JP2003277048A - FIRED ALUMINA PRODUCT, METHOD FOR MANUFACTURING FIRED ALUMINA PRODUCT AND FINE alpha ALUMINA POWDER OBTAINED BY USING FIRED ALUMINA PRODUCT - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide α alumina powder which easily yields a dense sintered compact, a fired alumina product for manufacturing the same, and a method for manufacturing the fired alumina product. <P>SOLUTION: The fired alumina product is characterized in that its BET specific surface area is 10 to 20 m<SP>2</SP>/g, its main crystalline phase is an α phase and does not substantially contain a θ phase and its average grain size is ≤0.5 μ. The method for manufacturing the fired alumina product is characterized in that an α alumina precursor not substantially containing metal elements exclusive of aluminum is fired in an atmosphere of ≤600 Pa in partial pressure of steam. The fine α alumina powder is characterized in that its purity is ≥99.99% and its BET specific surface area is ≥15 m<SP>2</SP>/g, intermediate alumina is not substantially included and the relative density of the sintered compact obtained by sintering at 1,250°C under atmospheric pressure is ≥95%. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a calcined alumina product, a method for producing a calcined alumina product, and a fine α-alumina powder obtained by using the calcined alumina product.

[0002]

2. Description of the Related Art α-alumina powder is a particle of alumina (Al ₂ O ₃ ) whose main crystal phase is α-phase, and is widely used as a raw material for manufacturing various sintered bodies such as light-transmitting tubes. It is used.

Examples of such α-alumina powder include α-alumina powder such as aluminum hydroxide, intermediate alumina, ammonium alum, aluminum chloride and ammonium aluminum carbonate.
It can be manufactured by a method of firing an alumina precursor in the air to obtain an alumina fired product, and pulverizing the obtained aluminum fired product (Patent Document 1). However, it has been difficult to obtain a dense sintered body with the conventional α-alumina powder obtained by such a manufacturing method.

[0004]

[Patent Document 1] JP-A-55-113615

[0005]

SUMMARY OF THE INVENTION Therefore, the present inventors have developed an α-alumina powder capable of easily providing a dense sintered body, a raw material thereof, an alumina calcined product, a method for producing such an alumina calcined product, and As a result of intensive studies on α-alumina powder obtained by pulverizing the alumina calcined product, when the α-alumina precursor is calcined in the air, the resulting alumina calcined product has a BET ratio due to the influence of moisture contained in the air. It was found that the surface area is small or contains the θ phase, and it is difficult to obtain a dense sintered body by sintering the α-alumina powder obtained by pulverizing the powder. By calcining the α-alumina precursor, it is possible to obtain a calcined alumina product having a relatively large BET specific surface area, the main crystal phase being the α phase, and the θ phase not being substantially contained. It was found that a fine α-alumina powder can be easily obtained by crushing this alumina calcined product, and a dense sintered body can be easily obtained by sintering the obtained fine α-alumina powder. The present invention has been reached.

[0006]

That is, the present invention is based on BE
T specific surface area is 10 to 20 m ² / g, and the main crystalline phase is α
The present invention provides an alumina calcined product which is a phase and which does not substantially contain the θ phase and has a particle size of 0.5 μm or less.

Further, in the present invention, the α-alumina precursor containing substantially no metal elements other than aluminum has a water vapor partial pressure of 6
Another object of the present invention is to provide a method for producing an alumina fired product, which is characterized by firing in an atmosphere of 00 Pa or less.

Further, the present invention has a purity of 99.99% or more,
A BET specific surface area of 15 m ² / g or more and substantially no intermediate alumina, and when sintered at 1250 ° C. under normal pressure, the relative density of the obtained sintered body is 95% or more. Alumina powder is provided.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The alumina calcined product of the present invention has a BET specific surface area of 10 m ^2.
/ G or more, preferably 12 m ² / g or more, more preferably 13 m ² / g or more, and 20 m ² / g or less, preferably 17 m ² / g or less. The average particle diameter of the fired alumina product is 0.5 μm or less, preferably 0.1 μm or less. The average particle size can be determined by taking a photograph of the fired product with a transmission electron microscope and measuring the particle size of the particles in the image. Further, this alumina calcined product has an α phase as a main crystal phase and does not substantially contain a phase other than the α phase, for example, a θ phase.
The crystal phase of the fired product of the alumina is X-ray diffraction (XR
D) It is possible to obtain a spectrum by measuring the spectrum.

The alumina calcined product of the present invention can be obtained by calcining the α-alumina precursor in an atmosphere having a water vapor partial pressure of 600 Pa or less.

The α-alumina precursor used here is
For example, it is a compound that becomes α-alumina by firing at a temperature of 1000 ° C. or higher, and specifically the crystal phase is γ-phase,
Crystalline intermediate alumina such as χ phase, θ phase, δ phase, ρ phase, κ phase, intermediate alumina such as amorphous intermediate alumina, gibbsite, boehmite, pseudoboehmite, bayerite, norstrandite, etc. In addition to crystalline aluminum hydroxide such as diaspore, aluminum hydroxide such as amorphous aluminum hydroxide, aluminum oxalate, aluminum acetate, aluminum stearate,
Examples include ammonium alum, aluminum lactate, aluminum laurate, ammonium carbonate, aluminum sulfate, aluminum ammonium sulfate, aluminum nitrate, and ammonium aluminum nitrate. These may be used alone or in combination of two or more.
Above all, it is recommended to use those containing intermediate alumina or aluminum hydroxide as a main component. The amount of intermediate alumina or aluminum hydroxide at this time is usually 60% by weight or more, preferably 80% by weight, based on the α-alumina precursor.
It is more than weight%. The α-alumina precursor is substantially free of metal elements other than aluminum, and is, for example, an element of silicon (Si), iron (Fe), titanium (Ti), sodium (Na), calcium (Ca). Each content is 50 ppm or less. The total amount of these is 10
It is preferably 0 ppm or less.

This α-alumina precursor is preferably calcined in the presence of a small amount of α-alumina. By calcining the α-alumina precursor in the presence of a small amount of α-alumina,
It is possible to manufacture an alumina calcined product that can obtain a finer α-alumina powder. When this α-alumina is used, its abundance is based on the α-alumina precursor,
It is usually 1% by weight or more, and 20% by weight or less, preferably 10% by weight or less.

To make the α-alumina precursor coexist with the α-alumina, for example, the α-alumina precursor may be mixed with the α-alumina particles, or the α-alumina precursor may be calcined to form a part of the α-alumina precursor. May be converted to α-alumina, and the α-alumina precursor may coexist with α-alumina. In the method of mixing the α-alumina precursor with the α-alumina particles, the particle size of the α-alumina particles to be mixed is preferably smaller than the particle size of the fine α-alumina powder obtained by firing and grinding the α-alumina precursor, For example, it is preferably 0.1 μm or less.

In the method of calcining the α-alumina precursor, α
Fine α-alumina can be present in the alumina precursor. The calcination at this time can be performed, for example, by holding the α-alumina precursor in the air at 800 ° C. or higher and 1200 ° C. or lower. The content of fine α-alumina can be adjusted by changing the firing temperature and time, and for example, the α-alumina content can be increased by increasing the firing temperature or prolonging the firing time.

As the α-alumina precursor containing the predetermined amount of α-alumina shown above, a commercially available product can be used.

The α-alumina precursor containing α-alumina includes
You may pulverize as needed. By pulverizing, α-alumina can be more uniformly dispersed in the α-alumina precursor. The pulverization can be performed using a vibration mill, a ball mill, a jet mill or the like. In the pulverization, it is preferable to reduce the contamination of silicon and calcium from the pulverizing medium. Therefore, alumina having a purity of 99% by weight or more is used as a material for the pulverizing medium of the vibration mill or the ball mill, the nozzle of the jet mill, or the liner. Recommended.

The α-alumina precursor used in the production of the calcined alumina is preferably low in bulk density (bulk specific gravity). For example, the bulk density of the oxide α-alumina (Al ₂ O ₃ ) is 0. 5g / cm ³ or less, further 0.3g / cm
It is preferably ³ or less. By calcining the α-alumina precursor having a low bulk density, an alumina calcined product suitable for obtaining a finer alumina powder can be manufactured. The α-alumina-equivalent bulk density is the bulk density obtained by dividing the α-alumina-equivalent mass of the α-alumina precursor by the volume of the α-alumina precursor.

The α-alumina precursor shown above or optionally ground α-alumina precursor is calcined. Firing is performed in an atmosphere in which the partial pressure of water vapor is controlled, and the partial pressure of water vapor is usually 600 Pa or less (total pressure 1 atm (0.1 MPa)).
In the case of the above gas, the dew point is 0 ° C. or less) while maintaining the atmosphere. It is preferable that the partial pressure of water vapor in the firing atmosphere is low, that is, 165 Pa or less (a dew point of -15 ° C or less if the gas has a total pressure of 1 atm), and 40 Pa or less (dew point of -30 ° C or less if the gas has a total pressure of 1 atm). ) Is preferable.

The firing may be carried out with an apparatus capable of adjusting the atmosphere to a water vapor partial pressure of 600 Pa or less.
Tubular electric furnace, box electric furnace, tunnel furnace, far infrared furnace,
It can be carried out by using a firing furnace such as a microwave heating furnace, a shaft furnace, a reverberation furnace, a rotary furnace, or a roller hearth furnace to discharge gas from the furnace or introduce gas. Further, when using an α-alumina precursor such as intermediate alumina that hardly generates water vapor during firing, put the α-alumina precursor in a container, introduce dry air having a water vapor partial pressure of 600 Pa or less, and then seal the container. You can also do it. Calcination is steam partial pressure 600P
As long as it is an atmosphere of a or less, it may be carried out under reduced pressure, for example, it may be carried out under a reduced pressure atmosphere of a total pressure of 600 Pa or less composed of gas such as air, hydrogen, helium, nitrogen and argon. The firing furnace used at this time may be either a batch type or a continuous type. The calcination may be carried out at a temperature necessary for the α-alumina precursor to undergo a phase transition to α-alumina, and the temperature at this time is usually 1000 ° C. or higher, preferably 1100 ° C. or higher, more preferably 1160 ° C. or higher, It is 1250 ° C or lower, preferably 1200 ° C or lower. The firing time varies depending on the type of firing furnace used and the firing temperature, but is usually 10 minutes or longer, preferably 30 minutes or longer and 12 hours or less.

As the gas introduced into the furnace, it is preferable to use a gas whose steam partial pressure is adjusted. For example, air is compressed by a compressor to condense the water contained in the air, and the condensed water is separated. Then, dry air obtained by decompressing, dry air obtained by removing moisture from the air by a dehumidifier, or dry nitrogen obtained by vaporizing liquid nitrogen is also suitably used. If it does not contain water,
It is also possible to use a commercially available cylinder gas filled with air, helium, nitrogen or the like.

The alumina powder obtained by firing may be subjected to particle size adjustment such as pulverization and classification, if necessary. The pulverization can be performed by a vibration mill, a ball mill, a jet mill, or the like, and the classification can be performed by using a sieve or the like.

The alumina calcined product of the present invention thus obtained is easily pulverized into fine particles. A fine alumina powder can be easily obtained by pulverizing the alumina calcined product. The fine alumina powder obtained by pulverization usually has a purity of 99.99% or more, a BET specific surface area of 15 m ² / g or more, a crystal phase substantially an α phase, and no θ phase. It is a thing. When this fine alumina powder was uniaxially pressed at a molding pressure of 30 MPa and then hydrostatically pressed (CIP) at a molding pressure of 100 MPa, the compact was sintered in air at 1250 ° C. under normal pressure for 2 hours. Relative density of 95% or more. This fine alumina powder is usually Si, F
The content of e, Ti, Na and Ca is 50p each in element conversion
pm or less, and their total amount is 100 ppm or less. Of course, by further improving the purity of the raw material α-alumina precursor, selecting the material of the firing furnace, and selecting the material of the grinding medium used at the time of optional grinding, it is possible to obtain those in which these elements are further reduced. You can

The fine α-alumina powder can be used as a raw material for producing a sintered body, for example. Examples of the sintered body obtained by sintering the fine α-alumina powder include semiconductor manufacturing equipment parts such as wafer handlers, electronic parts such as oxygen sensors and inkjet heads, mechanical parts such as rollers and gears, and metal halide lamps. Translucent tubes, removal of solids in gases such as exhaust gas, filtration of molten aluminum, removal of solids in liquids of beer, etc., ceramic filters (porous sintered bodies) used for selective permeation of hydrogen in fuel cells, etc. To be Further, such fine α-alumina powder is similar to the ordinary α-alumina powder, and is an additive for abrasives and magnetic media,
It can also be used as an additive to a toner, a thermally conductive filler added to a semiconductor sealant, or the like. When it is used as an abrasive, it can be used as it is or as an abrasive tape by being carried on the surface of a tape. It can be used for precision polishing of a metal surface such as a hard disk or C
It can also be used for MP polishing and the like.

[0024]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. BET specific surface area, crystalline phase and Si, F
The contents of e, Ti, Na and Ca were determined by the following method.

BET specific surface area (m ² / g): Determined by nitrogen adsorption method.

Crystal phase: A sample was analyzed by an X-ray diffractometer (trade name "R
int-2100 ", manufactured by Rigaku Denki Co., Ltd.), and the crystal phase was identified from the peak data of the obtained XRD spectrum, and the crystal phase having the highest relative peak intensity was selected as the main crystal phase.

Content (ppm) of Si, Fe, Ti, Na, Ca: Determined by optical emission spectroscopy.

Example 1 [Preparation of Intermediate Alumina Powder] Aluminum hydroxide obtained by hydrolyzing aluminum isopropoxide was calcined, and the main crystal phase was θ phase, and α alumina was 3% by weight.
The intermediate alumina containing was obtained. The α-alumina content in the intermediate alumina is obtained by analyzing the intermediate alumina with an X-ray diffractometer and comparing the obtained XRD spectrum with a standard spectrum obtained by adding a predetermined amount of α-alumina to the intermediate alumina. Then, the α-alumina content was calculated. The above intermediate alumina was pulverized by a jet mill to obtain an intermediate alumina powder having a bulk density (converted to α-alumina) of 0.21 g / cm ³ .

[Production of Alumina Burned Product] 100 g of this intermediate alumina powder was placed in an atmosphere firing furnace (trade name “Tube type atmosphere furnace”, manufactured by Motoyama Co., Ltd.) having a volume of 8 L (liter), and the dew point was −15 ° C. in the furnace. Dry air having a water vapor partial pressure of 165 Pa was introduced at a rate of 1 L / min to change the dew point of the atmosphere in the furnace to −
While maintaining the temperature at 15 ° C., the temperature was raised to 1170 ° C., and the temperature was maintained for 3 hours, followed by calcining under the condition of slow cooling to obtain a calcined alumina product. This alumina calcined product had a BET specific surface area of 13 m ² / g, a main crystal phase of α phase and no θ phase, and an average particle size of 0.1 μm.
The X-ray diffraction (XRD) spectrum of the intermediate alumina used here is shown in FIG. 1, and the XRD spectrum of the obtained calcined alumina is shown in FIG. The presence or absence of the θ phase in the fired alumina was analyzed by an X-ray diffractometer, and the θ phase (diffraction angle 32.
The peak intensity Z of 7 °) and the peak intensity W of the α phase (diffraction angle 57.5 °) were obtained, and the one having a ratio Z / W of more than 0.01 at this time was evaluated as having the θ phase.

[Production of Fine Alumina Powder] This alumina fired product was pulverized using a vibration mill (pulverization medium: made of alumina) to obtain fine alumina powder. This fine alumina powder has a BET specific surface area of 16 m ² / g and Si
Content 19ppm, Fe content 8ppm, Ti content 1
ppm or less, Na content 8 ppm, Ca content 3 ppm
And the purity was 99.996%. A transmission electron microscope (TEM) photograph of this powder is shown in FIG. This powder is uniaxially pressed at a molding pressure of 30 MPa, then a molding pressure of 100
It was molded by isostatic pressing (CIP) at MPa, and the relative density of the sintered body obtained by sintering this molded body in air at 1250 ° C. for 2 hours at normal pressure was 97%.

If the fine alumina powder shown above is used,
Ceramics having excellent mechanical strength and corrosion resistance can be easily obtained. Further, if this fine alumina powder is used as abrasive grains, it is possible to obtain an abrasive having a high polishing rate and free from polishing scratches.

Example 2 Aluminum isopropoxide was mixed with an average particle size of 0.1 μm.
After the addition of α-alumina powder of m, hydrolysis was performed to obtain aluminum hydroxide having a main crystal phase of pseudo-boehmite and containing 1% by weight of α-alumina.

100 g of the obtained aluminum hydroxide was added to
Firing was performed under the same conditions as in [Production of Alumina Calcined Product] of Example 1 to obtain an alumina calcined product. This alumina calcined product is
It has a BET specific surface area of 14 m ² / g, a main crystal phase of α phase and no θ phase, and an average particle size of 0.1 μm.
It was m.

If the fine alumina powder shown above is used,
Ceramics having excellent mechanical strength and corrosion resistance can be easily obtained. Further, if this fine alumina powder is used as abrasive grains, it is possible to obtain an abrasive having a high polishing rate and free from polishing scratches.

Example 3 An alumina calcined product was obtained by performing the same operation as in Example 1 except that the dew point of the air introduced into the furnace during the calcination was changed to 0 ° C. (steam partial pressure 600 Pa). This alumina calcined product had a BET specific surface area of 11 m ² / g, a main crystal phase of α phase and no θ phase, and an average particle size of 0.1.
It was 1 μm.

If the fine alumina powder shown above is used,
Ceramics having excellent mechanical strength and corrosion resistance can be easily obtained. Further, if this fine alumina powder is used as abrasive grains, it is possible to obtain an abrasive having a high polishing rate and free from polishing scratches.

Comparative Example 1 An alumina calcined product was obtained by the same procedure as in Example 1 except that the dew point of the air introduced into the furnace during the calcining was changed to 20 ° C. (steam partial pressure 2300 Pa). This alumina calcined product had a BET specific surface area of 9 m ² / g, a main crystal phase of α phase and no θ phase.

The same operation as in [Production of Fine Alumina Powder] of Example 1 was performed on this fired alumina product to obtain an alumina powder. This alumina powder had a BET specific surface area of 11 m ² / g. This powder is molded at a pressure of 30 MPa
By uniaxial pressing, then isostatic pressing (CIP) at a molding pressure of 100 MPa, and molding the molded body in air at 1250 ° C. for 2 hours at normal pressure. It was 90%.

Comparative Example 2 Alumina powder was obtained in the same manner as in Comparative Example 1 except that the firing temperature was changed to 1150 ° C. This alumina powder has a BET specific surface area of 10 m ² / g and a main crystal phase of α
Although it was a phase, it contained a θ phase.

Test Example 1 [Production of Alumina Burned Product of Example 1], except that an intermediate alumina powder having a bulk density (α-alumina conversion) of 0.2 g / cm ³ was used and the dew point of the furnace atmosphere and the firing temperature were changed. ] The same operation as above was performed to obtain an alumina calcined product. FIG. 4 shows the correlation between the firing temperature at each dew point and the BET specific surface area of the obtained alumina fired product.

Test Example 2 The same operation as in [Production of Alumina Burned Product] of Example 1 was carried out except that an intermediate alumina powder having a bulk density (converted to α-alumina) of 0.9 g / cm ³ was used and the firing temperature was changed. As a result, an alumina calcined product was obtained. FIG. 5 shows the correlation between the calcination temperature and the BET specific surface area of the obtained calcinated alumina.

Test Example 3 Alumina hydroxide powder was used, except that the firing temperature was changed.
The same operation as in [Production of Alumina Fired Product] of Example 1 was performed to obtain an alumina fired product. FIG. 6 shows the correlation between the calcination temperature and the BET specific surface area of the obtained calcinated alumina.

[0043]

The alumina calcined product of the present invention is suitable as a raw material for producing fine α-alumina powder. Further, according to the method for producing a calcined alumina product of the present invention, the calcined alumina product can be easily obtained. Furthermore, when the fine α-alumina powder of the present invention is sintered, a dense sintered body is obtained, so that a sintered body (ceramics) having excellent mechanical strength and corrosion resistance can be obtained.

[Brief description of drawings]

1 is an XRD spectrum of the intermediate alumina used in Example 1. FIG.

2 is an XRD spectrum of the calcined alumina material obtained in Example 1. FIG.

FIG. 3 TEM of the fine alumina powder obtained in Example 1.
Photo.

FIG. 4 is a firing temperature when firing an intermediate alumina powder having a bulk density of 0.2 g / cm ³ and the obtained alumina fired product B.
Correlation diagram of ET specific surface area.

FIG. 5: Baking temperature when firing an intermediate alumina powder having a bulk density of 0.9 g / cm ³ and B of the obtained alumina fired product
Correlation diagram of ET specific surface area.

FIG. 6 is a correlation diagram between the baking temperature when baking aluminum hydroxide and the BET specific surface area of the obtained baked alumina product.

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Claims (9)

[Claims] 1. A BET specific surface area of 10 to 20 m ² / g, a main crystalline phase is an α phase, a θ phase is not substantially contained, and an average particle diameter is 0.5 μm or less. A fired alumina product. 2. A method for producing a calcined alumina product, which comprises calcining an α-alumina precursor substantially free of metal elements other than aluminum in an atmosphere having a steam partial pressure of 600 Pa or less. 3. The method according to claim 2, wherein the α-alumina precursor is fired in the presence of α-alumina. 4. The bulk density of the α-alumina precursor converted to α-alumina is 0.5 g / cm ³ or less.
The manufacturing method described in. 5. The production method according to claim 2, wherein the α-alumina precursor has a main component of intermediate alumina or aluminum hydroxide. 6. An α-alumina precursor is calcined before firing,
The manufacturing method according to claim 3, wherein the α-alumina precursor is allowed to coexist with the α-alumina. 7. The method according to claim 3, wherein the α-alumina precursor is mixed with the α-alumina particles before the calcination so that the α-alumina precursor coexists with the α-alumina. 8. The manufacturing method according to claim 2, wherein the firing is performed at 1000 ° C. or higher and 1250 ° C. or lower. 9. A BET specific surface area of 1 with a purity of 99.99% or more.
12 m ² / g or more, containing substantially no intermediate alumina,
The relative density of the sintered body obtained by sintering at 50 ° C. and normal pressure is 9
Fine α-alumina powder characterized by being 5% or more.