JP5211467B2 - Method for producing polyhedral α-alumina - Google Patents

Method for producing polyhedral α-alumina Download PDF

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JP5211467B2
JP5211467B2 JP2006315847A JP2006315847A JP5211467B2 JP 5211467 B2 JP5211467 B2 JP 5211467B2 JP 2006315847 A JP2006315847 A JP 2006315847A JP 2006315847 A JP2006315847 A JP 2006315847A JP 5211467 B2 JP5211467 B2 JP 5211467B2
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alumina
raw material
polyhedral
particle size
firing
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JP2008127257A (en
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潤 水野
俊博 松葉
秀之 三上
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Nippon Light Metal Co Ltd
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Description

この発明は、均整で球状に近い８面体以上の多面体形状を有して粒度分布の狭いα-アルミナの製造方法に関する。 The present invention relates to a method for producing α-alumina having a regular and nearly spherical polyhedron shape having a nearly spherical shape and a narrow particle size distribution.

α-アルミナは樹脂に混ぜて放熱用フィラーとして、研磨材として、更にはセラミックフィルター等の焼結材用原料やプラズマ溶射材用原料等の用途に広く用いられており、特に放熱用フィラーや研磨材の用途には、樹脂への充填性や研磨精度の点から、粒子形状が均整であってできるだけ球状に近く、また、粒度分布が可及的に狭い（粒径が均一である）ことが求められている。   α-Alumina is mixed with resin as a heat-dissipating filler, used as an abrasive, and further used as a raw material for sintered materials such as ceramic filters and a raw material for plasma sprayed materials. For the use of the material, the particle shape should be uniform, as close to a sphere as possible, and the particle size distribution should be as narrow as possible (uniform particle size) in terms of resin filling properties and polishing accuracy. It has been demanded.

このようなα-アルミナを製造する方法としては、最も一般的には、原料のボーキサイトから水酸化アルミニウム（ギブサイト）又は遷移アルミナ（χ-アルミナ又はκ-アルミナ）を製造し、次いでこれ等を大気中で焼成してα-アルミナを製造する、いわゆるバイヤー法である。しかしながら、このバイヤー法においては、工業的に安価に得られる水酸化アルミニウム又は遷移アルミナは、通常その粒子が１０μmを超える凝集粒子であり、これを焼成して得られるα-アルミナも凝集した粗粒を含むため、用途に応じて解砕して用いられるが、α-アルミナの凝集粒子を解砕して得られたα-アルミナには微粉末が含まれて粒度分布も満足できるものではなく、形状も不定形である。   As a method of producing such α-alumina, most commonly, aluminum hydroxide (gibbsite) or transition alumina (χ-alumina or κ-alumina) is produced from bauxite as a raw material, and these are then used in the atmosphere. This is a so-called buyer method in which α-alumina is produced by firing in the inside. However, in this Bayer method, aluminum hydroxide or transition alumina obtained industrially at low cost is usually agglomerated particles whose particles exceed 10 μm, and α-alumina obtained by firing this is also agglomerated coarse particles However, the α-alumina obtained by crushing the α-alumina aggregated particles contains fine powder and the particle size distribution is not satisfactory. The shape is also irregular.

そこで、この問題を解決する方法として、これまでにも幾つかの提案がなされており、例えば、特開昭59-97,528号公報には、バイヤー法で得られた水酸化アルミニウム（ギブサイト）を１２００℃以上の温度で焼成する際に、ホウ素及び／又はフッ素を含むアンモニウム化合物を鉱化剤として添加することにより、平均粒子径１〜１０μm、結晶学上Ｃ軸に垂直な径ＤとＣ軸に平行な高さＨとの比（Ｄ／Ｈ比）が１〜２のα-アルミナを製造する方法が開示されている。   Therefore, several proposals have been made as a method for solving this problem. For example, JP-A-59-97,528 discloses that aluminum hydroxide (gibbsite) obtained by the Bayer method is 1200. By adding an ammonium compound containing boron and / or fluorine as a mineralizing agent when firing at a temperature of ℃ or higher, the average particle diameter is 1 to 10 μm, and the crystallographic vertical diameters D and C are perpendicular to the C axis. A method for producing α-alumina having a ratio with a parallel height H (D / H ratio) of 1 to 2 is disclosed.

しかしながら、この方法で得られたα-アルミナは、平均粒子径数十から１００μm程度までの凝集体形状の水酸化アルミニウムを原料としてロータリーキルンで焼成しているので、不可避的に粒子形状が不均一になり、粒度分布も広くなり、また、１μm以下のα-アルミナを製造することができないという問題がある。   However, the α-alumina obtained by this method is baked in a rotary kiln using aggregated aluminum hydroxide having an average particle diameter of several tens to about 100 μm as a raw material, so that the particle shape is inevitably uneven. Thus, the particle size distribution is widened, and α-alumina of 1 μm or less cannot be produced.

また、特開平3-131,517号公報には、水酸化アルミニウム又は遷移アルミナに融点８００℃以下のフッ素系フラックスを鉱化剤として添加し、９００〜１１００℃の温度で焼成することにより、直径２〜２０μm及び厚み０．１〜２μmであって直径対厚みの比が５〜４０である六角板状のα-アルミナを製造する方法が開示されている。   JP-A-3-131,517 discloses adding a fluorine-based flux having a melting point of 800 ° C. or less to aluminum hydroxide or transition alumina as a mineralizer and firing it at a temperature of 900 to 1100 ° C. A method for producing hexagonal plate-like α-alumina having a diameter of 20 μm and a thickness of 0.1 to 2 μm and a diameter to thickness ratio of 5 to 40 is disclosed.

しかしながら、この方法で得られたα-アルミナは、その粒子形状が全て六角板状であって研磨性や充填性に劣るという問題があり、また、平均粒子径２μm以下の微細なα-アルミナは得られておらず、また、フラックスの使用量も２〜２０重量%にも達して製造コストや焼成設備の腐食対策、排ガス処理対策などの点で問題がある。   However, the α-alumina obtained by this method has a problem that the particle shape is all hexagonal plate and is inferior in polishing property and filling property, and fine α-alumina having an average particle diameter of 2 μm or less is In addition, the amount of flux used has reached 2 to 20% by weight, and there are problems in terms of manufacturing costs, measures against corrosion of firing facilities, measures against exhaust gas treatment, and the like.

更に、特許第3,744,010号公報には、遷移アルミナ及び／又は熱処理により遷移アルミナとなるアルミナ原料を、フッ素ガス、臭素ガス、ヨウ素ガスから選ばれる少なくとも１種のハロゲンガスを雰囲気ガスの全体積に対し５〜１０体積%以上導入した雰囲気ガス中にて焼成することにより、均質で８面以上の多面体形状を有し、六方最密格子であるα−アルミナの六方格子面に平行な最大粒子径をＤとし六方格子面に垂直な粒子径をＨとしたときのＤ／Ｈ比が０．５以上５以下である、又は、Ｄ／Ｈ比が１以上３０以下であるα−アルミナ単結晶粒子からなるα−アルミナ粉末の製造方法が記載されている。   Further, Patent No. 3,744,010 discloses transitional alumina and / or an alumina raw material that becomes transitional alumina by heat treatment, and at least one halogen gas selected from fluorine gas, bromine gas, and iodine gas with respect to the total volume of the atmospheric gas. By firing in an atmosphere gas introduced in an amount of 5 to 10% by volume or more, a maximum particle diameter parallel to the hexagonal lattice plane of α-alumina, which is a homogeneous and has a polyhedral shape of 8 or more faces and a hexagonal close-packed lattice, is obtained. From α-alumina single crystal particles having a D / H ratio of 0.5 to 5 or a D / H ratio of 1 to 30 when the particle diameter perpendicular to the hexagonal lattice plane is H. A method for producing an α-alumina powder is described.

しかしながら、この方法においては、雰囲気ガスの全体積に対してハロゲンガスを５〜１０体積%以上導入した雰囲気ガス中で焼成する必要があることから、焼成炉には気密性や雰囲気調整のための機構が求められ、特殊な機構を備えた焼成炉が必要であり、また、ガスが到達しない粉体層内では形状や粒径が不均一になるなど、所望のα-アルミナが得られないという問題がある。
特開昭59-97,528号公報 特開平3-131,517号公報 特許第3,744,010号公報 However, in this method, it is necessary to perform firing in an atmospheric gas in which 5 to 10% by volume or more of a halogen gas is introduced with respect to the total volume of the atmospheric gas. A mechanism is required, a firing furnace equipped with a special mechanism is required, and the desired α-alumina cannot be obtained because the shape and particle size are not uniform in the powder layer where the gas does not reach. There's a problem.
JP 59-97,528 Japanese Patent Laid-Open No. 3-131,517 Japanese Patent No. 3,744,010

そこで、本発明者らは、気密性や雰囲気調整のための特殊な機構を備えた焼成炉を使用する必要がなく、また、アルミナ原料粉と調整雰囲気ガスとの接触程度の差による粒子形状及び粒度分布の不均一化を生じる虞がなく、これまでこの種のα-アルミナの製造に汎用されてきた定置炉を用いて安価に製造することができ、しかも、粒子形状が均整であって球状に近く、また、粒度分布が可及的に狭いα-アルミナの製造方法について鋭意検討し、本発明を完成した。   Therefore, the present inventors do not need to use a firing furnace equipped with a special mechanism for airtightness and atmosphere adjustment, and the particle shape and the difference in contact degree between the alumina raw material powder and the adjusted atmosphere gas There is no risk of non-uniform particle size distribution, and it can be manufactured at low cost using a stationary furnace that has been widely used for the production of this kind of α-alumina, and the particle shape is uniform and spherical. Further, the present invention was completed by intensively studying a method for producing α-alumina having a particle size distribution as narrow as possible.

従って、本発明の目的は、粒子形状が均整であって８面体以上の球状に近く、所定の平均粒子径を有してその粒度分布が狭く、種々の用途、特に放熱用フィラーや研磨材の用途に好適な多面体形状α-アルミナの製造方法を提供することにある。 Therefore, the object of the present invention is to have a uniform particle shape, close to a sphere of octahedron or more, have a predetermined average particle size and a narrow particle size distribution, and can be used for various applications, particularly for heat radiation fillers and abrasives. An object of the present invention is to provide a method for producing polyhedral α-alumina suitable for applications.

また、本発明の他の目的は、粒子形状が均整であって８面体以上の球状に近く、所定の平均粒子径を有してその粒度分布が狭い多面体形状のα-アルミナを工業的に安価に製造することができる多面体形状α−アルミナの製造方法を提供することにある。   Another object of the present invention is to provide industrially inexpensive polyhedral α-alumina having a uniform particle shape, nearly spherical to an octahedron or more, and having a predetermined average particle diameter and a narrow particle size distribution. Another object of the present invention is to provide a method for producing a polyhedral α-alumina that can be produced.

すなわち、本発明は、レーザー散乱法で測定された平均粒子径が０．５〜６μmであって、レーザー散乱法で測定された粒度分布の傾きが３．０以上であり、ＳＥＭ写真の画像解析により測定された結晶学上Ｃ軸に垂直な径ＤとＣ軸に平行な高さＨとの比（Ｄ／Ｈ比）が１〜３の範囲であって、８面体以上の多面体形状を有する多面体形状α−アルミナを製造するための方法に関するものである。 That is, according to the present invention, the average particle diameter measured by the laser scattering method is 0.5 to 6 μm, the gradient of the particle size distribution measured by the laser scattering method is 3.0 or more, and image analysis of the SEM photograph The ratio (D / H ratio) of the diameter D perpendicular to the C-axis and the height H parallel to the C-axis (D / H ratio) measured by the crystallography is in the range of 1 to 3, and has a polyhedral shape of octahedron or more The present invention relates to a method for producing polyhedral α-alumina.

また、本発明は、擬ベーマイト、γアルミナ、及びθアルミナから選ばれた１種又は２種以上の混合物からなるアルミナ原料にフッ素化合物又はフッ素化合物及びホウ素化合物をアルミナ換算基準で０．１〜２．０質量%の範囲で添加し、得られた原料混合物を充填嵩比重比９０%以下で焼成容器に充填し、焼成温度１１００℃以上で焼成することを特徴とする、８面体以上の多面体形状を有して粒度分布の狭い多面体形状α−アルミナの製造方法である。 Further, the present invention provides a fluorine compound or a fluorine compound and a boron compound in an alumina conversion standard of 0.1 to 2 to an alumina raw material composed of one kind or a mixture of two or more kinds selected from pseudoboehmite , γ alumina, and θ alumina. A polyhedral shape of octahedron or more, characterized by being added in a range of 0.0 mass%, filling the obtained raw material mixture into a firing container at a filling bulk specific gravity ratio of 90% or less, and firing at a firing temperature of 1100 ° C. or higher. And having a narrow particle size distribution in the polyhedral shape α-alumina.

本発明の多面体形状α−アルミナは、レーザー散乱法で測定された平均粒子径が通常０．５μm以上６μm以下、好ましくは０．５μm以上５μm以下であって、レーザー散乱法で測定された粒度分布の傾きが３．０以上（通常は上限が５．０程度）、好ましくは３．５以上であり、また、ＳＥＭ写真の画像解析により測定された結晶学上Ｃ軸に垂直な径ＤとＣ軸に平行な高さＨとの比（Ｄ／Ｈ比）が１以上３以下の範囲内、好ましくは１以上２以下又は２以上３以下の狭い範囲内の８面体以上の多面体形状を有するα−アルミナである。このような平均粒子径、粒度分布の傾き及びＤ／Ｈ比を有する本発明の多面体形状α−アルミナは、粒径が揃い、球形に近い形状であるために特に樹脂への充填性に優れており、また、粒径が揃い、球面ではなくて多面体形状であるために特に研磨精度等の研磨性に優れている。   The polyhedral α-alumina of the present invention has an average particle size measured by a laser scattering method of usually 0.5 μm or more and 6 μm or less, preferably 0.5 μm or more and 5 μm or less, and a particle size distribution measured by a laser scattering method. The diameters D and C perpendicular to the C-axis in crystallography measured by image analysis of SEM photographs are 3.0 or more (usually the upper limit is about 5.0), preferably 3.5 or more. Α having a polyhedral shape of octahedron or more within a range of a ratio of height H parallel to the axis (D / H ratio) of 1 or more and 3 or less, preferably 1 or more and 2 or less, or 2 or more and 3 or less. -Alumina. The polyhedral α-alumina of the present invention having such an average particle size, a particle size distribution gradient, and a D / H ratio has a uniform particle size and a shape close to a sphere, so that it is particularly excellent in filling into a resin. In addition, since it has a uniform particle size and is not a spherical surface but a polyhedral shape, it is particularly excellent in polishing properties such as polishing accuracy.

そして、本発明の８面体以上の多面体形状を有して粒度分布の狭い多面体形状α−アルミナは、擬ベーマイト、γアルミナ、及びθアルミナから選ばれた１種又は２種以上の混合物からなるアルミナ原料にフッ素化合物又はフッ素化合物及びホウ素化合物をアルミナ換算基準で０．１〜２．０質量%の範囲で添加し、得られた原料混合物を充填嵩比重比９０%以下で焼成容器に充填し、焼成温度１１００℃以上で焼成することにより製造することができる。 The polyhedral α-alumina having an octahedral or higher polyhedral shape and a narrow particle size distribution according to the present invention is an alumina composed of one or a mixture of two or more selected from pseudoboehmite , γ alumina, and θ alumina. Fluorine compound or fluorine compound and boron compound are added to the raw material in the range of 0.1 to 2.0% by mass on an alumina conversion basis, and the obtained raw material mixture is filled into a firing container at a filling bulk specific gravity ratio of 90% or less, It can be manufactured by firing at a firing temperature of 1100 ° C. or higher.

本発明の製造方法において、使用するアルミナ原料は、擬ベーマイト（Al2O3・H2O）、γアルミナ、及びθアルミナから選ばれた１種又は２種以上の混合物である必要があり、水酸化アルミニウム（ギブサイト）やχ-アルミナ、α-アルミナ等であっては所望の多面体形状α-アルミナを製造することが難しい。 In the production method of the present invention, the alumina raw material to be used must be one or a mixture of two or more selected from pseudo-boehmite (Al 2 O 3 .H 2 O) , γ alumina, and θ alumina , It is difficult to produce desired polyhedral α-alumina with aluminum hydroxide (gibbsite), χ-alumina, α-alumina and the like.

また、このアルミナ原料については、好ましくはＢＥＴ比表面積が５０m2/g以上、より好ましくは１００m2/g以上であるのがよく、また、好ましくはレーザー散乱法で測定された平均粒子径が予め４０μm以下、より好ましくは３０μm以下の範囲に調整されているのがよい。アルミナ原料について、そのＢＥＴ比表面積が５０m2/gより低くなったり、あるいは、平均粒子径が４０μmを超えると、得られるα−アルミナの粒子形状が不均整になる虞が生じる。また、アルミナ原料のＢＥＴ比表面積や平均粒子径については、その値が大きくなると生成するα-アルミナの粒径が大きくなる傾向がある。更に、アルミナ原料の粒度分布が広くなると生成するα-アルミナの粒度分布も広くなる傾向があるので、このアルミナ原料の粒度分布については、好ましくはその傾きが１．５以上、好ましくは２．０以上とするのがよい。 In addition, the alumina raw material preferably has a BET specific surface area of 50 m 2 / g or more, more preferably 100 m 2 / g or more, and preferably an average particle size measured by a laser scattering method is previously set. The thickness is adjusted to 40 μm or less, more preferably 30 μm or less. If the BET specific surface area of the alumina raw material is lower than 50 m 2 / g or the average particle diameter exceeds 40 μm, the resulting α-alumina particles may be irregularly shaped. As for the BET specific surface area and average particle diameter of the alumina raw material, the particle diameter of the α-alumina produced tends to increase as the value increases. Furthermore, since the particle size distribution of the α-alumina produced tends to become wider as the particle size distribution of the alumina raw material becomes wider, the particle size distribution of the alumina raw material preferably has an inclination of 1.5 or more, preferably 2.0. It is good to be the above.

本発明の製造方法においては、アルミナ原料の焼成時にこのアルミナ原料中にフッ素化合物又はフッ素化合物及びホウ素化合物からなる鉱化剤をアルミナ換算基準で０．１質量%以上２．０質量%以下、好ましくは０．３質量%以上１．５質量%以下の範囲で添加する必要がある。この鉱化剤添加量が０．１質量%より少ないと所望の多面体形状のα−アルミナが得られず、反対に、２．０質量%より多くしても添加効果が頭打ちになるほか、製造コストが増加し、また、設備への悪影響等も生じてマイナス要因が大きくなる。   In the production method of the present invention, during firing of the alumina raw material, a mineralizer comprising a fluorine compound or a fluorine compound and a boron compound in the alumina raw material is 0.1% by mass or more and 2.0% by mass or less, preferably on an alumina conversion basis. Needs to be added in the range of 0.3 mass% to 1.5 mass%. If the amount of mineralizer added is less than 0.1% by mass, the desired polyhedral α-alumina cannot be obtained. Costs increase and negative effects on the equipment occur, resulting in a large negative factor.

また、本発明の製造方法において、アルミナ原料に鉱化剤を添加して得られた原料混合物を焼成容器に充填して焼成する際には、重装嵩比重（JIS H1902-1977）に対する充填嵩比重（焼成容器に充填される際の嵩密度）の百分率割合で表される充填嵩比重比が９０%以下、好ましくは８５%以下の範囲となるように充填することが必要であり〔下限値は粉体の物性により通常は６４%程度までの値になるが、隙間（粒子間の空間）が多い軽装嵩比重の状態で焼成容器に充填されること〕、この充填嵩比重比が９０%を超えると一部に粒子異常成長が発生し易くなり、粒子形状が不均整になり易い。   Further, in the production method of the present invention, when a raw material mixture obtained by adding a mineralizer to an alumina raw material is filled in a firing container and fired, the filling bulk relative to the heavy bulk density (JIS H1902-1977) is increased. It is necessary to fill so that the filling bulk specific gravity ratio expressed as a percentage of the specific gravity (bulk density when filled in the firing container) is 90% or less, preferably 85% or less [lower limit value Is usually up to about 64% depending on the physical properties of the powder, but it should be filled into the firing container in a light bulk specific gravity with many gaps (spaces between particles)], and this filled bulk specific gravity ratio is 90% If it exceeds, abnormal particle growth is likely to occur in part, and the particle shape tends to be uneven.

更に、本発明の製造方法において、焼成炉としては、通常この種のα-アルミナの製造において一般的に用いられるトンネルキルン、シャトルキルン、ローラーハースキルン等の焼成炉を用いることができ、焼成時に鉱化剤が効果的にその作用を発揮するように、好ましくは密閉型焼成容器を用いて焼成できる定置炉であるのがよい。   Furthermore, in the production method of the present invention, a firing furnace such as a tunnel kiln, shuttle kiln, roller hearth kiln or the like generally used in the production of this kind of α-alumina can be used as the firing furnace. In order for the mineralizer to exert its effect effectively, it is preferably a stationary furnace that can be fired using a closed firing vessel.

更にまた、本発明の製造方法において、焼成容器内に充填した原料混合物の焼成条件については、その焼成温度が通常１１００℃以上、好ましくは１１５０℃以上１３００℃以下であり、また、焼成時の焼成温度での保持時間が通常１時間以上、好ましくは３時間以上１０時間以下である。特に、焼成温度については、１１００℃より低いと所望の多面体形状のα-アルミナが得られないという問題が生じ、反対に、１３００℃より高いとＤ／Ｈ比が３．０を超える板状傾向が強くなることと、粒子成長が頭打ちになり、製造コストが増加する等のマイナス要因が大きくなる。   Furthermore, in the production method of the present invention, as for the firing conditions of the raw material mixture filled in the firing container, the firing temperature is usually 1100 ° C. or higher, preferably 1150 ° C. or higher and 1300 ° C. or lower. The holding time at temperature is usually 1 hour or longer, preferably 3 hours or longer and 10 hours or shorter. In particular, when the firing temperature is lower than 1100 ° C., there is a problem that α-alumina having a desired polyhedral shape cannot be obtained, and conversely, when it is higher than 1300 ° C., the D / H ratio exceeds 3.0. , And the negative factors such as the growth of particles and the increase in manufacturing costs become large.

本発明の方法によって得られる多面体形状α-アルミナは、その粒子形状が均整であって８面体以上の球状に近く、所定の平均粒子径を有してその粒度分布が狭く、種々の用途、特に放熱用フィラーや研磨材の用途に好適に用いることができる。 The polyhedral α-alumina obtained by the method of the present invention has a uniform particle shape, is almost a sphere of octahedron or more, has a predetermined average particle diameter and a narrow particle size distribution, and has various applications, particularly It can be suitably used for heat dissipation fillers and abrasives.

また、本発明の多面体形状α-アルミナの製造方法によれば、このように粒子形状が均整であって球状に近く、所定の平均粒子径を有してその粒度分布が狭く、種々の用途、特に放熱用フィラーや研磨材の用途に好適な多面体形状α-アルミナを、工業的に安価に製造することができる。   In addition, according to the method for producing the polyhedral α-alumina of the present invention, the particle shape is uniform and close to spherical, and has a predetermined average particle diameter and a narrow particle size distribution, for various uses. In particular, polyhedral α-alumina suitable for use as a heat dissipation filler or an abrasive can be industrially produced at low cost.

以下、実施例及び比較例に基づいて、本発明の好適な実施の形態を具体的に説明する。   Hereinafter, preferred embodiments of the present invention will be described in detail based on examples and comparative examples.

実施例１〜７及び比較例１〜１１
［アルミナ原料及び鉱化剤］
アルミナ原料及び鉱化剤として、下記の表１に示すものを用いた。 Examples 1-7 and Comparative Examples 1-11
[Alumina raw material and mineralizer]
As the alumina raw material and mineralizer, those shown in Table 1 below were used.

ジェットミル（日本ニューマチック社製型式100SP）を用いてアルミナ原料を粉砕し、表２に示す平均粒子径及びＢＥＴ比表面積を有するアルミナ原料とし、このアルミナ原料に表２に示す割合で鉱化剤を添加し、よく混合して原料混合物を調製し、得られた原料混合物を焼成炉（シリコニット高熱工業社製電気炉、型式ECH-5070S）のムライト質焼成容器（300mm×300mm×10mm）に表２に示す充填嵩比重比で充填し、表２に示す焼成条件で焼成し、次いで放冷後に振動ボールミル（中央化工機社製、型式MB-6）を用いて解砕し、表２に示す性状〔粒子形状（D/H比）、平均粒子径及び粒度分布の傾き〕を有する焼成アルミナ（α-アルミナ）を製造した。   The alumina raw material is pulverized using a jet mill (Nippon Pneumatic Co., Ltd. Model 100SP) to obtain an alumina raw material having an average particle diameter and a BET specific surface area as shown in Table 2, and the mineralizer in the proportion shown in Table 2 in this alumina raw material And mix well to prepare a raw material mixture, and the resulting raw material mixture is displayed in a mullite firing container (300 mm x 300 mm x 10 mm) of a firing furnace (Electric furnace manufactured by Silicone Knit Co., Ltd., model ECH-5070S). 2 is filled at the filling bulk specific gravity ratio shown in FIG. 2, fired under the firing conditions shown in Table 2, and then allowed to cool and then crushed using a vibration ball mill (Chuo Kakoki Co., Ltd., model MB-6). A calcined alumina (α-alumina) having properties [particle shape (D / H ratio), average particle diameter, and gradient of particle size distribution] was produced.

アルミナ原料及び焼成アルミナの平均粒子径はレーザー散乱法粒度測定器（日機装社製Microtrac 9320HRA(×100)）を用いて測定し、また、アルミナ原料のＢＥＴ比表面積は比表面積自動測定装置（Micromeritics社製Flowsorb II 2300）を用いて測定し、アルミナ原料の充填嵩比重比は式（充填嵩比重／重装嵩比重）×１００(%)の値として算出し、焼成アルミナの粒子形状（D/H比）は走査電子顕微鏡（株式会社日立ハイテクノロジーズ製型式S-4700）で撮影したＳＥＭ写真より選出した２０個の粒子の画像解析で求め、また、焼成アルミナの粒度分布の傾きはレーザー散乱法粒度測定器（日機装社製Microtrac 9320HRA(×100)）を用いて測定した累積カーブが８４%となる点の粒径（d84%）と同１６%となる点の粒径（d16%）とから下記式で求められる粒度分布の傾き（ｎ）を求めた。
ｎ＝log[log(100/16)/log(100/84)]／log(d84%/d16%) The average particle size of the alumina raw material and calcined alumina is measured using a laser scattering particle size analyzer (Microtrac 9320HRA (× 100) manufactured by Nikkiso Co., Ltd.). Measured using Flowsorb II 2300), the packing bulk specific gravity ratio of the alumina raw material was calculated as the value of the formula (filling bulk specific gravity / heavy bulk specific gravity) × 100 (%), and the particle shape of the calcined alumina (D / H Ratio) was determined by image analysis of 20 particles selected from SEM photographs taken with a scanning electron microscope (model S-4700, manufactured by Hitachi High-Technologies Corporation). From the particle size (d16%) of the point where the cumulative curve measured using a measuring instrument (Microtrac 9320HRA (× 100) manufactured by Nikkiso Co., Ltd.) is 84% and the particle size (d16%) of 16% is the following. The slope (n) of the particle size distribution calculated by the equation Meta.
n = log [log (100/16) / log (100/84)] / log (d84% / d16%)

結果を表２に示す。なお、粒度分布の傾き（ｎ）は、傾き（ｎ）の値が大きいほど粒度分布が狭くて均一であることを示す。
また、実施例３、５及び７及び比較例１、３、９及び１１で得られた焼成アルミナ（α-アルミナ）について撮影されたＳＥＭ写真をそれぞれ図１〜７に示す。 The results are shown in Table 2. Note that the gradient (n) of the particle size distribution indicates that the larger the value of the gradient (n), the narrower and more uniform the particle size distribution.
Moreover, the SEM photograph image | photographed about the baking alumina ((alpha) -alumina) obtained in Example 3, 5 and 7 and Comparative Examples 1, 3, 9, and 11 is shown in FIGS.

表２及び図１〜７に示す結果から明らかなように、本発明の実施例に係るα-アルミナは、そのいずれも粒子形状がＤ／Ｈ比２〜３又はＤ／Ｈ比１〜２と均整であって８面体以上の球状に近く、０．５〜５μmの範囲内の平均粒子径を有してその粒度分布が粒度分布の傾き３．０以上と狭く、全体に均一でよく整っていることがわかる。これに対して、比較例１〜６のα-アルミナには、粒子の成長不良や一部に粒子の異常成長が認められるほか、比較例７〜１１のα-アルミナには、粒子形状（D/H比）が３を超えたり、不均一である場合があるほか、粒度分布の傾きについても３．０を下回るものが認められる。   As is apparent from the results shown in Table 2 and FIGS. 1 to 7, the α-alumina according to the examples of the present invention has a particle shape of D / H ratio 2-3 or D / H ratio 1-2. It is uniform and close to an octahedral or more spherical shape, has an average particle size in the range of 0.5 to 5 μm, and its particle size distribution is as narrow as the gradient of particle size distribution of 3.0 or more. I understand that. On the other hand, in the α-alumina of Comparative Examples 1 to 6, in addition to defective particle growth and abnormal particle growth in part, the α-alumina of Comparative Examples 7 to 11 has a particle shape (D / H ratio) may exceed 3 or be non-uniform, and the slope of the particle size distribution may be less than 3.0.

本発明の多面体形状α-アルミナは、その粒子形状が均整であって８面体以上の球状に近く、所定の平均粒子径を有してその粒度分布が狭く、種々の用途、特に放熱用フィラーや研磨材の用途に好適に用いることができ、工業的に極めて有用なものである。また、本発明の多面体形状α-アルミナの製造方法は、このような多面体形状α-アルミナを工業的に安価に製造することができる。   The polyhedral α-alumina of the present invention has a uniform particle shape, is nearly octahedral or more spherical, has a predetermined average particle size and a narrow particle size distribution, and has various applications, particularly a heat radiation filler, It can be suitably used for abrasives and is extremely useful industrially. In addition, the method for producing a polyhedral-shaped α-alumina of the present invention can industrially manufacture such a polyhedral-shaped α-alumina at a low cost.

図１は、本発明の実施例３に係る多面体形状α-アルミナのＳＥＭ写真である。FIG. 1 is an SEM photograph of polyhedral α-alumina according to Example 3 of the present invention. 図２は、本発明の実施例５に係る多面体形状α-アルミナのＳＥＭ写真である。FIG. 2 is an SEM photograph of polyhedral α-alumina according to Example 5 of the present invention. 図３は、本発明の実施例７に係る多面体形状α-アルミナのＳＥＭ写真である。FIG. 3 is an SEM photograph of polyhedral α-alumina according to Example 7 of the present invention.

図４は、比較例１に係るα-アルミナのＳＥＭ写真である。FIG. 4 is an SEM photograph of α-alumina according to Comparative Example 1. 図５は、比較例３に係るα-アルミナのＳＥＭ写真である。FIG. 5 is an SEM photograph of α-alumina according to Comparative Example 3. 図６は、比較例９に係るα-アルミナのＳＥＭ写真である。FIG. 6 is an SEM photograph of α-alumina according to Comparative Example 9. 図７は、比較例１１に係るα-アルミナのＳＥＭ写真である。FIG. 7 is an SEM photograph of α-alumina according to Comparative Example 11.

Claims (4)

擬ベーマイト、γアルミナ、及びθアルミナから選ばれた１種又は２種以上の混合物からなるアルミナ原料にフッ素化合物又はフッ素化合物及びホウ素化合物をアルミナ換算基準で０．１〜２．０質量%の範囲で添加し、得られた原料混合物を充填嵩比重比９０%以下で焼成容器に充填し、焼成温度１１００℃以上で焼成することを特徴とする、８面体以上の多面体形状を有して粒度分布の狭い多面体形状α-アルミナの製造方法。 A range of 0.1 to 2.0% by mass of a fluorine compound or a fluorine compound and a boron compound on an alumina basis based on an alumina raw material comprising one or a mixture of two or more selected from pseudoboehmite , γ alumina, and θ alumina In addition, the resulting raw material mixture is filled in a firing container at a filling bulk specific gravity ratio of 90% or less, and fired at a firing temperature of 1100 ° C. or higher, having an octahedral or higher polyhedral shape and a particle size distribution Process for producing a narrow polyhedral α-alumina. アルミナ原料は、ＢＥＴ比表面積が５０m2/g以上である請求項１に記載の多面体形状α−アルミナの製造方法。 The method for producing polyhedral α-alumina according to claim 1 , wherein the alumina raw material has a BET specific surface area of 50 m 2 / g or more. アルミナ原料は、レーザー散乱法で測定された平均粒子径が予め４０μm以下に調整されている請求項１に記載の多面体形状α−アルミナの製造方法。 The method for producing polyhedral α-alumina according to claim 1 , wherein the alumina raw material has an average particle diameter measured by a laser scattering method adjusted in advance to 40 μm or less. 原料混合物の焼成は、原料混合物を密閉型焼成容器に充填して定置炉により行われる請求項１〜３のいずれかに記載の多面体形状α−アルミナの製造方法。The method for producing a polyhedral α-alumina according to any one of claims 1 to 3, wherein the firing of the raw material mixture is performed by a stationary furnace after filling the raw material mixture in a closed firing container.
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