JPH0812322A - Alpha-alumina powder and its production - Google Patents

Abstract

PURPOSE:To directly produce alpha-alumina powder by a dry process using a mineral or compd. contg. Al and Si, e.g. bauxite or an aluminosilicate mineral such as kaolin or pyrophyllite as starting material. CONSTITUTION:A mineral or compd. contg. Al and Si is fired in the temp. range of 600-1,400 deg.C in introduced atmospheric gas contg. gaseous hydrogen fluoride at >=1.0vol.% concn. or contg. gaseous fluorine at >=1.0vol.% concn. and steam at >=10.1vol.% concn.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art α-Alumina powder is widely used as a raw material for abrasives, a raw material for sintered bodies, a raw material for plasma spraying materials, a raw material for fillers and the like.

As a method for producing α-alumina powder,
A method for producing transition alumina and / or an alumina raw material which becomes transition alumina by heat treatment by firing in the air is generally known. The alumina raw material that becomes the transition alumina by heat treatment is a precursor of the transition alumina that gives the desired α-alumina powder via the transition alumina, and specifically, aluminum hydroxide, vanadium sulfate (aluminum sulfate), Examples include so-called light vanes such as potassium aluminum sulfate and ammonium ammonium sulfate, ammonium aluminum carbonate, and alumina gel, such as alumina gel produced by an underwater discharge method of aluminum.

As a method of synthesizing transition alumina or an alumina raw material which becomes transition alumina by heat treatment, for example, aluminum hydroxide is a Bayer method, a hydrolysis method of an organic aluminum compound, or an aluminum compound obtained from an etching waste liquid such as an aluminum capacitor. Can be obtained by the method of synthesizing using

By firing in the above atmosphere, α
-In addition to the method for producing alumina powder, for example, a method by hydrothermal treatment of aluminum hydroxide (hereinafter referred to as hydrothermal treatment method), a method of adding flux to aluminum hydroxide and melting and precipitating (hereinafter referred to as flux method And a method of calcining aluminum hydroxide in the presence of a mineralizer are known.

However, in the above-mentioned various methods for producing α-alumina powder, since a raw material having a low content of metal elements such as silicon is required, aluminochemicals such as bauxite mineral, kaolin and pyrophyllite are required. In order to use aluminum and silicon-containing minerals such as silicate minerals as starting materials, it was necessary to carry out purification treatment by a process such as the Bayer method. Therefore, it is desired to develop a method for directly producing α-alumina powder from a mineral or compound containing aluminum and silicon by only a dry process.

[0007]

The object of the present invention is to directly use a mineral or compound containing aluminum and silicon, for example, an aluminosilicate mineral such as bauxite mineral, kaolin or pyrophyllite as a starting material in a dry process. It is to provide a method for producing α-alumina powder.

[0008]

The present invention comprises the following inventions. 1. A mineral or compound containing aluminum and silicon containing hydrogen fluoride gas having a concentration of 1.0 volume% or more, or fluorine gas having a concentration of 1.0 volume% or more and water vapor having a concentration of 0.1 volume% or more. A method for producing α-alumina powder, which comprises introducing an atmosphere gas and firing in a temperature range of 600 ° C or higher and 1400 ° C or lower.

2. Pretreatment and calcination of a mineral or compound containing aluminum and silicon in an atmosphere gas containing a chlorinating agent in a temperature range of 300 ° C. or more and 1400 ° C. or less, and then a hydrogen fluoride concentration of 1.0 vol% or more. Gas or an atmosphere gas containing fluorine gas having a concentration of 1.0 vol% or more and steam having a concentration of 0.1 vol% or more is introduced, and firing is performed in a temperature range of 600 ° C. or more and 1400 ° C. or less. The method for producing α-alumina powder.

3. Item 3. The method for producing an α-alumina powder according to Item 1 or 2, wherein the mineral or compound containing aluminum and silicon is a mineral or compound containing 1% by weight or more of silicon.

4. Item 3. The method for producing an α-alumina powder according to Item 1 or 2, wherein the mineral containing aluminum and silicon is a bauxite mineral, an aluminosilicate mineral, or a mullite mineral.

5. The compound containing aluminum and silicon is a mixture of aluminum oxide and silicon oxide, a compound containing aluminum, silicon, oxygen, or a mixture of a compound containing aluminum, silicon, oxygen and aluminum oxide and / or silicon oxide. Item 3. The method for producing an α-alumina powder according to Item 1 or 2.

6. Item 3. The method for producing an α-alumina powder according to Item 1 or 2, wherein a mineral or compound containing aluminum and silicon is fired in a temperature range of 800 ° C to 1200 ° C.

7. Item 3. The method for producing an α-alumina powder according to Item 2, wherein the chlorinating agent is one or more selected from the group consisting of hydrogen chloride, chlorine, phosgene, carbon tetrachloride, and aluminum chloride.

8. The concentration of chlorinating agent in the atmospheric gas is 1
The α according to the above item 2, which is 0% by volume or more.
-Alumina powder manufacturing method.

9. An α-alumina powder produced by the method according to Item 1. 10. An α-alumina powder produced by the method according to Item 2.

The present invention will be described in detail below. In the method for producing α-alumina powder of the present invention, a mineral or compound containing aluminum and silicon is used as a raw material. The content of silicon is usually 1% by weight or more of the raw material in terms of alumina. Examples of the minerals containing aluminum and silicon include bauxite minerals, aluminosilicate minerals such as kaolin and pyrophyllite, and mullite minerals.

As the compound containing aluminum and silicon, for example, a mixture of aluminum oxide and silicon oxide, aluminum, silicon, a compound containing oxygen, aluminum, silicon, a compound containing oxygen and aluminum oxide and / or Or a mixture with silicon oxide, and specifically, a mixture of transition alumina that becomes α-alumina by firing and amorphous silica or quartz, mullite, mullite with amorphous silica, quartz, cristobalite. A mixture etc. can be mentioned. Minerals or compounds containing aluminum and silicon are
Industrially, one containing aluminum or an aluminum compound as a main component can be used.

According to the present invention, a mineral or compound containing aluminum and silicon is introduced into an atmosphere gas containing hydrogen fluoride gas or fluorine gas and water vapor and then baked, so that the content of silicon becomes extremely high. Low α-alumina powder can be obtained.

In the bauxite minerals, aluminosilicate minerals such as kaolin and pyrophyllite, and natural minerals such as mullite minerals, which are used as raw materials of the present invention, alkali metals such as sodium and potassium, magnesium and calcium, etc. are usually used. Alkaline earth metal, aluminum such as iron and titanium, and metal elements other than silicon are contained,
These metal elements may remain in the α-alumina powder produced without being necessarily removed by firing in an atmosphere gas containing hydrogen fluoride gas or fluorine gas and water vapor.

Therefore, in the case of producing a higher purity α-alumina powder, bauxite mineral, kaolin, containing a small amount of metal elements other than aluminum and silicon,
Aluminosilicate minerals such as pyrophyllite, or minerals such as mullite minerals as a raw material, or pretreatment of the above raw material minerals to reduce the content of metal elements other than aluminum and silicon, Then hydrogen fluoride gas,
Alternatively, it is preferable to introduce fluorine gas and water vapor and perform firing in this atmosphere gas.

The pretreatment is carried out by firing in an atmosphere gas containing a chlorinating agent. By the pretreatment, metal impurities other than aluminum and silicon are removed, and α-alumina powder having higher purity can be obtained. Examples of the chlorinating agent used here include hydrogen chloride, chlorine, phosgene, carbon tetrachloride, aluminum chloride, and the like, and hydrogen chloride is preferably used.

The concentration of the chlorinating agent during the pretreatment and the pretreatment baking temperature are not necessarily limited because they depend on the type of metal impurities to be removed, but when the chlorinating agent concentration is 10% by volume or more,
The firing temperature is preferably in the temperature range of 300 ° C. or higher and 1400 ° C. or lower. The method of this pretreatment is described in detail in JP-A-62-246815.

In the present invention, the firing of the raw material is carried out in hydrogen fluoride gas or in an atmosphere gas containing fluorine gas and water vapor.

When hydrogen fluoride gas is used for calcination, its concentration is 1% by volume or more, preferably 5% by volume or more, more preferably 10% by volume or more.

When a mixed gas of fluorine gas and water vapor is used for firing, the concentration thereof is 1 volume% or more of fluorine gas and 0.1 volume% or more of water vapor, preferably 5 volume% or more of water vapor and water vapor. 1 volume% or more,
More preferably, it is 10 vol% or more of fluorine gas and 5 vol% or more of water vapor.

The hydrogen fluoride gas or the mixed gas of fluorine gas and water vapor may be diluted with an inert gas such as nitrogen or argon gas, hydrogen, air or the like before use. Further, the pressure of the hydrogen fluoride gas or the atmosphere gas containing the fluorine gas and the steam gas is not particularly limited and can be arbitrarily selected within a range industrially used.

The firing temperature is usually 600 ° C. or higher and 1400.
C. or less, preferably 700.degree. C. or more and 1300.degree. C. or less, more preferably 800.degree. C. or more and 1200.degree. C. or less. By controlling in this temperature range and firing, α-alumina powder having a narrow particle size distribution can be obtained with an industrially advantageous generation rate, in which agglomeration of α-alumina particles is unlikely to occur.

The firing time depends on the concentration of the atmosphere gas and the firing temperature and is not necessarily limited, but is preferably 1 minute or more, more preferably 10 minutes or more, which is shorter than the firing time of the conventional method. In this way, α-alumina powder can be obtained.

The supply source and supply method of the atmospheric gas are not particularly limited as long as the above-mentioned atmospheric gas can be introduced into the reaction system in which the raw materials are present. As a supply source,
Although cylinder gas can be used, a hydrofluoric acid solution, a fluorine compound such as ammonium fluoride, a fluorine-containing compound,
A fluorine-containing polymer compound or the like may be used as a raw material for hydrogen fluoride gas or fluorine gas. In this case, the above-mentioned predetermined gas composition is used.

As a gas supply method, either a continuous system or a batch system can be used. However, when elements other than aluminum, such as silicon and alkali metals, are contained in large amounts, they are scattered and removed as fluorides. Therefore, the continuous method is preferable. At this time, by collecting the scattered fluoride, a by-product can be obtained in addition to the desired α-alumina powder. Specifically, when kaolin mineral is used as a raw material, silicon tetrafluoride scatters during firing. By inducing this into water and hydrolyzing it, industrially useful silica can be obtained as a by-product. You can Further, hydrogen fluoride generated by hydrolysis can be used as a supply source of atmospheric gas.

The firing apparatus is not necessarily limited, and a so-called firing furnace can be used. It is desirable that the firing furnace be made of a material that is not corroded by hydrogen fluoride gas, fluorine gas, and the like, and further that a mechanism that can adjust the atmosphere be provided. Further, since an acid gas such as hydrogen fluoride gas or fluorine gas is used, it is desirable that the firing furnace be airtight. Industrially, it is desirable to carry out firing in a continuous manner, and for example, a tunnel furnace, a rotary kiln, a pusher furnace or the like can be used.

As the material of the apparatus used in the manufacturing process, since the reaction proceeds in an acidic atmosphere, it is desirable to use an alumina crucible, acid-resistant brick or graphite crucible or boat.

According to the method of the present invention, the content of the agglomerated particles that are homogeneous, have a plate-like particle shape, and are strongly bonded from a mineral or compound containing aluminum and silicon in a smaller number of steps than the conventional method. And a high-purity α-alumina powder can be obtained.

The α-alumina particles have a hexagonal close-packed lattice,
When D is the maximum particle diameter of the α-alumina particles parallel to the hexagonal lattice plane and H is the particle diameter perpendicular to the hexagonal lattice plane, D / H
Has a plate shape of about 1 to 30. Generate α
The content of the agglomerated particles that are firmly bound to the alumina powder is small, and for example, only a few of the agglomerated particles that can be lightly crushed with a shet mill are included. α-
The purity of the alumina powder depends on the purity of the raw material, but when the chlorinating agent is added for pretreatment, the purity is usually 98%.
% Or more.

[0036]

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

Compositions containing a silicon compound as a main component and an aluminum compound used as a raw material in the examples are as shown below. 1. Kaolin A Reagent manufactured by Hanai Chemical Co., Ltd. As a result of X-ray diffraction, only the peak of kaolinite (Al ₂ Si ₂ O ₅ (OH) ₄ ) was detected. 2. Kaolin B Reagent manufactured by Wako Pure Chemical Industries, Ltd. As a result of X-ray diffraction, peaks of kaolinite (Al ₂ Si ₂ O ₅ (OH) ₄ ) as well as pyrophyllite (Al ₂ Si ₄ O ₁₀ (OH) ₂ ) and quartz (SiO ₂ ) were detected. .

3. Frog Eye Clay The new head mountain frog eye 102 from Ceramica Sales Co., Ltd. As a result of X-ray diffraction, in addition to kaolinite (Al ₂ Si ₂ O ₅ (OH) ₄ ), quartz (SiO ₂ ), KMgAlSi ₄ O ₁₀
(OH) ₂ , Na _0.3 (Al, Mg) ₂ Si ₄ O ₁₀ (O
H) ₂ · nH ₂ O peaks were detected.

4. Mullite A A powder obtained by firing a powder obtained by mixing aluminum hydroxide synthesized by hydrolysis of aluminum isopropoxide and silica manufactured by Aerosil Co., Ltd. at 1400 ° C. in air. As a result of X-ray diffraction, mullite (Al ₆ Si
₂ O ₁₃ ), α-alumina, cristobalite (Si
A peak of O ₂ ) was detected.

5. Bauxite A A powder obtained by making bauxite (gove ore) into a slurry with water, grinding with an alumina ball mill, and drying at 130 ° C.
Results of X-ray diffraction, gibbsite (Al (OH) _3), hematite (Fe ₂ O _3), kaolinite (Al ₂ Si ₂ O
Peaks such as ₅ (OH) ₄ ) were detected. As a result of composition analysis by ICP emission analysis, Al ₂ O ₃ in oxide conversion:
47.4% by weight, Fe ₂ O ₃ : 14.5% by weight, SiO
₂ : 3.9 wt% and TiO ₂ : 3.2 wt%.

As the hydrogen fluoride gas, a decomposition gas of ammonium fluoride was used. Sublimation temperature of ammonium fluoride 2
The atmosphere was adjusted by introducing hydrogen fluoride gas obtained by heating to 20 ° C. into the furnace core tube. Ammonium fluoride is completely decomposed at a holding temperature of 1100 ° C., and 33% by volume of hydrogen fluoride (HF) gas and nitrogen (N
₂ ) The atmosphere was 17% by volume of gas and 50% by volume of hydrogen (H ₂ ) gas.

An alumina boat was filled with a composition containing an aluminum compound as a main component and containing a silicon compound, and firing was performed with an alumina furnace core tube (diameter 27 mm, length 1000 mm).
Tubular furnace using (MOTOYAMA CORPORATION: DSPSH-2
8). Temperature rising rate 3 while circulating nitrogen gas
The temperature was raised at 00 ° C./hour, and when the temperature reached the atmosphere introduction temperature, the atmosphere gas was introduced.

After reaching the predetermined temperature, the temperature was maintained for the predetermined time. These are referred to as holding temperature (firing temperature) and holding time (firing time), respectively. After the lapse of a predetermined holding time, the temperature was lowered to room temperature at 300 ° C./hour while circulating nitrogen gas to obtain the desired α-alumina powder.

The crystal phase of the powder used or obtained in the present invention was identified by an X-ray diffraction measuring device (RAD-C manufactured by Rigaku Denki Co., Ltd.). Also used in the present invention,
Alternatively, the composition analysis of the obtained powder was performed using an ICP emission spectrometer (manufactured by Seiko Denshi KK: SPS-1200VR).

Example 1 0.1 g of kaolin A was used as a raw material, and a decomposition gas of ammonium fluoride (2.91 g) was introduced into a tubular furnace as an atmosphere gas to carry out a reaction. Atmosphere gas introduction temperature is 700 ° C., holding temperature (firing temperature) is 1100 ° C.,
The holding time (firing time) was 30 minutes. The SEM photograph of the obtained powder is shown in FIG. As a result of X-ray diffraction, only the peak of α-alumina was detected, and no other peak was observed. The conditions and results are shown in Tables 1, 2, 3, and 4.

Examples 2-4 As raw materials, 0.2 g of kaolin B (Example 2), 0.2 g of mullite A (Example 3) and 0.19 g of frog eye clay
The reaction was carried out under the same conditions as in Example 1 except that (Example 4) was used. The conditions and results are shown in Tables 1, 2, 3, 4
Shown in

Example 5 0.19 g of bauxite A was used as a raw material, a gas consisting of 100% by volume of hydrogen chloride was introduced as an atmosphere gas into a tubular furnace from room temperature, and a holding temperature (baking temperature) was 800 ° C.
Pretreatment and baking were carried out with a holding time (baking time) of 180 minutes to obtain a powder. As the hydrogen chloride gas, a cylinder hydrogen chloride gas (purity 99.9%) manufactured by Tsurumi Soda Co., Ltd. was used. The powder obtained by the pretreatment firing was reacted under the same conditions as in Example 1. The conditions and results are shown in Tables 1, 2, 3, and 4.

Example 6 1.64 g of bauxite A was used as a raw material, and a gas consisting of 100% by volume of hydrogen chloride was introduced as an atmosphere gas into a tubular furnace from room temperature at a holding temperature (calcination temperature) of 1100.
Pretreatment and baking were performed at a temperature of 30 ° C. for a holding time (baking time) of 30 minutes to obtain a powder. The powder obtained by the pretreatment firing was reacted under the same conditions as in Example 1 except that a decomposition gas of ammonium fluoride (5.8 g) was used as an atmosphere gas. The conditions and results are shown in Tables 1, 2, 3, and 4. The SEM photograph of the obtained powder is shown in FIG.

Example 7 0.88 g of frog clay was used as a raw material, a gas consisting of 100% by volume of hydrogen chloride was introduced as an atmospheric gas into a tubular furnace from room temperature, and a holding temperature (baking temperature) was 1100 ° C. and a holding time was set. Pretreatment baking was performed with (baking time) set to 120 minutes to obtain a powder. The powder obtained by the pretreatment firing was reacted under the same conditions as in Example 1 except that a decomposition gas of ammonium fluoride (5.8 g) was used as an atmosphere gas. The conditions and results are shown in Tables 1, 2, 3, and 4. The SEM photograph of the obtained powder is shown in FIG. Table 5 shows the results of composition analysis of the powders obtained in Examples 6 and 7.

Comparative Example 1 Kaolin A (0.1 g) was calcined in air at 1100 ° C. for 30 minutes. The reaction conditions and results are shown in Tables 1, 2, 3, and 4.

Comparative Example 2 Bauxite A (0.1 g) in air at 1100 ° C. for 3 days
Bake for 0 minutes. The reaction conditions and results are shown in Tables 1, 2, 3,
4 shows.

Comparative Example 3 Frog eye clay (0.1 g) was calcined in air at 1100 ° C. for 30 minutes. The reaction conditions and results are shown in Tables 1, 2, 3, and 4.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

[0057]

[Table 5]

[0058]

EFFECTS OF THE INVENTION According to the method of the present invention, a homogeneous and particle-like plate-like material is obtained from a mineral or compound containing aluminum and silicon, for example, a natural clay mineral or bauxite, in a smaller number of steps than the conventional method. Thus, it is possible to obtain a high-purity α-alumina powder with a small content of the strongly bonded aggregated particles.

The α-alumina particles obtained are hexagonal close-packed lattices, where D is the maximum particle size parallel to the hexagonal lattice planes of the α-alumina particles and H is the particle size perpendicular to the hexagonal lattice planes.
It has a plate shape with a D / H of about 1 to 30. The α-alumina powder thus produced contains a small amount of strongly bonded aggregated particles, and for example, contains only a small amount of aggregated particles that can be lightly crushed with a shet mill or the like. The purity of the α-alumina powder depends on the purity of the raw material, but when the chlorinating agent is added for pretreatment, the purity is usually 98% or more.

The α-alumina powder obtained by the present invention is an abrasive, a sintering material, a plasma spray material, a filler, a raw material for a single crystal, a catalyst carrier, a raw material for a phosphor, a raw material for a sealing material, a ceramic filter. It is suitable as a raw material and is industrially extremely useful. In particular, the α-alumina powder obtained by the present invention has a plate-like particle shape, and thus is suitable as a filling material for a coating film.

[Brief description of drawings]

1 shows the particle structure of α-alumina powder observed in Example 1. FIG. A photo that replaces the drawing. Scanning electron micrograph at 4250x magnification.

FIG. 2 shows the particle structure of α-alumina powder observed in Example 6. A photo that replaces the drawing. Scanning electron micrograph at 4250x magnification.

FIG. 3 shows the particle structure of α-alumina powder observed in Example 7. A photo that replaces the drawing. Scanning electron micrograph at 4250x magnification.

Claims (10)

[Claims] 1. A hydrogen fluoride gas having a concentration of 1.0% by volume or more, or a fluorine gas having a concentration of 1.0% by volume or more and a concentration of 0.1% by volume or more, containing a mineral or compound containing aluminum and silicon. The method for producing an α-alumina powder, which comprises introducing the atmospheric gas containing water vapor and calcining in a temperature range of 600 ° C. or higher and 1400 ° C. or lower. 2. A mineral or compound containing aluminum and silicon in an atmosphere gas containing a chlorinating agent.
Pretreatment is performed in a temperature range of 0 ° C. or higher and 1400 ° C. or lower, and then hydrogen fluoride gas having a concentration of 1.0 volume% or more, or fluorine gas having a concentration of 1.0 volume% or more and a concentration of 0.1 volume A method for producing α-alumina powder, which comprises introducing an atmosphere gas containing water vapor of not less than 100% and firing it in a temperature range of 600 ° C. or more and 1400 ° C. or less. 3. The method for producing an α-alumina powder according to claim 1, wherein the mineral or compound containing aluminum and silicon is a mineral or compound containing 1% by weight or more of silicon. 4. The method for producing α-alumina powder according to claim 1, wherein the mineral containing aluminum and silicon is a bauxite mineral, an aluminosilicate mineral, or a mullite mineral. 5. The compound containing aluminum and silicon is a mixture of aluminum oxide and silicon oxide, a compound containing aluminum, silicon, oxygen, or a compound containing aluminum, silicon, oxygen and aluminum oxide and / or silicon oxide. The method for producing α-alumina powder according to claim 1 or 2, which is a mixture of 6. The method for producing an α-alumina powder according to claim 1, wherein the mineral or compound containing aluminum and silicon is fired in a temperature range of 800 ° C. or higher and 1200 ° C. or lower. 7. A chlorinating agent is hydrogen chloride, chlorine, phosgene,
The method for producing an α-alumina powder according to claim 2, which is one kind or two or more kinds selected from the group consisting of carbon tetrachloride and aluminum chloride. 8. The method for producing α-alumina powder according to claim 2, wherein the concentration of the chlorinating agent in the atmospheric gas is 10% by volume or more. 9. An α produced by the method according to claim 1.
-Alumina powder. 10. An α-alumina powder produced by the method according to claim 2.