Alumina Powder

Abstract

To provide an alumina powder that can be sintered to a higher density by press molding suitable for mass production and atmospheric sintering in the atmosphere. [Solution] Alumina powder that satisfies the following formula (1). 0<100×I 002 / (I 012 +I 002 +I 111 )<4.0 ···(1) In equation (1), I 002 , I 012 and I 111 are the peak intensity of the θ-phase 002 plane, the peak intensity of the α-phase 012 plane, and the peak intensity of the γ-phase 111 plane in the XRD pattern of the alumina powder, respectively.

Description

[Technical Field]

[0001] The present disclosure relates to alumina powders. [Background technology]

[0002] High strength, densely sintered ceramics have long been required for various applications.

[0003] Patent Document 1 describes that α-alumina powder is widely used as a raw material for producing various sintered bodies. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4366939 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, the demand for alumina powder has been increasing for semiconductor applications such as electrostatic chucks. In response to this demand, alumina powder has been developed that can be sintered to a higher density by press molding and atmospheric sintering in air, which is suitable for mass production (for example, a density of 3.94 g / cm can be achieved by press molding followed by atmospheric sintering at 1450°C in air). 3 There was a demand for alumina powder that could achieve densities of 1000 or more.

[0006] The present disclosure has been made in view of the above circumstances, and one of its objectives is to provide an alumina powder that can be sintered to a higher density by press molding suitable for mass production and atmospheric sintering in the atmosphere. [Means for solving the problem]

[0007] Aspect 1 of the present invention is The alumina powder satisfies the following formula (1): 0<100×I 002 / (I 012 +I 002 +I 111 )<4.0 ···(1) In equation (1), I 002 , I 012 and I 111 are the peak intensity of the θ-phase 002 plane, the peak intensity of the α-phase 012 plane, and the peak intensity of the γ-phase 111 plane in the XRD pattern of the alumina powder, respectively.

[0008] Aspect 2 of the present invention is BET specific surface area is 8 to 50 m 2 / g of the alumina powder according to embodiment 1.

[0009] Aspect 3 of the present invention is The alumina powder according to aspect 1 or 2, wherein the particle size D50 of the cumulative 50% from the fine particle side of the volume-based cumulative particle size distribution is 0.35 μm or less.

[0010] A fourth aspect of the present invention is The alumina powder according to any one of aspects 1 to 3 satisfies the following formula (2): 100×(D90-D10) / D50≦15 (2) In formula (2), D90 is the particle size at 90% cumulative from the fine particle side of the volume-based cumulative particle size distribution, D10 is the particle size at 10% cumulative from the fine particle side of the volume-based cumulative particle size distribution, and D50 is the particle size at 50% cumulative from the fine particle side of the volume-based cumulative particle size distribution.

[0011] A fifth aspect of the present invention is The alumina powder according to any one of Aspects 1 to 4, wherein the total content of Si, Na, Mg, Cu, and Fe is less than 50 ppm.

[0012] A sixth aspect of the present invention is 100×I in Equation (1) 002 / (I 012 +I 002 +I 1116. The alumina powder according to any one of Aspects 1 to 5, wherein the value of (a) is less than 0.5. [Effects of the Invention]

[0013] According to an embodiment of the present invention, it is possible to provide an alumina powder that can be sintered to a higher density by press molding suitable for mass production and atmospheric sintering in the atmosphere. DETAILED DESCRIPTION OF THE INVENTION

[0014] The inventors of the present invention have conducted extensive research to develop an alumina powder that can be sintered to a higher density by press molding suitable for mass production and atmospheric sintering in air. As a result, by incorporating a trace amount of θ-alumina (specifically, satisfying formula (1)), a crystalline phase different from α-alumina, which has traditionally been considered advantageous as a raw material for high-purity sintered bodies, we have been able to develop an alumina powder that can be sintered to a higher density by press molding suitable for mass production and atmospheric sintering in air. While the detailed mechanism is unclear, it is believed that the presence of a trace amount of θ-alumina effectively fills the gaps between particles, suppressing the generation of voids, thereby achieving dense sintering. The technical scope of the embodiments of the present invention is not limited by this mechanism. The following provides details of each requirement stipulated by the embodiment of the present invention.

[0015] [Peak intensity ratio in XRD pattern] The alumina powder according to the embodiment of the present invention satisfies the following formula (1). 0<100×I 002 / (I 012 +I 002 +I 111 )<4.0 ···(1) In equation (1), I 002 , I 012 and I 111 are the peak intensity of the θ-phase 002 plane, the peak intensity of the α-phase 012 plane, and the peak intensity of the γ-phase 111 plane in the XRD pattern of the alumina powder, respectively. The alumina powder can be sintered to a higher density by press molding suitable for mass production and atmospheric sintering in the atmosphere.

[0016] 100×I in equation (1), which is an index of the θ-alumina content 002 / (I 012 +I 002 +I 111 ) is preferably 1.6 or less, more preferably 1.0 or less, and even more preferably less than 0.5, which can further improve the density of the sintered body. Also, 100×I in Eq. (1) 002 / (I 012 +I 002 +I 111 ) may be greater than 0, for example, 0.01 or greater, greater than 0.1, or 0.2 or greater.

[0017] 100×I, which is an index of the α-alumina content 012 / (I 012 +I 002 +I 111 ) is preferably 95.0 or more and less than 100.0, more preferably 98.0 or more and less than 100.0, and even more preferably 99.0 or more and less than 100.0, from the viewpoint of enabling sintering to an even higher density.

[0018] 100×I, which is an index of the gamma alumina content 111 / (I 012 +I 002 +I 111 ) is preferably 0 or more and 1.0 or less, more preferably 0 or more and 0.5 or less, and even more preferably 0 or more and 0.1 or less, from the viewpoint of enabling sintering at an even higher density.

[0019] Alumina powder I according to an embodiment of the present invention 012 , I 002 and I 111 is determined by the method described in the Examples below.

[0020] [BET specific surface area] The BET specific surface area of ​​the alumina powder according to the embodiment of the present invention is set to 50 m from the viewpoint of easily suppressing aggregation of alumina particles. 2 / g or less, and 2 / g or less is more preferable, 2 / g or less is more preferable, 2 / g or less is even more preferable, 2 On the other hand, the BET specific surface area is preferably 8 m / g or less from the viewpoint of enabling sintering at a higher density. 2 / g or more is preferable.

[0021] The BET specific surface area of ​​the alumina powder according to the embodiment of the present invention can be determined by the BET flow method (single-point method) using nitrogen gas after pretreatment at 200°C for 20 minutes, in accordance with the method specified in JIS-Z-8830: 2013. The measurement can be performed using, for example, a fully automatic specific surface area measuring device (Macsorb HM-1201, manufactured by Mountech Co., Ltd.) or an equivalent device.

[0022] [Particle size distribution] The particle size D50 of the alumina powder according to the embodiment of the present invention, which is the cumulative 50% particle size from the fine particle side of the cumulative particle size distribution on a volume basis, is preferably 0.35 μm or less, more preferably 0.30 μm or less, and even more preferably 0.25 μm or less, from the viewpoint of enabling sintering at a higher density. The lower limit of D50 is not particularly limited, but may be, for example, 0.01 μm or more.

[0023] The alumina powder according to the embodiment of the present invention preferably satisfies the following formula (2) from the viewpoint of enabling sintering at a higher density. 100×(D90-D10) / D50≦15 (2) In formula (2), D90 is the particle size at 90% cumulative from the fine particle side of the volume-based cumulative particle size distribution, D10 is the particle size at 10% cumulative from the fine particle side of the volume-based cumulative particle size distribution, and D50 is the particle size at 50% cumulative from the fine particle side of the volume-based cumulative particle size distribution.

[0024] The left side of formula (2) is more preferably 10 or less, even more preferably 5 or less, and particularly preferably 1.5 or less. The lower limit of the left side of formula (2) is not particularly limited, but may be, for example, 0.01 or more or 0.1 or more.

[0025] The D10, D50, and D90 of the alumina powder according to the embodiment of the present invention can be measured using a particle size distribution analyzer. The particle size distribution analyzer can be a Microtrac particle size distribution analyzer MT-3300 manufactured by Microtrac Bell or an equivalent device. The measurement conditions can be, for example, the method described in the Examples below.

[0026] [Major impurities] The purity of the alumina powder according to the embodiment of the present invention is preferably 99.99% or higher. Furthermore, in order to enable sintering at a higher density, the alumina powder according to the embodiment of the present invention preferably has a total content of the major impurities, Si, Na, Mg, Cu, and Fe, of less than 50 ppm. The lower limit of the total content is not particularly limited, but may be, for example, more than 0 ppm or 0.1 ppm or higher. The total content can be measured by solid-state optical emission spectroscopy. A DC arc device manufactured by Teledyne Leeman Labs or an equivalent device can be used as a measuring device. Measurement conditions can be, for example, those described in the Examples below.

[0027] [form] The alumina powder according to the embodiment of the present invention is preferably spherical, and more specifically, the average roundness of the alumina powder (i.e., the average roundness of the alumina particles constituting the alumina powder) is preferably 0.71 or more. This narrows the gaps between the primary alumina particles, improving packing and facilitating an improvement in the sintered density of the alumina powder. The average roundness of the alumina powder may be 0.75 or more, or may be 0.78 or more. The average roundness of the alumina powder is determined by randomly selecting 50 or more alumina particles from an SEM image of the alumina powder, measuring the area S of the alumina particles on the SEM image and the major axis diameter L of the ellipse when the alumina particles are approximated as an ellipse, calculating the roundness of each particle using the following formula (3), and arithmetic mean value of the obtained values ​​is defined as the average roundness of the alumina powder. Roundness of one alumina particle = 4 × S / (π × L 2 )···(3)

[0028] The average aspect ratio of the alumina powder according to the embodiment of the present invention (that is, the average aspect ratio of the alumina particles constituting the alumina powder) is preferably 1.50 or less, since this can further improve the sintered density of the alumina powder. The average aspect ratio of the alumina powder in this specification is determined by measuring the maximum diameter and particle size in a direction perpendicular to the direction in which the maximum diameter was measured for 50 or more alumina particles (primary alumina particles) selected during the above-mentioned measurement of the average roundness of the alumina powder, and calculating the ratio of the "maximum diameter" to the "particle size in the perpendicular direction." The arithmetic mean value is the average aspect ratio of the alumina powder. The minimum value of the average aspect ratio defined in this way is 1. An average aspect ratio of 1.50 or less is presumed to mean that the average aspect ratio is close to 1 and that the primary alumina particles have a shape that is close to spherical. Near-spherical primary alumina particles have narrower gaps between multiple primary alumina particles, improving packing properties. The average aspect ratio of the alumina powder may be 1.40 or less, or 1.30 or less, 1.05 or more, 1.10 or more, or 1.20 or more.

[0029] In the alumina powder according to the embodiment of the present invention, it is preferable that θ-alumina having a particle size smaller than that of the α-alumina is dispersed in the α-alumina.

[0030] [Molding and sintering] The alumina powder according to the embodiment of the present invention can be sintered to a higher density by press molding suitable for mass production and atmospheric sintering in the air. For example, after press molding, it can be sintered at atmospheric pressure at 1450°C in the air to a density of 3.94 g / cm 3 or more, preferably 3.95 g / cm 3 A density of 2.00 g / cm or more can be achieved, more preferably 3.96 or more, and even more preferably 3.97 or more. Specific methods for molding and sintering can be those described in the Examples below. The density of the molded body can be, for example, 2.00 g / cm. 3 It is preferable that the concentration is 2.25 g / cm or more. 3 The upper limit of the density of the molded body is not particularly limited, but it is, for example, 2.50 g / cm 3 It may be the following:

[0031] [Application] The alumina powder according to the embodiment of the present invention is a suitable raw material for manufacturing components of semiconductor manufacturing equipment such as electrostatic chucks, etc. The alumina powder according to the embodiment of the present invention can also be used as a raw material for coating materials, thermal spray films, oxide sintered bodies, complex oxide sintered bodies, bearings, ceramic beads, fillers for semiconductor sealing resins, heat dissipation fillers, insulating fillers, light reflecting materials, light scattering materials, blasting materials, abrasive grains, biomaterials, dental materials, etc.

[0032] [Manufacturing method] The alumina powder according to the embodiment of the present invention can be produced, for example, by the following method.

[0033] (Manufacturing method example 1) Example 1 of the manufacturing method of the alumina powder according to the embodiment of the present invention is as follows: providing an aluminum-containing raw material; and calcining the aluminum-containing raw material. Each step will be described in detail below.

[0034] [Step of preparing aluminum-containing raw material] First, aluminum-containing raw materials are prepared. Examples of such raw materials include aluminum hydroxide (such as gibbsite, bayerite, nordstrandite, and those produced by discharging metallic aluminum in water), boehmite, pseudoboehmite, crystalline and amorphous intermediate alumina in the γ, χ, θ, δ, ρ, and κ phases, ammonium aluminum carbonate (AACH), ammonium alum, and X aluminum (X: nitrate, sulfate, fluoride, chloride, bromide, iodide, hydrogenate, nitride, sulfide, phosphide, antimony). Examples of suitable starting materials include boron dioxide, dodecaboride, diboride, arsenide, permanganate, silicic acid, phosphoric acid, monostearic acid, carbonic acid, acetic acid, formic acid, tetracarbonate, boron hydride, tris(8-quinolinolato), bis(2-ethylhexanoato)hydroxy), aluminate Y (Y: strontium, sodium), aluminosilicate, tetrahydridoaluminate, sodium tetrahydridoaluminate, aluminum isopropoxide, and organic aluminum compounds. The raw material may be in the form of a slurry.

[0035] As an example, an aluminum hydroxide slurry, which is an aluminum-containing raw material, may be prepared as follows. First, the seed crystal slurry and aluminum alkoxide are continuously fed into a mixer and mixed. This mixture is then subjected to high-speed rotational shear stirring in the mixer, whereby the water in the seed crystal slurry and the aluminum alkoxide undergo a hydrolysis reaction, producing a slurry containing aluminum hydroxide particles as a hydrolyzate (aluminum hydroxide slurry).

[0036] The supply amounts of the seed crystal slurry and aluminum alkoxide are preferably controlled so that the content of the seed crystals in the mixture is appropriate. The preferred content of the seed crystals is, in terms of oxide of the metal components in the mixture (the aluminum components contained in the aluminum alkoxide and the seed crystals), 1 part by mass or more, preferably 2 parts by mass or more, and 50 parts by mass or less, preferably 40 parts by mass or less, particularly preferably 30 parts by mass or less, per 100 parts by mass of the total amount of the aluminum components in the mixture.

[0037] The supply amounts of the seed crystal slurry and aluminum alkoxide are preferably controlled so that the compounding ratio (water contained in the seed crystal slurry) / (aluminum alkoxide) is in the range of about 1.5 to about 6.0 in molar ratio.

[0038] One of the features of this method is that the mixture is subjected to high-speed rotational shear stirring during mixing. In this specification, "high-speed rotational shear stirring" refers to stirring performed by mechanical energy such as shear force, pressure fluctuation, cavitation, collision force, and potential core that occurs between the turbine (rotor) and the stator (screen) when the clearance between the turbine (rotor) and the stator (screen) is small (e.g., 2 mm or less) and the turbine (rotor) rotates at high speed (e.g., peripheral speed of about 1 m / s to about 40 m / s).

[0039] Examples of mixers capable of performing such high-speed rotational shear mixing include the TK Homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.), Clearmix (manufactured by M Technique Co., Ltd.), Polytron Homogenizer, Megatron Homogenizer (KINEMATICA), and Supraton (manufactured by Tsukishima Kikai Co., Ltd.).

[0040] In the high-speed rotary shear stirring, the turbine (rotor) rotation speed is 3,000 rpm to 21,500 rpm, preferably 8,000 rpm to 15,000 rpm, for example, 10,000 rpm. When the rotation speed is within this range, the two liquids, water and aluminum alkoxide, in the seed crystal slurry can be mixed thoroughly, and aggregation of aluminum hydroxide in the resulting aluminum hydroxide slurry can be suppressed. This results in an aluminum hydroxide slurry containing fine aluminum hydroxide particles. Furthermore, the seed crystals can be uniformly dispersed in the aluminum hydroxide slurry.

[0041] The hydrolysis of aluminum alkoxide can be carried out using a continuous reactor. Examples of applicable continuous reactors include a tank continuous reactor and a pipeline continuous reactor. The tank continuous reactor is a method in which a seed crystal slurry and aluminum alkoxide are continuously supplied to a tank equipped with an agitator capable of high-speed rotary shear, and the hydrolysis of aluminum alkoxide (and the production of aluminum hydroxide particles) is carried out while continuously discharging the same amount of liquid as that supplied. The pipeline continuous reactor is a method in which a seed crystal slurry and aluminum alkoxide are continuously supplied to an agitator incorporated in a line capable of high-speed rotary shear. These continuous reactors are much more productive than batch reactors and can achieve uniform production conditions for aluminum hydroxide particles, thereby producing an aluminum hydroxide slurry containing aluminum hydroxide with a uniform particle size distribution and free of coarse agglomerates.

[0042] [Step of firing the aluminum-containing raw material] The raw material is calcined to obtain alumina powder. If the raw material is a slurry, it is dried by a known method, and the resulting dried product is calcined in a calciner to obtain alumina powder. From the viewpoint of increasing the α phase, the calcination may be carried out usually at 800° C. or higher, preferably 900° C. or higher, and more preferably 910° C. or higher. From the viewpoint of obtaining a fine alumina powder, the calcination may be carried out usually at 1000° C. or lower, preferably 980° C. or lower, further preferably 960° C. or lower, and particularly preferably 950° C. or lower.

[0043] The firing may be carried out in air or in an inert gas such as nitrogen gas or argon gas, and it is effective to perform the firing while maintaining a high water vapor partial pressure in the atmosphere. In particular, firing in an atmosphere with a high water vapor partial pressure (i.e., an atmosphere with a high dew point) allows the α phase to be obtained at a low firing temperature. Furthermore, the low firing temperature allows a small amount of the θ phase to remain.

[0044] The calcination can be carried out using a conventional calcination furnace such as a tubular electric furnace, a box-type electric furnace, a tunnel furnace, a far-infrared furnace, a microwave heating furnace, a shaft furnace, a reverberatory furnace, a rotary furnace, a roller hearth furnace, or a gas (LNG, LPG) furnace. The calcination may be carried out batchwise or continuously. It may also be carried out statically or fluidized.

[0045] As a method for controlling the dew point during calcination, when an electric furnace using electric energy as a heat source or a tubular furnace is used as the calcination furnace, a method of spraying water into the dry air introduced into the furnace or a method of introducing steam into the furnace are effective. When a gas combustion furnace is used as the calcination furnace, a method of introducing moisture generated by burning fuel such as gas or oil into the furnace is effective, and further introducing steam is even more effective.

[0046] The dew point can be calculated using a conversion table based on the amount of water vapor, or using a formula based on the water vapor pressure. The water vapor pressure and water vapor amount (absolute humidity) can be calculated from the saturated water vapor pressure or saturated water vapor amount and relative humidity, respectively. The saturated water vapor pressure can be calculated using the Tetens formula.

[0047] It is preferable to control the dew point inside the furnace to 30°C or higher (water vapor partial pressure of 4243 Pa or higher for gas with a total pressure of 1 atmosphere), more preferably to control the dew point to 40°C or higher (water vapor partial pressure of 7382 Pa or higher for gas with a total pressure of 1 atmosphere), even more preferably to control the dew point to 50°C or higher (water vapor partial pressure of 12350 Pa or higher for gas with a total pressure of 1 atmosphere), and particularly preferably to control the dew point to 60°C or higher (water vapor partial pressure of 19946 Pa or higher for gas with a total pressure of 1 atmosphere).

[0048] To facilitate the inclusion of the θ phase in the alumina powder, additives may be added to the raw materials before firing. Examples of additives include fluorine-based mineralizers (LiF2, AlF3, NaF, NaPF6, K2TiF6, MnF2, etc.), aluminum, aluminum chloride, metal oxides (Mg, Ca, Ti, Zr, V, Cr, Fe, Cu, Sr, La, Ce, Nd, Y, Ni, etc.), non-metal oxides (B, Si, etc.), and silane coupling agents.

[0049] (Manufacturing method example 2) Alumina powder manufacturing method example 2 according to an embodiment of the present invention is as follows: providing alpha alumina and theta alumina; mixing the alpha alumina and the theta alumina. Each step will be described in detail below.

[0050] [Step of preparing α-alumina and θ-alumina] First, α-alumina and θ-alumina are prepared. The α-alumina used as the raw material may be 100% α-phase, or may contain a small amount of intermediate phase, aluminum hydroxide, or the like. The raw material θ-alumina may be 100% θ-phase or may contain a small amount of other intermediate phases such as γ-phase. It is also desirable that the primary particle size of the θ-alumina is small.

[0051] [Step of mixing α-alumina and θ-alumina] The α-alumina and θ-alumina are mixed. The mixing may be dry mixing or wet mixing. The mixing may be carried out using a media mill including a bead mill such as a ball mill, vibration mill, dynamic mill, dyno mill, or sand grinder, or may be carried out using a mixer such as a jet mill, a disper mixer, a high-speed rotary shear mixer (TK Homomixer, Clearmix, Polytron Homogenizer, Megatron Homogenizer, or Supraton), a homogenizer, an ultrasonic disperser, a centrifugal mixer, or a revolutionary mixer. Further, the theta alumina may be uniformly dispersed in the alpha alumina by mixing, and then granulated using a spray dryer.

[0052] (Manufacturing method example 3) Alumina powder manufacturing method example 3 according to an embodiment of the present invention is as follows: providing alpha alumina; The method includes a step of introducing strain and / or defects into the α-alumina surface. Each step will be described in detail below.

[0053] [Step of preparing α-alumina] First, α-alumina is prepared. The α-alumina used as the raw material may be 100% α-phase, or may contain a small amount of intermediate phase, aluminum hydroxide, or the like.

[0054] [Step of introducing strain and / or defects into the α-alumina surface] Strain and / or defects are introduced into the α-alumina surface, which allows θ-alumina to form on the surface. The method for introducing strain and / or defects can be either dry or wet. The introduction of strain and / or defects can be carried out using a media mill including a bead mill such as a ball mill, vibration mill, dynamic mill, dyno mill, or sand grinder, or a mixer such as a jet mill, disper mixer, high-speed rotary shear mixer (TK Homomixer, Clearmix, Polytron Homogenizer, Megatron Homogenizer, Supraton), homogenizer, ultrasonic disperser, centrifugal mixer, or revolutionary mixer. After the introduction, calcination may be carried out as necessary. The calcination can be carried out in the same manner as in the above-mentioned Example 1 of Production Method.

[0055] In this manner, an alumina powder according to an embodiment of the present invention is obtained. The alumina powder obtained in this manner may have α-alumina particles dispersed therein, the θ-alumina particles having a particle size smaller than that of the α-alumina particles.

[0056] [Step of pulverizing the obtained alumina powder] The alumina powder according to the embodiment of the present invention can be obtained by the above-described production method, but the alumina powder may be further pulverized. For pulverizing the alumina powder, a media pulverizer such as a vibration mill, a ball mill, or a jet mill may be used. Furthermore, the pulverized alumina powder may be classified. [Example]

[0057] The following examples are provided to more specifically describe the embodiments of the present invention. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the above-described and below-described aims, and all such modifications are within the technical scope of the embodiments of the present invention.

[0058] (Preparation of alumina powder) Alumina particles (seed crystal raw material) were dispersed in water and then wet-pulverized in a ball mill. The mixture was then centrifuged at 4000 rpm for 30 minutes in a refrigerated centrifuge (manufactured by Himac: CR7N) to remove the precipitate. This yielded a seed crystal slurry in which the seed crystals were dispersed.

[0059] Aluminum isopropoxide and the seed crystal slurry were mixed and hydrolyzed using a precision emulsifying and dispersing machine, Clearmix CLM-2.2S (M Technique Co., Ltd.), at a rotation speed of 10,000 rpm, to obtain aluminum hydroxide slurry. The compounding ratio of aluminum isopropoxide to the seed crystal slurry was adjusted so that the aluminum component in the seed crystals was 5.6 parts by mass per 100 parts by mass of the total amount of aluminum components in the mixture (aluminum alkoxide and aluminum components contained in the seed crystals) converted into oxides. Note that this was calculated assuming that all of the aluminum isopropoxide was converted to alumina.

[0060] The resulting aluminum hydroxide slurry was dried at 150°C to obtain aluminum hydroxide particles, which were then placed in an alumina crucible and fired. The firing conditions were as follows: the temperature was raised to 950°C at a rate of 150°C / hour in an environment with a dew point of 60°C, and the temperature was maintained at that temperature for 4 hours. After firing, the particles were pulverized in a ball mill. In this way, an alumina powder of Sample No. 1 was obtained.

[0061] The alumina powder of sample No. 2 was obtained by changing the firing temperature from the preparation method of sample No. 1 to 930°C.

[0062] The alumina powder of sample No. 3 was obtained by changing the firing temperature from the preparation method of sample No. 1 to 910°C.

[0063] Alumina powder of sample No. 4, a comparative example, was produced by changing the production method of sample No. 1, except that the firing temperature was changed to 1170°C and the dew point to -15°C.

[0064] The alumina powder of Sample No. 5, which is a comparative example, was obtained by changing the firing temperature from the preparation method of Sample No. 1 to 900°C.

[0065] The alumina powder samples Nos. 1 to 5 were evaluated as follows.

[0066] [I 002 , I 012 and I 111 Measurement of First, an XRD pattern (CuKα) was obtained for each alumina powder using an X-ray diffractometer. In the XRD pattern, the minimum intensity value in the 2θ range of 23° to 40° (i.e., the background in the 2θ range of 23° to 40°) was determined. In the above XRD pattern, the maximum peak in the range of 2θ = 24° to 28° is the peak of the α phase 012 plane, and the value obtained by subtracting the above minimum intensity value from this peak intensity is I 012 It was decided. In the above XRD pattern, the maximum peak in the 2θ=32° to 33° range is the peak of the θ phase 002 plane, and the value obtained by subtracting the above minimum intensity value from this peak intensity is I 002 In addition, I 002 / I 012 If the value is smaller than 0.002, it is considered to be the intensity ratio of the skirt part of the α phase 104 plane (having a peak around 2θ = 35°), and there is no θ phase (I 002 =0). In the above XRD pattern, the intensity in the range of 2θ=17° to 23° was subtracted from the baseline intensity, which was a line connecting the intensities at 2θ=17° and 2θ=23°, to eliminate the influence of the background on the low angle side (i.e., in the XRD pattern, the intensity may increase substantially linearly as the angle approaches the low angle side). In the XRD pattern after this subtraction, the maximum peak in the range of 2θ=19.5° to 20° was determined to be the peak of the γ-phase 111 plane, and the peak intensity was determined to be the I 111 It was decided. I calculated as above 002 , I 012 and I 111Using the above, the index of alumina content is: 100 × I 002 / (I 012 +I 002 +I 111 Similarly, the index of α-alumina content: 100 × I 012 / (I 012 +I 002 +I 111 ) and gamma alumina content index: 100 × I 111 / (I 012 +I 002 +I 111 The index of the α-alumina content is also called the α-alumina ratio.

[0067] [Measurement of BET specific surface area] The BET specific surface area of ​​the alumina powder was determined by the BET flow method (single-point method) using nitrogen gas after pretreatment at 200°C for 20 minutes using a fully automatic specific surface area measuring device (Macsorb HM-1201, manufactured by Mountech Co., Ltd.) in accordance with the method specified in JIS-Z-8830:2013.

[0068] [D10, D50 and D90] The D10, D50, and D90 of alumina powder were measured as follows. The alumina powder to be measured was 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 Particle Size Distribution Analyzer MT-3300 manufactured by Microtrac Bell. Measurement time: 10 s, number of measurements: 2, particle refractive index: 1.77, solvent refractive index: 1.333. From the results, D10, D50, and D90 were calculated. The left side of equation (2) (100 × ((D90 - D10) / D50)) was also calculated.

[0069] [Average roundness] The average roundness of the alumina powder was determined by randomly selecting 50 or more alumina particles from an SEM image of the alumina powder, measuring the area S of the alumina particles on the SEM image and the major axis diameter L of the ellipse when the alumina particles were approximated as an ellipse, calculating the roundness of each particle using the following formula (3), and taking the arithmetic mean value as the average roundness of the alumina powder. Roundness of one alumina particle = 4 × S / (π × L 2 )···(3)

[0070] [Average aspect ratio] The average aspect ratio of the alumina powder was determined by measuring the maximum diameter and particle size in a direction perpendicular to the direction in which the maximum diameter was measured for 50 or more alumina particles selected when measuring the average roundness of the alumina powder described above, and calculating the ratio of the "maximum diameter" to the "particle size in the perpendicular direction." The arithmetic mean value was used as the average aspect ratio of the alumina powder.

[0071] [Measurement of major impurities] The total content of the major impurities in the alumina powder—Si, Mg, Cu, Fe, and Na—was measured by solid-state optical emission spectroscopy. Using a Teledyne Leeman Labs DC arc device, the powder sample was mixed with carbon powder, filled into a cup-shaped carbon electrode, and then arc discharge was induced between the powder and the counter carbon electrode. The concentration of each element in the sample was determined from the calibration curves for each element obtained from the emission intensity of a standard sample measured at the same time.

[0072] [Production of sintered bodies by press molding and atmospheric sintering] Each alumina powder was press-molded and pressurelessly sintered in air as follows, and its density was evaluated. An appropriate amount of alumina powder was uniaxially press-molded at 30 MPa using a φ20 mm mold, and then a pressure of 98 MPa was applied using an isostatic press to obtain a compact with a surface dimension of φ20 mm and a thickness of 5 to 10 mm. The density of the compact (weight / volume ratio) was measured using the Archimedes method. The compact was placed in an alumina crucible and placed in a box-shaped electric furnace, where it was heated to a sintering temperature of 1450°C at a heating rate of 200°C / hour under normal pressure. The compact was sintered at the sintering temperature for 2 hours under normal pressure to obtain an alumina sintered body. The density (weight / volume ratio) of this sintered body was measured by Archimedes' method.

[0073] The results are shown in Table 1.

[0074] [Table 1]

[0075] Table 1 reveals the following: Samples Nos. 1 to 3 satisfy the requirements according to the embodiment of the present invention (i.e., formula (1)), and thus can be made to a higher density (3.94 g / cm 3 ) by press molding and atmospheric sintering in air. 3 Furthermore, samples No. 1 and No. 2 achieved the 100×I 002 / (I 012 +I 002 +I 111 ) in formula (1) was greater than 0 and not greater than 1.6, and thus exhibited a higher sintered density. 002 / (I 012 +I 002 +I 111 ) satisfied the more preferable requirement of being greater than 0 and less than 0.5, and therefore exhibited a particularly high sintered density. On the other hand, Samples No. 4 and No. 5 did not satisfy formula (1), and therefore the sintered density was 3.94 g / cm 3 It was less than.

Claims

1. An alumina powder that satisfies the following formula (1): 0<100×I ００２ / (I ０１２ +I ００２ +I １１１ )<4.0 ・・・(1) In formula (1), I ００２ , I ０１２ and I １１１ are the peak intensity of the θ-phase 002 plane, the peak intensity of the α-phase 012 plane, and the peak intensity of the γ-phase 111 plane in the XRD pattern of the alumina powder, respectively.

2. BET specific surface area is 8 to 50 m ２ 2. The alumina powder according to claim 1, wherein the alumina powder has a SiO 2 content of 0.1 wt % or less.

3. 2. The alumina powder according to claim 1, wherein the particle size D50 of the cumulative 50% from the fine particle side of the cumulative particle size distribution on a volume basis is 0.35 μm or less.

4. The alumina powder according to claim 1, which satisfies the following formula (2): 100×(D90-D10) / D50≦15...(2) In formula (2), D90 is the particle size at 90% cumulative from the fine particle side of the volume-based cumulative particle size distribution, D10 is the particle size at 10% cumulative from the fine particle side of the volume-based cumulative particle size distribution, and D50 is the particle size at 50% cumulative from the fine particle side of the volume-based cumulative particle size distribution.

5. 2. The alumina powder according to claim 1, wherein the total content of Si, Na, Mg, Cu and Fe is less than 50 ppm.

6. 100×I in formula (1) ００２ / (I ０１２ +I ００２ +I １１１ 2. The alumina powder according to claim 1, wherein the σ is less than 0.5.

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