JPH11147757A - Light-transmitting ceramic, arc tube made therefrom, high-pressure discharge lamp using the arc tube, and production of light-transmitting ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a highly light-transmitting ceramic by using a compound selected from Er3 Al5 O12 , Tm3 Al5 O12 , Ho3 Al5 O12 , Dy3 Al5 O12 , Lu3 Al5 O12 , and Tb3 Al5 O12 . SOLUTION: This light-transmitting ceramic is obtained by using a compound of garnet structure shown by the formula: M3 Al5 O12 (M is Er, Tm, Ho, Dy, Lu or Tb), having the following characteristics: average three-point flexural strength: >=400 MPa; Weibull modulus: >=6; and the linear transmittance by visible rays except for intrinsic absorption: >=50%. This light-transmitting ceramic is obtained by the following process: a rare earth element and an aluminum inorganic acid salt are dissolved in water and mixed so as to be 0.005-1.0 mol/L in the total metallic ion concentration, the resulting aqueous solution is dripped into an aqueous solution of a carbonate such as Na2 CO3 adjusted to pH 7.5-11 under agitation; after ending the dripping, the system is aged, and the precipitate thus formed is filtered, washed with water, dried, and then preliminarily baked at 800-1,500 deg.C to effect conversion to a multiple oxide, which, in turn, is incorporated with a binder to carry out a molding operation followed by sintering the molded form at a temperature of >=1,500 deg.C but >=50 deg.C lower than the melting point of the final sintered compact.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a translucent ceramic, a method for producing the same, an arc tube using the obtained translucent ceramic, and a high-pressure discharge lamp using the arc tube.

[0002]

2. Description of the Related Art Various types of translucent ceramics are being studied for various applications. Among them, high-pressure discharge lamps such as high-pressure mercury lamps and high-pressure sodium lamps require the arc tube to withstand high pressure and high resistance at high temperatures. Therefore, available materials are limited. As a luminescent substance, metal halides having high luminous efficiency and excellent color rendering properties have recently attracted attention, but since a highly corrosive metal halide is enclosed in the arc tube, the reaction between the arc tube and the metal halide is at a high pressure. This leads to a decrease in discharge lamp characteristics.

[0003] As a material of a translucent ceramic arc tube,
Quartz glass (SiO2), translucent alumina (Al2O3), and the like have been used, but quartz glass is inferior in touch resistance and insufficient in heat resistance. Although translucent alumina can compensate for the disadvantages of quartz glass, it has a low linear transmittance of about 10 to 20% because of its hexagonal crystal structure, and both are insufficient as arc tube materials.

Recently, yttrium aluminum garnet (Y3Al5O12: hereinafter referred to as YA) has been used as an arc tube material.
G) (for example, see Japanese Patent Application Laid-Open No. 9-45).
287). YAG is a material having a cubic crystal structure and having both high transparency equivalent to quartz glass (theoretical transmittance 84%) and mechanical strength and heat resistance comparable to translucent alumina.

[0005] However, YAG easily reacts with a halide of a rare earth element used in a metal halide lamp, and this reaction causes white turbidity in the arc tube during lighting, thereby lowering the luminous flux retention rate. It is considered that the cloudiness reaction inside the arc tube proceeds by the following mechanism. (M'-X) (g) + (M "-O) (s) → (M'-O) (s) +
(M "+ X) (g) In the formula, (g) represents a gas, (s) represents a solid, X represents a halogen element, and M 'and M" represent a rare earth element. According to this mechanism, at high temperature, the metal halide (M′-X) (g) of the luminescent substance is converted to M ′
(g) and X (g), and the dissociated M '(g) deprives the oxide ceramic (M "-O) (s) of an oxygen atom, resulting in (M'-O)
It is considered that (s) is adhered and fixed to the inner wall of the arc tube. It is presumed that the arc tube becomes cloudy with this.

[0006] In order to avoid the above-mentioned cloudy reaction, the filling pressure of Hg-based gas or the like is increased to reduce the chance of contact between the metal atoms dissociated from the metal halide and the arc tube material, and to make the arc tube uniform. It is considered that the halogen cycle is smoothly performed by heating. However, if the filling pressure is increased or the arc tube is heated more than necessary, the arc tube is easily damaged.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a translucent ceramic which has high translucency and does not cause white turbidity when used as a discharge lamp, a method for producing the same, an arc tube and a high pressure discharge lamp using the same. Is to do.

[0008]

The present invention relates to a compound having a garnet structure having the composition formula M3Al5O12, wherein M is Er, Tm, Ho, D
Transparent ceramics that are at least one member of the group consisting of y, Lu, and Tb. Note that this compound is limited to a single-phase compound, and is included in the present invention because the linear transmittance of light decreases when the phase is divided into multiple phases or when there is segregation between materials. Absent. The invention also provides
Er3Al5O12, Tm3Al5O12, Ho3Al5O12, Dy3Al5
Transparent ceramics using a compound of a member of the group consisting of O12, Lu3Al5O12, and Tb3Al5O12. These are all compounds having a garnet structure, and the stable phase is only one phase having a garnet structure. For example, if the compound is produced by the method of claim 7, no segregation occurs. Preferably, the translucent ceramic has an average three-point bending strength of 400 MPa or more, a Weibull coefficient of 6 or more, and a linear transmittance of 50% or more in visible light excluding intrinsic absorption. Such a translucent ceramic can be used, for example, for an arc tube of a high-pressure discharge lamp.

A high-pressure discharge lamp according to the present invention is characterized in that at least a metal halide is enclosed in an arc tube made of translucent ceramics and an arc tube opening is hermetically sealed, wherein the arc tube is composed of Er3Al5O12, Tm3Al5O12. , H
o3Al5O12, Dy3Al5O12, Lu3Al5O12, and Tb3A
It is characterized by being made of a translucent ceramic using a one-membered compound of the group consisting of l5O12. Preferably, the arc tube opening of the high pressure discharge lamp is sealed with a sealing material made of a rare earth oxide, alumina and silica constituting the arc tube.

In the method for producing a translucent ceramic according to the present invention, the inorganic acid salt of a rare earth element and the inorganic acid salt of aluminum are combined so that the total metal ion concentration of both is 0.005 to 1.0 mol.
/ Litter and dissolved in water, pH 7.5-1
The resulting precipitate was washed with water, dried and calcined at 800 to 1500 ° C. to obtain a single-phase raw material for the composite oxide. After molding, at a temperature of 1500 ° C. or more, 50
Sinter at a temperature lower than ℃. As rare earth elements, E
At least one member of the group consisting of r, Tm, Ho, Dy, Lu, and Tb is preferable, and it is particularly preferable to use only one of these elements.

[0011]

In the translucent ceramic of the present invention, a compound having a garnet structure represented by the composition formula M3Al5O12 is used, wherein M is at least one element selected from the group consisting of Er, Tm, Ho, Dy, Lu, and Tb. I do. Also, in the present invention, E
r3Al5O12, Tm3Al5O12, Ho3Al5O12, Dy3Al5O
A member of the group consisting of 12, Lu3Al5O12, and Tb3Al5O12 is a translucent ceramic. Such compounds have high translucency, for example, at least 50% or more,
In addition, a linear transmittance of 60% or more was obtained in the experimental range. Note that the linear transmittance is measured at the wavelength of visible light, and when each compound has a specific absorption in the visible light region, it is measured at a wavelength without absorption. In addition, the linear transmittance is measured on a sample having a thickness of 1.0 mm whose surface is mirror-polished.

All of these compounds have a garnet structure, are stable at high temperatures and high pressures against metal halides sealed in an arc tube, and when Er is used as shown in Table 3, substantially all of them except for the Sc type are used. And Tm is stable to all metal halide-based luminescent materials except Sc-based and Er-based luminescent materials. Ho is stable for all metal halide luminescent materials except Sc-based, Er-based and Tm-based, and Sc-based and Ho-based for Dy, Lu and Tb.
It is stable against all metal halide-based luminescent materials except for those based on Er, Er and Tm. The translucent ceramic of the present invention is unstable to a luminescent substance such as ScI3,
This is not a problem unless a luminescent substance such as a c-based substance is used. And, in the discharge lamp using these compounds, the luminous flux maintenance ratio after 1000 hours from the lamp lighting becomes 90% or more.

[0013] The inventor first understood the stability of the translucent ceramic to the metal halide-based luminescent material from the viewpoint of the standard Gibbs energy of oxide formation accompanying halogen exchange. In the case of a YAG ceramic arc tube, the standard Gibbs energy of formation of yttrium oxide ({Gf}) is
The standard Gibbs energy of oxides of Sc, Tm, Dy, and Ho, which are rare earth elements that constitute a metal halide enclosed in an arc tube, is set to −1727 KJ / mol (Chemical Handbook, 1st edition, edited by The Chemical Society of Japan). ΔGf ゜) is -181
9.4KJ / mol, -1795KJ / mol, -1772K
At J / mol and -1791 KJ / mol, the absolute value is larger than the standard Gibbs energy of yttrium oxide. For this reason, YAG is thermodynamically unstable with respect to these rare earth elements, and when these luminescent substances are sealed in a YAG ceramic arc tube, a white turbidity reaction occurs on the inner surface of the arc tube due to halogen exchange, and the luminous flux is maintained. The ratio (the ratio of the luminous flux to the initial value, corresponding to the decrease in the linear transmittance) was considered to decrease.

The rare earth element whose standard Gibbs energy of oxide formation is smaller in absolute value than the standard Gibbs energy of yttrium oxide is La (−1).
706 KJ / mol), Ce (-1706 KJ / mol), Nd
(-1721 KJ / mol). When these elements were sealed in a YAG ceramic arc tube as a luminescent substance, no reaction occurred and no decrease in the linear transmittance of the high pressure discharge lamp was observed.

However, the standard Gibbs energy of formation of yttrium oxide is actually -1816 KJ / mo.
l (Chemical Handbook, 4th edition) cannot explain the fact that it reacts with Tm, Dy, and Ho-based luminescent substances and becomes cloudy. The prediction of the presence or absence of a cloudiness reaction by comparison of the standard Gibbs energies of oxide formation was applied to garnet compounds other than YAG. Therefore, evaluation using the standard generation Gibbs energy
Applicable, with exceptions.

For example, Dy ({Gf} =-
When using 1772 KJ / mol), Ho ({Gf} =-
1791KJ / mol), Lu ({Gf} =-1789KJ)
/ Mol) or a single phase compound having a garnet structure of Er, Dy, Tb and alumina, Er3Al5O12, Dy3Al5O12,
Ho3Al5O12, Lu3Al5O12, Tb3Al5O12 and the like are suitable for the translucent ceramics of the arc tube material, and a discharge lamp with high luminous efficiency and little decrease in linear transmittance can be obtained. For example, according to the present invention, 90 hours after the discharge lamp is turned on.
% Or more can be obtained.

The initial value of the translucent ceramic is preferably an average three-point bending strength of 400 MPa or more and a Weibull coefficient of 6 or more. When this condition is satisfied, as shown in FIG. 5, even if the temperature change between high temperature and room temperature is repeatedly given, the Weibull coefficient and the average three-point bending strength are slightly reduced and the thermal fatigue is small.

As a method of manufacturing a translucent ceramic used for an arc tube material or the like, similar to the case of YAG ceramics,
A method of making a powder mixture of a rare earth oxide and alumina transparent by a hot press method, a method of making an ultrafine powder of a rare earth oxide and Al2
A direct sintering method in which fine powder of O3 is mixed in a ball mill, and then subjected to CIP molding (isostatic pressing) and then sintering is used. In the case of YAG ceramics, the hot press method is disclosed in US Pat.
No. 18963. However, from the viewpoint of composition uniformity, it is preferable to use a single-phase raw material of the composite oxide as a starting material.

The single-phase raw material of the composite oxide can be easily obtained by the following procedure. An inorganic acid salt of the rare earth element and aluminum, such as hydrochloric acid, nitric acid, and sulfuric acid, that is, a mineral acid salt is dissolved in water. Then, these aqueous solutions are mixed with a rare earth element and aluminum having a total metal ion concentration of, for example, 0.005 to 1.0 mol.
/ Litter and mix according to any composition. If the metal ion concentration is higher than this, the contact between the particles increases, and during the calcination, the seizure of the particles occurs to deteriorate the dispersibility. If the metal ion concentration is lower than this, the production efficiency decreases.
The above mineral salt solution is dropped, for example, with stirring into an aqueous solution of carbonate adjusted to pH 7.5 to 11.0 by adding an alkali. The aqueous solution of the carbonate is not particularly limited. For example, ammonium carbonate, ammonium hydrogen carbonate,
An aqueous solution such as sodium carbonate is used.

After completion of the dropwise addition, the mixture is aged for 30 minutes to 100 hours with stirring. The pH of the aqueous carbonate solution decreases as the aqueous mineral salt solution drops, but then gradually rises to a constant value. Therefore, the aging may be performed until the pH rises and reaches a constant value, and there is no difference in sinterability even after aging for a long time. The ripening temperature is not particularly limited, but if the temperature is too high, ripening proceeds rapidly, and the particle size distribution of the resulting precipitated particles is widened. The precipitate obtained after aging was filtered and washed several times with water.
Dry at 200 ° C. The precipitate is heated at 800 ° C. to 1500
Calcination for several hours at ° C gives a single-phase raw material powder of the composite oxide. The reason for setting the calcination temperature in the range of 800 ° C. to 1500 ° C. is that if the temperature is lower than this, the reaction does not proceed sufficiently and a single-phase raw material cannot be obtained. This is because no excellent raw material powder can be obtained.

Under the above conditions, the inventor made Er3Al5O12, T
m3Al5O12, Ho3Al5O12, Dy3Al5O12, Lu3Al5O
It was confirmed that a single-phase raw material powder having a garnet structure, such as 12 or Tb3Al5O12, was obtained. The raw material powder thus obtained is molded into a desired shape by a known molding method such as press molding, cast molding, extrusion molding or injection molding.

First, 20 to 100 parts of a medium such as pure water or alcohol, and 0.2 to 10 parts of a binder and a deflocculant are added to 100 parts of the single-phase raw material powder and mixed in a ball mill for 10 hours or more. Disperse to obtain a slurry. When performing injection molding, no medium is added. Examples of the binder include methyl cellulose, acrylic emulsion, and polyvinyl alcohol, and examples of the deflocculant include ammonium salts of polyacrylic acid and polycarboxylic acids.

The prepared slurry is dried or concentrated as required. That is, in press molding, the slurry is dried using a drier such as a spray dryer to obtain granules of a single-phase raw material powder. The granules are molded using a mold or rubber mold having a desired shape. In the extrusion molding, the resin is concentrated to a viscosity that allows extrusion, and is molded by an extruder. In the casting, the slurry is cast using a gypsum mold, a porous resin mold, a porous ceramic mold, or the like to obtain a ceramic molded article having a shape of an arc tube. The molded body obtained by these methods is heated at a temperature of at least 1500 ° C. and at least 50 ° C. lower than the melting point of the sintered body for 1 hour to 100 hours in an atmosphere of oxygen, hydrogen, a rare gas or a mixed atmosphere or vacuum thereof. Upon sintering, a translucent ceramic having a garnet single phase and no segregation is obtained.

The sintering atmosphere is preferably in a vacuum or in hydrogen in order to obtain a ceramic having good translucency in a short time. The reason why the sintering temperature is set to a temperature of 1500 ° C. or more and lower than the melting point of the sintered body by 50 ° C. or more is that if the temperature is lower than 1500 ° C., sufficient densification does not occur, so that satisfactory transparency cannot be obtained. In the vicinity of the melting point, abnormal grain growth occurs and the strength is remarkably reduced. Therefore, the maximum sintering temperature is set to a temperature lower than the melting point by 50 ° C. or more. Immediately after sintering, the surface of the sintered body has irregularities, which causes light scattering to be translucent. Although it can be used as it is, when it is used as an arc tube for a high pressure discharge lamp, it is preferable to use a polishing material such as diamond or alumina to enhance the luminous efficiency, and to perform mirror polishing of the outer and inner surfaces of the sintered body. . As described above, a translucent ceramic suitable for the arc tube material is obtained.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. The structure of the high-pressure discharge lamp is shown in FIGS. The high-pressure discharge lamp 1 has a substantially cylindrical translucent ceramic arc tube 2 in which a metal halide is sealed as a light-emitting substance, and both ends of the arc tube 2 are hermetically sealed with a molten sealing material 16. It is sealed. In order to improve the adhesion to the arc tube 2 and to prevent the occurrence of microcracks, the sealing agent 16 is preferably made of the same rare earth element oxide, alumina and silica as used for the arc tube 2. preferable. Since a normal high-pressure discharge lamp uses glass frit as a sealing agent, the bonding strength with the arc tube 2 is low, and microcracks occur during use.

The ceramic arc tube 2 is exposed to a high temperature of 1000 ° C. or more and a high pressure of 40 atm or more when the high pressure discharge lamp is turned on. Therefore, the arc tube 2 is required to have sufficient strength,
For this reason, the three-point average three-point bending strength is required to be 400 MPa or more in accordance with JIS-R1601, and the Weibull coefficient is required to be six or more. The significance of this condition will be described later with reference to FIG. It is desirable that the luminescent material to be encapsulated is a rare earth halide (excluding Sc-based) having high luminous efficiency. The sealing material 16 is preferably a material which has a thermal expansion coefficient close to that of the arc tube 2, has low reactivity with the encapsulated luminescent substance, and can be melted at 1600 ° C. or less at the time of sealing. From these facts, the sealing agent 16 contains the arc tube 2
It is preferable to use an oxide of the same rare earth element as used in the above and alumina and silica.

Reference numeral 4 denotes a tungsten electrode, for example.
Is a W coil, and 10 is a lead pin. When a voltage is applied to the lead pin 10 to generate an arc discharge between the electrodes 4 and 4, the luminescent material sealed in the arc tube 2 is gasified to emit light. Reference numeral 12 denotes a W electrode 4 which is a lead pin 10 of Nb alloy.
A caulking portion 14 for bringing the sealing material 16 into close contact with the sealing member 16 is an alumina washer for preventing a reaction between the light emitting substance and the sealing material 16.

[0028]

Example 1 Lutetium aluminum garnet (Lu3A) was mixed with lutetium nitrate aqueous solution and aluminum nitrate aqueous solution.
(l5O12: hereinafter LuAG) composition, and water was added to make 0.01 mol / Litter in LuAG conversion. 500 ml of this solution was added to 100 Litter of a 2M aqueous solution of ammonium bicarbonate adjusted to pH 8.0 by adding aqueous ammonia.
The solution was dropped at a rate of / min. At this time, the mixed solution of the LuAG composition and the aqueous solution of ammonium bicarbonate were both placed in a thermostatic bath for 2 hours.
Maintained at 0 ° C. The minimum value of the pH during the dropping is 6.8.
The pH reached 8.0 about 6 hours after the completion of the dropping. After completion of the dropwise addition, the mixture was aged at 20 ° C. for 30 hours, and the cycle of filtration and washing was repeated six times. The precipitate obtained after washing with water was amorphous and the form was granular. After drying this amorphous precipitate in air at 150 ° C. for 24 hours,
By calcining at 50 ° C. for 3 hours, a LuAG raw material powder having an average primary particle size of 0.3 μm was obtained. This raw material powder had a garnet structure, and no segregation of Lu and Al elements was observed.

With respect to 200 g of the obtained LuAG raw material powder, E-503 and F-219 manufactured by Chukyo Yushi Co., Ltd.
(E-503 and F-219 are trade names of Chukyo Yushi Co., Ltd., respectively) in an amount of 12 g and 4 g, respectively, and as a binder, PVB-BL1 (PVB-BL manufactured by Sekisui Chemical)
1 was 1 g of Sekisui Chemical Co., Ltd.), and 50 g of ethanol was added. This mixture was mixed for 12 hours using a nylon pot and a nylon ball to obtain an alcohol slurry. This alcohol slurry was poured into a gypsum mold to obtain a molded product of 100 mm × 100 mm × 5 mm. This molded body was degreased at 700 ° C. for 5 hours, and then sintered in a vacuum furnace at a temperature of 1680 ° C. for 5 hours. At this time, the rate of temperature rise was 100 ° C./hr, and the degree of vacuum was 10 ⁻³ Torr or less.

The obtained sintered body was subjected to a three-point bending test according to JIS-R1601. The bending test was performed at 10 points, and the Weibull coefficient was determined using Weibull probability paper (Japanese Standards Association). As a result, the three-point bending strength was 530 MPa and the Weibull coefficient was 6.

The obtained sintered body was mirror-polished on both sides with diamond slurry, and the light linear transmittance was measured with a spectrophotometer. As a result, the linear light transmittance at a wavelength of 600 nm (a sample thickness of 1.0 mm and a measurement wavelength of 600 nm)
Was 62.4%. Further, this sample was placed in the atmosphere for 150 minutes.
Thermal etching was performed at 0 ° C for 2 hours, and the fine structure was observed with an optical microscope.
It was 2.6 μm.

[0032]

Example 2 In order to evaluate the efficiency of a high-pressure discharge lamp, a substantially cylindrical LuAG arc tube having a thickness of 1.0 mm was produced by casting in the same manner as in Example 1, and a high-pressure discharge lamp was produced using this. . This will be described below with reference to FIG. High pressure discharge lamp 1
Is Hg and Ar inside the translucent LuAG arc tube 2,
A halide of Dy-Tl-Na- (Br-I) was sealed as a light emitting substance, and both ends of the light emitting tube 2 were sealed with a sealing material 16. The distance between the two electrodes was 9.2 mm.
When a voltage is applied to the lead pin 10 with a constant power AC ballast of 100 W, discharge occurs between the electrodes, and the halide sealed in the arc tube 2 is gasified to emit light.

5 immediately after lighting of the high pressure discharge lamp in the second embodiment.
Table 1 shows the measurement results of the high-pressure discharge lamp efficiency (lamp efficiency) and the average color rendering index (Ra) up to the lapse of 000 hours.

[0034]

Table 1 Elapsed time after characteristic lighting of high-pressure discharge lamp (hr) Lamp efficiency (lm / W) Luminous flux maintenance rate (%) Average color rendering index (Ra) 085.0 100 90 90 83.3 98 88 500 79 .9 94 81 1000 77.4 91 77 2000 73.1 86 73 5000 62.0 73 66

The standard Gibbs energy of formation of Lu oxide used for the arc tube material is ΔG = 1789 KJ / mol, and that of rare earth Dy in the luminescent material is ΔG = −1772.
KJ / mol. Even after lighting for 1000 hours, the arc tube had almost no turbidity, and the luminous flux maintenance ratio was very good at 91%. However, as a luminescent substance, TmI3-HoI3
When -TlI-NaI was used, the luminous flux maintenance ratio after lighting for 100 hours was as low as 78%, and the inner surface of the arc tube was cloudy.
This can be explained by the fact that the standard Gibbs energy of formation of the oxide of the luminescent material Tm (ΔG = -1795 KJ / mol) is larger in absolute value than that of Lu. And in the test of the inventor, Tm oxide was generated on the inner surface of the arc tube.

[0036]

Embodiment 3 Dy3Al5O12 and Er3Al5O12, Yb3Al5
Each arc tube 2 is made of O12, and Dy
-Tl-Na- (Br-I) was used. FIG. 3 shows a change in the luminous flux maintenance factor of the high-pressure discharge lamp, and FIG. 4 shows a change in the average color rendering index (Ra). When the luminous flux maintenance rate after lighting for 100 hours is 90% or more, the luminous flux is slightly reduced by lighting after that, but when the luminous flux is less than 90%, the deterioration is remarkable thereafter, and in the case of Yb3Al5O12, the light is finally emitted. The tube burst after losing any light transmission. This is considered to be because light energy was accumulated as heat in the arc tube having a low luminous flux maintenance factor, and was exposed to an abnormally high temperature so that it could not withstand the internal pressure.

[0037]

Embodiment 4 FIG. 5 shows that Er3Al5O12 and Dy3Al5O12,
The relationship between the average three-point bending strength of SmAlO3 and the Weibull coefficient is shown. The bending strength and the Weibull coefficient were changed by changing the sintering temperature. FIG. 5 simultaneously shows the results of performing a heat-resistant fatigue test for a temperature change by repeating heating and cooling between 1200 ° C. and room temperature 1000 times at intervals of 10 minutes.
From this figure, it can be seen that when the initial Weibull coefficient is 6 or more and the average three-point bending strength is 400 MPa or more, the decrease in the Weibull coefficient is small, and it is possible to sufficiently cope with temperature changes.
Tm3Al5O12, Ho3Al5O12, Lu3Al5O12, and Tb3Al5O12 also have the same initial Weibull coefficient of 6 or more and an average three-point bending strength of 400 MPa or more.
Even after experiencing 000 temperature cycles, the Weibull modulus and average three-point bending strength remained in the same range.

[0038]

[Comparative Example] Table 2 shows that the average particle diameter of the sintered body was 1 for the arc tube material.
The result of the comparative example using YAG having a linear light transmittance of 83% in μm is shown. As a luminescent substance, Dy-Tl was used in the same manner as in Example 2.
-Na- (Br, I) was enclosed.

[0039]

Table 2 Comparative Example (using YAG arc tube) Elapsed time after lighting (hr) Lamp efficiency (lm / W) Luminous flux maintenance rate (%) Average color rendering index (Ra) 0 90 100 95 100 70 78 78 77 200 27 30 61

When YAG is used as the arc tube, the lamp efficiency and color rendering properties immediately after lighting are excellent, but after several tens of hours after lighting, the inner surface of the arc tube starts to become cloudy due to the reaction with Dy enclosed therein. After 200 hours, cloudiness became intense,
The luminous flux maintenance rate decreased to 30%. However, even when the arc tube material was YAG, when CsI-NdI3 was encapsulated as a light emitting element, almost no cloudiness inside the arc tube was observed even after 1000 hours from the lighting. The standard Gibbs energy of formation of Nd is −1721 KJ / mol, and the absolute value is smaller than that of Y.

[0041]

Embodiment 5 Rare earth oxide and aluminum oxide (Al2
Various translucent ceramic arc tubes made of the compound of O3) and high pressure discharge lamps using them were produced in the same manner as in Examples 1 and 2. The sample has an initial Weibull coefficient of 6
As described above, only those obtained under the sintering conditions having an average three-point bending strength of 400 MPa or more are shown. Table 3 shows the results of evaluating the reactivity with the arc tube by enclosing a rare earth luminescent substance in these high-pressure discharge lamps. In Table 3, x indicates that the reaction occurred after lighting for 100 hours and the arc tube became opaque, and x indicates that there was no opacity.
And Table 4 shows the initial characteristics of the arc tube materials shown in Table 3.

[0042]

[Table 3] Reactive luminescent material between arc tube material and luminous substance Arc tube material CeI3 NdI3 DyI3 HoI3 ErI3 TmI3 Er3Al5O12 ○ ○ ○ ○ ○ ○ Tm3Al5O12 ○ ○ ○ ○ × ○ Ho3Al5O12 ○ ○ ○ ○ × × O ○ ○ × × × Lu3Al5O12 ○ ○ ○ × × × Tb3Al5O12 ○ ○ ○ × × × Yb3Al5O12 ○ ○ × × × × × YAlO3 ○ ○ × × × × Y3Al5O12 ○ ○ × × × × Y4Al2O3 ○ ○ × × × × NdAlO3 × × × × SmAlO3 ○ ○ × × × × LaAlO3 ○ × × × × ×

[0043]

Table 4 Physical properties of various arc tube materials Arc tube material Crystalline linear transmittance (%) Three-point bending strength (MPa) Weibull coefficient Er3Al5O12 cubic 72 500 8 Tm3Al5O12 cubic 61 620 6 Ho3Al5O12 cubic 78 78 540 Dy crystals 69 440 7 Lu3Al5O12 cubic 60 530 7 Tb3Al5O12 cubic 70 570 6 Yb3Al5O12 cubic 75 600 6 YAlO3 orthorhombic 22 570 8 Y3 Al5 O12 cubic 83 800 9 Y4Al2O3 monoclinic 11 490 8 NdAlO3 cubic 53 480 7 SmAlO3 hexagonal Crystal 36 520 8 LaAlO3 hexagonal 45 460 7

Table 5 shows the luminous flux maintenance rate after 1000 hours of operation, and x in the table indicates that the discharge lamp was damaged. When the light-emitting substance was CeI3, NdI3, or DyI3, a luminous flux maintenance ratio of 90% or more was obtained in all the high-pressure discharge lamps after 1000 hours of operation.

[0045]

Table 5 Luminous flux maintenance rate of the arc tube (after lighting for 1000 hours) Emitting substance Arc tube material CeI3 NdI3 DyI3 HoI3 ErI3 TmI3 Er3Al5O12 91 91 91 92 94 90 Tm3Al5O12 91 92 91 92 × 91 91 × 95 91 92 × 95 91 Dy3Al5O12 90 90 96 × × × Lu3Al5O12 92 91 91 × × × Tb3Al5O12 91 91 90 × × ×

In the embodiment, Er3Al5O12, Tm3Al5O12,
Ho3Al5O12, Dy3Al5O12, Lu3Al5O12, Tb3Al5
Although O12 is shown, when the garnet compound is M3Al5O12, the M element is not a single element of Er, Tm, Ho, Dy, Lu, or Tb, but may be a mixture of these elements. These elements are elements having similar ionic radii and the like, and when these elements are mixed, the garnet compound often becomes more stable. When mixing these elements,
Translucent ceramics are garnet single phase, M element and A
The condition is that there is no segregation of the l element, especially no segregation between the M elements.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a high pressure discharge lamp according to an embodiment.

FIG. 2 is a side view of an electrode unit in the embodiment.

FIG. 3 is a characteristic diagram showing a change in a luminous flux maintenance ratio in an example.

FIG. 4 is a characteristic diagram showing a change in an average color rendering index (Ra) in the embodiment.

FIG. 5 is a diagram showing a relationship between an average three-point bending strength and a Weibull coefficient in Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High-pressure discharge lamp 2 Ceramic arc tube 4 W electrode 6,8 W coil 10 Lead pin 12 Caulked part 14 Washer 16 Sealing material

Continuation of the front page (72) Inventor Hitoshi Kubo 4-2-7 Komyobashi, Chuo-ku, Osaka City Kamijima Chemical Industry Co., Ltd.

Claims (7)

[Claims] 1. A translucent ceramic compound having a garnet structure having a composition formula of M3Al5O12, wherein M is at least one member of the group consisting of Er, Tm, Ho, Dy, Lu, and Tb. 2. Er3Al5O12, Tm3Al5O12, Ho3Al5
O12, Dy3Al5O12, Lu3Al5O12, and Tb3Al5O12
A translucent ceramic using a one-member compound of the group consisting of: 3. An average three-point bending strength of 400 MPa or more,
A Weibull coefficient of 6 or more, and a linear transmittance of visible light excluding intrinsic absorption of 50% or more,
The translucent ceramic according to claim 2. 4. An arc tube using the translucent ceramic according to claim 2. 5. A high-pressure discharge lamp in which at least a metal halide is enclosed in an arc tube made of translucent ceramic and an arc tube opening is hermetically sealed, wherein the arc tube is made of Er3Al5O12, Tm3Al5O12, Ho3Al5.
O12, Dy3Al5O12, Lu3Al5O12, and Tb3Al5O12
A high-pressure discharge lamp comprising a translucent ceramic using a one-member compound of the group consisting of: 6. The high pressure discharge lamp according to claim 5, wherein the arc tube opening is sealed with a sealing material made of a rare earth oxide, alumina and silica constituting the arc tube. 7. An inorganic acid salt of a rare earth element and an inorganic acid salt of aluminum having a total metal ion concentration of 0.005.
After dissolving in water so as to be ~ 1.0 mol / Litter, p
H 7.5 to 11.0 was dropped into a carbonate aqueous solution to precipitate,
The obtained precipitate is washed with water, dried and calcined at 800 ° C. to 1500 ° C. to obtain a single-phase raw material of the composite oxide. After molding the single-phase raw material, the melting point of the sintered body is raised to 1500 ° C. or higher. Sintering at a temperature lower by at least 50 ° C. than the above.