JPH0696114B2 - Method and apparatus for producing inorganic powder by hydrothermal synthesis - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an inorganic powder by hydrothermal synthesis and an apparatus therefor.

(Problems to be solved by conventional techniques and inventions) The demand for inorganic powders used in the ceramics industry and electronics industry, especially inorganic oxide powders, is increasing year by year. For example, catalyst carriers, IC substrates, barium ferrite. There is a demand for a method for rapidly producing high-purity oxide powder having fine particles, which is excellent as a raw material for ceramics such as high-grade white ceramics. As one of the synthesis processes corresponding to these various applications,
The hydrothermal synthesis method has attracted attention because it has a small number of process steps and the environment is less polluted because the reaction is carried out in a closed system.

However, when hydrothermally synthesizing high-purity inorganic powder, it is necessary to uniformly stir the reactants to keep the temperature and reactivity uniform. In addition, the equipment used for hydrothermal synthesis of inorganic powder is one that industrially applies heat from the outside of a sealed container such as an autoclave, and a laboratory also uses a container of similar structure. Therefore, the reaction is chemical and therefore it is necessary to keep the pressure vessel at a high temperature and to keep the reaction time long in order to accelerate the reaction. That is, in terms of manufacturing, there are many disadvantages such as high cost.

Up to now, a thermal decomposition container for pretreatment for chemical analysis in which a Teflon container is covered with a stainless steel jacket has also been used as a pressure container for simple hydrothermal treatment. This is characterized by the fact that several hundreds of atmospheric pressure can be maintained simply by tightening a bolt type screw or screw lid, but the drawback is that it is not possible to promote the uniformity or promotion of the reaction because it does not have a stirring system. there were.

For stirring, there are an electromagnetic induction stirring method in which an internal stirring blade is inserted inside, a method of directly rotating the stirring blade by a motor, a shaking method of moving the autoclave main body, an automatic reversal method, a rotation method and the like. However, in these methods, although uniform stirring is possible, there is no effect of accelerating the reaction, crushing, or reducing the particle size, and the reaction rate cannot be increased.

Yoshimura et al. (The Ceramic Society of Japan 97 [1] 16-21 (198
9)) has published a method for synthesizing barium ferrite fine particles by combining hydrothermal synthesis with a method of mixing a solution with an attritor that stirs balls with a propeller. However, in this method, since hundreds (200 to 700) of stainless steel balls are driven from the outside of the pressure vessel by using the propeller, a large stress is applied to the propeller and the shaft,
There were problems such as wear and corrosion deformation of the seal part.

The problem of the present invention is that the reactants can be well stirred during the hydrothermal reaction, the reaction rate can be increased, and the structure of the reaction apparatus, the operation is simple, and the above-mentioned problems such as wear of the seal portion and corrosion deformation occur. It is an object of the present invention to provide a method for producing an inorganic powder by hydrothermal synthesis and a device therefor.

(Means for Solving the Problem) The present invention is based on hydrothermal synthesis in which at least water and a reactant are sealed in a pressure reaction vessel and heated to cause a hydrothermal reaction to produce an inorganic powder. In the method for producing an inorganic powder, a hydrothermal method characterized in that a small-sized stirring medium is sealed in the pressure reaction container, and the pressure reaction container is rotated to stir the pressure reaction container. The present invention relates to a method for producing an inorganic powder by synthesis.

Further, the present invention is a pressurized reaction vessel having a sealed space for sealing at least water and a reactant to perform a hydrothermal reaction, a small piece-shaped stirring medium contained in the sealed space, The present invention relates to an apparatus for producing an inorganic powder by hydrothermal synthesis, which comprises a rotating means for rotating a pressurized reaction vessel and a heating means for heating the pressurized reaction vessel from the outside.

The “pressurized reaction vessel” includes single and double vessels.

The shape of the "small piece stirring medium" can be selected variously, but for example, a bead shape is preferable.

The composition of the "flake stirring medium" is preferably the same as or similar to the composition of the reactants, or it is preferably the same or similar to one of the reactants.

The composition of the “small piece stirring medium” is also preferably composed of a substance which is inert to the hydrothermal solution during the hydrothermal reaction.

The speed of rotation of the pressure vessel is preferably 20-100 rpm, 50
More preferably, it is set to 100 rpm.

Raw material: Beads: Solvent: The volume ratio of the space in the container (the space obtained by subtracting the volume of the entire mixture from the space of the entire container) is 1.2 to 1.9: 5.0 to 7.
It is preferably set to 5: 6.0 to 10.0: 1.3 to 6.2.

(Example) First, a pressure reactor suitable for carrying out the method for producing an inorganic powder according to the present invention will be described.

The pressurized reaction container 31 of this embodiment includes the outer container 1, the inner container 2, the pressing member 3, and the pressing member 4 as constituent elements.

The outer container 1, the pressing member 3, and the pressing member 4 are preferably made of a metal having high corrosion resistance such as stainless steel. Inner container 2
Is preferably made of a synthetic resin having chemical resistance and heat resistance such as fluororesin, chlorinated polyether, allyl resin, polyallyl sulfone, and polymethylpentene.

The outer container 1 is composed of a bottomed outer cylinder 11 made of stainless steel and an outer lid 12, and has a cylindrical shape as a whole having a substantially constant outer diameter. The bottomed outer cylinder 11 is a disc-shaped bottom portion 15 that is detachably locked to a cylinder body 13 and an annular locking portion 13a formed on the inner periphery of the lower portion thereof.
It has a cylindrical shape with its center part slightly narrowed. In addition, an annular bank 17 that substantially covers most of the outer circumference of the outer lid 12 is formed on the upper portion of the bottomed outer cylinder 11. A female screw 19 is formed on the inner peripheral portion of the bank portion 17. The outer lid 12 has a thick disk shape, and a male screw 14 which is screwed into the female screw 19 of the bottomed outer cylinder 11 is formed on the outer peripheral portion of the lower portion thereof. A central female screw hole 12a into which the pressure member 4 is screwed is formed in the central portion of the outer lid 12. As the pressing member 4, a stainless steel male screw bolt is used. Pressure member 4
Is screwed into the central female screw hole 12a of the outer lid 12 of the outer container 1,
2 is inserted, and the tip portion 41 thereof abuts on the center of the upper surface of the pressing member 3. It should be noted that the head 42 of the pressing member 4 projects only partly from the upper surface of the upper bank portion 16 of the outer lid 12.

Furthermore, ring-shaped bank portions 16 and 18 are formed on the upper surface and the lower surface of the outer lid 12, respectively.

As the pressing member 3, a thick disk-shaped member is used.

The inner container 2 is composed of a bottomed inner cylinder 21 and an inner lid 22, and has a cylindrical shape having a protruding portion that protrudes in the radial direction on the upper outer peripheral portion. A seating surface 23 is formed on the top of the cylindrical bottomed inner cylinder 21. The inner lid 22 has a mating surface 24 having a trapezoidal cross section for seating on the seating surface 23 of the bottomed inner cylinder 21 on the lower surface of the disk-shaped portion, and is formed in a substantially truncated cone shape. Mating surface of inner lid 22
The cross-sectional shape of 24 is trapezoidal, and the seating surface 23 of the bottomed inner cylinder 21 is shaped to match it, and when the bottomed inner cylinder 21 and the inner lid 22 are crimped, the upper surface of the bottomed inner cylinder 21 facing each other is formed. An air gap A was formed between the inner lid 22 and the lower surface. Since this space A serves as a sufficient pressure-bonding margin, the pressing of the inner cover 22 to the bottomed inner cylinder 21 by the pressing member 4 via the pressing member 3 is adjusted, so that the bottomed inner cylinder of the inner lid 22 is adjusted. It is possible to maintain the close contact with 21 in a desired state. In addition, the hypotenuse of the seating surface 23 and the mating surface 24 is an inner cylinder with a bottom.
The vertical axis of 21 is 30 degrees.

This pressure reactor 31 is placed between the two cylindrical rotation transmission rods 10, and the two cylindrical rotation transmission rods are rotated in the same direction as indicated by arrows, for example, so that the pressure reaction vessel is rotated. Rotate 31 in the opposite direction.

In the pressure reaction apparatus of FIG. 1, the outer container 1 firmly holds the outer peripheral portion of the inner container 2 housed therein, and the pressurizing member 4 and the pressing member 3 make the inner container 2 have a bottom. Inner cylinder
Since the inner lid 22 and the inner lid 22 are firmly brought into close contact with each other, even if a high pressure is generated inside the inner container 2, the liquid tight state can be sufficiently maintained. Further, the bottomed outer cylinder 11 and the outer lid 12 are screwed together by the female screw 19 formed on the upper inner peripheral portion of the bottomed outer cylinder 11 and the male screw 14 formed on the lower outer peripheral portion of the outer lid 12. Due to the high pressure generated inside the inner container 2 due to the high temperature heating, the bottomed outer cylinder 11 is deformed outward in the radial direction, and the bottomed outer cylinder 11 is deformed.
The outer lid 12 and the outer lid 12 are not irremovably attached.
The screwing of 11 and the outer lid 12 does not become loose.

Further, since the pressurized reaction vessel 31 has a columnar shape with a substantially constant outer diameter as a whole, the rotating torque is not transmitted to the outer lid 12 even if it is rotated in a horizontal position, and the bottomed outer cylinder 11 and the outer lid 12 are rotated.
The screwing with does not loosen.

Further, since the annular bank 18 is formed on the lower surface of the outer lid 12, the stress is not concentrated only on the central portion of the pressing member 3, and the pressing member 3 is not deformed. Since the outer lid 12 contacts the pressing member 3 by the annular bank 18 formed on the lower surface thereof, the contact area is small and the frictional force is also small. Therefore, the outer lid 12
The operation of screwing the bottomed outer cylinder 11 while contacting the pressing member 3 is also smooth.

Distilled water, a reactant, and a small piece of stirring medium are accommodated in the bottomed inner cylinder 21, the mating surface 24 of the inner lid 22 is seated on the seating surface 23 of the bottomed inner cylinder 21, and the inner container 2 in this state Is housed in the bottomed outer cylinder 11 of the outer container 1. Thereafter, the pressing member 3 is placed on the inner lid 22, and the outer lid 12 screwed with the pressure member 4 is screwed onto the bottomed outer cylinder 11 and then tightened to store the inner container 2 in the outer container 1. Complete. Next, the head 42 of the pressure member 4 is rotated clockwise to bring the tip end 41 of the pressure member 4 into contact with the pressure member 3. From this state, the head 42 of the pressing member 4 is further rotated, and the tip 41 is further pressed against the pressing member 3. Due to this pressing force, the inner lid 22 is vertically pressed against the bottomed inner cylinder 21, and the mating surface 24 of the inner lid 22 surely adheres to the seating surface 23 of the bottomed inner cylinder 21.
The inside of is kept liquid tight.

The pressure reaction container 31 thus prepared is placed horizontally on the pair of rotation transmission rods 10 and kept at a constant temperature by an electric furnace and warm air, and the pressure reaction container 31 is rotated.

By selecting the reactants to be sealed in the pressurized reaction vessel 31, the product can be varied. The table below shows these combinations.

Examples of the material of the flaky stirring medium which is inert to the hydrothermal reaction include alumina and quartz.

When the inorganic powder is hydrothermally synthesized as in this example, since the pressure reaction container 31 is horizontally placed and rotated, the reactants in the inner container 2 are well uniformly stirred. Moreover, since the flaky stirring medium is put in the inner container 2 at the same time, the flaky stirring medium is vigorously stirred in water and the reaction body as the container rotates, so that the solid reactant is crushed. . It is thought that the chemical reaction during hydrothermal synthesis occurs from the surface of the reaction particles, and the solid reaction particles are pulverized to make the reaction particles finer, and a new surface appears on the reaction particles to cause a chemical reaction. The points are increased, the reaction speed is improved, the reaction time is shortened, the productivity is improved, and the cost can be reduced. Furthermore, since the product particles are also pulverized, it becomes possible to make them finer and uniform.

Hereinafter, more specific experimental examples will be described.

Experimental Example 1 Using feldspar as an inorganic raw material, water and AlCl ₃ or H as a solvent
Using Cl, and changing the weight of the alumina bead spheres to be sealed in the inner container to 0 g, 5 g, and 25 g, hydrothermal synthesis was performed using the pressure reactor of FIG. 1 as described above, and kaolinite The difference in the amount of production was confirmed by the X-ray analysis pattern.

The outer container, outer lid, and bottom lid are made of stainless steel (SUS 316), and the inner container is tetrafluoroethylene (Teflon: volume 28 ml)
Created in. The pressurized reaction vessel was placed on a rotation transmission rod having a thickness of 5 cm which was laid parallel to the inside of the warm air type thermostat and the vessel was rotated. The rotation transmission rod was rotated by a chain from a motor outside the thermostat.

FIG. 2 shows the X-ray analysis pattern of the sample after hydrothermal synthesis under the same conditions.

2M-AlCl _3, when compared with each per bead without addition of IN-HCl, despite almost pH of the solvent is the same,
When a solvent of 2M-AlCl ₃ is used, a peak can be observed at 12.4 °, which is the reflection on the kaolinite (001) surface, which is the produced mineral. The feldspar has a Si / Al of 2, whereas the kaolinite has an S
Since i / Al is 1, it is considered that when leaching at the same rate, the presence of an aluminum component in the solvent favors equilibrium for kaolinite formation.

When the amount of beads is increased to 0 g, 5 g, and 25 g under the same conditions, the peak of 12.4 °, which is the reflection on the kaolinite (001) surface, increases with the increase of the amount of beads. That is, it was confirmed that the kaolinite formation was improved under the same conditions by mixing the alumina beads.

Experimental Example 2 Hydrothermal synthesis was performed in the same manner as in Experimental Example 1. However, using AlCl ₃ as the solvent, the amount of feldspar (3,4,5g), the concentration of AlCl ₃ (1,1.5,2M /), the amount of AlCl ₃ (6,8,10ml), the amount of alumina beads (20,25,30g), temperature (180,200,220 ° C), and hydrothermal treatment days (2,5,8 days) were set at each of three levels, and the experiment was conducted based on the experimental design method. After hydrothermal synthesis was performed, the pressurized reaction vessel was rapidly cooled, a sample was taken out, and the kaolinite conversion rate and specific surface area were examined by powder X-ray analysis and differential thermogravimetric analysis. The results are shown in the table below.

No leak was observed even if the container was taken out of the thermostat and then put into water for rapid cooling. Three factors, the reaction temperature and the reaction time AlCl ₃ addition concentration, were significant in the contribution rate to the formation of kaolinite. At the reaction temperature, 180 ° C to 2
The kaolinite conversion rate increased with increasing temperature at 20 ℃. In addition, in the concentration of AlCl ₃ added, the kaolinitization rate was high at a low concentration of 1M /, and the kaolinitization rate tended to decrease as the concentration increased. Furthermore, in the reaction time, the kaolinitization rate increased up to 5 days within the range of this test, but the kaolinitization rate did not change much over 8 days as compared with 5 days.

Fig. 3 shows the weight loss of a sample prepared by hydrothermal synthesis measured by a differential thermal analyzer in the temperature range of 20 to 115 ° C.
Value of kaolinite converted from kaolinite structural water desorption amount from 00 to 600 ℃ (kaolinite conversion rate)
And the particle size distribution relationship using a particle size distribution meter by the X-ray transmission method.

The kaolinitization rate in the figure is 0%, that is, the particle size of the feldspar raw material has a maximum peak at about 10 μm, and the kaolinitization rate is 27%.
%, That is, when 27% by weight is changed from feldspar to kaolinite, there are three peaks of about 10 μm, about 5 μm, and about 1 μm. This peak is considered to be the peak of the feldspar raw material, the peak of the feldspar crushed by the rotation of the pressure vessel, and the peak associated with the production of kaolinite. Furthermore, the particle size of the sample with a kaolinite conversion rate of 49% is
The peak at about 1 μm is higher than that of the sample having a kaolinitization rate of 27%. This result shows that the feldspar raw material is crushed by the rotation of the pressure vessel during hydrothermal synthesis, the particle size of the feldspar raw material alone becomes small, and the peak due to the kaolinite particle size becomes high.

When observed with a transmission electron microscope, hexagonal plate-like particles are formed on the surface of the feldspar along with the formation of kaolinite. That is, since the reaction occurs from the surface of the feldspar and kaolinite is produced, it is considered that the more the feldspar raw material is made finer and the more it is pulverized, the more advantageous the production of kaolinite is.

FIG. 4 confirms the difference between the kaolinite production rate when the pressure vessel is rotated during hydrothermal synthesis and the kaolinite production rate when the pressure vessel is not rotated in the conventional case under the same conditions.
The reaction conditions are shown in the figure. The maximum production rate of kaolinite is about 50% when the pressure vessel is rotated, but when making ceramics, since the mixing weight ratio of feldspar and clay is generally 1: 1, feldspar production by hydrothermal synthesis About 50%
Can be used as it is as a raw material for ceramics instead of kaolinite, which has the advantage of saving the effort of mixing feldspar and clay. The relationship between the reaction time and the amount of kaolinite produced shows a linear relationship in both the method of rotating the pressure vessel and the method of not rotating. It was confirmed that the reaction time required to generate the same amount of kaolinite could be reduced to about 1/2 compared to the conventional method, and the feldspar raw material was crushed by rotating the simple pressure vessel during hydrothermal synthesis. It is considered to be a so-called mechanochemical reaction that kaolinite is generated from the surface of feldspar.

(Effect of the Invention) According to the method for producing an inorganic powder by hydrothermal synthesis and the apparatus therefor according to the present invention, since the pressure reaction vessel is rotated to stir the inside of the pressure reaction vessel, Sealed water,
The reactants are well agitated. Since the small-sized stirring medium is sealed in the pressurized reaction container, the small-sized stirring medium moves violently as the container rotates, and the solid reactant is crushed and made into fine particles. A new surface appears and the number of chemical reaction points increases, or the liquid reactant flows violently to improve the reaction rate, shorten the reaction time, improve productivity and reduce costs.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a pressure reactor, FIG. 2 is a graph showing an X-ray disintegration pattern, FIG. 3 is a graph showing the relationship between kaolinitization rate and particle size distribution, and FIG. Is a graph showing the relationship between the kaolinite conversion rate and the reaction time. 1 ... Outer container, 2 ... Inner container 3 ... Pressing member, 4 ... Pressurizing member 31 ... Pressurizing reaction container

Continuation of front page (51) Int.Cl. ⁵ Identification number Reference number in the office FI Technical indication location C01G 25/02 C04B 33/04 (72) Inventor Ryoto Tone 3-150 Omoteyama, Tenpaku-ku, Nagoya-shi, Aichi Japan Gaishi Yagoto

Claims (2)

[Claims] 1. A method for producing an inorganic powder by hydrothermal synthesis, wherein at least water and a reactant are hermetically sealed in a pressure reaction container and heated to cause a hydrothermal reaction to produce an inorganic powder. Sealing a small piece of stirring medium in the pressure reaction vessel,
A method for producing an inorganic powder by hydrothermal synthesis, characterized in that the pressure reaction vessel is rotated and agitation in the pressure reaction vessel is performed. 2. A pressurized reaction vessel having a sealed space for sealing at least water and a reactant to carry out a hydrothermal reaction,
Inorganic by hydrothermal synthesis, having a small piece stirring medium housed in the sealed space, a rotating means for rotating the pressure reaction vessel, and a heating means for heating the pressure reaction vessel from the outside. Powder manufacturing equipment.