JPH0478562B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention removes water and oil by heating a water-in-oil emulsion produced by mixing oil with an aqueous solution of a water-soluble metal compound and using ultrasonic vibration. The present invention relates to a method for manufacturing ceramic microspheres.

[Prior Art] As a method for producing ceramic microspheres of this type, the present applicant has developed a method for producing a suspension of fine ceramic powder dispersed in water, which has approximately the same specific gravity as the suspension and which is not mixed with water. A patent application was filed for a method for obtaining ceramic microspheres by dispersing them in the form of small droplets in a high-boiling liquid that does not react with ceramic fine powder (Japanese Patent Application Laid-Open No. 1983-1999).
263628), and also filed a patent application for a method for obtaining ceramic microspheres by dispersing a suspension or sol of ceramic fine powder in an alcohol solution into liquid paraffin in the form of small droplets, and then evaporating the alcohol ( (Japanese Patent Publication No. 62-262734).

[Problems to be Solved by the Invention] The conventional manufacturing method described above is an excellent method for obtaining truly spherical ceramic microspheres having a uniform particle size. Since the ceramic microspheres are dispersed in the form of small droplets in a liquid, the average particle size of the resulting ceramic microspheres depends on the orifice diameter, and only relatively large particles ranging from several μm to several tens of μm can be produced.

Furthermore, in the conventional manufacturing method described above, it is necessary that the particle size of the ceramic fine powder used to prepare the suspension is always much smaller than the particle size of the target ceramic microspheres. Therefore, there was a problem in that fine ceramic powder made by a special manufacturing method such as an alkoxide hydrolysis method had to be used.

An object of the present invention is to provide a method for producing ceramic microspheres that does not require fine ceramic powder as a starting material and that can produce ceramic microspheres with a narrow particle size distribution and an average particle size on the submicron order. It's about doing.

Another object of the present invention is to provide a method for producing ceramic microspheres that can produce ceramic microspheres with a desired average particle size by changing the frequency of ultrasonic waves for producing a water-in-oil emulsion. .

[Means for Solving the Problems] In order to achieve the above object, the method for producing ceramic microspheres of the present invention includes mixing an aqueous solution in which a water-soluble metal compound is dissolved with an oil that is insoluble in this aqueous solution and has a higher boiling point than water. Then, ultrasonic vibration is applied to this mixed liquid to generate a water-in-oil emulsion, and this emulsion is heated at a temperature below the boiling point of water to evaporate the water in the droplets in which the water-soluble metal compound is dissolved. After dispersing a spherical water-soluble metal compound in the oil phase, this dispersion is heated in a temperature range that is higher than the temperature at which the water-soluble metal compound decomposes and becomes a metal oxide and lower than the temperature at which grain growth of the metal oxide starts. In this method, the oil is removed by evaporation or decomposition to obtain metal oxide microspheres.

The starting material of the present invention is a water-soluble metal compound constituting the target ceramic. This water-soluble metal compound is dissolved in water at a temperature of 20 to 50°C at a predetermined composition ratio to prepare an aqueous solution.

This aqueous solution is mixed with oil to form a water-in-oil emulsion. The oil is not particularly limited as long as it is insoluble in the water solubility and has a boiling point higher than water.
Paraffin oil is preferred from the viewpoint of toxicity and cost.
Further, when producing an emulsion, it is better to use an emulsifier in order to make the emulsion exist stably for a long time. This emulsifier may be any emulsifier such as an ionic emulsifier or a nonionic emulsifier. 35 to 100 parts by weight of oil and 1 to 6 parts by weight of emulsifier are mixed with 100 parts by weight of the above aqueous solution.

One of the characteristics of the present invention is that the emulsion is generated by ultrasonic vibration. When the emulsion is generated by a means other than ultrasonic vibration, such as a stirring homogenizer or a pressure homogenizer, the diameter of the droplets is partially on the order of submicrons, but on average it is on the order of submicrons. Moreover, since the distribution width of the droplet size is wide, the average particle size of the ceramic microspheres finally obtained is large and irregular. Therefore, methods other than ultrasonic vibration are not suitable for the present invention. The frequency of this ultrasound is 10kHz~
A range of 100kHz is preferred. Ultrasound is generally a sound wave with a frequency above the audible range, that is, 20 kHz or more, but in the present invention, even at a frequency of 10 kHz, the average diameter of the droplet can be made to the order of submicrons, so the frequency is 10 kHz. In the above, the term ultrasonic wave is also used for sound waves below 20kHz. When the frequency is increased to make the ultrasound stronger, the average particle size of the ceramic microspheres, which is the final product of the present invention, becomes even finer.On the other hand, when the frequency is lowered to make the ultrasound weaker, the average particle size becomes larger. . From this, by appropriately selecting the frequency of the ultrasonic waves, the average particle size can be set to a desired value.

When heating the generated emulsion to evaporate the water in the droplets in which the water-soluble metal compound is dissolved, the higher the heating temperature, the faster the water in the droplets can be removed, but if the temperature exceeds 100°C, the water will boil. temperature below 100°C, preferably 70°C, as this will cause the emulsion to break.
~95℃ is good.

Furthermore, the heating temperature when evaporating or decomposing the oil and thermally decomposing the water-soluble metal compound is at least the temperature at which the water-soluble metal compound decomposes into a metal oxide and lower than the temperature at which grain growth of this metal oxide starts. It is necessary that there be.

[Function] When oil is mixed with an aqueous solution in which a water-soluble metal compound is dissolved, an emulsifier is added if necessary, and ultrasonic vibration is applied, a strong cavitation effect due to ultrasonic waves is uniformly applied to the entire mixed liquid, and the water-soluble metal compound is dissolved. It is finely divided into droplets on the order of submicrons and dispersed in the oil phase. By appropriately setting the frequency of the ultrasonic waves, a desired average particle size of the microspheres can be determined.

When this emulsion is heated to evaporate the water in the droplets in which the water-soluble metal compound is dissolved, the droplets are concentrated and the spherical water-soluble metal compound on the order of submicrons is dispersed in the oil phase.

By heating the oil liquid in which the water-soluble metal compound is dispersed to evaporate or decompose the oil and thermally decompose the water-soluble metal compound, submicron-order metal oxide microspheres can be obtained.

[Effects of the Invention] As described above, the manufacturing method of the present invention involves generating an emulsion in which droplets of a water-soluble metal compound on the order of submicrons are dispersed in an oil phase by ultrasonic vibration, and then heating this emulsion. Since ceramic microspheres are produced by sequentially removing water and oil, powder particles that are close to perfect spheres can be obtained without using fine ceramic powder as a starting material as in the past.

In particular, since the emulsification is carried out by ultrasonic vibration and the evaporation and decomposition temperature of the oil is below the grain growth initiation temperature of the metal oxide, the resulting particles are essentially in point contact with each other and do not aggregate, but are Ceramic microspheres have an average particle size on the order of microns and a narrow particle size distribution.

Furthermore, by appropriately selecting the frequency of the ultrasonic waves, the average particle diameter of the microspheres can be set to a desired value.

[Example] Next, an example of the present invention will be described together with a comparative example.

<Example 1> An aqueous solution was prepared by dissolving 10 g of ZrO(NO ₃ ) _{2.2H 2} O in 50 g of water at 40°C. Add 25g of paraffin oil to this aqueous solution and use polyoxyethylene as an emulsifier.
After adding 1 g of nonyl phenyl ether, ultrasonic vibration was applied for 15 seconds using an ultrasonic generator (B-30 manufactured by Branson) to produce a water-in-oil emulsion. The frequency of the ultrasound at this time was 30kHz.
Place this emulsion in a dryer at 80°C under atmospheric pressure.
The water was removed by evaporation. The emulsion became a suspension in which ZrO ₂ particles were dispersed. This suspension was calcined at a temperature of 700°C under atmospheric pressure for 3 hours to decompose and remove the oil, yielding ZrO ₂ spheres. When the particle size of this ZrO ₂ sphere was measured using a scanning electron microscope, it was found to be extremely fine with an average particle size of 0.1 μm and a particle size distribution width of ±0.02 μm, with little variation.
They were monodisperse ceramic microspheres of ZrO ₂ .

<Comparative Example 1> Example 1 except that the emulsion was generated using a stirring homogenizer instead of the ultrasonic generator.
_Two ZrO spheres were obtained in the same manner. When the particle size of this ZrO ₂ was measured in the same manner as in Example 1, it was found to be ceramic microspheres with a wide particle size distribution of 0.1 to 3 μm.

<Example 2> ZrO(NO ₃ ) _{2.2H 2} O 5.34g and Pb(CH ₃ COO)
The same procedure as in Example 1 was used except that an aqueous solution of 6.76 g of 2.3H ₂ O dissolved in 50 g _of water at 40°C was used.
_Three spheres of PbZrO were obtained. As in Example 1, this PbZrO ₃
When the particle size of the sphere was measured, it was 0.1, the same as in Example 1.
Extremely fine ±0.02μm with narrow particle size distribution
They were monodisperse ceramic microspheres of PbZrO ₃ .

<Comparative Example 2> Example 2 except that the emulsion was generated using a pressure homogenizer instead of the ultrasonic generator.
_Three PbZrO spheres were obtained in the same manner. When the particle size of this PbZrO ₃ was measured in the same manner as in Example 1, it was found to be ceramic microspheres with a wide particle size distribution of 0.1 to 3 μm, the same as in Comparative Example 1.

<Example 3> Example 1 except that the ultrasonic frequency was 10kHz
_Two ZrO spheres were obtained in the same manner. When the particle size of this ZrO ₂ was measured in the same manner as in Example 1, the average particle size was 0.7 μm, which was slightly larger than in Example 1, and the particle size distribution width was ±0.11 μm, which was slightly wider than in Example ₁ . It was a micro sphere.

<Example 4> ZrO ₂ spheres were obtained in the same manner as in Example 1 except that the frequency of the ultrasonic waves was 100 kHz. When the particle size of this ZrO ₂ was measured in the same manner as in Example 1, the average particle size was 0.02 μm, which was much smaller than in Example 1, and the particle size distribution width was ±0.003 μm, which was much narrower than in Example _1.
They were monodisperse ceramic microspheres.

Claims (1)

[Claims] 1. Mixing an aqueous solution in which a water-soluble metal compound is dissolved with an oil that is insoluble in this aqueous solution and has a higher boiling point than water, and applying ultrasonic vibration to this mixture to produce a water-in-oil emulsion, This emulsion is heated at a temperature below the boiling point of water to evaporate the water in the droplets in which the water-soluble metal compound is dissolved, and the spherical water-soluble metal compound is dispersed in the oil phase. The ceramic material is heated in a temperature range above the temperature at which the metallic compound decomposes to become a metal oxide and below the temperature at which the grain growth of the metal oxide begins, to evaporate or decompose and remove the oil, thereby obtaining metal oxide microspheres. Method for manufacturing microspheres. 2. The method for producing ceramic microspheres according to claim 1, wherein microspheres having a desired average particle size are obtained by selecting the frequency of the ultrasonic waves from a range of 10kHz to 100kHz. 3. The method for producing ceramic microspheres according to claim 1, wherein a water-in-oil emulsion is produced by adding an emulsifier together with oil to an aqueous solution in which a water-soluble metal compound is dissolved.