anode. Tungsten containing 1 mass% thorium was used as the cathode. The tungsten electrode of the present disclosure was found to have an effect of extending the lifespan in high-power discharge lamps. Table 1 shows the emitted oxygen amount, potassium content, average crystal grain size, density, and illuminance retention rate (lamp lifespan), including the lamp lifespan results. The measurement methods for these are based on “(2) Measurement of oxygen emitted amount” and “(3) Method for measuring composition, average crystal grain size, and density.”

[0089] If the tungsten material has the above characteristics, the same effect can be obtained regardless of the diameter in millimeters. There are no restrictions on manufacturing conditions, and sintering may be performed using a high-temperature press (HIP, HP), and there are no restrictions on plastic processing methods such as forging, rolling, or extrusion.

[0090] Tungsten materials can achieve the same effect not only with simple shapes but also by drilling holes or grooving them through machining.

[0091] In Table 1, lamp life is expressed as the illuminance retention rate after 750 h of illumination. Assuming the illuminance at the time of initial illumination is 100% and the illuminance judged as unusable is less than 90%, the range from 100% to 95% or higher is designated as A, the range from less than 95% to 93% or higher is B, the range from less than 93% to 91% or higher is C, and the range from less than 91% is D.

[0092] In samples No. 16 to 18, it was confirmed that the roughness retention rate decreases due to the influence of a high oxygen release amount or coarsening of the crystal grain size. Specifically, the oxygen release amount needs to be greater than 1 ppm and less than or equal to 20 ppm. Preferably, the oxygen release amount is 4 ppm or more and 9 ppm or less. The potassium content needs to be 5 ppm or more and 30 ppm or less.

[0093] [Appendix 1]

[0094] A tungsten-containing material in which the amount of oxygen generated at 2100℃ to 2300℃ detected by oxygen analysis according to the oxygen separator method exceeds 1 ppm and is 20 ppm or less, and contains potassium of 5 ppm or more and 30 ppm or less.

[0095] [Book 2]

[0096] A material containing tungsten as described in Appendix 1, having a crystal grain size of 200 μm or less.

[0097] [Book 3]

[0098] A material containing tungsten as described in Appendix 1 or 2, characterized by having a density of 19.1 g / cm³ or more.

[0099] [Book 4]

[0100] A material comprising tungsten for use as a discharge lamp electrode, as described in any 1 of Appendix 1 to 3.

[0101] [Book 5]

[0102] DC discharge lamp electrode using a tungsten-containing material as described in Appendix 4.

[0103] The embodiments and examples disclosed herein should be considered as illustrative and not limiting in all respects. The scope of the invention is defined by the claims, not by the description above, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

Claim 1 A tungsten-containing material, wherein the amount of oxygen generated at 2100°C to 2300°C detected by oxygen analysis according to the oxygen separator method is greater than 1 ppm and less than or equal to 20 ppm, contains potassium at a level of 5 ppm or more and less than or equal to 30 ppm, and the total content of the composition other than tungsten is 30 ppm or more and less than or equal to 300 ppm. Claim 2 A material comprising tungsten having a crystal grain size of 200 μm or less, according to claim 1. Claim 3 A material containing tungsten according to claim 1 or 2, characterized by having a density of 19.1 g / cm³ or more. Claim 4 A material comprising tungsten for use as a discharge lamp electrode in claim 1 or 2. Claim 5 A DC discharge lamp electrode using a material containing tungsten as described in paragraph 4.

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