JP4043805B2 - Method and apparatus for producing hollow alumina particles - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing hollow alumina particles, and more particularly to a production method capable of controlling the particle size of hollow alumina particles. Moreover, this invention relates to the manufacturing apparatus for enforcing the said method.
[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 methods for producing hollow alumina particles, recently, ultrasonic waves are applied to an aluminum nitrate aqueous solution to generate fine droplets of the aluminum nitrate aqueous solution in the form of a mist. Sonic spray pyrolysis has been proposed. According to this ultrasonic spray pyrolysis method, since micro droplets are instantaneously fired, micro alumina hollow particles close to a true sphere can be obtained.
[0004]
[Problems to be solved by the invention]
However, in the conventional ultrasonic spray pyrolysis method, since fine droplets generated by the action of ultrasonic waves are sent to the firing furnace as they are, various hollow alumina particles having different particle sizes 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 such a condition, and it aims at providing the manufacturing method and manufacturing apparatus of the hollow alumina 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, the present invention provides the following alumina hollow particle production apparatus and production method.
(1) A storage container for storing an aqueous solution of aluminum nitrate or an aqueous solution of aluminum acetate, an ultrasonic generator for irradiating the aqueous solution with ultrasonic waves, a main body for flowing in droplets generated by ultrasonic irradiation, and an inside of the main body In the liquid droplet selection section, the liquid droplet selection section including the air introduction pipe and a pipe having one end facing the air introduction pipe and the other end connected to a furnace pipe installed in the firing furnace. An apparatus for producing hollow alumina particles, characterized in that air is jetted from the air introduction pipe, and droplets floating above the air introduction pipe are sent to the furnace pipe by an air flow and fired in the air.
(2) Using the manufacturing apparatus described in (1) above, ultrasonic waves are radiated to an aluminum nitrate aqueous solution or an aluminum acetate aqueous solution to generate droplets that are flown into a droplet sorter and eject air from an air introduction tube. The alumina is characterized in that droplets floating above the air introduction tube are introduced into the furnace tube by an air flow and baked in the air, and the baked particles are separated from solid particles based on the specific gravity difference. A method for producing hollow particles.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail.
[0008]
The method for producing hollow alumina particles of the present invention is based on the ultrasonic spray pyrolysis method. That is, FIG. 1 (A) is a schematic configuration diagram showing an example of an apparatus suitable for carrying out the production method of the present invention. First, an aluminum nitrate aqueous solution or an aluminum acetate aqueous solution 1 filled in a storage container 10 is used. Ultrasonic waves are emitted from the ultrasonic generator 11 to generate fine droplets 1a of an aluminum nitrate aqueous solution or an aluminum acetate aqueous solution in the form of a mist. At the same time, a certain amount of air is introduced into the storage container 10 through the air introduction tube 12, and the generated aluminum nitrate aqueous solution or the micro droplet 1 a of the aluminum acetate aqueous solution is raised inside the supply tube 13 to the droplet sorting unit 14. send.
[0009]
As shown in an enlarged view in FIG. 1B, the droplet sorting unit 14 includes an air introduction tube 16 that is horizontally inserted toward the center of the main body 15. Then, by introducing a certain amount of air into the main body 15 through the air introduction pipe 16, the air flows into the main body 15 through the supply pipe 13, and the floating microdroplets 1 a of the aqueous aluminum nitrate solution or the aqueous aluminum acetate solution are generated by the air current It is configured to send out to the furnace tube 21 of the firing furnace 20. Therefore, the lighter, ie, smaller than a certain particle size, microfluid that floats above the position of the air introduction pipe 16 in the microdroplet 1a of the aluminum nitrate aqueous solution or the aluminum acetate aqueous solution that floats inside the main body 15. Only the droplet 1b is sent out to the furnace tube 21 by the airflow.
[0010]
The furnace tube 21 is maintained at a firing temperature, for example, 1200 to 1300 ° C. by the heater 22, and the fine droplets 1b of the aluminum nitrate aqueous solution or the aluminum acetate aqueous solution are decomposed and fired while passing through the furnace tube 21 to be alumina. The hollow particles 30 are deposited on the end of the furnace tube 21. Here, the thermal decomposition / baking time in the baking furnace 20 is adjusted by the amount of air supplied from the air introduction pipe 16 in the liquid low sorting section 14. Further, the gas (NOx) generated during pyrolysis and firing was absorbed after washing with an appropriate alkali 40.
[0011]
As schematically shown in FIG. 2, the above-described decomposition and firing mechanism is such that the microdroplets 1 b of the aqueous aluminum nitrate solution or the aqueous aluminum acetate solution are made of alumina by instantly oxidizing the aluminum ions present in the outer peripheral portion thereof. An outer shell 30a is formed, and at the same time, an aluminum nitrate or aluminum acetate aqueous solution 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 microdroplet 1b of the aluminum nitrate aqueous solution or the aluminum acetate aqueous solution as the starting material is substantially maintained, and the alumina hollow particles 30 are obtained. In the present invention, since the fine droplets 1b of the aluminum nitrate or aluminum acetate aqueous solution are sorted by the particle size by the droplet sorting unit 14 as described above, the obtained alumina hollow particles 30 have a uniform particle size. Become.
[0012]
Moreover, as shown also in the Example mentioned later, according to said method, the micro droplet 1b of aluminum nitrate aqueous solution or aluminum acetate aqueous solution becomes a solid alumina particle, so that it becomes small diameter. The generation mechanism of the solid particles is assumed as follows.
[0013]
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.
[0014]
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 above-described method, the droplet selection unit 14 can separate the minute droplet 1b having a certain particle diameter or less, but cannot separate the smaller droplet 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.
[0015]
Moreover, in this invention, the internal structure (hollow formation state) of the alumina hollow particle 30 produced | generated by the density | concentration of aluminum nitrate aqueous solution or aluminum acetate aqueous solution is controllable based on said method.
[0016]
FIG. 3 is a diagram schematically showing the state of formation of the hollow alumina particles 30 when a micro-droplet 1b of a high concentration aluminum nitrate aqueous solution or aluminum acetate 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.
[0017]
As described above, according to the production method of the present invention, it is possible to easily obtain alumina hollow particles in a certain particle size range. Further, alumina hollow particles having different internal structures can be obtained depending on the concentration of the aluminum nitrate aqueous solution or the aluminum acetate aqueous solution.
[0018]
The alumina hollow particles obtained by the above pyrolysis / firing are predominantly δ-alumina or γ-alumina. Therefore, it is preferable to refire at 1300 ° C. for about 1 to 2 hours to convert to stable α-alumina.
[0019]
【Example】
The present invention will be further described below with reference to examples, but the present invention is not limited thereto.
[0020]
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: 0.032 minutes
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.
[0022]
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). It can be seen that substantially spherical hollow particles are formed.
[0023]
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.
[0024]
(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.
[0025]
(Example 3)
A 0.5M aluminum acetate aqueous solution was treated using the production apparatus shown in FIG. The processing conditions are as follows.
-Air supply amount to the air introduction pipe 12: 1500 mL / min-Air supply amount to the air introduction pipe 16: 1500 mL / min-Temperature of the firing furnace 20: 1300 ° C
・ Pyrolysis and firing time: 0.032 minutes
When the obtained powder was taken out and subjected to X-ray diffraction analysis, it was confirmed to be γ-alumina. Therefore, the powder was refired at 1300 ° C. for 2 hours. X-ray diffraction analysis of the refired powder confirmed that it was α-alumina.
[0027]
Moreover, when the scanning electron micrograph and the transmission electron micrograph of the powder after rebaking were photographed, the average particle size was 650 nm and the particle size range was about 50 to 1000 nm. The average particle wall thickness was 20 nm.
[0028]
Example 4
A 0.9 M aluminum acetate aqueous solution was treated under the same conditions as in Example 3 and refired to obtain a powder having an average particle size of 400 nm and a particle size range of about 150 to 900 nm. And when the transmission electron micrograph of this powder was image | photographed, it was confirmed that it is a sponge-like hollow particle in which the hollow part was formed inside.
[0029]
【The invention's effect】
As described above, according to the present invention, hollow alumina particles having a uniform particle diameter can be obtained based on the ultrasonic spray pyrolysis method.
[Brief description of the drawings]
FIG. 1A is a schematic configuration diagram showing an apparatus suitable for carrying out the manufacturing method of the present invention, and FIG. 1B is an enlarged view of a droplet sorting unit.
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.
4 is a scanning electron micrograph (a) and a transmission electron micrograph (b) of the powder after refired obtained in Example 1. FIG.
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 or aluminum acetate aqueous solution 1b Microdroplet 10 of aluminum nitrate aqueous solution or aluminum acetate aqueous solution 10 Storage container 11 Ultrasonic generator 12 Air introduction pipe 13 Supply pipe 14 Droplet sorter 15 Main body 16 Air introduction pipe 20 Firing furnace 21 Furnace tube 22 Heater 30 Hollow alumina particles 30a Outer shell 30b Gel 30c Alumina 30d Minute void 40 Alkali

Claims (7)

A storage container for storing the aqueous solution of aluminum nitrate or acetate aqueous solution of aluminum, and ultrasonic generator for irradiating ultrasonic waves to the aqueous solution, rush droplets generated by the ultrasonic wave irradiation in the body and the body for flowing the air stream A liquid droplet sorting section including an air introduction pipe, and a pipe having one end facing the air introduction pipe and the other end connected to a furnace pipe installed in the firing furnace,
The alumina hollow characterized in that, in the droplet selection unit, air is ejected from the air introduction tube, and droplets floating above the air introduction tube are sent to the furnace tube by an air flow and fired in the air. Particle production equipment . Using the manufacturing apparatus according to claim 1, ultrasonic waves are radiated to an aluminum nitrate aqueous solution or an aluminum acetate aqueous solution to generate droplets, which are caused to flow into a droplet sorter, and air is ejected from an air introduction tube. the droplets float above the inlet pipe is introduced into the furnace tube by a gas stream and calcined in air, and characterized that you fractionation with solid particles based on specific gravity difference from the particles after firing to luer Lumina A method for producing hollow particles. The resulting hollow alumina particles, further refiring to method for producing alumina hollow particles according to claim 2, wherein Rukoto. 0. With 5 M aqueous solution of aluminum nitrate, and method for producing alumina hollow particles according to claim 3, wherein the obtaining a hollow alumina particles having a particle diameter of 150 to 5 00n m. 0. Using aluminum nitrate aqueous solution of 9 M, in particle size 1 50 to 9 nm, and a hollow alumina particles according to claim 3, wherein the obtaining a spongy hollow alumina particles having a plurality of fine hollow portion therein Production method. 0. 5 with M acetic acid aqueous solution of aluminum, a manufacturing method of hollow alumina particles according to claim 3, wherein the obtaining the alumina hollow particles having a particle diameter 5 0 to 10 00n m. Acetic acid aqueous solution of aluminum 0.9 M, at a particle size 150～900Nm, and inside of the hollow alumina particles according to claim 3, wherein Rukoto obtain a sponge-like alumina hollow particles having a plurality of fine hollow portion Production method.

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