JPH0489317A - Easily-sintering powder material for microwave dielectric material - Google Patents

Abstract

PURPOSE:To obtain a powder material having small average particle size, narrow particle size distribution, and improved low-temp. sintering property and purity by synthesizing the powder by hydrothermal synthesis. CONSTITUTION:Hydroxide crystals or hydroxide precipitates as the source material containing <=10ppm impurity ions are dispersed in water by >=1/20 source material/H2 mass ratio. This dispersion liquid is put in an autocleve for the hydrothermal synthesis at >=10kg/cm<2> pressure and 100-374 deg.C. Thus, the powder material for microwave dielectric material having good sintering property and <=1mum average particle size is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a microwave dielectric powder, particularly to a powder synthesized by a hydrothermal synthesis method and having excellent dielectric properties.

(Prior art) As the amount of communication information increases, communication systems using microwaves, such as satellite communication and satellite broadcasting, are rapidly developing. A dielectric material with a small Q value (a large Q value) is used. The following materials are used for this dielectric material powder. Namely, MgTiOs, (CaLa)Ties
ToTiOs, MgTi20s-TiO□MgO-N
d2O5, (La20g)-TiOz, (CaSrBa
) (ZrT i)02, Ba(Mg+/3Taz/5
)o3゜Ba(Zn+7sNbt7s)Ox Ha(Zn+zs
Taxzs)Ox, Ba(Zn+z, Nbtzs)Os
-3r(Zn+zsNbz7a)Oa,Ba(NiTa
)Ox-Ba(ZrZnTa)Oz, Ba(ZnTa
)Os-BaZrO+, (SrCa)(LiNbTi
)03, (ZrSn)Ti14, BaTt40m, Ba
2TllIO□. and BaO・4T102・o, lWO
3 etc.

Conventionally, microwave dielectric material powders having the above-mentioned compositions have been prepared in the same way as ordinary ceramics by weighing, mixing, and
It was manufactured through processes such as firing. For example, Ba(
Zn+zsTa2zs)Os-Ba(Zn+zsNb2
zs) About Ox ceramics (abbreviated as BZTN) ("
Trends in Microwave Dielectric Ceramics (Overview)], Electronic Ceramics, March 1988 issue, Volume 19)
is introduced in. According to this, first, the active ingredients in the obtained solid raw material are quantitatively analyzed, and the raw materials are weighed and collected so as to have a desired chemical composition ratio. Next, in order to uniformly carry out the solid phase reaction, dry mixing using a miller or the like or wet mixing using a ball mill or the like is performed. The mixed raw materials are calcined at a temperature slightly lower than the firing temperature (approximately 1000° C.) and then pulverized. The calcination is carried out at 900° C. to 1100° C. for 2 to 10 hours so that no gas is generated due to thermal decomposition of carbonate during sintering and the sinterability of the powder is not lost. Grinding after calcination adjusts the particle size of the powder to an average particle size of 2 to 10 μm,
Abnormal expansion and contraction in subsequent processes is reduced, making it easier to obtain dense ceramics. Granules are made by adding a binder, lubricant, and water to the crushed powder.

Binders include polyvinyl alcohol and starch, and lubricants include stearate and carpowax. The granulated powder is placed in a mold of a predetermined shape and compressed under pressure using a hydraulic press or mechanical press.

When molding a thick plate, columnar, or cylindrical sample, it is necessary to smooth the powder flow in the mold and make the stress distribution uniform. When the stress distribution is non-uniform, firing distortion occurs and the distribution of density etc. of the sintered body becomes non-uniform. The molding pressure is about 1 to 3 t/an. 1550°C) for the required time (2 to 120 hours).

These sintered bodies are finished by grinding or polishing to the required dimensions to form the final product.

(Problem to be solved by the invention) The quality factor Q of manufactured ceramics is given by the reciprocal of the dielectric loss, or in order to reduce the dielectric loss and increase Q, grain boundaries, impurities, lattice defects, etc. Homogeneous, except for
It is necessary to use dense ceramics with little warping or bending. This is because the temperature stability of the dielectric constant and dielectric loss of microwave dielectric ceramics directly determine the quality of the resonator.

Conventionally, microwave dielectric powder has been manufactured by mixing and calcining solid powder raw materials as described above, which tends to contain various impurities during the mixing and calcining process, and the average grain size of the manufactured powder Since the diameter was large, 1 μm or more, and the particle size distribution was wide, it was necessary to increase the firing temperature. For this reason, the composition tends to change during high-temperature firing, and when it is made into a sintered body, grain size, impurities, lattice defects, etc. are likely to occur, it is non-uniform, warps, bends easily, it is difficult to become dense, and the Q value is low. It had the problem of becoming smaller.

In order to solve the above-mentioned problems with conventional microwave dielectric powders, the present inventors have only synthesized barium ferrite, barium titanate (BaTxOz), lead-containing oxide powders for piezoelectric ceramics and capacitors, etc. As a result of repeated efforts and efforts to improve the previously used hydrothermal synthesis method so that it can be used in the production of microwave dielectric powder, a new technology has been developed that has a low impurity content, a small average particle size, and a narrow particle size distribution.
The firing temperature is low, the composition is less likely to change during firing, and when it is made into a sintered body, grain boundaries, impurities, lattice defects, etc. are less likely to occur, it is homogeneous, and it is easy to warp and bend ((, dense () , a method for producing powder with a large Q value was discovered, and the present invention was achieved.

(Means for solving problems) That is, the gist of the present invention is as follows.

An easily sinterable microwave dielectric powder synthesized by a hydrothermal synthesis method.

The present invention will be explained in more detail below.

The microwave dielectric powder referred to in the present invention is a ceramic raw material powder with a high Q value used in a dielectric resonator for a microwave circuit.

If the applicable powder composition of the present invention is specifically shown below, for example, MgTi0a, (CaLa)TiO2-MgTi
Os, MgTi20s-TiOz, MgO-Nd2
O2, ct, a2os)-'rio2, (CaSrBa
) (ZrTi)Os, Ba(Mg+7sTa2/5)
Os, Ba(Zn+zsNbtzs)Ox-Ba(Zn
+zsTa2z*)Os, Ba(Zn+zsNb2zs
)Ox-3r(Zn+zsNb2zz)Os,Ba(N
iTa)Oz-Ba(ZrZnTa)Os, Ba(Z
nTa)Os-BaZrOs, (SrCa) (LiN
bTi)Os, (ZrSn)Tilt, BaTt40s
, BazTl*02o , BaO・4T10t・0.1
I can give you things like WOs.

However, the present invention is not limited to the above composition.

In producing the easily sinterable microwave dielectric powder of the present invention, a hydrothermal synthesis method is used. Hydrothermal synthesis is well known as a single crystal synthesis method in which high-temperature, high-pressure water or an aqueous solution is involved in the reaction. This method is also suitable for the synthesis of powders with high densities.

Here, a case will be described in which BaTt40s is synthesized. As raw materials for hydrothermal synthesis, hydroxides of Ba and Ti are preferred, and commercially available hydroxide crystals may be used, or hydroxide precipitates may be synthesized by neutralizing an acidic solution or the like. When neutralizing an acidic solution, it is preferable to filter the precipitate once and wash it thoroughly so that impurity ions such as chlorine ions are reduced to loppm or less.

This is because, if such ions remain, the sinterability of the produced ceramic powder may be significantly inhibited.

During washing, hydroxides of basic elements such as Ba are dissolved in water, so hydroxide raw materials of elements that are easily soluble in water are not precipitated by neutralization, but are highly pure. It is preferred to use hydroxide crystals. This is because it is easy to match the stoichiometry of the powder to be manufactured.

Next, the hydroxide crystals or hydroxide precipitate are dispersed in pure water. Basic elements such as Ba have high solubility in water, so
It is necessary to appropriately select the ratio between the amount of hydroxide and the amount of water. This is because if the amount of water is too large, basic elements such as Ba remain dissolved in the aqueous medium even after the hydrothermal reaction, making it impossible to synthesize a powder having the desired composition. In the case of BaTt40s, the reaction may be carried out at a mass ratio of approximately 1/2o or more (Ba(OH)z .8H20 crystal/H20).

Water in which Ba and Ti hydroxides are dispersed is charged into an autoclave, and a hydrothermal reaction is allowed to proceed. The reaction temperature and reaction pressure conditions not only control the reaction rate and powder particle size, but also change the crystal system of the powder to be synthesized, so the temperature and pressure conditions must be selected to match the crystal system to be synthesized. Must be. B
In the case of aTi40*, 150°C to 300°C, 10
If the reaction is carried out at a rate of kg/an'-100 kg/an'', powder with a crystal grain size of about 0.3 μm can be synthesized.

Since the pressure of the system at the reaction temperature is determined by the filling ratio of water to the volume of the autoclave, an appropriate value for the filling ratio of water must be selected according to the temperature and pressure to be reacted. BaT i , 0. 200″C and 30
When reacting at a rate of approximately 5 kg/am, the filling rate should be approximately 5.
0% is a good choice.

In the case of the easily sinterable microwave dielectric powder of the present invention, the reaction is carried out at a high temperature of 100°C or higher. This is because at temperatures below 100°C, the reaction rate is too low and is not suitable for practical use. When the temperature is increased, the reaction rate increases and the particle size of the powder produced increases. Above 374°C, which is the critical point of water, the reaction rate and particle size of the powder become particularly large. In order to give the powder low-temperature sinterability, it is necessary to give the powder an average particle size of about 0.3 μm, so it is necessary to keep the reaction temperature below the critical point.

The synthesized powder is removed by filtration or centrifugation and dried. If necessary, granulation may be performed by a spray drying method.

The autoclave may be of a batch type or a continuous type. In general, a batch type is suitable when producing high-quality products in small quantities, and a continuous type is suitable when producing a small number of products in large quantities.

(Function) In the present invention, a hydrothermal synthesis method is used as the manufacturing method for microwave dielectric powder, so the average particle size is as small as 1 μm or less, the particle size distribution is narrow, the low-temperature sinterability is excellent, and the amount contained in the raw material is small. It is a high-purity powder that does not contain impurities or impurities that are easily mixed into the powder during the calcination and crushing process in the solid phase method, and the firing temperature can be selected low, and the Q when made into a sintered body is low. You can obtain high value microwave dielectric powder.

(Example) The present invention will be further described in detail below with reference to Examples.

[Example 1] A 2N NaOH aqueous solution was added dropwise to 250 g of a 16% titanium chloride aqueous solution with stirring until the pH reached 10, thereby obtaining a slurry of titanium hydroxide precipitate. This slurry was centrifuged and the supernatant was removed to obtain a precipitate.

Next, ion-exchanged water was added to this precipitate, and the mixture was dispersed while stirring in an ultrasonic washing machine to form a slurry again. Repeat the steps of centrifugation and redispersion of the precipitate three times in this way,
Chlorine ions adhering to the precipitate were washed away. After the fourth centrifugation, the supernatant liquid was collected and silver nitrate was added dropwise, but no white precipitate was formed, indicating that most of the chlorine ions attached to the precipitate had been removed.

Furthermore, B with a purity of 98% is added to the slurry of this titanium hydroxide precipitate.
Mix 67,876 g of a(OH)t・8H20, add ion-exchanged water to this precipitate mixture, and bring the total amount to 1500 g.
The slurry obtained by stirring and dispersing in an ultrasonic cleaning chamber was charged into a Hastello C 41 autogel.
240° in 120 minutes while stirring at 00 to 150 rpm
The temperature was raised to C and hydrothermal treatment was performed for 0.5 hour.

After the reaction was completed, the slurry was filtered and washed with water. After drying in a vacuum dryer, the X-ray diffraction pattern was measured using a Rigaku Denki RAD-It Type B diffraction device, and the chemical composition was further analyzed by fluorescence X-ray measurement. As expected, it was Bat. It was revealed that a crystal having a composition of Ti4°O9° was obtained. In addition, the particle size distribution of the powder measured by a centrifugal sedimentation particle size distribution analyzer was 0.1
It was distributed between μm and 0.5 μm, and its histogram had a single peak. The average particle size was 0.3 μm as shown in Table 1. Further, the impurity content was measured by optical emission spectrometry, and the results are shown in Table 2, and all the elements were 10 ppm or less, indicating high purity.

A 5 wt % aqueous solution of PVA was added to this powder in an amount of 5 wt % based on the mass of the powder and granulated. The granulated powder was placed in a cylindrical mold with a diameter of 8 mm, and molded by pressure compression at lt/cm' using a hydraulic press. The molded body was placed in a magnesia sheath with a lid and fired at 1200°C for 5 hours in an oxidizing atmosphere. As shown in Table 1, the density of the sintered body was 99% of the theoretical density. Further, when ε and Q value were measured, ε was 4o and Q was 12,300 at room temperature. For the measurement, a network analyzer manufactured by Y) (P Company was used, and a jig manufactured by Uchiin Seisakusho Co., Ltd. was used as the sample holder. The measurement frequency was 1 GHz.

[Comparative example I]

BaCO5 and Tie2 raw materials were weighed so that the Ba:Ti ratio was 1:4. Next, wet mixing was performed using a ball mill in order to uniformly perform the solid phase reaction. The mixed raw materials were calcined at 1000''C for 10 hours, and then wet-pulverized using a ball mill.

When the X-ray diffraction pattern was measured, BaTiJ
A diffraction pattern marked * was obtained. When the chemical composition of this powder was analyzed by fluorescence X-ray measurement, it was found to be Bat and oTla as expected. 0. . It has become clear that the composition of In addition, when the particle size distribution of the powder was measured using a centrifugal sedimentation particle size distribution analyzer, it was found that the particle size distribution ranged from 0.5 μm to 7.0 μm.
It was distributed within 5 μm, and its histogram had multiple peaks. The average particle size is 2.0 as shown in Table 1.
It was 3 μm. However, the amount of impurities determined by emission analysis is as shown in Table 2, including Na, Ca, AI SF
The content of eSMn was higher than that in Example 1.

A 5 wt % aqueous solution of PVA was added to this powder in an amount of 5 wt % based on the mass of the powder and granulated. The granulated powder was placed in a cylindrical mold and compressed using a hydraulic press at It/an' to form the mold. Even when the compact was placed in a magnesia sheath with a lid and fired for 5 hours at 1200"C in an oxidizing atmosphere, sufficient sintered compact density could not be obtained. Sinterability was improved by increasing the firing temperature one after another. As a result of confirmation, as shown in Table 1, 1380°
When fired for 5 hours at C, the density of the sintered body was 99% of the theoretical density.
%, and a density equivalent to that of Example 1 was obtained. but,
The dielectric constant at room temperature was 38, and the Q value was 8,800, which was particularly inferior to Example 1 in terms of Q value.

[Example 2] 250g of 25wt% tantalum chloride aqueous solution and 2N Na
An OH aqueous solution was added dropwise while stirring until the pH reached 10 to obtain a slurry of tantalum hydroxide precipitate. The slurry was centrifuged and the supernatant was removed to obtain a precipitate. Ion-exchanged water was added to the precipitate and dispersed while stirring in an ultrasonic washing machine to form a slurry again.

The steps of centrifugation and redispersion of the precipitate were repeated three times in this way to wash away the chlorine ions attached to the precipitate. After the fourth centrifugation, the supernatant liquid was collected and silver nitrate was added dropwise, but no white precipitate was formed, indicating that most of the chlorine ions attached to the precipitate had been removed.

Furthermore, 3.5 g of MgO fine powder with a purity of 99.8% and a particle size of approximately 0.3 μm and Ba (OHz) were added to the tantalum hydroxide precipitate.
-315.3 g of -8H20 was mixed, ion-exchanged water was added to this precipitate mixture to make a total volume of 15001 nl, and the slurry obtained by stirring and dispersing in an ultrasonic cleaning chamber was charged into a Hastelloy C 4i7 autoclave. 100
While stirring at ~150 rpm, the temperature was raised to 240°C in 120 minutes, and hydrothermal treatment was performed for 0.5 hour.

After the reaction was completed, the slurry was filtered and washed with water. After drying in a vacuum dryer, the X-ray diffraction pattern was measured, and no peaks appeared except for the Ba(MgtzsTazzs)Ox diffraction pattern, indicating that it was a single phase. When the chemical composition of this powder was analyzed by fluorescence X-ray measurement, as expected, Ba:Mg:Ta=3
．． It was revealed that the composition was 0:1.0:2.0. The particle size distribution of the powder measured by a centrifugal sedimentation particle size distribution analyzer was distributed between 0.1 μm and 0.5 μm, and its histogram had a single peak. Further, the average particle size was 0.3 μm as shown in Table 1.

The impurity elements found by emission spectroscopy are shown in Table 2, and the content of each element was 10 ppm or less.

A 5 wt % aqueous solution of PVA was added to this powder in an amount of 5 wt % based on the mass of the powder and granulated. The granulated powder was placed in a cylindrical mold and compressed using a hydraulic press at It/an' to form the mold. The molded body was placed in a magnesia sheath with a lid and fired at 1200°C for 5 hours in an oxidizing atmosphere. The results are shown in Table 1, and the density of the sintered body was 99% of the theoretical density. Further, when the dielectric constant and Q value were measured, the dielectric constant at room temperature was 20 and the Q value was 19.200.

[Comparative Example 2] BaC0z, MgO and Taxes raw materials Ba: Mg
: The samples were weighed and collected so that the Ta ratio was 3:1:2. Next, wet mixing using a ball mill or the like was performed in order to uniformly perform the solid phase reaction. The mixed raw materials were calcined at 1000°C for 10 hours and then wet-pulverized using a ball mill.

When the X-ray diffraction pattern was measured, it was found that Ba(Mg
A diffraction pattern of +zsTa27s)Ox was obtained. The chemical composition of this powder was analyzed by fluorescence X-ray measurement, and as expected, Ba:Mg:Ta=3. O:1.
It was revealed that the composition had a composition of 0:2.0. However, the amount of impurities determined by emission analysis is as shown in Table 2, including Na, Ca, Al, Fe, Mn, and Nb.
The content was higher than that in Example 2.Furthermore,
When the particle size distribution of the powder was measured using a centrifugal sedimentation particle size distribution analyzer, it was found to be between 0.5 μm and 7.5 μm,
The histogram had multiple peaks. Moreover, the average particle size was 2.3 μm.

A 5 wt % aqueous solution of PVA was added to this powder in an amount of 5 wt % based on the mass of the powder and granulated. The granulated powder was placed in a cylindrical mold and compressed using a hydraulic press at It/cm''.As shown in Table 1, the formed body was placed in a magnesia sheath with a lid and oxidized. 5 at 1200°C in a sexual atmosphere
Even after firing for a long time, sufficient density of the sintered body could not be obtained. Furthermore, by increasing the firing temperature and checking the sinterability, 1
When fired at 500°C for 5 hours, the density of the sintered body was 99% of the theoretical density, and the same density as in Example 2 was obtained. However, the dielectric constant at room temperature was 20, and the Q value was 14,900, which was considerably inferior to Example 2, especially in terms of Q value.

(Note) Unit: 2 ppm Table 2 [Effects of the Invention] The easily sinterable microwave dielectric powder of the present invention has a small average particle size of 1 μm or less, a narrow particle size distribution, and has excellent low-temperature sinterability. It is a high-purity powder that does not contain any impurities, and when made into a sintered body, grain boundaries, impurities, lattice defects, etc. are difficult to enter, it is homogeneous, has little warping, bending, is dense, and has a high Q value. Wave dielectric powder can be obtained, and its industrial significance is extremely large.

Claims (1)

[Claims] An easily sinterable microwave dielectric powder synthesized by a hydrothermal synthesis method.