JPH0132186B2 - - Google Patents

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, particles having shape anisotropy constituting ceramics are aligned in a uniaxial direction, This invention relates to a method for producing ceramics with good orientation. [Background of the Invention] Some piezoelectric materials inherently have relatively good dielectric properties, piezoelectric properties, and electro-optic effects. One example is a ferroelectric material with a tungsten bronze crystal structure. In this material's crystal system, the crystal grains have large dimensional anisotropy, such as needle shapes, and the direction of easy polarization is Limited. Therefore, even if this material is used in piezoelectric ceramics, the crystal axes of the particles in ceramics are oriented in arbitrary directions, so efficient polarization cannot be performed even when an external electric field is applied. First, it has been impossible to take advantage of the good piezoelectric properties and electro-optical effects inherent to this material. For this reason, research on this crystal system is mainly directed to applied research as a single crystal material. On the other hand, in a ferroelectric material made of a bismuth layered compound, the particles are in the form of a plate. Ceramics that can be polarized can be manufactured, and ceramics that exhibit good piezoelectric properties have been obtained. However, in the above-mentioned material with a tungsten bronze type structure consisting of acicular crystal grains,
If you only use the hot press method with uniaxial pressure,
Since the acicular particles are only randomly oriented within the pressurized surface and it is impossible to align the particles in a specific direction, it has not been possible to obtain one that exhibits good piezoelectric properties. [Object of the Invention] Therefore, an object of the present invention is to provide a manufacturing method for obtaining ceramics in which the particles are uniaxially oriented from a ceramic material made of particles having dimensional 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-rolling the molded body from different directions. The above objective is achieved by applying pressure (hot place). Examples of particles having the above-mentioned dimensional anisotropy include, for example, PbNb ₂ O ₆ having a tungsten bronze crystal structure formed by a flux method.
Needle-shaped or rod-shaped crystal particles are used. [Embodiments of the Invention] Examples of the present invention will be described in detail below.
Various materials can be considered as materials with crystal grains having dimensional anisotropy, such as needle-like or rod-like shapes. By uniaxially orienting the particles, its excellent dielectric properties,
A ferroelectric material having a tungsten bronze type crystal structure, which is expected to utilize piezoelectric properties and electro-optical properties, will be selected to demonstrate the effectiveness of the present invention. Ferroelectric materials having the above-mentioned tungsten bronze type crystal structure include PbNb ₂ O ₆ ,
_{Sr2NaNb5O15 , Sr2KNb5O15 , PbXBa1 - XNb2O6 , _ _}
Sr _X Ba _1-X Nb ₂ O ₆ , (Pb, K)Nb ₂ O ₆ ,
K ₃ Li ₂ Nb ₅ O ₁₅ , Ba ₂ NaNb ₅ O ₁₅ , Ba ₂ LiNb ₅ O ₁₅ ,
_The main components include K ₃ Li _{2 Nb 5 -X Ta}
An example using PbNb ₂ O ₆ will be described. First, acicular crystal particles of PbNb ₂ O ₆ were synthesized using a flux method. All reagents used here are pure
It is a reagent with a high purity of over 99.5%. PbO _{and Nb2O5}
was prepared to have a composition of PbNb ₂ O ₆ , pre-calcined at a temperature of 900℃ for 2 hours, an equal weight of KCl was added, and the mixture was mixed for 15 minutes in an electric mortar. Approximately 100 grams of the mixture was placed in an alumina crucible. and heated at a temperature of 900° to 1200°C for 1 to 8 hours to react. After the above heat treatment, the mixture was washed by placing it in a 2 liter glass beaker filled with boiling water.
The KCl moiety was removed. 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. After washing by changing the hot water more than 10 times, the obtained PbNb ₂ O ₆
The Cl ^- ions remaining at the end of the needle-like particles could not be detected by detection using an AgNO ₃ solution. The results of observation of the thus obtained acicular and columnar particles using an electron microscope are shown in FIGS. 1a and 1b. 1st
The particles in Figure a were obtained by heat treatment in a KCl flux at a temperature of 1050°C for 5 hours, and the particles in Figure 1 b
The particles were obtained by heat treatment at a temperature of 1200°C for 5 hours. When the synthesis temperature was lower than 900°C, the development of needle-like particles was poor and only short particles were obtained.
Furthermore, at temperatures exceeding 1200°C, the particles grow thicker and the dimensional anisotropy of the particles decreases, so a heat treatment temperature range of 900° to 1200°C was appropriate for this material. In particular, those synthesized at temperatures between 1000° and 1100°C have a large needle-like ratio (length/thickness or diameter).
It was between 20 and 40. Also, if the synthesis time is too short, the particles will not grow, and if it is too long, the particles will grow too much and become thicker, resulting in an acicular ratio close to 1.
In this example, particles having a length of 2 μm or more, an acicular ratio of 1.2 or more, and a dimensional anisotropy of 100 or less were obtained by heat treatment for 1 to 8 hours. Especially 1050°~1100
The acicular ratio was large for those reacted for 3 to 6 hours within the temperature range, and the diameter was 1.5 to 1.5 for those reacted for 5 hours.
Good acicular particles with a diameter of 2 μm and a large acicular ratio of 20 to 40 were obtained. Next, this powder consisting of acicular particles is poured into ion-exchanged water, and a dispersant is added to fully disperse the powder. After that, large particles and ultrafine particles are removed by sedimentation classification, and the acicular particles are I took out the chisel. The dispersion was filtered and thoroughly washed and dried. This ceramic material made of acicular particles is granulated while adding 8% by weight of 7% by weight PVA solution,
Further, the sized particles are as shown in Figure 2a.
It was preformed into a cylindrical molded body with a diameter of 15 mm and a height of about 20 mm. The two mutually orthogonal directions on the bottom surface of this cylindrical molded body are defined as the X axis and the Y axis, respectively, and the height direction of the cylinder is defined as the Z axis. Next, this molded body was placed in a high-purity alumina die having an inner diameter of 40 mm, and a first hot press (hot pressing) was performed in the vertical direction, that is, in the Z-axis direction. The pressure _P1 in this case, the direction of pressure application, and the shape of the sample after hot pressing are shown in FIG. 2b. In this case, the alumina die and the sample were heated at a rate of 150° C./hour, a pressure of 100 Kg/cm ² was applied at a temperature of 1200° C., and hot pressing was performed for 3 hours. After the first hot press, the temperature is lowered, the sample is taken out, the direction of the sample is changed so that pressure can be applied from the direction perpendicular to the first press, and the sample is placed in the alumina die again. Then, as shown in FIG. 2c, a second hot press was carried out at a pressure P ₂ from the direction of the Y axis perpendicular to the Z axis. This second hot pressing was carried out at a temperature of 1250° C. and a pressure of 100 Kg/cm ² was applied for 3 hours to form the sample into the shape shown in FIG. 2c. Note that since we used a hot press device that can apply pressure only from one axis, the first
The sample that had been hot-pressed for the first time was once cooled down and taken out from the die, but two pieces perpendicular to each other were
If you use a hot press device that can apply pressure from the axial direction, following the first press from the Z-axis direction,
It goes without saying that the second pressurization from the axial direction can be performed successively, and thereby similar effects can be obtained. In addition, in this embodiment, the second
As shown in Figure a, the sample was preformed into a cylindrical shape, but the shape of this molded body may be rectangular or cubic.The first pressurization was performed from the Y-axis direction, and the second pressurization There is no difference in the effect obtained even if the pressure is applied from the Z-axis direction. After the second hot pressing, the sample taken out has a shape in which a cylinder is crushed in the radial direction, as shown in FIG. 3a. In addition, as shown in Figure 3b, the planes perpendicular to the _X -axis, Y _- axis, and Z _- axis of this sample were designated S . First, _{the S} show. As is clear from FIG. 4, the acicular particles are randomly oriented in the _SZ plane perpendicular to the pressing direction. On the other hand, in the S _X plane parallel to the pressure direction, no particles oriented in the pressure direction are observed. From this, it is understood that the particles are oriented in a direction perpendicular to the direction of pressurization. Next, as shown in Figure 3b, the sample was hot-pressed twice from two directions perpendicular to each other.
Electron micrographs of the S _X plane, S _Y plane, and S _Z plane are shown in Figure 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 X-ray diffraction pattern, FIG. 6a shows the synthesized acicular particle powder, FIG. 6b shows the S _Y plane, and FIG. 6c shows the S _X plane. Figure 6a shows the diffraction pattern when PbNb ₂ O ₆ is oriented in a random direction, and Figure 6b shows (h,
In Fig. 6c, the relative intensity of the diffraction line with the plane index of (o, o, l) is strong, and the relative intensity of the diffraction line with the plane index of (h, k, o) is strong. )
Almost no diffraction peaks from planes with indexes were 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, the sample () includes a pair of electrodes facing the S _Y plane, and the long axis of the particles is oriented in a direction parallel to the electrodes. The sample () is equipped with a pair of electrodes facing the _S The shape of the sample for measurement is 1 mm thick, short side 5
It is a rectangular square plate with a long side of 7 mm and a dielectric constant of
It was determined from the capacitance at 1kHz. Piezoelectric constants were determined from the frequencies at which resonance and antiresonance occur, and impedance. The polarization treatment was performed at a temperature of 110° C. by applying a voltage of 2 kV per 1 mm of thickness for 10 minutes. The measurement results are shown in Table 1 below. For comparison, Table 1 shows samples that were hot-pressed only from the Z-axis direction for the first time, with a pair of electrodes facing the S _Z plane perpendicular to the pressing direction. The characteristics of the sample ('), which was prepared in the same way, and the characteristics of the sample ('), which had a pair of electrodes facing each other in the _S

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a ceramic material having the same desired properties as a single crystal can be produced without producing a single crystal of a material having crystallographic anisotropy. be able to. 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 the selection of the heating source and heating method can be made easier. It is wide and also
Since 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 whose single crystal is difficult to grow can be fired relatively easily, and it has become possible to provide a material that utilizes anisotropy.

[Brief explanation of drawings]

Figure 1 a and b were synthesized using the flux method.
Electron micrographs of PbNb ₂ O ₆ -based particles, Figure 2 a~
Fig. 3c is an explanatory diagram showing the relationship between the molded body and the direction of hot pressing in the method of the present invention, and Fig. 3a and b are explanatory diagrams showing the direction of the second hot pressing and the direction of the surface of the sample observed with an electron microscope. Figure 4a,
b is an electron micrograph showing the state of particle orientation obtained by the first hot pressing, FIGS. 5 a to c are electron micrographs showing the state of particle orientation obtained by the second hot pressing, and FIGS. , FIG. 7 is an explanatory diagram showing the direction of a plate-shaped sample cut out from a sample subjected to the second hot pressing.

Claims (1)

[Scope of 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.
A first hot press is carried out in the direction of , and then a second hot press is carried out in a second direction different from the first direction and perpendicular thereto, whereby the particles are uniaxially A method for producing ceramics, characterized by obtaining ceramics oriented in the following manner. 2. The method for manufacturing ceramics according to claim 1, wherein the particles are at least one of crystalline particles and amorphous particles. 3. The method for manufacturing ceramics according to claim 1 or 2, wherein the particles having dimensional anisotropy are at least one of needle-shaped and rod-shaped particles. 4. In the method for manufacturing ceramics as set forth in claim 3, the particles are synthesized by a flux method, and the acicular ratio thereof exceeds 1.
Said method in a range of 100 or less. 5. The method for producing ceramics as set forth in any one of claims 1 to 4, wherein the particles are crystal particles having an anisotropic crystal structure. 6. The method for manufacturing ceramics according to claim 5, wherein the ceramic material is 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 comprises crystal grains having a tungsten bronze type crystal structure. 9. In the method for manufacturing ceramics according to claim 8, the ceramic material comprises PbNb ₂ O ₆ , (Pb,K)Nb ₂ O ₆ , Sr ₂ NaNb ₅ O ₁₅ ,
Sr ₂ KNb ₅ O ₁₅ , Pb _X Ba _1-X Nb ₂ O ₆ , Sr _X Ba _1-X
Nb ₂ O ₆ , K ₃ Li ₂ Nb ₅ O ₁₅ , Ba ₂ NaNb ₅ O ₁₅ ,
Ba ₂ LiNb ₅ O ₁₅ , K ₃ Li ₂ Nb _5-X Ta _X O ₁₅ , (Pb, Ba,
La) Nb ₂ O ₆ . 10. The method for producing ceramics according to any one of claims 1 to 9, wherein the first and second hot pressings are performed consecutively. .