JP5128782B2 - Method for manufacturing dielectric ceramics - Google Patents

Description

  The present invention relates to an oxide-based dielectric ceramic obtained by a combustion synthesis method and having a predetermined composition excellent in dielectric characteristics, and a method for producing the same.

  In recent years, with the remarkable development of high-frequency communication technology such as mobile phone and satellite communication, the demand for dielectric ceramics for high-frequency devices such as dielectric resonators and filters is increasing. As for the frequency of the communication signal and the size of the communication device, for example, when the relative dielectric constant of the antenna substrate incorporated in the communication device is increased, the frequency and size can be further reduced. The relative permittivity is a parameter indicating the degree of polarization inside the dielectric. The higher the relative permittivity of the dielectric ceramic used in the antenna material, the shorter the wavelength of the signal propagating through the electronic component circuit, and the higher the signal Turn into. Therefore, if an electronic component having a high relative dielectric constant can be used, the frequency can be increased, the circuit can be shortened, and the communication device can be downsized. Moreover, low dielectric loss and good temperature stability are required at the same time for dielectric ceramics used in the above devices.

Conventionally, BaO—Re ₂ O ₃ —TiO ₂ (Re: rare earth element, the same applies hereinafter) dielectric is known as a dielectric ceramic having both low dielectric loss and good temperature stability (for example, patents). It is used for various applications. These are based on the paraelectric phase to keep the dielectric loss low.
However, these dielectric ceramics have a relative dielectric constant of about 80 to 90, which is not necessarily sufficient to cope with the above-described recent applications. For example, a dielectric having a high dielectric constant with a relative dielectric constant of about 120 Development is desired.

In addition, for the conventional synthesis of dielectric ceramics as described above, external heating must be performed for a long time using a furnace capable of heating from 1000 ° C. to around 2000 ° C. For this reason, the synthesis of ceramics requires enormous energy and a large heating mechanism, and there is a problem that the manufacturing cost increases.
JP 62-72558 A JP-A-6-12915

  The present invention has been made to address such problems, and an object of the present invention is to provide dielectric ceramics obtained by a combustion synthesis method and having excellent dielectric characteristics with a relative dielectric constant of 95 or more, and a method for producing the same.

The dielectric ceramic of the present invention is a dielectric ceramic obtained by a combustion synthesis method containing at least Ca, Ti, O, and Re (rare earth elements) as constituent elements, and the dielectric ceramic is CaO in molar composition ratio. : (26−x), SrO: x, Re ₂ O ₃ : 8, TiO ₂ : y (0 ≦ x ≦ 26, 40 ≦ y ≦ 60).
The dielectric ceramic is composed of Ti powder having a specific surface area of 0.01 to ² m ² / g, an ion-binding substance serving as an oxygen supply source, TiO ₂ , CaCO ₃ , SrCO ₃ , and Re ₂ O _3. In the reaction raw material containing at least the above, each powder is blended in such a ratio that the dielectric ceramic has the above molar composition ratio, and obtained by a combustion synthesis method in which the adiabatic flame temperature is 1500 ° C. or higher.
The element symbols are Sr (strontium), Ca (calcium), Ti (titanium), O (oxygen), Nd (neodymium), and Zr (zirconium), respectively.

The Re ₂ O ₃ is Nd ₂ O ₃ .
Further, the reaction raw material contains BaO ₂ and ZrO ₂ .
In addition, a part of the Ti powder as the reaction raw material is replaced with TiO ₂ powder and blended.

The dielectric ceramic production method of the present invention is a dielectric ceramic production method containing at least Ca, Ti, O, and Re (rare earth elements) as constituent elements, and has a specific surface area of 0.01 to 2 as a reaction raw material powder. m ² / g Ti powder, an ion-binding substance serving as an oxygen source, TiO ₂ , CaCO ₃ , SrCO ₃ , and Re ₂ O ₃ , and the resulting dielectric ceramic is CaO in molar composition ratio. : (26−x), SrO: x, Re ₂ O ₃ : 8, TiO ₂ : y (0 ≦ x ≦ 26, 40 ≦ y ≦ 60) The step of reacting the blended product by a combustion synthesis method with an adiabatic flame temperature of 1500 ° C. or higher, the step of pulverizing the reaction product obtained by the combustion synthesis reaction, and washing the pulverized powder with water And a process.

The dielectric ceramic of the present invention (containing at least Ca, Ti, O, and Re (rare earth elements) as constituent elements) is obtained by a combustion synthesis method, and has a molar composition ratio of CaO: (26−x), SrO: x, Since Re ₂ O ₃ : 8 and TiO ₂ : y (0 ≦ x ≦ 26, 40 ≦ y ≦ 60), the relative dielectric constant is high and the dielectric properties are excellent. Moreover, since it synthesize | combines by a combustion synthesis method, compared with the method of performing the conventional external heating, it can manufacture at low cost and a short time, and is low cost.

At the time of combustion synthesis reaction, a part of Ti powder is replaced with TiO ₂ powder, so there is no risk of explosion or ignition during mixing, and the replaced TiO ₂ powder acts as a reaction diluent in the combustion synthesis reaction. Therefore, the control of the adiabatic flame temperature becomes easy.

  The dielectric ceramic manufacturing method of the present invention determines the blending ratio of each reaction raw material powder so as to have a predetermined composition excellent in dielectric characteristics, so that a dielectric ceramic having excellent dielectric characteristics with few impurities can be obtained. it can. Moreover, since the by-products can be sufficiently removed by pulverizing the synthetic powder and then washing with water, a sintered body close to the theoretical density can be obtained.

The dielectric ceramic of the present invention includes at least Ca, Ti, O, and Re (rare earth elements), and if necessary, Ba and Zr as constituent elements, CaO—SrO—Re ₂ O ₃ —BaO—ZrO ₂ —TiO. _{It is a two-} system dielectric ceramic and can be obtained by combustion synthesis. The dielectric ceramic of the present invention has a molar composition ratio of CaO: (26−x), SrO: x, Re ₂ O ₃ : 8, TiO ₂ : y (0 ≦ x ≦ 26, 40 ≦ y ≦ 60). By doing so, it has excellent dielectric properties.
As a combustion synthesis method, Ti powder having a specific surface area of 0.01 to ² m ² / g, an ion-binding substance serving as an oxygen supply source, TiO ₂ , CaCO ₃ , SrCO ₃ , and Re ₂ O ₃ are used. Examples include a method of blending each powder in a reaction raw material at least in such a proportion that the dielectric ceramics has the above molar composition ratio and performing a combustion synthesis reaction in which the adiabatic flame temperature is 1500 ° C. or higher.

The Ti powder used in the present invention is preferably a fine powder and has a specific surface area of 0.01 to ² m ² / g. A preferable specific surface area in which combustion waves propagate and is easy to handle is 0.1 to 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. Moreover, it can replace with Ti powder and can also use hydrogenated Ti powder. 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 Ti powder used in the present invention was 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. As the shape having a large specific surface area, there are a particle having a plurality of irregularities formed on the surface of a spherical particle, a particle 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 will be 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, the TiO ₂ powder that can be blended by replacing a part of the Ti powder 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 TiO ₂ powder. Specifically, when the blending ratio of TiO ₂ is increased, the reaction progress rate 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 the TiO ₂ powder is used, impurities may be mixed into the reaction product, and if it is used in excess of a predetermined amount as shown in the examples and the like described later, the combustion wave will not propagate. In consideration of the cost and the adiabatic flame temperature required for the reaction, it is preferable to use them in combination.

Ti constituting a part of the dielectric ceramic of the present invention is supplied from the Ti metal powder and the TiO ₂ powder. The blending amount of these powders at the time of synthesis is determined according to the above molar composition ratio, and y is optimally 50.

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 and nitrites such as NaNO ₂ .
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.

The ion binding substance to be blended in the present invention is blended in an amount (minimum necessary amount) or more that can oxidize unoxidized Ti metal to TiO ₂ by oxygen atoms that can be released from the inside of the molecule.

SrCO ₃ powder is used as the Sr supply source constituting a part of the dielectric ceramic of the present invention, and CaCO ₃ powder is used as the Ca supply source. By using these metal carbonates, the handleability is excellent.
The compounding amount of these metal carbonate powders at the time of synthesis is determined according to the molar composition ratio. That is, for example, when 40 to 60 mol of TiO ₂ is blended, 26 mol is blended in the total amount of CaCO ₃ and SrCO ₃ powder. Here, when the amount of CaCO ₃ is (26−x) mol (0 ≦ x ≦ 26), x is preferably 6 to 24, and most preferably x = 8, because various dielectric properties are excellent. is there.

As a source of rare earth element Re, rare earth element oxide (Re ₂ O ₃ ) powder is used. 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. It is preferable that at least Nd is included since the effect of improving the dielectric characteristics is great.

The compounding amount of these Re ₂ O ₃ powders at the time of synthesis is determined according to the molar composition ratio. That is, for example, when 40 to 60 mol of TiO ₂ is blended, 8 mol of Re ₂ O ₃ powder is blended. When two or more rare earth oxides are used, the total amount is 8 moles.

The dielectric ceramic of the present invention preferably contains a trace amount of Ba and Zr as its constituent elements. By mixing a small amount of Ba and Zr elements, Ba having a large ionic radius enters the position of Ca and Sr serving as the skeleton, so that the relative dielectric constant increases. When a small amount of Zr having an ionic radius larger than that of Ti is added, the lattice spacing is increased and the relative dielectric constant is improved.
BaO ₂ is used as the Ba supply source, and ZrO ₂ is used as the Zr supply source. BaO ₂ powder is a peroxide and is an oxygen source as well as a Ba source.
The compounding amount of each of these powders that are the source of trace elements at the time of synthesis is, for example, 0.01 to 5 mol when TiO ₂ is compounded in an amount of 40 to 60 mol. More preferably, 0.2 mol each is blended.

The optimum composition of the dielectric ceramic of the present invention is CaO: 18, SrO: 8, Re ₂ O ₃ : 8, TiO ₂ : 50, BaO: 0.2, ZrO ₂ : 0.2 in molar composition ratios. Each reaction raw material in the case of the optimum composition is blended at a molar ratio of CaCO ₃ : SrCO ₃ : Re ₂ O ₃ : TiO ₂ : BaCO ₃ : ZrO ₂ = 18: 8: 8: 50: 0.2: 0.2. It should be noted that an appropriate amount of an ion-binding substance such as NaClO ₄ is blended in the minimum necessary amount or more.

In the step of blending the above reaction raw materials in a predetermined ratio, if sodium perchlorate or the like and Ti powder are brought into direct contact, there is a risk of ignition, explosion, or the like. Therefore, the Ti powder is preferably preliminarily mixed with a stable metal carbonate (CaCO ₃ , SrCO _3, etc.) to form a stable intermediate material, and then mixed with sodium perchlorate or the like.
The stirrer used for the preliminary mixing can be used without particular limitation, such as mixing using a tumbler, Henschel mixer, ball mill, mortar and pestle. Moreover, the stirrer used for mixing by adding sodium perchlorate or the like to the obtained intermediate raw material has sufficient clearance between the stirrer blade and the stirrer wall surface, so that Ti powder, sodium perchlorate, etc. It is preferable to use a Henschel mixer to which a shearing force is not applied by stirring, a ball mill without stirring blades, or the like.

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

The mixture blended at the predetermined ratio is reacted by the 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.
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 size is 10 μm or less, and can be performed 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 becomes insufficient, and the ion-binding salt as a by-product tends to remain.

The fine powder after the pulverization step contains an ion-binding salt that is a by-product. 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 salts can be removed by washing with water as described above.
When salts are present in the synthetic powder after the combustion synthesis reaction, the sinterability is hindered. As a standard for reducing the salt to such an extent that the sinterability is not hindered, 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.

Dielectric ceramics (synthetic powder) are obtained through the above steps. Moreover, you may sinter this powder after washing | cleaning and drying according to a use. 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 powder obtained by the combustion synthesis and to remove a trace amount of impurities, it is possible to calcine at 900 to 1100 ° C.

Example 1 to Example 10, Comparative Example 1 to Comparative Example 3
Dielectric ceramics were synthesized by the following method. Each reaction raw material was mixed for 5 hours using a ball mill at a molar mixing ratio (molar ratio) shown in Table 1 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.
In Table 1, Ti metal powder is TSP-350 or TILOP-150 manufactured by Sumitomo Titanium, and NaClO ₄ , TiO ₂ , SrCO ₃ , CaCO ₃ , BaO ₂ , and ZrO ₂ are reagents manufactured by Wako Pure Chemical Industries, Ltd. Nd ₂ O ₃ was a Shin-Etsu Chemical Co., Ltd. product.

Combustion waves propagated through the compositions of Examples 1 to 10, and synthetic powder and by-product (NaCl) were obtained by the combustion synthesis method. The synthetic powder was pulverized using an alumina mortar to obtain an unwashed dielectric 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 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 dielectric 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, the propagation of combustion waves exhibiting excellent dielectric properties was generated in all examples, and synthetic powders were obtained. Among the obtained synthetic powders, the dielectric ceramics having the composition of Example 7 having a blending ratio of CaO: 18, SrO: 8, Re ₂ O ₃ : 8, TiO ₂ : 50, BaO: 0.2, ZrO ₂ : 0.2. Showed the best dielectric properties.

  Since the dielectric ceramic of the present invention is close to the theoretical density and has excellent dielectric properties, it can be used for dielectric antennas, capacitors, dielectric resonators, filters, pressure sensors, ultrasonic motors and the like.

Claims (4)

A method for producing a dielectric ceramic comprising at least Ca or Sr , Ti, O, Re (rare earth element) as a constituent element,
At least a Ti powder having a specific surface area of 0.01 to ² m ² / g, an ion-binding substance as an oxygen supply source, TiO ₂ , CaCO ₃ , SrCO ₃ , and Re ₂ O ₃ as a reaction raw material powder. The dielectric ceramics obtained have a molar composition ratio of CaO: (26−x), SrO: x, Re ₂ O ₃ : 8, TiO ₂ : y (0 ≦ x ≦ 26, 40 ≦ y ≦ 60) A step of blending with,
Reacting the compound blended at the predetermined ratio by a combustion synthesis method in which the adiabatic flame temperature is 1500 ° C. or higher;
Crushing the reaction product obtained by the combustion synthesis reaction;
And a step of washing the pulverized powder with water. Wherein Re ₂ O ₃ is a manufacturing method of dielectric ceramics according to claim 1, characterized in that the Nd ₂ O _3. Wherein the reactants, and BaO _2, The process of claim 1 or claim 2, wherein the dielectric ceramic is characterized to include and ZrO _2. A part of Ti powder which is the reaction raw material, manufacturing method of claim 1, claim 2 or claim 3, wherein the dielectric ceramics, which comprises mixing replaced with TiO ₂ powder.