JP2007141531A - Combustion synthesis method and dielectric ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion synthesis method for easily eliminating cracked gas and salt as by-products and obtaining high-quality oxide dielectric ceramics; and to provide dielectric ceramics such as BaRe<SB>2</SB>Ti<SB>5</SB>O<SB>14</SB>and Ca0-SrO-Li<SB>2</SB>O-Re<SB>2</SB>O<SB>3</SB>-TiO<SB>2</SB>manufactured by this method. <P>SOLUTION: This combustion synthesis method for dielectric ceramics uses reaction materials including at least metal powder containing an element of the fourth group with a specific surface area of 0.01-2 m<SP>2</SP>/g and a substance serving as an oxygen supply source. The combustion synthesis method comprises a mixing process for mixing the metal powder and the substance serving as the oxygen supply source together to form material powder, and a combustion synthesis process for turning the material powder obtained in the mixing process into a sintered body by a combustion synthesis reaction performed in a pressure condition below an atmospheric pressure at adiabatic flame temperature 1500°C or more. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for combustion synthesis of dielectric ceramics performed under a pressure condition below atmospheric pressure. In particular, as a dielectric ceramic, BaRe ₂ Ti _m O _{2m + 4} system (wherein 3 ≦ m ≦ 7; m is The integer Re is a rare earth element), or a CaO—SrO—Li ₂ O—Re ₂ O ₃ —TiO ₂ dielectric ceramic used for the production of a combustion synthesis method.

BaRe ₂ Ti ₅ O ₁₄ , BaRe ₂ Ti ₄ O ₁₂ , CaO − are used as dielectric ceramics having good dielectric properties used in electronic parts such as antennas, capacitors, resonators, filters, pressure sensors, and ultrasonic motors. Oxide ceramics such as SrO—Li ₂ O—Re ₂ O ₃ —TiO ₂ are known.

In order to synthesize conventional dielectric ceramics as described above, external heating must be performed for a long time using a furnace capable of heating from about 1000 ° C. to about 2000 ° C. For this reason, the synthesis of ceramics requires enormous energy and a large heating mechanism, which increases the manufacturing cost. For example, when manufacturing BaRe ₂ Ti ₅ O _14- based dielectric ceramics, BaO, Nd ₂ O ₃ and TiO ₂ powders are wet mixed in a ball mill, and the dried powder is calcined at 1100 ° C. for 5 hours. And pulverized into dielectric ceramic powder. Similarly, in the case of producing CaO—SrO—Li ₂ O—Re ₂ O ₃ —TiO ₂ dielectric ceramics, CaCO ₃ , SrCO ₃ , Li ₂ O, Re ₂ O ₃ and TiO _{2 are used.} Each powder is wet-mixed with a ball mill, and the dried powder is calcined at 1100 ° C for 5 hours and pulverized to obtain a dielectric ceramic powder.

On the other hand, synthesis of ceramic powder by a combustion synthesis method (self propagating high temperature synthesis (SHS)) has been proposed as a manufacturing method without external heating. This method uses the heat generated during the formation of intermetallic compounds and ceramics. Powders that are constituent elements of the compound are mixed well to make a green compact. When high temperature is applied to a part of the powder, it ignites. This is a method of obtaining a sintered body by proceeding a synthesis reaction while generating heat of formation.
Combining two types of materials, intermetallic compounds or non-oxide ceramics and oxide ceramics, using three types of raw materials as a starting material: one type of metal oxide and two different types of metal elements. Has been proposed (see Patent Document 1). In addition, there has been proposed a method for producing oxide ceramics by subjecting a mixed powder composed of two or more kinds of metal oxide powders to high frequency heating for a predetermined time to perform combustion synthesis (see Patent Document 2).

However, the oxide-based dielectric ceramics cannot be obtained by the combustion synthesis method of Patent Document 1. In the combustion synthesis method of Patent Document 2, it is possible to produce oxide-based dielectric ceramics in a short time as compared with the conventional production method in which firing is performed for a long time, but only a metal oxide is used as a reaction raw material. Therefore, the reaction system has a small reaction heat and requires a high-frequency heating device that performs heating from the outside. Further, in the combustion synthesis methods of Patent Document 1 and Patent Document 2, BaRe ₂ Ti _m O _{2m + 4} and CaO—SrO—Li ₂ O—Re ₂ O ₃ —TiO ₂ dielectric ceramics have been obtained. Absent. In the combustion synthesis method, in order to completely propagate the combustion wave with only the first ignition without any external heating, the mixing ratio of the powder as each constituent element and the physical properties such as the metal powder as the heat source (Specific surface area), the removal of decomposition gas and salt remaining in the composite, etc. are important, and it is not easy to produce ceramics having a desired composition with high quality by this method.

The present inventors have applied for a method for combustion synthesis of BaRe ₂ Ti _m O _{2m + 4} and CaO—SrO—Li ₂ O—Re ₂ O ₃ —TiO ₂ dielectric ceramics (Japanese Patent Application No. 2005). -177001, Japanese Patent Application No. 2005-282394). During these combustion synthesis reactions, a large amount of carbon dioxide gas as decomposition gas and NaCl as a by-product salt was generated from the raw material powder, and when cooled, NaCl solidified and covered the furnace and the surface of the composite. . It was also observed that the pressure inside the furnace increased with the pressure of the cracked gas, the generation of cracked gas from the raw material powder was suppressed, and the synthesis reaction became intermittent.
Japanese Patent Laid-Open No. 5-9009 JP 2002-211907 A

The present invention has been made to cope with such a problem, and it is possible to easily remove a by-product decomposition gas and a by-product salt, and to obtain a high-quality oxide-based dielectric ceramic. It is an object of the present invention to provide a combustion synthesis method and a BaRe ₂ Ti ₅ O ₁₄ -based or CaO-SrO-Li ₂ O-Re ₂ O ₃ -TiO ₂ -based dielectric ceramic produced by the method.

The combustion synthesis method of the present invention is a dielectric ceramic using a reaction raw material containing at least a metal powder containing a Group 4 element having a specific surface area of 0.01 m ² / g to ² m ² / g and a substance serving as an oxygen supply source. A combustion synthesis method comprising: mixing a raw material powder by mixing at least the metal powder and the substance serving as the oxygen supply source; and a raw material powder obtained in the mixing step. And a combustion synthesis step of forming a sintered body by a combustion synthesis reaction with adiabatic flame temperature of 1500 ° C. or higher under a pressure condition of less than atmospheric pressure. The atmospheric pressure is 101.325 kPa.

  The combustion synthesis step is a step of combustion synthesis of the raw material powder in a chamber connected to a vacuum pump.

The dielectric ceramic is a BaRe ₂ Ti _m O _{2m + 4} type ceramic (where 3 ≦ m ≦ 7; m is an integer Re is a rare earth element), and the Group 4 element is Ti, and the reaction raw material As described above, Re ₂ O ₃ or Re (OH) ₂ and BaO ₂ are included. In addition, each element symbol is Ba (barium), Ti (titanium), Ca (calcium), Sr (strontium), Li (lithium), and O (oxygen), respectively.

The dielectric ceramic is a CaO—SrO—Li ₂ O—Re ₂ O ₃ —TiO ₂ (Re is a rare earth element) ceramic, wherein the Group 4 element is Ti, and the reaction raw material is CaCO _3. And SrCO ₃ , Li ₂ CO ₃ , and Re ₂ O ₃ .

  The dielectric ceramic of the present invention is an oxide-based dielectric ceramic and is manufactured by the combustion synthesis method described above.

  The combustion synthesis method of the present invention can synthesize oxide-based dielectric ceramics by only the first ignition without any external heating, and performs a combustion synthesis reaction under reduced pressure, so that by-product decomposition gas and by-product salt are not generated. It becomes easy to discharge out of the system, and it is possible to reduce decomposition gas and by-product salt remaining in the composite. As a result, the cleaning process for removing by-product salts from the composite can be simplified, and the quality of the dielectric ceramic as the composite can be improved.

Since the dielectric ceramic of the present invention is manufactured by the above manufacturing method, it can be manufactured in a short time and is excellent in mass productivity. In addition, it uses a Ti powder having a specific surface area of 0.01 m ² / g to ² m ² / g and is obtained by combustion synthesis with an adiabatic flame temperature of 1500 ° C. or higher, so it has excellent sintered body characteristics.

The combustion synthesis method of the present invention uses a reaction raw material containing at least a metal powder containing a Group 4 element having a specific surface area of 0.01 m ² / g to ² m ² / g and a substance serving as an oxygen supply source. A mixing step of mixing raw materials, and a combustion synthesis step of converting the raw material powder obtained in this mixing step into a sintered body by a combustion synthesis reaction with an adiabatic flame temperature of 1500 ° C. or higher under a pressure condition of less than atmospheric pressure. This is a method of synthesizing dielectric ceramics.

  As the metal powder containing a Group 4 element serving as a heat source that can be used in the present invention, a Group 4 A element metal powder is preferable. Specific examples include Ti (titanium), Zr (zirconium), and Hf (hafnium). Among these, Ti is preferable because ceramics having excellent dielectric properties can be obtained. As Ti, in addition to Ti metal powder, hydrogenated Ti metal powder can be used. The Group 4 A element can be used alone or in combination.

The shape of the metal containing Group 4 element that can be used in the present invention is preferably a fine powder, a specific surface area of ^{0.01 m 2 / g~2 m 2 /} g. Combustion wave propagates, and the preferred range of the specific surface area so easy to handle a ^{0.1 m 2 /g~0.6 m 2 / g} . When the specific surface area is less than 0.01 m ² / g, the contact area between the metal powder that is the heat source and the peroxide that is the oxygen supply source is small, so the combustion wave does not propagate and the dielectric ceramics cannot be synthesized. There is. 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.

Even when the average particle diameter of the metal powder that can be used for combustion synthesis is the same, a difference in reactivity was recognized when the specific surface area was 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 μm 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.

Further, a part of the metal powder can be replaced with the same kind of Group 4 element metal oxide, and these can be used together. A metal oxide such as TiO ₂ acts as a reaction diluent in the combustion synthesis reaction, and the adiabatic flame temperature can be controlled by adjusting the blending amount of the metal oxide. Specifically, when the blending ratio of the metal oxide is increased, the progress rate of the reaction is lowered and the adiabatic flame temperature is lowered.
Further, purification is generally required to form a single metal. For example, since Ti powder is expensive, there is an effect that cost reduction can be achieved by using the Ti powder and TiO ₂ powder in combination.
However, if a large amount of metal oxide powder such as TiO ₂ is used, impurities may be mixed into the reaction product, and if it is used over a predetermined amount, the combustion wave will not propagate. It is preferable to use in combination in consideration of the adiabatic flame temperature required for the heat treatment.

As the substance serving as the oxygen supply source used in the present invention, an ion-binding substance that generates oxygen by heating is blended. Examples of the ion binding substance include chlorates such as KClO ₃ , NaClO ₃ and NH ₄ ClO ₃ , perchlorates such as KClO ₄ , NaClO ₄ and NH ₄ ClO ₄ , and chlorites such as NaClO ₂ , Bromates such as KBrO ₃ , nitrates such as KNO ₃ , NaNO ₃ and NH ₄ NO ₃ , iodates such as NaIO ₃ and KIO ₃ , permanganates such as KMnO ₄ and NaMnO ₄ .3H ₂ O, Dichromates such as K ₂ Cr ₂ O ₇ , (NH ₄ ) ₂ Cr ₂ O ₇ , Periodates such as NaIO ₄ , Periodic acids such as HIO ₄ · 2H ₂ O, CrO _3, etc. Examples thereof include chromic acids, nitrites such as NaNO ₂ , calcium hypochlorite trihydrate such as Ca (ClO) ₂ .3H ₂ O, and the like.
Among these, perchlorates, chlorates and chlorites are preferable, and it is more preferable to use NaClO ₄ and KClO ₄ which can remove by-products NaCl and KCl by repeatedly washing with pure water. . Further, it is particularly preferable to use NaClO ₄ which is advantageous in terms of cost. In the case of perchlorates, the generated carbon dioxide gasifies, so it does not remain in the synthetic powder.

When the dielectric ceramic as the target product contains a rare earth element Re, a rare earth element oxide (Re ₂ O ₃ ) or hydroxide (Re (OH) ₂ ) is used as a supply source of the rare earth element Re. . As Re, Nd (neodymium), Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (Terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium). Of these, La, Pr, Nd, Sm and the like are particularly important industrially.
Further, Re in the dielectric ceramic of the present invention may be a single rare earth element or a mixture of two or more rare earth elements. In addition to the above, an element capable of improving the dielectric characteristics can be blended.

The dielectric ceramics obtained by the combustion synthesis method of the present invention include (a) BaRe ₂ Ti _m O _{2m + 4} system (where 3 ≦ m ≦ 7; m is an integer Re is a rare earth element), (b) CaO— Examples thereof include oxide-based dielectric ceramics such as SrO—Li ₂ O—Re ₂ O ₃ —TiO ₂ (Re is a rare earth element). These can be obtained by combusting and synthesizing the above-mentioned metal powder and the substance serving as the oxygen supply source with necessary reaction raw materials as appropriate.

As a dielectric ceramic obtained by combustion synthesis method of the present invention, the BaRe ₂ Ti _m O _{2m + 4} system (a); in (3 ≦ m ≦ 7 wherein m is an integer Re is a rare earth element), m = 5 A reaction system in the case of synthesizing BaNd ₂ Ti ₅ O _{14 in} which Re is Nd (neodymium) is illustrated.
In the reaction system, BaNd ₂ Ti ₅ O ₁₄ uses Ti powder as the metal powder, sodium perchlorate (NaClO ₄ ) as the oxygen source, and Re ₂ O ₃ or Re ( OH) ₂ and BaO ₂ are used, and after these reaction raw materials are mixed in a predetermined ratio, they are obtained by a combustion synthesis method in which the adiabatic flame temperature is 1500 ° C. or higher under a pressure condition of less than atmospheric pressure. The chemical reaction formula of this combustion synthesis reaction is as shown in the following formula (1) or (2).

In the above formulas (1) and (2), BaO ₂ is not only a Ba supply source but also an oxygen supply source. BaCO ₃ can also be used as a Ba supply source.
When TiO ₂ is included as a reaction diluent, x ≠ 10 in the above formulas (1) and (2). When x = 1, since the amount of Ti powder is small and the heat source is insufficient, the combustion wave does not propagate and a sintered body cannot be obtained. In addition, when TiO ₂ is not completely contained, when x = 10, the reaction proceeds rapidly and the synthetic powder is scattered in the chamber, which may make it difficult to collect the synthetic powder.

Mixing each reaction raw material at a predetermined ratio means mixing at a molar mass ratio satisfying the above formula. That is, in the case of the above formula (1), if the molar mass of Ti powder is x mol, TiO ₂ is (10-x) mol, NaClO ₄ is (x-1) / 2 mol, Regardless of the mass, 2 mol of BaO _{2 and} 2 mol of Nd ₂ O ₃ are blended. In the case of the above formula (2), 4 mol of Nd (OH) ₂ and x / 2 mol of NaClO ₄ are blended in place of Nd ₂ O ₃ .
The target BaRe ₂ Ti ₅ O ₁₄ can be easily obtained in a short time by blending each reaction raw material at this ratio and performing combustion synthesis. Further, most of the by-product decomposition gas is removed by suction under reduced pressure, and only the by-product salt NaCl remains in the synthesized product. This NaCl is easily synthesized by water washing described later. Can be separated and removed.

As described above, the blending ratio of Ti powder and TiO ₂ is determined by the value of x in the above formula (1) or (2). A preferable range of x during the synthesis of BaNd ₂ Ti ₅ O ₁₄ is 2 ≦ x ≦ 8. If x is less than 2, the heat generation source Ti powder is insufficient and the reaction diluent is too much TiO ₂ . There is. In addition, if x exceeds 8, there is a possibility that the amount of heat source is so large that the reaction proceeds rapidly and the synthetic powder is scattered.

Examples of dielectric ceramics obtained by the combustion synthesis method of the present invention include (b) a reaction system for synthesizing CaO—SrO—Li ₂ O—Re ₂ O ₃ —TiO ₂ (where Re is a rare earth element) ceramic. To do.
In the reaction system, the CaO—SrO—Li ₂ O—Re ₂ O ₃ —TiO ₂ ceramic is composed of Ti powder as a metal powder, sodium perchlorate (NaClO ₄ ) as a material serving as an oxygen supply source, and a reaction raw material. Combustion synthesis method using CaCO ₃ powder, SrCO ₃ powder, Li ₂ CO ₃ powder and Re ₂ O ₃ , mixing these reaction raw materials at a predetermined ratio, and then adiabatic flame temperature of 1500 ° C. or higher Is obtained.

The substance serving as the oxygen supply source is blended in such an amount that the Ti metal can be oxidized to TiO ₂ by oxygen atoms that can be released from the inside of the molecule. Specifically, with respect to Ti metal powder 2 mol, in a proportion of NaClO ₄ powder 1 mol.
The amount of the metal carbonate, a CaCO ₃ powder for the entire raw materials except NaClO _4, a total amount of 16 mole% of SrCO ₃ powder, Li ₂ CO ₃ powder is 9 mol%. When the blending amount of the CaCO ₃ powder is (16−x) mol% (0 <x <16), x is preferably 0.5 to 6 and most preferably x = 1 because various dielectric properties are excellent. .

The blending amount of the Re ₂ O ₃ powder is 12 mol% with respect to the whole raw material excluding NaClO ₄ . The Re ₂ O ₃ powder is preferably a combination of Sm ₂ O ₃ powder and other Re ′ ₂ O ₃ (Re ′ is a rare earth element other than Sm) powder. Here, as other Re ₂ O ₃ powders, there are La ₂ O ₃ powder, Nd ₂ O ₃ powder and the like, and it is preferable to use Nd ₂ O ₃ powder having a large effect of improving the dielectric properties. Sm ₂ O ₃ powder to the entire raw materials except NaClO _4, when the Nd ₂ O ₃ powder in the amount of each (12-y) mol% and y mole% (0 <y <12) , y is 3 9 is preferred, most preferably y = 6.

(B) An example of a combustion synthesis reaction for obtaining a dielectric ceramic having an optimum composition in the CaO—SrO—Li ₂ O—Re ₂ O ₃ —TiO ₂ system (Re is a rare earth element) ).

After mixing each reaction raw material at the blending ratio shown in the above reaction formula, the target CaO—SrO—Li ₂ O—Sm is produced by a combustion synthesis method in which the adiabatic flame temperature is 1500 ° C. or higher under a pressure condition of less than atmospheric pressure. _{A 2} O ₃ —Nd ₂ O ₃ —TiO ₂ dielectric ceramic can be easily obtained in a short time.
Most of the CO ₂ gas as a by-product is removed by suction under reduced pressure, and only the by-product salt NaCl remains in the composition, and this NaCl is easily synthesized by water washing described later. Can be separated and removed.

The compounding ratio of Ti powder (x mol%) and TiO ₂ powder ((63-x) mol%) is determined by the value of x. A preferable range of x is 15 ≦ x ≦ 50. When x is less than 15 as shown in the reaction formula (6), the Ti powder as the heat source is insufficient and the reaction diluent is too much TiO ₂ , so that the combustion wave does not propagate completely. Therefore, the sintered body characteristics may be inferior. In addition, as shown in Reaction Formula (5), when x exceeds 50, including the case where TiO ₂ is not blended, the amount of heat source increases and the reaction proceeds rapidly, causing problems such as scattering of raw material powder and reaction products. It can happen.

  In the mixing step in the present invention, the method of mixing the reaction raw materials can be employed without any particular limitation, such as mixing with a stirrer or mixing using a mortar and pestle. Examples of the stirrer include a tumbler, a Henschel mixer, and a ball mill. It is preferable to use a Henschel mixer, a ball mill, or the like that is excellent in mass productivity and has less load on the metal powder or peroxide powder such as shearing force.

The mixed raw material is put into a crucible and subjected to combustion synthesis. The material of the crucible is preferably non-oxide such as carbon (C), silicon carbide (SiC), silicon nitride Si ₃ N ₄ or the like. it can. Among these, a carbon (C) material is preferable because it is excellent in heat conduction and shape workability.
As a method for charging the mixed raw material powder into the crucible, there can be used a method in which the raw material powder is laid down in a powder bed shape, compressed after being laid down, or pressed into a crucible into a crucible.

The combustion synthesis method is performed under a reduced pressure below atmospheric pressure, and the adiabatic flame temperature of the combustion synthesis reaction 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). It should be noted that an inert gas atmosphere such as nitrogen gas or carbon dioxide gas can be used as long as the dielectric properties of the reaction product are not deteriorated.

Combustion synthesis is performed under reduced pressure in the chamber lower than atmospheric pressure (101.325kPa = 1 atm). The preferred degree of vacuum is 0.003 atm to 0.1 atm (0.3 kPa to 10.1 kPa). By removing the decomposition gas and by-product salt generated from the mixed raw material during combustion synthesis from the chamber, the pressure equilibrium in the combustion synthesis reaction proceeds to the product generation side, and the decomposition gas and by-product salt are also removed from the product. Gas and desalting are facilitated, by-product salt remaining in the composition can be reduced, and the washing step for desalting the composition can be simplified.
A vacuum pump is used as means for depressurizing the inside of the chamber, and the chamber and the vacuum pump are connected by piping to keep the inside of the chamber at a reduced pressure. By installing a filter and trap device to capture the powder in the pipe connecting the chamber and the vacuum pump, by-product salt sucked from the chamber is blocked in the vacuum pump as the combustion synthesis reaction proceeds. Can be prevented.

  The method for igniting the mixed powder for initiating combustion synthesis is not particularly limited as long as the metal powder can ignite and generate heat. A method in which a carbon film is ignited to generate heat and used as a heat source and brought into contact with the mixed powder to ignite and generate heat is preferable because it is excellent in handling. The combustion synthesis reaction is completed in about 1 to 60 seconds.

  The reaction product is agglomerated in the crucible. The pulverization of the reaction product is not particularly limited as long as the average particle diameter is 100 μm or less, and can be carried out with a jet mill, a ball mill, a mortar and a pestle. When the average particle size exceeds 100 μm, the washing in the subsequent washing step is not sufficient, and the ion-binding salt that is a by-product salt tends to remain.

The fine powder after the pulverization step contains an ion-binding salt that is a by-product salt. For example, when NaClO ₄ is used as a raw material, NaCl is generated, and when KClO ₄ is used as a raw material, KCl is generated. These by-product salts can be removed by washing with water.
When by-product salts are present in the synthetic powder after the combustion synthesis reaction, the sinterability is hindered. The standard for reducing by-product salts to such an extent that the sinterability is not hindered is that the electrical conductivity of the cleaning solution 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 synthetic powder is washed and dried and then sintered to obtain a dielectric ceramic. When sintering, a molding binder such as polyvinyl butyral can be blended. Examples of the sintering conditions include conditions of molding at a pressure of 10 MPa to 100 MPa and firing at a temperature of 1200 ° C. to 1500 ° C. in an air atmosphere.
Moreover, in order to further stabilize the crystal structure of the synthetic powder obtained by the combustion synthesis or to remove a trace amount of impurities, it is possible to calcine at 900 ° C. to 1100 ° C.

  Dielectric ceramics obtained by the above combustion synthesis method have excellent sintered body properties after combustion synthesis and are densified close to the theoretical density, so they can be used in dielectric antennas, capacitors, resonators, pressure sensors, ultrasonic motors, etc. It can be used suitably.

Examples 1 to 4
The intermediate raw material powder was obtained by dry-mixing each component shown in Table 1 for 5 hours using a ball mill at a predetermined molar blending ratio (mol%). Ti powder was added to a ball mill containing the obtained intermediate raw material powder, and dry mixed for 5 hours to obtain mixed raw material powder.
A carbon crucible was installed in the chamber in the combustion synthesizer, mixed raw material powder (100 g) was spread in the carbon crucible, and the carbon film for ignition was brought into contact with a part of the mixed powder to close the chamber. After reducing the residual oxygen in the chamber using a vacuum pump, argon (Ar) gas was sealed, and the internal pressure of the chamber was set to 0.1 MPa. Next, the vacuum pump was continuously operated to reduce the internal pressure of the chamber to 0.3 kPa.
Combustion waves propagated through the compositions of Examples 1 to 4, and synthetic powders were obtained by the combustion synthesis method. The pressure in the chamber during the reaction was kept below 10 kPa. The synthetic powder was pulverized using an alumina mortar to obtain an unwashed dielectric ceramic powder having an average particle size of 1 μm.

In Table 1, Ti powder is TSP-350 manufactured by Sumitomo Titanium Co., Ltd., TiO ₂ and NaClO ₄ are manufactured by Wako Pure Chemical Industries, Ltd., each reagent is BaO ₂ is manufactured by Kanto Chemical Co., Inc., and Nd ₂ For O ₃ , Shin-Etsu Chemical Co., Ltd. products were used.

Comparative Examples 1 to 3
The combustion synthesis reaction was started at atmospheric pressure of 0.1 MPa in the chamber. As the combustion synthesis reaction progressed, the chamber internal pressure increased to a maximum of 500 kPa, and the propagation of combustion waves occurred intermittently. In Comparative Example 1 and Comparative Example 2, ground ceramic powder having an average particle diameter of 1 μm was obtained in the same manner as in Example 1. In Comparative Example 3, the combustion wave did not propagate and synthetic powder could not be obtained.

The obtained unwashed dielectric ceramic powder was sufficiently washed with water, and NaCl adhered to the powder was removed to obtain a dielectric ceramic. The crystal phase of the obtained dielectric ceramic powder was identified using an X-ray diffractometer (XRD). The results are shown in Table 1 as the ceramic composition.
The relative dielectric constant and dielectric loss tangent were measured by the following methods.
1% by weight of a molding binder (polyvinyl butyral resin) was added to and mixed with the obtained ceramic powder. Next, the mixed powder was put into a 10 mm × 80 mm mold, and a pressure of 1.5 ton / cm ² was applied to obtain a green body (10 mm × 90 mm × 3 mm). The green body was held at 600 ° C. for 1 hour to remove organic components, and then fired at 1300 ° C. for 3 hours. The obtained sintered body was processed into a 70 mm × 1.5 mm × 1.5 mm test piece, and the relative dielectric constant and dielectric loss tangent were measured in the frequency band of 1 and 5 GHz by using the cavity resonator method. Here, relative permittivity and dielectric loss tangent are values at 25 ° C.

Example 5 to Example 9
Each reaction raw material was mixed for 5 hours using a ball mill at a molar mixing ratio (mol%) shown in Table 2 to obtain a mixed powder. A carbon crucible was installed in the chamber in the synthesizer, and the mixed powder (100 g) was spread in the carbon crucible, and a carbon film for ignition was brought into contact with a part of the mixed powder to close the chamber. After reducing the residual oxygen in the chamber using a vacuum pump, argon (Ar) gas was sealed, and the internal pressure of the chamber was set to 0.1 MPa. Next, the vacuum pump was continuously operated, the internal pressure of the chamber was reduced to 0.3 kPa, and ignition was performed. Combustion waves propagated and synthetic powder and by-product (NaCl) were obtained by the combustion synthesis method. The pressure in the chamber during the reaction was kept below 10 kPa. The synthetic powder was pulverized using an alumina mortar to obtain an unwashed dielectric ceramic powder having an average particle size of 2 μm.

In Table 2, Ti metal powders are TSP-350 and TILOP-150 (classified and adjusted to a specific surface area of 0.005 m ² / g by Sumitomo Titanium), CaCO ₃ , TiO ₂ , SrCO ₃ , Li ₂ CO. _{3. For} NaClO _4, reagents manufactured by Wako Pure Chemical Industries, Ltd., and for Sm ₂ O ₃ , Nd ₂ O ₃ , products manufactured by Shin-Etsu Chemical Co., Ltd. were used.

Comparative Example 4 to Comparative Example 11
The combustion synthesis reaction was started at atmospheric pressure of 0.1 MPa in the chamber, and as the combustion synthesis reaction progressed, the chamber internal pressure increased to a maximum of 800 kPa, and the propagation of combustion waves was intermittent. The same treatment as in Example 5 was performed to obtain a crushed ceramic powder having an average particle size of 2 μm.

The obtained unwashed dielectric ceramic powder was sufficiently washed with water, and NaCl adhered to the powder was removed to obtain a dielectric ceramic. The crystal phase of the obtained dielectric ceramic powder was identified using an X-ray diffractometer (XRD). The results are shown in Table 2 as the ceramic composition.
The relative dielectric constant and dielectric loss tangent were measured by the following methods.
1% by weight of a molding binder (polyvinyl butyral resin) was added to and mixed with the obtained ceramic powder. Next, the mixed powder was put into a 10 mm × 80 mm mold, and a pressure of 1.5 ton / cm ² was applied to obtain a green body (10 mm × 90 mm × 3 mm). This green body was held at 600 ° C. for 1 hour to remove organic components, and then fired at 1300 ° C. for 3 hours. The obtained sintered body was processed into a 70 mm × 1.5 mm × 1.5 mm test piece, and the relative dielectric constant and dielectric loss tangent were measured in the frequency band of 1 and 5 GHz using the cavity resonator method. Here, relative permittivity and dielectric loss tangent are values at 25 ° C.

  As shown in Table 1 and Table 2, in each Example in which combustion synthesis was performed under a reduced pressure below atmospheric pressure, there was little by-product salt in the synthetic powder, and almost no by-product salt was obtained in the washing process for 30 minutes after synthesis. Could be removed. Moreover, each Example was excellent in the dielectric characteristics compared with each Comparative Example.

  The combustion synthesis method of the present invention can easily produce dielectric ceramics by a smooth chemical reaction by easily removing decomposition gases and salts generated as by-products, so that dielectric ceramics can be produced safely and at low cost. . The obtained dielectric ceramics can be suitably used in the field of electronic components such as antennas, capacitors, resonators, filters, pressure sensors, and ultrasonic motors.

Claims (5)

A dielectric ceramic combustion synthesis method using a reaction raw material containing at least a metal powder containing a Group 4 element having a specific surface area of 0.01 m ² / g to ² m ² / g and a substance serving as an oxygen supply source,
The combustion synthesis method includes a mixing step of mixing at least the metal powder and a substance serving as an oxygen supply source to obtain a raw material powder;
A combustion synthesis step in which the raw material powder obtained in the mixing step is made into a sintered body by a combustion synthesis reaction with an adiabatic flame temperature of 1500 ° C. or higher under a pressure condition of less than atmospheric pressure. Combustion synthesis method.   The combustion synthesis method according to claim 1, wherein the combustion synthesis step is a step of combustion synthesis of the raw material powder in a chamber connected to a vacuum pump. The dielectric ceramic is a BaRe ₂ Ti _m O _{2m + 4} type ceramic (where 3 ≦ m ≦ 7; m is an integer Re is a rare earth element), and the Group 4 element is Ti, and the reaction raw material The combustion synthesis method according to claim 1, wherein Re ₂ O ₃ or Re (OH) ₂ and BaO ₂ are included. The dielectric ceramic is a CaO—SrO—Li ₂ O—Re ₂ O ₃ —TiO ₂ (Re is a rare earth element) ceramic, wherein the Group 4 element is Ti, and the reaction raw material is CaCO ₃ The combustion synthesis method according to claim 1, wherein SrCO ₃ , Li ₂ CO ₃ , and Re ₂ O ₃ are included.   An oxide-based dielectric ceramic manufactured by the combustion synthesis method according to any one of claims 1 to 4.