Alumina sintered body and method for manufacturing the same

Abstract

To provide an alumina sintered body with high light transmittance. [Solution] Alumina sintered body with a porosity of 1.20% or less.

Description

Technical Field

[0001] The present disclosure relates to an alumina sintered body and a method for manufacturing the same, and more particularly, to an alumina sintered body having a low porosity and thus high translucency by performing sintering in a vacuum atmosphere and / or hot isostatic pressing (HIP) treatment, and a method for manufacturing the same.

Background Art

[0002] Alumina sintered bodies are excellent in heat resistance, mechanical strength, chemical stability, and hardness, and are widely used in various industrial fields such as refractories, spark plugs, semiconductor manufacturing equipment members, bioceramics, and media for dispersion and pulverization. In particular, translucent alumina sintered bodies are applied to lighting members, optical components, jewelry, etc., and further improvement in translucency is expected while maintaining mechanical strength.

[0003] As a method for obtaining a translucent alumina sintered body, it is known to perform high-temperature sintering on a sintered body after pre-sintering in a mixed atmosphere of hydrogen and nitrogen (Patent Document 1). However, it is difficult to remove the residual pores generated in the primary sintering process in a translucent alumina sintered body manufactured by such a method, and this becomes a light scattering source, so there is room for improvement in the translucency of the alumina sintered body.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present disclosure has been made in view of such a situation, and an object thereof is to provide a translucent alumina sintered body with reduced porosity and a method for manufacturing the same.

Means for Solving the Problems

[0006] One aspect of the present invention is: This is an alumina sintered body with a porosity of 1.20% or less.

[0007] Aspect 2 of the present invention is, In the cumulative distribution of grain size based on the number of grains, the grain size D represents the 10% cumulative value from the finest grains. 10,gr,n The alumina sintered body according to Embodiment 1, wherein the particle size is 1.0 μm or less.

[0008] A third aspect of the present invention is: In the cumulative distribution of grain size based on the number of grains, the grain size D represents the 50% cumulative value from the finest grains. 50,gr,n The alumina sintered body according to embodiment 1 or 2, wherein the diameter is 1.5 μm or less.

[0009] Aspect 4 of the present invention is In the cumulative distribution of grain size based on the number of grains, grain size D represents the 90% cumulative value from the finest grains. 90,gr,n The alumina sintered body is according to any one of embodiments 1 to 3, wherein the thickness is 2.0 μm or less.

[0010] Aspect 5 of the present invention is The crystal grain size D in the cumulative distribution of crystal grain size based on the number of grains, starting from the finest grains and reaching 100% cumulative size. 100,gr,n The alumina sintered body is according to any one of embodiments 1 to 4, wherein the diameter is 3.5 μm or less.

[0011] Aspect 6 of the present invention is, A process to obtain a molded body by molding an alumina composition, wherein the alumina composition has a particle size D that is 50% of the total particle size from the fine side in the volume-based cumulative particle size distribution. 50,p,v A process that includes alumina powder of 0.40 μm or less, The process of sintering the molded body, (i) Performing the sintering under a vacuum atmosphere, and / or (ii) Performing HIP treatment after sintering, Processes including, This is a method for producing an alumina sintered body, which includes [the specified element].

[0012] Aspect 7 of the present invention is The step of sintering the molded body is a manufacturing method according to embodiment 6, wherein (i) the sintering is performed in a vacuum atmosphere.

[0013] Aspect 8 of the present invention is The step of sintering the molded body is a manufacturing method according to embodiment 6 or 7, which includes (ii) performing a HIP treatment after sintering. [Effects of the Invention]

[0014] According to embodiments of the present invention, it is possible to provide an alumina sintered body having high light transmittance and a method for producing the same. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a cross-sectional SEM image of Example 3. [Figure 2] Figure 2 shows a cross-sectional SEM image of Comparative Example 1. [Modes for carrying out the invention]

[0016] The inventors investigated from various angles to provide an alumina sintered body with high light transmittance. As a result, they found that an alumina sintered body with a porosity of 1.20% or less has high light transmittance. Furthermore, in the volume-based cumulative particle size distribution, the particle size D from the finest particle side at the 50% cumulative level... 50,p,v In addition to using alumina powder with a specific value or lower, we found that the light transmittance of the alumina sintered body can be improved by (i) performing the sintering in a vacuum atmosphere and / or (ii) performing HIP treatment after sintering when molding and then sintering the alumina composition containing the alumina powder. The details of each requirement defined in the embodiments of the present invention are shown below.

[0017] 1. Alumina sintered body The alumina sintered body according to an embodiment of the present invention can take any form, for example, square plate shape, disk shape, rod shape, spherical shape, etc. The alumina sintered body according to an embodiment of the present invention is applied to various products such as optical members, semiconductor manufacturing apparatus members, electrostatic chucks, support wafers, bioceramics such as artificial teeth, tableware, jewelry, bearings, media for dispersion and pulverization, etc. Hereinafter, the alumina sintered body will be described in detail.

[0018] (Porosity of alumina sintered body) The alumina sintered body according to an embodiment of the present invention has a porosity of 1.20% or less. Thereby, light scattering can be sufficiently suppressed and the translucency can be improved. The porosity is preferably 0.90% or less, more preferably 0.50% or less, still more preferably 0.20% or less, and even more preferably 0.10% or less. The porosity can be measured by the method of the examples described later.

[0019] (Crystal grain size of alumina sintered body) From the viewpoint of further improving the translucency, the alumina sintered body according to an embodiment of the present invention has a crystal grain size D at 10% cumulative from the fine particle side in the number-based cumulative distribution of crystal grain size. 10,gr,n is preferably 1.0 μm or less, more preferably 0.6 μm or less, still more preferably 0.4 μm or less, and even more preferably 0.3 μm or less.

[0020] From the viewpoint of further improving the translucency, the alumina sintered body according to an embodiment of the present invention has a crystal grain size D at 50% cumulative from the fine particle side in the number-based cumulative distribution of crystal grain size. 50,gr,n is preferably 1.5 μm or less, more preferably 1.2 μm or less, still more preferably 1.0 μm or less, and even more preferably 0.5 μm or less.

[0021] From the viewpoint of further improving the translucency, the alumina sintered body according to an embodiment of the present invention has a crystal grain size D at 90% cumulative from the fine particle side in the number-based cumulative distribution of crystal grain size. 90,gr,nHowever, it is preferably 2.0 μm or less, more preferably 1.5 μm or less, even more preferably 0.8 μm or less, and even more preferably 0.5 μm or less.

[0022] In the embodiment of the present invention, the alumina sintered body, from the viewpoint of further improving light transmittance, has a crystal grain size D from the fine grain side to 100% cumulative distribution of crystal grain size based on the number of grains. 100,gr,n However, it is preferably 3.5 μm or less, more preferably 2.0 μm or less, even more preferably 1.5 μm or less, and even more preferably 1.2 μm or less.

[0023] In an embodiment of the present invention, the crystal grain size D of the alumina sintered body 10,gr,n , D 50,gr,n , D 90,gr,n and D 100,gr,n , can be measured by the method described in the later examples.

[0024] (Sintering density of alumina sintered body) In an embodiment of the present invention, the alumina sintered body has a sintering density of 3,800 g / cm³, with the viewpoint of further improving light transmittance. 3 Preferably, it should be 3.850 g / cm³ or more. 3 It is more preferable that the amount be greater than or equal to 3,900 g / cm³. 3 It is even more preferable that the amount be greater than or equal to 3,950 g / cm³. 3 The above is even more preferable. In embodiments of the present invention, the sintering density of the alumina sintered body can be measured by the Archimedes method.

[0025] 2. Method for manufacturing alumina sintered body The method for manufacturing an alumina sintered body according to an embodiment of the present invention is as follows: (A) A step of molding an alumina composition to obtain a molded body, wherein the alumina composition has a particle size D that is 50% of the total particle size from the fine side in the volume-based cumulative particle size distribution. 50,p,v A process that includes alumina powder of 0.40 μm or less, (B) A step of sintering the molded body, (i) Performing the sintering under a vacuum atmosphere, and / or (ii) Performing HIP treatment after sintering, A process that includes, and The above manufacturing method can improve the light transmittance of the alumina sintered body. Each step is described in detail below.

[0026] [(A) Step of molding an alumina composition to obtain a molded body] In this process, a predetermined alumina composition is molded to obtain a molded body. The alumina composition according to the embodiment of the present invention contains alumina powder. The alumina composition according to the embodiment of the present invention may consist of alumina powder alone, or it may contain other components other than alumina powder. The alumina composition may be in any form, such as powder, granules, slurry, gel, feedstock, or pellets, but it is preferable that the alumina composition be in powder or granule form. The requirements for the alumina powder in the alumina composition are described in detail below.

[0027] (D of alumina powder) 50,p,v ) In process (A), the alumina powder is divided into particles with a particle size of D, which represents the 50% cumulative particle size from the finest particle side in the volume-based cumulative particle size distribution. 50,p,v The particle size D of the alumina powder is 0.40 μm or less. 50,p,v If the grain size exceeds 0.40 μm, the crystal grain size of the alumina sintered body increases, and its light transmittance decreases. Alumina powder particle size D 50,p,v The particle size D of the alumina powder is preferably 0.35 μm or less, more preferably 0.30 μm or less, even more preferably 0.25 μm or less, preferably 0.08 μm or more, more preferably 0.10 μm or more, and even more preferably 0.12 μm or more. 50,p,v By setting the range to this extent, it is possible to manufacture an alumina sintered body with particularly excellent light transmission.

[0028] Alumina powder particle size D 50,p,v This is measured by laser diffraction / scattering. Alumina powder particle size D 50,p,vAn example of measurement conditions is described below. Alumina powder is added to a 0.2% sodium hexametaphosphate aqueous solution and dispersed using an ultrasonic homogenizer for 7 minutes. The dispersion is placed in a measurement cell and degassed. Then, using a Microtrac particle size distribution analyzer MT-3300 manufactured by Microtrac-Bell Co., Ltd., the volume-based cumulative particle size distribution of the alumina powder is determined by measuring with a measurement time of 10 s, 2 measurements, particle refractive index of 1.77, and solvent refractive index of 1.333, and the particle size D is determined from the result. 50,p,v We seek.

[0029] (BET specific surface area of ​​alumina powder) In process (A), the BET specific surface area of ​​the alumina powder is 4 m². 2 / g or more 20m 2 It is preferable that the BET specific surface area of ​​the alumina powder be less than or equal to 7 m². 2 / g or more 20m 2 / g or less, more preferably 8m 2 / g or more 17m 2 / g or less, and more preferably 9m 2 / g or more 13m 2 It is less than / g. By setting the BET specific surface area of ​​the alumina powder within this range, it is possible to produce an alumina sintered body with particularly excellent light transmission.

[0030] The BET specific surface area of ​​the alumina powder according to the embodiment of the present invention is determined by the nitrogen adsorption single-point method in accordance with the method specified in JIS Z 8830:2013 "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption". Specifically, as an example of the measurement method, 0.1 g of alumina powder is placed in a cell using a fully automatic specific surface area measuring device Macsorb manufactured by Mountec Co., Ltd., pre-treatment is performed at 200°C for 20 minutes, and then measurement is performed by nitrogen adsorption.

[0031] (Light bulk density of alumina powder) In process (A), the bulk density of the lightly packaged alumina powder is 0.6 g / cm³. 3 More than 1.5g / cm 3 The following is preferable: The bulk density of the alumina powder in the light packaging is more preferably 0.7 g / cm³.3 More than 1.4g / cm 3 More preferably, 0.8 g / cm³ 3 More than 1.3g / cm 3 Even more preferably, 0.9 g / cm³ 3 More than 1.2g / cm 3 The following is true: By setting the bulk density of the alumina powder within this range, it is possible to produce an alumina sintered body with particularly excellent light transmission.

[0032] The bulk density of the alumina powder according to the embodiment of the present invention is determined as the initial bulk density according to the method specified in JIS R 1628:1997 "Method for measuring the bulk density of fine ceramic powders".

[0033] (Bulk density of heavily loaded alumina powder) In process (A), the bulk density of the alumina powder is 0.9 g / cm³. 3 More than 1.7g / cm 3 The following is preferable: The bulk density of the alumina powder is more preferably 1.0 g / cm³. 3 More than 1.6g / cm 3 More preferably, 1.1 g / cm³ 3 More than 1.5g / cm 3 More preferably, 1.2 g / cm³ 3 More than 1.4g / cm 3 The following is true: By setting the bulk density of the heavy alumina powder within this range, it is possible to produce an alumina sintered body with particularly excellent light transmission.

[0034] The bulk density of the alumina powder according to the embodiment of the present invention is determined as the tapped bulk density according to the method specified in JIS R 1628:1997 "Method for measuring the bulk density of fine ceramic powders".

[0035] (Average roundness of alumina powder) In step (A), it is preferable that the average roundness of the multiple alumina particles constituting the alumina powder (hereinafter also simply referred to as "average roundness of the alumina powder") is 0.71 or higher. This makes it easier to improve the slipperiness of the alumina powder and further improves the light transmittance of the resulting alumina sintered body. The average roundness of the alumina powder is more preferably 0.75 or higher, and even more preferably 0.78 or higher.

[0036] The average roundness of the alumina powder according to the embodiment of the present invention can be determined by analyzing SEM images of the alumina powder. An example of the measurement method is described below. Using a scanning electron microscope (for example, a scanning electron microscope S-5500 manufactured by Hitachi High-Tech Corporation), SEM images of the alumina powder are taken at an acceleration voltage of 1 keV. When acquiring SEM images of the alumina powder, the magnification is adjusted so that 100 to 300 primary alumina particles constituting the alumina powder are visible per image. Fifty alumina particles are randomly selected from the obtained SEM images, and the area of ​​the alumina particles on the SEM image is denoted as S, and the major axis diameter of the ellipse when the alumina particles are approximated as an ellipse is denoted as L. The roundness of each particle is calculated using the following formula (1), and the arithmetic mean is taken as the average roundness of the alumina powder. Roundness of one alumina particle = 4 × S / (π × L) 2 )···(1)

[0037] (Impurities in alumina powder) In process (A), the alumina powder may contain unavoidable impurities in addition to alumina (Al2O3). Unavoidable impurities include elements introduced depending on the raw materials, materials, manufacturing equipment, etc. The alumina powder preferably contains 0.1% by mass or less of the total content of major impurities Si, Mg, Cu, Fe, Ca, and Na, more preferably 0.01% by mass or less, and even more preferably 0.001% by mass or less. This improves the density of the alumina sintered body and also improves its light transmittance. Furthermore, it can improve the mechanical strength, chemical stability, plasma resistance, and wear resistance of the alumina sintered body.

[0038] In embodiments of the present invention, the total content of Si, Mg, Cu, Fe, Ca, and Na in the alumina powder can be measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) or solid-state atomic emission spectroscopy. In embodiments of the present invention, the total content (mass%) of the major impurities Si, Mg, Cu, Fe, Ca, and Na may be calculated and subtracted from 100 to obtain the "purity of the alumina powder." The formula for calculating the purity of the alumina powder is as shown in formula (2) below. Alumina powder purity (%) = 100 - Total content of major impurities (mass%) ... (2)

[0039] (α-alumina content in alumina powder) In step (A), the alumina powder preferably contains α-alumina from the viewpoint of obtaining excellent sinterability and light transmittance. The alumina powder may be a mixture containing α-alumina and one or more selected from the group consisting of γ-alumina, η-alumina, θ-alumina, δ-alumina, boehmite, and pseudo-boehmite. The α-alumina content in the alumina powder can be determined from the α-conversion rate of alumina obtained from the powder X-ray diffraction profile, and the α-conversion rate is preferably 90% or more, more preferably 95% or more, and even more preferably 99% or more. The α-conversion rate is the diffraction peak intensity (I) derived from the alumina α-phase (012) plane that appears at 2θ = 25.6° in the powder X-ray diffraction profile. 25.6 ) and the diffraction peak intensity of the alumina γ phase, η phase, χ phase, κ phase, θ phase, or δ phase that appears around 2θ=46° (I 46) can be calculated using the following formula (3). αization rate=I 25.6 / ( I 25.6 +I 46 ) × 100 (%) ... (3)

[0040] The alumina powder described above may be prepared by known methods, or commercially available products (for example, NXA-100, NXA-150, etc., manufactured by Sumitomo Chemical Co., Ltd.) may be used.

[0041] (Ingredients other than alumina powder) When molding an alumina composition, components other than alumina powder may also be molded together, as long as they do not deviate from the purpose of this disclosure. That is, an alumina composition containing alumina powder may be molded to obtain a molded body. Other components include inorganic compounds other than alumina, binders, sintering aids, coloring additives, resins, aqueous solvents, non-aqueous solvents, dispersants, plasticizers, surfactants, and surface treatment agents. The alumina powder content in the alumina composition is preferably 40.0% by mass or more. More preferably, the alumina powder content is 60.0% by mass or more, even more preferably 80.0% by mass or more, even more preferably 90.0% by mass or more, and particularly preferably 98.0% by mass or more. The alumina content may be 100% by mass (i.e., the alumina composition consists of alumina powder). By setting the alumina powder content within this range, an alumina sintered body with particularly excellent light transmittance can be produced. The alumina powder content can be calculated from the Al content obtained by elemental analysis (quantitative analysis) of the alumina composition by ICP-AES. If the alumina composition contains a binder, the binder content in the alumina composition is preferably 0.1 to 5.0% by mass. The binder content in the alumina composition is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, particularly preferably 0.8% by mass or more, preferably 5.0% by mass or less, more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less, and particularly preferably 2.5% by mass or less.

[0042] (Forming of alumina composition) In step (A), the method for forming the alumina composition is not particularly limited, and known methods such as mechanical pressing, cold isostatic pressing (CIP), hot pressing, casting, pressure casting, sheet forming, gel casting, extrusion, injection molding, additive manufacturing, rolling granulation, fluid bed granulation, and spray drying can be used.

[0043] [(B) Process of sintering the molded body] The sintering method for the molded body obtained in process (A) must satisfy at least one of the following conditions (i) and (ii): (i) Sintering is carried out under a vacuum atmosphere. (ii) After sintering, HIP treatment is performed. Except that at least one of the above conditions (i) and (ii) is met, known methods can be employed, such as heating and sintering in an electric furnace or combustion furnace, hot pressing, discharge plasma sintering, microwave sintering, laser sintering, etc. These known sintering methods may be performed in addition to (i) or (ii), or (i) or (ii) itself may be performed using these known sintering methods. In (ii), sintering may be performed in an atmosphere other than a vacuum atmosphere, such as an atmosphere of air, oxygen, hydrogen, argon, nitrogen, or a mixture thereof, and sintering methods in such atmospheres can be used. (i) and (ii) will be described in detail below.

[0044] (i) Sintering in a vacuum atmosphere The light transmittance of the alumina sintered body can be improved by performing the sintering in process (B) under a vacuum atmosphere. The vacuum level is 10 2 Pa~10 -5It is preferable to use Pa. This makes it possible to produce an alumina sintered body with particularly excellent light transmittance. The sintering temperature in a vacuum atmosphere is not particularly limited, but for example, 1050 to 1600°C is preferred from the viewpoint of obtaining a dense sintered body while maintaining a small grain size. The holding time at the above sintering temperature is also not particularly limited, but for example, 0.5 to 5 hours is preferred from the viewpoint of densifying the sintered body. The heating rate to the above sintering temperature is also not particularly limited, but for example, 50 to 600°C / hour is preferred from the viewpoint of promoting densification of the sintered body. Furthermore, a step of temporarily holding at a constant temperature during the heating process may be included. The heater material of the heat treatment furnace for sintering in a vacuum atmosphere is not particularly limited, but for example, graphite or tungsten is preferred from the viewpoint of reducing contamination of the sintered body.

[0045] (ii) HIP treatment after sintering The light transmittance of the alumina sintered body can also be improved by performing HIP treatment after sintering. The HIP treatment method is not particularly limited, and known methods such as the capsule method and the capsule-free method can be used. Furthermore, multiple HIP treatments may be performed using the same conditions or a combination of different methods. The pressure during HIP treatment is not particularly limited, but is preferably 50 to 300 MPa. The atmosphere during HIP treatment is also not particularly limited, but is preferably an argon atmosphere, nitrogen atmosphere, oxygen atmosphere, or a mixture thereof. The holding temperature during HIP treatment is also not particularly limited, but is preferably 1000 to 1500°C. The holding time at the above holding temperature is also not particularly limited, but is preferably 1 to 10 hours. The heating rate to the above holding temperature is also not particularly limited, but is preferably 50 to 600°C / hour. By using these ranges, densification of the sintered body can be promoted and the light transmittance can be improved. The heater material of the HIP treatment furnace is not particularly limited, but may be graphite or molybdenum.

[0046] The manufacturing method according to the embodiment of the present invention may include other steps, as long as they do not depart from the purpose of this disclosure. For example, a degreasing step may be performed after step (A) and before sintering in step (B) as needed. The degreasing method is not particularly limited, and known methods such as heating degreasing in an air atmosphere, oxygen atmosphere, nitrogen atmosphere, argon atmosphere, or vacuum atmosphere can be used. As an example, the molded body may be degreased by firing it in an air atmosphere at a temperature of 500 to 1200°C for 1 hour or more, preferably at a temperature of 600 to 800°C for 2 hours or more. The average heating rate from room temperature to the firing temperature may be, for example, 100°C / hr. [Examples]

[0047] The embodiments of the present invention will be described in more detail below with reference to examples. The embodiments of the present invention are not limited by the following examples, and can be implemented with appropriate modifications within the scope that is consistent with the spirit described above and below, and all such modifications are included within the technical scope of the embodiments of the present invention.

[0048] (Preparation of alumina slurry) Alumina powder (NXA-100, D, manufactured by Sumitomo Chemical Co., Ltd.) 50,p,v :0.21μm, BET specific surface area 10.8m 2 / g, Average roundness: 0.80, Purity: 99.99%, Alpha-gelatinization rate: 100%, Light packaging bulk density: 1.0g / cm³ 3 Heavy packaging bulk density: 1.3 g / cm³ 3 I prepared ). The above-mentioned alumina powder (1700g), pure water (1054g), and dispersant (7.95g, SN Dispersant-5468, manufactured by Sunopco Co., Ltd.), along with alumina beads (3540g, φ2-SSA999W, manufactured by Nikkatoh Co., Ltd.), were filled into a pot (volume 3L) with an alumina-lined interior and uniformly dispersed under conditions of 65rpm for 6 hours to prepare an alumina slurry.

[0049] (Preparation of alumina granules) The obtained alumina slurry (705g), pure water (69.6g), binder (17.4g, SA-261P manufactured by Japan Coating Resin Co., Ltd.), and plasticizer (4.35g, PEG-400 manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed and stirred for 10 minutes. The resulting slurry was spray-dried using a spray dryer (Li-8 type manufactured by Okawara Chemical Machinery Co., Ltd.) under the conditions of a flow rate of 79g / min, atomizer rotation speed of 18000rpm, inlet temperature of 180℃, outlet temperature of 90℃, and hot air differential pressure of 1.1kPa to produce alumina granules.

[0050] (Preparation of alumina sintered bodies) The obtained alumina granules (alumina composition) were molded to obtain a molded body. The molded body was then degreased by holding it at 600°C for 2 hours in an atmospheric environment (calcination). The heating rate to 600°C was 100°C / hour. After degreasing, the surrounding area was reduced to create a vacuum atmosphere (10 -3 The molded body was sintered by holding it at 1180°C for 2 hours at a pressure of Pa. The heating rate to 1180°C was 300°C / hour. After sintering, HIP treatment was performed by holding it at 1175°C for 1 hour under conditions of argon atmosphere, 150 MPa, and argon. The heating rate to 1175°C was 600°C / hour, and a molybdenum heater was used as the heater. This obtained the alumina sintered body of Example 1.

[0051] From Example 1, the conditions of the sintering process (atmosphere during sintering, holding temperature during sintering, heating rate to the holding temperature during sintering, and presence or absence of the above-mentioned HIP treatment after sintering) were changed to obtain the alumina sintered bodies of Examples 2 to 11 and Comparative Example 1, as shown in Table 1.

[0052] [Table 1]

[0053] The alumina sintered bodies of Examples 1 to 11 and Comparative Example 1 were evaluated as follows.

[0054] [Cross-sectional SEM observation] The obtained alumina sintered body was cut, and the cut surface was polished with a cross-section polisher. The obtained cross-section was observed using a Hitachi High-Tech Corporation FE-SEM (S-5500) at an acceleration voltage of 1 keV and a magnification of 10,000x. The scale was set to 10 nm / pix. As an example of an alumina sintered body, Figure 1 shows a cross-sectional SEM image of the alumina sintered body of Example 3, and Figure 2 shows a cross-sectional SEM image of the alumina sintered body of Comparative Example 1. As shown in Figure 1, the alumina sintered body of Example 3 was very dense and showed almost no pores. On the other hand, as shown in Figure 2, pores (black areas in the SEM image) were scattered in the alumina sintered body of Comparative Example 1.

[0055] [Porosity] The porosity (void ratio) of the alumina sintered body was calculated by image analysis of the cross-sectional SEM images obtained above. The quantitative analysis software TRI / 3D-BON (manufactured by RATOC Systems Engineering) was used for image analysis. Specifically, the above software was opened, noise was removed from each cross-sectional SEM image using a median filter (3x3), and the image was inverted once to make the pores appear as bright contrast. Multiple 2-tone conversions were performed on each image using Auto-LW to identify the pores in each image. Unnecessary parts were identified and deleted. The area of ​​the pores measured by these processes was divided by the total area of ​​the analysis region, and this value was calculated as the porosity using the 2D label density.

[0056] [Cumulative distribution of crystal grain size based on the number of crystals] Image analysis was performed on the cross-sectional SEM images obtained above to determine the number-based cumulative distribution of grain size in the alumina sintered body. Cellpose image analysis software was used, adjusting the cross-sectional SEM images to 1280 × 890 pixels, with a resolution of 0.01 μm / pix and a target diameter of 50 pixels. The analysis model was set to Cyto. Based on the assigned major axis (grain size), the cumulative grain size (number-based D) representing 10% of the number-based cumulative distribution of grain size was determined from the finest grain side. 10,gr,n ), 50% of the crystal grain size (based on the number of particles) 50,gr,n ), 90% of the crystal grain size (based on the number of particles) 90,gr,n ) and 100% grain size (number basis D 100,gr,n) was sought.

[0057] [Sintering density] The sintering density of the obtained alumina sintered body was measured in water at 22°C using the Archimedes method.

[0058] [Total light transmittance] The total light transmittance of the obtained alumina sintered body was measured using a haze meter NDH-8000 manufactured by Nippon Denshoku Industries Co., Ltd. The apparatus settings conformed to the measurement method for total light transmittance (TT) in JIS K7361-1:1997. Measurements were taken after the apparatus was warmed up for 30 minutes after startup. The thickness of the alumina sintered body was set to 0.3 mm, and to prevent it from falling into the apparatus, the alumina sintered body was placed on a glass petri dish. For the alumina sintered body on the glass petri dish, the total light transmittance including the glass petri dish was evaluated. The total light transmittance of Comparative Example 1 was set to 1 as the baseline, and the ratio of the total light transmittance of each example to this baseline (total light transmittance ratio) was calculated.

[0059] The results are shown in Table 2.

[0060] [Table 2]

[0061] From the results in Table 2, it was found that the alumina sintered body according to the embodiment that satisfies the requirements specified in this embodiment has a porosity of 1.20% or less and exhibits a higher total light transmittance ratio compared to the alumina sintered body of the comparative example. From this, it was confirmed that the alumina sintered body according to this embodiment has excellent light transmittance.

[0062] The results in Table 2 show that the alumina sintered body produced using the manufacturing method according to this embodiment exhibits a higher total light transmittance ratio compared to the alumina sintered body of the comparative example. This confirms that the manufacturing method according to this embodiment can provide an alumina sintered body with high light transmittance.

Claims

1. Alumina sintered body with a porosity of 1.20% or less.

2. In the cumulative distribution of grain size based on the number of grains, the grain size D represents the 10% cumulative value from the finest grains. １０，ｇｒ，ｎ The alumina sintered body according to claim 1, wherein the particle size is 1.0 μm or less.

3. In the cumulative distribution of grain size based on the number of grains, grain size D represents the 50% cumulative value from the finest grains. ５０，ｇｒ，ｎ The alumina sintered body according to claim 1 or 2, wherein the diameter is 1.5 μm or less.

4. In the cumulative distribution of grain size based on the number of grains, grain size D represents the 90% cumulative value from the finest grains. ９０，ｇｒ，ｎ An alumina sintered body according to any one of claims 1 to 3, wherein the diameter is 2.0 μm or less.

5. The crystal grain size D in the cumulative distribution of crystal grain size based on the number of grains, starting from the finest grains and reaching 100% cumulative size. １００，ｇｒ，ｎ An alumina sintered body according to any one of claims 1 to 4, wherein the diameter is 3.5 μm or less.

6. A process to obtain a molded body by molding an alumina composition, wherein the alumina composition has a particle size D that is 50% of the cumulative particle size distribution from the fine side. ５０，ｐ，ｖ The process includes a step containing alumina powder of 0.40 μm or less, The process of sintering the molded body, (i) Performing the sintering in a vacuum atmosphere, and / or (ii) Performing HIP treatment after sintering, Processes including, A method for producing an alumina sintered body, including the method described above.

7. The manufacturing method according to claim 6, wherein the step of sintering the molded body includes (i) carrying out the sintering in a vacuum atmosphere.

8. The manufacturing method according to claim 6 or 7, wherein the step of sintering the molded body includes (ii) performing a HIP treatment after sintering.

Images