JP4378535B2 - Method for producing precisely oriented polycrystalline hexagonal zinc oxide sintered body - Google Patents

Description

  The present invention relates to a precisely oriented polycrystalline ceramic sintered body, a method for producing the sintered body, and an apparatus used for the production method.

  Ceramic sintered bodies are widely used as abrasives, cutting materials, high temperature materials, etc. For example, alumina-based sintered bodies are excellent in corrosion resistance, mechanical strength, hardness, wear resistance, etc. Used for mechanical parts, electrical and electronic materials, optical materials, etc.

  Such a ceramic sintered body can be improved in characteristics such as toughness, strength, and translucency by controlling its microstructure, and has been refined as an example of such microstructure control. Oriented ceramic sintered bodies are known.

As a method for producing an oriented ceramic sintered body, a ceramic powder is dispersed in a solvent to prepare a slurry, and the slurry is solidified and formed in a magnetic field and then sintered to obtain an oriented ceramic sintered body. Has been proposed. (See Patent Documents 1 to 3)
JP 2002-53367 A JP 2002-193672 A JP 2003-112974 A

  According to the techniques described in these patent documents, an oriented ceramic sintered body can be obtained without depending on the shape of the raw material particles by operating in a non-contact manner. Depending on the difference in magnetic susceptibility, it can be oriented only in a direction with high stability in a magnetic field. Therefore, depending on the target substance, the intended functional properties and the crystal orientation direction may not coincide, and it is difficult to obtain a ceramic sintered body oriented in a desired direction. Moreover, the oriented ceramics obtained were oriented only in one axial direction, and a ceramic sintered body oriented in two axial directions could not be obtained.

  Accordingly, the present invention eliminates these problems of the prior art, and the direction perpendicular to the a-axis or c-axis in which the a-axis or c-axis is oriented in a predetermined direction and the c-axis or a-axis is oriented in the predetermined direction. An object of the present invention is to provide a finely oriented polycrystalline ceramic sintered body having an in-plane orientation, a method for producing the sintered body, and an apparatus used for the production method.

As a result of intensive studies, the present inventors have found that the above problem can be solved by applying a rotating magnetic field to a slurry in which non-ferromagnetic ceramic crystal particles are dispersed in a solvent, thereby completing the present invention. Is.
That is, the present invention employs the following configurations 1 to 10.
1. (1) Hexagonal zinc oxide crystal particles having an average particle diameter of 10 nm to 5 μm are dispersed in a solvent, (2) a rotating magnetic field is applied to the resulting slurry to orient the crystal particles, and (3) drying (4) The obtained molded body is sintered in an oxygen-containing atmosphere, and the a-axis or c-axis is oriented in a predetermined direction, and the c-axis or a-axis There were plane orientation in the a-axis or c-axis perpendicular direction oriented in the predetermined direction, fine orientation polycrystalline orientation of the c axis, characterized in that a 0.05 to 0.99 Lotgering factor A method for producing a hexagonal zinc oxide sintered body.
2. The precisely-oriented polycrystalline hexagonal zinc oxide sintered body has diffraction peaks (002) and (004) in X-ray diffraction, and has a degree of orientation of 0.2 or more in terms of Lotgering factor. 2. The method for producing a precisely-oriented polycrystalline hexagonal zinc oxide sintered body according to 1, characterized in that:
3. (2) The finely oriented film according to 1 or 2, wherein the slurry is accommodated in a horizontally rotatable container, and a magnetic field is applied in a state where the container is horizontally rotated to orient crystal grains. A method for producing a crystalline hexagonal zinc oxide sintered body.
4). (1) The precisely oriented polycrystal according to any one of 1 to 3, wherein the hexagonal zinc oxide crystal particles are dispersed in a solvent such that the solid content in the slurry is 10 to 50% by volume. A method for producing a hexagonal zinc oxide sintered body.
5. (2) The method for producing a precisely oriented polycrystalline hexagonal zinc oxide sintered body according to any one of 1 to 4, wherein a magnetic field of 1 T or more is applied to the slurry.
6). (3) The method for producing a precisely-oriented polycrystalline hexagonal zinc oxide sintered body according to any one of 1 to 5, wherein the molded body is sintered at 1000 to 1500 ° C.

  According to the present invention, the a-axis or c-axis is oriented in a predetermined direction, and the c-axis or a-axis is in-plane oriented in a direction perpendicular to the a-axis or c-axis oriented in the predetermined direction. It is possible to manufacture a precisely oriented polycrystalline ceramic sintered body having an arbitrary shape having a performance close to that in a short time at a low cost. In order to obtain a single crystal ceramic, it is necessary to complete the crystal over a long period of time at a high temperature, such as by melting and growing. However, the present invention provides a crystal similar to the single crystal ceramic through a low temperature and a short process. This is the first production of a bulk-oriented, precisely-oriented polycrystalline ceramic sintered body having a structure and nearly the same performance, and its practical value is extremely high.

  In the present invention, (1) non-ferromagnetic ceramic crystal particles are dispersed in a solvent, (2) a rotating magnetic field is applied to the resulting slurry to orient the non-ferromagnetic particles, and (3) drying (4) By sintering the obtained molded body in an oxygen-containing atmosphere, the a-axis or c-axis is oriented in a predetermined direction, and the c-axis or a-axis is the predetermined Finely-oriented polycrystalline ceramics sintered with in-plane orientation in the direction perpendicular to the a-axis or c-axis oriented in the direction and a degree of orientation of 5 to 99%, that is, a Lotgering factor of 0.05 to 0.99 Manufacture the body.

The Lotgering factor f is calculated by the following equation (1) using the peak intensity of the X-ray diffracted from the target crystal plane.
f = (ρ−ρ ₀ ) / (1−ρ ₀ ) (1)
Here, ρ ₀ is calculated by using the X-ray diffraction intensity (I ₀ ) of the non-oriented sample, and in the case of c-axis orientation, the (00l) plane (all perpendicular to the c-axis) with respect to the sum of all diffraction intensities. The total ratio of the diffraction intensity of (surface) is obtained by the following equation (2).
ρ ₀ = ΣI ₀ (00l) / ΣI ₀ (hkl) (2)
ρ is calculated using the X-ray diffraction intensity (I) of the orientation sample. In the case of c-axis orientation, the above equation (2) is used as the ratio of the total diffraction intensity of the (00l) plane to the sum of the total diffraction intensities. Similarly to the above, it is obtained by the following equation (3).
ρ = ΣI (00l) / ΣI (hkl) (3)
In the case of a-axis orientation, the (h00) plane is the target, and in the c-axis orientation, it is (00l).

FIG. 1 is a schematic view (plan view) showing an example of a rotating device in a magnetic field used when producing a precisely oriented polycrystalline ceramic formed body (formed body before sintering) of the present invention.
The device 1 controls a rotation unit 3 having a mold (not shown) for accommodating slurry between a pair of superconducting magnets 2 and 2, a motor 4 for driving the rotation unit 3, and rotation of the rotation unit 3. The rotation control device 5 is provided. The rotating part 3 and the part connected thereto are made of a nonmagnetic material such as glass, plastic such as brass or Teflon (registered trademark) so as not to be affected by a high magnetic field.
A slurry in which non-ferromagnetic ceramic crystal particles are dispersed in a solvent such as water is poured into the mold of the rotating unit 3 of the apparatus 1 and the slurry is dried while rotating the rotating unit 3 horizontally in a magnetic field. Thus, a molded body oriented in two axial directions can be obtained. By sintering this molded body in an oxygen-containing atmosphere, the degree of orientation of the molded body is improved, and a desired precisely-oriented polycrystalline ceramic sintered body can be obtained.
In this apparatus, the coiled superconducting magnets 2 and 2 are fixed and the mold for containing the slurry is rotated. However, the mold for storing the slurry is fixed and the superconducting magnet can be rotated around the fixed mold. By installing, it can also be configured to apply a rotating magnetic field.

Examples of the non-ferromagnetic ceramic crystal particles used as a raw material for producing a precisely oriented polycrystalline ceramic sintered body in the present invention include lithium niobate, potassium niobate, lithium tantalate, aluminum nitride, and lead zirconate titanate. Examples include materials, bismuth-based layered structural materials, zinc oxide, silicon nitride, titanium dioxide, tin oxide, aluminum oxide (alumina), zirconia, and hydroxide apatite. These should be used alone or in combination of two or more. Can do. The ceramic crystal particles have an average particle size of about 5 nm to 20 μm, preferably about 10 nm to 5 μm, particularly preferably about 0.2 to 5 μm, an aspect ratio of about 1 to 5, preferably about 2 to 3, and a specific surface area. Is usually about 1.0 to 15 m ² / g. When the particle size of the ceramic particles becomes small, the particle orientation becomes difficult due to thermal disturbance or the like.
Particularly preferable ceramic crystal particles include hexagonal zinc oxide particles, aluminum oxide particles, silicon nitride particles, and KSr ₂ Nb ₅ O ₁₅ particles having an average particle diameter of 10 nm to 5 μm.

As the solvent for dispersing the ceramic crystal particles, water, an alcohol such as ethanol, an organic solvent such as ether, toluene, or methyl ethyl ketone, or a mixed solvent in which these are appropriately mixed is used. In addition, when an aqueous solvent is used as a solvent when forming a slurry, a known dispersant such as ammonium polyacrylate, ammonium polycarboxylate, ammonium citrate, or amine dispersant can be used. When a solvent is used, a polyethyleneimine dispersant can be used.
The content of the ceramic crystal particles in the slurry can be appropriately selected according to the type, particle size, etc. of the particles. Usually, the solid content in the slurry is 10 to 50% by volume, particularly 30 to 50% by volume. It is preferable to set the degree.

  A rotating magnetic field of 1 T (tesla) or more, usually about 1 to 10 T, is applied to the slurry, and a superconducting magnet is suitably used to generate such a high magnetic field. By continuously applying a rotating magnetic field, both the a-axis and the c-axis of the ceramic crystal particles are oriented, and then dried and solidified to produce a compact. By firing the obtained molded body in an oxygen-containing atmosphere, a precisely oriented polycrystalline ceramic sintered body in which orientation is promoted can be obtained.

Hereinafter, based on FIGS. 2 to 4, taking as an example the case of producing a precisely oriented polycrystalline ceramic sintered body from a slurry in which zinc oxide particles are dispersed in a solvent, the precisely oriented polycrystalline ceramic sintered body of the present invention, This will be described in detail.
FIG. 2 is a schematic diagram showing a fine particle structure of a molded body described in Patent Documents 1 to 3 shown above and obtained by orienting zinc oxide particles in a conventional static magnetic field. Before applying the static magnetic field, the zinc oxide particles are uniformly dispersed in the slurry and the direction of the crystal axis is random (FIG. 2A). When a magnetic field is applied, the c-axis having a high magnetic susceptibility is perpendicular to the magnetic field direction in the zinc oxide particles, and as a result, the a-axis having a low magnetic susceptibility is aligned with the magnetic field direction (FIG. 2B). When the dried and solidified molded body is sintered, a ceramic sintered body uniaxially oriented in the a-axis direction is obtained. In this sintered body, the c-axis is oriented in the direction perpendicular to the magnetic field, but the in-plane direction is obtained. Are random and have a fine structure as shown in FIG. 4A.

  FIG. 3 is a schematic diagram showing a microstructure of a molded body obtained by orienting zinc oxide particles in a rotating magnetic field according to the present invention, where A is a state before applying the magnetic field, and B is simply a magnetic field (static magnetic field). ) Is applied, C is the state immediately after rotating the container containing the slurry while applying the magnetic field, and D is the state in which the application of the rotating magnetic field is continued to obtain a precisely oriented ceramic compact.

  According to the present invention, by first applying a static magnetic field, the c-axis having a high magnetic susceptibility becomes perpendicular to the magnetic field direction, and as a result, the a-axis having a low magnetic susceptibility is aligned with the magnetic field direction (FIG. 3B). Next, by rotating the container and applying a rotating magnetic field to the slurry, as seen in FIGS. 3C to 3D, the c-axis having a large magnetic susceptibility always faces in a direction perpendicular to the magnetic field, and the directions of the c-axis are also aligned. . When the dried and solidified shaped body is sintered, a finely oriented polycrystalline ceramic sintered body oriented in two directions of the a-axis direction and the c-axis direction as shown in FIG. 4B is obtained. This sintered body has a crystal structure similar to that of single crystal ceramics. By controlling the direction in which a magnetic field is applied, the c-axis of the ceramic sintered body is oriented in a predetermined direction, and the a-axis is c-axis. In-plane orientation in a direction perpendicular to the surface. For example, zinc oxide is a hexagonal crystal and a material having excellent piezoelectric characteristics in the c-axis direction, but according to the present invention, it is biaxially oriented in the c-axis direction and the a-axis direction, and has a bulk shape similar to single crystal ceramics. It became possible for the first time to produce a precisely oriented polycrystalline sintered body. This polycrystalline sintered body can be manufactured in a short time and at a low cost, and can be widely applied to electronic devices and optical functional materials by utilizing its piezoelectric characteristics.

When aluminum oxide particles are used instead of zinc oxide particles, it is possible to obtain a precisely oriented polycrystalline sintered body in which the a axis is oriented in a predetermined direction and the c axis is in-plane oriented in a direction perpendicular to the a axis. it can. When silicon nitride particles or KSr ₂ Nb ₅ O ₁₅ particles are used, the c-axis is oriented in a predetermined direction and the a-axis is in-plane oriented in the direction perpendicular to the c-axis, as with the zinc oxide particles. A precisely oriented polycrystalline sintered body can be obtained.

EXAMPLES Next, the present invention will be further described with reference to examples, but the following specific examples are not intended to limit the present invention.
Example 1
Plate-like zinc oxide particles having a particle size of 0.4 to 0.6 μm were dispersed in water using ammonium polyacrylate as a dispersant to prepare a slurry having a solid content of 30% by volume. The viscosity of the slurry was adjusted to 10 to 200 (mPa · s) at a shear rate of 10 (l / s).
Using the apparatus of FIG. 1, 5 mL of this slurry is poured into a 30 mm diameter Teflon (registered trademark) mold provided in the rotating unit 3, and the rotating unit is rotated at a rotation speed of 0.5 Hz, while a superconducting magnet is used. While applying a magnetic field of 2 or 2 to 10 T, it was dried at 25 ° C. for 1 day to obtain a zinc oxide molded body.
The obtained zinc oxide molded body is taken out of the mold, pre-sintered at 1100 ° C. for 1 hour in the air, and then sintered at 1300 ° C. for 2 hours in the air atmosphere to obtain a polycrystalline zinc oxide sintered body. It was. The XRD diffraction pattern of the 1300 ° C. sintered body is shown in FIG.

(Comparative Example 1)
In Example 1 above, except that the rotating part 3 of the device 1 was not rotated and a static magnetic field was simply applied, molding was performed in the same manner as in Example 1, and pre-sintering and sintering at 1300 ° C. were similarly performed. The XRD diffraction pattern of the joined body is shown in FIG.

(Comparative Example 2)
In Example 1 above, except that no magnetic field was applied, the XRD diffraction pattern of the sintered body formed in the same manner as in Example 1 and preliminarily sintered and sintered at 1300 ° C. is shown in FIG. It was shown to.

In the sintered body sintered after forming by applying the static magnetic field of Comparative Example 1, the peaks of the (100) plane and the (110) plane appear in the magnetic field direction, and the a-axis is directed to the magnetic field. [FIG. 5 (b)].
On the other hand, the (002) plane peak appears in the sintered body sintered after forming by applying the rotating magnetic field of the present invention. [FIG. 5A]. From this result, it was found that the zinc oxide sintered body obtained by the present invention has an a-axis orientation structure in the magnetic field direction and a c-axis orientation structure perpendicular to the magnetic field and in the rotation axis direction.

(Evaluation by the Lotgering method)
The crystal structure of the zinc oxide compact before presintering obtained in Example 1 and the presintered 1100 ° C. sintered body were also examined by XRD, and the degree of crystal orientation was measured together with the 1300 ° C. sintered body by the Lotgering method. The evaluation results are shown in FIG.
The Lotgering factor is an index representing how much the peak intensity of the target surface with respect to the sum of all peak intensities changes with respect to the non-oriented sample in the oriented sample. It becomes 1 in the orientation. Even if this factor is 0.1, a clear difference is observed in the diffraction pattern, but if it is 0.5 or more, it can be regarded as a sample with very high orientation. In this evaluation, since the C plane is the object, the evaluation was performed based on the peak intensity of (002) and (004).
According to FIG. 6, although it is oriented to some extent even before pre-sintering, the degree of orientation increases as the sintering temperature increases. Turned out to be. As described above, the crystal structure of the formed body oriented by applying the rotating magnetic field was maintained even during the sintering, and the degree of orientation was further promoted by the sintering. This is due to particle growth during sintering, and small particles that are difficult to orient during molding are taken into large particles that are easily orientated.

( Reference Example 1 )
Using aluminum oxide (alumina) particles with a particle size of 0.4 to 0.6 μm as raw materials, using ammonium polyacrylate as a dispersant, dispersing in water to prepare a slurry with a solid content of 30% by volume did. The slurry was prepared such that the viscosity was 10 (mPa · s) at a shear rate of 10 (1 / s).
Using the apparatus of FIG. 1, this slurry was dried at 25 ° C. for 1 day in the same procedure as in Example 1 while applying a magnetic field of 10 T to obtain an alumina molded body. The obtained alumina molded body was taken out of the mold and sintered at a temperature of 1600 ° C. for 2 hours in an air atmosphere to obtain a polycrystalline alumina sintered body.
The XRD diffraction pattern of this sintered body is shown in the upper part of FIG. The lower diagram of FIG. 7 is an XRD diffraction pattern of a sintered body that was formed without applying a rotating magnetic field and then sintered at 1600 ° C. for comparison. By rotating magnetic field shaping, the (300) peak increased, and it was revealed that it was oriented in the a-axis. FIG. 8 shows the degree of orientation (Lottgering factor) at the stage where the sintering temperature is raised to 1200 to 1600 ° C. It became clear that the degree of orientation increased with increasing sintering temperature, and the grain orientation structure became more prominent.

( Reference Example 2 )
As raw materials, silicon nitride (Si ₃ N ₄ ) particles having a particle size of 0.4 to 0.6 μm are used, and dispersed in water using ammonium polyacrylate as a dispersant. The solid content is 30% by volume. A slurry was prepared. The slurry was prepared such that the viscosity was 10 (mPa · s) at a shear rate of 10 (1 / s).
Using the apparatus of FIG. 1, this slurry was dried at 25 ° C. for 1 day while applying a magnetic field of 10 T in the same procedure as in Example 1 to obtain a silicon nitride molded body. The XRD diffraction pattern of the obtained silicon nitride molded body is shown in FIG. In FIG. 9, the uppermost figure is produced with a rotating magnetic field, and the (002) peak is slightly higher, indicating that the c-axis is oriented in a predetermined direction. In addition, the peak of (101) including the c-axis is also high. There are many a-axes in the direction perpendicular to the rotation axis, and the c-axis does not appear much. If this molded body is sintered at a temperature of 1800 ° C. or higher under oxygen-free conditions, the orientation structure is considered to become more remarkable.
The center diagram of FIG. 9 is measured with the XRD measurement surface perpendicular to the above diagram. Further, the lower diagram of FIG. 9 is an XRD diffraction pattern of a molded body produced without applying a rotating magnetic field for comparison.
Nitrogen silicon does not contribute to the improvement of mechanical properties because the a-axis is parallel to the magnetic field direction in a conventional static magnetic field. As in the present invention, the mechanical characteristics are expected to be improved by aligning the c-axis.

( Reference Example 3 )
As a raw material, KSr ₂ Nb ₅ O ₁₅ (KSN) having a particle size of 0.4 to 0.6 μm was used after solid-phase synthesis. The particles were dispersed in water using ammonium polyacrylate as a dispersant to prepare a slurry having a solid content of 30% by volume. The slurry was prepared such that the viscosity was 10 (mPa · s) at a shear rate of 10 (1 / s).
Using the apparatus of FIG. 1, this slurry was dried at 25 ° C. for 1 day in the same procedure as in Example 1 while applying a magnetic field of 10 T to obtain a KSN compact. The obtained KSN compact was removed from the mold and sintered in the air at a temperature of 1300 ° C. for 2 hours to obtain a polycrystalline KSN sintered compact.
An XRD diffraction pattern of this sintered body is shown in the upper part of FIG. In addition, the lower figure of FIG. 10 is an XRD diffraction pattern of a molded body produced without applying a rotating magnetic field for comparison. It has been clarified that the c-axis peaks of (001) and (002) are increased by rotating magnetic field shaping. FIG. 11 shows the degree of orientation (Lottgering factor) at the stage where the sintering temperature is raised to 700 to 1300 ° C. It became clear that the degree of orientation increased with increasing sintering temperature, and the grain orientation structure became more prominent.

According to the present invention, it is possible to produce precisely oriented ceramics from various non-ferromagnetic ceramic crystal particles such as zinc oxide, alumina, silicon nitride, metal niobate, and the like. In other words, since various non-ferromagnetic ceramic crystal particles can be used as raw materials, it is possible to produce ceramics that are polycrystalline but have a structure close to a single crystal, so that it is possible to develop piezoelectric elements having various characteristics. Become.
Although the strength of the magnetic field used in each of the above examples is 10 Tesla, the strength of the magnetic field can be appropriately selected. Since it is better in terms of cost to reduce the strength of the magnetic field, it seems better to reduce it to about 5 Tesla industrially.

It is a figure which shows an example of the apparatus used for manufacture of a precisely oriented polycrystalline ceramic molded object (molded object before sintering) by this invention. It is a schematic diagram which shows the fine structure of the molded object which orientated the zinc oxide particle in the conventional static magnetic field. It is a schematic diagram which shows the fine structure of the molded object which orientated the zinc oxide particle in the rotating magnetic field of this invention. It is a schematic diagram which shows the crystal structure of the sintered compact which sintered the molded object of FIG.2 and FIG.3. It is a XRD diffraction pattern of the sintered compact obtained in Example 1 and Comparative Examples 1 and 2. It is a figure which shows the result of having evaluated the sintered compact obtained in Example 1 by the Lotgering method. 3 is an XRD diffraction pattern of a sintered body obtained in Reference Example 1 . It is a figure which shows the result of having evaluated the sintered compact obtained in Reference Example 1 by the Lotgering method. 4 is an XRD diffraction pattern of a molded body obtained in Reference Example 2 . 4 is an XRD diffraction pattern of a sintered body obtained in Reference Example 3 . It is a figure which shows the result of having evaluated the sintered compact obtained in Reference Example 3 by the Lotgering method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotating device in magnetic field 2 Superconducting magnet 3 Rotating part 4 Motor 5 Rotation control device

Claims (6)

(1) Hexagonal zinc oxide crystal particles having an average particle diameter of 10 nm to 5 μm are dispersed in a solvent, (2) a rotating magnetic field is applied to the resulting slurry to orient the crystal particles, and (3) drying (4) The obtained molded body is sintered in an oxygen-containing atmosphere, and the a-axis or c-axis is oriented in a predetermined direction, and the c-axis or a-axis There were plane orientation in the a-axis or c-axis perpendicular direction oriented in the predetermined direction, fine orientation polycrystalline orientation of the c axis, characterized in that a 0.05 to 0.99 Lotgering factor A method for producing a hexagonal zinc oxide sintered body. The precisely-oriented polycrystalline hexagonal zinc oxide sintered body has diffraction peaks (002) and (004) in X-ray diffraction, and has a degree of orientation of 0.2 or more in terms of Lotgering factor. The method for producing a precisely oriented polycrystalline hexagonal zinc oxide sintered body according to claim 1, wherein: (2) The precision according to claim 1 or 2, wherein the slurry is accommodated in a horizontally rotatable container, and crystal grains are oriented by applying a magnetic field in a state where the container is horizontally rotated. A method for producing an oriented polycrystalline hexagonal zinc oxide sintered body. (1) The precision orientation according to any one of claims 1 to 3, wherein the hexagonal zinc oxide crystal particles are dispersed in a solvent so that a solid content in the slurry is 10 to 50% by volume. A method for producing a polycrystalline hexagonal zinc oxide sintered body. (2) The method for producing a precisely oriented polycrystalline hexagonal zinc oxide sintered body according to any one of claims 1 to 4, wherein a magnetic field of 1 T or more is applied to the slurry. (3) The method for producing a precisely-oriented polycrystalline hexagonal zinc oxide sintered body according to any one of claims 1 to 5, wherein the compact is sintered at 1000 to 1500 ° C.

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