JPH05132319A - Production of dielectric material powder - Google Patents

Abstract

PURPOSE:To produce powder of dielectric material having excellent dielectric characteristics and raw material powder of dielectric material useful especially in a microwave range. CONSTITUTION:In producing powder of dielectric material consisting essentially of barium, titanium and a rare earth element, the production consists of (a) a process of manufacturing a raw material mixture comprising barium and a rare earth element as main components among constituent components, (b) a process of calcining the mixture produced in the process (a), (c) a process of blending the calcined mixture obtained by the process (b) with a raw material comprising the residual titanium component as a main component so as to give the objective composition, (d) a process of calcining the blend obtained by the process (c) in series to give powder of dielectric material. Since titanium is added in the process (c), selective reaction of barium and rare earth is prevented to produce powder of dielectric powder having uniformity and excellent characteristics free from defects.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a dielectric powder having excellent dielectric properties, and more particularly to a method for producing a raw material powder for a dielectric used in the microwave region.

[0002]

2. Description of the Related Art A communication system using microwaves, that is, satellite communication and satellite broadcasting is rapidly developing with the increase of communication information amount, and the relative dielectric constant of the resonant element of the communication and broadcasting apparatus is large and the quality factor Q is large. Has been developed and put to practical use, with a large value (small dielectric loss) and a temperature coefficient τf of resonance frequency close to O. Of these, MgTiO ₃ , (CaLa) TiO ₃
-MgTiO ₃ , MgTi ₂ O ₅ -TiO ₂ , MgO-Nd ₂ O ₃ , (La ₂ O ₃ ) -TiO ₂ ,
(CaSrBa) (ZrTi) O ₃ , Ba (Mg _1/3 Ta _2/3 ) O ₃ , Ba (Zn _1/3 Nb _2/3 )
O ₃ -Ba (Zn _1/3 Ta _2/3 ) O ₃ , Ba (Zn _1/3 Nb _2/3 ) O ₃ -Sr (Zn _1/3 Nb
_2/3 ) O ₃ , Ba (NiTa) O ₃ -Ba (ZrZnTa) O ₃ , Ba (ZnTa) O ₃ -BaZr
O ₃ , (SrCa) (LiNbTi) O ₃ , (ZrSn) TiO ₄ , BaTi4O ₉ , Ba ₂ Ti
Dielectrics such as ₉ O ₂₀ and BaO 4 TiO ₂ 0.1 WO ₃ have a high quality factor Q but a low relative permittivity (relative permittivity εr = 25
Therefore, when the resonator is used in, for example, the 0.1 to 4 GHz band, the resonator cannot be downsized sufficiently. Therefore, for this application, oxides of barium, titanium and rare earth elements such as BaO-TiO ₂ -Nd ₂ O ₃ system {Be
r. Dt. Keram. Ges. 55 (1978) No. 7; JP 60-354
A dielectric such as '06 publication} is used.

Conventionally, as a method for producing a dielectric powder, compound powders such as oxides and carbonates containing various metals as constituents are weighed to obtain a desired composition, mixed together, and then calcined in air. In general, a method of repeating the solid-phase reaction by pulverization and calcination several times to manufacture is common.

[0004]

However, in the above conventional method, since the raw material powders are mixed at once, a selective reaction between the raw material powders is likely to occur in the solid-phase reaction during calcination.
Specifically, the titanium component easily reacts selectively with the barium component and the rare earth element component, respectively, and a composite oxide of titanium and barium, for example, Ba ₄ Ti ₁₃ O ₃₀ , BaTi ₄ O ₉ , BaTi ₂ O ₅
Etc. and complex oxides of titanium and rare earth elements, such as R ₂ Ti
Intermediate products such as ₂ O ₇ (R: rare earth element) are easily generated. Therefore, there is a problem that the quality factor Q of the sintered body produced using the obtained dielectric powder is lowered. This is probably because it is difficult to improve the homogeneity of the composition at the atomic level, and many impurity phases are generated and lattice defects are present.

Therefore, in the conventional method, a method of repeating calcination and pulverization or a method of increasing the calcination temperature is adopted in order to improve the homogeneity of the composition, but not only is the process complicated and impractical, but also The strong agglomeration of the powder due to high temperature calcination must be crushed, and there is a problem that impurities are mixed in during crushing. The present invention has been made in order to solve the above problems, and provides a method for producing a dielectric powder having excellent composition uniformity and excellent dielectric properties of a sintered body, particularly a quality factor Q.

[0006]

That is, according to the present invention, in producing a dielectric powder containing barium, titanium, and a rare earth element as main components, (a) containing barium and a rare earth element as main components Manufacturing a raw material mixture to
(b) calcining the mixture obtained in the step (a),
(c) a step of blending the raw material containing the remaining titanium component as a main component so that the calcined product obtained in the step (b) has a desired composition, (d) the blend obtained in the step (c) A method for producing a dielectric powder, characterized in that the steps of calcining an object are combined.

The present invention will be described in more detail below. The rare earth elements referred to in the present invention are as defined in general, La, C
e, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
b, Lu and Y are 17 kinds of elements of Sc, and La, Ce, Pr, Nd, Pm, Sm, Eu, depending on the characteristics of the required dielectric material.
Gd, Tb and Dy are useful. The present invention is a method for producing a dielectric powder containing barium, titanium and at least one of the rare earth elements as a main component, but the additive component other than this main component is not particularly limited. For example, Pb, Sr,
Ca, Zr, Hf, Bi, Mn, Al, Mg, Si, Ge, Te, Ni, Tl and
Cr and the like can be mentioned. Further, the addition process of these additive components is carried out in one or more of the steps (a), (b) or (c) described below, or is obtained by the step (c). It may be added to the dielectric powder of the invention. As the additive component, a single compound of the additive component such as an oxide or carbonate, or a complex compound of several additive components may be added in the form of powder or solution.

Hereinafter, each step will be described in order. (a) About process. In step (a) of the present invention, a raw material mixture containing barium and a rare earth element as main components among the constituent components is manufactured. Examples of barium raw materials include carbonates, oxides, hydroxides, chlorides, nitrates, sulfates, and organic acid salts such as oxalates, formates, and acetates. It is preferable that the baking does not leave impurities. As the raw material for the rare earth element, oxides are preferable, and salts such as carbonates are preferable. Further, depending on the desired composition, a raw material containing several kinds of rare earth elements such as a light rare earth oxide mixture may be used. Alternatively, a metal may be used as a raw material.

The production of the raw material mixture in the step (a) is not particularly limited and a known method can be used. However, considering the characteristics of the powder finally obtained, the respective components are uniformly distributed. The raw material mixture is preferably in powder form,
A method in which a particle having a small particle size and a narrow particle size distribution is obtained is preferable. These production methods are roughly classified into a solid phase method, a liquid phase method and a gas phase method, and any method may be used, but the solid phase method is preferable in terms of productivity and production efficiency. The solid phase method is a method of mixing the raw materials of the above constituents in powder form. Mixing is a mixer,
Either a dry method or a wet method using a ball mill, a vibration mill or the like may be used, but the wet method is more efficient.

Examples of the liquid phase method include a method of producing from a melt such as a melt spraying method and a plasma jet method, and a method of producing from a solution by precipitation formation and solvent removal. The method of forming a precipitate includes a coprecipitation method, a uniform precipitation method, an alkoxide method, an electrolytic method, a sol-gel method, etc., and a method of removing a solvent is a spray drying method, a freeze drying method, a heat kerosene method, a liquid drying method, an emulsion method. and so on.

The vapor phase method includes an evaporation-condensation method and a vapor phase chemical reaction method. The former is a method in which a raw material is heated to a high temperature by using an arc or a plasma jet to be vaporized, and then rapidly cooled by a large temperature gradient of the arc or the plasma flame to be agglomerated into particles. The latter gas phase chemical reaction method is based on a chemical reaction of a volatile compound vapor, and includes a thermal decomposition of a single chemical species and a reaction between two or more chemical species.

About (b) step. In the step (b) of the present invention, the mixture obtained in the step (a) is calcined. The optimum calcination temperature varies depending on the composition, but it is 800 ℃ ~
The temperature is preferably 1500 ° C, more preferably 1000 ° C to 1300 ° C.
If the calcination temperature is lower than 800 ° C, the solid-phase reaction is difficult to proceed,
If the temperature is higher than 0 ° C, strong agglomeration of the powder will proceed and the powder characteristics will deteriorate. As a method of calcination, specifically, calcination in an ordinary electric furnace or the like can be mentioned.

(B) A ball mill, a vibration mill, a jet mill, a stirring mill, a planetary mill for improving powder characteristics (preferably having a small particle size and a narrow particle size distribution) before and / or after the step. It is preferable to grind with a disintegrator such as a dyno mill. In ball mills, vibration mills, etc., the average particle size of crushed powder is limited to around 1 μm, but jet mills,
Planetary mills, stirring mills, dyno mills, etc. have more powerful crushing ability and can be pulverized.

About (c) step. In the step (c), the calcined product obtained in the step (b) is mixed with a raw material containing the remaining titanium component as a main component so as to have a desired composition. Examples of the raw material of the titanium component include oxides, hydroxides, chlorides, nitrates, sulfates and oxalates, formates, acetates, organic acid salts such as alkoxides, and metals, but the following (d) It is preferable that the calcination in the process does not leave impurities. When the raw material is in the form of powder, the particle size thereof is preferably fine although it varies depending on the particle size of the powder obtained in the step (b), specifically 5 μm or less, preferably 1 μm or less.

The method of blending the raw materials in the step (c) is not particularly limited as long as it is a method capable of uniformly mixing, and a known method can be used, but considering the characteristics of the powder finally obtained, The powder form is preferable, and a method in which a powder having a small particle size and a narrow particle size distribution is obtained is preferable. As a blending method of these, a dry method,
It can be performed by any of the wet methods.
The dry method means mixing by a usual mixing method such as a mortar mixer and a ball mill.

What is the wet method? After mixing the calcined product obtained in step (b) with a solution-form raw material containing a titanium component as a main component, a precipitant such as aqueous ammonia, ammonium carbonate, ammonium oxalate, an aqueous alcohol solution or There are a method of obtaining a precipitate of a mixture of both by reacting with water, or a method of removing a solvent, for example, a spray drying method, a freeze drying method, a heat kerosene method, a liquid drying method, an emulsion method and the like. In addition, as in step (b), a ball mill, a vibration mill, a jet mill, or a mill for improving powder properties (preferably having a small particle size and a narrow particle size distribution) before and / or after the step (c),
It is preferable to grind with a disintegrating machine such as a stirring mill, a planetary mill or a dyno mill.

(D) About process. In the step (d), the compound obtained in the step (c) is calcined.
The calcination temperature in step (d) is 700 ° C to 1300 ° C, preferably 900 ° C to 1100 ° C. This is because if the calcination temperature is less than 700 ° C, the solid-phase reaction of the mixed powder is insufficient, and if it exceeds 1300 ° C, the powder becomes coarse. Also, as in step (c), (d)
In order to improve the powder properties before and / or after the step, it is preferable to grind with a disintegrator such as a ball mill, a vibration mill, a jet mill, a stirring mill, a planetary mill or a dyno mill.

[0018]

EXAMPLES Examples of the present invention will be specifically described below. Example 1 BaCO ₃ powder and Sm ₂ O ₃ powder were wet-mixed with a ball mill for 20 hours so that the molar ratio of Ba: Sm was 1: 1. After heating and drying the obtained mixture slurry, the temperature is 1200 ° C in air (indicated as calcination 1 in Table 1).
It was calcined for 2 hours. The calcined product was wet crushed for 20 hours with a ball mill. After heating and drying the obtained pulverized product slurry, the obtained powder and TiO2 powder have a molar ratio of Ba: Sm: Ti of
It was weighed so as to be 1: 2: 4, and wet mixed with a ball mill for 20 hours to mix the titanium component. The resulting formulation was calcined in air at a temperature of 1050 ° C. (denoted as Calcination 2 in Table 1) for 2 hours. The obtained calcined product was wet pulverized again for 20 hours using a ball mill. The resulting slurry was dried by heating, and then an appropriate amount of polyvinyl alcohol was added and kneading was performed, followed by granulation with a 32 mesh sieve. Granulated powder is pressure molded at a molding pressure of 800 kg / cm ² , and the temperature is 1350 ° C in air.
(Indicated as sintering in Table 1) and fired for 5 hours.

The sintered body thus obtained had a diameter of about 10 mm and a height of about 4 mm.
It was processed into a cylindrical shape of mm. The density of this sintered body is the theoretical density
The density was 97.2%, which was high density (Table 1). For evaluation of the dielectric properties of this sintered body, εr, quality factor Q and τf in the GHz band were measured by a transmission method using a cavity type resonator. The measurement was performed using a Yokogawa Hewlett-Packard network analyzer (model number: YHP 8510) and a measuring jig manufactured by Murata Manufacturing Co., Ltd. (model number: DRG 8553).
The resonance mode used was the TE01δ mode. The resonance frequency of the sample was 3 to 4 GHz. In general, when measuring dielectric properties in the GHz band, the measured values often differ depending on the measuring method, and it is necessary to give due consideration to the measuring methods when comparing the measured values. In particular, care must be taken when measuring the quality factor Q. Regarding the temperature dependence of the resonance frequency fo, measure in the range of -30 ℃ to +80 ℃,
The temperature coefficient τf was calculated. The results are shown in Table 1. The values of the quality factor Q in the table are the resonance frequency fo and the quality factor Q.
The relational expression fo × Q = and the relational expression between and are converted into the value at 1 GHz and shown.

[0020]

[Table 1]

[Comparative Example 1] A powder having the same composition as in Example 1 was synthesized by a conventional method. Same composition as in Example 1 (Ba: Sm: Ti
Used in Example 1 so that the molar ratio of BaCO was 1: 2: 4).
_{The three} powders and the Sm ₂ O ₃ and TiO ₂ powders were weighed and put into a ball mill all at once, and wet mixed for 20 hours. The obtained composition was calcined in air at a temperature of 1050 ° C. (in Table 1, for convenience of preparation of the table, shown in the column of calcination 2) for 2 hours. The obtained calcined product was wet pulverized again for 20 hours using a ball mill. The resulting slurry was dried by heating, and then an appropriate amount of polyvinyl alcohol was added and kneading was performed, followed by granulation with a 32 mesh sieve.
The granulated powder was pressure-molded at a molding pressure of 800 kg / cm ² and fired in air at a temperature of 1350 ° C for 5 hours. The obtained sintered body was processed into a cylindrical shape having a diameter of about 10 mm and a height of about 4 mm. The density of this sintered body was 67.4% of the theoretical density, which was low. This indicates that the powder of Example 1 has high sinterability.

[Comparative Example 2] The powder obtained in Comparative Example 1 was used for calcination at 1450 ° C, which was increased by 100 ° C for 5 hours. The density of the obtained sintered body was 95.3% of the theoretical density. This is almost the same as in the first embodiment. The results of measuring the dielectric properties of this sintered body by the same method as in Example 1 are shown in Table 1. It can be seen that the value is considerably lower than the quality factor Q obtained for the sintered body of Example 1.

[Examples 2 to 9] BaCO ₃ powder and rare earth oxide powder (Sm ₂ O ₃ , La to have the composition shown in Table 1).
₂ O ₃ , Pr ₆ O ₁₁ , Nd ₂ O ₃ , Eu ₂ O ₃ ) with a ball mill to 20
Wet mixed for hours. After heating and drying the obtained mixture slurry, the temperature shown in Table 1 in air (calcination 1: (b)
It was calcined at the calcination temperature of the process) for 2 hours. The calcined product was wet crushed for 20 hours with a ball mill. After heating and drying the obtained pulverized product slurry, the obtained powder and TiO ₂ powder are weighed so as to have the composition shown in Table 1, and are weighed with a ball mill.
The titanium component was blended by time wet mixing. The obtained blend was calcined in air at the temperature shown in Table 1 (calcination 2: the calcination temperature of step (d)) for 2 hours. The obtained calcined product was wet pulverized again for 20 hours using a ball mill. The resulting slurry was dried by heating, and then an appropriate amount of polyvinyl alcohol was added and kneading was performed, followed by granulation with a 32 mesh sieve. The granulated powder was pressure-molded at a molding pressure of 800 kg / cm ² and fired in air at the temperature (sintering: firing temperature) shown in Table 1 for 5 hours. The density (%) and dielectric properties (εr,
Q and τ f) are shown in Table 1.

[Comparative Examples 3 to 6] Similar to Comparative Example 1, powders were synthesized by a conventional method. The BaCO ₃ powder, the rare earth oxide powder and the TiO ₂ powder used in the examples were weighed so that the compositions shown in Table 1 were obtained, and they were all put together in a ball mill and wet mixed for 20 hours. The obtained composition was calcined in air at a temperature shown in Table 1 (in Table 1, for convenience of preparation of the table, shown in the column of calcination temperature in step (d)) for 2 hours. The obtained calcined product was wet pulverized again for 20 hours using a ball mill. The resulting slurry was dried by heating, and then an appropriate amount of polyvinyl alcohol was added and kneading was performed, followed by granulation with a 32 mesh sieve. The granulated powder was pressure-molded at a molding pressure of 800 kg / cm ² and fired in air at the temperature shown in Table 1 for 5 hours. Table 1 shows the density and dielectric properties of the obtained sintered body.

[0025]

According to the method of the present invention in which the raw material mixing and the calcination are performed in two steps, a dielectric powder having a high uniformity and a small impurity phase can be obtained, and the quality factor is particularly high in the microwave region. It is possible to produce a powder having high dielectric properties and high dielectric properties.

Claims (1)

[Claims] 1. A method for producing a dielectric powder containing barium, titanium and a rare earth element as main components, wherein (a) a step of producing a raw material mixture containing barium and a rare earth element as main components, b) a step of calcining the mixture obtained in the step (a), (c) a raw material mainly containing the remaining titanium component so that the calcined product obtained in the step (b) has a desired composition And a step of calcining the mixture obtained in the step (c), and a step of calcination of the mixture obtained in the step (c).