JP2000154059A - Production of piezoelectric ceramics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the pore diameter, and the number of pores and to increase denseness and mechanical strength by pulverizing the source material power and the calcined material each in a wet state and controlling each pulverizing time to a specified or longer period. SOLUTION: The pulverization time is controlled to >=20 hours for the source material and to >=60 hours for the calcined material. Preferably, fine lead dioxide powder having <=1.0 μm average particle size and fine zirconia power having <=1.0 μm average particle size are used as the source material powder. As for the source material of the titanium component, titania powder generally used can be used. By using the source powder above described and pulverizing the powder in a wet state, a mixture powder containing fine particles having <=1.5 μm particle size by >=85 wt.% can be obtd., and a calcined powder containing fine particles having <=1.5 μm particle size by >=90 wt.% can be obtd. The calcining temp. can be decreased to 760 to 800 deg.C. The average diameter of the pores in the obtd. sintered body is <4 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing a material having a small average pore diameter and a small number of pores even at a relatively low calcining temperature.
The present invention relates to a method for producing a piezoelectric ceramic made of a dense sintered body. In addition, the present invention relates to a method for producing a piezoelectric ceramic which is dense, has high mechanical strength, and has excellent piezoelectric properties at a relatively low firing temperature. The piezoelectric ceramic obtained by the manufacturing method of the present invention is suitable for low-temperature firing that can be integrally sintered together with internal electrodes in a multilayer piezoelectric transformer, a multilayer filter, a multilayer capacitor, a bimorph, and the like.

[0002]

2. Description of the Related Art Piezoelectric ceramics are stable with little change in temperature and time-dependent change of the resonance frequency of mechanical vibration, and have a low mechanical quality factor by changing the composition by the content or substitution of component elements. It has excellent properties such that it can be arbitrarily controlled. Therefore, piezoelectric vibrators (resonators) and the like using the same are widely used in devices or systems such as frequency filters, ultrasonic devices, and acoustic devices. Lead zirconate titanate, which is well known under the abbreviation of PZT, is a typical composition. In particular, in applications such as multilayer piezoelectric transformers, the composition is as low as possible to enable simultaneous firing with internal electrodes. There is a need for piezoelectric ceramics that can be fired at a temperature and have sufficient denseness and mechanical strength even at a low temperature.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and the raw material powder and the calcined product are pulverized in a wet process for a long period of time, so that the pore diameter is small, the pores are small, the density is high, and It is an object of the present invention to provide a method for producing a piezoelectric ceramic made of a sintered body having high mechanical strength. In addition, the present invention uses a specific raw material powder having a small particle size, and pulverizes the raw material powder and the calcined product in a wet manner for a long period of time, at a relatively low firing temperature at which simultaneous firing with an internal electrode is possible. It is an object of the present invention to provide a method for producing a piezoelectric ceramic which is dense and has excellent piezoelectric characteristics.

[0004]

According to a first aspect of the present invention, there is provided a method of manufacturing a piezoelectric ceramic, comprising the steps of mixing and pulverizing raw material powders to form a mixed powder, calcining the mixed powder to form a calcined product, and After preparing the slurry by pulverizing the calcined product, forming and firing a sintered body, in a method for producing a lead zirconate titanate-based piezoelectric ceramics,
The pulverization of the raw material powder and the pulverization of the calcined product are both wet pulverization, and the pulverization time of the raw material powder is 20 hours or more, and the pulverization time of the calcined material is 60 hours or more.

In a fifth aspect of the present invention, there is provided a method for manufacturing a piezoelectric ceramic, comprising: mixing and pulverizing raw material powders to form a mixed powder; calcining the mixed powder to form a calcined product; A method for producing a lead zirconate titanate-based piezoelectric ceramic, comprising the steps of: preparing a slurry by pulverizing, shaping and firing to form a sintered body, wherein the raw material powder has an average particle size of 1.0 μm Using the following lead dioxide powder and zirconia powder having an average particle size of 1.0 μm or less,
The pulverization of the raw material powder and the pulverization of the calcined product are both wet pulverization, and the pulverization time of the raw material powder is 20 hours or more, and the pulverization time of the calcined material is 60 hours or more.

The piezoelectric ceramic obtained by the manufacturing method of the present invention is a lead zirconate titanate-based piezoelectric ceramic well known as PZT. In this PZT, there is a point at which the electromechanical coupling coefficient, the dielectric constant, and the piezoelectric constant are maximized substantially at the center of both compositions of lead titanate and lead zirconate. Therefore, also in the present invention, it is preferable to use one having a molar ratio of titanium to zirconium in the range of 0.92 to 1.08. When the molar ratio is less than 0.92 or exceeds 1.08, the piezoelectric properties tend to decrease.

In the first and fifth inventions, the pulverization of the raw material powder and the pulverization of the calcined product are both wet pulverization, the pulverization time of the raw material powder is 20 hours or more, and the pulverization time of the calcined material is 60 hours or more. And The pulverization time of this raw material powder is preferably 24 hours or more, particularly 30 hours or more, and more preferably 40 hours or more.
It is preferably at least 70 hours, more preferably at least 70 hours.
Further, as a raw material powder, a fine lead dioxide powder having an average particle size of 1.2 μm or less, particularly 1.0 μm or less as in the fifth invention, and an average particle size of 1.0 μm or less, particularly 0.8 μm
It is preferable to use the following fine zirconia powder. As a raw material of the titanium component, titania powder or the like generally used in the production of lead zirconate titanate-based piezoelectric ceramics can be used without any particular limitation.

In the first invention, both the raw material powder and the calcined material are wet-ground for a long time, so that 85% by weight or more consists of fine particles having a particle size of 1.5 μm or less as in the second invention. It can be a mixed powder, and can be a calcined powder comprising 90% by weight or more of fine particles having a particle size of 1.5 μm or less. In the fifth invention, 90% by weight or more has a particle diameter of 1.90% by using a specific fine raw material powder in addition to a long-time wet pulverization, as in the sixth invention.
It can be a mixed powder composed of fine particles of 5 μm or less, and a calcined powder composed of fine particles of 95% by weight or more having a particle size of 1.5 μm or less.

According to the first aspect of the present invention, the calcination temperature is set to the same value as in the third aspect of the invention by using the mixed powder composed of fine particles as described above. 760 which is 20-25 ° C lower than the short case
８００800 ° C. Further, since the calcined powder is also a powder composed of fine particles, particularly in the fifth invention, the calcining temperature can be further reduced to 710 to 750 ° C and the baking temperature is 880, as in the seventh invention. ~ 930 ° C. Further, according to the production method of the present invention, the piezoelectric ceramic formed of a dense sintered body having a small particle size of 2 μm or less, particularly 1.5 μm or less despite the low calcination temperature or calcination temperature. Is obtained. Further, the average diameter of the pores contained in the sintered body is also the fourth diameter.
And as in the eighth invention, it is as small as 4 μm or less, particularly 3 μm or less, and the number of pores is small. Therefore, the mechanical strength is greatly improved.

Further, in the manufacturing method of the fifth invention, since the firing temperature can be lowered to about 900 ° C., Ag, C
An inexpensive conductive material having low heat resistance, such as u, can be used as an internal electrode or the like and fired simultaneously. This is especially true for applications such as multilayer piezoelectric transformers, where Pt, Pd
Since there is no need to use an expensive conductive material having a high melting point, such is also advantageous in terms of cost.

Further, in the first invention, as in the prior art, if fired at, for example, about 1000 ° C., and in the fifth invention, even if fired at a low temperature of about 900 ° C., the dielectric constant (ε
_r ) is 1000 or more, the coupling coefficient (Kr) is 50% or more,
A piezoelectric ceramic having a required piezoelectric characteristic having a mechanical quality factor (Qm) of 800 or more and a Curie point of 300 ° C. or more can be obtained. This piezoelectric characteristic can be further improved by using a zirconia-made cobblestone instead of an alumina-made cobblestone as in the ninth invention as used in the pulverization of the raw material powder and the calcined product.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to examples. (1) Investigation in case of wet grinding for a long time corresponding to the first invention Example 1 A predetermined amount of a lead oxide powder, a zirconia powder and a titania powder having an average particle diameter shown in Table 1 was weighed, and 15 m was weighed.
After mixing in a vibration mill using zirconia cobblestone of mφ, an appropriate amount of ion-exchanged water was added thereto, and the mixture was pulverized for 24 hours by a wet method. Then, it dried using the vibration fluidization dryer. Next, after calcining at 780 ° C. for 2 hours in an air atmosphere, an appropriate amount of an organic binder and water are added to the calcined product, and
The mixture was pulverized with a zirconia ball having a diameter of mm for 72 hours in a wet system to prepare a slurry. After that, casting molding with a doctor blade, drying, and 0.3-0.5
An unsintered sheet having a thickness of mm was obtained. Next, this sheet was punched out to obtain a disk-shaped formed body of 25 mmφ.

On the other hand, two pellets composed of a large amount of Pb and Zr (compound for compensating for composition: 25 mmφ, 1 mm in thickness) are prepared, and the compact is sandwiched between these pellets. It was fired at 975 ° C. for 2 hours in an atmosphere to obtain a sintered body. The density of the sintered body was measured by the Archimedes method. The average particle diameter, average pore diameter, and number of pores were measured by a scanning electron microscope photograph.

Examples 2 to 4 and Comparative Examples 1 to 8 The method, time and calcining temperature of the raw material powder, and the method, time and calcining temperature of the calcined material are shown in Tables 1 and 3, In the same manner as in Example 1, a sintered body was obtained. The density, average particle size, average pore diameter, and number of pores of these sintered bodies were measured in the same manner as in Example 1. The results are also shown in Tables 1 to 3. In the comparative examples of Tables 2 and 3, alumina cobblestone was used instead of zirconia cobblestone.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

According to the results shown in Table 1, in each of the examples, including Example 1 in which the pulverization time of the raw material powder was close to the lower limit, the obtained sintered body was sufficiently densified and had a high density.
The average particle size is also small. In addition, it can be seen that a piezoelectric ceramic made of a sintered body of excellent quality has a small average pore diameter and a small number of pores. Further, in Examples 1 and 3 where the calcination was performed at a temperature within the range of the third invention, the density was higher and the density was higher than in Examples 2 and 4 where the calcination temperature was higher. Is supported.

On the other hand, according to the results shown in Tables 2 and 3, although the pulverization of the raw material powder and the calcined product is of a dry type and the pulverization time is short in Comparative Examples 1 and 2, only the pulverization of the calcined product is of a wet type. Similarly, in Comparative Example 3 in which the pulverization time is short, although the densification is performed when the firing temperature is high, the average pore diameter is large and the number of pores is large. Comparative Example 4 in which the pulverization of the raw material powder and the calcined product was of a wet type, but the pulverization time was short.
And 6, and Comparative Examples 5 and 7 to 8 in which the pulverization time of the calcined product is long but the pulverization time of the raw material powder is short, the densification is increased when the firing temperature is high, but the average pore diameter is large and the number of pores is large. You can see that. Comparative Example 8 having a low firing temperature
Then, the densification is not enough and the density is low.

(2) Examination in the case of using a fine raw material powder corresponding to the fifth invention and pulverizing it for a long time by a wet method Example 5 Lead dioxide powder and zirconia powder having the average particle diameters shown in Table 4 In addition, a predetermined amount of titania powder is weighed, and 15
After mixing in a vibrating mill using zirconia balls of mmφ, an appropriate amount of ion-exchanged water was added thereto, and the mixture was wet-processed for 48 hours.
Crushed for hours. Then, it dried using the vibration fluidization dryer. Next, after calcining at 730 ° C. for 2 hours in an air atmosphere, an appropriate amount of an organic binder and water are added to the calcined product, and
pulverized by zirconia cobblestone of mmφ in wet condition for 72 hours,
A slurry was prepared. After that, it was casted with a doctor blade, dried, and dried to 0.3 to 0.5 mm.
An unsintered sheet having a thickness was obtained. Next, this sheet was punched out to obtain a disk-shaped formed body of 25 mmφ.

On the other hand, pellets composed of a large amount of Pb and Zr (composition for compensating for composition: diameter 25 mm, thickness 1 mm)
Sheets, sandwiching the molded body between these pellets,
The sintered body was obtained by firing in an electric furnace at 900 ° C. for 2 hours in the air atmosphere. The density, average particle diameter, average pore diameter and number of pores of this sintered body were measured in the same manner as in Example 1. Also,
The front and back surfaces of this sintered body are precisely polished to a thickness (0.2-0.
35) ± 0.005 mm and a baking temperature of 720
The silver electrode was baked at 0 ° C. Then, the sample was polarized by applying a DC voltage of 35 kv / cm for 20 minutes in an insulating oil at 80 ° C. to obtain a specimen. R. E. FIG. Ε _r and Kr were measured according to the standard circuit method. In addition, Qm was measured using an impedance analyzer based on the resonance-antiresonance method.

Examples 6 to 9 and Comparative Examples 9 to 14 Kind and average particle size of lead oxide, average particle size of ZrO ₂ , grinding time and calcining temperature of raw material powder, and grinding time and calcining temperature of calcined product Was as shown in Tables 4 to 6, and a sintered body was obtained in the same manner as in Example 5. The density, average particle size, average pore diameter, and number of pores of these sintered bodies were measured in the same manner as in Example 1. Further, for Examples 6 to 9,
ε _r , Kr and Qm were measured in the same manner as in Example 5.
The results are shown in Tables 4 to 6. In the comparative examples of Tables 5 and 6, alumina cobblestone was used instead of zirconia cobblestone.

[0023]

[Table 4]

[0024]

[Table 5]

[0025]

[Table 6]

According to the results in Table 4, in Examples 5 to 9,
Although the firing temperature is as low as 900 ° C., the obtained sintered body is sufficiently densified and has a density of 7.934 g / cm ^3.
Above is high and the average particle size is small. In addition, piezoelectric ceramics having a small number of pores, a small average pore diameter, and a good quality sintered body have been obtained. Further, the dielectric constant (ε _r ) is 1
It can be seen that a piezoelectric ceramic having excellent piezoelectric properties of 000 or more, a coupling coefficient (Kr) of 50% or more, and a mechanical quality factor (Qm) of 800 or more is obtained.

On the other hand, according to the results shown in Tables 5 and 6, although both the pulverization of the raw material powder and the calcined product are of the wet type, the pulverization time of Comparative Example 9 is short, and the pulverization time of the calcined material is long. In Comparative Example 10 where the pulverization time of the raw material powder is short and in Comparative Example 11 where the pulverization time of the raw material powder is long but the pulverization time of the calcined product is short, the densification is not sufficiently performed at the firing temperature of 925 ° C., and the average pore diameter is large. It turns out that there are many numbers. In addition, although the pulverization of the raw material powder and the calcined product was both wet and the pulverization time was sufficiently long, the types or average particle diameters of the raw material powders were out of the range of Comparative Examples 12 to 12.
14 shows that at a firing temperature of 900 to 925 ° C, densification was not sufficient, the average pore diameter was large, and the number of pores was large.

(3) Comparison of the pore diameter and the number of pores by electron micrographs between the case within the range of the present invention and the case outside the range, and the correlation between the firing temperature and the density of the sintered body. Is an electron micrograph at a magnification of 1300, which was obtained by polishing the surface of the piezoelectric ceramic of Example 5 manufactured by the method of the second invention, observing the polished surface with a scanning electron microscope, and photographing it at a magnification of 1300. It can be seen that even a large sintered body has a size of about 2 μm and a good quality sintered body having a relatively small number of pores. On the other hand, FIG. 2 is an electron micrograph taken similarly for the piezoelectric ceramic of Comparative Example 3, and it is clear that the pore diameter is larger than that of FIG.

FIG. 3 shows the firing temperature when the firing temperature was changed between 87 and 950 ° C. in Example 5 and the firing temperature was changed between 900 and 1025 ° C. in Comparative Example 3. FIG. 4 is a graph showing the correlation between the density and the density of the sintered body. As is clear from FIG. 3, in Example 5, a sufficiently densified sintered body of 7.900 g / cm ³ or more can be obtained not only at the high temperature side but also at a temperature of 900 ° C. or less. . On the other hand, Comparative Example 3
It can be seen that in order to obtain a density of about 7.900 g / cm ³ , firing at a temperature of at least 950 ° C. is necessary. Moreover, when fired at 950 ° C., the resulting sintered body has many pores having a large diameter. In practice, the sintered body is not sufficiently densified unless the firing temperature is further increased to about 1000 ° C.

In the present invention, the above specific examples
Not limited to those described in the examples,
Various modifications can be made within the scope of the invention.
You. For example, a part of Pb is formed by Sr, Ba, Cr, etc.
And a part of Ti and / or Zr can be substituted with Sn
Etc. can be substituted. 1% by weight or less
MnO_TwoExcellent temperature characteristics by adding
Can be obtained. Furthermore,
La_TwoO_ThreeAnd rare earth element oxides such as WO_Three, Nb
_TwoO_Five, Ta_TwoO_Five, Bi_TwoO_Three0.5-1.5% by weight
By adding _r, Kr and Qm etc.
It can also be adjusted appropriately. Also, MnO_TwoAnd WO_ThreeAnd
When used together, a piezoelectric cell with excellent stability over time and high Qm
This piezoelectric ceramic can be lamix
Is a low temperature of 1000 ° C or less like a multilayer piezoelectric transformer.
Especially in the piezoelectric material which is preferably fired at
Useful.

[0031]

According to the method for manufacturing a piezoelectric ceramic of the first invention, the pulverization of the mixed raw material powder and the pulverization of the calcined material are both wet pulverization and long-term pulverization for a specific time or more. In addition, the calcining temperature can be lowered, the pore diameter is small, the number of pores is small, and a dense piezoelectric ceramic having high mechanical strength can be obtained. Further, according to the method of manufacturing a piezoelectric ceramic of the fifth invention, in the manufacturing method of the first invention, the firing temperature is reduced by using a lead dioxide powder and a zirconia powder having a specific average particle size as the raw material powder. Therefore, it can be co-fired with a conductive material for forming an internal electrode, and this manufacturing method is particularly useful in applications such as a multilayer piezoelectric transformer.

[Brief description of the drawings]

FIG. 1 shows the surface of a piezoelectric ceramic of Example 5 polished,
It is the electron microscope photograph at a magnification of 1300 times, which was obtained by observing the polished surface with a scanning electron microscope.

FIG. 2 shows the surface of the piezoelectric ceramic of Comparative Example 3 polished,
It is the electron microscope photograph at a magnification of 1300 times, which was obtained by observing the polished surface with a scanning electron microscope.

FIG. 3 is a graph showing the correlation between the firing temperature and the density of a sintered body when the firing temperature is changed in Example 5 and Comparative Example 3.

Claims (9)

[Claims] 1. A step of mixing and pulverizing raw material powders to form a mixed powder, a step of calcining the mixed powder to form a calcined product, and a step of preparing a slurry by pulverizing the calcined product and then molding the mixture. ,
A method for producing a lead zirconate titanate-based piezoelectric ceramic, comprising a step of firing to obtain a sintered body, wherein both the pulverization of the raw material powder and the pulverization of the calcined material are wet pulverization, and the pulverization of the raw material powder A method for producing a piezoelectric ceramic, wherein the time is 20 hours or more, and the pulverization time of the calcined product is 60 hours or more. 2. 85% by weight or more of the mixed powder comprises particles having a particle size of 1.5 μm or less, and 90% by weight or more of the powder obtained by pulverizing the calcined product comprises particles having a particle size of 1.5 μm or less. The method for producing a piezoelectric ceramic according to claim 1. 3. The method for producing a piezoelectric ceramic according to claim 1, wherein the calcination temperature is 760 to 800 ° C. 4. The method for producing a piezoelectric ceramic according to claim 1, wherein the average pore diameter of the pores contained in the sintered body is 4 μm or less. 5. A step of mixing and pulverizing raw material powders to form a mixed powder, a step of calcining the mixed powder to form a calcined product, and a step of preparing a slurry by pulverizing the calcined product and then forming the mixture. ,
In a method for producing lead zirconate titanate-based piezoelectric ceramics, comprising a step of firing to form a sintered body, as the raw material powder, a lead dioxide powder having an average particle diameter of 1.0 μm or less and an average particle diameter of 1. Using a zirconia powder of 0 μm or less, the pulverization of the raw material powder and the pulverization of the calcined material are both wet pulverization, and the pulverization time of the raw material powder is 20 μm.
And a pulverizing time of the calcined product is 60 hours or more. 6. 90% by weight or more of the mixed powder comprises particles having a particle size of 1.5 μm or less, and 95% by weight or more of the powder obtained by pulverizing the calcined product comprises particles having a particle size of 1.5 μm or less. The method for producing a piezoelectric ceramic according to claim 5. 7. The method according to claim 5, wherein the calcining temperature is 710 to 750 ° C., and the calcining temperature is 870 to 930 ° C. 8. The method according to claim 5, wherein the average pore diameter of the pores contained in the sintered body is 4 μm or less.
13. The method for producing a piezoelectric ceramic according to the above item. 9. The method for producing a piezoelectric ceramic according to claim 1, wherein the cobblestone used in grinding the raw material powder and the calcined product is made of zirconia.