JPH1154086A - Tungsten electrode material and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode material having satisfactory ignitablility and excellent wear resistance by containing both a compound of tungsten and boron and a compound of lanthanum and boron. SOLUTION: This electrode material is preferably obtained by adding lanthanum boride powder to metal tungsten powder in a ratio of 10-75 VOL.% of the whole body followed by sufficient dry mixing, and discharge plasma sintering the resulting mixing powder. The sintering is performed at about 1600-1800 deg.C to provide an electrode material having desired form and dimension. When the addition quantity of lanthanum boride is less than 10% by volume, desired electron emitting characteristic cannot be provided, and when it exceeds 75%, it is too brittle to be resistant to practical use. The preferable average particle size of metal tungsten powder is 2-4 μm, and the preferable average particle size of lanthanum boride is 1-3 μm. The electrode material is preferably used as an electrode material for a high-pressure discharge lamp, especially as a negative electrode tor a mercury lamp or xenon lamp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode material for a high pressure discharge lamp or the like, and more particularly to a tungsten electrode material suitable for use as a cathode material for a mercury lamp or a xenon lamp.

[0002]

2. Description of the Related Art A well-known electrode material such as an electrode for a high pressure discharge lamp is a tungsten electrode material to which thorium oxide is added, that is, a so-called thoriated tungsten material. Thorium oxide is an excellent electron-emitting material and has been widely used.

[0003]

The tungsten electrode material to which thorium oxide is added has excellent electron emission characteristics, but has a low recrystallization temperature and is easily recrystallized, so that the electrode shape is liable to change. There was a problem. Further, the tungsten electrode material to which thorium oxide is added has a problem that the operating temperature is high, and therefore, the temperature of the electrode tends to be high and the consumption amount is large.

Further, thorium oxide powder, which is a raw material,
Since it is a radioactive substance, it is becoming increasingly difficult to obtain raw materials, which increases costs, and there is also a problem that strict control is required for its storage and handling by law.

In recent years, applications of high pressure discharge lamps and the like have been diversified, and there has been a demand for electrode materials having higher performance than conventional ones. That is, in a high-pressure discharge lamp, the current applied to the cathode is extremely high in density, so
High heat resistance is required. At the same time, a stable discharge is always required depending on the use and purpose, such as when the light is continuously turned on for a long time or when the blinking is repeatedly performed for a long time.

[0006] Therefore, in operating at high temperature and high pressure during operation, in order to keep the crystal structure constant and maintain stable discharge, it is necessary to supply the electron-emitting substance stably from the inside.

The present inventors have found that a tungsten electrode material to which lanthanum boride is added has excellent performance, and have already filed patent applications for inventions related thereto (Japanese Patent Application Laid-Open Nos. 6-91391 and 7-91391). 292188
issue).

An object of the present invention is to provide an electrode material having performance equal to or higher than that of the electrode material according to the present invention.

[0009]

The present inventors have conducted various studies for the purpose of solving the above problems, and as a result, have found that the following electrode materials are excellent, and have completed the present invention. First, the first invention has a gist of a tungsten-based electrode material characterized by containing both a compound of tungsten and boron and a compound of lanthanum and boron.

Next, a second aspect of the present invention is to provide lanthanum boride to tungsten powder in an amount of 10 to 75 vol. The present invention provides a method for producing a tungsten-based electrode material, characterized by obtaining an electrode material in which a powder added at a ratio of% is sintered to obtain a compound of tungsten and boron and a compound of lanthanum and boron.

The sintering of the powder compact in the above-mentioned production method is preferably performed by a discharge plasma sintering method. The discharge plasma sintering method is a method in which an on / off DC pulse voltage is applied to a powder compact and heating is performed using a discharge phenomenon that occurs between powder particles. Sintering is also possible.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to specific examples. This electrode material is manufactured, for example, as follows. First, lanthanum boride LaB ₆ powder is added to metal tungsten powder as a raw material, and mixed until uniformly dispersed. The addition amount of lanthanum boride LaB ₆ powder, whole 10～75Vol. %. If the added amount of lanthanum boride is less than 10% by volume, desired electron emission characteristics cannot be obtained, and if it is more than 75%, it is too brittle and cannot withstand practical use. The preferred average particle size of the metal tungsten powder is, for example, 2 to 4 microns, and the preferred average particle size of the lanthanum boride powder is, for example, 1 to 3 microns.

The obtained mixed powder is sintered by a discharge plasma sintering method to obtain an electrode material having a desired shape and dimensions. In the discharge plasma sintering method, for example, a mixture of a die made of carbon and upper and lower punches is filled with the mixed powder as much as possible without gaps, and the upper and lower punches are connected to a power supply, and the inside of the apparatus is evacuated and energized Is carried out. This sintering is performed according to a predetermined pressurization pattern and temperature rise pattern. When the predetermined sintering temperature is reached, the temperature and pressure are maintained for a certain period of time. Cool in a vacuum atmosphere to a temperature free of The preferred sintering temperature is about 1600 to 1800 ° C. If the sintering temperature is too high, the desired sintered body cannot be obtained because lanthanum boride is melted first.

In the electrode material obtained by the above sintering,
Both borides of tungsten and lanthanum are present. Examples of borides of tungsten include WB, W
₂ B, there is a W ₂ B _5, and the like. Examples of lanthanum borides include LaB ₆ and LaB ₄ . When the amount of lanthanum boride LaB ₆ was relatively small, pure tungsten W was detected by X-ray diffraction, but when the amount of lanthanum boride was large, pure tungsten was not detected. Since the sintered body obtained as described above is considerably brittle, it has been difficult to perform such processes as forging and plastic working.

This electrode material contains a boron compound of lanthanum in addition to a boron compound of tungsten, and has a low work function and a high electron emission property, so that it has excellent wear resistance and excellent arc ignition property. It is.

The electrode material containing tungsten as a main component can be used as an electrode for an electron tube, an electrode for laser excitation, various kinds of plasma electrodes, etc. by changing a processing shape or the like.

According to experiments by the present inventors, it has been found that excellent performance can be obtained if the round bar manufactured as described above is processed into a specific shape and used. First, as a material having the above composition, a diameter of 0.2 to 15 m
A round bar shape of m is preferable. It is preferable that the tip of the round bar is pointed in a conical shape in the range of 15 to 65 degrees. FIG. 2 shows a preferable tip shape. The angle α of the conical tip portion 2 of the electrode material 1 varies depending on the type, output, size, etc. of the discharge lamp, and the diameter of the round bar (wire bar) varies. Therefore, it is preferable to appropriately select within the above range. When the angle is out of this range, the tip tends to be worn out and the illuminance tends to fluctuate due to the fluctuation of the arc.

Furthermore, it is longer to slightly cut the conical pointed tip to form a flat portion 3 as shown in FIG. 2A so that the tip does not become too sharp. Lifetime and stable electron emission performance can be obtained. The cut length is preferably 1 mm or less, and 0.2 to 0.8 mm. If the cut length is too small, the stability is lacking, and if the cut length is too large, the arc characteristics are deteriorated. This cutting need not necessarily be performed by actually cutting, but may be performed by another method such as polishing. Further, the shape of the flat portion 3 may not be a flat shape, and may be formed as a convex curved surface 4 as shown in FIG. 2B, for example.

[0019]

EXAMPLES To a tungsten powder having an average particle size of 2.7 microns and a purity of 99.9% or more, a lanthanum boride powder having an average particle size of 1 to 2 microns was added and thoroughly mixed in a dry system. Table 1 shows the amount of lanthanum boride to be added. The obtained mixed powder was sintered as a raw material by a discharge plasma sintering method. The sintering apparatus used was a discharge plasma sintering machine (trade name: DR. SINTER series) manufactured by Sumitomo Coal Mining Co., Ltd. A round bar having a diameter of 3.2 mm was cut out from the obtained sintered body.

The tip of the obtained round bar was ground into a 30 ° conical shape, and the sharp tip was cut to a length of 0.2 mm. Table 1 also shows comparative examples having different compositions, tip shapes, and the like.

[0021]

[Table 1]

FIG. 1 shows the results obtained by performing continuous lighting for 100 hours, 300 hours, and 700 hours using these electrode materials and measuring the amount of consumption. This lighting test was performed in an argon atmosphere pressurized to 20 atm in a chamber, using an electrode material made of the round bar whose tip was processed as a cathode, a pure tungsten material as an anode, an arc distance of 2 mm, and a constant voltage of 12 A. Was.

Table 2 shows that the same material was used under the same conditions under the same conditions for 20 minutes of lighting and 5 minutes of rest as one cycle, and this was repeated 100 times and 500 times, respectively.
It is a measure of the number of firings within seconds. In the same table, data of the comparative example is also shown.

[0024]

[Table 2]

[0025]

As described above, according to the present invention,
It is possible to relatively easily obtain a tungsten-based electrode material having better ignition performance than conventional thoriated tungsten electrode material and extremely excellent wear resistance.

[Brief description of the drawings]

FIG. 1 is a graph showing a result of a wear test.

FIG. 2 is a diagram illustrating a preferred tip shape of an electrode material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrode material 2 Conical tip 3 Flat part (tip cut part)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuyoshi Akane, 105-1, Hirosato, Otoe-cho, Fukagawa-shi, Hokkaido 1 Inside Toho Metal Co., Ltd. 105-1 in Toho Metal Co., Ltd. Fukagawa Plant (72) Inventor Hiroo Matsumoto 105-1, 1 Toho Metal Co., Ltd. in Fukagawa Plant

Claims (3)

[Claims] 1. A tungsten-based electrode material comprising both a compound of tungsten and boron and a compound of lanthanum and boron. 2. Lanthanum boride is added to tungsten powder in an amount of 10 to 75 vol. %. A method for producing a tungsten-based electrode material, comprising sintering a powder added in a proportion of 10% to obtain an electrode material in which a compound of tungsten and boron and a compound of lanthanum and boron coexist. 3. The method according to claim 2, wherein the sintering is performed by a discharge plasma sintering method.