JP2001158660A - Optically transmitting rare earth-aluminum garnet sintered product and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide optically transmitting rare earth-aluminum garnet sintered product that has high light straight transmittance and high mechanical strength. SOLUTION: This optically transmitting rare earth-aluminum garnet sintered product has a void volume of <=100 vol. ppm; the molar ratio of rear earths/Al of 0.599<=R/Al<=0.601; Si<=15 wt.ppm in 0.599<=R/Al<=0.600; and Si (wtppm)<=15000×(R/Al)-8985 in 0.600<=R/Al<=0.601.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a compound represented by the general formula R3Al5O12 (R
The present invention relates to a translucent sintered body having a garnet structure represented by one of Y, Dy, Ho, Er, Tm, Yb, and Lu). The sintered body of the present invention is, for example, a sapphire substitute window material, a polarizing plate, an envelope for a discharge lamp, a corrosion-resistant member such as a semiconductor manufacturing apparatus,
It is suitably used for decorative articles and the like.

[0002]

2. Description of the Related Art A general formula R3Al5O12 (R is Y, Dy, H
The rare earth aluminum garnet compound represented by any one of o, Er, Tm, Yb, and Lu) is a sintered body having a cubic crystal structure and excellent translucency and heat resistance. Is obtained, so that it can be applied to various uses. In particular, by completely removing pores and foreign phases, which are light scattering sources, transparency comparable to that of a single crystal can be obtained despite being a polycrystal, and thus application to various optical materials is expected.

[0003] Among them, yttrium aluminum garnet (Y3Al5O12: YAG) ceramics exhibit excellent translucency over a wide range from the visible region to the infrared region.
In view of the strength, heat resistance, and freedom of shape that are the advantages of ceramics, application to sapphire alternative window materials, arc tube materials for discharge lamps, corrosion-resistant members, and the like is being studied. On the other hand, a translucent rare earth aluminum garnet sintered body using a rare earth element other than yttrium is relatively expensive, because a rare earth element cannot be found in a specific use.
Despite the fact that the production conditions are almost the same as for YAG ceramics, there are few reports on production methods.

[0004] As methods for producing translucent YAG ceramics, which have been extensively studied, a hot press method (US Pat. No. 3,767,745) and a ball mill mixing of oxide fine powder and CIP molding have been employed. A sintering method (Japanese Unexamined Patent Publication No. Hei 3-218963) and the like are known. The hot pressing method makes it difficult to manufacture a complex-shaped product, which is one of the characteristics of ceramics. In the oxide fine powder mixing method, although a sintered body with good translucency can be obtained, in order to increase the reactivity and suppress the separation of yttria and alumina based on the specific gravity difference at the time of mixing, ultrafine yttria powder is used. Used. For this reason, it is necessary to produce yttria and alumina separately, and since an ultrafine powder is used, the molding density tends to be low. If the molding density is low, the shrinkage during sintering is large, and it is difficult to apply to applications requiring dimensional accuracy. In order to obtain a sintered body having a sufficient translucency, it is necessary to add SiO2 as a sintering aid and perform sintering for several tens of hours. Also, a method of obtaining a light-transmitting sintered body using a single-phase YAG fine powder (Japanese Patent Application Laid-Open No. 2-92817) is disclosed. Requires auxiliary agents.

[0005] Generally, light scattering sources in ceramics having a cubic crystal structure are pores and heterophases, and these must be completely removed in order to obtain a sintered body having excellent translucency. Rare earth aluminum garnet sintered body 2
In a component-based oxide, the generation of a foreign phase can be suppressed by strictly controlling the composition. The presence of the pores is not preferable because it not only reduces the light transmittance, but also can be a source of destruction. Therefore, in order to obtain a sintered body having excellent translucency and high mechanical reliability, the problem is how to remove pores.

In the conventional method, densification and grain growth rate are controlled by a sintering aid and firing conditions, and pores are discharged through crystal grain boundaries by volume diffusion due to grain growth. However, in the production of ceramics using ordinary raw material powders and mechanical molding methods, uniform packing of the raw material particles is not possible, and pores of a size more or less cannot be removed by ordinary sintering. Therefore, even in a translucent ceramic generally called a dense body, pores of several hundred volppm or more remain inside the sintered body, and it is not possible to obtain a polycrystalline body having the same optical characteristics as a single crystal. Have difficulty. For example, Journal of Material Science (Journ
al of Materials Science) 34 (1999) 1189-1195 reported that at least 150 volppm of pores existed in Nd-doped YAG ceramics obtained by the vacuum sintering method. Very much.

By the way, in the production of translucent alumina, it is disclosed that a sintered body having no pores can be obtained by hot isostatic pressing (HIP) (Japanese Patent Laid-Open No. 8-301666). issue). In HIP, a high pressure of several hundred kgf / cm2 or more is applied to a sample isotropically at a high temperature, and pores in ceramics are removed by plastic deformation. On the other hand, Y
Journal of American Ceramics Society (J. Am. Ceram. Soc) 79 [7] 1927-3 is an example of applying HIP to AG ceramics to produce a nonporous sintered body.
3 (1996) has been reported. However, according to this report, it is impossible to produce a nonporous YAG sintered body because Ar gas as a pressure medium remains as pores inside the sintered body. As described above, a poreless sintered body of rare earth aluminum garnet including YAG is not known in the conventional method.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a rare earth aluminum garnet sintered body excellent in light transmittance and a method for producing the same.

[0009]

The translucent rare earth aluminum garnet sintered body of the present invention has a crystal structure represented by a general formula R3Al5O12 (R is one of rare earth elements of Y, Dy, Ho, Er, Tm, Yb, Lu). A) a sintered body having a garnet structure represented by the following formula, wherein the pores in the sintered body are 100 volppm or less, and the light linear transmittance at a wavelength other than the specific absorption wavelength in the visible to infrared region is 5 mm thick. 83% or more. The amount of pores is expressed in units of volppm, and the amount of impurities is expressed in units of wtppm.

The molar ratio of the rare earth element to aluminum is 0.599 ≦ R / Al ≦ 0.601, and the ratio of the rare earth element to aluminum is 0.599 ≦ R / Al ≦ 0.6.
00, the content of Si in the sintered body was 15 wtppm or less, and the ratio of rare earth element to aluminum was 0.600 <R / Al ≦
0.601, the Si in the sintered body is Si (wtppm) ≦ 1500
0 × (R / Al) −8985.

The method for producing a translucent rare earth aluminum garnet sintered body according to the present invention has a specific surface area of 3 to 15 m ² / g.
And a general formula R3Al5O12 (R is any one of Y, Dy, Ho, Er, Tm, Yb, and Lu) prepared by using a raw material powder in which agglomerated particles exceeding 3 μm have a weight fraction of 5% or less. Primary firing of a ceramic molded body represented by a rare earth element) has an average particle diameter of 3 μm or less and a theoretical density ratio of 94%.
By densifying as above and subjecting this primary sintered body to hot isostatic pressing, the pores in the sintered body are 100 volppm or less,
The sintered body is characterized in that the sintered body has a thickness of 5 mm and a linear transmittance of light of 83% or more at wavelengths other than the specific absorption wavelength in the visible to infrared region.

The primary firing is preferably performed at 1450 ° C. or more and 1700 ° C. or less. The HIP is performed at a temperature of 1400 ° C. or more and 1800 ° C. or less and 800 kg using an atmosphere such as Ar.
It is preferable to carry out at a rate of f / cm2 or more and 2000 kgf / cm2 or less.

[0013]

The present inventors have found that the pores are 100 volppm.
It has been found that a rare earth aluminum garnet sintered body having a thickness of 5 mm and a luminous linear transmittance of 83% or more in the visible to infrared region other than the specific absorption wavelength can be produced. For this purpose, for example, after forming a high-density easily sinterable raw material powder in which the composition ratio of a rare earth element and aluminum, the Si content, the primary particle diameter, and the secondary aggregated particle diameter are controlled, the average particle diameter is 3 μm. Hereinafter, 1 for the theoretical density ratio of 94% or more
Next baking and HIP may be performed.

The molar ratio between the rare earth element and aluminum is 0.599 ≦ R / Al ≦ 0.601 on a molar basis, and the upper limit content of Si is changed according to this molar ratio. This molar ratio in the range of 0.599 to 0.601 is a transparent region when the Si concentration is low, and the condition that the Si concentration is not more than the upper limit content is a condition for preventing the formation of a liquid phase at the grain boundary. This is a condition for preventing gas from entering in the HIP process and preventing generation of pores.

The pores are removed, for example, by baking the sample at a high temperature while isotropically applying a high pressure to discharge the pores by grain growth and accelerate the discharge of the pores by plastic deformation. In contrast to the conventional method in which pores are discharged only by the volume diffusion effect due to grain growth, in the present invention, by adding a plastic deformation effect, pores of a size which cannot be removed normally can be removed. Even when HIP is used, if SiO2 such as a sintering aid exists in excess of the upper limit concentration,
Under high temperature and high pressure, segregation occurs at the grain boundary, and Ar or the like of the pressure medium enters and expands by annealing after HIP. For this reason, pores cannot be removed.

[0016]

EXAMPLE A high purity rare earth aluminum garnet raw material powder is formed by a casting method. The amount of Si in the raw material powder used here is such that R / Al is 0.599 ≦ R / Al ≦
In the range of 0.600, 15 ppm or less, 0.600 <R / A
In the range of 1 ≦ 0.601, Si (ppm) ≦ 15000 × (R
/ Al) -8985. In any case, the amount of Si is more preferably 5 ppm or less.

When the aluminum content is higher than the normal composition,
Si forms a liquid phase together with excess aluminum and segregates at the grain boundaries. A gas such as Ar penetrates into the sintered body through the segregated grain boundary phase, and a sufficient HIP effect is not generated. On the other hand, when the rare earth is more than the normal composition, Si is added together with the excess rare earth element, for example, YAP or YAP in YAG.
AM is formed and localized at the triple point of polycrystalline YAG. The limit amount of Si that forms a liquid phase on the aluminum excess side is 15
At ppm, since Si is localized at the triple point on the yttrium excess side, the amount of Si forming a liquid phase at the grain boundary increases with the excess amount of yttrium. Therefore, if the amount of Si is limited, an inflow route of Ar to the grain boundary is not formed, and the effective HI
The P effect occurs.

The raw material composition largely affects the optical characteristics of the obtained sintered body. The present inventors have found that Si promotes grain growth and expands the transparent composition region of the polycrystal as described above. In the conventional method, several hundred ppm or more of SiO2 is added as a sintering aid, and the transparent composition range is not so strict. The present inventors have found that when 100 ppm of Si is present, the transparent composition range of YAG ceramics is 0.1%.
It has been found that 594 ≦ R / Al ≦ 0.606. However, when the amount of Si is reduced, the transparent composition range also changes. In the case of no addition of Si, abnormal grain growth occurs when the aluminum content exceeds the normal composition and conversely, a heterogeneous phase having a completely different refractive index occurs when the rare earth content becomes excessive. . Therefore, in order to obtain a sufficient transparent body, the composition is more strictly controlled, and the composition is controlled to 0.1.
599 ≦ R / Al ≦ 0.601.

There is no problem if a grain growth inhibitor such as Ca and Mg is added as required. However, if it is added more than necessary, it segregates at the grain boundaries and becomes not only a light scattering source, but also it is difficult to sufficiently exhibit the HIP effect as in the case of Si. Therefore, the amount of addition should be kept to the minimum necessary amount, and a total of 80
It is preferable that the content be not more than ppm. The method and timing for adding these auxiliaries are not particularly limited, but they need to be uniformly added to the molded body.

The raw material powder used is easy to sinter, has a specific surface area of 3 to 15 m 2 / g, and has a uniform particle size distribution of secondary aggregated particles exceeding 3 μm having a weight fraction of 5% or less. I do. The sinterability depends on the particle diameter of the raw material powder, and the sinterability improves as the fine powder is used, but the specific surface area is 3 m.
If it is less than 2 / g, it is not easy to densify at low temperature. If it is more than 15 m 2 / g, the powder is too fine, handling is not easy, and it is difficult to increase the molding density. Therefore, from the viewpoint of sinterability, packing property, and ease of handling, the specific surface area of the raw material used is preferably 3%.
１５15 m 2 / g. In addition to adjusting the specific surface area, the size of the secondary aggregated particles of the raw material powder also becomes a problem.
Between the secondary aggregated particles and between the secondary aggregated particles, there are voids as large as several μm, which are larger than those generated by general molding. Since these voids cannot be eliminated by the primary firing and the HIP treatment, a raw material powder containing secondary aggregated particles exceeding 3 μm in a weight fraction of 5% or less is used.

As the molding method, any of extrusion molding, injection molding, press molding and the like generally used in the production of ceramics may be used, but a cast molding method is preferred for obtaining a dense sintered body with good yield. The size of pores that can be removed by HIP is submicron or less, and it is impossible to remove defects of several microns or more caused by poor packing during molding by primary firing and HIP processing.
In extrusion molding or injection molding, since a raw material powder is mixed with a large amount of a binder to form a highly viscous compound and then molded, air bubbles of several μm to several tens μm are likely to enter. In press molding, generally, in order to improve powder handling properties, the raw material powder is once granulated and then molded. At this time, a gap of several μm is likely to be generated at the triple point formed between the granules, particularly between the granules in the vicinity. On the other hand, in casting, large defects as large as several μm occur only when bubbles enter the casting slip, and such bubbles can be easily removed by ultrasonic waves or vacuum. Therefore, molding is performed by a casting method, and the molding density is 59%.
% Is preferable.

The obtained molded body is subjected to a binder removal treatment by thermal decomposition. At this time, the processing temperature, time, and atmosphere
Although it depends on the type of the molding aid added, if the sample becomes closed voids, it becomes difficult to remove the binder. Therefore, the sintering is performed for a sufficient time at a temperature at which sintering does not start. The atmosphere is most commonly an oxygen atmosphere, and if necessary, humidified hydrogen or A
r or under reduced pressure.

After the debinding, the sample is evacuated to vacuum, air,
First firing in an atmosphere such as hydrogen, the average particle size is 3 μm or less,
Densify to a theoretical density ratio of 94% or more. At the time of the HIP treatment, if the average particle diameter of the primary fired body is too large, plastic deformation does not occur, so that it is difficult to remove pores. In order to crush the pores by plastic deformation, the average particle size of the sample is 3 μm.
It is necessary that the thickness be less than or equal to 1 μm. Even if the average particle size is 3 μm or less, it is difficult to remove pores if the particles are not densified to some extent. Therefore, the primary fired body is preferably densified to 94% or more of the theoretical density, more preferably 96% or more.

If the primary firing temperature is too low, it is difficult to sufficiently densify, and if it is too high, grain growth proceeds, and in any case, it is difficult to remove pores by HIP treatment. Become. Therefore, firing is preferably performed at a temperature of 1450 ° C. or more and 1700 ° C. or less. For example, when a sintering aid is not used, 1500 ° C to 1650 ° C, Ca,
When a grain growth inhibitor such as Mg is added in an amount of 80 ppm or less, it is preferable to perform firing in a temperature range of 1600 ° C. to 1700 ° C. When the holding time is too short, the surface structure is not sufficiently closed and the pores are not sufficiently closed. When the thickness of the sample is large, the sample is held for at least 2 hours to make the surface and the inside uniform, but for a sample of 3 mm or less, holding for about 1 hour is sufficient.

In order to remove pores in the obtained primary sintered body, HIP processing is performed. The removal of pores by the HIP treatment is due to plastic deformation under high temperature and high pressure. When the processing temperature is low, mass transfer does not occur, so that plastic deformation does not occur. Conversely, if the treatment temperature is too high, the sample grows during the temperature rise, so that no plastic deformation occurs. Therefore, the HIP temperature is preferably from 1400 ° C to 1800 ° C, and particularly preferably from 1550 ° C to 1650 ° C.
Further, when the HIP temperature is higher than the primary sintering temperature by 100 ° C. or more, the grain growth is promoted and the mechanical strength of the ceramics is reduced.
Preferably, the temperature is in the range of the primary sintering temperature ± 50 ° C.

It is also important to select the HIP pressure, and it is difficult to remove pores if the pressure is insufficient even if the temperature is optimized. In order to crush pores at a temperature of 1400 ° C. or more, a pressure of 800 kgf / cm 2 or more is preferable, and particularly, when a sample thickness is 5 mm or more, a pressure of 1000 kgf / cm 2 or more is preferable. If the HIP pressure exceeds 2000kgf / cm2,
Maintenance and management of the high-pressure vessel is not easy, and if pressure reduction during cooling is not performed properly, there is a problem that dew condensation occurs in the pressure vessel, which is not preferable. Therefore, the HIP pressure is preferably 800 kgf / cm2 or more and 2000 kgf / cm2 or less.

[0027]

Test Example 1 0.5 mol / L yttrium nitrate aqueous solution 15
The liter and 25 liter of a 0.5 mol / L aqueous solution of aluminum nitrate were mixed to obtain a mixed solution having a YAG composition. This solution was added dropwise at a rate of 1.5 liter / min into 40 liters of a 2M aqueous solution of ammonium carbonate adjusted to pH 8.0 by adding aqueous ammonia. At this time, the mixed solution of the YAG composition and the aqueous solution of ammonium hydrogen carbonate were both maintained at 30 ° C. The minimum value of the pH during the dropping was 7.0, and the pH reached a constant value of 7.8 in about 3 hours after the completion of the dropping. After completion of the dropwise addition, the mixture was cured at 30 ° C. for 48 hours, and then filtered and washed with water six times to obtain a YAG precursor. Ultrapure water (conductivity: 18 MΩ · cm) was used in all of the precursor production steps.

The obtained YAG precursor is heated at 1300 ° C. in air.
For 5 hours to prepare a YAG raw material powder having a primary particle size of 0.4 μm. The purity of the raw material powder was analyzed using ICP, and it was found that the purity was 99.95% or more, the content of Si was 3 ppm, and the molar ratio of Y / Al was 0.600. The weight fraction of the aggregated particles exceeding 3 μm was 1% or less.

To 200 g of the obtained YAG raw material powder, 4.2 g of Kyoeisha Chemical Floren G-700 was used as a deflocculant.
Sekisui Chemical PVB-B as a binder
1 g of L1 was added, 50 g of ethanol was added, and mixed for 12 hours using a nylon pot and a nylon ball.
An alcohol slurry was obtained. This slurry was poured into a gypsum mold to obtain a molded body of 50 mm × 50 mm × 10 mm. The temperature of this molded body was raised at 10 ° C./hr in an oxygen stream,
Degreasing was performed at 50 ° C. for 100 hours, and the density of the molded body after the degreasing treatment was 60.7%. Next, the molded body is placed in a vacuum furnace for 15 minutes.
Primary firing was performed at a temperature of 00 ° C. for 2 hours. At this time, the temperature raising rate was 400 ° C./hr, and the pressure was 10 ⁻³ Torr or less. 1
The theoretical density ratio of the next fired body was found to be 96.4% by Archimedes' method. As a result of observing the microstructure inside the sintered body with an optical microscope, the average particle diameter of the sintered body was 1.2 μm.
m.

The primary fired body is heated at 500 ° C./hr for 15 hours.
The temperature was raised to 50 ° C., and the pressure was increased to 1250 kgf / cm 2 in Ar.
HIP was performed for hours. From the obtained sintered body, approximately 40 × 8
Ten samples of × 0.5 mm were cut out and both surfaces were mirror-polished with diamond slurry, and the pores in all the samples were observed using a transmission microscope. As a result of observing the number of pores and the pore diameter and converting the volume, the amount of pores was 7 volppm. Also, 5.
After being cut to a thickness of 0 mm and mirror-polished on both sides, the linear transmittance was measured by a spectrophotometer. As a result, it was 84% at a wavelength of 500 nm.

[0031]

Test Examples 2 to 9 High-purity lutetium aluminum garnet (Lu3Al5O12:
LuAG) SiO2 was added to the raw material powder, and a sintered body was produced in the same manner as in Test Example 1 (Test Examples 2 to 9). Table 1 shows the relationship between the amount of Si in the sintered body and the porosity. The molar ratio between Lu and aluminum in this sample was Lu / Al = 0.5.
99. From Table 1, the porosity in the sintered body was 100 vo
It can be seen that in order to make it less than lppm, it is necessary to make Si in the sintered body less than 15ppm.

[0032]

Table 1 Relationship between Si and porosity in sintered body Si / ppm Porosity / volppm Linear light transmittance (500 nm / 5 mm thickness) Test Example 2 3 3 84 Test Example 3 8 43 84 Test Example 4 14 72 83 Test Example 5 17 110 80 Test Example 6 22 240 77 Test Example 7 50 600 72 Test Example 8 120 950 65 Test Example 9 500 1350 60

[0033]

Test Examples 10 to 14 In the same manner as in Test Example 1, high-purity LuAG raw material powders having different compositions were prepared, SiO2 was added, and a sintered body was prepared in the same manner as in Test Example 1. Table 2 shows the relationship among the composition, the Si content, and the porosity of the sintered body. Table 2
Therefore, when Lu / Al = 0.601, Si is 30 ppm
Until the porosity is 100 volppm or less, it can be seen that the porosity sharply increases when the Si content is more than 100 volppm. Test Examples 13 and 14 also show that even when the amount of Si is small, pores cannot be sufficiently removed even with a slight composition deviation.

[0034]

Table 2 Test Examples 10 to 14 Lu / Al Si / ppm Porosity / volppm Test Example 10 0.601 3 3 Test Example 11 0.601 28 81 Test Example 12 0.601 35 270 Test Example 13 0.5983 1400 Test Example 14 0.603 3 220

[0035]

Test Examples 15 to 24 In the same manner as in Test Example 1, high-purity ytterbium aluminum garnet (Yb3Al5O1
2: Abbreviated as YbAG) A precursor was produced, and the temperature and time during calcination were variously changed to produce high-purity YbAG raw material powders having different primary particle diameters and agglomeration degrees. The raw material composition is R /
Al was 0.600, and the purity was analyzed by ICP. As a result, in all cases, the purity was 99.95% or more and the content of Si was 3 ppm or less. Using these raw material powders, a molded body was prepared in the same manner as in Test Example 1, and after performing a binder removal treatment, the average crystal particle diameter was 3 μm or less at 1575 ° C. in a vacuum furnace, and the theoretical density ratio was 94% or more. Primary firing was performed. 2000 kgf /
HIP was performed at 1600 ° C. in cm 2. BET of raw material powder
Table 3 shows the surface area value, the weight fraction of the aggregated particles having a size of 3 μm or more, and the porosity contained in the obtained sintered body. Test Examples 15 to 19 show that the porosity of the sintered body depends on the weight fraction of the aggregated particles of 3 μm or more in the starting material powder, and the porosity increases as the ratio increases.

[0036]

Table 3 Test Examples 15 to 24 BET (cm2 / g) 3 μm or more agglomerated particles (wt%) Porosity (ppm) Test Example 15 3.4 4.1 57 Test Example 16 5.8 2.2 21 Test Example 17 8.4 1.0 3 Test Example 18 11.0 3.3 9 Test Example 19 14.6 4.6 34 Test Example 20 2.7 4.6 110 Test Example 21 3.5 6.2 185 Test Example 22 6.8 10.8 630 Test Example 23 12.3 8.5 565 Test Example 24 16.7 4.8 250

Various rare earth aluminum garnet sintered bodies were prepared in the same manner as in Test Example 1, and the three-point bending strength at room temperature was measured in accordance with JIS1601. The firing conditions, porosity, three-point bending strength and Weibull coefficient are shown in the table below. The lower the porosity, the higher the strength, and in all cases, the three-point bending strength was 350 MPa or more.

[0038]

[Table 4] Porosity of various materials and 3-point bending strength material Primary firing HIP temperature Pressure porosity 3-point bending strength Wiper coefficient (℃ × hr) (℃ × hr) (kgf / cm2) (ppm) (MPa) Y3Al5O12 1550 × 2 1550 × 2 1250 7 430 7 Dy3Al5O12 1500 × 2 1525 × 3 1500 25 410 6 Ho3Al5O12 1550 × 2 1600 × 3 1000 68 365 7 Er3Al5O12 1600 × 3 1650 × 2 800 92 350 6 Tm3Al5O12 1650 × 5 1700 × 5 1800 35 395 7 Yb3Al5O12 1575 × 3 1600 × 2 800 50 380 7 Lu3Al5O12 1525 × 3 1550 × 2 1250 3 450 8

From Tables 1 to 4, it can be seen that a porosity of 100 ppm or less is a condition for a sample having a thickness of 5 mm at 500 nm and a linear transmittance of 83% or more. And Si
Increases the porosity, and it can be seen that the relationship between the porosity and the Si concentration is different depending on whether the rare earth is excessive or the aluminum is excessive. Further, agglomerated particles of 3 μm or more in the starting material also increase the porosity, the BET surface area of the starting material is preferably 3 to 15 m 2 / g, and the increase in the porosity is not sufficient in terms of mechanical strength required for high pressure discharge lamps and the like. It turns out to be undesirable.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Seiki Imagawa 4-4-7 Koraibashi, Chuo-ku, Osaka Inside Kamishima Chemical Industry Co., Ltd. (72) Inventor Hiroki Yamazaki 4-2-7 Koraibashi, Chuo-ku, Osaka-shi K-jima Chemical Industry Co., Ltd. F-term (reference) 4G031 AA07 AA29 BA15 BA20 CA07

Claims (3)

[Claims] 1. A sintered body having a garnet structure having a crystal structure represented by a general formula R3Al5O12 (R is any one of rare earth elements of Y, Dy, Ho, Er, Tm, Yb, and Lu). Characterized in that the sintered body has pores of 100 volppm or less, and has a linear light transmittance other than the specific absorption wavelength of at least 83% at a thickness of 5 mm over the visible to infrared region. Aluminum garnet sintered body. 2. The molar ratio of the rare earth element to aluminum is 0.599 ≦ R / Al ≦ 0.601, and the ratio of the rare earth element to aluminum is 0.599 ≦ R / A.
1 ≦ 0.600, Si in the sintered body is 15 wtppm or less, and the ratio of rare earth element to aluminum is 0.600 <R / A
When l ≦ 0.601, Si in the sintered body is Si (wtppm) ≦ 15
The translucent rare earth aluminum garnet sintered body according to claim 1, wherein 000 × (R / Al) −8985. 3. The resin having a specific surface area of 3 to 15 m ² / g and a thickness of 3 μm
R3Al5O12 (R is Y, Dy, H
o, Er, Tm, Yb, or Lu), a ceramic molded body represented by one of the following rare earth elements is subjected to primary firing to be densified to an average particle diameter of 3 μm or less and a theoretical density ratio of 94% or more. By subjecting the primary sintered body to hot isostatic pressing, the pores in the sintered body are 100 volppm or less, and the light linear transmittance at a wavelength other than the specific absorption wavelength in the visible to infrared region is 5 mm. A method for producing a sintered body of a translucent rare earth aluminum garnet, wherein the sintered body is 83% or more.