JP2001199718A - Alpha-alumina superfine particle and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently obtain high purity α-alumina superfine-particle powder having an average particle diameter of <=0.1 μm and containing very little of impurities such as metallic oxides except alumina. SOLUTION: A method for producing α-alumina superfine particles features firing γ-alumina superfine particles produced by a gas phase method up to substantial transformation into α-alumina superfine particles. This α-alumina superfine-particle powder substantially composed of the α-alumina phase and having an average particle diameter of <100 nm is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a polymer having an average particle size of several tens.
The present invention relates to a high-purity α-alumina ultrafine particle powder having a nanometer order and containing almost no impurities such as metal oxides other than alumina, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, methods for producing α-alumina powder include alum pyrolysis, organometallic hydrolysis, ethylene chlorohydrin, spark discharge, ammonium aluminum carbonate pyrolysis, and improved Bayer's method. It is known that the average particle size is 0.1 μm or less α-
Alumina powder was not obtained. Patent No. 2944839
In No. 2, a method is proposed in which a barrier layer such as silica is formed on the surface of boehmite particles and firing is performed.However, since the barrier substance remains as an impurity and is generated as an aggregate of primary particles, Need to be crushed.

[0003]

According to the present invention, high-purity α-alumina ultrafine particles having an average particle size of 0.1 μm or less and containing almost no impurities such as metal oxides other than alumina are efficiently obtained. It is done for the purpose of.

[0004]

Means for Solving the Problems The present inventor uses γ-alumina ultrafine particles produced by a gas phase method as a raw material, and when firing the γ-alumina to obtain an α-alumina, the average particle size is controlled by controlling the calcination conditions. It has been found that α-alumina ultrafine particles having a particle size of less than 0.1 μm are efficiently produced, and the present invention has been completed based on this finding.

That is, the present invention provides a method for producing α-alumina ultrafine particles, which comprises firing the γ-alumina ultrafine particles produced by a gas phase method until the particles are substantially converted to an α-alumina phase. An object of the present invention is to provide α-alumina ultrafine particle powder substantially comprising an α-alumina phase and having an average particle size of less than 100 nm. In addition, “substantially transform into α-alumina phase” or “consisting substantially of α-alumina phase” means that the weight percentage of α-alumina phase in all alumina phases is 70% or more, preferably 85%. As mentioned above, more preferably, it is 95% or more.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of the present invention, as a raw material, a gas phase such as a reaction gas phase method such as an electric furnace method, a chemical flame method or a plasma method, or a plasma heating method for heating and evaporating aluminum oxide (molten pool evaporation method) is used. Γ-alumina particles produced by the phase method are used, but a method of oxidizing aluminum vapor generated by a direct current plasma method or a high frequency induction plasma method or a spherical, non-porous and high-purity γ-alumina by a molten pool evaporation method Ultrafine particles are preferred. The γ-alumina particles used as a raw material in the method of the present invention preferably have an average particle diameter of 50 nm or less.

When γ-alumina is fired at a high temperature of 1200 ° C. or more, it is transformed into an α phase via a δ phase and a θ phase to be thermally stabilized and has a high hardness. This increases the particle size. In the present invention, the term γ-alumina does not mean only γ-alumina in a strict sense, but refers to α-alumina, α-alumina or other such α-alumina.
-Refers to γ-alumina in a broad sense including transformations other than alumina. In the method of the present invention, spherical γ-alumina particles are calcined in a fluidized state using a rotary kiln or the like, and
In the range of 200 ° C. to 1300 ° C. (preferably 1250 ° C. or less) and 5 minutes to 30 minutes (preferably 20 minutes or less), the firing temperature and time necessary and sufficient for the transition to the α phase are controlled. .

If the firing temperature is less than 1200 ° C., the transition to the α phase is incomplete, and if the firing temperature exceeds 1300 ° C.,
-It is not preferable because the particle size of the alumina particles increases.

[0009]

Next, the present invention will be described by way of examples.

The sample particles were measured and analyzed by the following methods. (1) Average particle size The specific surface area [m ² / g] was measured by the BET method using a specific surface area measuring device ASAP-2010 (manufactured by Shimadzu Corporation), and the following equation was obtained using the specific surface area and density [g / cm ³ ]. Was calculated by Average particle size (nm) = 6 × 10 ³ / (density × specific surface area) (2) Crystal system (degree of transition to α phase) Intensity of crystal peak using X-ray diffractometer MINIFLEX (manufactured by Rigaku Corporation) Was analyzed, and the degree of transition to the α phase was calculated.

Example 1 Using an arc discharge type plasma generator, an aluminum metal rod installed in a chamber as an anode was evaporated by a plasma flame generated by arc discharge, and the generated aluminum vapor was oxidized to form γ-alumina. 95% or more, specific surface area 53 m ² / g, average particle diameter 31 nm, bulk specific gravity 0.28, alumina purity 99.9% or more, spherical γ-
An alumina particle powder was obtained. Next, a reaction tube (core tube) having an inner diameter of 100 mm and a length of 1.2 m (heating zone of 1.0 m).
Γ-alumina particles were fired at a temperature of 1250 ° C. for 20 minutes (residence time in a reaction tube) using a rotary kiln having The kiln setting condition is kiln gradient 4
The kiln rotation speed was 1.6 rpm and the feeder screw rotation speed was 2.0 rpm. The alumina particles after firing are
Observation with a transmission electron microscope confirmed that a true spherical ultrafine particle state was maintained. Further, γ-alumina particles are 95% or more α-alumina particles (Corundom,
(Hexagonal system), and were ultrafine particles having an average particle size of 96 nm and an alumina purity of 99.9% or more. Example 2, Comparative Example Fine particles were obtained in the same manner as in Example 1 except that the firing temperature and the firing time were changed as shown in Table 1. The crystal form of the fine particles in each of the examples was in a phase transition to a structure mainly composed of α-alumina, and was ultrafine particles having an average particle diameter of less than 100 nm. On the other hand, the crystal form of the fine particles of the comparative example substantially maintained the structure of γ-alumina as it was.

Table 1 also shows various physical properties obtained for the fine particles of each of the above examples.

[Table 1]

From the above results, it can be seen that γ-
It is understood that α-alumina ultrafine particles having an average particle diameter of less than 0.1 μm can be efficiently produced by using alumina ultrafine particles as a raw material and firing at a relatively low firing temperature.

[0014]

The α-alumina ultrafine particle powder of the present invention comprises:
Ultrafine particles having an average particle size of several tens of nanometers, which have not been conventionally obtained industrially, are of high purity consisting essentially of an α-alumina phase, and have high hardness and heat resistance. Because of its large surface area, it can be expected to be used for applications such as abrasives, high-temperature combustion catalyst carriers, and ceramic molded bodies. Further, according to the method of the present invention, by using γ-alumina ultrafine particles produced by a gas phase method as a raw material and controlling the calcination conditions, the average particle size which could not be conventionally produced industrially is 0.1 μm. It is possible to efficiently produce ultra-fine α-alumina fine particles having a fineness of less than 50 nm or less. In addition, continuous production is possible.

Claims (5)

[Claims] 1. A method for producing ultrafine α-alumina particles, which comprises firing ultrafine γ-alumina particles produced by a gas phase method until they are substantially transformed into an α-alumina phase. 2. The method according to claim 1, wherein the spherical ultrafine γ-alumina particles are calcined in a fluidized state. 3. The method according to claim 1, wherein the firing temperature is controlled to be 1200 ° C. or more and 1300 ° C. or less, and the firing time is controlled to be 5 minutes or more and 30 minutes or less. 4. Ultrafine α-alumina powder having an average particle diameter of substantially less than 100 nm and consisting essentially of an α-alumina phase. 5. An average particle size of 50 nm or less.
The powder described.