JPH11224647A - Ceramic discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic discharge lamp that is equipped with a bulb which is formed from a polycrystalline alumina sintered body and has high transmissivity, and can provide long use life. SOLUTION: In a ceramic discharge lamp which is composed by placing a pair of electrodes 21 opposite to each other and enclosing a metal halide in a bulb 10 formed from a transmissive polycrystalline alumina sintered body containing a crystalline particle abnormal growth suppressing metal oxide, the bulb 10 is of a type undergone an out-of-phase substance elimination process,. at least for its inside surface, to eliminate out-of-phase substances formed from a composite oxide of a crystalline particle abnormal growth suppressing metal oxide and alumina. In this case, the crystalline particle abnormal growth suppressing metal oxide is one or more kinds of oxides of magnesium, lanthanum, yttrium and praseodymium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic discharge lamp having a bulb made of a translucent polycrystalline alumina sintered body.

[0002]

2. Description of the Related Art At present, a discharge lamp such as a high-pressure or low-pressure mercury discharge lamp or a metal halide lamp is used as a light source for a backlight of a liquid crystal display device or a light source of an ultraviolet ray processing device. In such a discharge lamp, a pair of discharge electrodes are arranged in a translucent bulb so as to face each other, and a luminous substance made of mercury, a rare gas, and, if necessary, a halide of various metals is enclosed. It is configured. The bulb of the discharge lamp is usually formed of quartz glass, has a spherical or elliptical spherical arc tube portion, and a sealing tube portion integrally connected to both ends thereof, and has an electrode at the tip. When the structure is sealed in the sealing tube portion, a hermetic sealing structure is formed in the sealing tube portion, and a current supply portion extending airtightly in the arc tube portion is configured.

On the other hand, as the translucent material, translucent ceramics such as alumina, yttria, yttrium-aluminum-garnet (so-called "YAG") and zirconia are known. Compared with glass, it has advantages such as high mechanical strength, high heat resistance temperature, and excellent corrosion resistance to specific metal elements. Therefore, recently, attention has been paid to a ceramic discharge lamp in which a bulb is formed of such translucent ceramics, particularly, a translucent polycrystalline alumina sintered body.

However, in a ceramic discharge lamp provided with a bulb made of a translucent polycrystalline alumina sintered body, the following problems arise when a metal halide lamp is obtained by enclosing a metal halide in the bulb. This has been found by the present inventors' research. That is, the translucent polycrystalline alumina sintered body is doped with at least one of oxides of magnesium, lanthanum, yttrium, and praseodymium as a metal oxide for suppressing abnormal growth of crystal grains, for the reason of the manufacturing method. . This is because in the sintering step of alumina powder to obtain a translucent polycrystalline alumina sintered body, the metal oxide for suppressing abnormal growth forms a complex oxide such as spinel or garnet which is a hetero-phase substance with alumina. However, since this composite oxide forms a solid solution of calcium contained as an impurity in the alumina powder, an Al-Ca-O-based liquid phase is prevented from being formed, and as a result, alumina crystal particles become abnormal. This is because crystal growth of alumina is effectively prevented, and as a result, a polycrystalline alumina sintered body having a uniform particle diameter and high translucency can be obtained.

[0005] In such a polycrystalline alumina sintered body containing a metal oxide for suppressing abnormal growth of crystal grains, the above-mentioned hetero-phase substance is formed at the alumina grain boundary, that is, the crystal grains adjacent to the alumina crystal grains. This foreign phase material has low chemical stability against metal halides, and therefore, has a ceramic discharge lamp provided with a bulb made of the polycrystalline alumina sintered body. In, the foreign phase material is corroded by the metal halide to generate impurities in the bulb early, and as a result, the performance of the discharge lamp is reduced at an early stage, and the service life is short.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made based on the above circumstances, and its object is to provide:
An object of the present invention is to provide a ceramic discharge lamp having a highly translucent bulb made of a sintered body of polycrystalline alumina and having a long service life.

[0007]

In order to achieve the above object, a ceramic discharge lamp according to the present invention comprises a bulb made of a translucent polycrystalline alumina sintered body containing a metal oxide for suppressing abnormal growth of crystal grains. In a ceramic discharge lamp in which a pair of electrodes are arranged to face each other and a metal halide is sealed, the bulb is:
At least the inner surface is subjected to a hetero-phase substance removing treatment for removing a hetero-phase substance consisting of a composite oxide of a metal oxide for suppressing abnormal growth of crystal grains and alumina. Here, the metal oxide for suppressing abnormal growth of crystal grains is at least one of oxides of magnesium, lanthanum, yttrium, and praseodymium.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a ceramic discharge lamp according to the present invention will be described in detail. FIG. 1 is an explanatory cross-sectional view showing a configuration of an example of a ceramic discharge lamp of the present invention. In this ceramic discharge lamp, the bulb 10 comprises a substantially spherical arc tube portion 11 surrounding the discharge space S, and a straight tubular sealing tube continuously extending outward from both ends of the arc tube portion 11. And a portion 12 formed of a translucent polycrystalline alumina sintered body. The bulb 10 usually has a maximum outer diameter of the arc tube portion 11 of 4.0.
１５15 mm, the inner volume is 25〜1500 mm ³ , the outer diameter of the sealing tube 12 is 1.6〜3.2 mm, and the inner diameter is 0.5
1.0 mm and a length of 4.0 to 12 mm.

In the bulb 10, a pair of electrodes 21 are arranged so as to face each other. Electrode 21 in the illustrated example
Is formed by winding a metal coil around the tip of an electrode rod 22 extending along the tube axis from inside the sealing tube portion 12 into the arc tube portion 11. At the base end of the electrode rod 22, a rod-shaped intermediate lead 23 extending in the same direction as the electrode rod 22 is provided.
The rod-shaped external leads 24 extending in the same direction are integrally connected by, for example, welding, and are electrically connected. Specifically, the electrode 21 is located inside the arc tube part 11 and the tip of the external lead 24 is located outside,
Further, the base end portion of the electrode rod 22 and the intermediate lead 23 are in a state of being positioned in the sealing tube portion 12. here,
As a material of the electrode rod 22 and the metal coil, for example, tungsten is used, as a material of the intermediate lead 23, for example, niobium is used, and as a material of the external lead 24, for example, platinum is used.

[0010] A sleeve 26 made of ceramic is disposed inside the sealing tube portion 12 of the bulb 10 so as to approach the arc tube portion 11 with the electrode rod 22 inserted therethrough. As a material forming the sleeve 26, polycrystalline alumina, silica glass, or the like can be used, but it is preferable that the material is the same as the material of the valve 10. The length of the sleeve 26 is, for example, 4 to 6 mm, depending on the length of the sealing tube 12.

The sleeve 26 has an outer diameter of the sealing tube portion 12.
It is desirable to have a shape that matches the inner diameter of the electrode rod 22 and that matches the outer diameter of the electrode rod 22. Especially sleeve 2
It is preferable that the difference between the outer diameter of No. 6 and the inner diameter of the sealing tube portion 12 is small, specifically, 0.12 mm or less. As a result, the gap between the two becomes narrower, and the amount of the enclosing material that enters and condenses can be reduced. As a result, the vapor pressure of the luminous substance in the luminous tube portion 11 is constantly reduced. The height required for realizing the color rendering properties of the period can be maintained.

Further, the sleeve 26 in the sealing tube portion 12
The hermetic sealing structure is formed on the outer end side portion located further outside than that. Specifically, frit glass 3 for sealing is used.
0 is injected into the outer end side portion of the sealing tube 12, and the gap between the base end of the electrode rod 22 protruding from the outer end of the sleeve 26 and the intermediate lead 23 and the inner wall surface of the sealing tube 12. In addition to filling the gap, a bead portion 31 of frit glass is formed on the outer end of the sealing tube portion 12 so as to protrude outward.
The portion including the connection portion is fixed in a buried state, and the distal end portion of the external lead 24 projects outward from the bead portion 31 of the frit glass. Here, as the frit glass 30 for sealing, for example, alumina
A silica-rare earth oxide-based material can be preferably used.

An appropriate metal halide is sealed in the bulb 10 as a luminescent substance. As the metal halide, a conventionally known metal halide can be used.
There is no particular limitation.

In this ceramic discharge lamp,
The valve 10 is provided on a surface of a valve material made of a translucent polycrystalline alumina sintered body containing a metal oxide for suppressing abnormal growth of crystal grains made of at least one of oxides of magnesium, lanthanum, yttrium and praseodymium. In this case, a foreign substance removal treatment for removing a foreign substance consisting of a composite oxide of a metal oxide for suppressing abnormal growth of crystal grains and alumina is performed.

Specifically, an alumina powder composition obtained by mixing a raw material alumina powder with a metal oxide for suppressing abnormal growth of crystal grains and an appropriate binder as necessary is added to the arc tube portion 11.
And molded into a predetermined shape comprising the sealing tube portion 12 and sintered at a temperature of, for example, about 1100 to 1900 ° C. to obtain a valve material made of a translucent polycrystalline alumina sintered body. Subject to substance removal treatment. In other words, the surface of the bulb material, at least the surface including the portion forming the inner surface of the arc tube portion 11 of the bulb 10, is subjected to a foreign phase substance removal treatment, and a ceramic discharge lamp may be manufactured using this.

Here, as the raw material alumina powder, those having an average particle size of, for example, 0.1 to 2 μm are preferably used. The mixing ratio of the metal oxide for suppressing abnormal growth of crystal grains is usually, for example, 0.01 to 0.1 part by weight with respect to 100 parts by weight of alumina powder. 0 if the substance is magnesium oxide
02 to 0.06 parts by weight, 0.0 in the case of lanthanum oxide
2 to 0.1 parts by weight, 0.0% in the case of yttrium oxide
The amount is preferably from 1 to 0.06 parts by weight and, in the case of praseodymium oxide, from 0.01 to 0.06 parts by weight.

[0017] The foreign substance removal treatment for the valve material is as follows.
For example, it can be performed by the following method. (1) Thermal etching method In this method, the valve material is kept at a high temperature in a reduced-pressure atmosphere, whereby the foreign material exposed on the surface of the valve material is thermally decomposed and removed. In practice, for example, a heat treatment is performed using a vacuum heating furnace at a temperature of 1500 ° C. or more under a reduced pressure condition of a pressure of 10 ⁻³ Pa or less for about 12 hours or more. (2) Chemical etching method In this method, the valve material is immersed in hot sulfuric acid, whereby the foreign material exposed on the surface of the valve material is thermally decomposed and removed. In practice, for example, the valve material is immersed in a 10% sulfuric acid solution maintained at a temperature of about 200 ° C. by an autoclave for about 1 hour.

The translucent polycrystalline alumina sintered body constituting the bulb 10 has an average crystal particle diameter of 20 to 40 μm.
m. Here, the average crystal grain size means 1.5 times the intercept length.

Since the bulb 10 of the ceramic discharge lamp of the present invention is made of a polycrystalline alumina sintered body containing a metal oxide for suppressing abnormal growth of crystal grains, the bulb 10 basically has high translucency. Have. Moreover, the valve 10 is
Since at least the inner surface of the arc tube portion 11 has been subjected to the foreign phase substance removal treatment, impurities are generated from the foreign phase substance at an early stage even though the metal halide is sealed as a light emitting substance, and the discharge space is formed. Since a suitable discharge atmosphere is stably maintained for a long time without being released to S, a long service life is obtained.

[0020]

EXAMPLE An alumina powder having an average particle size of 0.5 μm was used as a raw material, and a mixture of 100 parts by weight of 0.04 parts by weight of magnesium oxide was molded at a temperature of 1700 ° C.
As a result, a valve material made of a translucent polycrystalline alumina sintered body having an average particle size of about 30 μm and basically having the configuration shown in FIG. 1 was obtained. In addition, the content ratio of calcium in the raw material alumina powder was about 6 ppm. The valve material obtained here is used in a vacuum heating furnace.
By holding at a temperature of 1700 ° C. for 15 hours under a reduced pressure atmosphere of 10 ⁻⁵ Pa, the surface of the valve material is subjected to a foreign phase substance removal treatment, and the valve material obtained here is used to have the configuration shown in FIG. A ceramic discharge lamp was manufactured. In the valve material after the foreign phase substance removal treatment,
The surface coverage of magnesium oxide by Auger electron spectroscopy (AES) was about 1.2%.

The ceramic discharge lamp obtained here has a maximum outer diameter of the light tube 11 of the bulb 10 of 8.7 m.
m, the overall length is 36 mm, the wall pressure is almost uniform and 0.7 mm, the internal volume is about 0.3 mm ³ , and the electrode is 0.3 mm in diameter.
0.2 mm in diameter at the tip of the tungsten electrode rod 22
It consists wound tungsten coil 6 turns, the light emitting tube portion 11 enclosing 13kPa argon, iodide dysprosium as a light-emitting substance - iodide thallium - sodium iodide (Dy ₃ -TlI-NaI) 4mg
And 5.4 mg of mercury.

The ceramic discharge lamp of the present invention manufactured as described above is continuously lit under the rated conditions of a lamp input of 75 W, a lamp voltage of 90 V and a lamp current of 0.95 A. Luminous flux of 1
00%). Table 1 shows the results. Also, for comparison, a ceramic discharge lamp for comparison was manufactured in exactly the same manner except that the bulb material which was not subjected to the foreign phase substance removal treatment was used as it was, and the same lighting test was performed. I asked. Table 1 shows the results. The numerical values in Table 1 are average values for the present invention and three ceramic discharge lamps for comparison.

[0023]

[Table 1]

As is apparent from Table 1, according to the ceramic discharge lamp of the present invention, since the bulb has been subjected to the treatment for removing the hetero-phase substance, a high luminous flux is maintained even after a long lighting time has elapsed. Rate is obtained. On the other hand, in the comparative ceramic discharge lamp, it is understood that the luminous flux maintenance factor is reduced early. More specifically, for example, the lighting time until the luminous flux maintenance factor is reduced to 80% is 1500 hours for the lamp of the present invention, while the comparative lamp is 1000 hours, and the luminous flux maintenance characteristics are as high as 50%. It is clear that is improved.

[0025]

The ceramic discharge lamp of the present invention is provided with a highly translucent bulb made of a polycrystalline alumina sintered body containing a metal oxide for suppressing abnormal growth of crystal grains, and has been used for a long time. Life is obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing a configuration of an example of a ceramic discharge lamp of the present invention.

[Explanation of symbols]

 Reference Signs List 10 bulb S discharge space 11 arc tube part 12 sealing tube part 21 electrode 22 electrode rod 23 intermediate lead 24 external lead 26 sleeve 30 frit glass 31 bead part

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor: Shoji Miyanaga 1194, Sado, Bessho-cho, Himeji-shi, Hyogo Ushio Electric Co., Ltd. Inside

Claims (2)

[Claims] 1. A bulb made of a translucent polycrystalline alumina sintered body containing a metal oxide for suppressing abnormal growth of crystal grains, a pair of electrodes are arranged so as to face each other and a metal halide is enclosed. In the ceramic discharge lamp formed as described above, at least the inner surface of the bulb is subjected to a hetero-phase substance removing treatment for removing a hetero-phase substance composed of a composite oxide of a metal oxide for suppressing abnormal growth of crystal grains and alumina. A discharge lamp made of ceramic, characterized in that the discharge lamp is made of a ceramic material. 2. The metal oxide for suppressing abnormal growth of crystal grains,
The ceramic discharge lamp according to claim 1, wherein the discharge lamp is at least one of oxides of magnesium, lanthanum, yttrium, and praseodymium.