JP2003261375A - High density alumina produced by pressureless sintering and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide a light emission tube of a high intensity discharge (HID) lamp and a semiconductor production apparatus member of high quality. <P>SOLUTION: The high density alumina is produced by adopting a pressureless sintering in an air atmosphere as a firing method. The high density alumina has a relative density of ≥99.5%, provided that the theoretical density of α-alumina is 3.987 g/ml, and has light transmittance that the total transmittance of visible rays is ≥85% in a thickness of 0.6 mm, and straight line transmittance is ≥20% in a thickness of 1 mm. As the molding method therefor, a cast molding method is adopted. A porous alumina mold having a pore size of ≤0.6 μm, a porosity of ≥15% and a purity of ≥90% is used. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

The present invention relates to a high-density alumina which is inexpensive and excellent in quality and has a light-transmitting property, and a manufacturing technique thereof.

[0002]

2. Description of the Related Art Alumina is the most general-purpose oxide-based ceramics having high hardness and excellent wear resistance, thermal conductivity, electrical insulation and corrosion resistance. It is widely used in electrical and electronic materials, optical materials, structural materials, biomaterials, heat insulating materials, chemical resistant materials, and abrasive materials. For example, spark plugs for automobile engines, IC packages for semiconductor integrated circuits, and artificial materials. Bone / artificial roots, grinding balls, cutting tools, etc. Alumina, which is usually used in these industrial products, is made by using inexpensive powder having a purity of 99.9% or less manufactured by the Bayer method, etc., and the relative density of the sintered body is the theory of α-alumina. When the density is 3.987 g / ml, it is often 99% or less. On the other hand, alumina used as light emitting tubes for high-intensity discharge lamps (HID lamps) such as high-pressure sodium lamps and metal halide lamps and semiconductor manufacturing equipment members requires a high-density sintered body with a relative density of 99.5% or more. In particular, arc tubes are required to have translucency in the visible light range.

In order for polycrystalline alumina to transmit light, the surface is smooth, there is no impurity layer at the crystal grain boundaries, and no pores larger than the wavelength of light remain in the crystal grain boundaries or grains. It must be Therefore, it is necessary to use a high-purity raw material, to make no major defects in the molding process, and to almost completely remove the residual pores in the sintering process.
For the production method of high density alumina having translucency,
Generally, the following method is adopted. First, the raw material powder is a high-purity submicron-sized alumina powder having a purity of 99.9% or more. The molding method includes isotropic pressure molding (CIP molding), injection molding and cast molding. The sintering method is vacuum sintering or hydrogen atmosphere sintering, and further high temperature isotropic pressure pressurization treatment (HIP treatment).

The problems of the prior art will be described. In the method of manufacturing high density alumina having translucency, in the molding method, the density of the sintered body and the translucency are lowered due to the generation of large defects in the molded body and the contamination of the molded body with impurities, and the limit of shape imparting The cost increase in the sintering process is a big problem. First, in the CIP molding method, the shape that can be molded is limited. For example, in the HID lamp arc tube,
It was limited to a straight tube shape, and when used in an HID lamp, many problems remained in the metal gas sealing technology, which greatly affected the life of the lamp. For this reason, the shape of the light-transmitting tube is a modified tube with both ends thinner than the central part, which is the discharge part,
Attempts have been made to facilitate sealing. With this shape, the CIP molding method cannot be applied. Further, in the injection molding method, a mixture of ceramic powder and resin is pressed into a mold to give a shape. Therefore, a combustible core is required to produce a tubular molded body, and a difference in thermal expansion between the core and the molded body during the firing process causes a reduction in yield.
Further, the contamination of the molded body with iron from the screw of the injection molding machine or the mold is severe, which reduces the density of the sintered body and the translucency.

In the cast molding method, gypsum is usually used as a mold material. In this case, the molded body is contaminated with calcium, which causes cracks in the sintered body after sintering, which causes a decrease in density and translucency of the sintered body. In order to remove calcium in the molded body, it is necessary to carry out the step of acidizing the molded body with hydrochloric acid or the like after calcining the molded body as in JP-A-8-301666. Further, as long as the plaster mold is used, the molding speed is slow and it is difficult to construct a mass production system, and a large amount of plaster mold is generated as industrial waste.

Next, the translucent high density alumina is sintered by vacuum sintering or hydrogen atmosphere sintering. This is a method adopted to minimize the pores remaining in the sintering process, and the pores remaining in the vacuum and hydrogen atmosphere sintering are removed by the HIP process. However, in any of the vacuum, hydrogen atmosphere, and HIP methods, the equipment is expensive and requires a large amount of maintenance costs. In particular, in the hydrogen atmosphere sintering method, the exhaustion of furnace materials, heaters, etc. due to the corrosiveness of hydrogen at high temperatures and the replacement of a large amount of inert gas impede the reduction of the sintering cost.

[0007]

SUMMARY OF THE INVENTION According to the present invention, α-alumina powder having a high purity and an extremely narrow particle size distribution width is prepared and molded by a cast molding method which is free from contamination such as calcium and iron and has good productivity. Moreover, the relative density is 99.5% when the theoretical density of α-alumina is set to 3.987 g / ml by sintering by the atmospheric pressure sintering method which is the least costly.
As described above, a high-density alumina having a total transmittance of visible light of 85% or more at a thickness of 0.6 mm and a linear transmittance of 20% or more at a thickness of 1 mm is manufactured, and is inexpensive and excellent in high brightness. It is an object to provide an arc tube of a discharge lamp (HID lamp) and a semiconductor manufacturing device member.

[0008]

[Means for Solving the Problems]

The present invention has a relative density of 99.5 when the theoretical density of α-alumina produced by employing atmospheric pressure sintering as a firing method is 3.987 g / ml.
A high density alumina having a total transmittance of visible light of not less than 85% and a linear transmittance of not less than 85% at a thickness of 0.6 mm and a linear transmittance of not less than 20% at a thickness of 1 mm is defined as the gist. As a molding method, a cast molding method using a porous alumina mold having a purity of 90% or more is adopted. In that case, the present invention uses a cast molding method using a porous alumina mold having a purity of 90% or more as a molding method. The relative density of α-alumina, which was produced by adopting atmospheric pressure sintering in an air atmosphere as a firing method, was 99.5 when the theoretical density of α-alumina was 3.987 g / ml.
% High density alumina having a total visible light transmittance of 0.6% at a thickness of 85% or more and a linear transmittance of 1 mm at a thickness of 20% or more.

A porous alumina type having a pore diameter of 0.6 μm or less, a porosity of 15% or more, and a purity of 90% or more is used. In that case, the present invention provides a pore diameter of 0.6 μm or less and a porosity of 15%. As described above, the theoretical density of α-alumina produced by adopting the casting method using a porous alumina mold having a purity of 90% or more and adopting atmospheric pressure sintering in the atmosphere as the firing method is 3. It has a relative density of 99.5% or more at 987 g / ml, a total transmittance of visible light of 85% or more at a thickness of 0.6 mm, and a linear transmittance of 20% or more at a thickness of 1 mm. Density alumina.

Further, in the present invention, a high-purity alumina powder raw material having a narrow particle size distribution width of 99.9% or more obtained by adjusting the particle size distribution width and a porous alumina type having a purity of 90% or more are used. And then cast-molded, and then the molded body is subjected to atmospheric pressure sintering in an air atmosphere to obtain a theoretical density of α-alumina of 3.98.
When the relative density at 7 g / ml is 99.5% or more,
The gist is a method for producing high-density alumina, which is characterized by high-density alumina having a total visible light transmittance of 0.6 mm and a transmissivity of 85% or more and a linear transmittance of 1 mm and a transmissivity of 20% or more.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The alumina powder raw material used in the present invention is a high-purity alumina of 3N (99.9%) or more known as a raw material for alumina tools and translucent alumina.
A raw material powder having an extremely narrow particle size distribution width obtained by adjusting the particle size distribution width is used. By using the raw material powder having a narrow particle size distribution width, it is possible to prevent generation of large residual pores in the sintering process in a microscopic view. Generally, a molded body produced by using an alumina raw material having a wide particle size distribution width causes pore growth in the sintering process,
The pores are left in the sintered body. The small powder has a large surface energy as compared with the large powder, and the small powder moves to the large powder side and grows grains during the sintering process, but pores remain therein. Therefore, by using a raw material powder with a narrow particle size distribution width, the difference in surface energy level between the powders becomes small, and it becomes possible to prevent the generation of large residual pores in the sintering process from a microscopic viewpoint. .

In the present invention, first, an alumina raw material powder having an extremely narrow particle size distribution width is prepared. The alumina raw material powder having an extremely narrow particle size distribution width may be obtained by any preparation method. High-purity alumina powder of 3N (99.9%) or more, which has been used as a raw material for translucent alumina, may be sized by an elutriation classification method. Also,
When the purity is 99.99% and the particle size distribution is arranged by a logarithmic normal distribution, an alumina powder having a standard deviation of 1.24 and a narrow particle size distribution width is produced by a vapor phase synthesis method. Furthermore, a molded body of 3N (99.9%) or higher high-purity alumina powder, which has been used as a raw material for translucent alumina so far, is heated at a suitable temperature between 700 and 1000 ° C. It is possible to narrow the width of the particle size distribution by holding it for about 50 hours. That is, the above 70
By holding at a suitable temperature between 0 to 1000 ° C. for 5 to 50 hours, fine particles having a particle size distribution grow and the width of the particle size distribution becomes narrow as a whole.

The present invention employs a casting method that has not been used for producing a high density alumina having a light transmitting property. The cast molding method is capable of molding complicated and large-sized products, and high-density molded products have been obtained. Therefore, researches on molding methods of alumina, zirconia, silicon nitride, etc. have been actively conducted. The basic technique of the casting method adopted by the present invention is disclosed in Japanese Patent Laid-Open No. 6-170821 of the present inventor.
No. The publication describes a slurry casting method characterized by using a specific shaping die. The present invention, in the casting method of ceramics, applies the external pressure to the slurry, which is a problem of the conventional technique that the shaping speed is slow. This problem is solved by controlling the porosity and the pore diameter of the ceramics molding die instead of the above means. That is, in the cast molding of ceramics, the molding speed is dramatically improved by using porous ceramics having controlled porosity and pore diameter instead of the gypsum mold.

In the present invention, a porous alumina type is used. In the above-mentioned JP-A-6-170821, the vitreous binder 10
Sintered compacts of ceramic compound powder raw material, preferably alumina powder raw material, containing less than 2.0% by weight and having a particle size of 2.0 μ or less and having a pore diameter of 0.6 μ.
It is described below that a mold having a porosity of 30% by volume or more is used. As the glassy binder, known alkali metal compounds and alkaline earth metal compounds are used.

In the present invention, it is preferable to use a porous alumina type having a pore diameter of 0.6 μm or less, a porosity of 15% by volume or more and a purity of 90% or more, for the following reason. is there. Since the ceramic powder produced by cast molding contains submicron powder, in the porous alumina type having a pore size of 0.6 μm or more, particles of 0.6 μm or less enter the porous type and cause clogging. Therefore, the water absorption pressure (capillary force) of the porous type is lowered, and the molding speed is slowed. Regarding the porosity, the porous alumina mold used when producing a thick cast-molded body needs to have a high molding speed, and therefore the pore diameter is reduced to enhance the capillary force and It is necessary to increase the porosity in order to quickly move the liquid medium absorbed in the mold. On the other hand, 1 mm or 2 m
When casting a molded article with a thin thickness of m or less, if the molding rate is too fast, it becomes difficult to control the thickness by the casting time. Therefore, by lowering the porosity of the porous alumina mold and slowing the molding rate, Need to control. For the above reasons, the pore size of the porous alumina type is 0.6μ.
m or less and porosity of 15 vol% or more.

The control of the porosity and the pore diameter of the porous ceramics mold will be described. Porous ceramics are manufactured by various methods, but the simplest method is obtained by molding a ceramic raw material and sintering at a temperature 100 to 400 ° C. lower than the sintering temperature at which a dense sintered body is obtained. . The porosity, which is the most important factor of the porous ceramics, is determined by the molding density and the sintering temperature. The lower the molding density and the sintering temperature, the higher the porosity. Regarding the control of the pore diameter, if a well-sized ceramic raw material is used, the pore diameter can be controlled to about 1/3 of the average particle diameter. The porous alumina used as a mold material is manufactured by a method of controlling the pore diameter and the porosity by adding 0 to 10 wt% of a vitreous binder to sized alumina. The well-sized alumina powder is a powder having a narrow particle size distribution, and the standard deviation σ of the lognormal distribution formula is in the range of 1.0 to 2.0.

The meaning of controlling the pore size of the casting mold will be described. In cast molding of ceramics,
When the slurry is pressurized, the higher the pressure, the faster the molding speed. The osmotic pressure ΔP of the liquid in the hydrophilic porous body can be represented by the formula I because it is due to the wetting effect of the liquid in the casting at normal pressure.

[Equation 1] Here, γLcosθ is the free energy of wetting, and r is the pore radius. From the formula I, it can be seen that the material having a larger free energy of wetting with water and the porous ceramic having a smaller pore diameter have a higher osmotic pressure and a higher molding speed in casting. In addition, the ceramic raw material is becoming finer particles, and the ceramic powder dispersed in the slurry enters the pores when the porosity of the casting mold is large,
It is significant that the pore size can be controlled because it also causes clogging.

A performance comparison between porous alumina and gypsum as a mold material will be described. Problems of the conventional cast molding method using a gypsum mold are (1) slow molding speed, (2) Ca contamination of the molded body due to wear and dissolution of the gypsum mold, and deterioration of dimensional accuracy. For the friction and dissolution of the gypsum mold, it has been considered to use a deplaster mold such as a resin mold, but it is necessary to apply pressure because the mold material is hydrophobic. In addition, although a mold made of a sintered ceramic compound sintered body and having a pore diameter of 1 μm or less has been developed, only a study on making a gypsum mold that can be used semipermanently has been made. Kaisho 62-24
4603 publication). The molding speed in cast molding is an important factor for obtaining a molded product having a uniform structure. That is, since the ceramic raw material dispersed in the slurry aggregates with the passage of time, the compact density decreases with the passage of the shaping time. This agglomeration phenomenon becomes stronger as the ceramic raw material becomes finer particles. Since the casting speed is governed by the water absorption pressure and water absorption speed of the gypsum mold, it has been attempted to increase the molding speed by applying external pressure to the slurry. As a plaster mold,
45 parts of water was added to 100 parts of α-gypsum generally used for cast molding of fine ceramics, and the mixture was stirred for 5 minutes and allowed to stand for 5 minutes to obtain a plaster mold (referred to as mold 1). On the other hand, for porous alumina, 30 M of each alumina having an average particle size of 20 μm, 3 μm, and 1.3 μm is used.
Press molded at a pressure of pa, 1650 ° C. for 20 μm alumina, 1 for 3 μm and 1.3 μm.
It was sintered at 400 ° C. to obtain a porous body (referred to as mold 2 to mold 4). Furthermore, for an average particle size of 1.3 μm, 3
One test piece was press-molded at a pressure of 60 MPa and the sintering temperature was changed (1400 ° C, 1500 ° C, 15 ° C).
50 ° C.) A porous body (types 5 to 7). Table 1 shows the physical properties of gypsum and porous alumina, that is, the average pore diameter (mercury porosimeter method), porosity (weight method in water), and free energy of wetting with water (penetration rate method).

[0020]

[Table 1] ───────────────────────────────────                               Average Pore Size Porosity Wetting Free Energy        Type Specimen μm% mN / m ───────────────────────────────────   1 gypsum 4.39 43.5 0.92   2 Alumina 20 μm 7.46 45.1 7.98   3 Alumina 3 μm 1.12 43.4 11.87   4 Alumina 1.3 μm 0.56 40.4 14.37   5 Alumina 1.3 μm 0.47 36.6 14.90   6 Alumina 1.3 μm 0.45 30.3 14.82   7 Alumina 1.3 μm 0.42 24.0 8.59 ───────────────────────────────────

In Table 1, the average pore diameter of the plaster of type 1 is 4.4 μm, whereas the average pore diameter of the porous alumina is smaller than the average particle diameter of the raw materials used in types 2 to 4. The average particle size of the raw materials used is about 1/3. It is proved that the mold 4 and the mold 5 are different from each other only in the molding density, and the molds 5 and 6 are different from each other only in the sintering temperature, and the porosity is determined by the molding density and the sintering temperature. . The free energy of wetting of porous alumina increases as the average pore diameter decreases, and does not show a constant value. It is considered that this depends on the shape of the pores and the state of the surface of the pores, but in any case, the free energy of wetting of the porous alumina is 8 to 14 times as large as that of gypsum. Therefore, from the equation, it can be said that, as compared with gypsum, the smaller the average pore diameter, the higher the osmotic pressure due to the wetting effect.

7 types of porous materials shown in Table 1, type 1 to type 7
The alumina casting test was carried out. 30 parts of water to 100 parts of alumina having an average particle size of 0.6 μm
Parts, polycarboxylic acid ammonium salt 0.4 as a dispersant
Parts, and an alumina slurry prepared by adding 1.5 parts of an acrylic binder, the thickness L of the wall thickness with respect to the casting time t was measured, and the rate constant (L2 / t) of the wall thickness was calculated.
FIG. 1 shows the relationship between the water penetration pressure ΔP and the inking rate constant. In FIG. 1, the rate of infiltration rate of gypsum is 20 for alumina.
Although it shows a value slightly larger than μm, the average pore size of porous alumina decreases and the rate of deposition rate increases, and the rate of deposition rate of 1.3 μm of alumina is up to about 12 times that of gypsum. Indicates the value. This fact is that if porous ceramics, which is a material with high free energy of wetting against water and has an average pore size as small as possible, is used as a casting mold for ceramics, the molding speed is dramatically faster than that of a plaster mold. It teaches that

Sintering is performed by atmospheric pressure sintering in an air atmosphere.
If high-purity alumina raw material with an extremely narrow particle size distribution width is used and a molded product with no air holes is created during the molding process, it is possible to manufacture a high-density alumina that has translucency even by the atmospheric pressure sintering method. is there. The sintering method of the present invention is performed by the most inexpensive atmospheric pressure sintering. In general, a molded body produced by using an alumina raw material having a certain particle size distribution width causes pores to grow in the sintering process, particularly in the early and middle stages of sintering, so that the pores in the sintered body remain. Smaller powders have a larger surface energy than powders with a larger particle size, and smaller powders move to the larger powder side during the sintering process, leaving pores therein. Therefore, by using a raw material powder with a narrow particle size distribution width, the difference in surface energy level between the powders becomes small, and it becomes possible to prevent the generation of large residual pores in the sintering process from a microscopic viewpoint. . Therefore, if high-purity alumina with an extremely narrow particle size distribution is used and a molded body with no air holes is produced during the molding process, a high-purity high-density alumina sintered body that has translucency even under normal pressure sintering can be manufactured. It is possible to In addition, a molded body of 3N (99.9%) or higher high-purity alumina powder, which has been used as a raw material for translucent alumina, is used in the firing process at 700 to 10%.
It is possible to narrow the particle size distribution width by holding the powder at a suitable temperature between 00 ° C. for 5 to 50 hours. That is, at an appropriate temperature between 700 and 1000 ° C., 5
By holding for up to 50 hours, fine particles having a particle size distribution grow and the particle size distribution width becomes narrow as a whole. As a result, the same effect as in the case of using the raw material powder having a narrow particle size distribution width can be obtained, and as a result, it is possible to produce a high-purity high-density alumina sintered body having translucency by pressureless sintering. It is possible.

Regarding HID lamp arc tubes, HID (high intensity discharge, high intensity discharge, high pressure / low pressure sodium lamps, mercury lamps, metal halide lamps, etc.)
d) Lamps are energy-saving lamps that can obtain high brightness with low power consumption, and due to their high efficiency and good color rendering properties, their usage range has recently been rapidly expanding. Heretofore, a translucent alumina arc tube has been used as the arc tube of the high pressure / low pressure sodium lamp, and a quartz glass arc tube has been used as the arc tube of the mercury lamp and the metal halide lamp. However, in order to commercialize and popularize energy-saving metal halide lamps that are even more energy efficient, it is possible to inexpensively supply arc tubes that achieve higher brightness and longer life by raising the temperature of the arc tubes. The development of things to do is essential. In recent years, translucent alumina has been highlighted as a light-emitting tube that meets such demands, and is being studied. INDUSTRIAL APPLICABILITY The present invention provides an inexpensive manufacturing technique for a translucent alumina tube, contributes to a reduction in the manufacturing cost of an energy-saving HID lamp, and contributes to energy-saving measures by promoting the spread of HID lamps. is there.

[0025]

The function of the present invention is to replace the plaster mold with a pore size of 0.6 μm.
Hereinafter, by adopting a casting method using a porous alumina mold having a porosity of 15% or more and a purity of 90% or more, a high density molded body free of calcium contamination can be obtained, and the porous alumina mold is a gypsum mold. Capillary force, that is, suction force is large compared to, and the molding speed is much faster,
It is possible to mold high density alumina at low cost. In addition, the porous alumina type can be used semipermanently and does not generate industrial waste unlike the gypsum type.

The sintering method of the present invention is performed by atmospheric pressure sintering in the cheapest atmosphere. Generally, in a molded body produced using an alumina raw material having a certain particle size distribution width, pores grow in the sintering process, and the pores remain in the sintered body. Smaller powders have higher surface energy than larger ones, and smaller powders move to the larger powder side during the sintering process, leaving pores there. Therefore, by using the raw material powder having a narrow particle size distribution width, the difference in surface energy unit between the powders becomes small, and it becomes possible to prevent the generation of large residual pores in the sintering process in a microscopic view.
Therefore, if a high-purity alumina raw material with an extremely narrow particle size distribution width is used and a molded body without atmospheric holes is manufactured in the molding process, it is possible to manufacture a high-density alumina having a light-transmitting property even by an atmospheric pressure sintering method. It is possible.

[0027]

The details of the present invention will be described with reference to Examples. The present invention is not limited to these examples.

Example 1 A method for producing an alumina sintered body prepared by casting using a high-purity alumina raw material having a narrow particle size distribution width, using a porous alumina mold, and then performing normal pressure sintering Show. Purity 99.99%, average particle diameter 0.45 μm, 0.03 mass% in terms of magnesium oxide, with respect to 100 g of alumina powder having a standard deviation of 1.24 when the particle diameter distribution is arranged by a logarithmic normal distribution, a dispersant ( 0.225 mass% of polycarboxylic acid ammonium salt), 1.5 mass% of binder (acrylic) and 43.8 mass% of distilled water were added, and a slurry was prepared using a plastic pot and a ball.

This has an average pore diameter of 0.4 μ and a porosity of 19%.
(A) and 29% (B) porous alumina molds were used for casting. The thickness of the molded body after 60 seconds was 1.9 mm in the mold A and 2.2 mm in the mold B. 16 after drying
When sintered at 50 ° C. for 5 hours, all of the obtained sintered bodies were white and showed translucency, and a high-density sintered body having a bulk specific gravity of 3.98 and a relative density of 99.8% was obtained. It was The present sintered body was a high density sintered body equivalent to or higher than the conventional sintered body produced by hydrogen atmosphere sintering or the like.

Example 2 The data of total transmittance and linear transmittance are specified. Purity 9
Dispersant (polycarboxylic acid ammonium salt) was added to alumina powder having 9.99%, an average particle diameter of 0.45 μm, and a standard deviation of 1.24 when the particle diameter distribution is arranged in a lognormal distribution.
0.3 mass%, binder (polyvinyl alcohol-based or acrylic-based) 2 mass%, distilled water 43.
8 mass% was added to make a slurry using plastic spots and balls. This has an average pore diameter of 0.
50 μm × 50 mm × 3 mm by casting using a porous alumina mold with 4 μm, porosity of 25% and purity of 99.8%.
Flat plate and outer diameter 11 mm, length 30 mm, thickness 0.8
A cylindrical molded body of mm was produced. After drying, it was sintered by atmospheric pressure sintering at 1650 to 1750 ° C. for 3 hours. All the obtained sintered bodies were white and showed translucency.
The high density sintered body had a relative density of 99.6 to 99.8%. The flat plate sintered body has a size of 40 × 40 × 1 mm, and the cylindrical sintered body has an outer diameter of 9 mm, a length of 25 mm, and a thickness of 0.6 to 0.7 m.
m, and the surface roughness of both sintered bodies was polished to about 0.4 μm Ry. FIG. 2 shows an example of the result of measuring the linear transmittance using a flat plate sintered body. In the visible wavelength region, the linear transmittance was 30% or more in all cases. As a result of measuring the total transmittance using a cylindrical sintered body, the total transmittance was 89.
It showed 60% to 91.96%. Both the linear transmittance and the total transmittance were extremely high values for an alumina sintered body prepared by atmospheric pressure sintering in an air atmosphere.

[0031]

According to the present invention, when the theoretical density of α-alumina is set to 3.987 g / ml at low cost, the relative density is 99.5.
%, It is possible to produce a high-density alumina having a total transmittance of visible light of not less than 85% at a thickness of 0.6 mm and a linear transmittance of not less than 20% at a thickness of 1 mm. Considering that the energy saving type HID lamp and the semiconductor manufacturing equipment, which are the final products, are highly needed by the society, the present invention can provide a light emitting tube for HID lamp and a semiconductor manufacturing equipment member which are inexpensive and excellent in quality. .

[Brief description of drawings]

FIG. 1 shows the relationship between the water penetration pressure ΔP and the inking rate constant.

FIG. 2 shows the results of measurement of linear transmittance using the flat plate sintered body of Example 2.

Claims (4)

[Claims] 1. The theoretical density of α-alumina prepared by employing atmospheric pressure sintering as a firing method is 3.9.
It has a relative density of 99.5% or more at 87 g / ml, a total transmittance of visible light of 85% or more at a thickness of 0.6 mm, and a linear transmittance of 20% or more at a thickness of 1 mm. Density alumina. 2. The high-density alumina according to claim 1, wherein a casting method using a porous alumina mold having a purity of 90% or more is adopted as a molding method. 3. The inexpensive high-density alumina according to claim 2, wherein a porous alumina type having a pore diameter of 0.6 μm or less, a porosity of 15% or more, and a purity of 90% or more is used. 4. A high-purity alumina powder raw material having an extremely narrow particle size distribution width of 99.9% or more obtained by adjusting the particle size distribution width is cast-molded using a porous alumina mold having a purity of 90% or more. Then, the molded body is sintered under atmospheric pressure at atmospheric pressure to obtain a relative density of 99.5% or more when the theoretical density of α-alumina is 3.987 g / ml, and the total transmittance of visible light is 85% or more at 0.6 mm thickness and linear transmittance of 1 m
A method for producing high-density alumina, which is characterized in that the high-density alumina has a light-transmitting property of 20% or more in m thickness.