JPS61106463A - Manufacture of ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Technical field to which the invention pertains] The present invention relates to a method for manufacturing ceramics, and in particular, by hot pressing multiple times from different directions, the particles having shape anisotropy constituting the ceramic are aligned in a uniaxial direction, and the orientation is improved. Concerning how to produce good ceramics. [Background of the Invention] Some piezoelectric materials inherently have relatively good dielectric properties. There are materials with piezoelectric properties and electro-optic effects. - An example is a ferroelectric material with a tungsten bronze type crystal structure.
The directions in which polarization is easy are limited. Therefore, even if this material is tried to be used in piezoelectric ceramics, the crystal axes of the particles in ceramics are oriented in arbitrary directions, so efficient polarization cannot be performed even if an electric field is applied from the outside. It has been impossible to take advantage of the good piezoelectric properties and electro-optic effects inherent to this material. For this reason, research into this crystal system. It is mainly aimed at applied research as a single crystal material. On the other hand, in ferroelectric materials made of bismuth layered compounds,
The particles are plate-shaped, so it is possible to produce ceramics in which the crystal grains are oriented by the Hondogress method using -axial pressure, and therefore ceramics that can be efficiently polarized and have good piezoelectric properties. What is shown is obtained. However, for the above-mentioned material with a tungsten bronze type structure made of acicular crystal grains, if only the biaxial hot press method is applied, the acicular grains will only be oriented randomly within the pressurized surface, and the acicular grains will be oriented in a specific manner. Because it is impossible to align the particles in the direction. No material showing good piezoelectric properties was obtained. [Object of the Invention] Therefore, an object of the present invention is to provide a manufacturing method for obtaining a ceramic material in which the particles are uniaxially oriented from a ceramic material made of particles having unidimensional anisotropy. [Summary of the Invention] The present invention involves adding a molding binder to a ceramic material made of pre-grown particles with dimensional anisotropy, pre-forming it into a predetermined shape, and hot-heating the molded body from different directions. The above objective is achieved by applying pressure (honotosores). As the particles having the above-mentioned dimensional anisotropy, for example, needle-shaped or rod-shaped crystal particles such as PbNb2O6 having a tungsten bronze type crystal structure formed by a flux method are used. [Embodiments of the Invention] Examples of the present invention will be described in detail below. Various materials can be considered as materials having dimensional anisotropy such as needle-like or rod-like crystal grains, but here, when zero particles are oriented in a uniaxial direction, the uniaxial orientation of the particles can be easily confirmed, and By orienting the particles in a uniaxial direction,
Its excellent dielectric properties. The effectiveness of the present invention will be demonstrated by selecting a ferroelectric material having a tungsten bronze type crystal structure that is expected to utilize piezoelectric properties and electro-optical properties. As the ferroelectric material having the above-mentioned tungsten bronze crystal structure, PbNb2O6゜5r2NaNb5
015.5r2KNb5015. Pb) (Ba1zN
b206°5rXBa4, Nb2o6. (Pb, K
) Nb206. K3Li2Nb5015゜Ba 2
N8 Nb 5015, Ba2NaNb5015,
K5Li2Nb5-X”aXo15-(Pb, Ba,
La)Nb206 and the like can be cited as its main components, but here an example using PbNb2O6' will be described. first. Synthesis of acicular crystal particles of PbNb2O6 by flux method

[-1. All reagents used here have a purity of 99.5
% or higher purity reagent. PbO and Nb2O5
Blend to have a composition of bNb2O6. A mixture of 1 equivalent weight of KCl was added to the mixture calcined for 2 hours at a temperature of 900°C and mixed for 15 minutes in an electric mortar.
00 grams into an alumina crucible. The reaction was carried out by heating at a temperature of 900° to 1200°C for 1 to 8 hours. After the above heat treatment, the mixture was placed in a 2 liter glass beaker filled with hot water and washed to remove the KC1 portion. At that time, washing was performed using hot water of ion-exchanged water while stirring, and repeated washing was performed by replacing the hot water. When cleaning was performed by changing the hot water more than 10 times, the Ct-
The ions were undetectable by detection using AgNO3 solution. The results of observation of the thus obtained acicular and columnar particles using an electron microscope are shown in FIGS. 1(a) and 1(b). The particles in FIG. 1(a) were obtained by KCtC rough flux medium
Figure 1(b)
The particles were obtained by heat treatment at a temperature of 1200° C. for 5 hours. When the synthesis temperature was less than 900°C, the development of needle-shaped particles was poor and only short particles were obtained. 4ft:,t
At temperatures exceeding 200°C, each particle grows thicker and the dimensional anisotropy of each particle decreases, so for this material, a heat treatment temperature range of 9000 to 1200°C was appropriate. Especially 1
The acicular ratio (
The length/thickness or diameter) was large, ranging from 20 to 40. Also, if the synthesis time is too short, particle growth will not proceed,
If the length is too long, the grains will grow too much and become thicker, resulting in an acicular ratio close to 1. In this example, heat treatment for 1 to 8 hours results in a particle length of 2 μm or more and an acicular ratio of 1.2 or more. Particles having a dimensional anisotropy of 100 or less were obtained. Especially 10
Those reacted for 3 to 6 hours within the range of 50° to 1100°C have a large needle-like ratio, and those reacted for 5 hours have a diameter of 1.
．． Good acicular particles with a diameter of 5 to 2 μm and a large acicular ratio of 20 to 40 were obtained. Next, this powder made of acicular particles is poured into ion-exchanged water, and a dispersant is added to sufficiently disperse the powder. Large particles and ultrafine particles are removed by sedimentation classification, and only acicular particles are separated. I took it out. This dispersion was thoroughly filtered, and while being filtered, it was thoroughly washed and dried. This ceramic material made of acicular particles contains 7% by weight of P.
The granules were granulated while adding 8% by weight of the VA solution and then sized, as shown in FIG. 2(a). It was preformed into a cylindrical molded body with a diameter of 15 ms and a height of about 20 pieces. The two directions perpendicular to each other on the bottom surface of this cylindrical molded body are the Y-axis and Y-axis, respectively, and the height direction of one cylinder is Z.
The axis. Next, this molded body was placed in a high-purity alumina die having an inner diameter of 4 Q mm, and a first hot press (hot pressing) was performed in the vertical direction, that is, in the Z-axis direction. In this case, the pressure P1, the direction of pressurization, and the shape of the sample after hot pressing are
Shown in Figure (b). In this case, the alumina die and sample were heated at a rate of 150°C/hour, and at a temperature of 1200°C,
0) A pressure of C9/(4) was applied and hot pressing was performed for 3 hours. After the first hot pressing, the temperature was lowered and the sample was taken out, and this sample was subjected to the first heating. Pressure was applied from a direction perpendicular to the pressure direction, and the sample was reoriented and set in the alumina die again. Hot pressing was performed at a pressure of P2 from the direction of the Y axis perpendicular to the Z axis.This second hot pressing was performed at a temperature of 1.
A pressure of 100 kg/ca was applied for 3 hours at 250° C., and the sample was shaped as shown in FIG. 2(c). In addition, since we used a hot press device that can press only from the -axis direction, the sample that had been hot pressed for the first time as described above was cooled down and taken out from the die, but the two axes that are orthogonal to each other were used. If a hot press device that can apply pressure from the direction is used, the first pressurization from the Z-axis direction can be followed by the second pressurization from the Y-axis direction. Needless to say, this effect can be obtained. In addition, in this embodiment, @2 figure (a
), the sample was preformed into a cylindrical shape, but the shape of this molded body may also be a rectangular parallelepiped or a cube. There is no difference in the effect obtained even if the pressure is applied from the Z-axis direction. After the second hot press, the sample taken out was
As shown in Figure (a), one cylinder has a shape crushed in the radial direction. Also, as shown in Figure 6(b), the planes perpendicular to the X-axis, Y-axis, and Z-axis of this sample are SX, respectively.
As SY and SZ, the orientation state of particles on each surface was observed using an electron microscope. First, after mirror-polishing the face and 82 sides of the sample that was subjected to the first hot pressing from the Z axis,
The results observed after thermal etching at 150° C. are shown in FIGS. 4(a) and 4(b). As is clear from FIG. 4, the acicular particles are randomly oriented on the 82 plane perpendicular to the pressing direction. On the other hand, in the Sx plane parallel to the pressing direction,
No particles oriented in the direction of pressure are observed. From this, 1
It is understood that the particles are oriented in a direction perpendicular to the direction of application of pressure. Next, as shown in Figure 6(b), the SX plane and S
Electron micrographs of Y plane and 82 plane are shown in Fig. 5(a), (
Shown in b) and (c). As is clear from this figure, the particles having dimensional anisotropy are oriented in the X-axis direction perpendicular to the direction of pressure in each of the two hot presses. FIG. 6 shows the xm diffraction mother turn, FIG. 6(a) shows the synthesized acicular particle powder, and FIG. 6(b) shows the SY plane. FIG. 6(c) is the SX plane. Figure 6(a) shows PbNb
This is the diffraction pattern when 2O6 is oriented in a random direction, and in comparison with FIG. The intensity is strong, and in Figure 6 (c), (o, O, Z)
The relative intensity of the diffraction line with the plane index is strong <, (h, to, o
) were hardly observed. This fact indicates that when the long axis of the acicular crystal grain is oriented in one direction, the crystallographic crystal axis is also oriented in a specific uniaxial direction. Next, a plate sample as shown in FIG. 7 was cut out and its dielectric properties and piezoelectric properties were measured. Here, sample (1) is S
Equipped with a pair of electrodes facing the Y plane. The long axes of the particles are oriented in a direction parallel to the electrodes. The sample (■) is equipped with a pair of electrodes facing the SX surface. The long axes of the particles are oriented perpendicular to the electrode. The shape of the measurement sample is: Thickness: 5, short side 5, long side 7.
It is a rectangular square plate of a seagull, and the dielectric constant was determined from the electrostatic capacity at 1 kHz. The piezoelectric constants were determined from the frequency at which one resonance and one antiresonance occur and the impedance. The polarization treatment was performed at a temperature of 110° C. by applying a voltage of 2 kV per thickness for 10 minutes. The measurement results are shown below.
Shown in the table. Table 1 shows, for comparison, samples that were hot-pressed only from the Z-axis direction in the first round, and were equipped with a pair of electrodes facing 82 planes perpendicular to the pressing direction. The characteristics of the sample (I') and the characteristics of the sample (■') having a pair of electrodes facing each other in the SX plane parallel to the pressing direction are shown together. As is clear from Table 1 above, in this example, the anisotropy of the properties of the ceramics could be further increased by performing hot pressing twice in directions perpendicular to each other. For example, only the first hot press. The anisotropy (ratio) of the dielectric constant ε at room temperature (I′ and 8
/II' ε3) is 0.88, but if the second hot press is performed, this anisotropy ratio changes to 0.75. This relative permittivity shows a maximum value near one Curie temperature, and the anisotropy of the maximum value εmax of the relative permittivity is 1.6 to 3.
The anisotropy of the electromechanical coupling coefficient Kt in the thickness direction also shows a change of more than twice from 1.9 to 4.0. This means that if hot pressing is performed twice from two orthogonal directions as in this example, ceramic particles with uniaxially oriented ceramic particles can be produced compared to when hot pressing is performed once. It has been shown that this method is not only effective for the production of ceramics, but also extremely suitable for producing materials that take advantage of the anisotropy of the properties of the materials that make up the ceramics. Furthermore, the anisotropy of the dielectric constant as described above is directly related to the anisotropy of the electro-optic effect, and together with the densification effect by hot pressing, it is possible to obtain an excellent electro-optic material. can. In addition, in the above example, PbNb2
After calcination and synthesis of O6, KCtC rough flux medium crystal was grown, but pbo, Nb2O5 and KCl
and 900° to 1200° in the same manner.
When the mixture was reacted by heating at a temperature of 1 to 8 hours, needle-like crystals similar to those of Habo were obtained. Moreover, the optimum conditions for forming PbNb606 in KCtC rough flux were 1 to 8 hours at a temperature of 900° to 1200°C, but other 5r2KNb5015.5r2NaNb
5015. Pb) (Ba, -> (Nb206.5rXBa1-XN
b206°Ba2NaNb5015. (Pb, K)N
b206. K3Li2Nb5015゜Ba2LtNb
5015. K5Lt21'Jb5-X'I'aXo1
5. When synthesizing acicular particles of a material having a tungsten bronze type crystal structure, such as (Pb+Ba, La)Nb206, etc., optimal conditions may be selected depending on the material. In addition, in the above example, the first hot press was performed at a temperature of 1200°C and a pressure of 100 k17/ctM for 3
A second hot press was carried out at a temperature of 1250°C and a pressure of 100 kli'/clr was applied for 3 hours.
It varies depending on the dimensional anisotropy of the particles, etc. 1For example, the temperature of the first hot press is 1151]' to 125
The temperature may be selected within the range of 0°C, and the applied pressure may be set within the range of 20 to 20°C.
It can also be changed within the range of 0 kg/C,i,
The pressurization time can be set at a time range of about 0.5 to 10 hours, and the temperature of the second real f1/s]180
It is good also within the range of 1280 degrees Celsius. In short, it is sufficient that conditions that promote orientation of acicular or rod-shaped particles are satisfied. Next, considering the pressing direction of the second hot pressing [7], it is mechanically possible to perform the second hot pressing from a direction perpendicular to the pressing direction of the first hot pressing. is the most efficient way to promote particle orientation, and the angle formed by these two pressurizing directions must be [7] does not have to be a right angle; for example, 80', 100', 60'
Even if pressure is applied from a direction such as 120° or 120°, the force of the component perpendicular to the first pressurizing direction is used. Similarly to the above, a ceramic with uniaxially oriented particles is produced,
It is easy to analogize with scales. In addition, in order to improve the -axis orientation, hot pressing is performed for a third time, a fourth time, etc. from a direction different from the desired orientation direction, preferably from a direction perpendicular to the desired orientation direction. Repetition is even more effective. In the above embodiments, crystal grains having a tungsten bronze crystal structure are used as the material forming the ceramic. Amorphous particles may be used, or both crystalline particles and amorphous particles may be used. [Effects of the Invention] As is clear from the above description, one aspect of the present invention is achieved. Ceramic materials having desired properties similar to those of single crystals can be produced without producing single crystals of crystallographically anisotropic materials. Growing a single crystal requires a temperature higher than the melting point of the material, but according to the method of the present invention, the desired ceramic can be obtained at the sintering temperature, so it is easy to select the heating source and heating method. Wide and wide. Refractories, crucibles, etc. can also be used at lower temperatures. It is also possible to obtain cheaper and more economical materials. Further, according to the present invention, even a material that is difficult to grow as a single crystal can be fired relatively easily, and it has become possible to provide a material that utilizes anisotropy.

[Brief explanation of drawings]

Figures 1 (a) and (b) show P synthesized by the flux method.
bElectron micrographs of Nb2O6-based particles, Figure 2(a)~
FIG. 6(c) is an explanatory view showing the relationship between the molded body and the hot pressing direction in the method of the present invention, and FIG. 6(a). (b) is an explanatory diagram showing the direction of the second hot press and the direction of the surface of the sample observed with an electron microscope, and Figure 4 (a)
, (b) is an electron micrograph showing the particle orientation state after the first hot press, FIGS. 5(a) to (C) are electron micrographs showing the particle orientation state after the second real press, and FIG. Figures (a) to (c) are X-ray diffraction diagrams, and Figure 7 is an explanatory diagram showing the direction of a plate-shaped sample cut from a sample subjected to the second hot pressing. Patent applicant Mitsubishi Mining Cement Co., Ltd.

Claims (1)

[Claims] 1. A molding binder is added to a ceramic material made of particles having dimensional anisotropy grown in advance, and the molded body is preformed into a predetermined shape. performing a second hot press, and then performing a second hot press from a second direction different from the first direction, thereby obtaining a ceramic in which the particles are uniaxially oriented; A method for producing ceramics characterized by: 2. The method for producing ceramics according to claim 1, wherein the particles are at least one of crystalline particles and amorphous particles. 3. The method for producing ceramics according to claim 1 or 2, wherein the particles having dimensional anisotropy are at least one of acicular and rod-shaped particles. 4. The method for producing ceramics as set forth in claim 3, wherein the particles are synthesized by a flux method, and the acicular ratio thereof is in the range of more than 1 and 100 or less. 5. A method for producing ceramics as set forth in any one of claims 1 to 4, wherein the particles are crystal grains having an anisotropic crystal structure. 6. The method for manufacturing ceramics according to claim 5, wherein the ceramic material is made of a piezoelectric material. 7. The method for manufacturing ceramics according to claim 5, wherein the ceramic material is made of a ferroelectric material. 8. The method for manufacturing ceramics according to claim 1, wherein the ceramic material is composed of crystal grains having a tungsten bronze type crystal structure. 9. The method for manufacturing ceramics according to claim 8, wherein the ceramic material is PbNb_2O
_6, (Pb, K)Nb_2O_6, Sr_2NaNb
_5O_1_5, Sr_2KNb_5O_1_5, Pb
_xBa_1_-_xNb_2O_6, Sr_xBa_
1_-_xNb_2O_6, K_3Li_2Nb_5O
_1_5, Ba_2NaNb_5O_1_5, Ba_2
LiNb_5O_1_5, K_3Li_2Nb_5_-
_xTa_xO_1_5, (Pb, Ba, La)Nb_
2O_6. 10. Any one of claims 1 to 9
In the method for manufacturing ceramics described in 1., the first direction and the second direction are directions perpendicular to each other. 11. In the method for manufacturing ceramics according to any one of claims 1 to 10, the first and second hot pressings are performed consecutively. Method.