JP3440498B2 - α-alumina - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to 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 the obtained α-alumina powder is used as an abrasive, a filler, and a raw material for a single crystal. It was not always sufficient for such purposes.

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.

Furthermore, when calcination of sodium-containing aluminum hydroxide obtained by the Bayer method, sodium is efficiently removed, and at the same time, a method for controlling the particle size, such as aluminum fluoride and fluoride such as cryolite, and British Patent No. 990801 discloses a method of calcination in the presence of chlorine-containing compounds such as chlorine and hydrogen chloride, and West German Patent discloses a method of calcination in the presence of boric acid and ammonium chloride, hydrochloric acid or aluminum chloride. 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, the research on the reaction equilibrium constant between α-alumina sintered with a particle size of 2 to 3 mm and hydrogen chloride and aluminum chloride of the product is 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 Patent Publication 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.

[0010]

Therefore, the object of the present invention is to solve the above-mentioned problems and to start from various alumina raw materials, and to obtain a high-purity homogeneous α-alumina single crystal particle which is not agglomerated particles. To provide a powdered α-alumina. In particular, it has the shape of an octahedron or higher polyhedron,
D / H is 0.5 or more and 3.0 or less, and number average particle diameter is 5 μm
Is 30 μm or less, the particle size distribution is narrow, the alumina purity is high, the composition within the particles is uniform, and the α-alumina single crystal particles having uniform structure and no distortion are homogeneous. To provide.

[0011]

The present invention comprises the following inventions. (1) It has a polyhedron shape that is homogenous, has no crystal seeds inside, and has eight 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 a hexagonal lattice plane. When the vertical particle diameter is H, it is composed of α-alumina single crystal particles having a D / H ratio of 0.5 or more and 3.0 or less, and the number average particle diameter of the α-alumina single crystal particles exceeds 5 μm. Is 30 μm or less, and the sodium content is 0.0 in terms of Na ₂ O.
It is less than 5% by weight, and the purity of alumina is 99.90% by weight.
The above is the α-alumina. (2) From the fine particle side of the cumulative particle size distribution of α-alumina single crystal particles, a cumulative particle size of 10% and a cumulative particle size of 90% are D10 and
The α-alumina according to the item (1), which has a particle size distribution in which D90 / D10 is 10 or less when D90. (3) The α-alumina according to item (1) or (2), which has an alumina purity of 99.95% by weight or more. (4) The α-alumina according to item (1), (2) or (3), which is used as a raw material for a single crystal. (5) The α-alumina according to item (1), (2) or (3), which is used as a raw material for a high-purity sintered body.

The present invention will be described in detail below. The α-alumina of the present invention is manufactured by using transition alumina as a raw material or an alumina raw material which becomes transition alumina by heat treatment. By transitional alumina is meant all of the alumina having the polymorphic form represented by Al ₂ O ₃ except the α form. Specifically, γ-alumina, δ-alumina, θ-alumina and the like can be exemplified.

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. Specifically, aluminum hydroxide; van sulphate (aluminum sulphate); so-called light vans such as potassium aluminum sulphate and aluminum ammonium sulphate; ammonium aluminum carbonate as well as alumina gels, for example alumina gels produced by the underwater discharge method of aluminum. Etc. can be mentioned.

The method for 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.

The transition alumina can be obtained by a method of heat treating aluminum hydroxide, a decomposition method of aluminum sulfate, a light van decomposition method, a vapor phase decomposition method of aluminum chloride or a decomposition method of ammonium aluminum carbonate.

An atmosphere in which the above transition alumina or an alumina raw material which becomes transition alumina by heat treatment is hydrogen chloride gas in an amount of 1% by volume or more, preferably 5% by volume or more, more preferably 10% by volume or more based on the total volume of the atmosphere gas. Bake in 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 steam can 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.

The appropriate firing time depends on the concentration of the atmospheric gas and the firing temperature and is not necessarily 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. The desired α-alumina can be obtained in a shorter time than the firing time of the conventional method.

The source and method of supplying 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 for chlorine gas or the like, their vapor pressure or decomposition It is also possible to use it so that it has the above-mentioned predetermined gas composition. When using decomposition gas such as ammonium chloride,
Operational problems may occur due to the precipitation of solid substances in the firing furnace, and the higher the hydrogen chloride gas concentration, the lower the temperature, the shorter the firing time, and the more highly pure alumina can be obtained. Therefore, 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.

The number average particle diameter of the present invention exceeds 5 μm and is 30.
In order to obtain α-alumina having an alumina purity of not more than 99 μm and a purity of 99.90 wt% or more, the content of impurities of alumina raw materials having the alumina purity of 99.9 wt% or more is as small as possible. It is desirable to select raw materials. Particularly preferred examples are aluminum hydroxide powder obtained by the hydrolysis method of aluminum isopropoxide or transition alumina obtained by firing the aluminum hydroxide powder thus obtained.

[0023]

EXAMPLES Next, the present invention will be described in more detail by way of 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) (D90 / D10) value was measured using Mastersizer (manufactured by Malvern Instruments Ltd.) having a laser scattering method as a measurement principle. (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 Faces and Crystal Habit (1) Number of Crystal Faces SEM (scanning electron microscope, manufactured by JEOL Ltd .: T-300) photograph of α-alumina was taken and determined by image analysis of the photograph. (2) Evaluation of Crystal Habit Further, as an evaluation of the shape of the α-alumina particles in the present invention, the crystal habit of the crystal was observed. 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 mixed amount of impurity ions was measured by optical emission analysis, and the impurities were calculated as oxides. The chlorine content was determined by potentiometric titration. The impurity content (wt%) thus obtained was subtracted from 100 wt% to obtain the alumina purity. 5. Measurement of Na ₂ O The amount of sodium ions mixed in was measured by emission analysis and converted into 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., secondary particle size: about 4 μm) 1. Aluminum hydroxide A A powder obtained by synthesizing aluminum isopropoxide by hydrolysis, and has a secondary particle size of about 8 μm. 3. Aluminum hydroxide C Powder by the Bayer method (trade name: C12, manufactured by Sumitomo Chemical Co., Ltd., secondary particle size: about 47 μm)

As the hydrogen chloride gas, a cylinder hydrogen chloride gas (purity 99.9%) manufactured by Tsurumi Soda Co., Ltd. was used. Chlorine gas is cylinder chlorine gas (purity 99.4 made 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 atmosphere 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, in Comparative Example 1, since the hydrogen chloride gas concentration was low, the atmosphere gas was stopped after the introduction of the atmosphere gas instead of the above gas flow method 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 aluminum hydroxide and transition alumina (γ-alumina) are used as alumina raw materials and hydrogen chloride gas is used as atmosphere gas. Firing temperature (holding temperature)
Was 1100 ° C or 800 ° C. The experimental conditions and the experimental results are shown in Tables 1 and 2. Examples 1 and 2
1 and 2 are SEM photographs of the powdery α-alumina obtained in Example 2, and FIG. 3 is a particle size distribution of the powdery α-alumina obtained in Example 2.

Example 4 Instead of hydrogen chloride gas as an atmosphere gas, chlorine gas 35 was used.
The transitional alumina was calcined using vol%, steam 5 vol% and nitrogen gas 60 vol%. It is a high-purity α-alumina equivalent to that obtained in Example 1. The experimental conditions and the experimental results are shown in Tables 1 and 2.

Comparative Examples 1 to 3 Alumina raw materials were fired by a conventional firing method and a method of firing in an atmosphere gas having a low hydrogen chloride gas concentration.
The experimental conditions and the experimental results are shown in Tables 1 and 2. SE of powdery α-alumina obtained in Comparative Examples 1 and 2
The M photographs are shown in FIGS. 4 and 5, respectively.

[0036]

[Table 1]

[0037]

[Table 2]

The α-alumina, which is not the agglomerated particles obtained as described above, is composed of α-alumina single crystal particles having high alumina purity, structural homogeneity and a narrow particle size distribution. It is suitable as a raw material for binders, plasma spraying materials, fillers, raw material for single crystals, raw material for catalyst carriers, raw material for phosphors, raw material for sealing materials, raw material for ceramic filters, etc. Is. In particular, since the α-alumina of the present invention has an extremely high purity, yttrium aluminum garnet (Y
AG), sapphire, ruby, and other single crystal raw materials and high-purity sintered body raw materials.

[0039]

The α-alumina of the present invention has various types,
It is obtained from alumina raw material of purity, shape, particle size and composition, and unlike the hydrothermal treatment method, it does not have crystal seeds inside, so it is structurally and compositionally homogeneous and of high purity. Of α-alumina single crystal particles having a fine shape, a narrow particle size distribution, and an octahedral or higher polyhedron shape that is not agglomerated particles. Specifically, the particles constituting the α-alumina single crystal powder of the present invention have a number average particle size of more than 5 μm and 30 μm or less and a D / H ratio of 0.5 or more and 3.0 or less, D90 / D10 when the particle size distribution is 10% cumulative and 90% cumulative 90% from the fine particle side of the cumulative particle size distribution, respectively.
The ratio is as narrow as 10 or less, preferably 9 or less, particularly preferably 7 or less, the alumina purity is 99.90% by weight or more, and the sodium content is very high, less than 0.05% by weight in terms of Na ₂ 0. It has the excellent feature of being pure.

[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 obtained in Example 2.

FIG. 4 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. 5 shows the particle structure of α-alumina observed in Comparative Example 2. A photo that replaces the drawing. Scanning electron micrograph at 1900x magnification.

FIG. 6 shows a crystal habit of α-alumina single crystal particles.

Front page continuation (72) Inventor Takashi Watanabe 6 Kitahara, Tsukuba City, Ibaraki Sumitomo Chemical Co., Ltd. (56) Reference JP-A-63-303809 (JP, A) JP-A-6-191833 (JP, A) ) JP-A-6-191835 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C01F ^7/ 00-7/76

Claims (6)

(57) [Claims] 1. A hexagonal lattice having a maximum grain size D parallel to the hexagonal lattice plane of α-alumina, which is a hexagonal close-packed lattice, having a polyhedral shape of eight or more faces that is homogeneous and has no crystal seeds inside. When the particle diameter perpendicular to the plane is H, the D / H ratio is 0.5 or more and 3.0.
It consists of the following α-alumina single crystal particles, and the number average particle diameter of the α-alumina single crystal particles exceeds 5 μm and is 30 μm.
m or less, the sodium content in terms of Na ₂ O is less than 0.05% by weight, and the alumina purity is 99.90.
Α-alumina, characterized in that it is at least wt%. 2. The cumulative particle size distribution of α-alumina single crystal particles is 10% cumulative and 90% cumulative from the fine particle side, respectively.
The α-alumina according to claim 1, which has a particle size distribution in which D90 / D10 is 10 or less, where D and D90 are 10, respectively. 3. The α-alumina according to claim 1, which has an alumina purity of 99.95% by weight or more. 4. Na content is Na ₂ 5 converted to O
ppm or less, any one of claims 1 to 3, characterized in that
Α-alumina described therein. 5. One of claims 1 to 4 for use as a raw material for a single crystal.
Rekani description of α- alumina. 6. is a raw material for high purity sintered body according to claim 1 to 4
Α-alumina according to any one of 1 .