JP2007054799A - Manufacturing method of combustion synthesis material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of combustion synthesis material which can prevent contaminants from mixing, can shorten a processing time, and can be pulverized. <P>SOLUTION: The manufacturing method has: a step of reacting a mixture in a reaction device by a combustion synthesis method; and a pulverizing step for pulverizing coarse products after the reaction. The pulverizing step accelerates the coarse products by a jet stream formed by being jetted from a pulverizing nozzle, and makes the accelerated coarse products collide with each other and pulverize, or makes the coarse products accelerated by a collision board collide, so as to pulverize the coarse products provided by the combustion synthesis method using a jet milling device for progressing the pulverization. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an oxide-based ceramic combustion synthetic material.

Oxide ceramics (general formula ABO ₃ ) are used in various applications because they have excellent dielectric properties, superconductivity, proton conductivity, etc., depending on the combination of A and B in the general formula. Typical dielectric ceramics include BaTiO ₃ used for ceramic capacitors, PZT (PbZrO ₃ -PbTiO ₃ ), which is the main material of piezoelectric and pyroelectric ceramics, and high-temperature proton conductive oxidation for fuel cells. Examples thereof include SrCeO ₃ , BaCeO ₃ , CaZrO ₃ , SrZrO ₃ , and BaZrO ₃ .

Conventionally, in order to synthesize ceramics as described above, external heating must be performed using a furnace of about 1000 ° C. to 2000 ° C. For this reason, the synthesis of ceramics requires enormous energy and a large heating mechanism, which increases the manufacturing cost.
As a manufacturing method without external heating, synthesis of ceramic powder by combustion synthesis has been proposed (see Patent Document 1). The combustion synthesis method is a method of synthesizing substances in a chain manner by utilizing a large amount of chemical heat reaction released at the time of compounding without requiring external heating.
The reaction product is agglomerated in a reaction vessel such as a crucible. The reaction product is pulverized for subsequent cleaning and / or sintering. Conventionally, this grinding has been performed using a ball mill.

However, in the pulverization using a ball mill, there is a problem that contaminants due to wear of balls and pots are easily mixed and it is difficult to increase the purity of the combustion synthetic material. Furthermore, since the ball milling method requires a grinding time of 20 to 40 hours, there is a problem that the production efficiency is low.
Japanese Patent Laid-Open No. 5-9009

  The present invention has been made in order to cope with such a problem, and an object of the present invention is to provide a method for producing a combustion synthetic material capable of preventing contamination from being mixed, reducing the processing time, and finely pulverizing.

The method for producing a combustion synthesis material of the present invention comprises a step of reacting a mixture in a reaction apparatus by a combustion synthesis method, and a pulverization step of pulverizing a crude product after the reaction. By accelerating the crude product by a jet stream formed by jetting, by colliding the accelerated crude product with each other by collision or grinding, or by colliding the accelerated crude product with a collision plate, A crude product obtained by a combustion synthesis method is pulverized by using a jet mill apparatus that advances pulverization.
The jet mill device is characterized in that at least the surfaces of the inner surface member, the guide member for guiding the pulverized particles, and the impingement plate are formed of the same combustion synthetic material as the crude product.

In the method for producing a combustion synthetic material according to the present invention, since a crude product obtained by the combustion synthesis method is pulverized using a jet mill device, contamination can be suppressed. In particular, since the inner surface member, the guide member, and the collision plate of the jet mill apparatus are formed of the same combustion synthetic material as the crude product, contamination can be further suppressed.
Further, since the pulverization proceeds in the jet mill apparatus by collision or grinding of the crude products, a coarse product powder having a finer particle size distribution than that of the ball mill method can be obtained.
As a result, the specific surface area of the pulverized powder increases, and cleaning and sintering, which are subsequent processes, can be easily performed.

The combustion synthetic material of the present invention is an oxide ceramic obtained by a combustion chemical reaction.
In the step of reacting the mixture in the reactor by the combustion synthesis method, the reaction system in the combustion synthesis method is as follows: (a) As a by-product that generates only gas, for example, a metal powder containing a group 4 element; As a reaction system using a reaction raw material containing at least a carbonate of an element containing a group element and a peroxide of an element containing a group 2 element, (b) generating gas and sublimate as a by-product, for example, Examples include a reaction system using a reaction raw material containing at least a metal powder containing a Group 4 element, a carbonate of an element containing a Group 2 element, and sodium perchlorate.

The reaction system (b) may be a group 4 metal powder, a group 2 carbonate, and a group 2 peroxide alone, or a reaction product obtained by adding a group 4 metal oxide to the piezoelectric. It is preferable because of its excellent properties, dielectric properties, cost and the like. Moreover, each reaction raw material is mix | blended in the predetermined ratio which satisfy | fills the chemical reaction formula in a combustion synthesis method. For example, when an oxide-based ceramic such as barium titanate (BaTiO ₃ ) or calcium titanate (CaTiO ₃ ) is synthesized as the main product, it is generated according to the following chemical reaction formula. The Group 4 metal powder, the Group 2 carbonate, and the Group 2 peroxide are blended in amounts corresponding to respective molar masses necessary for the following reaction. In the reaction system, carbon dioxide (CO ₂ ) is generated as a by-product.
In addition, when blending Group 4 metal oxides, blend them at a rate that allows the adiabatic flame temperature to be maintained at 1500 ° C or higher. The adiabatic flame temperature can be lowered by increasing the proportion of the Group 4 metal oxide.

Ti + 2TiO ₂ + BaCO ₃ + 2BaO ₂ → 3BaTiO ₃ + CO ₂ ↑
Ti + 2TiO ₂ + CaCO ₃ + 2CaO ₂ → 3CaTiO ₃ + CO ₂ ↑
Ti + 2TiO ₂ + BaCO ₃ + 2CaO ₂ → 3 (Ba _1/3 , Ca _2/3 ) TiO ₃ + CO ₂ ↑
Ti + 2TiO ₂ + CaCO ₃ + 2BaO ₂ → 3 (Ba _2/3 , Ca _1/3 ) TiO ₃ + CO ₂ ↑

The reaction system of (b) above is a group 4 metal powder, a group 2 carbonate, and NaClO ₄ alone, or the addition of a group 4 metal oxide to this, and the reaction product has excellent detergency. It is preferable because of its excellent piezoelectricity and dielectric properties.
The reaction raw materials are blended at a predetermined ratio. In the combustion synthesis reaction, for example, in the case of strontium titanate (SrTiO ₃ ), the reaction raw materials are produced according to the following chemical reaction formula. Each reaction raw material is blended in an amount corresponding to the molar mass required for the reaction between the Group 4 metal powder and the Group 2 carbonate, but the oxygen generating substance can be blended in an amount greater than the molar mass necessary for the reaction.

Ti + SrCO ₃ + 0.5NaClO ₄ → SrTiO ₃ + CO ₂ ↑ + 0.5NaCl

Examples of the reaction apparatus for synthesizing the combustion synthetic material of the present invention include a crucible, a reaction vessel similar to a crucible, a setter, and the like.
In addition, a plurality of raw materials serving as an element source constituting the main product is a known mixing device for ball mills and mortars prepared by mixing raw materials mixed in an atomic ratio capable of forming the main product in the reaction system (b) or (b) To be mixed.
In the reaction system (a) or (b), the shape of the metal containing a group 4 element as a reaction raw material is preferably a fine powder, and the specific surface area is 0.01 to ² m ² / g. A preferable specific surface area is 0.1 to 0.6 m ² / g because the combustion wave propagates and is easy to handle. When the specific surface area is less than 0.01 m ² / g, the contact area between the metal powder that is a heat generation source and the peroxide that is an oxygen supply source is small, so that combustion waves may not propagate and ceramics may not be synthesized. In addition, metal powders having a specific surface area exceeding 2 m ² / g are not preferable because they are extremely active and difficult to handle.
In the present invention, the specific surface area of the metal powder is a value measured by the BET method.

Moreover, even if the average particle diameter of the metal fine powder is the same, a difference in reactivity is recognized when the specific surface area is different. That is, when a metal powder having a specific surface area larger than that of a spherical shape was used, the combustion synthesis reaction proceeded more rapidly. Examples of the shape having a large specific surface area include particles having a plurality of irregularities formed on the surface of spherical particles, particles having an irregular shape as a whole, or a combination thereof.
The average particle size that can be used in the present invention is 150 μm or less, preferably 0.1 to 100 μm. If it exceeds 150 μm, mixing with other raw materials becomes insufficient, and combustion waves may not propagate. An image analysis method is preferable as a method for measuring the average particle diameter of particles having irregularities formed on the surface or an irregular shape.

The mixed powder as a reaction raw material is accommodated in a reactor such as a graphite crucible, ignited, and reacted by a combustion synthesis method. Regarding the conditions of the combustion synthesis method, the adiabatic flame temperature of the reaction system is 1500 ° C or higher. This is because the combustion wave propagates at 1500 ° C. or higher.
Combustion synthesis is performed in a chamber, and the atmosphere is preferably a rare gas atmosphere such as helium (He), neon (Ne), argon (Ar), or krypton (Kr). Note that a nitrogen gas, carbon dioxide atmosphere, or the like can be used as long as the dielectric properties of the reaction product are not deteriorated. Also, oxygen gas can be used if the oxygen partial pressure can be controlled.
In the combustion synthesis, a chemical reaction proceeds simultaneously and frequently from the ignition part to obtain a reaction product. The combustion synthesis reaction is completed in about 1 to 60 seconds.

The pulverization step for pulverizing the crude product after the reaction is performed using a jet mill apparatus. The jet mill device accelerates the test sample by a jet stream formed by jetting from the crushing nozzle, and collides with the colliding plate arranged in the device by collision or grinding of the accelerated test samples. It is an apparatus which advances grinding | pulverization by making it.
An example of a jet mill apparatus is shown in FIG. FIG. 1 is a schematic diagram of a jet mill apparatus.
The jet mill apparatus 1 includes a mill body 2 composed of a frame 2a having a circular cavity and a liner portion 2b which is an inner surface member constituting the inside of the frame 2a, and is inclined with respect to the center of the circular cavity. A plurality of pulverizing nozzles 3 for generating a high-speed jet airflow A therein, a product outlet 4 disposed at substantially the center of the mill body 2, a guide member 5 or a collision plate 6 for guiding pulverized particles, and a sample S are supplied. And a nozzle 7 for the purpose.

The sample to be crushed S supplied from the nozzle 7 is accelerated by the jet airflow A formed in the mill main body 2, and is finely pulverized by collision and grinding of the accelerated samples to be crushed.
In the present invention, the liner portion 2b, the guide member 5 for guiding the sample to be crushed, or the collision plate 6 is formed of the same material as the sample to be crushed. For this reason, the sample to be ground is not contaminated by other substances. Further, since the pulverization by the jet mill method is easy to classify, the average particle size distribution becomes narrow. Therefore, sintering in a later process becomes easy. Furthermore, the processing time is 0.5 Kg / h to 1000 Kg / h, which is significantly shorter than the ball mill method.
The average particle size finely pulverized by the jet mill method can be adjusted to 0.5 to 2.0 μm, and the standard deviation can be adjusted within σ = 1.5 μm.

  Examples of commercially available jet mill apparatuses include Se-Shin Company Co-Jet System α-mkII, Single Track Jet Mill, SK-Jet O Mill, and Super STJ-400 Mill.

Oxide ceramics are obtained by sintering the combustion synthetic material finely powdered by the jet mill apparatus. When sintering, a molding binder such as polyvinyl butyral can be blended. Sintering conditions include a condition of forming at a pressure of 10 to 100 MPa and firing at a temperature of 1200 to 1500 ° C. in an air atmosphere.
Moreover, in order to further stabilize the crystal structure of the synthetic fine powder obtained by the combustion synthesis and to remove a trace amount of impurities, it is possible to calcine at 900 to 1100 ° C.
In the reaction system (a), only carbon dioxide gas is generated as a by-product, but sodium chloride (NaCl) is generated in the reaction system (b). In this case, the obtained sintered body is finely pulverized and then washed with water to remove NaCl. By finely pulverizing using a jet mill device, water washing and the like are facilitated.

  When salts such as NaCl are present in the synthetic powder after the combustion synthesis reaction, the sinterability is hindered. The standard for reducing the salt to such an extent that the sinterability is not hindered is that the electrical conductivity of the cleaning liquid is 150 μS / cm or less. That is, regardless of the number of washings and the amount of washing, the electric conductivity of the washing water after washing should be 150 μS / cm or less when the synthetic powder is washed with water.

  The combustion synthetic material obtained by the combustion synthesis method described above has little dielectric contamination, is close to the theoretical density, and has excellent dielectric properties, so that it has a dielectric antenna, capacitor, dielectric resonator, filter, and pressure sensor. Can be used for ultrasonic motors.

Example 1
As the compounding raw material, 1 mol of Ti metal powder (specific surface area 0.3 m ² / g), 1 mol of SrCO ₃ and 0.5 mol of NaClO ₄ were used. These raw materials were mixed for 5 hours using a ball mill. The mixed powder (100 g) was pressed and solidified into a pellet and placed in a graphite crucible in the chamber of the synthesizer. A carbon film for ignition was brought into contact with the upper surface of the pellet to ignite. Combustion waves propagated by ignition, and a crude product was obtained by the combustion synthesis method. The chamber was filled with argon (Ar) gas and the internal pressure was 0.1 MPa.
The obtained crude product was pulverized using a Co-Jet system α-mkII manufactured by Seishin Corporation.
The grinding conditions were as follows: throughput 300 g / h, inert gas (argon), air flow 0.64 MPa, 1 pass.
The particle size distribution of the finely pulverized combustion synthetic material was measured by a laser diffraction method. As a result, the average particle size was 1.8 μm, and its standard deviation was 1.5 μm.
Next, 10 g of the combustion synthetic material and 200 ml of distilled water as a cleaning solution were placed in a beaker and subjected to ultrasonic cleaning for 10 minutes. After the cleaning treatment, the electric conductivity of the cleaning liquid was measured using an electric conductivity meter. After the measurement, the washing solution was removed, 200 ml of fresh distilled water was added, and ultrasonic washing was performed for 10 minutes. Again, the electrical conductivity of the cleaning solution was measured using an electrical conductivity meter. This operation was repeated 6 times. After removing the washing liquid and drying at 120 ° C. for 24 hours, identification of the crystal phase of the powder was performed using an X-ray diffractometer (XRD). As a result of XRD, it was found that the combustion synthetic material was SrTiO ₃ .

1% by mass of a molding binder (polyvinyl petital resin) was added to and mixed with the fine powder of the combustion synthetic material obtained. Next, 4 g of the mixed powder was put into a mold having a diameter of 20 mm, and a green body was formed by applying a pressure of 1.5 ton / cm ² . The green body was put into an electric furnace in an air atmosphere and held at 600 ° C. for 1 hour to remove organic components, followed by firing at 1300 ° C. for 3 hours.
All of the obtained sintered bodies were 5.10 g / cm ³ (relative density: about 98.5%) or more with respect to the theoretical density of 5.18 g / cm ³ , and were sufficiently densified.

Example 2
The same conditions and method as in Example 1 were used except that a jet mill apparatus in which the inner surface member (liner portion), guide member, and collision plate surface of the Co-Jet system α-mkII were coated with SrTiO ₃ was used. A powdered combustion composite was obtained.
The particle size distribution of the obtained combustion synthetic material was measured by a laser diffraction method. As a result, the average particle size was 1.7 μm, and its standard deviation was 1.4 μm.
The amount of impurities (Al ₂ O ₃ ) measured by X-ray fluorescence analysis was less than 0.1% by weight.

Comparative Example 1
A fine-combustion combustion synthetic material was obtained under the same conditions and method as in Example 1 except that a ball mill apparatus was used instead of the Co-Jet system α-mkII jet mill apparatus. Milling conditions for pulverization using a ball mill apparatus, Al ₂ O ₃ manufactured by apparatus volume: 300 ml, medium: Al ₂ O ₃ (diameter 5 mm, 100 cc), the solvent: 100 cc, rotating speed: 100 rpm , Processing time: 15 hours.
The particle size distribution of the obtained combustion synthetic material was measured by a laser diffraction method. As a result, the average particle size was 2.5 μm, and the standard deviation was 2.5 μm.
The amount of impurities (Al ₂ O ₃ ) measured by fluorescent X-ray analysis was 1.2% by weight.

In the method for producing a combustion synthetic material according to the present invention, since a crude product obtained by the combustion synthesis method is pulverized using a jet mill device, the resulting product is less contaminated with impurities and is excellent in production efficiency.
The combustion synthetic material obtained by the production method of the present invention is close to the theoretical density and has excellent dielectric properties, so it is suitable in the field of electronic components such as antennas, capacitors, resonators, pressure sensors, and ultrasonic motors. Available.

It is a schematic diagram of a jet mill apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Jet mill apparatus 2 Mill main body 3 Grinding nozzle 4 Product exit 5 Guide member 6 Colliding plate 7 Nozzle

Claims (2)

A method for producing a combustion synthetic material, comprising: a step of reacting a mixture in a reactor by a combustion synthesis method; and a pulverization step of pulverizing a crude product after the reaction,
In the pulverization step, the crude product is accelerated by a jet stream formed by being ejected from a pulverization nozzle, and the coarse product accelerated by the collision or grinding of the accelerated crude products or the collision plate is performed. A method for producing a combustion synthetic material, characterized in that a crude product is pulverized by using a jet mill device that advances pulverization by colliding the product.   2. The jet mill apparatus according to claim 1, wherein at least surfaces of an inner surface member of the apparatus, a guide member for guiding pulverized particles, and the collision plate are formed of the same combustion synthetic material as the crude product. The manufacturing method of the combustion synthetic | combination material of description.

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