JPH06191835A - Production of alpha-alumina - Google Patents

Abstract

PURPOSE:To obtain a fine and uniform high purity powdery alpha-alumina narrow in particle size distribution and made of an alpha-alumina single crystal particle containing no aggregated particle and having polyhedron shape more than octahedron from an alumina raw material of various kinds, purity, shape, particle size and composition. CONSTITUTION:This powdery alpha-alumina made of alpha-alumina single crystal article is produced by firing a transition alumina and/or an alumina raw material to be the transition alumina by heat treating in an atmospheric gas containing >=1vol.% gaseous hydrogen chloride or in which >=1vol.% gaseous hydrogen chloride and >=0.1vol.% steam are introduced at >=600 deg.C to <=1400 deg.C, preferably >=800 deg.C to <=1200 deg.C. Aluminum hydroxide, alum, alum earth, etc., are used as the alumina raw material to be the transition alumina by heat treating.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing α-alumina.

[0002]

2. Description of the Related Art α-Alumina powder is widely used as an abrasive, a raw material for a sintered body, a plasma spray material, a filler and the like. The α-alumina powder obtained by a conventional general production method has a problem that it is a polycrystalline body having a non-uniform shape, contains many agglomerated particles, has a wide particle size distribution, and has a low alumina purity depending on the application. It was In order to overcome these problems, α-alumina powder has been used in a specific application by a special manufacturing method described later. However, even by such a method, the shape and particle size of α-alumina cannot be arbitrarily controlled, and it has been difficult to produce α-alumina powder having a narrow particle size distribution.

As a special method for producing α-alumina powder, a method of hydrothermal treatment of aluminum hydroxide (hereinafter, referred to as
Known methods include a hydrothermal treatment method), a method of adding flux to aluminum hydroxide to melt and precipitate (hereinafter referred to as a flux method), a method of firing aluminum hydroxide in the presence of a mineralizer, and the like.

First, as a hydrothermal treatment method, Japanese Patent Publication No.
No. 22886 discloses a method of controlling the particle size by adding corundum as a seed crystal, but it is a synthesis under high temperature and high pressure, and there is a problem that the obtained α-alumina powder becomes expensive. . According to the research by Matsui et al. (Hydrothermal reaction, Volume 2, pages 71 to 78: Growth of alumina single crystal by hydrothermal method), hydrothermal growth method (hydrothermal treatment method)
Therefore, cracks are present in the α-alumina single crystal obtained by growing the chromium-containing alumina single crystal on the sapphire (α-alumina) seed crystal. In order to clarify the cause, we investigated the internal uniformity of the crystal and found that there was a large strain at the boundary between the seed crystal and the grown crystal, and the etch pit density was considered to correspond to the dislocation density in the grown crystal near the boundary. It is also confirmed that the cracks are related to such strains and defects, and in the case of the hydrothermal growth method, OH groups and water are likely to be contained in the crystal, which may cause the strains and defects. It is supposed to be.

Next, the flux method has been proposed as a method of controlling the shape and particle size of α-alumina powder for the purpose of using it as an abrasive, a filler and the like. For example, JP-A-3-
No. 131517 discloses that hexagonal α-alumina hexagons having a hexagonal close-packed lattice having an average particle diameter of 2 to 20 μm by calcining aluminum hydroxide in the presence of a fluorine-based flux having a melting point of 800 ° C. or less. Let D be the maximum particle size parallel to the lattice plane and H be the particle size perpendicular to the hexagonal lattice plane.
A method for producing hexagonal plate-shaped α-alumina particles having a / H ratio of 5 to 40 is disclosed. However, with this method, a fine α-alumina powder having a particle size of 2 μm or less cannot be formed, and the shape is all plate-like, and it is impossible to arbitrarily control the shape and particle size. Further, the obtained α-alumina powder was not always sufficient for use as an abrasive, a filler, a raw material for a single crystal and the like.

The most common and cheapest method for producing α-alumina powder is the Bayer method. In the Bayer method, aluminum hydroxide or transition alumina is obtained in the intermediate step of producing α-alumina powder from the raw material bauxite. The α-alumina powder is produced by firing aluminum hydroxide or transition alumina in the atmosphere.

Aluminum hydroxide or transition alumina which is industrially inexpensively obtained in the intermediate stage is usually agglomerated particles having a particle size of more than 10 μm, and these aluminum hydroxide or transition alumina can be obtained by firing in the air. The obtained conventional α-alumina powder was an irregularly-shaped powder containing agglomerated coarse particles. This α-alumina powder containing agglomerated coarse particles is made into a product through a crushing process using a ball mill or a vibration mill according to each application, but crushing is not always easy, and therefore crushing is not necessary. A costly and difficult to disintegrate an α-alumina powder, which causes disintegration of fine powder and inclusion of foreign substances due to long-term disintegration, and becomes an α-alumina powder particularly unsuitable as an abrasive. Had.

Several proposals have been made to solve such problems. For example, as a method for improving the shape of α-alumina particles, JP-A-59-97528 discloses that aluminum hydroxide by Bayer method is used as a raw material and boron containing ammonium and a boron-based mineralizer are used. By calcination, the average particle size is 1 to 10 μm
And a method for producing an α-alumina powder having a D / H ratio close to 1 is disclosed. However, this method has the drawback that the boron- or fluorine-containing substance added as a mineralizer remains in the α-alumina and forms aggregates during firing.

Further, when calcining the sodium-containing aluminum hydroxide obtained by the Bayer method, it is possible to efficiently remove sodium and at the same time, to control the particle size, fluorides such as aluminum fluoride and cryolite, and The method of calcination in the presence of a chlorine-containing compound such as chlorine and hydrogen chloride is British Patent No. 990801, and the method of calcination in the presence of boric acid and ammonium chloride, hydrochloric acid or aluminum chloride is West German Patent No. 1767
No. 511, respectively. However, in the former method, a mineralizer such as aluminum fluoride is mixed in a solid state, or chlorine and fluorine gas are supplied without adding water and fired, so that the generated alumina particles have a non-uniform shape. There was a quality problem such as a wide particle size distribution of the powder. In the latter method, boric acid added as a mineralizer remains in α-alumina as a boron-containing substance.
Further, since these methods are mainly aimed at sodium removal, sodium produced by reaction with sodium
There is a disadvantage that the sodium salt such as aCl or Na ₂ SO ₄ has to be fired at a high temperature of 1200 ° C. or higher in order to sublime or decompose it.

Regarding the reaction between alumina and hydrogen chloride gas, a study on the reaction equilibrium constant between α-alumina sintered with a particle size of 2 to 3 mm and hydrogen chloride and aluminum chloride as a product is described by Zeitschrift Furet. An Organiche und Argemeine Chemie (Zeit.
fur Anorg. und Allg. Chem. )
209, 21 (1932). In this report, α-alumina is generated in a place different from the place where the raw material is placed, but only hexagonal plate-shaped ones are obtained.

Japanese Examined Patent Publication (Kokoku) No. 43-8929 discloses a method for producing alumina containing a small amount of impurities and having an average particle size of 10 μm or less by calcining alumina hydrate together with ammonium chloride. However, the alumina powder obtained by this method had a wide particle size distribution. Therefore, until now, no single crystal particles of α-alumina have been obtained which are sufficiently satisfactory in terms of the purity and the homogeneity of the structure within the particles.

[0012]

Therefore, an object of the present invention is to solve the above-mentioned problems and to start from various alumina raw materials, and to obtain a powdery form of homogeneous α-alumina single crystal particles which are not agglomerated particles. Of α-alumina. In particular, it has a polyhedron shape of octahedron or more, D / H of 0.5 or more and 3.0 or less, narrow particle size distribution, high alumina purity, uniform composition in particles, and structurally homogeneous. Na α
-To provide powdery α-alumina composed of alumina single crystal particles.

[0013]

The present invention comprises the following inventions. (1) Transition alumina and / or alumina raw material which becomes transition alumina by heat treatment, hydrogen chloride gas at 1% by volume
A method for producing α-alumina, which comprises firing at 600 ° C. or higher in an atmosphere gas containing the above. (2) A transition alumina and / or an alumina raw material which becomes a transition alumina by heat treatment is introduced at a temperature of 600 ° C. or higher by introducing 1 volume% or more of chlorine gas and 0.1 volume% or more of steam into an atmosphere gas. A method for producing α-alumina, comprising:

(3) The firing temperature is 600 ° C. or higher and 1400
The method for producing α-alumina according to item (1) or (2), which has a temperature of at most 0 ° C. (4) The method for producing α-alumina according to item (1) or (2), wherein the firing temperature is 800 ° C or higher and 1200 ° C or lower. (5) The method for producing α-alumina according to the item (1), (2) or (3), characterized in that aluminum hydroxide is used as an alumina raw material which becomes transition alumina by heat treatment. (6) The method for producing α-alumina according to item (1), (2), or (3), characterized in that light vane or vanadium sulphate is used as an alumina raw material to be transition alumina by heat treatment.

(7) The transition alumina and / or the alumina raw material which becomes the transition alumina by heat treatment is heated to 600 ° C. in an atmosphere gas containing hydrogen chloride gas in an amount of 1% by volume or more.
It is fired at 1400 ° C. or less, has a uniform, polyhedral shape with 8 or more faces, and has a maximum particle diameter D parallel to the hexagonal lattice plane of α-alumina, which is a hexagonal close-packed lattice, and is perpendicular to the hexagonal lattice plane. A method for producing α-alumina, characterized in that powdery α-alumina composed of α-alumina single crystal particles having a D / H of 0.5 or more and 3.0 or less, where H is the particle diameter. (8) At 600 ° C. or higher and 1400 ° C. or lower, by introducing 1 vol% or more of chlorine gas and 0.1 vol% or more of steam into the atmosphere gas, the transition alumina and / or the alumina raw material to be transition alumina by heat treatment are introduced. It is calcined and has a polyhedral shape of 8 or more faces that is homogeneous and has a maximum particle diameter D parallel to the hexagonal lattice surface of α-alumina, which is a hexagonal close-packed lattice, and a particle diameter H perpendicular to the hexagonal lattice surface. When D / H is 0.
A method for producing α-alumina, which comprises obtaining powdery α-alumina consisting of α-alumina single crystal particles having a particle size of 5 or more and 3.0 or less.

(9) The method for producing α-alumina comprising α-alumina single crystal particles according to item (7) or (8), which has a polyhedral shape with 10 or more faces. (10) The number average particle diameter of α-alumina single crystal particles is 0.1.
If the particle size is 30 μm or more and 30 μm or less, the particle size of 10% cumulative and 90% cumulative from the fine particle side of the cumulative particle size distribution are D10 and D90, respectively.
The method for producing α-alumina according to item (7) or (8), which has a particle size distribution in which D90 / D10 is 10 or less. (11) The method for producing α-alumina according to item (7) or (8), wherein the alumina purity is 99.90% by weight or more.

The present invention will be described in detail below. In the production of α-alumina of the present invention, transition alumina or an alumina raw material which becomes a transition alumina by heat treatment is used as a raw material. By transitional alumina is meant all of the alumina having the polymorphic form represented by Al ₂ O ₃ except the α form. Specific examples include γ-alumina, δ-alumina, and θ-alumina.

The alumina raw material which becomes the transition alumina by the heat treatment means a transition alumina precursor which gives the desired powdery α-alumina via the transition alumina in the firing step of the production method of the present invention. In particular,
Aluminum hydroxide; van sulphate (aluminum sulphate); so-called light vanes such as potassium aluminum sulphate and aluminum ammonium sulphate; ammonium aluminum carbonate, as well as alumina gels such as alumina gels produced by the underwater discharge method of aluminum. it can.

The method of synthesizing the transition alumina and the alumina raw material which becomes the transition alumina by heat treatment is not particularly limited. For example, aluminum hydroxide is Bayer method, organoaluminum compound (aluminum isopropoxide, etc.)
Can be obtained by the hydrolysis method described above or a method of synthesizing an aluminum compound obtained from an etching waste liquid such as a capacitor as a starting material.

According to the method of the present invention, aluminum hydroxide or transition alumina having a particle size of 10 μm or more obtained by an industrially inexpensive method such as the Bayer method is used as a raw material, and the target powdery α -Alumina can be obtained. The transition alumina can be obtained by a method of heat-treating aluminum hydroxide, a method of decomposing aluminum sulfate, a method of decomposing vanadium, a method of decomposing aluminum chloride or a method of decomposing ammonium ammonium carbonate.

In the present invention, the transition alumina or the alumina raw material which becomes the transition alumina by the heat treatment is
Firing is performed in an atmosphere gas of hydrogen chloride gas of 1 vol% or more, preferably 5 vol% or more, more preferably 10 vol% or more with respect to the total volume of the atmosphere gas. An inert gas such as nitrogen, hydrogen, or argon, and air can be used as a diluent gas for hydrogen chloride gas, which is an atmospheric gas. The pressure of the atmosphere gas containing hydrogen chloride gas is not particularly limited, and can be arbitrarily selected within the industrially used range. By firing in such an atmosphere gas, the target powdery α-alumina can be obtained at a relatively low firing temperature as described later.

Instead of hydrogen chloride gas, a mixed gas of chlorine gas and water vapor may be used. In an atmosphere gas in which chlorine gas and water vapor are introduced into transition alumina or an alumina raw material to be transition alumina by heat treatment, chlorine gas is 1 volume% or more, preferably 5 volume% or more, and more preferably 10 volume% with respect to the total volume of the atmosphere gas. Volume% or more and steam 0.1 volume% or more, preferably 1 volume% or more, more preferably 5 volume% or more are introduced and fired. An inert gas such as nitrogen, hydrogen, or argon, and air can be used as the chlorine gas and the dilution gas of the steam to be introduced. The pressure of the atmosphere gas containing chlorine gas and water vapor is not particularly limited, and can be arbitrarily selected within a range industrially used. By firing in such an atmosphere gas, the target powdery α-alumina can be obtained at a relatively low firing temperature as described later.

The firing temperature is 600 ° C. or higher, preferably 60.
0 ° C or more and 1400 ° C or less, more preferably 700 ° C or more and 1300 ° C or less, further preferably 800 ° C or more and 120
It is 0 ° C or lower. By controlling and firing in this temperature range, at a production rate that is industrially advantageous, aggregation of α-alumina particles to be produced is unlikely to occur, and powder consisting of α-alumina single crystal particles having a narrow particle size distribution immediately after firing. A
-Alumina can be obtained. When the particle diameter of the transition alumina used as a raw material or the alumina raw material which becomes the transition alumina by heat treatment is large, for example, when the average particle diameter of the agglomerated particles exceeds 10 μm,
The firing temperature is preferably relatively high, particularly preferably 800 ° C. or higher.

The appropriate firing time depends on the concentration of the atmospheric gas and the firing temperature and is not limited, but is preferably 1 minute or longer, more preferably 10 minutes or longer.
It is sufficient to calcine until the alumina raw material crystallizes into α-alumina. According to the production method of the present invention, the target powdery α
-Alumina can be obtained.

The supply source and supply method of the atmospheric gas are not particularly limited. It is sufficient that the above-mentioned atmosphere gas can be introduced into the reaction system in which the raw material such as transition alumina exists. For example, although cylinder gas can usually be used as a supply source, when a chlorine compound such as a hydrochloric acid solution or ammonium chloride or a chlorine-containing polymer compound is used as a raw material such as hydrogen chloride gas, the vapor pressure or It can also be used by being decomposed into the above-mentioned predetermined gas composition. When a decomposition gas such as ammonium chloride is used, solid substances may be deposited in the firing furnace to impair operation, and the higher the hydrogen chloride gas concentration, the lower the temperature, the shorter the firing time, and Since it becomes possible to obtain high-purity alumina, it is preferable to supply hydrogen chloride or chlorine directly into the firing furnace from a cylinder or the like. As a gas supply method, either a continuous method or a batch method can be used.

The firing apparatus is not necessarily limited, and a so-called firing furnace can be used. The firing furnace is hydrogen chloride gas,
It is desirable that it is made of a material that is not corroded by chlorine gas or the like, and further that it is desirable to have a mechanism that can adjust the atmosphere. Further, since an acid gas such as hydrogen chloride gas or chlorine gas is used, it is preferable that the firing furnace be airtight. Industrially, it is preferable to carry out firing in a continuous manner, and for example, a tunnel furnace, a rotary kiln or a pusher furnace can be used. As the material of the apparatus used in the manufacturing process, it is desirable to use a crucible or boat made of alumina, quartz, acid-resistant brick or graphite, since the reaction proceeds in an acidic atmosphere.

According to the above manufacturing method, α- which is not agglomerated particles
Alumina can be obtained. Depending on the raw material used or production conditions, it may be agglomerated particles or may contain agglomerated particles, but even in that case, agglomeration is mild, and by simple crushing, it is not easily agglomerated particles α- Alumina can be produced.

[0028]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

Various measurements in the present invention were carried out as follows. 1. Measurement of number average particle size and particle size distribution of α-alumina (1) The (D90 / D10) value was measured using Mastersizer (manufactured by Malvern Instruments Ltd.) whose measurement principle is a laser scattering method. (2) An SEM (scanning electron microscope, manufactured by JEOL Ltd .: T-300) photograph of α-alumina is taken, 80 to 100 particles are selected from the photograph and image analysis is performed, and the average circle equivalent diameter is averaged. The value and its distribution were obtained. The equivalent circle diameter is a value converted into the diameter of a perfect circle having the same area.

2. Measurement of Crystal Shape (D / H) of α-Alumina In the present invention, the shape of α-alumina means the maximum particle diameter parallel to the hexagonal lattice plane of α-alumina, which is a hexagonal close-packed lattice, and D is the hexagonal lattice plane. D / H when the vertical particle size is H
Says the ratio. (D / H) is a SEM (scanning electron microscope, manufactured by JEOL Ltd .: T-300) photograph of α-alumina, 5 to 10 particles are selected from the photograph, and image analysis is performed. It was calculated as an average value.

3. Evaluation of number of crystal planes and crystal habit (1) Number of crystal planes SEM (scanning electron microscope, manufactured by JEOL Ltd .: T-300) photographs of α-alumina were taken and determined by image analysis of the photographs. (2) Evaluation of Crystal Habit In addition, the crystal habit of the crystal was observed as an evaluation of the shape of the α-alumina particles in the present invention. The crystal habit (represented by A to I) of the α-alumina particles obtained by the present invention is shown in FIG. α-alumina is a hexagonal crystal, and the crystal habit is a-plane {1
It refers to the crystal morphology characterized by the appearance of crystal planes consisting of 120}, c-plane {0001}, n-plane {2243} and r-plane {1012}. Crystal planes a, c, n and r are shown in FIG.

4. Measurement of Alumina Purity The amount of impurity ions mixed was measured by optical emission analysis, and the content of impurities was calculated in terms of oxide. The chlorine content was determined by potentiometric titration. The total amount (% by weight) of the content of impurities thus obtained was subtracted from 100% by weight to obtain the alumina purity. 5. Measurement of Na ₂ O The amount of sodium ions mixed in was measured by optical emission analysis and calculated in terms of oxide.

The raw materials such as transition alumina used in the examples are as follows. 1. Transition Alumina A Transition alumina obtained by firing aluminum hydroxide obtained by the hydrolysis method of aluminum isopropoxide (trade name:
AKP-G15, manufactured by Sumitomo Chemical Co., Ltd., particle size: about 4μ
m)

2. Transition Alumina B Transition Alumina by Meitan method (trade name: CR125, manufactured by Baikowski, particle size: about 4 μm) 3. Transition Alumina C Aluminum hydroxide C is calcined in air at 800 ° C. to obtain transition alumina, secondary particle size: about 30 μm

4. Aluminum hydroxide A powder obtained by hydrolysis of aluminum isopropoxide, secondary particle size: about 8 μm 5. Aluminum hydroxide B Powder by Bayer method (trade name: C301, manufactured by Sumitomo Chemical Co., Ltd., secondary particle size: about 2 μm) 6. Aluminum hydroxide C Powder by the Bayer method (trade name: C12, manufactured by Sumitomo Chemical Co., Ltd., secondary particle size: about 47 μm)

7. Mingbang [AlNH ₄ (SO ₄ ) / 12H ₂ O] Alumina raw material that becomes transition alumina by heat treatment. A reagent manufactured by Wako Pure Chemical Industries, Ltd. was used. 8. Bun Sulfur [Al ₂ (SO ₄ ) ₃ / 16H ₂ O] Alumina raw material that becomes transition alumina by heat treatment. A van sulphate manufactured by Sumitomo Chemical Co., Ltd. was used.

As the hydrogen chloride gas, a cylinder hydrogen chloride gas (purity 99.9%) manufactured by Tsurumi Soda Co., Ltd. and a decomposition gas of ammonium chloride were used. When using decomposition gas of ammonium chloride, ammonium chloride is sublimed at a sublimation temperature of 300.
The atmosphere was adjusted by introducing hydrogen chloride gas obtained by heating to 0 ° C. into the furnace core tube. Ammonium chloride was completely decomposed at a holding temperature of 1100 ° C., and the atmosphere was 33% by volume of hydrogen chloride gas, 17% by volume of nitrogen gas, and 50% by volume of hydrogen gas, respectively. As the chlorine gas, cylinder chlorine gas (purity 99.4%) manufactured by Fujimoto Sangyo Co., Ltd. was used. The volume% of water vapor was controlled by changing the saturated water vapor pressure with the temperature of water, and was introduced into the furnace by nitrogen gas.

An alumina raw material such as transition alumina or aluminum hydroxide was filled in an alumina boat. The filling amount was 0.4 g and the filling depth was 5 mm. The firing was carried out in a tubular furnace (DSPSH-28 manufactured by Motoyama Co., Ltd.) using a quartz furnace core tube (diameter 27 mm, length 1000 mm).
While circulating the nitrogen gas, the temperature was raised at a temperature rising rate of 500 ° C./hour, and the atmosphere gas was introduced when the atmosphere introduction temperature was reached.

The atmospheric gas concentration was adjusted by adjusting the gas flow rate with a flow meter. The flow rate of the atmospheric gas was adjusted so that the linear flow rate was 20 mm / min. This method will be referred to as a gas flow method. However, Example 5 and Comparative Example 1
Regarding the above, since the concentration of hydrogen chloride gas was low, the atmosphere gas was stopped after the introduction of the atmosphere gas instead of the above-described gas flow type firing. The total pressure of the atmospheric gas was all atmospheric pressure.

After reaching the predetermined temperature, the temperature was maintained for the predetermined time. This is the holding temperature (firing temperature)
And retention time (firing time). After the lapse of a predetermined holding time, the product was naturally cooled to obtain the desired powdery α-alumina. The partial pressure of water vapor was controlled by changing the saturated water vapor pressure with the temperature of water, and the water vapor was introduced into the firing furnace by nitrogen gas.

Examples 1 to 5 are examples in which transition alumina (γ-alumina) is used as the alumina raw material and the hydrogen chloride gas concentration in the atmosphere gas is changed. The introduction temperature of the atmospheric gas was 20 ° C. and the holding temperature was 1100 ° C. The holding time was changed according to the hydrogen chloride gas concentration. The experimental conditions and the experimental results are shown in Tables 1 and 2. A SEM photograph of the powdery α-alumina obtained in Example 1 is shown in FIG. The SEM photograph of the powdery α-alumina obtained in Example 2 is shown in FIG. 2, and the particle size distribution is shown in FIG.

Example 6 In Example 1, the holding temperature (firing temperature) and the holding time (firing time) were changed. The experimental conditions and the experimental results are shown in Tables 1 and 2.

Examples 7 and 8 In Example 1, the atmosphere gas introduction temperature and the holding time (firing time) were changed. The experimental conditions and the experimental results are shown in Tables 1 and 2.

Examples 9 to 15 Various alumina raw materials were used. In Examples 9 to 12, a decomposition gas of ammonium chloride as a hydrogen chloride gas was introduced into the reaction system as an atmospheric gas and used. The experimental conditions and the experimental results are shown in Tables 1 and 2.

[0045]

[Table 1]

[0046]

[Table 2]

Examples 16 to 18 As the aluminum hydroxide, a powder (aluminum hydroxide C) obtained by the Bayer method having a large particle size was used. The experimental conditions and the experimental results are shown in Tables 3 and 4. The SEM photograph of the powdery α-alumina obtained in Example 16 is shown in FIG. Example 19 As the transition alumina, transition alumina C obtained by firing aluminum hydroxide powder (aluminum hydroxide C) having a large particle size by the Bayer method was used. The experimental conditions and the experimental results are shown in Tables 3 and 4.

Examples 20 and 21 Examples in which chlorine gas and water vapor were introduced into the atmosphere gas. The experimental conditions and the experimental results are shown in Tables 3 and 4. SE of powdery α-alumina obtained in Example 20
The M photograph is shown in FIG.

Comparative Examples 1 to 5 Atmospheric gas and holding temperature (firing temperature) were outside the range of the present invention. The experimental conditions and the experimental results are shown in Tables 3 and 4. The powdery α-obtained in Comparative Examples 1 and 5
SEM photographs of alumina are shown in FIGS. 6 and 7, respectively.

[0050]

[Table 3]

[0051]

[Table 4]

The α-alumina single crystal particles having a narrow particle size distribution, not the agglomerated particles obtained as described above, are used.
-Alumina is suitable as an abrasive, a raw material for a sintered body, a plasma spray material, a filler, a raw material for a single crystal, a raw material for a catalyst carrier, a raw material for a phosphor, a raw material for a sealing material, a raw material for a ceramic filter, etc. It is extremely useful industrially. In particular, according to the method of the present invention, high-purity α-alumina can be obtained. Therefore, yttrium aluminum garnet (YAG), sapphire, ruby and other single crystal raw materials and high-purity sintered bodies, which cannot be applied to low-purity products, can be obtained. It can be used as a raw material. Further, the fine particles of α-alumina obtained by the method of the present invention are suitable for precision abrasives, raw materials for sintered bodies and raw materials for ceramic filters.

[0053]

Industrial Applicability According to the method for producing α-alumina of the present invention, alumina raw materials of various types, purities, shapes, particle sizes and compositions are highly purified and fine with a certain level or more of alumina purity. It is possible to obtain α-alumina composed of α-alumina single crystal particles having a uniform, narrow particle size distribution and a polyhedral shape of octahedron or more that is not agglomerated particles. Specifically, the α-alumina particles obtained by the method of the present invention have an average particle size of 0.1 μm or more and 30 μm or less, a D / H ratio of 0.5 or more and 3.0 or less, and a particle size distribution of D90 / D1 when the particle size of cumulative 10% and cumulative 90% from the fine particle side of the cumulative particle size distribution is D10 and D90, respectively.
0 ratio is 10 or less, preferably 9 or less, particularly preferably 7
It has the excellent characteristics that the alumina purity is 99.90% by weight or more, and the sodium content is less than 0.05% by weight in terms of Na ₂ 0, which is high purity.

[Brief description of drawings]

1 shows the particle structure of α-alumina observed in Example 1. FIG. A photo that replaces the drawing. Scanning electron micrograph at 930 times magnification.

FIG. 2 shows the particle structure of α-alumina observed in Example 2. A photo that replaces the drawing. Scanning electron micrograph at 930 times magnification.

FIG. 3 shows a particle size distribution of α-alumina of Example 2.

FIG. 4 shows the particle structure of α-alumina observed in Example 16. A photo that replaces the drawing. Scanning electron micrograph at 1900x magnification.

FIG. 5 shows the particle structure of α-alumina observed in Example 20. A photo that replaces the drawing. Scanning electron micrograph at 930 times magnification.

FIG. 6 shows the particle structure of α-alumina observed in Comparative Example 1. A photo that replaces the drawing. Scanning electron micrograph at 930 times magnification.

FIG. 7 shows the particle structure of α-alumina observed in Comparative Example 5. A photo that replaces the drawing. Scanning electron micrograph at 1900x magnification.

FIG. 8 shows the crystal habit of α-alumina single crystal particles.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Watanabe 6 Kitahara, Tsukuba-shi, Ibaraki Sumitomo Chemical Co., Ltd.

Claims (11)

[Claims] 1. A transition alumina and / or an alumina raw material which becomes a transition alumina by heat treatment, and hydrogen chloride gas
A method for producing α-alumina, which comprises firing at 600 ° C. or higher in an atmosphere gas containing at least vol%. 2. A transition alumina and / or an alumina raw material which becomes a transition alumina by heat treatment is introduced at a temperature of 600 ° C. or higher by introducing chlorine gas of 1 volume% or more and steam of 0.1 volume% or more into an atmosphere gas. A method for producing α-alumina, comprising: 3. The method for producing α-alumina according to claim 1, wherein the firing temperature is 600 ° C. or higher and 1400 ° C. or lower. 4. The method for producing α-alumina according to claim 1, wherein the firing temperature is 800 ° C. or higher and 1200 ° C. or lower. 5. The method for producing α-alumina according to claim 1, 2 or 3, wherein aluminum hydroxide is used as an alumina raw material which becomes a transition alumina by heat treatment. 6. A method for producing α-alumina according to claim 1, 2 or 3, characterized in that bright ban or sulfur sulphate is used as an alumina raw material which becomes transition alumina by heat treatment. 7. A transition alumina and / or an alumina raw material which becomes a transition alumina by heat treatment, and hydrogen chloride gas is added to 1
600 ℃ or more in the atmosphere gas containing more than 1% by volume
Particles that are fired at 400 ° C. or less, have a uniform, polyhedral shape with eight or more faces, and have a maximum particle diameter D parallel to the hexagonal lattice surface of α-alumina, which is a hexagonal close-packed lattice, and a particle perpendicular to the hexagonal lattice surface. A method for producing α-alumina, characterized in that powdery α-alumina composed of α-alumina single crystal particles having D / H of 0.5 or more and 3.0 or less, where H is the diameter. 8. A transition alumina and / or an alumina raw material which becomes a transition alumina by heat treatment by introducing chlorine gas in an amount of 1 volume% or more and steam in an amount of 0.1 volume% or more to 600 ° C. or more and 1400 ° C. Bake below,
D is the maximum particle diameter that is homogeneous and has a polyhedral shape of eight or more faces and that is parallel to the hexagonal lattice surface of α-alumina, which is a hexagonal close-packed lattice, and H is the particle diameter perpendicular to the hexagonal lattice surface. / H
The method for producing α-alumina is characterized in that powdery α-alumina consisting of α-alumina single crystal particles having a ratio of 0.5 to 3.0 is obtained. 9. The method for producing α-alumina comprising α-alumina single crystal particles according to claim 7, which has a polyhedral shape having 10 or more faces. 10. An α-alumina single crystal particle having a number average particle size of 0.1 μm or more and 30 μm or less and a cumulative particle size distribution of 10% cumulative and 90% cumulative from the fine particle side, respectively.
The method for producing α-alumina according to claim 7 or 8, wherein D90 / D10 has a particle size distribution of 10 or less. 11. The method for producing α-alumina according to claim 7, wherein the purity of alumina is 99.90% by weight or more.