CN112262454B

CN112262454B - Cathode member for discharge lamp, and method for manufacturing cathode member for discharge lamp

Info

Publication number: CN112262454B
Application number: CN202080003268.4A
Authority: CN
Inventors: 青山齐; 沟部雅恭; 友清宪治; 中野康彦
Original assignee: Toshiba Corp; Toshiba Materials Co Ltd
Current assignee: Toshiba Corp; Toshiba Materials Co Ltd
Priority date: 2019-02-18
Filing date: 2020-02-18
Publication date: 2024-04-09
Anticipated expiration: 2040-02-18
Also published as: CN112262454A; JP7098812B2; JPWO2020171065A1; WO2020171065A1

Abstract

The discharge lamp cathode member includes a main body portion having a wire diameter of 2mm or more and 35mm or less and a distal end portion which is tapered from the main body portion to the distal end. The cathode part contains a tungsten alloy according to ThO ₂ The conversion amount of thorium is 0.5 to 3 mass%. When electron back scattering diffraction analysis is performed on a region including a center and having a unit area of 90 μm×90 μm on a cross section passing through the center of the body portion while along the longitudinal direction of the body portion, a crystal grain map obtained by the electron back scattering diffraction analysis has tungsten crystal grains including tungsten and thorium crystal grains including thorium. In the cumulative distribution diagram of the grain size distribution of a plurality of thorium grains in the grain diagram, the grain size at which the cumulative frequency is 90% is 3.0 μm or more.

Description

Cathode member for discharge lamp, and method for manufacturing cathode member for discharge lamp

Technical Field

Embodiments relate to a cathode member for a discharge lamp and a discharge lamp.

Background

Discharge lamps are broadly classified into low-pressure discharge lamps and high-pressure discharge lamps. Examples of the low-pressure discharge lamp include arc discharge type discharge lamps of various types, such as special lighting, paint curing devices, ultraviolet (UV) curing devices, sterilization devices, and optical cleaning devices for semiconductors, which are used for general lighting, roads, tunnels, and the like. Examples of the high-pressure discharge lamp include a water supply/discharge treatment device, an outdoor illumination device such as a general illumination device or a game field, a UV curing device, an exposure device such as a semiconductor or a printed wiring board, a high-pressure mercury lamp such as a wafer inspection device or a projector, a metal halide lamp, an ultrahigh-pressure mercury lamp, a xenon lamp, a sodium lamp, and the like. Such discharge lamps are used in various devices such as lighting devices, image projection devices, and manufacturing devices.

For example, a projection display device using a discharge lamp is known. In recent years, home theatres and digital cinema have been popular. These use projection type display devices called projectors. Conventional projection display devices have an influence on the lifetime of a lamp and the flickering of emitted light due to the consumption of electrodes of a discharge lamp. In order to cope with such a problem, a Pulse Width Modulation (PWM) driving is known as a driving method of the discharge lamp. In this way, the electrode consumption of the discharge lamp can be managed by the control circuit.

If the electrodes of the discharge lamp are consumed, the lamp voltage drops. Thereby, light emitted from the discharge lamp is deviated. Such a phenomenon is called a flicker (flicker) phenomenon. Flicker affects flicker of an image, etc. Therefore, there is a need for an electrode for a discharge lamp having high durability.

0001, there is known a technique of controlling the particle size of tungsten crystals in a cross section in a longitudinal direction (side direction) and a cross section in a radial direction (circumferential direction) of a cathode member for a discharge lamp. The cathode assembly manufactured by the above technique was subjected to a durability test, and a voltage was applied thereto in a state in which the cathode assembly was electrically heated, and the emission current density (mA/mm) after 10 hours was measured ² ) And an emission current density (mA/mm) after 100 hours ² ) It is known to have excellent characteristics.

Discharge lamps are used in various devices such as lighting devices, image projection devices, and manufacturing devices. The lamp performance decreases if the electrodes of the discharge lamp are consumed. The discharge lamp needs to be replaced if the lamp performance is degraded. Therefore, further lifetime of the electrode is desired. The conventional cathode member for a discharge lamp exhibits excellent durability for about 100 hours, but the durability is reduced over a long period of time.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open publication No. 2011-3486

Patent document 2: japanese patent No. 5800922 specification

Disclosure of Invention

The cathode member for a discharge lamp according to an embodiment includes a main body portion having a wire diameter of 2mm or more and 35mm or less and a distal end portion which tapers from the main body portion to a distal end. The cathode part contains a tungsten alloy according to ThO ₂ The conversion amount of thorium is 0.5 to 3 mass%. When electron back scattering diffraction analysis is performed on a region including a center and having a unit area of 90 μm×90 μm on a cross section passing through the center of the body portion while along the longitudinal direction of the body portion, a crystal grain map obtained by the electron back scattering diffraction analysis has tungsten crystal grains including tungsten and thorium crystal grains including thorium. The thorium crystal grains are defined by a difference in crystal orientation angle between measurement points at 2 or more points in succession in the crystal grain diagram being-5 degrees or more and +5 degrees or less, respectively, and including thorium. The size of the thorium grains is defined by the equivalent circle diameter of the thorium crystallization region in the grain diagram. In the cumulative distribution diagram of the grain size distribution of a plurality of thorium grains in the grain diagram, the grain size at which the cumulative frequency is 90% is 3.0 μm or more.

Drawings

Fig. 1 is a side view showing an example of a cathode member for a discharge lamp.

Fig. 2 is a view showing an example of a cross section in the longitudinal direction of the main body.

Fig. 3 is a diagram showing cumulative distribution of thorium grains of example 1 and comparative example 1.

Fig. 4 is a graph showing frequency distribution diagrams of thorium crystal grains of example 1 and comparative example 1.

Fig. 5 is a diagram showing a configuration example of a discharge lamp.

Detailed Description

Hereinafter, embodiments will be described with reference to the drawings. The relationship between the thickness and the planar dimensions of the components and the ratio of the thicknesses of the components described in the drawings are different from those of the actual products. In the embodiment, substantially the same constituent elements are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

Fig. 1 is a side view showing an example of a cathode member for a discharge lamp. The discharge lamp cathode member 1 includes a main body 2 having a wire diameter of 2mm or more and 35mm or less, and a distal end 3 extending from the main body 2 to the tip thereof so as to be thinner. Fig. 1 shows a discharge lamp cathode member 1, a main body 2, a distal end 3, a center 4, a line diameter W of the main body 2, and a length T of the main body 2. Fig. 2 is a view showing an example of a longitudinal cross section of the center 4 of the body 2. Fig. 2 shows a direction a along the length T direction (side direction) of the main body 2, a cross section 5 passing through the center 4 along the direction a, and a direction b perpendicular to the cross section 5 (the radial W direction (circumferential direction) of the main body 2). In the present specification, the cathode member for a discharge lamp may be simply referred to as a "cathode member".

The body portion 2 has a cylindrical shape. The wire diameter W is the diameter of the cross section in the circumferential direction. When the circumference is elliptical, the line diameter W represents the maximum diameter. If the wire diameter W of the main body 2 is less than 2mm, there is a possibility that the discharge lamp emits insufficient light. If the wire diameter W exceeds 35mm, the discharge lamp tends to be large. Therefore, the wire diameter W is preferably 2mm or more and 35mm or less, more preferably 5mm or more and 20mm or less. The length T of the main body 2 is preferably 10mm to 600 mm.

The distal end portion 3 has a shape that becomes thinner from the main body portion 2 to the tip. Therefore, the region from the point where tapering starts to the end is the tip 3. The tip portion 3 has an acute angle shape in a cross section in the direction a of the cathode member 1. The cathode member 1 is not limited to such a shape, and the tip end portion 3 may have another shape such as an R shape or a planar shape in a cross section in the direction a of the cathode member 1. When the tip end portion 3 has a tapered shape, discharge can be efficiently performed between the pair of electrode members of the discharge lamp.

The cathode part is made of oxide (ThO) ₂ ) A tungsten alloy containing 0.5 mass% or more and 3 mass% or less of thorium (also referred to as a thorium component) in terms of conversion. When the content is less than 0.5 mass%, the effect of addition is small, and when it exceeds 3 mass%, the sinterability and the workability are deteriorated. Thus, the thorium content is expressed as oxides (ThO ₂ ) The amount of the catalyst is preferably 0.5% by mass or more and 3% by mass or less, more preferably 0.8% by mass or more and 2.5% by mass or less.

In the case of Electron Back Scattering Diffraction (EBSD) analysis of a region including the center 4 and having a unit area of 90 μm×90 μm in the cross section 5, a crystal grain map obtained by EBSD analysis has crystal grains including tungsten (tungsten crystal grains) and crystal grains including thorium (thorium crystal grains).

The EBSD irradiates the crystalline sample with electron rays. Electrons are diffracted and released from the sample as reflected electrons. The diffraction pattern is projected, and crystal orientation and the like can be measured from the projected pattern. X-ray diffraction (XRD) is a method for determining an average value of crystal orientations in a plurality of crystal grains. In contrast, EBSD can measure the crystal orientation of each crystal. The same analysis method as that of EBSD is sometimes referred to as Electron Back Scattering Pattern (EBSP) analysis.

EBSD analysis was performed using a thermal electron emission scanning electron microscope (TFE-SEM) JSM-6500F manufactured by Japanese electronics Co., ltd. And a DigiView IV slow scan CCD camera manufactured by TSL Solution Co., ltd., OIM Data collector.7.3 x, OIM Analyzer.8.0.

The measurement conditions for the EBSD analysis include an acceleration voltage of electron beam of 20kV, an irradiation current of 12nA, a tilt angle of the sample of 70 degrees, a unit area of a measurement region of 90 μm by 90 μm, and a measurement interval of 0.3 μm/step. The cross section 5 is a measurement surface, and a diffraction pattern is obtained by irradiating the cross section 5 with an electron beam. The surface roughness Ra of the measurement surface of the measurement sample is reduced to 0.8 μm or less. The cross section 5 passes through the center of the distal end portion 3 and through the center 4 of the thickness T of the body portion 2. The measurement area contains a center 4.

Tungsten crystal grains are defined by tungsten crystal regions in which the difference in crystal orientation angle at measurement points of 2 or more points in succession in the crystal grain diagram is-5 degrees or more and +5 degrees or less, respectively, and which contain tungsten. In other words, a tungsten crystal region in which 2 or more points exist continuously at a measurement point having a difference in crystal orientation angle within 5 degrees can be identified as tungsten crystal grains. In addition, tungsten crystalline regions can be identified using the EBSD analysis apparatus described above.

The grain size of tungsten grains is defined by the equivalent circle diameter of the tungsten crystalline region in the grain map. The average particle diameter of the plurality of tungsten crystal grains is, for example, preferably 20 μm or less, and more preferably 15 μm or less. This makes it possible to make the distribution state of the plurality of thorium crystal grains uniform. That is, thorium crystal grains having a predetermined particle size distribution can be uniformly dispersed. This can improve discharge characteristics.

The average particle diameter can be calculated from the crystal grains recognized in the region of 90 μm×90 μm per unit area. The particle size here is the equivalent circle diameter. The boundaries of the regions protruding from the regions of 90 μm×90 μm in unit area were calculated as the end portions of the crystal grains. The average particle diameter is the median diameter. That is, the cumulative particle diameter.

The thorium crystal grains are defined by a difference in crystal orientation angle between measurement points at 2 or more points in succession in the crystal grain diagram being-5 degrees or more and +5 degrees or less, respectively, and including thorium. In other words, a region where thorium crystals exist continuously at a measurement point having a difference in crystal orientation angle of 5 degrees or less at 2 points or more can be identified as thorium crystal grains. In addition, the thorium crystallization region can be identified using the apparatus for EBSD analysis described above.

The size of the thorium grains is defined by the equivalent circle diameter of the thorium crystallization region in the grain diagram. The particle size distribution of the plurality of thorium grains is represented by a cumulative distribution diagram and a frequency distribution diagram.

The cumulative distribution diagram shows the relationship between the particle diameter (μm) on the horizontal axis and the cumulative frequency (%) on the vertical axis. The horizontal axis is divided into a plurality of particle size ranges at intervals of, for example, 0.125 μm to 0.25 μm. The cumulative distribution diagram of the thorium crystal grains shows the relationship between the particle size and the cumulative frequency of the thorium crystal grains present in the region of 90 μm×90 μm per unit area. The upper limit of the cumulative frequency is 100%.

The frequency distribution diagram shows the relationship between the particle diameter (μm) on the horizontal axis and the frequency (%) on the vertical axis. The horizontal axis is divided into a plurality of particle size ranges at intervals of, for example, 0.125 μm to 0.25 μm. The frequency distribution chart shows relatively which grain size is larger among the grain sizes of the grains existing in the grain map, for example.

Particle diameter D with a cumulative frequency of 90% in the cumulative distribution diagram of thorium grains ₉₀ Preferably 3.0 μm or more. Particle diameter D ₉₀ The upper limit of (2) is not particularly limited, but is, for example, 4.5 μm or less. The grain size of the thorium grains is defined by the equivalent circle diameter of the above-mentioned thorium crystallization region in the grain diagram.

Particle diameter D ₉₀ The particle diameter of the thorium crystal grain is 3.0 μm or more, which means that the particle diameter of the thorium crystal grain is relatively large. Particle diameter D of conventional cathode part ₉₀ Below 3.0 μm. Thorium grains are present in the grain boundaries of tungsten grains with each other. By enlarging the thorium grains, the grain growth of tungsten grains can be suppressed.

The effect of suppressing the grain growth of base material grains, such as tungsten grains, is also called pinning effect, by the presence of grain boundary grains, such as thorium grains, in the grain boundaries of the base material grains. If the pinning effect is uneven, the pinning effect causes rapid growth of base material grains. By increasing the particle size of the thorium grains, the pinning effect can be made uniform. As a result, tungsten grains can be uniformly grown.

Particle diameter D with a cumulative frequency of 100% in the cumulative distribution diagram of thorium grains ₁₀₀ Preferably 4.8 μm or less, more preferably 4.5 μm or less. The thorium grains are evaporated by irradiation. Therefore, if coarse thorium grains are included, large voids are formed in the trace of evaporated thorium grains, which may reduce the durability of the cathode member 1.

Particle diameter D with cumulative frequency of 50% ₅₀ Preferably 1.8 μm or more. Thereby enabling the pinning effect to be more uniform. Particle diameter D ₅₀ The upper limit of (2) is not particularly limited, but is, for example, 3.0 μm or less.

The frequency distribution pattern of the thorium crystal grains preferably has a very small point in the range of particle diameters of 2 μm or more and 3 μm or less. This can increase the proportion of thorium crystal grains having a particle diameter of 3 μm or more.

The minimum point is the bottom point of the trough of the frequency profile. The maximum point is the peak of the mountain of the histogram. A mountain having a frequency distribution pattern indicates that the number of crystal grains having a particle diameter corresponding to the peak of the mountain is large. In addition, the valleys having the frequency distribution pattern indicate that the number of crystal grains having a particle diameter corresponding to the bottom points of the valleys is small.

The frequency distribution pattern of the thorium crystal grains preferably has a region in which the difference between the frequency of the very small point in the range of the particle diameter of 2 μm or more and 3 μm or less of the frequency distribution pattern and the frequency of the maximum point closest to the very small point is 10% or more. This means that the frequency distribution pattern has large valleys. By having large valleys, the number of thorium grains approaching the grain size can be increased. By approximating the particle size of the thorium crystal grains, the pinning effect can be made uniform.

Preferably, the cathode assembly 1 does not have a recrystallized structure. It is important to control the particle size of thorium grains, tungsten grains, and the like before recrystallization. Thus, even if the tungsten crystal has a recrystallized structure, abnormal growth of the tungsten crystal grains can be suppressed. In other words, the cathode member of the embodiment is a cathode member before recrystallization.

The recrystallized structure is a structure in which the strain (internal stress) in the crystal is reduced by heat treatment at the recrystallization temperature. The recrystallization temperature of the tungsten alloy containing thorium is 1300K to 2000K (1027 ℃ C. To 1727 ℃ C. Inclusive). The cathode member 1 needs to be formed by performing processing for forming the distal end portion 3. It is also necessary to form the main body by performing processing for adjusting the wire diameter W of the main body 2. The deformation caused by these processes can be alleviated by the recrystallization heat treatment. The recrystallization formed at a temperature of 1300K or more and 2000K or less is referred to as primary recrystallization. The primary recrystallization is accompanied by grain growth as compared with before the heat treatment. The recrystallization formed at a temperature exceeding 2000K is referred to as secondary recrystallization. The secondary recrystallization further produces grain growth compared to the primary recrystallization. Generally, the grains of the secondary recrystallization are increased by more than 30 times before the heat treatment. Therefore, the presence or absence of recrystallization can be determined from the particle size. When the discharge lamp is turned on, the temperature of the cathode electrode rises to a temperature exceeding 2000 ℃. Thus, the cathode member 1 has a recrystallized structure. If the crystal grain growth agent is used continuously for a long time, the high temperature state is continued, so that the crystal grain growth agent is a use environment which is easier to grow crystal grains. In general, the secondary recrystallized grains are 30 times or more larger than those before the heat treatment. Therefore, the presence or absence of the recrystallized structure can be determined from the particle size.

The cathode member according to the embodiment can control the crystal orientation and the like before recrystallization, and thus can suppress grain growth. As a result, the flickering lifetime of the discharge lamp can be prolonged.

The conventional discharge lamp causes a flickering phenomenon when about half of the guaranteed life required of the discharge lamp has elapsed. As a result of this, it was found that abnormal growth of crystal grains occurred in tungsten crystal grains of the cathode member for discharge lamp over a certain period of time.

The cathode member for a discharge lamp according to the embodiment can suppress occurrence of abnormal grain growth of tungsten grains. This can provide a cathode member for a discharge lamp having a long lifetime.

The cathode assembly of the embodiment may be applied to a discharge lamp. Fig. 5 is a diagram showing a configuration example of a discharge lamp. Fig. 5 shows a cathode member 1, an anode member 6, an electrode support rod 7, and a glass tube 8.

The cathode assembly 1 is connected to an electrode support rod 7. The anode member 6 is connected to another electrode supporting rod 7. The connection is performed by brazing or the like. The cathode member 1 and the anode member 6 are disposed in opposition to each other in the glass tube 8, and are sealed together with a part of the electrode support rod 7. The inside of the glass tube 8 is kept vacuum.

The cathode assembly 1 may be applied to any one of a low-pressure discharge lamp and a high-pressure discharge lamp. Examples of the low-pressure discharge lamp include arc discharge lamps used in various types of special lighting, paint curing devices, UV curing devices, sterilization devices, and optical cleaning devices for semiconductors, which are used in general lighting, roads, tunnels, and the like. Examples of the high-pressure discharge lamp include a water supply/discharge treatment device, an outdoor illumination device such as a general illumination device or a game field, a UV curing device, an exposure device such as a semiconductor or a printed wiring board, a high-pressure mercury lamp such as a wafer inspection device or a projector, a metal halide lamp, an ultrahigh-pressure mercury lamp, a xenon lamp, a sodium lamp, and the like. Such discharge lamps are used in various devices such as lighting devices, image projection devices, and manufacturing devices. The cathode member according to the embodiment is suitable for a high-pressure discharge lamp because of its excellent durability.

The power of the discharge lamp is, for example, 100W to 10kW. A discharge lamp with a power lower than 1000W was used as a low-pressure discharge lamp, and a discharge lamp with a power higher than 1000W was used as a high-pressure discharge lamp.

The discharge lamp has a guaranteed lifetime set according to the application. One of the guaranteed lifetimes is the flicker lifetime. The flicker phenomenon is a phenomenon in which the power of the discharge lamp fluctuates as described above, and the power drops although a voltage is applied to bring the power of the discharge lamp to 100%.

The discharge lamp for digital cinema is constituted by a discharge lamp having a power in a range of 1kW to 7kW. The power of the discharge lamp is selected in contrast to the screen size. The power was 1.2kW at a screen size of 6 m. The power was 4kW at a screen size of 15 m. The power was 7kW at a screen size of 30 m. The rated life of the discharge lamp with a power of 1.2kW is set to about 3000 hours. The rated life of the discharge lamp with a power of 4kW is set to about 1000 hours. The rated life of the discharge lamp with a power of 7kW is set to about 300 hours. The life of a discharge lamp for digital cinema is shortened as the power increases. As described above, the life of the discharge lamp is various depending on the application and the use condition.

In the conventional cathode member for a discharge lamp, a flickering phenomenon occurs when a period of about half of the lifetime elapses. When a flicker phenomenon occurs in a discharge lamp for a digital cinema, a flicker of a picture occurs, and a beautiful image cannot be seen, so that it is necessary to replace the above-mentioned components before the rated life. The cathode member according to the embodiment can suppress abnormal growth of crystal grains of tungsten crystals in use of the discharge lamp. Therefore, occurrence of a flicker phenomenon can be suppressed.

Projection display devices such as digital cinema have a reduced image quality if flicker occurs. Therefore, suppression of the flicker phenomenon is strictly required. Therefore, the cathode assembly of the embodiment is suitable for a discharge lamp for a digital cinema. The discharge lamp for digital cinema is exemplified here, but the same applies to other applications.

Next, a method example of manufacturing the cathode member according to the embodiment will be described. The method of manufacturing the cathode member according to the embodiment is not particularly limited as long as the cathode member having the above-described configuration can be formed, but the following method is exemplified as a method of manufacturing the cathode member with high yield.

The manufacturing method of the cathode component for the discharge lamp comprises the following steps: a step of mixing a tungsten source powder with a thorium source powder to form a mixed powder, a step of forming a compact using the mixed powder, a step of sintering the compact by preliminary sintering to form a preliminary sintered body, and a step of sintering the preliminary sintered body by electric conduction sintering.

The frequency distribution chart of the particle size distribution of the tungsten source powder has a plurality of peaks including the 1 st peak and the 2 nd peak adjacent to each other, and the peak-to-peak distance between the 1 st peak and the 2 nd peak is preferably 10 μm or more. Thus, a mixed powder of large powder and small powder can be formed. The mixed powder has small powder in the grain boundaries of the large powder. This makes it possible to make the grain boundary sizes of tungsten grains uniform. Thorium grains are present in the grain boundaries of tungsten grains with each other. By making the grain boundary sizes of tungsten grains uniform with each other, the size of thorium grains present in the grain boundary can be adjusted.

The frequencies of the peaks including the 1 st peak and the 2 nd peak are preferably 2% or more, respectively. This can improve the effect of making the grain boundary size uniform.

In order to prepare such tungsten source powder, it is preferable to mix 1 st tungsten source powder having a 1 st peak in a particle size range of less than 10 μm with 2 nd tungsten source powder having a 2 nd peak in a particle size range of 10 μm or more to form mixed tungsten powder. Preferably, 30 mass% or more and 50 mass% or less of the mixed tungsten powder is the 1 st tungsten source powder (tungsten source powder having a small particle size), and the remainder is the 2 nd tungsten source powder (tungsten source powder having a large particle size).

The frequency distribution pattern of the particle size distribution of the 1 st tungsten source powder preferably has a 1 st peak, which is a frequency in the particle size range of 4 to 7 μm inclusive and 4 to 6% inclusive. The frequency distribution pattern of the 2 nd tungsten source powder preferably has a 2 nd peak, which is a frequency of 6% or more and 8% or less in the particle diameter range of 20 μm or more and 50 μm or less.

The particle size distribution of the tungsten source powder was measured using the Microtrac company 9320-X100. The apparatus can measure particle size by a laser diffraction method. The peak position and frequency can be read from the particle size distribution obtained from the measurement.

The thorium source powder can be formed, for example, by forming thorium oxide (ThO ₂ ) To adjust the amount of thorium in the tungsten alloy.

The thorium source powder and the tungsten source powder can be mixed using, for example, a wet method or a dry method.

The wet process evaporates a liquid component from a solution containing thorium nitrate and tungsten powder, for example, and decomposes the thorium component into thorium oxide by heating at 400 ℃ to 900 ℃ in an atmosphere. By this step, a tungsten powder containing thorium oxide powder can be formed.

The dry process pulverizes the mixed thorium oxide powder, for example by means of a ball mill. By this step, the agglomerated thoria powder can be broken down, and the agglomeration of the thoria powder can be reduced. In addition, a small amount of tungsten powder may be added during the mixing step.

Preferably, the agglomerated powder or coarse particles which have been sieved and not completely pulverized are removed from the pulverized and mixed thorium oxide powder as required. It is preferable that agglomerated powder or coarse particles exceeding the maximum diameter of 10 μm are removed by sieving.

Next, thorium oxide powder and tungsten powder are mixed. Tungsten powder is added in such a way that the target thorium oxide concentration is finally reached. The mixed powder of thorium oxide powder and tungsten powder is charged into a mixing vessel, and the mixing vessel is rotated to uniformly mix the thorium oxide powder and tungsten powder. In this case, the mixing vessel is formed in a cylindrical shape and rotated in the circumferential direction, whereby smooth mixing can be performed. By this step, a tungsten powder containing thorium oxide powder can be produced.

The above wet method or dry method can produce tungsten powder containing thorium oxide powder. Among the wet method and the dry method, the wet method is preferable. Since the dry method mixes the raw material powder and the container while rotating the mixing container, the raw material powder and the container are rubbed, and impurities are easily mixed. The content of the thorium oxide powder is preferably 0.5% by mass or more and 3% by mass or less. In addition, if the wet process is used, the thorium oxide powder tends to infiltrate into the gaps between the tungsten powder. Whereby the grain sizes of the tungsten grains and the thorium grains are easily controlled.

The molded article is formed using, for example, tungsten powder containing thorium oxide powder. In forming the molded article, a binder may be used as needed. The molded article has, for example, a cylindrical shape having a diameter of 5mm to 50 mm. The length of the molded article is arbitrary.

The preliminary sintering is preferably performed at a temperature of 1250 ℃ to 1500 ℃.

The electrical conduction sintering is preferably performed so as to reach a temperature of 2100 ℃ or higher and 2500 ℃ or lower. At temperatures below 2100 c, insufficient densification may occur and the strength may decrease. If it exceeds 2500 ℃, the thorium and tungsten grains excessively grow, and the target crystal structure may not be obtained.

By the above production method, a sintered body (ingot) of a tungsten alloy containing thorium can be obtained. Further, if the preliminary sintered body has a cylindrical shape, the sintered body also has a cylindrical shape. Hereinafter, an example of a cylindrical sintered body having a cylindrical shape will be described.

The above manufacturing method may further include a first processing step and a second processing step.

The first working process is to process an ingot by at least one working selected from forging, rolling, and extrusion, and adjust, for example, a wire diameter W of the ingot.

These processes can reduce the wire diameter W. Thus, the pores in the cylindrical sintered body can be reduced. The first working process is preferably a forging process or an extrusion process. Since the forging or extrusion is easy to process the entire circumference of the cylindrical sintered body, the effect of reducing the pores is high.

The forging process is a process of applying pressure by hammering the cylindrical sintered body with a hammer. The rolling process is a process of sandwiching the sintered body between two or more rolls. Extrusion processing is a method of extruding from a die orifice by strong pressure.

Since the forging process is performed by hammering, local deviations in crystal orientation are likely to occur. The extrusion process is prone to cause a difference in crystal orientation between the central portion and the surface portion due to a strong stress when passing through the extrusion die. In the case of rolling, the crystal orientation can be easily controlled by adjusting the stress from the rolls.

The machining rate in the first machining step is preferably, for example, 10% to 30%. If the processing rate is less than 10%, the effect of reducing the pores is small. If the processing rate exceeds 30%, control of crystal orientation becomes difficult. The first processing step may be performed in a plurality of times as long as the processing rate is within a range of 10% or more and 30% or less.

Regarding the working ratio, when the cross-sectional area of the cylindrical sintered body before working is a and the cross-sectional area of the cylindrical sintered body after working is B, the working ratio = [ (a-B)/a can be used]X 100% was determined. For example, the processing rate when a cylindrical sintered body having a diameter of 25mm is processed into a cylindrical sintered body having a diameter of 20mm will be described. Since the cross-sectional area A of a circle having a diameter of 25mm is 460.6mm ² The cross-sectional area B of a circle with a diameter of 20mm is 314mm ² So the processing rate is 32% = [ (460.6-314)/460.6]×100％。

The machining rate of the first machining step is 10% or more and 30% or less, and can be obtained by using the cross-sectional area of the cylindrical sintered body (ingot) before the first machining step as the cross-sectional area a.

The second working process is, for example, rolling. The crystal orientation is easy to control in the case of rolling. The rolling is a method of reducing the cross-sectional area while being pinched by a plurality of rolls. The crystal orientation can be controlled if the processing is performed only by rolling processing. The second processing step is performed after the first processing step.

In the second working step, the rolling working is performed at a working rate of 30% to 70%, preferably 40% to 70%. The machining rate in the second machining step is 30% or more and 70% or less, and the cross-sectional area of the cylindrical sintered body after the first machining step can be obtained as the cross-sectional area a.

The cross-sectional area after the first working process is taken as a cross-sectional area A to control the working ratio. If the processing ratio is in the range of 30% to 70%, 1 processing may be performed or 2 or more times may be performed. If the processing rate is less than 30% or more than 70%, the targeted crystal orientation is not obtained.

The first working process and the second working process are preferably cold working. Cold working is a method of working an object at a temperature equal to or lower than the recrystallization temperature. Processing performed in a heated state at or above the recrystallization temperature is referred to as hot processing. If the sintered body is thermally processed, the cylindrical sintered body is recrystallized. If cold worked, it will not be recrystallized. It is important to control the grains by the structure that is not recrystallized.

The cylindrical sintered body having a wire diameter of 2mm to 35mm formed in the above steps is cut into a desired length. Next, a step of forming the tapered distal end portion 3 is performed. The machining of the distal end portion 3 may be performed by cutting the distal end portion 3 into a predetermined taper shape. If necessary, surface polishing is performed so that the surface roughness Ra is 5 μm or less. The cathode member according to the embodiment can be manufactured by the above steps.

The discharge lamp can be manufactured as follows. First, the cathode member 1 is connected to the electrode support rod 7. The connection may be made by brazing or the like. A member for connecting the anode member 6 to the electrode support rod 7 is prepared. The cathode member 1 and the anode member 6 are disposed and fixed to face each other in the glass tube 8, and are sealed together with a part of the electrode support rod 7. A vacuum is formed inside the glass tube 8. In the step of manufacturing the discharge lamp, heat treatment at a temperature equal to or higher than the recrystallization temperature of the cathode member may be performed as needed.

Examples

Examples 1 to 7 and comparative example 1

The tungsten source powder is mixed with the thorium source powder to form a mixed powder. Table 1 is a table for explaining tungsten source powder and thorium source powder. The tungsten source powder is a mixed tungsten powder of a 1 st tungsten powder having a particle size distribution showing a frequency distribution pattern of a 1 st peak and a 2 nd tungsten powder having a particle size distribution showing a frequency distribution pattern of a 2 nd peak. Table 1 shows the content of the 1 st tungsten powder and the content of the 2 nd tungsten powder in the mixed tungsten powder, and the peak particle diameters and peak frequencies of the 1 st and 2 nd tungsten powders. The mixed powder is prepared by mixing a liquid component from a solution containing thorium nitrate and tungsten powderEvaporating, and heating at 400-900deg.C to decompose thorium into thorium oxide in air. The content of thorium source powder is ThO ₂ And (5) conversion. The thorium source powder has an average particle diameter of 3 μm or less.

TABLE 1

As can be seen from Table 1, in examples 1 to 7, the content of the thorium source powder was expressed as ThO ₂ The content of the 1 st tungsten source powder of the mixed tungsten powder is 40 to 50 mass% in terms of 0.5 to 2.6 mass%, the content of the 2 nd tungsten source powder is 50 to 60 mass%, the frequency distribution diagram of the tungsten source powder has a 1 st peak in a particle size range of 8 μm or less and a 2 nd peak in a particle size range of 20 μm or more, and the peak frequencies are all 3% or more in frequency.

Next, a molded body was formed using the mixed powder. Then, the molded body is sintered by preliminary sintering to form a preliminary sintered body. Next, the preliminary sintered body was sintered by electric current sintering to produce a cylindrical sintered body (ingot). Table 2 is a table for explaining preliminary sintering and energization sintering.

TABLE 2

Next, the cylindrical sintered body (ingot) is processed by the first processing step, and then processed by the second processing step. Table 3 is a diagram for explaining the first processing step and the second processing step.

The first and second working steps are cold working.

TABLE 3 Table 3

Next, the cold-worked cylindrical sintered body is worked by cutting. Further, a tapered distal end portion is formed at the end portion of the cylindrical sintered body subjected to the cutting process. The taper angle of the tip portion is 60 degrees or more and 80 degrees or less. Through the above steps, a cathode member for a discharge lamp was manufactured. Table 4 is a table for explaining the dimensions of the cathode member.

TABLE 4 Table 4

The manufactured cathode member was analyzed by EBSD analysis, and a grain pattern of tungsten grains and a grain pattern of thorium grains were produced. The measurement conditions and the like are the same as those described in the embodiment, and therefore, the description thereof is omitted here.

Using the grain map of the thorium grains, a cumulative distribution map of the thorium grains is made, and a frequency distribution map is made. Fig. 3 is a diagram showing cumulative distribution of thorium grains of example 1 and comparative example 1. Fig. 4 is a graph showing frequency distribution diagrams of thorium crystal grains of example 1 and comparative example 1. The solid lines in fig. 3 and 4 represent example 1, and the broken lines represent comparative example 1.

From the cumulative distribution pattern, the particle diameter D of the thorium grains is calculated ₉₀ Particle diameter D ₅₀ 、D ₁₀₀ . In the frequency distribution map, the presence or absence of a minimum point in a particle diameter range of 2 μm or more and 3 μm or less, and the presence or absence of a portion in which a difference between a frequency of a minimum point in a particle diameter range of 2 μm or more and 3 μm or less and a frequency of a maximum point closest to the minimum point is 10% or more are confirmed. Further, the average particle diameter of tungsten crystal grains was calculated using the crystal grain map of tungsten crystal grains. Table 5 is a table for explaining thorium grains and tungsten grains.

TABLE 5

In the cathode parts of examples 1 to 7, the particle diameter D of the thorium crystal grains ₉₀ At 3.0 μmParticle diameter D of 3.9 μm or less ₅₀ Particle diameter D of 1.8 μm or more and 4.0 μm or less ₁₀₀ Is less than 4.8 mu m. The tungsten crystal grains have an average particle diameter of 4 μm or more and 7.8 μm or less.

In the cathode members of examples 1 to 7, the frequency distribution pattern had very small points in the range of particle diameters of 2 μm or more and 3 μm or less. The difference between the frequency of the minimum point in the particle diameter range of 2 μm or more and 3 μm or less and the frequency of the maximum point closest to the minimum point is 10% or more. In comparative example 1, although the frequency distribution pattern of the thorium crystal grains has a minimum value, the frequency distribution pattern is outside the range. In addition, particle diameter D of tungsten crystal grains ₅₀ All were 20 μm or less.

Next, durability of the cathode member for a discharge lamp was evaluated by a durability test. A discharge lamp was manufactured using a cathode member for a discharge lamp. The durability test was performed by a lighting test, and the blinking life of the discharge lamp was measured. The lamp voltage at the time of lighting was 40V, and the lamp voltage at the time of non-lighting was 20V. The lighting state is set to 3 hours, and the non-lighting state is set to 2 hours, and the lighting state and the non-lighting state are alternately repeated. Flicker is defined as occurring when the variation of the lamp voltage in the lit state or unlit state is 1V or more. The total of lighting time until flicker occurs is defined as a flicker lifetime.

The average particle diameter (μm) of tungsten crystal grains was measured after 800 hours passed under the same conditions. Average particle diameter D ₅₀ The measurement of (2) was performed by using a cross section of the distal end portion in the lateral direction, and a portion of 0.5mm from the distal end was measured. The results are shown in table 6.

TABLE 6

As is clear from table 6, the discharge lamps using the cathode members of examples 1 to 7 have a longer life than the discharge lamp using the cathode member of comparative example 1. This is because the pinning effect of the thorium crystal grains is uniformly exhibited, and the coarsening of the tungsten crystal grains can be suppressed. In addition, by using a tungsten source powder having a plurality of peaks in the frequency distribution diagram, the particle size distribution of thorium crystal grains can be controlled.

While the present invention has been described with reference to several embodiments, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other modes, and various omissions, substitutions, modifications, and the like can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and their equivalents. The foregoing embodiments may be implemented in combination with each other.

Claims

1. A cathode member for a discharge lamp comprising a main body portion having a wire diameter of 2mm or more and 35mm or less and a tip portion which is tapered from the main body portion to a tip end thereof,

the cathode part comprises a tungsten alloy according to ThO ₂ Contains 0.5 to 3 mass% of thorium in terms of conversion,

when performing electron back scattering diffraction analysis on a region having a unit area of 90 μm×90 μm including the center on a cross section passing through the center of the main body portion while along the longitudinal direction of the main body portion, a crystal grain pattern obtained by the electron back scattering diffraction analysis has tungsten crystal grains including tungsten and thorium crystal grains including thorium,

the thorium grains are defined by a difference in crystal orientation angle between measurement points at 2 points or more in succession in the grain diagram being-5 degrees or more and +5 degrees or less, respectively, and including a thorium crystallization region of the thorium,

the grain size of the thorium crystallites is defined by the equivalent circle diameter of the thorium crystallization region in the crystallite map,

in a cumulative distribution diagram of the grain size distribution of a plurality of the thorium grains in the grain diagram, the grain size having a cumulative frequency of 90% is 3.0 μm or more,

the frequency distribution diagram of the particle size distribution of the thorium crystal particles has a very small point in the particle size range of 2 μm or more and 3 μm or less.

2. The cathode member for a discharge lamp according to claim 1, wherein a particle diameter of 1.8 μm or more, in which a cumulative frequency of 50% in a cumulative distribution of a particle size distribution of the thorium crystal grains.

3. The cathode member for a discharge lamp according to claim 1, wherein a difference between a frequency of the minimum point of the frequency distribution map and a frequency of a maximum point closest to the minimum point is 10% or more.

4. The cathode member for a discharge lamp according to claim 1, wherein the tungsten crystal grains have an average particle diameter of 20 μm or less.

5. The cathode member for a discharge lamp according to claim 2, wherein the tungsten crystal grains have an average particle diameter of 20 μm or less.

6. The cathode member for a discharge lamp according to claim 1, wherein the cathode member has no recrystallized structure.

7. The cathode member for a discharge lamp according to claim 2, wherein the cathode member has no recrystallized structure.

8. A discharge lamp comprising the cathode assembly for a discharge lamp according to claim 1.

9. The discharge lamp of claim 8, which is a digital cinema discharge lamp.

10. A method for manufacturing a cathode member for a discharge lamp, comprising the steps of:

a step of mixing a tungsten source powder having a particle size distribution showing a frequency distribution pattern including a 1 st peak and a 2 nd peak with a thorium source powder having an average particle diameter of 3 μm or less to form a mixed powder;

a step of forming a molded body having a diameter of 5mm or more and 50mm or less using the mixed powder;

a step of sintering the molded body by preliminary sintering at a temperature of 1250 ℃ to 1500 ℃ inclusive to form a preliminary sintered body; and

sintering the pre-sintered body by means of electric sintering at a temperature of 2100 ℃ to 2500 ℃;

the peak-to-peak distance between the 1 st peak and the 2 nd peak is 10 μm or more.

11. The method according to claim 10, wherein the frequency of the 1 st peak and the frequency of the 2 nd peak are 2% or more, respectively.

12. The method according to claim 10, wherein the particle diameter of the 1 st peak is smaller than 10 μm, and the particle diameter of the 2 nd peak is 10 μm or more.