JP2002173375A - Piezoelectric ceramic sintered by utilizing microwave and hot press, method of producing the same and piezoelectric actuator using the piezoelectric ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic which has a high electromechanical coupling factor and a remarkably improved piezoelectric constant, and to provide a method and a device for producing the same, by which the piezoelectric ceramic is sintered in a short time in comparison with conventional sintering. SOLUTION: The piezoelectric ceramic is obtained by charging a piezoelectric base material into a nonmetal mold disposed in a microwave sintering furnace, raising the temperature of the piezoelectric base material in at least sintering process by sintering the base material using the microwave mentioned above and at the same time, subjecting the piezoelectric base material charged in the nonmetal mold to pressure-treatment by hot press. The piezoelectric ceramic obtained by the process mentioned above is substantially free from pores and has a high electromechanical coupling factor and a high piezoelectric constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic sintered by using a microwave and a hot press. In particular, the pores in the material are extremely small,
A piezoelectric ceramic with improved high electromechanical coupling coefficient and piezoelectric constant, and a manufacturing method and a manufacturing apparatus capable of performing sintering in a shorter time than conventional sintering can be provided.
The present invention relates to a piezoelectric ceramic which has a large piezoelectric constant and can be applied to a piezoelectric actuator or the like, a method and an apparatus for manufacturing the same, and a piezoelectric actuator using the same.

[0002]

2. Description of the Related Art Conventionally, barium titanate, zircon / lead titanate (PZT), bismuth, and niobium porcelains are known as piezoelectric ceramics, and materials for vibration measurement such as bimorphs, ultrasonic vibrators, and accelerations. Has been used as. These materials have many advantages such as being easier to produce than single crystals such as quartz and Rochelle salt by sintering operation, being able to be sintered into an arbitrary shape, and being appropriately polarized. On the other hand, unlike crystals, there are drawbacks in that properties are easily influenced by sintering conditions, and that the piezoelectric properties are accompanied by polarization, so that products tend to vary.

[0003] Similarly, for piezoelectric ceramics made of various materials, the raw material powder is placed in a mold and uniaxially formed. In PZT, the maximum temperature is set to 1200 to 13 in an electric furnace.
Since the sintering is carried out at a temperature of 00 ° C. for 1 to 5 hours, the sintering time as a whole needs to be 24 hours or more. Thus, in sintering in an electric furnace, sintering takes a long time due to resistance heating, and in order to obtain higher piezoelectric characteristics, there is no other way but to raise the sintering temperature and lead to evaporation of lead and grain growth. Was.

[0004] Also, hot pressing using an electric furnace has not been practical. The reason is that it is difficult to control the grain growth and the temperature of the sample sample by heating for a long time, and the peripheral jigs such as a mold and a rod are broken. Further, such a hot press may reduce the pores and improve the density, but cannot improve the piezoelectric characteristics. Furthermore, there is a problem that it is difficult to obtain high quality piezoelectric ceramics by heating the mold for a long time. Further, although the fine structure was improved, the improvement of the piezoelectric characteristics could not be expected.

[0005] Similar sintering problems have been encountered with other piezoelectric materials. As a result, sintered piezoelectric ceramics have low material density, many pores in the material, low electromechanical coupling coefficient and low piezoelectric constant, and these characteristics are sufficiently improved. The challenge was to improve productivity such as sintering in a shorter time. In addition, the present inventors have intensively studied the sintering of piezoelectric ceramics using microwaves, but still have a problem in sintering the piezoelectric material. In microwave sintering, absorption is determined by the magnitude of the dielectric constant and frequency. The dielectric constant of PZT and the like has the advantage that absorption is large compared to alumina and zirconia, but on the contrary, it is difficult to control the sintering temperature. It was a point. Further, there still remain technical problems such as cracking of a sample such as PZT and difficulty in obtaining high piezoelectric characteristics. The main reason is that it is extremely difficult to solve the above problem only by microwave sintering. In particular, pores in the material remain, the electromechanical coupling coefficient, and the piezoelectric constant are not sufficient. These characteristics are sufficiently improved, and productivity is improved by sintering in a shorter time than conventional sintering methods. Was an issue.

[0006]

SUMMARY OF THE INVENTION According to the present invention, there is provided a piezoelectric ceramic having a high electromechanical coupling coefficient, a significantly improved piezoelectric constant, and a sintering process in a shorter time than conventional sintering. A device and the like are to be solved. As a result, the present invention relates to a piezoelectric ceramic which can be applied to a piezoelectric actuator or the like having these characteristics, a method of manufacturing the same, and a piezoelectric actuator using the same.

[0007]

According to the present invention, a piezoelectric material is placed in a non-metallic mold in a microwave sintering furnace, and the material is heated by sintering with the microwave at least in a sintering process. In the sintering process, the piezoelectric ceramic obtained by subjecting the material in the mold to a pressure treatment by a hot press has a high electromechanical coupling coefficient and a high piezoelectric constant with substantially no pores. Provided by piezoelectric ceramics sintered using microwaves and hot pressing. Similarly, the present invention provides a method of manufacturing a piezoelectric ceramic by sintering a piezoelectric material,
Put the piezoelectric material into the non-metal mold in the microwave sintering furnace,
At least in the sintering process, the material is heated by microwaves, and in the sintering process, the material in the mold is subjected to a pressure treatment by a hot press. Provided by a method for producing a piezoelectric ceramic to be sintered by heating.

[0008] In the method of manufacturing a piezoelectric ceramic, a hot press may be performed in a microwave sintering process.
The method is characterized in that the pressure is increased within a range of from about 100 MPa to about 100 MPa, more preferably within a range of from about 20 MPa to about 40 MPa. Further, when a step of performing the pressing with a mold made of a non-metallic material having a dielectric constant lower than that of the sintered sample sample is added, more specifically, a step of performing the pressing in an alumina rod and a mold is added. A method for producing piezoelectric ceramics sintered using microwaves and hot pressing is provided.

Further, the maximum sintering temperature range is 1000
In the range of from 1 ° C. to 1250 ° C., and further comprising a step of pressing the hot press with an alumina rod, and a step of maintaining the press of the hot press from the stage of reaching the maximum sintering temperature. Provided more effectively.

According to the present invention, there is provided an apparatus comprising a microwave sintering furnace for sintering a piezoelectric material to produce a piezoelectric ceramic. Hot pressing means for pressurizing the piezoelectric material, a microwave generator for sintering, a heating means in a non-metal mold by the microwave generator, a heating means and a maximum sintering temperature An apparatus for producing piezoelectric ceramics sintered by using microwave and hot press, comprising a control unit and a gas atmosphere supply unit into the sintering furnace.

Further, in the apparatus for producing piezoelectric ceramics, in the microwave sintering process, the pressure of a hot press is applied to a mold made of a nonmetallic material having a dielectric constant smaller than a dielectric constant of a sintered sample sample. The present invention is provided by an apparatus for manufacturing a piezoelectric ceramic that is sintered by using a hot press. Further, as the piezoelectric ceramic, the piezoelectric ceramic obtained by the above-described manufacturing method is effectively provided by a piezoelectric ceramic having a high density, a fine crystal structure substantially free from pores by SEM observation, and having excellent piezoelectric characteristics. You.

Further, in the piezoelectric ceramics obtained by the above-described manufacturing method, a piezoelectric ceramic having a high density and a fine crystal structure substantially free from pores by SEM observation and having excellent piezoelectric characteristics is provided as a driving source or a vibration pickup. It is effectively provided as a piezoelectric actuator mounted as a piezoelectric actuator.

[0013]

Embodiments of the present invention will be specifically described below. Referring to the drawings, FIGS. 1 to 8 show a manufacturing apparatus of a piezoelectric ceramic sintered by using microwave and hot press, various characteristic diagrams of the piezoelectric ceramic, and a piezoelectric actuator using the same according to the present invention. FIG. 3 is an explanatory diagram showing a basic configuration. More specifically, FIG. 1 is a sintering apparatus, and FIG. 2 is a heating temperature curve diagram of a sintering schedule at the time of manufacturing. FIG. 3 is a diagram showing the relationship between the sintering temperature and the density of the sample, FIG. 4 is a surface state diagram of the element drawn from an SEM photograph of the piezoelectric ceramics observed with a scanning electron microscope, and FIG. Fig. 6
7 is a diagram showing the relationship between the sintering temperature and the piezoelectric constant of the sample, FIG. 7 is an external view of the piezoelectric ceramic, FIG. 8 is a vibration characteristic diagram of the piezoelectric ceramic, and FIG. 9 is a block diagram for measuring the vibration characteristic of the piezoelectric ceramic. FIG. 10 is an explanatory diagram of a use state of a bimorph type actuator using piezoelectric ceramics.

FIG. 1 shows an applicator (hereinafter, referred to as a hybrid sintering method) applicable to a sintering method using microwaves and a hot press according to the present invention.
It is called microwave sintering furnace. FIG. The microwave sintering furnace 10 is entirely cylindrical, the length of the cylindrical portion 12 is 700 mm, and the diameter is about 600 mm.
Both ends are surrounded by a dome portion 11. A sample sample 2 is placed in a mold 5 and sintered at the center of the microwave sintering furnace 10. The range in which the sample to be sintered can be uniformly sintered is 300 mm in length and width, and 200 mm in height.

The microwave sintering furnace 10 used in the embodiment has a microwave output of 10 kW, an oscillation frequency of 28 GHz, and has a capability of sintering up to 2000 ° C. at the maximum. In this embodiment, the oscillation frequency is set to 28 GHz. However, even if the oscillation frequency is higher than 28 GHz, the frequency is not particularly limited to this.
It is considered that it can be used from about GHz to about 100 GHz. Gyratron can be used as the oscillation source.
Up to 2000 by drive output from microwave oscillator
If it can be sintered to about ° C, it can be used sufficiently. The hot press portion was tested in a form in which the sample sample in the mold could be pressed by the alumina rod 4.

A hot press portion is mounted on a mold in a microwave sintering furnace 10 and can be pressurized to a maximum of 49 kN. Alumina rod 4 presses sample 2 in the mold from above at the rod end face. The pressurizing means adjusts the pressurizing level by pushing down a rod 4 linked to a cylinder (not shown). The use of the alumina rod is based on the fact that there is no microwave reflection like a metal, the uniform microwave incidence on the sample can be achieved, and the heat resistance is high. Heat resistance can be obtained only up to about 600 ° C with metal,
It is not suitable for sintering sample samples. Similarly, the mold 5 was made of alumina.

[0017]

EXAMPLE 1 Hereinafter, a method of manufacturing a piezoelectric ceramics sintered using a microwave and a hot press will be described with respect to Example 1. A. Sample Sample Sintering Step The sample sample was finished to have a diameter of 17 mm and a thickness of 20 mm. In order to clarify the performance of the hybrid sintering method, a zircon / lead titanate (PZT) C82 material was selected as an actuator material manufactured by Fuji Ceramics Co., Ltd., whose properties are well known.

This powder was used for confirming the characteristics and was 17 m in diameter.
m, molded to a thickness of 20 mm, and separately, a length of 60 mm,
Two types having a width of 30 mm and a thickness of 20 mm were formed. This was first heated at 700 ° C. for 5 hours for de-buying, and then hybrid sintering was performed. Here, the de-buying is used for the purpose of adding a binder for forming the powder and facilitating the forming. If the molded body is sintered as it is, carbon dioxide gas is emitted, which causes cracks and deterioration of characteristics. Therefore, before sintering, heating is performed at a temperature of about 700 ° C. to remove the binder. In addition, a sample sample for a comparative example using conventional sintering was prepared and debubbling was performed at the same temperature.

The microwave sintering furnace used is 28 GH
z, a 10 KW output gyratron and a microwave input port 1. The incident microwave is reflected by the inner wall and has the highest dielectric constant.
Is absorbed by The sample 2 is heated by the microwave. For the measurement of the sintering temperature, a hole having a diameter of 5 mm and a depth of 1.5 mm was made in the sample bottom, and a platinum thermocouple 3 was brought into direct contact with the sample sample. The temperature was controlled by a feedback control method using a computer, and the temperature error was controlled within a range of 5 ° C. by controlling the microwave output.

FIG. 2 shows the sintering schedule of the hybrid sintering method. It is the figure which showed the heating temperature curve and the hot press state in the sintering schedule at the time of manufacture. In the microwave sintering furnace, the temperature is raised from room temperature to the maximum temperature of about 1250 ° C. in about 40 minutes shown in FIG. 2 in the atmosphere, maintained at the maximum temperature for 30 minutes, and then cooled at the same rate as the rate of temperature rise. I let it. The overall cycle was 2 hours, but the actual sintering time was about 8 hours since there was no forced cooling. The sintering temperature was from 1100 ° C. to 1250 ° C., and experiments were performed at 50 ° C. intervals. The hot pressing was performed at a pressure of 20 MPa, and was held for 30 minutes when the temperature reached the maximum. These were polarized to obtain the piezoelectric ceramic of the present invention.

In this experiment, the heating rate was 600 ° C./h to 60 ° C.
Select at 00 ° C / h and the maximum temperature is from 1,000 ° C to 1,2
The test was attempted at 50 ° C. When the sintering temperature reaches the maximum temperature, 1MP using the alumina rod set in the mold 5
Apply a pressure of a to 50 MPa. The alumina rod 4 was recirculated from the cooling water inlet 6 to prevent overheating, discharged from the cooling water outlet 9, and continued until sintering was completed. Pressing by a hot press was applied only for the holding time at the maximum temperature, and the experiment was performed without pressurizing other times. For monitoring, the state of microwave sintering and hot pressing was checked while observing through the viewing window 7.

As a result, as shown in FIG. 2, the entire cycle was 1.5 to 2 hours, and the conventional PZT was held for 1 to 5 hours in an electric furnace, and the overall sintering time was 2 hours.
It was recognized that the total sintering time required for 4 hours or more was completed in a time of 1 or less which is sufficient compared with the conventional sintering.

B Polarization The sintered sample has a disk shape of 15 mm in diameter and 1 mm in thickness.
The plate was cut into a plate having a length of 40 mm, a width of 20 mm, and a thickness of 0.5 mm, and a gold electrode was formed by sputtering. Polarization was performed by applying a voltage of 2 kV / mm in silicon oil at 170 ° C. and holding for 30 minutes.

Embodiment 2 Hereinafter, a method of manufacturing piezoelectric ceramics which is sintered using microwaves and a hot press in a microwave sintering furnace will be described with respect to embodiment 2. This was carried out by the microwave sintering furnace 10 used in Example 1. A. Sample Sample Sintering Step As the sample sample, the actuator material C82 used in Example 1 was selected. This powder was formed into a diameter of 17 mm and a thickness of 20 mm for confirming the characteristics. Further, a length of 60 mm and a width of 30 m were separately prepared for preparing an actuator to be described later.
m and a thickness of 20 mm were molded. Then 700 ° C
For 5 hours to perform de-buying, and hybrid sintering was performed.

B. Processing Conditions for Gas Atmosphere and the Like Hybrid sintering was performed in an environment in which gas was supplied from the gas inlet 8 to an oxygen concentration of 99.5% or more instead of the air atmosphere of Example 1. In addition, the pressing value of the hot press was changed at 20 MPa and 40 MPa, and polarization was performed in the same manner as in Example 1 to obtain a piezoelectric ceramic. The pressure value is not limited to 20 MPa or 40 MPa, but can be sufficiently applied at least from 10 MPa to about 100 MPa. It should be determined from the improvement of pores and other characteristics described below.

Evaluation Method Regarding Examples 1 and 2 Each characteristic of the piezoelectric ceramics was measured as follows. The piezoelectric characteristics of the sample 24 hours after the polarization treatment were measured by a resonance anti-resonance method using an impedance analyzer HP4194A manufactured by Hewlett-Packard Company. For evaluation of the fine structure, the density was determined by the Archimedes method, and the crystal particles, pores, crystal grain size, etc. were measured by SEM observation with a scanning electron microscope. The characteristics of hybrid sintering were also investigated by X-ray diffraction. To further investigate the actuator characteristics,
A sample was adhered to the surface of an aluminum beam having a length of 150 mm, a width of 25 mm, and a thickness of 1.5 mm, one end thereof was fixed, and a voltage of 100 V was applied to measure the response of the opposite free end.

Results The results show that the piezoelectric ceramics of the present invention shown in FIGS. 3 to 7 have extremely good piezoelectric characteristics. (1) Improvement of density of hybrid sintered sample a. FIG. 3 shows the relationship with the sintering temperature. The density of the sample obtained by the hybrid sintering method reached 95% of the theoretical density. The hybrid sintering was carried out at a temperature of 1100 ° C.
Despite the sintering temperature being 100 ° C. or more lower than 0 ° C., the density reached 95% of the theoretical density. Further, in the hybrid sintering method, hot press pressure is 40 MPa, and sintering temperature is 1150.
Above ° C, the theoretical density showed 98%. This is understood as the synergistic effect of the press by the hot press which is a hybrid sintering method and the sintering temperature. The density of the ceramics is naturally lower than 100% because of the very large number of pores. However, the theoretical density used here is the value obtained by calculating from the molecular weight etc. the density of the sintered body without any defects. It is. Furthermore, the fact that the theoretical density value is not provided is due to ceramics. Since it cannot be calculated accurately, it is shown as 98% of the theoretical density (including error) as a relative value.

The combined use effect of hot pressing is presumed to be as follows. Conventional sintering requires a long time to reach the maximum temperature due to resistance heating. Therefore, when hot-pressing, it is likely that sintering has progressed to some extent or not, and concerns about production and quality control will remain. Since the maximum temperature is reached very quickly in microwave sintering, the time for applying the hot press and the pressing time are clarified, and it is assumed that a stable effect is exhibited.

Conventionally, sintering is heated from the outside, and microwaves are heated from the inside. In conventional sintering, pores or pores remain inside because sintering proceeds from the outside, and microwaves are sintered from the inside, so pressurization by hot pressing is promoted at the stage where pores or pores are easily expelled to the outside. It is speculated that this is not the case. Further, the pressing time as well as the pressing value range of the hot press should be selected in relation to the microwave sintering time. In the example, the pressurization time was selected in accordance with the time interval of the maximum temperature region by the microwave. However, the temperature is raised by sintering as well as the pressing time of the hot press, which is not limited thereto, and the pressing timing in the mold in the sintering process is also applied from the stage before the maximum temperature range by the microwave. When the method of pressing is adopted, it is also possible to adopt the method of applying pressure during cooling. Needless to say, these can be adopted on the premise of improving the piezoelectric characteristics and the like in the present invention, such as when these are applied alone, in combination, or when both stages are continuously pressed.

B. The results of pore elimination are shown in FIGS. 4A, 4B, 4C and 4D made from electron micrographs. The following is an illustration of selected representative sintering temperatures of the results of the experiment. 4A shows a hybrid sintering method in which the sintering temperature is 1150.
° C, (B) is a conventional sintering method and the sintering temperature is 1150 ° C,
(C) is a hybrid sintering method in which the sintering temperature is 1250 ° C.
And (D) shows the sintering temperature of 1250 ° C. in the conventional sintering method.

The comparison is a result of a SEM observation using a scanning electron microscope. The SEM observation of the sample sample by a scanning electron microscope is a comparison result of measuring the average crystal grain size, average porosity, and the like of crystal particles, pores, and crystal particles. S
For the preparation of the sample for EM observation, the sample surface was mirror-polished and then etched with nitric acid. Microscopic magnification was observed at 3000 times. The micrograph shows a non-porous portion (crystal particle) 13 partitioned by a line in the figure, which is a non-porous portion, and pores 14 of the pore portion shown in a dispersed state with black stains. In the hybrid sintering method, in the sample sintered under the hot press pressure of 40 MPa, the crystal grain grows to about 4 to 6 μm compared to the conventional sintered sample having an average crystal grain size of about 2.5 μm, but almost no pores can be confirmed. Was. As a result, a state in which pores could hardly be confirmed was evaluated as a sample having substantially no pores.

In the present invention, the state of black spots dispersed at several μm obtained by SEM observation is described as pores. Actually, it has the meaning shown in FIG. 4 drawn from the micrograph obtained by the SEM microscope, and thus should be understood as their meaning when it is appropriate to express them as pores or voids. is there. In the evaluation of the piezoelectric ceramic after sintering, the expression that substantially no pores exist was also used. This means that there is almost no state of black spots dispersed at several μm obtained by SEM observation. It should be understood that if numerically defined by the area ratio of the state of black spots under a microscope described below, the conventional sintering method is about 3%, which means that it is considerably less than that.

In contrast, in the sample obtained by the conventional sintering method, it is recognized that the pores decrease with the sintering temperature. Porosity by area ratio is about 3
% Or more. In addition, it is recognized that it is also remarkably present in an extremely shallow portion under the microscope. While the crystal grains grow, the a. It can be understood that the synergistic effect between the pressurization by the hot press which is the hybrid sintering method and the sintering temperature is the same.

(2) Improvement of piezoelectric characteristics of hybrid-sintered sample c. FIG. 5 shows the relationship between the electromechanical coupling coefficient Kp and the sintering temperature. The Kp of the hybrid-sintered sample has a sintering temperature of 1
At a temperature of 150 ° C. or lower, the best characteristics were obtained under the influence of a gas atmosphere and pressure, and a pressure of 40 MPa by hot pressing and sintering in the atmosphere were best. The maximum value of Kp for hybrid sintering was about 75% at 1250 ° C., showing a very significant difference of 11% from 64% for conventional sintering. In the present invention, the definition of having a high electromechanical coupling coefficient and piezoelectric constant is used in comparison with that obtained by a conventional sintering method. The meaning is to be understood as meaning of a significant difference with the above-mentioned results and the explanation about the piezoelectric constant described later. However, since the variation between products unique to piezoelectric ceramics and the change with time after polarization are not small, the difference should be understood as meaning a significant difference including a slight reduction.

Kp is 1200 ° C. to 1250 ° C.
Within the range, it is hardly affected by the gas atmosphere and the pressure.
It was recognized that sufficient characteristics could be ensured by applying a pressure of MPa or more. d. FIG. 6 shows the relationship between the piezoelectric constant d31 and the sintering temperature.
The value of the piezoelectric constant d31 of the hybrid sintering increases as the sintering temperature increases. However, it is hardly affected by the atmosphere and pressure, but slightly from 1150 ° C to 1250 ° C.
In the range of, a better result was obtained with 20 MPa than with a pressure of 40 MPa. In the hybrid sintering method under a pressure of 20 MPa, d31 was 38% higher than that of the conventional sintering, showing a very significant difference, and a remarkable improvement effect was recognized.

E. FIG. 7 shows the piezoelectric ceramic vibration characteristics. Piezoelectric ceramics obtained by hybrid sintering are expected to be effectively used as bimorph-type flexural vibrators and various actuators combined therewith, in addition to use as single elements. FIG. 7 is a vibration characteristic diagram, FIG. 8 is an external view of a piezoelectric ceramic used therein, and FIG.
FIG. 4 is a block diagram for measuring vibration characteristics.

FIG. 8 shows a general structure of the piezoelectric ceramic 18. The two pieces of piezoelectric ceramics are manufactured by forming the electrode surfaces 15 on the upper and lower sides by silver coating or other means, sandwiching the shim plate 16, and heating and pressing with an adhesive such as an epoxy system. Lead wires 17, 17 are attached to this. In FIG. 9, this piezoelectric ceramic was attached to one end of an aluminum plate by adhesion, one end of which was fixed to a fixed end 25, and the other end of the aluminum plate was formed as a free end to form an actuator, and a bending vibration test was performed. Vibration was performed from the function generator 20 via the power amplifier 21 at a frequency of 55 Hz and a terminal voltage of 100 V at peak-to-peak. The free end sine wave vibration was detected by a laser head 24, the displacement was monitored by a laser displacement meter 23, and the waveform was monitored by an oscilloscope 22. As a result, as shown in FIG. 7, in comparison of the vibration characteristics of the actuator made by the hybrid sintering and the actuator made by the conventional sintering method, the former was able to confirm about twice the output as compared to the latter actuator. .

FIG. 10 is an explanatory view showing an outline of a fluid pump called a micropump which can be used in medical equipment and the like suitable for use of the piezoelectric ceramics obtained by the present invention.
Specifically, the bimorph-type ceramics 26 is mounted on the peripheral surface or a specific side surface of the pump 31 as an actuator to function as a pump. Fluids are liquids and gases, and are expected to be used for medical and chemical analyses. Specifically, the bimorph displacement element 26 is driven at a low frequency by an external drive source. The bimorph displacement elements 26 on the left and right in the figure perform movements depending on the drive frequency, with the action of expanding the pump from the inside to the outside and the action of narrowing it down. Due to this bending effect, a bimorph vibration displacement 32 shown by a dotted line in the figure is given.

The bimorph displacement element 26 is operated by interlocking with a means such as a diaphragm for changing the internal volume of the pump, so that fluid is sucked from the fluid inlet 27 and the fluid outlet 2
Ejection from 8 can be realized in combination with ball valves 29, 30. The upper and lower ball valves 29, 30 act as a valve by gravity operation and a check valve, respectively. For example, when fluid is sucked into the pump 31, the ball valve 29
Rises, and the fluid flows in. At this time, the ball valve 30 is operated so that the valve is closed at the upper portion, and the fluid is stored in the pump.

Although one embodiment of the hybrid sintering method according to the present invention has been described above, the present invention is not limited to this. Higher piezoelectric characteristics can be expected in a microwave sintering furnace of 28 GHz or more by using a gyratron. Further, in the case of application to other piezoelectric materials, it is expected that a material having a high piezoelectric characteristic by sintering in the related art will further improve the piezoelectric characteristic. Further, it is also effective for lead-based piezoelectric ceramics, other non-lead materials such as bismuth-based materials and barium titanate-based materials. For anisotropic materials such as bismuth-type materials, it is expected that the anisotropy will be enhanced by hot pressing, and the improvement of the properties can be expected. Sintering at a high temperature was indispensable for obtaining high piezoelectric characteristics, but sintering at a low temperature can provide characteristics comparable to those of conventional sintering.

[0041]

According to the present invention, various characteristics of the PZT-based material obtained by the hybrid sintering method are examined with respect to the sintering temperature, hot press pressure and atmosphere, and the electromechanical coupling coefficient Kp and the piezoelectric constant d31 are extremely small. , Higher density,
With respect to the fine structure such as the particle diameter in the crystal, an excellent piezoelectric ceramic not obtained by the conventional sintering method was obtained. Obtaining a high electromechanical coupling coefficient and a piezoelectric strain constant is judged to be a very suitable result for use of an actuator. Regarding data such as the electromechanical coupling coefficient Kp and d31 value that greatly affect the characteristics, a sintering effect equivalent to that of the conventional sintering method was obtained even at a low temperature of about 1,100 ° C. The sintering time can be reduced to about one tenth as compared with the conventional sintering.

Although it was difficult to improve the above quality only by microwave sintering at 28 GHz or more, a remarkable effect was confirmed by using a hot press together. As a manufacturing method, microwave sintering can be performed by using a peripheral jig such as an alumina rod or a mold other than a metal having a dielectric constant smaller than that of a sample sample, and quality can be improved by hot pressing. Sintering was performed in both oxygen and air as the sintering atmosphere, and it was confirmed that the microstructure and piezoelectric characteristics were improved. According to the method of the present invention, the effect of microwave sintering and pressurization by hot pressing achieve internal sintering and rapid sintering of the material, and the above-mentioned improvement of the piezoelectric characteristics can improve the fine structure with few pores and little grain growth. It is understood from obtaining a sintered body having.

Simultaneous microwave sintering at 28 GHz or higher and hot pressing, sintering in either atmosphere, or oxygen, and a mold other than a metal having a dielectric constant smaller than that of the sample, It is particularly important to use a peripheral jig such as a rod. Simultaneous execution of microwave sintering and hot pressing makes it possible to obtain a sintered body that has a good microstructure with few pores and little grain growth because it has the feature that internal sintering of piezoelectric material and rapid sintering are possible. High piezoelectricity can be expected.

By the hybrid sintering method, the density of the sample reached 98% of the theoretical density at the maximum. Although the hybrid sintering method promotes the growth of the crystal grains of the sample sample, a sintered body having almost no pores can be manufactured as compared with the conventional sintering method. Electromechanical coupling coefficient Kp of hybrid sintered sample
Reached a maximum of 75% and showed a large value compared to the conventional sintering method of piezoelectric constant d31. Regarding the actuator characteristics, a large output could be obtained as compared with the conventional sintering. From the above results, the hybrid sintering method is an effective method for improving the characteristic surface of piezoelectric ceramics and improving the characteristics of a driving source or a vibration pickup as an actuator. Further, if a PZT-based material having higher characteristics is applied, higher characteristics can be expected.

[0045]

[Brief description of the drawings]

FIG. 1 is a schematic view of a side cross section of a microwave sintering furnace of the present invention.

FIG. 2 is a diagram showing a heating temperature curve and a hot press state in a sintering schedule at the time of production.

FIG. 3 is a diagram showing a relationship between a sintering temperature and a sample density.

FIG. 4 is a surface state diagram of an element drawn from an SEM photograph of piezoelectric ceramics observed with a scanning electron microscope.

FIG. 5 is a diagram showing a relationship between a sintering temperature and an electromechanical coupling coefficient of a sample.

FIG. 6 is a diagram showing a relationship between a sintering temperature and a piezoelectric constant of a sample.

FIG. 7 is an external view of a piezoelectric ceramic.

FIG. 8 is a vibration characteristic diagram of a piezoelectric ceramic.

FIG. 9 is a block diagram for measuring vibration characteristics of a piezoelectric ceramic.

FIG. 10 is an explanatory diagram of a use state of a piezoelectric actuator using piezoelectric ceramics.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microwave insertion port 2 Sample sample 3 Thermocouple 4 Alumina rod 5 Die 6 Cooling water inlet 8 Gas inlet 9 Cooling water outlet 10 Microwave sintering furnace 13 Non-pored part 14 Pores 15 Electrode surface 16 Shim plate 17 Lead Wire 18 Piezoelectric Ceramics 20 Function Generator 23 Laser Displacement Meter 24 Laser Head 25 Fixed End 26 Bimorph Displacement Element 27 Fluid Inlet 28 Fluid Outlet 29 Ball Valve 30 Ball Valve 31 Pump 32 Bimorph Vibration Displacement

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Hiroshi 1-13-10 Uesugi, Aoba-ku, Sendai-shi, Miyagi F term (reference) 4G054 AA05 AC00 BA02 BA43 BB04 BB05 BB06

Claims (11)

[Claims] 1. A piezoelectric material is placed in a non-metallic mold in a microwave sintering furnace, and the material is heated by sintering with the microwave at least in a sintering process. Using a microwave and a hot press characterized by having a high electromechanical coupling coefficient and a high piezoelectric constant in a piezoelectric ceramic obtained by subjecting the material in a mold to a pressure treatment by a hot press and having substantially no pores. And sintered piezoelectric ceramics. 2. A method for producing a piezoelectric ceramic by sintering a piezoelectric material, wherein the piezoelectric material is placed in a non-metal mold in a microwave sintering furnace, and the material is raised by microwaves at least during the sintering process. A method for producing piezoelectric ceramics which is sintered by using microwave and hot press, wherein the material is heated and pressurized by hot pressing in the mold in the sintering process. 3. The method of manufacturing a piezoelectric ceramic according to claim 2, wherein in the microwave sintering step, a hot press is applied in a range of 10 to 100 MPa. Manufacturing method of piezoelectric ceramics to be sintered. 4. The method for producing a piezoelectric ceramic according to claim 2, wherein a hot press is applied at a pressure of 20 to 40 MPa in a microwave sintering process. Manufacturing method of piezoelectric ceramics to be bonded. 5. The method of manufacturing a piezoelectric ceramic according to claim 1, further comprising a step of performing hot pressing in a microwave sintering process using a mold made of a nonmetallic material having a dielectric constant lower than that of the sintered sample. 3. The method according to claim 2, wherein
A method for producing a piezoelectric ceramic which is sintered by using the microwave and hot press described in the above. 6. The method of manufacturing a piezoelectric ceramic according to claim 2, further comprising a step of performing hot pressing in an alumina rod and a mold in a microwave sintering process. For producing piezoelectric ceramics sintered using microwaves and hot pressing. 7. The method for producing a piezoelectric ceramic according to claim 1, wherein a maximum sintering temperature range in a microwave sintering process is one.
The process is characterized by adding a step of pressing the hot press with an alumina rod in the range of 000 ° C. to 1250 ° C. and a step of maintaining the press of the hot press from the stage when the maximum sintering temperature is reached. A method for producing a piezoelectric ceramic, wherein the piezoelectric ceramic is sintered by using the microwave and hot press according to any one of claims 2 and 6. 8. An apparatus comprising a microwave sintering furnace for producing a piezoelectric ceramic by sintering a piezoelectric material, the apparatus comprising a non-metallic mold for sintering a piezoelectric material, and the piezoelectric material in the mold. Hot press pressing means for pressing the material, a microwave source for sintering, a means for raising the temperature in a non-metal mold by the microwave source, a means for controlling the temperature and a maximum sintering temperature control means, An apparatus for producing piezoelectric ceramics sintered by using microwaves and hot pressing, comprising: a gas atmosphere supply means for supplying the gas atmosphere into the sintering furnace. 9. The apparatus for manufacturing a piezoelectric ceramic according to claim 8, wherein in the microwave sintering process, the pressure of the hot press is a mold made of a nonmetallic material having a dielectric constant smaller than that of a sintered sample. An apparatus for manufacturing piezoelectric ceramics that is sintered using waves and hot pressing. 10. A piezoelectric ceramic obtained by the method according to claim 2, which has a high density, a fine crystal structure substantially free from pores by SEM observation and excellent piezoelectric characteristics. 11. A piezoelectric ceramic obtained by the method according to any one of claims 2 to 7, wherein the piezoelectric ceramic has a high-density, fine-crystal structure substantially free from pores by SEM observation and excellent in piezoelectric properties. A piezoelectric actuator mounted as a drive source or vibration pickup.