JP4172926B2 - Alumina hollow particle production equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a production apparatus for hollow alumina particles, and more particularly to a production apparatus capable of controlling the particle diameter of hollow alumina particles.
[0002]
[Prior art]
For example, composite materials in which ceramic particles are dispersed in a base material such as metal are widely used for the purpose of reducing the weight of the material and increasing the strength. Among these, alumina hollow particles have low thermal conductivity and high thermal stability, and have characteristics such as hot load softening temperature, hot elastic modulus, and low reheat shrinkage. It attracts attention as a functional filler to be imparted.
[0003]
As one of the production equipment for hollow alumina particles, recently, an ultrasonic wave is applied to an aluminum nitrate aqueous solution to generate fine droplets of the aluminum nitrate aqueous solution in the form of a mist. A manufacturing apparatus using a sonic spray pyrolysis method has been proposed. According to this alumina hollow particle manufacturing apparatus, minute droplets are fired instantaneously, so that minute alumina hollow particles close to a true sphere can be obtained.
[0004]
[Problems to be solved by the invention]
However, in the conventional alumina hollow particle production apparatus, the fine droplets generated by the action of ultrasonic waves are sent to the firing furnace as they are, so that various alumina hollow particles having different particle diameters are mixed, and the composite material In order to use it as a raw material, classification work is required separately.
[0005]
This invention is made | formed in view of the said subject, and it aims at providing the manufacturing apparatus of the alumina hollow particle which can control particle size, employ | adopting an ultrasonic spray pyrolysis method.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, an apparatus for producing hollow alumina particles according to claim 1 of the present invention comprises an ultrasonic generator that irradiates an aqueous solution of aluminum nitrate with ultrasonic waves and generates fine droplets of the aqueous solution in the form of a mist. , An alumina hollow particle production apparatus comprising a firing furnace for thermally decomposing and firing the micro droplets and a moving means for moving the micro water droplets into the firing furnace, the moving means being substantially at the center. Air is introduced from a horizontally inserted air introduction tube to generate an air flow, and only the minute droplets that are supplied from below and are suspended in the height of the air introduction tube are supplied with the air flow. It has the droplet selection part moved to the inside of the above-mentioned calcination furnace.
[0007]
According to the alumina hollow particle manufacturing apparatus having the above-described configuration, it is possible to obtain alumina hollow particles having a predetermined particle size or less while employing an ultrasonic spray pyrolysis method. At that time, among the mist-like microdrops supplied to the droplet sorting section, only the lighter, that is, the microdroplets with a certain particle size or less floating above can be moved into the firing furnace. Alumina hollow particles having a predetermined particle size or less can be obtained.
Depending on the concentration of the aqueous aluminum nitrate solution used, alumina hollow particles having different particle diameters can be obtained, and further, sponge-like alumina hollow particles having a plurality of minute voids inside can be obtained.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail. FIG. 1 (A) is a schematic configuration diagram showing an embodiment of an alumina hollow particle production apparatus of the present invention, FIG. 1 (B) is an enlarged view of a droplet sorting section in FIG. 1 (A), and FIG. FIG. 3 is a schematic diagram for explaining the generation mechanism of particles, FIG. 3 is a schematic diagram for explaining the generation mechanism of sponge-like alumina hollow particles, and FIG. 4 (a) is a diagram of the powder after recalcination obtained in Example 1. Scanning electron micrograph, FIG. 4B is a transmission electron micrograph of the powder after recalcination obtained in Example 1, and FIG. 5 is the particle size distribution of the powder after refiring obtained in Example 1. 6 is a transmission electron micrograph of the powder after recalcination obtained in Example 2, and FIG. 7 is a graph showing the particle size distribution of the powder after refiring obtained in Example 2.
[0011]
As shown in FIG. 1 (A), the alumina hollow particle production apparatus of the present embodiment includes a storage container 10 filled with an aqueous aluminum nitrate solution 1 and ultrasonic waves that generate fine droplets 1a of the aqueous aluminum nitrate solution in a mist form. A generator 11, a droplet sorting unit 14 that is a moving unit that moves only the minute droplets 1 b having a predetermined particle size or less to the firing furnace 20, and a firing furnace 20 that thermally decomposes and fires the minute droplets 1 b are provided. Yes.
Further, the supply to the storage container 10 is supplied to supply the micro droplet 1a to the air introduction pipe 12 for introducing the air into the storage container 10 and the droplet sorting unit 14, which are means for moving the micro droplet 1a. A tube 13 is provided. The supply pipe 13 extends vertically toward the droplet sorting unit 14 provided above and communicates with the center bottom of the main body 15 of the droplet sorting unit 14.
[0012]
In the production apparatus for hollow alumina particles in the present embodiment, first, the aluminum nitrate aqueous solution 1 filled in the storage container 10 is irradiated with ultrasonic waves from the ultrasonic generator 11 to form fine droplets 1a of the aluminum nitrate aqueous solution in a mist form. generate. At the same time, a certain amount of air is introduced into the storage container 10 through the air introduction pipe 12, and the generated fine droplets 1 a of the aluminum nitrate aqueous solution are sent to the droplet sorting unit 14 through the supply pipe 13.
[0013]
The droplet sorting unit 14 is provided almost directly above the storage container 10 and is inserted horizontally toward the center of the main body 15 which is a glass sphere, as shown in an enlarged view in FIG. An air introduction pipe 16 is provided. The air introduction pipe 16 is horizontally held by a support portion 17 having a side portion of the main body 15 extending in a cylindrical shape toward the outside, and is opened near the other side portion inside the main body 15. It has an end and forms an inlet 16a for the introduced air. The main body 15 has a droplet introduction tube 18 extending from the other side in the direction opposite to the air introduction tube 16. The droplet introduction tube 18 extends horizontally to the central portion in the furnace tube 21 of the firing furnace 20.
[0014]
By introducing a certain amount of air into the main body 15 through the air introduction tube 16, a lateral air flow is generated toward the droplet introduction tube 18. Then, the micro droplet 1a of the aluminum nitrate aqueous solution flowing in from the lower supply tube 13 and floating inside the main body 15 is sent out to the droplet introduction tube 18 and further to the furnace tube 21 by this air flow. It has become.
Therefore, among the fine droplets 1a of the aluminum nitrate aqueous solution floating inside the main body 15, only the fine droplets 1b having a predetermined particle diameter or less floating near the jet port 16a of the air introduction tube 16 are flown into the furnace tube. 21 is sent out.
[0015]
The firing furnace 20 includes a furnace tube 21 provided in the lateral direction at the center and a heater 22 that covers the furnace tube 21 in the circumferential direction. Further, a droplet introduction tube 18 extending from the droplet sorting unit 14 is horizontally inserted into the furnace tube 21. The droplet introduction tube 18 has an open end at the center of the furnace tube 21 and ejects a micro droplet 1b of an aluminum nitrate aqueous solution introduced from the droplet sorting unit 14 in the left direction in the figure. The furnace tube 21 is maintained at a firing temperature, for example, 1200 to 1300 ° C. by the heater 22, and the micro droplet 1 b is decomposed and fired to pass through the furnace tube 21 to become alumina hollow particles 30. Deposit at the end of the. Here, the thermal decomposition and firing time in the firing furnace 20 is adjusted by the amount of air supplied from the air introduction pipe 16 in the droplet sorting section 14. Further, the gas (NOx) generated during pyrolysis and firing was absorbed after washing with an appropriate alkali 40.
[0016]
As schematically shown in FIG. 2, the above-described decomposition and firing mechanism is such that the aluminum droplet aqueous solution 1 b has an aluminum shell present in the outer peripheral portion thereof is instantly oxidized and the outer shell 30 a made of alumina is formed. At the same time, an aluminum nitrate gel 30b is formed inside the outer shell 30a. Next, the moisture contained in the gel 30b is released, and along with this release, aluminum ions are oxidized while moving outward, and the generated alumina 30c is sequentially deposited on the inner wall of the outer shell 30a. It is thought that it grows thick and eventually becomes alumina hollow particles 30. Therefore, the particle diameter of the microdroplets 1b of the aluminum nitrate aqueous solution as the starting material is substantially maintained, and the alumina hollow particles 30 are obtained. In this embodiment, since the aluminum nitrate fine droplets 1b are sorted by the particle size by the droplet sorting unit 14 as described above, the resulting alumina hollow particles 30 have a uniform particle size.
[0017]
Moreover, as shown also in the Example mentioned later, according to said manufacturing apparatus, the micro droplet 1b of aluminum nitrate aqueous solution becomes a solid alumina particle, so that it becomes a small diameter. The generation mechanism of the solid particles is assumed as follows.
[0018]
That is, since the concentration of the droplets is the same regardless of the particle size of the droplets, the outer shell 30a having a wall thickness equivalent to that of the large-diameter droplets is generated by firing. However, in the case of a small-diameter droplet, the thickness of the outer shell 30a is relatively large with respect to the particle size, and the outer shell 30a is formed up to a portion closer to the center. Therefore, in a small-diameter droplet, the hollow portion becomes small and becomes a solid particle.
[0019]
As shown also in the Example mentioned later, a hollow particle and a solid particle produce | generate by distinguishing clearly on the boundary of a certain particle size. In the manufacturing apparatus described above, the liquid droplet sorting unit 14 can sort out the fine liquid droplets 1b having a predetermined particle diameter or less, but cannot separate fine liquid droplets having a smaller diameter. However, since fine droplets with a certain particle size or less become solid particles, the solid particles are separated in advance by the difference in specific gravity, and the particle size distribution is obtained in advance. Can be easily separated with a sieve.
[0020]
Moreover, in the manufacturing apparatus of this embodiment, the internal structure (hollow formation state) of the alumina hollow particles 30 produced | generated can be controlled with the density | concentration of aluminum nitrate aqueous solution.
[0021]
FIG. 3 is a diagram schematically showing a state of formation of the alumina hollow particles 30 when the fine droplet 1b of the high concentration aluminum nitrate aqueous solution is used. At the time of firing, first, an outer shell 30a made of alumina is similarly formed. However, since the gel 30b has a higher concentration, that is, a lower water content, the release of water does not proceed smoothly and is generated locally. The alumina 30c aggregates to form a structure similar to a network structure. Then, after the moisture is released, a large number of small voids 30d derived from the network structure are generated, and the whole of the sponge-like alumina hollow particles 30 is obtained.
[0022]
As described above, according to the manufacturing apparatus of the present embodiment, alumina hollow particles in a certain particle size range can be easily obtained. Further, alumina hollow particles having different internal structures can be obtained depending on the concentration of the aqueous aluminum nitrate solution.
[0023]
The alumina hollow particles obtained by the above pyrolysis / firing are predominantly δ-alumina. Therefore, it is preferable to refire at 1300 ° C. for about 1 hour to convert to stable α-alumina.
[0024]
【Example】
The present invention will be further described below with reference to examples, but the present invention is not limited thereto.
[0025]
(Example 1)
A 0.5M aluminum nitrate aqueous solution was treated using the production apparatus shown in FIG. The processing conditions are as follows.
-Air supply amount to the air introduction tube 12: 500 mL / min-Air supply amount to the air introduction tube 16: 100 mL / min-Temperature of the firing furnace 20: 1300 ° C
・ Pyrolysis and firing time: 6.8 minutes [0026]
When the obtained powder was taken out and subjected to X-ray diffraction analysis, it was confirmed to be δ-alumina. Therefore, the powder was refired at 1300 ° C. for 1 hour. X-ray diffraction analysis of the refired powder confirmed that it was α-alumina.
[0027]
In addition, a scanning electron micrograph and a transmission electron micrograph of the powder after refiring were taken. A scanning electron micrograph is shown in FIG. 4 (a), and a transmission electron micrograph is shown in FIG. 4 (b). From these, it can be seen that substantially spherical hollow particles are generated.
[0028]
Furthermore, the particle size distribution of the powder after recalcination was determined. The result is shown in FIG. 5, which is roughly divided into two distribution curves. From a comparison with an electron micrograph, the small diameter side (a) is solid particles, the average particle diameter is 56.6 nm, about 30 The particle size range was ˜60 nm. Moreover, the large diameter side (b) was a hollow particle, the average particle diameter was 275.7 nm, and was the particle size range of about 150-500 nm.
[0029]
(Example 2)
A 0.9M aluminum nitrate aqueous solution was treated under the same conditions as in Example 1, and a transmission electron micrograph of the powder after recalcination was taken. As shown in FIG. 6, it can be seen that the particles are sponge-like hollow particles having hollow portions formed therein. Moreover, when the particle size distribution of the powder after recalcination was calculated | required, as shown in FIG. 7, it was an average particle diameter of 568 nm, and was the particle size range of about 150-900 nm. In addition, based on the result of Example 1, solid particles were previously removed with a sieve.
[0030]
【The invention's effect】
As described above, according to the alumina hollow particle production apparatus of the present invention, since it has a droplet sorting unit that moves only micro droplets of an aluminum nitrate aqueous solution having a predetermined particle size or less to a firing furnace, While adopting the sonic spray pyrolysis method, alumina hollow particles having a uniform particle diameter can be obtained.
[Brief description of the drawings]
1A and 1B show an embodiment of a method for producing alumina hollow particles of the present invention, in which FIG. 1A is a schematic configuration diagram, and FIG. 1B is an enlarged view of a droplet sorting unit in FIG.
FIG. 2 is a schematic view for explaining a generation mechanism of alumina hollow particles.
FIG. 3 is a schematic view for explaining a generation mechanism of sponge-like alumina hollow particles.
FIG. 4 is a micrograph of the powder after recalcination obtained in Example 1, (a) is a scanning electron micrograph, and (b) is a transmission electron micrograph.
5 is a graph showing the particle size distribution of the powder after recalcination obtained in Example 1. FIG.
6 is a transmission electron micrograph of the powder after refired obtained in Example 2. FIG.
7 is a graph showing the particle size distribution of the powder after recalcination obtained in Example 2. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Aluminum nitrate aqueous solution 1a Microdroplet 1b of aluminum nitrate aqueous solution Microdroplet 10 of aluminum nitrate aqueous solution below predetermined particle size 10 Storage container 11 Ultrasonic generator 12 Air introduction pipe 13 Supply pipe 14 Droplet sorter 15 Main body 16 Air introduction Pipe 16a Ejection part 17 Support part 18 Droplet introduction pipe 20 Firing furnace 21 Furnace pipe 22 Heater 30 Alumina hollow particles 30a Outer shell 30b Gel 30c Alumina 30d Micro void 40 Alkali

Claims (1)

An ultrasonic generator for irradiating an aqueous solution of aluminum nitrate with ultrasonic waves to generate fine droplets of the aqueous solution in a mist form, a firing furnace for thermally decomposing and firing the fine droplets, and the fine water droplets in the firing furnace In the apparatus for producing alumina hollow particles provided with moving means for moving to
The moving means introduces air from an air introduction tube inserted substantially horizontally in the center to generate an air flow, and the mist-like micro droplets are supplied from below to float the height of the air introduction tube. apparatus for producing alumina hollow particles characterized by having a droplet sorting unit that moves only the microdroplets in the sintering furnace by the air flow.

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