Alumina composition

Abstract

To provide an alumina composition from which an alumina sintered compact having high translucency can be produced even by normal pressure sintering in an air atmosphere.SOLUTION: An alumina composition comprising alumina particles and particles of oxides other than alumina, wherein the particles of oxides comprise oxides containing cations having an ionic radius in six coordination of 0.41 Å or more and 1.2 Å or less, the particle size D50 at a cumulative percentage of 50% from the fine particle side in the volume-based cumulative particle size is 5.0 μm or less, and the D50 of the alumina particles is 0.40 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an alumina composition, and in particular to an alumina composition suitable for artificial teeth. [Background technology]

[0002] All-ceramic artificial teeth are excellent in biosafety and aesthetics. Translucent zirconia is known as a ceramic material suitable for artificial teeth (Patent Document 1). Translucent zirconia has improved translucency and chemical stability by adding yttria to zirconia powder and sintering it. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-150064 Summary of the Invention [Problem to be solved by the invention]

[0004] Translucent zirconia has lower translucency than natural teeth, and there is room for improvement in terms of aesthetics. Translucent alumina is being considered as a translucent ceramic to replace translucent zirconia. Because translucent alumina has high translucency, it is expected to be possible to manufacture artificial teeth that are more natural and have excellent aesthetics.

[0005] Alumina compositions such as alumina powder and alumina granules are used as raw materials for translucent alumina. The alumina raw materials are compression molded, calcined, and sintered to obtain translucent alumina. The translucency of alumina is improved by sintering in a vacuum / hydrogen atmosphere or by hot isostatic pressing (HIP). However, since sintering of artificial teeth is performed by dental technicians, who are the users, normal pressure sintering is usually performed in an air atmosphere using a general-purpose firing furnace, which may result in insufficient improvement in the translucency of translucent alumina.

[0006] Therefore, an object of one embodiment of the present invention is to provide an alumina composition that can produce an alumina sintered body with high translucency even when sintered under atmospheric pressure in an air atmosphere. [Means for solving the problem]

[0007] Aspect 1 of the present invention is The alumina particles and oxide particles made of oxides other than alumina are included, The oxide particles are It is made of an oxide containing a cation whose ionic radius in 6-coordination is 0.41 Å or more and 1.2 Å or less, and The particle size D50 of the cumulative 50% from the fine particle side of the volume-based cumulative particle size distribution is 5.0 μm or less, The alumina composition has a D50 of 0.40 μm or less.

[0008] Aspect 2 of the present invention is 2. The alumina composition of embodiment 1, wherein the cations are cations of one or more elements selected from the group consisting of Ti, Sn, Zr, Y, and Sr.

[0009] Aspect 3 of the present invention is In the alumina composition according to aspect 1 or 2, the content of the oxide particles is 50 ppm by mass or more and 5000 ppm by mass or less in terms of elements constituting the cations.

[0010] A fourth aspect of the present invention is Aspect 4. The alumina composition according to any one of Aspects 1 to 3, wherein the oxide particles have a D50 of 0.5 μm or less.

[0011] A fifth aspect of the present invention is The alumina composition according to any one of Aspects 1 to 4, wherein the alumina content is 90.0 mass % or more.

[0012] A sixth aspect of the present invention is The BET specific surface area of ​​the alumina particles is 7m 2 / g or more 20m 2 / g or less.

[0013] A seventh aspect of the present invention is Aspect 7. The alumina composition according to any one of Aspects 1 to 6, wherein the alumina particles and the oxide particles are present as primary particles or secondary particles.

[0014] Aspect 8 of the present invention is The alumina composition according to any one of Aspects 1 to 7 is a granule formed by binding the alumina particles and the oxide particles with a binder. [Effects of the Invention]

[0015] According to the alumina composition according to one embodiment of the present invention, a highly translucent alumina sintered body can be produced even by atmospheric sintering in an air atmosphere. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is an electron backscatter diffraction (EBSD) mapping of the cross section of the alumina sintered body obtained in Example 5 (magnification: 500 times). [Figure 2] FIG. 2 is an electron backscatter diffraction (EBSD) mapping of the cross section of the alumina sintered body obtained in Example 8 (magnification: 500 times). [Figure 3] FIG. 3 shows a scanning transmission electron microscope (STEM) image and element mapping (Al, Sn) of the alumina sintered body obtained in Example 5 (magnification: 120,000 times). [Figure 4] FIG. 4 shows a scanning transmission electron microscope (STEM) image and element mapping (Al, Sn) of the alumina sintered body obtained in Example 5 (magnification: 1,000,000 times). DETAILED DESCRIPTION OF THE INVENTION

[0017] The inventors have conducted extensive research to obtain an alumina composition that can produce an alumina sintered body having high translucency even when sintered under atmospheric pressure in an air atmosphere. The inventors have found that in order to improve the translucency of an alumina sintered body, the grain size in the alumina sintered body should be reduced. It is believed that when a conventional alumina composition is sintered under atmospheric pressure in an air atmosphere, the grain size of the alumina sintered body becomes large, resulting in insufficient translucency.

[0018] As a result of investigations by the inventors, it was discovered for the first time that an alumina sintered body with sufficiently high translucency can be produced even by atmospheric sintering in an air atmosphere by using an alumina composition containing oxide particles and alumina particles, by using oxide particles made of an oxide containing cations with a predetermined ionic radius, and by controlling the particle size D50 of the oxide particles and alumina particles within an appropriate range, and this discovery led to the completion of the present invention.

[0019] An alumina composition according to one embodiment of the present invention will be described in detail below.

[0020] (1) Alumina composition The alumina composition according to the embodiment of the present invention includes alumina particles and oxide particles. In this specification, the term "oxide particles" refers to particles made of an oxide other than alumina. In other words, alumina particles are not included in the oxide particles. The alumina composition may optionally include binders, dispersants, plasticizers, color additives, and the like.

[0021] The alumina composition is preferably in a powder or granular form. In this specification, a powdered alumina composition may be referred to as "alumina powder," and a granular alumina composition may be referred to as "alumina granules." The translucent alumina sintered body can be produced using either alumina powder or alumina granules.

[0022] (Powdered alumina composition: alumina powder) In this specification, the term "powdered" refers to a state in which each oxide particle and alumina particle is not bonded to other particles (oxide particles or alumina particles). Specifically, a powdered alumina composition refers to a state in which the alumina particles and oxide particles exist as individual unit particles (primary particles) or as an aggregate of two or more primary particles (secondary particles). The primary particles and secondary particles may be mixed.

[0023] When present as secondary particles, each secondary particle may consist of only alumina particles, only oxide particles, or a mixture of alumina particles and oxide particles. However, the alumina powder as a whole must contain both alumina particles and oxide particles. Different types of secondary particles may be present. Secondary particles are simply aggregates of two or more primary particles, and these particles are not bonded to each other. Therefore, secondary particles can easily separate into primary particles. For example, if ultrasonic vibrations are applied to secondary particles in a dispersion medium, they can be separated into primary particles.

[0024] (Granular alumina composition: alumina granules) A granular alumina composition (alumina granules) is composed of one or more types of oxide particles (primary particles) and alumina particles (primary particles) bound together with a binder. That is, a granular alumina composition necessarily contains oxide particles, alumina particles, and a binder. Each granule may be composed of only alumina particles, only oxide particles, or alumina particles and oxide particles. However, the alumina granule as a whole must contain both alumina particles and oxide particles. Different types of granules may be mixed together. The granular alumina composition is basically composed of granules only, but may contain small amounts (for example, 10 mass % or less of the entire alumina composition) of one or more types of primary particles and secondary particles.

[0025] The content of the binder contained in the alumina granules is an amount sufficient to bind the primary particles together. From this perspective, the alumina granules preferably contain 0.1 to 5.0 mass% of the binder when the total mass of the alumina granules (including the binder) is taken as 100 mass%. The content of the binder contained in the alumina granules is preferably 0.1 mass% or more, more preferably 0.3 mass% or more, even more preferably 0.5 mass% or more, particularly preferably 0.8 mass% or more, and is preferably 5.0 mass% or less, more preferably 4.0 mass% or less, even more preferably 3.0 mass% or less, and particularly preferably 2.5 mass% or less when the total mass of the alumina granules is taken as 100 mass%. The binder content can be determined from the weight loss measured by thermal analysis.

[0026] The BET specific surface area of ​​the alumina composition is, for example, 1 to 20 m 2 The BET specific surface area of ​​the alumina composition is determined by the single-point nitrogen adsorption 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."

[0027] (2) Oxide particles Next, the oxide particles contained in the alumina composition will be described in detail. As described above, the term "oxide particles" in this specification refers to particles made of an oxide other than alumina.

[0028] (ionic radius of cation in 6-coordination) The oxide particles contained in the alumina composition are made of an oxide containing a cation having an ionic radius in hexacoordination of 0.41 Å or more and 1.2 Å or less. As a result of various investigations, the inventors have found that an alumina sintered body with high translucency cannot be produced when the ionic radius of the cation in hexacoordination is less than 0.41 Å or more than 1.2 Å. The reason why the ionic radius of the cation in hexacoordination affects the translucency of the alumina sintered body is presumed to be because alumina, which is the matrix of the alumina sintered body, is hexacoordination, and some of the cations in the oxide particles exist by substituting for the alumina matrix.

[0029] The ionic radius of the cation in hexacoordination (hereinafter sometimes simply referred to as "cation ionic radius") is preferably 0.60 Å to 0.90 Å, more preferably 0.60 Å to 0.73 Å, even more preferably 0.68 Å to 0.72 Å, and particularly preferably 0.68 Å to 0.71 Å. By setting the ionic radius of the cation within this range, an alumina sintered body with particularly excellent translucency can be produced.

[0030] The type of cation contained in the oxide particles can be identified from cations other than Al originating in the alumina particles by elemental analysis of the alumina composition using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The ionic radius of each cation in hexacoordination can be found in R.D. Shannon, Acta Crystallogr., Sect. A 32, 751 (1976).

[0031] Preferred cations include cations of one or more elements selected from the group consisting of Ti, Sn, Zr, Y, and Sr. The ionic radii of these cations in hexacoordination are as follows:

[0032] [Table 1]

[0033] (D50 of oxide particles) The particle size D50 of the oxide particles at 50% cumulative size from the fine side of the volume-based cumulative particle size distribution (sometimes referred to as "volume-based D50" or simply "D50") is 5.0 μm or less. If the D50 of the oxide particles exceeds 5.0 μm, the grain size of the alumina sintered body becomes large, and the translucency decreases. The D50 of the oxide particles is preferably 4.0 μm or less, more preferably 3.5 μm or less, even more preferably 2.0 μm or less, even more preferably 1.0 μm or less, and particularly preferably 0.5 μm or less, and is preferably 0.05 μm or more, more preferably 0.10 μm or more, and even more preferably 0.15 μm or more. By setting the D50 of the oxide particles within this range, an alumina sintered body with particularly excellent translucency can be produced.

[0034] The D50 of oxide particles is measured by laser diffraction / scattering. When measuring the D50 of oxide particles after mixing alumina particles and oxide particles (i.e., in the state of an alumina composition), the oxide particles can be isolated from the mixture and then D50 measured. Isolation can be performed by known methods based on the difference in specific gravity between alumina particles and oxide particles or the difference in particle size between them. The fact that the isolated particles are oxide particles can be confirmed by elemental analysis such as ICP-AES or SEM-EDX. When the alumina composition is in the form of granules (alumina granules), the alumina granules are calcined at 600° C. to remove the binder, and then the oxide particles are isolated and D50 is measured.

[0035] An example of the conditions for measuring the D50 of oxide particles is described below. The oxide particles are added to a 0.2% aqueous solution of sodium hexametaphosphate 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, measurements are performed for 10 seconds, twice, with a particle refractive index of 1.77 and a solvent refractive index of 1.333. The particle size distribution of the oxide particles is determined, and the D50 is calculated from the results.

[0036] Another method for measuring the D50 of oxide particles is to observe an alumina composition using SEM or TEM. First, the oxide particles are identified in an SEM or TEM image. Identification methods include identifying oxide particles from image contrast due to the difference between the average atomic numbers of the elements constituting the alumina particles and the average atomic numbers of the elements constituting the oxide particles, or identifying oxide particles through elemental analysis such as EDX analysis. All oxide particles contained in the observation area are identified, and the circle-equivalent diameter of each oxide particle is determined using image processing software. From these data, the particle diameter D50 of the 50% cumulative particle size from the fine side of the cumulative particle size distribution based on the number of oxide particles (sometimes referred to as "number-based D50") is calculated, and the volume-based D50 is calculated by converting it to a volume-based value. In SEM and TEM observations, the magnification is 1000 to 200,000 times, and the observation area has a short side of 1.5 μm or more and a long side of 2.0 μm or more.

[0037] (D90 of oxide particles) The particle size D90 of the oxide particles, which is the cumulative 90% particle size from the fine side of the volume-based cumulative particle size distribution, is preferably 20.0 μm or less, more preferably 10.0 μm or less, even more preferably 3.0 μm or less, even more preferably 1.0 μm or less, and particularly preferably 0.5 μm or less, and is preferably 0.05 μm or more, more preferably 0.10 μm or more, and even more preferably 0.15 μm or more. The method for measuring D90 of oxide particles is the same as the method for measuring D50, in which the particle size distribution of the oxide particles is determined and D90 is calculated from the results.

[0038] (Oxide particle content) The content of oxide particles contained in the alumina composition is preferably 50 ppm by mass or more and 5000 ppm by mass or less, calculated as the elements constituting the cations. The content of oxide particles is more preferably 100 ppm by mass or more and 3000 ppm by mass or less, even more preferably 200 ppm by mass or more and 2000 ppm by mass or less, and even more preferably 300 ppm by mass or more and 1000 ppm by mass or less. By setting the content of oxide particles within this range, an alumina sintered body with particularly excellent translucency can be produced.

[0039] Regarding the content of oxide particles, as described above, the alumina composition is subjected to elemental analysis (and quantitative analysis) by inductively coupled plasma atomic emission spectroscopy (ICP-AES) to identify the cations contained in the oxide particles, and then the content of the identified cations is determined.

[0040] (3) Alumina particles Next, the alumina particles contained in the alumina composition will be described in detail.

[0041] (D50 of alumina particles) The particle size D50 of the alumina particles, which is the cumulative 50% particle size from the fine particle side in the cumulative particle size distribution on a volume basis, is 0.40 μm or less. If the alumina particles have a D50 of more than 0.40 μm, the grain size of the alumina sintered body becomes large, and the translucency decreases. The D50 of the alumina particles is preferably 0.35 μm or less, more preferably 0.30 μm or less, even more preferably 0.25 μm or less, and is preferably 0.08 μm or more, more preferably 0.10 μm or more, even more preferably 0.12 μm or more. By setting the D50 of the alumina particles within this range, an alumina sintered body with particularly excellent translucency can be produced.

[0042] The method for measuring D50 of alumina particles is the same as the method for measuring D50 of oxide particles.

[0043] (BET specific surface area of ​​alumina particles) The BET specific surface area of ​​the alumina particles is 7m 2 / g or more 20m2 The BET specific surface area of ​​the alumina particles is preferably 8 m / g or less. 2 / g or more 17m 2 / g or less, more preferably 9m 2 / g or more 13m 2 By setting the BET specific surface area of ​​the alumina particles within this range, an alumina sintered body with particularly excellent translucency can be produced.

[0044] The specific surface area (BET specific surface area) of alumina particles is determined by the single-point nitrogen adsorption method in accordance with JIS Z 8830:2013, "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption." When measuring the BET specific surface area of ​​alumina particles after mixing alumina particles with oxide particles (i.e., in the state of an alumina composition), the alumina particles can be isolated from the mixture and the BET specific surface area measured. The method for isolating the alumina particles is the same as the method described above.

[0045] (Alumina content) The alumina content in the alumina composition is preferably 90.0% by mass or more. The alumina content is more preferably 95.0% by mass or more, even more preferably 96.0% by mass or more, even more preferably 97.0% by mass or more, particularly preferably 98.0% by mass or more, and preferably less than 100% by mass. By setting the alumina content within this range, an alumina sintered body with particularly excellent translucency can be produced. The alumina content can be calculated from the Al content determined by elemental analysis (quantitative analysis) of the alumina composition by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0046] (4) Method for producing alumina composition Although the method for producing the alumina composition of the embodiment is not particularly limited, it is preferable to adopt the following production method, since it allows for the reproducibility of the alumina composition having the above physical properties. Note that, based on the disclosure of the present application, a person skilled in the art may arrive at a different method for producing the alumina granule of the embodiment. Below, (i) a method for producing a powdered alumina composition (alumina powder) and (ii) a method for producing a granular alumina composition (alumina granules) will be described.

[0047] (i) Method for producing alumina powder The method for producing the alumina powder includes a step of preparing oxide particles and alumina particles, and a step of mixing the oxide particles and alumina particles.

[0048] (Step of Preparing Oxide Particles and Alumina Particles) To obtain the desired oxide particles, first, a cation having an ionic radius of 0.41 Å or more and 1.2 Å or less in hexacoordination (e.g., Ti 4+ , Sn 4+ , Zr 4+ , Y 3+ , Sr 2+ Oxide raw material particles made of an oxide containing an oxide such as ZnO, ZnS, ZnO ... If the D50 of the oxide raw material particles exceeds 5.0 μm, they are pulverized using a ball mill or the like to adjust the D50 to 5.0 μm or less. Note that oxide particles commercially available for addition to sintered ceramics have a D50 of more than 5.0 μm, so pulverization is essential. When the D50 of the oxide raw material particles is 5.0 μm or less, they may be used as oxide particles as they are, or may be further pulverized using a ball mill or the like.

[0049] To obtain the desired alumina particles, alumina raw particles are prepared by a known method. Commercially available alumina particles may be used as the alumina raw particles. Alumina particles having a D50 of 0.40 μm or less are prepared from the alumina raw particles. If the D50 of the alumina raw material particles exceeds 0.40 μm, the particles are pulverized using a ball mill or the like to adjust the D50 to 0.40 μm or less. When the D50 of the alumina raw material particles is 0.40 μm or less, they may be used as alumina particles as they are, or may be further pulverized in a ball mill or the like.

[0050] The D50 of the oxide raw material particles and the alumina raw material particles is measured in the same manner as the above-mentioned method for measuring the D50 of the oxide particles. In this way, oxide particles and alumina particles having desired properties are prepared.

[0051] (Step of mixing oxide particles and alumina particles) The resulting oxide particles and alumina particles are mixed in a desired ratio by any method, including, but not limited to, a mixer, a ball mill, a media agitation mill, and the like. In this way, alumina powder is obtained.

[0052] (ii) Manufacturing method of alumina granules The method for producing alumina granules includes the steps of preparing oxide particles and alumina particles, preparing a slurry containing the oxide particles and alumina particles, and granulating the alumina granules from the slurry.

[0053] (Step of Preparing Oxide Particles and Alumina Particles) As in the above-mentioned "(i) Method for producing a powdered alumina composition", oxide particles and alumina particles adjusted to a predetermined D50 are prepared.

[0054] (Step of preparing a slurry containing oxide particles and alumina particles) The resulting oxide particles, alumina particles, a binder, and a solvent are blended, and optionally, appropriate amounts of a dispersant, a plasticizer, and a coloring additive are blended, followed by mechanical stirring and mixing to prepare a slurry containing the oxide particles and the alumina particles. The stirring and mixing can be performed by a conventional method, such as a method of stirring and mixing using a stirring blade or a stirrer while irradiating ultrasonic waves from the outside, a method using various grinding media such as a ball mill or a Dyno Mill, or a method using various agitators such as an attritor or a pin mill.

[0055] As the binder, organic binders such as polyvinyl alcohol, polyvinyl acetal, various acrylic polymers, methyl cellulose, polyvinyl acetate, polyvinyl butyral, various waxes, and various polysaccharides can be used.

[0056] It is preferable to select a suitable solvent depending on the type of binder used and the granulation method of the alumina granules. When granulating the alumina granules using a spray dryer, an acrylic binder is suitable. In this case, water is mainly used as the solvent. Depending on the type of binder used and the granulation method, various organic solvents (acetone, ethanol, toluene, etc.) can be used.

[0057] A dispersant can be added as desired, and it is preferable to select a suitable dispersant depending on the type of solvent used. When the solvent is water, polycarboxylic acid ammonium salts (e.g., trade name: SN-D5468, manufactured by San Nopco) are typically used as dispersants. When an organic solvent is used, ethyl oleate, sorbitan monooleate, sorbitan trioleate, polycarboxylic acid-based dispersants, etc. are also used. Polyester-based dispersants (trade name: Texahol 3012, manufactured by San Nopco) are also suitable. However, various dispersants can be used without being limited to these.

[0058] Depending on the organic binder used, it may be possible to prepare a slurry with lower viscosity without using a dispersant, thereby increasing the concentration of alumina granules in the slurry. In such cases, it is not necessary to add a dispersant.

[0059] A plasticizer can be added as desired, and it is preferable to select a suitable plasticizer depending on the type of binder and organic solvent used together. Plasticizers used together with organic binders include ethylene glycol, diethylene glycol, polyethylene glycol, glycerin, polyglycerin, various esters, etc. When an organic solvent is used, dibutyl phthalate, diethylhexyl phthalate, etc. are particularly used, but the present invention is not limited to these.

[0060] Coloring additives can be added as desired. Examples of coloring additives include compounds of chromium, manganese, cobalt, nickel, iron, and the like, which can be added singly or in combination. Examples of compounds include oxides, nitrates, acetates, hydroxides, and chlorides. The coloring additives are preferably added so that the amount of coloring additive, calculated as a metal element, is 10 to 3,000 ppm when the alumina content in the alumina granules is taken as 100% by mass.

[0061] The resulting slurry may be defoamed under reduced pressure. Various antifoaming agents may also be used. Depending on the subsequent molding method, various pH adjusters and flocculants may be added to adjust the viscosity to 10 to 500 centipoise. For example, in granulation using a spray dryer, in order to produce spherical granules, the viscosity of the slurry is preferably adjusted to 30 to 300 centipoise by adjusting the pH with an aqueous hydrochloric acid solution, aqueous ammonia, or the like. Furthermore, the concentration of oxide particles and alumina particles in the slurry can be increased by static settling, centrifugation, vacuum concentration using a rotary evaporator, or the like.

[0062] Another method for preparing a slurry containing oxide particles and alumina particles is to separately prepare an oxide slurry containing oxide particles and an alumina slurry containing alumina particles, and then mix the oxide slurry and the alumina slurry. In the above-described method for preparing a slurry, instead of mixing both oxide particles and alumina particles, an oxide slurry or an alumina slurry can be prepared by mixing either oxide particles or alumina particles. By blending an oxide slurry and an alumina slurry in a predetermined ratio and stirring and mixing them, a slurry containing oxide particles and alumina particles is obtained.

[0063] (Process for granulating alumina granules from slurry) The resulting slurry is used to granulate alumina granules containing oxide particles and alumina particles. The method for granulating alumina granules from the slurry can be a known spray drying granulation method or oscillating extrusion granulation method. Specifically, the alumina granules can be granulated by spray drying the obtained slurry using a spray dryer or the like.

[0064] (Variation: Method of directly granulating alumina granules from oxide particles and alumina particles) In the above-described method for producing alumina granules, the alumina granules are granulated using a slurry containing oxide particles and alumina particles. However, the oxide particles and alumina particles may be granulated directly into alumina granules without forming a slurry. For example, oxide particles, alumina particles, a binder, and various additives as desired may be mixed and granulated in an agitation granulator to produce granulated powder, and this granulated powder may be repeatedly extruded and granulated in an oscillating granulator and dried to produce alumina granules.

[0065] These granulation methods for alumina granules can be appropriately selected depending on the amount of granules for ceramic molding, the properties of the desired ceramic molded body, etc. The oscillating extrusion granulation method is a method in which particles granulated to a particle size of, for example, about several mm are crushed on a mesh and the finer particles are allowed to fall, and the mesh is successively made finer to obtain particles of a predetermined particle size or less.

[0066] (4) Manufacturing method of alumina sintered body An example of a suitable method for producing an alumina sintered body using the alumina composition according to the embodiment will be described below. The alumina composition is subjected to uniaxial press molding, cold isostatic pressing (CIP) molding, etc. to produce a molded body. In the case of CIP molding, alumina granules are uniaxially press molded at a pressure of 20 to 40 MPa, preferably 25 to 35 MPa, and then isostatically pressed at 98 MPa or more, preferably 150 to 200 MPa, in a CIP molding machine, and the obtained molded body is processed into a predetermined shape.

[0067] Two examples of firing conditions for producing an alumina sintered body are given below. The firing conditions shown as examples are set assuming atmospheric sintering in an air atmosphere using a general-purpose firing furnace, but a translucent alumina sintered body can also be produced under other firing conditions.

[0068] (Condition 1) Sintering process The compact is fired in an air atmosphere at a temperature in the range of 1250 to 1550°C for 2 hours or more to obtain an alumina sintered body. The average heating rate from room temperature to the sintering temperature is, for example, 200°C / hr.

[0069] In the alumina composition according to the embodiment, by controlling the type of cation contained in the oxide particles and the D50 of the oxide particles and alumina particles, crystal grain growth is unlikely to occur even when sintered in an air atmosphere (under atmospheric pressure) at a temperature range of 1250 to 1550°C, for example, as in Condition 1. Therefore, the grain size of the obtained alumina sintered body is small, and an alumina sintered body with high translucency can be manufactured.

[0070] (Condition 2) ·Degreasing process The compact is degreased by firing in an air atmosphere at a temperature range of 500 to 1200°C for at least 1 hour, preferably at a temperature range of 600 to 800°C for at least 2 hours. The average heating rate from room temperature to the firing temperature is, for example, 100°C / hr. Sintering process After the debinding step, the alumina sintered body is obtained by firing for 2 hours or more at a temperature in the range of 1200 to 1700°C, preferably 1250 to 1450°C. The sintering temperature in the sintering step is set to be equal to or higher than the sintering temperature in the debinding step. The average temperature rise rate from the firing temperature in the debinding step to the sintering temperature in the sintering step is set to, for example, 200°C / hr.

[0071] Condition 2 is suitable not only for obtaining an alumina sintered body by low-temperature sintering, but also for obtaining a translucent alumina sintered body using alumina granules containing a sintering aid. By setting the temperature condition of the sintering step to 1350 to 1700°C, particularly 1400 to 1450°C, the translucency of the alumina sintered body can be further improved.

[0072] (5) Translucency evaluation of alumina sintered body By using the alumina composition according to the embodiment, an alumina sintered body having high translucency can be manufactured by atmospheric sintering in an air atmosphere. For example, an alumina sintered body having a total transmittance (TT) of 40% or more and a parallel transmittance (PT) of 0.3% or more can be manufactured. The transmittance measurement for evaluating the light transmittance conforms to the measurement method for total transmittance (TT) and parallel transmittance (PT) of JIS K7361-1:1997. The thickness of the alumina sintered body after surface polishing is set to 0.9 to 1.1 mm, and the total transmittance (TT) and parallel transmittance (PT) are measured. [Example]

[0073] An alumina composition (alumina granules) was prepared by the following procedure, and an alumina sintered body was manufactured using the composition. The types and physical properties of the oxide particles and alumina particles used to prepare the alumina granules are summarized in Table 2.

[0074] Example 1 (Preparation of alumina slurry) Alumina particles (1700 g, manufactured by Sumitomo Chemical Co., Ltd., NXA-100), pure water (1054 g), a dispersant (7.95 g, manufactured by San Nopco Co., Ltd., SND-5468), and alumina beads (3540 g, manufactured by Nikkato Co., Ltd., φ2-SSA999W) were charged into an alumina-lined pot (volume 3 L) and uniformly dispersed at 65 rpm for 6 hours to obtain an alumina slurry.

[0075] (Preparation of oxide slurry) Tin(IV) oxide particles (153 g, Fujifilm Wako Pure Chemical Industries, Ltd.) and pure water (2847 g) were stirred for 10 minutes using a rotating blade, and then circulated once in a wet disperser (Shinmaru Enterprises, Dynomill) at a peripheral speed of 8 m / s, a flow rate of 500 mL / min, and alumina beads φ0.5 mm (2690 g). The mixture was then circulated for 30 minutes to uniformly disperse the particles, yielding an oxide slurry (tin oxide slurry).

[0076] (Preparation of alumina granules) The resulting alumina slurry (700 g) was mixed with 63.4 g of purified water, 5.1 g of the resulting oxide slurry, 17.6 g of binder (50% solids by mass, Chuorika Kogyo SA-261P), and 4.3 g of plasticizer (4.3 g, Fujifilm Wako Pure Chemical Industries PEG-400) and stirred for 10 minutes. The resulting slurry was spray-dried using a spray dryer (Okawahara Chemical Engineering L-8i) at a flow rate of 79 g / min, an atomizer rotation speed of 18,000 rpm, an inlet temperature of 180 °C, an outlet temperature of 90 °C, and a hot air differential pressure of 1.1 kPa to obtain alumina granules.

[0077] (Production of sintered alumina) The obtained alumina granules (1 g) were filled into a φ20 mm cylindrical mold and subjected to uniaxial press molding at a pressure of 30 MPa for 30 seconds, followed by cold isostatic pressing (CIP) at a pressure of 200 MPa for 3 minutes five times to obtain an alumina compact. This alumina compact was heated to 1450°C at a heating rate of 200°C / hr in air and held at that temperature for 2 hours to obtain an alumina sintered body. The surface of this alumina sintered body was mirror-polished and then its translucency was evaluated.

[0078] Example 2 An alumina slurry was prepared in the same manner as in Example 1. Instead of the tin (IV) oxide particles used in Example 1, zirconia (IV) particles (manufactured by Kojundo Chemical Laboratory Co., Ltd.) were used to prepare an oxide slurry (zirconia slurry). Alumina granules and an alumina sintered body were produced in the same manner as in Example 1, except that the amount of oxide slurry (zirconia slurry) added was changed to 5.5 g.

[0079] Example 3 An alumina slurry was prepared in the same manner as in Example 1. Instead of the tin (IV) oxide particles used in Example 1, titanium (IV) oxide particles (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were used to prepare an oxide slurry (titanium oxide slurry). Alumina granules and an alumina sintered body were produced in the same manner as in Example 1, except that the amount of oxide slurry (titanium oxide slurry) added was changed to 6.7 g.

[0080] Example 4 An alumina slurry was prepared in the same manner as in Example 1. Instead of the tin (IV) oxide particles used in Example 1, yttrium oxide particles (manufactured by Shin-Etsu Chemical Co., Ltd.) were used to prepare an oxide slurry (yttrium oxide slurry). Alumina granules and an alumina sintered body were produced in the same manner as in Example 1.

[0081] Example 5 An alumina slurry was prepared in the same manner as in Example 1. Tin(IV) oxide particles (153 g, Fujifilm Wako Pure Chemical Industries, Ltd.) and pure water (2847 g) were stirred for 10 minutes using a rotating blade, and then circulated once in a wet disperser (Shinmaru Enterprises, Dynomill) at a peripheral speed of 8 m / s, a flow rate of 500 mL / min, and alumina beads φ0.5 mm (2690 g). The mixture was then circulated for 95 minutes to uniformly disperse the particles, yielding an oxide slurry (tin oxide slurry). Alumina granules and an alumina sintered body were produced in the same manner as in Example 1.

[0082] Example 6 An alumina slurry was prepared in the same manner as in Example 1. An oxide slurry (tin oxide slurry) was prepared in the same manner as in Example 5. Alumina granules and alumina sintered body were produced in the same manner as in Example 1, except that the amount of oxide slurry (tin oxide slurry) added was changed to 10.2 g.

[0083] Example 7 An alumina slurry was prepared in the same manner as in Example 1, except that the type of alumina particles was changed to NXA-150 (manufactured by Sumitomo Chemical Co., Ltd.). An oxide slurry (tin oxide slurry) was prepared in the same manner as in Example 5. Alumina granules and an alumina sintered body were produced in the same manner as in Example 1.

[0084] Example 8 An alumina slurry was prepared in the same manner as in Example 1. Tin(IV) oxide particles (153 g, Fujifilm Wako Pure Chemical Industries, Ltd.) and pure water (2847 g) were stirred for 10 minutes using a rotating blade, and then uniformly dispersed by one circulation in a wet disperser (Dynomill, Shinmaru Enterprises, Ltd.) at a peripheral speed of 8 m / s, a flow rate of 500 mL / min, and alumina beads φ0.5 mm (2690 g) to obtain an oxide slurry (tin oxide slurry). Alumina granules and an alumina sintered body were produced in the same manner as in Example 1.

[0085] Example 9 An alumina slurry was prepared in the same manner as in Example 1. Strontium carbonate particles (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were calcined in air at 1300°C for 2 hours to obtain strontium oxide particles. These strontium oxide particles (117 g) and pure water (2223 g) were stirred for 10 minutes using a rotating blade, then circulated once in a wet disperser (manufactured by Shinmaru Enterprises, Dynomill) at a peripheral speed of 8 m / s, a flow rate of 500 mL / min, and 0.5 mm diameter alumina beads (2690 g). The mixture was then circulated for 30 minutes to uniformly disperse the mixture, obtaining an oxide slurry (strontium oxide slurry). Alumina granules and an alumina sintered body were produced in the same manner as in Example 1, except that the amount of oxide slurry (strontium oxide slurry) added was changed to 4.9 g.

[0086] (Comparative Example 1) An alumina slurry was prepared in the same manner as in Example 1. Silica particles (150 g, EVONIK, AEROSIL 200) and pure water (4850 g) were stirred for 10 minutes using a rotating blade, and then circulated once in a wet disperser (Shinmaru Enterprise, Dynomill) at a peripheral speed of 8 m / s, a flow rate of 500 mL / min, and alumina beads φ0.5 mm (2690 g). The mixture was then circulated for 30 minutes to uniformly disperse the particles, yielding an oxide slurry (silica slurry). Alumina granules and an alumina sintered body were produced in the same manner as in Example 1, except that the amount of oxide slurry (silica slurry) added was changed to 14.9 g.

[0087] (Comparative Example 2) An alumina slurry was prepared in the same manner as in Example 1, except that the type of alumina particles was changed to AKP-20 (manufactured by Sumitomo Chemical Co., Ltd.). An oxide slurry (tin oxide slurry) was prepared in the same manner as in Example 5. Alumina granules and an alumina sintered body were produced in the same manner as in Example 1.

[0088] Table 2 shows the physical properties and various measured values ​​of the oxide particles and alumina particles used in the examples and comparative examples. The composition ratios of oxide, alumina, and binder contained in the obtained alumina composition (alumina granules) are shown in Table 3. The composition ratios were calculated from the compounding ratios of oxide particles, alumina particles, and binder during the production of the alumina granules, and do not include optional components such as moisture and plasticizers in the granules. Table 4 shows the measured values ​​and evaluation of the light transmittance of the obtained alumina sintered bodies. The measurement methods for the values ​​shown in Tables 2 and 4 were as follows.

[0089] (D50 and D90 of oxide particles, D50 of alumina particles) The D50 and D90 of the oxide particles and the D50 of the alumina particles were measured as follows: The measurements were carried out before the oxide particles and the alumina particles were mixed. The particles to be measured were added to a 0.2% aqueous solution of sodium hexametaphosphate and dispersed using an ultrasonic homogenizer for 7 minutes. The dispersion was placed in a measurement cell and degassed. The particle size distribution was determined using a Microtrac Bell Microtrac particle size distribution analyzer MT-3300, with a measurement time of 10 seconds, two measurements, a particle refractive index of 1.77, and a solvent refractive index of 1.333. The D50 and D90 were then calculated from the results.

[0090] (BET specific surface area of ​​alumina particles) The specific surface area (BET specific surface area) of the alumina particles was determined by the single-point nitrogen adsorption method, in accordance with JIS Z 8830:2013, "Measurement of the specific surface area of ​​powders (solids) by gas adsorption." Using a Mountech fully automatic specific surface area analyzer, Macsorb, 0.1 g of alumina particles was placed in a cell, pretreated at 200°C for 20 minutes, and then measured by nitrogen adsorption.

[0091] (Translucency of sintered alumina) The translucency (transmittance) of the alumina sintered body was measured using a haze meter NDH8000 manufactured by Nippon Denshoku Industries Co., Ltd. The instrument settings conformed to the measurement method for total transmittance (TT) and parallel transmittance (PT) of JIS K7361-1:1997. A small diameter attachment was attached, and the measurement diameter was set to the small diameter. Measurements were performed after warming up the instrument for 30 minutes after starting up. The thickness of the sintered body for translucency measurement was set to 0.9 to 1.1 mm after surface polishing, and the total transmittance (TT) and parallel transmittance (PT) were measured. In the evaluation of light transmittance, a total transmittance (TT) of 40% or more and a parallel transmittance (PT) of 0.3% or more was evaluated as pass (◯), and any other cases were evaluated as fail (×).

[0092] [Table 2]

[0093] [Table 3]

[0094] [Table 4]

[0095] (Observation of sintered structure of alumina sintered body) The alumina sintered bodies of Examples 5 and 8 were cut, and electron backscatter diffraction (EBSD) images were taken at 500x magnification to perform grain mapping (Figs. 1 and 2). Image analysis was used to determine the particle size distribution, and the cumulative 10% particle size (number-based D10), 30% particle size (number-based D30), 50% particle size (number-based D50), 70% particle size (number-based D70), and 90% particle size (number-based D90) were determined, starting from the finest particle side of the cumulative particle size distribution based on number. The analysis results are shown in Table 5.

[0096] [Table 5]

[0097] The alumina sintered body of Example 5 had a smaller grain size than the alumina sintered body of Example 8. Therefore, it was confirmed that the alumina sintered body of Example 5 had higher translucency than the alumina sintered body of Example 8 (Table 4).

[0098] (Mapping of sintered alumina) The alumina sintered body of Example 5 was cut and observed with a scanning transmission electron microscope (STEM) at magnifications of 120,000 and 1,000,000, and the presence of Al and Sn was mapped by energy dispersive X-ray spectroscopy (EDX) (Figs. 3 and 4). Sn mapping confirmed that oxide particles, SnO2, existed at the grain boundaries of the crystal grains.

Claims

1. The alumina particles and oxide particles made of oxides other than alumina are included, The oxide particles are The oxide comprises a cation having an ionic radius of 0.41 Å or more and 1.2 Å or less in hexacoordination; The particle size D50 of the cumulative 50% from the fine particle side of the volume-based cumulative particle size distribution is 5.0 μm or less, The alumina composition, wherein the alumina particles have a D50 of 0.40 μm or less.

2. 2. The alumina composition of claim 1, wherein the cations are cations of one or more elements selected from the group consisting of Ti, Sn, Zr, Y, and Sr.

3. 2. The alumina composition according to claim 1, wherein the content of the oxide particles is 50 ppm by mass or more and 5000 ppm by mass or less in terms of elements constituting the cations.

4. 2. The alumina composition of claim 1, wherein the oxide particles have a D50 of 0.5 μm or less.

5. 2. The alumina composition according to claim 1, wherein the alumina content is 90.0 mass% or more.

6. The BET specific surface area of ​​the alumina particles is 7 m ２ / g or more 20m ２ 2. The alumina composition of claim 1, wherein the alumina composition has a SiO2 content of 0.15 wt % or less.

7. 2. The alumina composition of claim 1, wherein the alumina particles and the oxide particles are present as primary particles or secondary particles.

8. 2. The alumina composition according to claim 1, which is a granule formed by binding the alumina particles and the oxide particles with a binder.

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