JP2769290B2 - Manufacturing method of ceramic fine powder by mist pyrolysis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fine ceramic powders such as oxides, nitrides, fluorides, etc., and relates to sintering raw material powders, photocatalysts or catalyst carriers, semiconductor sealants, abrasives, and liquid crystal spacers. , Lubricants or additives, dental additives, pigments, paints, cosmetics, crystals for YAG lasers, friction agents for magnetic materials, and the like.

[0002]

2. Description of the Related Art Conventionally, ceramic powders such as oxides, nitrides and fluorides have been used for various purposes, and various methods for producing the same have been proposed. It's being used.

For example, in the production of powder for sintering raw materials, there are a thermal decomposition method, a hydrolysis method, a sol-gel method, a coprecipitation method, a uniform precipitation method, a hydrothermal method, a gas phase method and the like.

[0004] Production of the powder for the catalyst carrier includes a sol-gel method, a coprecipitation method and a gas phase method.

[0005] However, in these production methods, mass production is difficult, and the particle size of the powder is too small to obtain a fine powder. May occur,
It was difficult to control the particle size and the particle size distribution.

[0006] Under such circumstances, the present invention provides an oxide,
It is an object of the present invention to provide a production method capable of producing fine powder having excellent particle size, particle size distribution, porosity and the like as ceramic powders such as nitrides and fluorides, and also capable of mass production.

In order to achieve the object, the production method of the present invention uses an aqueous solution in which ultrafine particles obtained by hydrolyzing a metal alkoxide are suspended as a raw material solution, and ultrasonically sprays the raw material solution to form a fine particle. The mist is dried and thermally decomposed in a heating furnace to obtain a monodispersed oxide, nitride or fluoride ceramic fine powder.

[0008]

The present invention will be described below in more detail.

One of the features of the present invention is that a fine mist is generated by using a specific raw material solution by an ultrasonic spray technique.

[0010]

[0011]

[0012]

As a raw material solution, a solution in which a metal alkoxide is dissolved can be considered. However, in order to dissolve the metal alkoxide, an organic solvent such as an alcohol is required, and as a result, it is necessary to introduce a gas such as nitrogen or argon in the pyrolysis process, which increases the production cost when viewed industrially. This can cause Moreover, since the metal alkoxide is unstable even in an alcohol-based solvent,
Long-term storage and manufacturing becomes difficult. In order to enable production in an air atmosphere and increase the stability of a solution, it is necessary to disperse a metal alkoxide as a raw material in an aqueous solution. However, when the metal alkoxide is dispersed in water, the metal alkoxide immediately precipitates and cannot be sprayed as a raw material solution. Therefore, in the present invention,
The metal alkoxide is hydrolyzed to prepare an aqueous solution in which fine particles as a hydrolysis reaction product are suspended. For example,
After hydrolyzing the metal alkoxide, sol is formed by peptization with nitric acid, and further diluted with water to obtain an oxide equivalent of 1 to 10 wt.
% Aqueous solution. The aqueous solution thus prepared enables a thermal decomposition reaction in an air atmosphere. Also,
Because of the excellent storage stability, it is possible to produce fine particles having excellent quality stability over a long period of time.

The raw material solution prepared as described above is atomized by ultrasonic spraying to generate fine mist.

The ultrasonic spraying device may be a device provided with an ultrasonic vibrator in the spraying device. The spray flow rate and the vibration frequency of the ultrasonic wave are determined as appropriate. For example, ultrasonic waves having a frequency of about 1.6 MHz are applied while spraying at a flow rate of about 10 ml / min.

Next, the generated fine mist is dried and thermally decomposed in a heating furnace. As a heating furnace for drying and thermal decomposition, a vertical or horizontal heating furnace may be used by an appropriate heating method such as infrared heating, microwave induction heating, or resistance heating. An electric furnace using an infrared heating method or a microwave induction heating method is suitable for increasing the thermal decomposition efficiency of the mist.

As a carrier gas for sending the mist into the heating furnace, an oxidizing gas such as air, oxygen, or an oxygen-containing gas, or an inert gas such as nitrogen or argon is used. In this regard, since the raw material solution according to the present invention is an aqueous solution containing a hydrolysis product of a metal alkoxide, there is an advantage that economically advantageous air can be used.

The particle size, particle size distribution, or porosity of the fine powder can be controlled by increasing or decreasing the flow rate of the fine powder. The flow rate depends on the length of the heating furnace, but is not limited as long as it is about 1 liter / min or more.
Change within a range of about 0 liter / min. Generally, when the flow rate is reduced, the particle size of the produced powder can be reduced, and the particle size distribution can be narrowed. Also, increasing the flow rate can increase the porosity (to make it porous).

Although the drying and thermal decomposition temperature depends on the material of the raw material, appropriate temperatures are generally set within a range of 200 to 400 ° C. for the drying temperature and 500 to 900 ° C. for the thermal decomposition temperature. By changing the thermal decomposition temperature for the same raw material solution, powder can be synthesized from crystalline to amorphous,
Fine powders of various properties can be produced.

FIG. 1 shows an example of equipment suitable for carrying out the present invention. The whole is a vertical arrangement, and a spray chamber equipped with an ultrasonic oscillator is installed below, and a transparent quartz tube (40 mmφ × 2000 mm) and two vertical electric furnaces (drying furnace, heat (Spray pyrolysis apparatus) equipped with a pyrolysis furnace. Glass filter or electric precipitator, aspirator for collecting generated fine powder at upper outlet of quartz tube
(Suction unit) is provided.

As an example of the operation of this equipment, first, the raw material solution is atomized at a vibration frequency of 1.6 MHz at a rate of 10 ml / min by an ultrasonic atomizer, and the generated mist is air (or nitrogen). , Argon, oxygen, etc.)
Pass through a drying oven and a pyrolysis oven at a flow rate of 0 liter / min. The drying furnace is set at 200-400 ° C, and the pyrolysis furnace is 5
The temperature is set in the range of 00 to 900 ° C. The lengths of the drying oven and the pyrolysis oven are 600 mm and 800 mm. When the mist passes through the drying furnace and the pyrolysis furnace at the set temperature, fine particles are generated and collected by an electric dust collector provided at the outlet of the quartz tube. In addition to this, it can be collected by a method of attaching it to filter paper and collecting it, or a cyclone.

Next, an embodiment of the present invention will be described.

[0023]

Example 1 This example relates to the synthesis of spherical alumina fine particles. First, aluminum secondary butoxide was used as a raw material. 0.1 ml mol of aluminum secondary butoxide was dissolved in ethanol at 80 ° C. under reflux, hydrolyzed with 100 mol of water, and the solution gelled was peptized by adding 5 wt% of nitric acid. Ultrafine particles produced by peptization were diluted to 1 liter with water to obtain a raw material solution. The raw material solution was atomized at a vibration frequency of 1.6 MHz using PZT (lead titanium sanzirconate) piezoelectric ceramics. This is 400 ° C with air at a flow rate of 3 liter / min.
And a pyrolysis furnace at 900 ° C.

FIG. 2 shows an SEM photograph of the produced fine particles. Further, as shown in FIG. 3, a SEM photograph of the fine particles obtained when the flow rate was increased to 7 liter / min, the surface state was changed by increasing the flow rate, irregularities were observed, and the porosity inside the particles was reduced. It can be seen that it has increased. Since the fine particles are very porous, they can be used as catalyst carriers.

[0025]

Example 2 This example relates to the synthesis of spherical silica fine particles. First, ethyl orthosilicate was used as a raw material.
0.1 mol of ethyl orthosilicate is dissolved in water, and the pH of the solution is adjusted to acidic using a small amount of carbon dioxide in the air.
Aged for 4 hours. As a result, the ethyl orthosilicate was partially hydrolyzed and polycondensed, and the vapor pressure of the ethyl orthosilicate was reduced to form a sprayable solution. The raw material solution is put in the spray chamber, and using PZT (lead titanium sanzirconate) piezoelectric ceramics installed in the lower part of the spray chamber,
Atomization was performed at a vibration frequency of 1.6 MHz. This was passed through a drying furnace at 400 ° C. and a pyrolysis furnace at 900 ° C. with air at a flow rate of 5 liter / min.

FIG. 4 shows an SEM photograph of the produced fine particles. Conventionally, when synthesizing fine particles by mist pyrolysis from ethyl orthosilicate, it was necessary to partially hydrolyze ethyl orthosilicate with nitric acid to lower the vapor pressure of ethyl orthosilicate, but this method requires that There is no need to perform an operation, and no nitric acid is mixed into the silica fine particles, so that high-purity silica spherical particles can be obtained. This silica can be used as a semiconductor sealant.

[0027]

Embodiment 3 This is an example of the synthesis of spherical titanium oxide fine particles. First, titanium tetraethoxide was used as a raw material. After dissolving 0.1 mol of titanium tetraethoxide in water and peptizing with 5 wt% of nitric acid, the produced titanium oxide sol was diluted to 1 liter with water to obtain a raw material solution. PZT
Using a piezoelectric ceramic of (lead titanium zirconate), the raw material solution was atomized at a vibration frequency of 1.6 MHz. This was passed through a drying furnace at 400 ° C. and a pyrolysis furnace at 900 ° C. with air at a flow rate of 5 liter / min.

FIG. 5 shows an SEM photograph of the generated fine particles. In order to obtain titanium oxide, a method in which an alkoxide of titanium (for example, titanium tetraethoxide or titanium isopropoxide) is dissolved in ethanol and spray pyrolysis is performed in a nitrogen atmosphere (Example 4 described later). compared,
In this method, by spraying a sol of titanium oxide,
Spray pyrolysis has become possible in the atmosphere. Further, as shown in FIG. 6A, the produced powder can be used as it is as a ceramic raw material or a powder for photocatalyst since it is crystallized into anatase.

[0029]

Comparative Example 1 This example is a synthesis example of spherical titanium oxide fine particles. As a raw material, titanium tetraethoxide which is an alkoxide of titanium was used. 0.1 mol of titanium tetraethoxide was dissolved in ethanol to prepare a raw material solution. The raw material solution was atomized at a vibration frequency of 1.6 MHz using PZT (lead titanium zirconate) piezoelectric ceramics. The fine mist generated by atomization is dried in a drying oven at 400 ° C. with nitrogen gas at a flow rate of 5 liter / min and 90
It was passed through a 0 ° C. pyrolysis furnace. FIG. 6B shows a powder X-ray diffraction diagram of the titanium oxide fine particles generated by the thermal decomposition.
Similar fine powders were produced when titanium isopropoxide was used instead of titanium tetraethoxide, but all required an organic solvent such as ethanol.

[0030]

[Reference Example 1] In this example, the particle size
This is an example in which the particle size distribution and the porosity are controlled. As the raw material solution, 0.1 mol / liter aqueous solutions of aluminum nitrate, cobalt nitrate, nickel nitrate, and zinc nitrate were used. Each raw material solution was atomized at a vibration frequency of 1.6 MHz using PZT (lead titanium sanzirconate) piezoelectric ceramics. The fine mist generated by the atomization was passed through a drying furnace at 400 ° C. and a pyrolysis furnace at 900 ° C. with air (carrier gas). Air flow rate 1-10 liters /
The range was changed in the range of min, and the influence of the flow rate of the carrier gas on the particle size of the obtained fine particles was investigated.

FIG. 7 shows the result of examining the particle size (particle size) of the particles while changing the flow rate of the carrier gas (the flow rate of the mist). The lower the flow rate,
It can be seen that the particle size of the resulting powder (alumina, cobalt oxide, nickel oxide, zinc oxide) can be reduced.

FIG. 8 shows the result of examining the particle size distribution of the particles while changing the flow rate of the carrier gas. The dependence of the particle size distribution of the particles on the flow velocity can be seen. It can be seen that the particle size distribution of the produced powder (alumina, cobalt oxide, nickel oxide, zinc oxide) can be narrowed as the flow rate is reduced.

FIG. 9 shows the result of examining the porosity of the particles while changing the flow rate of the carrier gas, and the porosity dependence of the particles depending on the flow velocity is seen. It can be seen that the porosity of the generated fine particles can be controlled by changing the flow rate.

[0034]

Reference Example 2 This is an example in which the crystal structure is controlled by the thermal decomposition temperature. As the raw material solution, 0.1 mol / liter aqueous solutions of aluminum nitrate, cobalt nitrate, nickel nitrate, and zinc nitrate were used. 1.6MHz using PZT (lead titanium sanzirconate) piezoelectric ceramics
Each raw material solution was atomized at a vibration frequency of. The fine mist generated by atomization is air-flowed at a flow rate of 5 l / min.
After passing through a drying oven at 0 ° C., it was sent to a pyrolysis oven.
At this time, the influence of the pyrolysis temperature on the crystallinity of the obtained fine particles was investigated by variously changing the set temperature of the pyrolysis furnace. As can be seen from the investigation results in FIG. 10, the crystallinity of the fine particles changes according to the thermal decomposition temperature. The lower the thermal decomposition temperature, the more the particles become amorphous, and the higher the thermal decomposition temperature, the higher the crystallinity of the fine particles. You can see that it is.

[0035]

As described in detail above, according to the present invention,
It is easy to increase the size of the device, mass production is possible, it is possible to produce at a low temperature and in a short time, and further, the flexibility of the metal component ratio is high, and the particle size can be controlled to 0.1 to 3 μm. Can be Therefore, the ceramic fine particles obtained by the present invention can be used for the following applications.

(1) When used as a raw material of a sintered body, it can be sintered in a short time at a temperature several hundred degrees lower than that of a commercially available powder. (2) When used as a substrate material, the dimensional accuracy of the ceramic substrate can be accurately predicted, and the shrinkage dimension due to firing can be predicted. (3) When used as a sealant for semiconductor ICs, stress concentration can be reduced, and the shock due to thermal shock can be reduced.
Fluidity during processing is improved. (4) When used as an abrasive (lens, toothpaste, etc.)
Uniform polishing can be performed, and micro-level polishing can be performed. (5) The silica fine powder can be used as a liquid crystal spacer. (6) When used as a lubricant or an additive (for a piston ring of an engine, a machine, or the like), wear resistance and dispersibility can be improved. (7) When used as a dental filler (eg, a composite resin for protecting pulp), the packing density is improved. (8) When used as a raw material for pigments, paints, and cosmetics, it can block ultraviolet absorption and improve the coating condition (good "paste"). (9) It can be used as a photocatalyst (eg, in the case of titanium oxide and zinc oxide), can be used for wastewater treatment containing organic harmful substances, and can accelerate the decomposition of water and organic halides (decomposition reaction rate). . (10) It can be used as a crystal for a YAG laser (Nd ³ + doped YAG). (11) It can be used as a standard sample for laser light scattering measurement. (12) When used as a catalyst carrier, the rate of chemical reaction is accelerated, and for example, the desulfurization reaction of heavy oil using a Ni-Co-Mo alloy as a catalyst can be accelerated. (13) By dispersing in a tape together with a magnetic material as a friction material for a magnetic material, a cleaning effect of the head and an improvement in the wear resistance of the tape itself can be expected.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of equipment for implementing the present invention.

FIG. 2 is an SEM photograph (particle structure) of the spherical alumina fine particles (flow rate 3 liter / min) obtained in Example 1,
(A) is a magnification of 1 μm for 2 cm, and (b) is a magnification of 1 μm for 5 cm.

FIG. 3 is an SEM photograph (particle structure) of the spherical alumina fine particles (flow rate: 7 liter / min) obtained in Example 1,
(A) is a magnification of 1 μm for 5 cm, and (b) is a magnification of 1 μm for 2 cm.

FIG. 4 is an SEM of the spherical silica fine particles obtained in Example 2.
It is a photograph (particle structure), (a) is a magnification of 1 μm for 5 cm,
(B) is a magnification of 1 μm for 2 cm.

FIG. 5 shows S of the spherical titanium oxide fine particles obtained in Example 3.
It is an EM photograph (particle structure), (a) is a magnification of 1 μm for 8 cm, and (b) is a magnification of 1 μm for 1 cm.

FIGS. 6A and 6B are SEM photographs (particle structures) of the spherical titanium oxide fine particles obtained in Example 3 and Comparative Example 1, wherein FIG. 6A is the case of Example 3 and FIG. .

FIG. 7 is a graph showing the effect of the flow rate of a carrier gas on the particle size of fine particles.

FIG. 8 is a graph showing the effect of the flow rate of a carrier gas on the particle size distribution of fine particles.

FIG. 9 is a graph showing the effect of the flow rate of the carrier gas on the porosity of the fine particles.

FIG. 10 is a graph showing the effect of a thermal decomposition temperature on the crystallinity of fine particles.

Claims (6)

(57) [Claims] 1. A compound obtained by hydrolyzing a metal alkoxide.
An aqueous solution in which ultrafine particles are suspended is used as a raw material solution.
The material solution is ultrasonically sprayed into fine mist,
Is dried and pyrolyzed in a heating furnace to obtain monodispersed oxides and nitrides
Alternatively, a method for producing ceramic fine powder by mist pyrolysis, comprising obtaining a ceramic fine powder of fluoride . 2. The method according to claim 1, wherein the drying temperature is 200 to 400 ° C. and the thermal decomposition temperature is 500 to 900 ° C. 3. A heating furnace using an infrared heating method or a microwave induction heating method as a heating furnace.
The method described in. 4. The method according to claim 1, wherein the ultrasonically sprayed fine mist is passed through a heating furnace using a carrier gas of air, oxygen or an oxygen-containing gas or an inert gas. 5. The method according to claim 1, wherein the particle size, the particle size distribution or the porosity of the fine powder is controlled by the flow rate of the fine powder.
The method according to 2, 3, or 4. 6. The method according to claim 5, wherein the particle size of the obtained fine powder is in the range of 0.1 to 3 μm.