JPH08298099A - Arc tube for metal vapor discharge lamp - Google Patents

Abstract

(57) [Summary] [Constitution] The content of yttrium-aluminum-garnet is 99.8% or more, the content of the oxide of the group 2a element of the periodic table is 600 ppm or less, and the content of SiO ₂ is 90 ppm.
A light-transmitting tube is formed of a yttrium-aluminum-garnet sintered body having a relative density of 09.0 ppm or less and a relative density of 99.0% or more to form an arc tube for a metal vapor discharge lamp. [Effect] The linear transmittance of visible light can be set to 40% or more, and a long-life arc tube for metal vapor discharge lamp can be obtained which hardly corrodes even when exposed to a metal halide for 3000 hours.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc tube for a metal vapor discharge lamp.

[0002]

2. Description of the Related Art Conventionally, it has been used for indoor and outdoor lighting such as roads, tunnels and auditoriums, general lighting for stores, back lamps for OHP and liquid crystal projectors, sterilizing lamps, automobile head lamps, etc. The structure of the metal vapor discharge lamp is, for example, one in which an arc tube 1 in which a metal halide is enclosed is arranged inside a bottomed cylindrical body 11 as shown in FIG. Further, as a detailed structure of the arc tube 1, as shown in FIG. 1, a DyI ₃ -InI-TlI-
A metal halide such as LiI is sealed, and the both ends of the light-transmitting tube 2 are sealed by attaching glass 4 to the closing body 3 made of a cermet material. Further, an electrode mandrel 5 is embedded in one end of the closing body 3, and a lead rod 6 is buried in the other end thereof. By applying a voltage to the lead rod 6 to cause a discharge between the electrode mandrel 5, light is emitted. The metal halide enclosed in the tube 2 was designed to emit light.

The characteristics required of the light-transmitting tube 2 which constitutes the arc tube 1 for such a metal vapor discharge lamp are as follows. High linear transmittance from visible rays to ultraviolet rays 1. 2. Less susceptible to erosion by metal halides. The flexural strength is 30 kg / mm ² or more, and there is a material formed of translucent alumina or sapphire as a material having these characteristics (see JP-A-53-64976).

[0004]

However, in the case where the light-transmitting tube 2 is formed of light-transmitting alumina, the light-transmissive alumina has a hexagonal crystal structure, so that light is not mixed in the grain boundary layer. There was a problem of causing refraction. Therefore, the linear transmittance of visible light with a wall thickness of 1 mm was as bad as about 30% at maximum, and the linear transmittance could not be further improved.

Although it is required that such a light-transmitting tube 2 can be used for 3000 hours, the light-emitting tube 1 generates heat up to nearly 1000 ° C. during use, and therefore, the light-transmitting tube 2 made of light-transmitting alumina. However, this heat reacts with the metal halide enclosed inside, and is greatly corroded in a short time, leading to the end of its life.

On the other hand, the transparent tube 2 formed of sapphire has excellent linear transmittance of visible light and high corrosion resistance due to metal halides, but due to manufacturing problems, Due to the restriction of the shape, it was not possible to manufacture a light-transmitting tube 2 having a complicated shape like the light-transmitting tube 2 shown in FIG.

On the other hand, in recent years, since the yttrium-aluminum-garnet sintered body has a linear transmittance of visible light equivalent to that of sapphire, it has been proposed to form the transparent tube 2 by this sintered body. (JP-A-6
See JP-A-3-260856 and JP-A-4-233154).

However, these yttrium-aluminum-garnet sintered bodies contain about 1% by weight of sintering aids and impurities, and the sintering aids and impurities present in the grain boundary layer are metal halogen. However, there is a problem that the transparent tube 2 is eroded by reacting with the oxide.

An object of the present invention is to provide a metal composed of a yttrium-aluminum-garnet sintered body which has a high linear transmittance of visible rays to ultraviolet rays and is hardly corroded by metal halides even after being used for 3000 hours or more. It is to provide an arc tube for a vapor discharge lamp.

[0010]

In view of the above-mentioned problems, the present invention provides a light-transmitting tube which constitutes an arc tube for a metal vapor discharge lamp with a yttrium-aluminum-garnet crystal content of 99.8% by weight or more, The content of the oxide of Group 2a element of the periodic table is 600 ppm or less, and the content of SiO ₂ is 9
It is characterized by being formed from a yttrium-aluminum-garnet sintered body having a relative density of 99.0% or more, which is 00 ppm or less.

Further, in the present invention, the average crystal grain size of yttrium-aluminum-garnet crystal is 12 to 80 μm.
The above-mentioned yttrium-aluminum-garnet sintered body is used to form a light-transmitting tube to constitute an arc tube for a metal vapor discharge lamp.

That is, in the present invention, a high-purity yttrium-aluminum-garnet sintered body (hereinafter referred to as YAG) which is made of only YAG crystals without adding any sintering aid to the light-transmitting tube.
It is characterized in that the yttrium-aluminum-garnet crystal (hereinafter referred to as YAG crystal) content is 99.8% by weight or more, preferably 99.9% by weight. It is formed of the above YAG sintered body. Therefore, the metal halide enclosed in the translucent tube is unlikely to be eroded, and the impurities and the sintering aid hardly cause light absorption or diffusion. Moreover, since the YAG sintered body has a cubic crystal structure and has no birefringence in the grain boundary layer, the linear transmittance of visible light to ultraviolet light can be 40% or more.

However, if the number of defects (gaps) between the YAG crystals increases, the incident light is attenuated by the defects and the linear transmittance decreases, so that the relative density of the YAG sintered body is 99.0.
% Or more is required.

In the present invention, the average crystal grain size of the YAG crystal is in the range of 3 to 80 μm.

This is because the average crystal grain size of the YAG crystal is 3
If it is less than μm, it becomes difficult to densify the YAG sintered body, so that the relative density of the YAG sintered body cannot be made 99.0% or more. If the average crystal grain size is larger than 80 μm, the YAG sintered body cannot be densified due to abnormal grain growth and the bending strength required for the light-transmitting tube is less than 30 kg / mm ^2. Because.

A more preferable average grain size of YAG crystals is 12 to 80 μm.

This is because the YAG sintered body, which is generally made of YAG crystals having a small particle size, can have a smoother surface and can increase the initial light transmittance. Since the light-transmitting tube is exposed to a high temperature of about 1000 ° C., the grain boundary layer on the surface of the YAG sintered body is gradually corroded by this heat to become an uneven surface, and light scattering occurs on this surface. . Then, if the particle size of the YAG crystal is small, the proportion of the grain boundary layer that is eroded increases, so that light scattering becomes more intense, and the linear transmittance is significantly reduced.

Therefore, the average crystal grain size of the YAG crystal is 1
If it is provided in the range of 2 to 80 μm, it is possible to prevent the linear transmittance from decreasing after being used for 3000 hours, and to maintain it at 70% or more. The maintenance factor here is the ratio of the linear transmittance after 3000 hours of use to the initial linear transmittance.

By the way, in the present invention, although the light-transmitting tube is formed of a YAG sintered body having a YAG crystal content of 99.8% or more, the erosion by the metal halide was severe.

The inventors of the present invention have conducted extensive studies to reduce the erosion caused by metal halides.
It has been found that SiO ₂ and / or elements of Group 2a of the periodic table such as Mg and Ca contained as impurities in the YAG sintered body react with metal halides to promote erosion.

That is, although the above-mentioned SiO ₂ and Group 2a elements of the Periodic Table are contained as impurities in the starting materials and mixed in the manufacturing process, the Group 2a elements of the Periodic Table are converted into oxides. More than 600ppm,
Alternatively, when the content of SiO ₂ is more than 900 ppm, the reaction with the metal halide is so strong that the YAG sintered body is largely corroded.

Therefore, in the present invention, the content of SiO ₂ contained in the YAG sintered body is 900 ppm or less, and the content of Group 2a element oxide of the periodic table is 600 ppm or less,
Preferably, the content of SiO ₂ is 300 ppm or less,
And the content of Group 2a element oxide of the periodic table is 200ppm
It is important to do the following:

On the other hand, the light-transmitting tube constituting the arc tube for a metal vapor discharge lamp according to the present invention can be manufactured as follows.

First, the purity of each starting material is 9
Al ₂ O ₃ powder having a BET specific surface area of 5 m ² / g or more and an average particle diameter of about 1.0 μm and Y ₂
A predetermined amount of O ₃ powder is mixed and then calcined, and this is crushed to obtain a raw material powder. Then, this raw material powder is formed into a molded body having a predetermined shape by a normal ceramic molding method such as an isostatic pressing method, a casting molding method, an extrusion molding method, and is fired at a firing temperature of 1700 to 1900 ° C. in a vacuum atmosphere. After that, the light-transmitting tube can be obtained by mirror-finishing the inner and outer surfaces.

As another production method, the starting raw materials each having a purity of 99.8% or more, a BET specific surface area of 5 m ² / g or more, and an average particle diameter of about 1.0 μm are used.
A predetermined amount of l ₂ O ₃ powder and Y ₂ O ₃ powder were mixed and pre-baked, and 0.5 wt.
A raw material powder is prepared by adding at least wt% and mixing and pulverizing. Then, this raw material powder is formed into a formed body having a predetermined shape by an ordinary ceramic forming method and fired at a firing temperature of about 1600 to 1900 ° C. in a vacuum atmosphere. After that, a light-transmitting tube can be obtained by mirror-finishing the inner and outer surfaces.

Incidentally, 0.5% by weight or more of YAG powder having a purity of 99.9% or more was added during the manufacturing process because the added YAG powder serves as a nucleus to promote YAG formation,
This is because the grain growth can be made uniform. As described above, in the arc tube for metal vapor discharge lamp according to the present invention, since the light-transmitting tube is formed of the high-purity YAG sintered body, it is possible to improve the linear transmittance of visible rays to ultraviolet rays. 40% or more linear transmittance with a wall thickness of 1 mm, and even 70%
The above can be done. In addition, the content of SiO ₂ and the oxide of the Group 2a element of the periodic table, which are mixed in the YAG sintered body, is set to a certain level or less, and the average crystal grain size of the YAG crystal is set within a certain range, so that the metal halide may It is possible to obtain a highly reliable arc tube which is not easily corroded and has almost no decrease in linear transmittance even after being used for 3000 hours. Moreover, since the YAG sintered body can be formed by a general ceramic forming method, it is possible to easily form a translucent tube having a complicated shape.

The arc tube for a metal vapor discharge lamp according to the present invention is a sodium lamp in addition to a metal halide lamp,
It goes without saying that it can also be used as a mercury lamp or a xenon lamp.

[0028]

EXAMPLES An example of an arc tube for a metal vapor discharge lamp according to the present invention will be described below.

FIG. 1 is a longitudinal sectional view showing an arc tube 1 for a metal vapor discharge lamp according to the present invention. The inside of a translucent tube 2 made of a YAG sintered body having a substantially cylindrical shape with a curved surface at the center. To Dy
I ₃ -InI-TlI-LiI is sealed, and both ends of the light-transmitting tube 2 are sealed by attaching a glass 4 with a closing body 3 made of an Al ₂ O ₃ -Mo cermet material. Further, an electrode mandrel 5 is embedded in one end of the closing body 3, and a lead rod 6 is buried in the other end so as not to come into contact with the electrode mandrel 5 inside, and a voltage is applied to the lead rod 6. By applying and discharging between the electrode mandrel 5, the DyI ₃ -InI-TlI-LiI enclosed in the arc tube 2 emits light.

In order to manufacture the transparent tube 2, a purity of 9
Al ₂ O ₃ powder having a BET specific surface area of 5 m ² / g or more and an average particle size of 1.0 μm and Y ₂ O ₃ powder at a ratio of 0.43: 0.57 by weight ratio of 9.8%. The mixture was put into a ball mill and mixed and pulverized with a solvent in an alumina ball having a purity of 99.99% or more to obtain a uniform powder. Then, this powder is pre-baked at a temperature of about 1300 ° C., and again mixed and pulverized with a high-purity alumina ball together with a binder to prepare a slurry, which has a curved surface at the center as shown in FIG. 1 by a casting method. A substantially cylindrical shaped body was formed. After that, the molded body was baked in a vacuum atmosphere at a baking temperature of 1800 to 1850 ° C. for about 2 to 5 hours, and finally the inner and outer surfaces were mirror-finished to obtain a light-transmitting tube 2 according to the present invention.

Further, when the composition of the YAG sintered body constituting the light transmitting tube 2 is analyzed, the content of YAG crystal is 99.9.
%, The content of SiO ₂ was 100 ppm or less, and the content of Group 2a element oxide of the periodic table was 100 ppm or less. Moreover, when the relative density and bending strength of the YAG sintered body and the average crystal grain size of the YAG crystal were measured, respectively, the relative density was 99.9% and the bending strength was 35 kg / mm.
² or more and the average crystal grain size of YAG crystal is 12
μm. Furthermore, the YAG which constitutes this transparent tube 2
The linear transmittance of visible light of 600 nm at a thickness of 1 mm of the sintered body was 81%, and the linear transmittance after exposure to the metal halide for 3000 hours was 60%.

(Experimental Example) Here, a plate-like body made of a YAG sintered body was prepared by changing the contents of MgO, CaO and SiO ₂ which are oxides of elements of Group 2a of the Periodic Table, and was subjected to bending. Intensity, linear transmission of visible light, and 3000
The degree of erosion when exposed to metal halides for a period of time was measured.

First, the sample YAG sintered body had a purity of 99.8% and a BET specific surface area of 5 m ² / m as in the example.
Al ₂ O ₃ powder having an average crystal grain diameter of 1.0 μm and Y ₂ O ₃ powder of not less than g and charged into a ball mill at a weight ratio of 0.43: 0.57, and a purity of 99.99 together with a solvent.
% After mixing and crushing with alumina balls of more than 130%
It was calcined at about 0 ° C to form granules. Next, at least one of MgO, CaO, and SiO ₂ is appropriately added to the granules, and the mixture is pulverized again with high-purity alumina balls to obtain a powder having an average particle diameter of 0.4 to 2.0 μm, and further a binder. Was added and wet pulverized, followed by drying with a spray drier, and a granulated body that passed through a mesh of No. 80 mesh was used as a secondary raw material. Then, this secondary raw material is filled in a mold and molded under a pressure of ² ton / cm ² , and then baked in a vacuum atmosphere at a baking temperature of 1800 to 1900 ° C. for 2 to 30 hours, and Φ20 × 1.8 mm. To obtain a plate-like body. Then, both sides of this plate-shaped body were polished and further mirror-finished to finally obtain a plate-shaped body having a thickness of 1 mm. In addition,
As another comparative example, a sample made of translucent alumina having a purity of 99.9% was also prepared.

Then, these samples were irradiated with visible light of 600 nm and the linear transmittance was measured by an infrared spectrometer,
Next, the sample was heated to 1000 ° C. to obtain 3000 as DyI ₃ -InI-TlI-LiI gas as a metal halide.
The erosion depth after time exposure was measured.

The evaluation standard in this experiment is 600 nm.
Has a linear transmittance of visible light of 40% or more and 3000
Those having an erosion depth of less than 10 μm when exposed to the DyI ₃ -InI-TlI-LiI gas for a time were regarded as excellent.

The characteristics of each sample and the results are shown in Table 1.

[0037]

[Table 1]

First, as can be seen from Table 1, the sample No. 1
In the translucent aluminas 6 to 19, the content of alumina crystals was as high as 99.9%, but all the linear transmittances were 40% or less because the crystal structure was hexagonal.
Moreover, MgO, which easily reacts with the DyI ₃ -InI-TlI-LiI gas, is contained in an amount of 600 ppm or more,
The erosion depth after 0 hours was as large as 10 μm or more.

Sample No. In No. 12, since the relative density of the YAG sintered body is less than 99.0%, the linear transmittance is 3
5% and 40% or more could not be satisfied.

Further, the sample No. In 13 to 15, YA
Since the relative density of the G sintered body was 99.0% or more, the linear transmittance could be 40% or more, but YAG
The content of SiO ₂ contained in the sintered body is 900 pp
Since the content of the oxide of m or more and / or the group 2a element of the periodic table was 600 ppm or more, the erosion depth after 3000 hours was all 10 μm or more and large erosion was performed. In particular,
Sample No. 1 containing the largest amount of SiO ₂ and oxide of Group 2a element of the periodic table. The 14 YAG sintered bodies were most eroded.

On the other hand, the sample No. The YAG sintered bodies 1 to 11 according to the present invention have a YAG crystal content of 99.8.
% And the relative density of the YAG sintered body was 99.0% or more, the linear transmittance could be 40% or more. Moreover, since the content of SiO ₂ contained in the YAG sintered body is 900 ppm or less, and the content of the oxide of the group 2a element of the periodic table is 600 ppm or less, 300
The maximum erosion depth after 0 hours is 5 μm, which is the standard 10 μm.
It was also possible to satisfy less than.

Next, among the YAG sintered bodies according to the present invention,
Prepare plate-like bodies having a thickness of 1 mm and made of a YAG sintered body in which the average crystal grain size of the YAG crystals is changed, measure the bending strength of these plate-like bodies, and irradiate them with visible light of 600 nm. The linear transmittance was measured. Further, each plate-shaped body was heated to 1000 ° C. to heat DyI ₃ -InI-TlI-Li.
After being exposed to the atmosphere of I gas for 3000 hours, the linear transmittance was measured again, and the maintenance rate was calculated.

The characteristics of each sample and the results are shown in Table 2.

[0044]

[Table 2]

As a result, first, if the average crystal grain size of the YAG crystal is 3 μm or more, the initial linear transmittance is 40%.
It turns out that the above can be done. Further, when the average crystal grain size of the YAG crystal is 12 μm or more, the initial linear transmittance is 7
It can be seen that the maintenance rate after 3000 hours can be 70% or more as well as 0% or more. However, Y
If the average crystal grain size of the AG crystal is larger than 80 μm, the bending strength becomes less than 30 kg / mm ^2, and it becomes difficult to use it as the translucent tube 2.

Therefore, the optimum average crystal grain size of the YAG crystal should be in the range of 3 to 80 μm, and more preferably in the range of 12 to 80 μm. You can get a tube,
It is understood that a long-life arc tube for metal vapor discharge can be obtained by using this light-transmitting tube.

[0047]

As described above, in the arc tube for a discharge lamp according to the present invention, the translucent tube has a yttrium-aluminum-garnet crystal content of 99.8% by weight or more, and the 2a group element of the periodic table. If the oxide content is less than 600ppm,
In addition, since the yttrium-aluminum-garnet sintered body having a relative density of 99.0% or more and a SiO ₂ content of 900 ppm or less, the initial linear transmittance of visible light to ultraviolet light can be 40% or more. At the same time, since the metal halide sealed in the arc tube is hardly corroded, the arc tube can have a long life.

In the present invention, the average crystal grain size of the yttrium-aluminum-garnet crystal is 3 to 80.
By providing in the range of μm, it is possible to greatly improve the linear transmittance of visible rays to ultraviolet rays of 70% or more, and further to maintain the linear transmittance after 3000 hours of 7%.
It is possible to obtain a long-life arc tube with 0% or more.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an arc tube for a metal vapor discharge lamp according to the present invention.

FIG. 2 is a schematic view showing a general metal vapor discharge lamp.

[Explanation of symbols]

 1 Light emitting tube for metal vapor discharge lamp 2 Light transmitting tube 3 Closure body 4 Glass 5 Electrode mandrel 6 Lead rod

Claims (2)

[Claims] 1. A light emitting tube for a metal vapor discharge lamp in which a metal halide is sealed inside a light-transmitting tube, wherein the light-transmitting tube has a yttrium-aluminum-garnet crystal content of 99.8% by weight or more, The content of the oxide of Group 2a element of the periodic table is 600 ppm or less, and the content of SiO ₂ is 9
An arc tube for a metal vapor discharge lamp, which is formed from a yttrium-aluminum-garnet sintered body having a relative density of 99.0% or more, which is 00 ppm or less. 2. The arc tube for a metal vapor discharge lamp according to claim 1, wherein the yttrium-aluminum-garnet crystal has an average crystal grain size of 3 to 80 μm.