JPH04160007A - Continuous production of spherical superfine particles - Google Patents

Abstract

PURPOSE:To improve the purity of the particle by preparing a seed particle capable of forming the same material as the desired ceramic fine powder by a reaction consuming the raw alkoxide or capable of forming the same material by drying or calcining on the upstream side of the same system as the main reaction. CONSTITUTION:The N2 gas contg. the saturated alkoxide such as aluminum ethoxide leaving an alkoxide vaporizer 1 and the N2 gas contg. saturated steam leaving a water vaporizer 2 are mixed in a nucleus generator 4, and the mixture is hydrolyzed at 150-180 deg.C to generate the seed particles as a nucleus. The gas contg. the seed particle is cooled in a first-stage condenser 5 and supersaturated, and nuclear condensation is carried out with the seed particle as the nucleus to obtain a droplet aerosol. The aerosol is passed through a reheating part 7 and a second-stage condenser 6 to regulate the droplet diameter and then sent to a main reactor 8. The aerosol is mixed with steam in the amt. of 3-5 times the theoretical amt. sent from a main-reaction water vaporizer 3, and the mixture is hydrolyzed to convert the droplets into the spherical superfine particles of Al2O3, etc., having 0.05-5mum average diameter which are collected by the filter of a collector 9.

Description

[Detailed description of the invention] [Field of industrial application] In the field of new material development, by controlling the purity, particle shape, particle size distribution, etc. of ultrafine powder, it can be made into a material obtained by sintering or dispersing it. , is expected to add a variety of new functions. Among these, ceramic fine powder with submicron size, narrow particle size distribution, and spherical particles is expected to find expanded applications as sintering raw material powder, filler, abrasive, standard particles, etc.

The present invention relates to a method for continuously producing ultrafine spherical particles of uniform particle size.

[Conventional technology]

Conventionally, most of the ceramic fine powders were produced by direct C without going through droplets.
Manufactured by VD. Production methods via droplets have also been used, but in that case - seed particles were not used in boat fishing. By the way, when producing spherical titanium dioxide particles by hydrolyzing droplets of a tetravalent liquid titanium compound such as titanium (IV) ethoxide, AgC1! ,
A method is known in which the particle is used as a seed particle. (M, Visc.
a et al,, Journalof Co11o
ID and Interface 5science,
vol, 68+No, 2. P30B~319.1
979). It is also known to produce submicron-sized alumina powder by condensing aluminum sec-butoxide vapor to form droplets, followed by a chemical reaction between the droplets and water vapor in a turbulent flow system. There is (T, T,
Kodas et al., Powder Technology;
50, pp. 47-53, 1987).

In this study, turbulent flow systems and laminar flow systems have been investigated, and it has been reported that adding seed particles before condensation reduces the condensation of droplets on the condenser wall and considerably narrows the particle size distribution.

[Problem to be solved by the invention]

Direct CVD without using droplets resulted in not only a wide particle size distribution but also irregular particle shapes. In the case of the method using droplets, spherical fine particles can be obtained, but the particle size distribution is extremely wide, and there are also problems in production efficiency. AgCj! Although the method using seed particles such as the above produces spherical fine particles with a narrow particle size distribution, there is a problem in that the purity decreases. Kodas et al. have disclosed a method using the same material as seed particles, but there was a problem that the particle size distribution was wide.

An object of the present invention is to solve the above-mentioned problems and provide a means for producing ceramic fine powder having an extremely narrow particle size distribution and high purity.

[Means to solve the problem]

The present invention provides a method for continuous production of spherical ultrafine particles that achieves the above object, and is a droplet CVD method for producing fine ceramic powder by reacting an alkoxide with water vapor. This method is characterized by producing seed particles that are the same substance as the target ceramic fine powder, or that can become the same substance by drying or firing, by a reaction operation that consumes a part of the raw material alkoxide upstream of the same system as the main reaction.

The spherical ultrafine particles are ceramics, such as Al2O2,
TiO! , S i Oz, Z r O, etc., complex oxides such as BaTio3, mullite (3A 1
These are composite particles such as tOs・2Sift). Average particle size is about 0.05 to 5p, preferably 0.05 to 0.3
- degree, and the distribution has a geometric standard deviation of 1.2 to 1.4,
In particular, it is about 1.25 to 1.35.

These are produced by the reaction of alkoxides and water vapor. Alkoxides are liquid during reaction; for example, when producing alumina, aluminum ethoxide,
Aluminum isopropoxide, aluminum butoxide, etc. can be used, and in the case of titania, titanium (IV) ethoxide, titanium (IV) isopropoxide, etc. can be used.

The seed particles are the same material as the target ceramic, or can be made into the same material by drying, firing, etc.

Examples of substances that can be converted into the same substance by drying or firing include hydroxides.

The reaction between the alkoxide and water vapor may be carried out at about 50 to 130°C, and the pressure may be increased, reduced, or normal pressure, for example, about 780 to 850 Torr. The alkoxide and water vapor may be brought into contact in parallel flow,
Contact may be made through cross flow. The mixing ratio of alkoxide and water vapor should be such that the amount of water vapor is in excess (approximately 3 to 5 times the number of moles required for the reaction with the alkoxide. It is preferable to use an inert diluent gas.This diluent gas also functions as a carrier gas, and nitrogen gas, argon gas, helium gas, etc. can be used, but nitrogen gas is preferable because it is cheap and easily available. The dilution ratio is about 500 to 2000 times for alkoxide and 5 to 2000 times for water vapor in terms of molar ratio.
About 30 times is preferable.

In this method, the present invention uses droplet CVD in which a fine ceramic powder is obtained by reacting an alkoxide, which serves as the nucleus of a droplet, with water vapor. The method is characterized in that a reaction operation that consumes a portion of the raw material alkoxide upstream produces seed particles that are the same substance as the target ceramic fine powder, or that can become the same substance by drying or firing.

Specifically, the reaction that consumes a portion of the raw material alkoxide upstream in the same system as the main reaction is carried out by blowing a portion of steam into the flow of the raw material alkoxide. The amount of water vapor mixed is the amount that generates seed particles, and is about 2 to 8% of the theoretical amount required for reaction with the raw material alkoxide, especially 2.5%.
Approximately 5% is appropriate. In order to supply this water vapor at an appropriate concentration, it is preferable to dilute it with a diluent gas and mix it. The same diluent gas as described above is used. The seed particles that serve as the nucleus are generated at a temperature at which the alkoxide does not condense.
For example, a temperature of about 150 to 180°C is appropriate.

The pressure may be increased pressure, reduced pressure, or normal pressure, for example 78
It may be about 0 to 850 Torr.

After seed particles are formed, the feed alkoxide stream is cooled to condense alkoxide vapor onto the seed particles.

If the condenser temperature is too low, seed particles are likely to be trapped on the wall surface due to thermophoresis, making it easier for nuclear-free condensation nucleation to occur. Moreover, if it is too high, condensation will be insufficient. Therefore, a temperature at which 95% or more of the alkoxide vapor is condensed is appropriate.

After condensation, the main reaction is carried out in the main reactor under the above conditions, and then collected using a cyclone, filter, electrostatic collection, etc., dried, and, if necessary, calcined.

[Effect]

FIGS. 4 and 5 show examples of the effects of operating conditions on the average diameter, geometric standard deviation, number concentration, and volume concentration when aluminum tri-secondary butoxide is used as the raw material. The temperature of the main reactor is 100°C. A mark indicates a case where there is a seed, and a mark indicates a case without a seed.

3.5% of the total raw material alkoxide is converted to seed particles. The effects and mechanisms of the two factors here are considered as follows. That is, in the method of the present invention, by introducing seed particles, vapor condenses and grows on the surface of the seed particles (heterogeneous nucleation), so the particle size distribution is narrow due to the particle size dependence of the growth rate. The number concentration becomes high. Furthermore, if the condenser temperature is too low, seed particles are likely to be captured on the wall surface due to thermophoresis, making it easy for non-nuclear condensation nucleation to occur. At this time, since the temperature difference is large, the generated nuclei are also likely to be captured on the wall surface, the vapor concentration decreases, and the temperature distribution tends to be uneven, resulting in uneven generation and growth of the nuclei. As a result, the diameter of the particles is small overall, the distribution is wide, and the number concentration is low. Naturally, the particle volume concentration is low and losses are high.

〔Example〕

Example 1 The apparatus shown in FIG. 1 was used. This device consists of an alkoxide evaporator 1, a water evaporator 2 for generating seed particles that will become the nucleus, a water evaporator 3 for the main reaction, and a nuclear generator 4 that generates the seed particles that will become the nucleus.
, a condenser 5.6 for alkoxide vapor, a reheating section 7 provided between the condensers, a main reactor 8, a collector 9, etc. Nitrogen gas, which is a diluted carrier gas, is sent from the cylinder 10 via a flow control valve II to each evaporator 1.2.3 containing an alkoxide liquid or water, where it is bubbled.

Nitrogen gas containing alkoxide in a saturated state from the alkoxide evaporator 1 and nitrogen gas containing water vapor in a saturated state from the water evaporator 2 are mixed in a nuclear generator 4, and undergo a hydrolysis reaction to form seed particles that become nuclei. generate. The alkoxide-containing gas is extracted from the branch pipe 12 as necessary and subjected to compositional analysis or the like. The gas containing the seed particles is cooled to a supersaturated state in the first stage condenser 5, and undergoes nucleated condensation using the seed particles as a core to form droplet aerosol. After passing through the reheating section 7 and the second stage condenser 6, the droplet diameter is adjusted and sent to the main reactor 8. There, it is mixed with an excess amount of water vapor sent from the water evaporator 3, and undergoes a hydrolysis reaction, converting the individual droplets into solid particles. The solid particles thus generated are collected by the filter of the collector 9. 12 is a vacuum pump that sucks the collector 9. A branch pipe is provided on the outlet side of the main reactor 8, and a diluter 13, an electrostatic classifier 14, and a condensation nucleus measuring device 15 are connected in series.

The gas extracted from the branch pipe is diluted with nitrogen gas supplied from a nitrogen gas cylinder 16 in a diluter 13, classified by an electrostatic classifier, and generated particles are counted by particle size by a condensation nucleus measuring device 15. Particle size distribution and concentration are required.

A continuous production experiment of alumina particles was conducted using the above apparatus. The alkoxide is aluminum trisec-butoxide (A/! (C, H5CH(CHj) O)
3) (ATSB) was used. The ATSB flow rate flowing out from the alkoxide evaporator 1 is set to 1. OXlo-3mol/w
In, the Nz flow rate is 1.0 mol/lll1n, and the H z O flow rate flowing out from the water evaporator 2 for seed particle generation is 4.5 Xl0-'mol/min.

The N2 flow rate is 6.6 Xl0-'mol/mfn, and the H20 flow rate flowing out from the main reaction water evaporator 3 is 1.5 Xl0.
-”mol/ll1in, N2 flow rate 0.22+mol
/sin. The temperature of the nuclear generator is 160-180°C
1 The pressure was controlled at 780-860 Torr, and the condenser temperature was 79°C. The temperature of the main reactor was controlled at 50°C and the pressure was controlled at 780-850 Torr. In addition, the condenser was set to one stage.

Analysis of the gas flowing out from the main reactor 8 under steady state conditions revealed that the geometric mean particle size of the solid particles was 0.142μ, the geometric standard deviation was 1.269, and the yield was 77.5%. The particle size distribution is shown in Figure 2. The solid particles were perfectly spherical.

The obtained solid particles were calcined in a Matsufuru furnace at 1200°C for 1 hour, and the crystal structure was examined by X-ray diffraction, and it was found to be completely α-alumina. This one was also perfectly spherical.

As a result of measuring the metal elements in the raw material ATSB used in this example by ICP emission spectroscopy, the purity of /l was 99.5%.
Met. On the other hand, as a result of compositional analysis of calcined alumina powder by titration and other methods, the ratio of A2 in the metal elements was 99.
5%, and the calcined powder maintained the purity of the raw material.

Example 2 A continuous production experiment of alumina particles was conducted in the same manner as in Example 1 except that the number of stages of the condenser was changed to two.

As a result, the geometric mean particle size was 0.113 fm, the geometric standard deviation was 1.309, and the yield was 50.0%. The particle size distribution is shown in Figure 3.

〔Effect of the invention〕

By the method of the present invention, spherical ultrafine particles having an extremely narrow particle size distribution can be easily obtained with high purity.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing an outline of an apparatus used in an example of the present invention. Figures 2 and 3 are particle size distribution charts of particles obtained in Examples, and Figures 4 and 5 are graphs of condenser temperature, geometric mean diameter, geometric standard deviation, number concentration, and volume concentration of particles produced. It is a graph showing the relationship.

Claims (1)

[Claims] In droplet CVD, which produces fine ceramic powder by reacting alkoxide and water vapor, when introducing seed particles that become the nucleus of droplets, a reaction operation that consumes a part of the raw material alkoxide upstream in the same system as the main reaction is used to produce the target ceramic. A method for continuous production of spherical ultrafine particles, characterized by producing seed particles that are the same substance as fine powder or can become the same substance by drying or firing.