JPH02167868A - Cellular ceramics, dried body for producing the same and production thereof - Google Patents

Abstract

PURPOSE:To obtain ceramics, having macropores of a uniform specific diameter and three-dimensional communicating pores and excellent in strength and cutting properties by thickening or gelatinizing a slurry or fluid gel containing ceramic raw material powder, a high polymer substance and bubbles and holding the pores therein. CONSTITUTION:The above-mentioned cellular ceramics have macropores of 20-2000mu pore diameter and three-dimensional communicating pores consisting of interstices between particles. The afore-mentioned ceramics are produced by mixing ceramic raw material powder with a dispersion or fluid gel of a high polymer substance, stirring the resultant mixture, including air therein, providing a slurry containing spherical bubbles, casting the slurry, thickening or gelatinizing the slurry, holding the bubbles, drying the obtained slurry to afford a high-strength dried body having spherical macropores without causing cracking, etc., due to nearly isotropic shrinkage, as necessary, forming and processing the dried body and then calcining the resultant compact.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Application" The present invention relates to porous ceramics, dried bodies for producing the porous ceramics, and methods for producing them.

"Prior art and its problems" As a method for producing porous ceramics by a wet method,
Conventionally, foaming methods and methods of adding pyrolyzable beads are known. Among these, the foaming method is a method in which a foaming agent such as hydrogen peroxide solution is added to a slurry of ceramic raw material powder, and the slurry is dried and foamed to make it porous, but it is difficult to control the pore size and porosity. There was a problem. On the other hand,
The method of adding pyrolyzable beads is to knead the slurry and beads of organic polymeric material, form a bottom shape, and then burn out the polymeric material by heating to make it porous. However, since the beads do not shrink during drying, distortion occurs, and since a large amount of beads are used, there are problems in that degreasing is difficult.

``Object of the Invention'' The present invention provides a porous ceramic having uniform macropores and three-dimensionally communicating micropores, and having excellent strength and machinability, and a porous ceramic that does not cause cracking or the like in the drying process. The purpose is to provide a method that can be manufactured without any problems.

"Structure of the Invention" The porous ceramic according to the present invention has a pore diameter of 20 to 200.
It has macropores of 0 μm and three-dimensional communicating pores consisting of particle gaps.

The dried body for producing porous ceramics according to the present invention is obtained by casting a slurry or fluid gel containing ceramic raw material powder, a polymeric substance, and air bubbles, thickening or gelling it to retain air bubbles, and drying it. It is characterized by being obtained by

In addition, the method for producing a dry body according to the present invention includes casting a slurry or fluid gel containing ceramic raw material powder, a polymeric substance, and air bubbles, thickening or gelling it to retain air bubbles,
Characterized by drying.

According to the present invention, the porous ceramic of the present invention can be manufactured by molding the dried body as required and then firing it.

In the method of the present invention, the surface of the spherical secondary particles having an average particle size of about 10 to 100 μm obtained by spray heat drying is further polished by a suitable means such as a jet mill, that is, the particle size is about 0.1 to 2 μm. It is preferable to use the powder by pulverizing it to such an extent that 1 to 10%, preferably 3 to 7%, of amorphous fine powder is generated, or by adding raw material powder in a fine powder state. In this case, Since the fine powder acts as a binder between the granulated secondary particles, ceramics with higher strength can be obtained. When fine powder is added, it is sufficient to add 1 to 10% by weight of -a, preferably 3 to 7% by weight.

In the method of the present invention, the granular powder of the ceramic raw material thus prepared is mixed with a dispersion liquid or fluid gel of a polymeric substance.

As used herein, the term "dispersion" of a polymeric substance is meant to include true solutions, colloidal solutions, and suspensions of the polymeric substance.

When a dispersion of a certain type of polymeric substance, such as methylcellulose, is heated, its viscosity increases as the temperature rises, and it reversibly gels at a certain temperature. Furthermore, some materials, such as polyvinyl alcohol, reversibly gel when some additive is added, such as boric acid or borax. In any case, in the method of the present invention, the ceramic raw material is mixed with the granular powder in the state of a dispersion before gelling or a fluid gel having fluidity before completely gelling and solidifying. conduct.

When granular powder of a ceramic raw material is mixed with such a dispersion or fluid gel of a polymeric substance and stirred to incorporate air, a slurry containing spherical air bubbles is obtained. When this is poured into a mold, gelled to retain air bubbles, and dried, it contracts almost isotropically, resulting in a highly strong dried product with spherical macropores without cracking.

In addition, in the case of polymeric substances that do not form gels, the dispersion liquid is mixed with granular powder of the ceramic raw material, air bubbles are incorporated into the dispersion liquid by stirring, the mixture is poured into a mold, and the mixture is thickened. When dried, a dried product similar to the above can be obtained.

Furthermore, in the method of the present invention, the dispersion or fluid gel of the polymer substance may be stirred in advance to incorporate air, and then mixed with the granular powder of the ceramic raw material. After mixing the polymeric substance and the granular powder of the ceramic raw material, a dispersion medium may be added to form a slurry, and the slurry may be stirred to incorporate air.

The polymeric substance used in the method of the present invention is preferably water-soluble because water is used as a dispersion medium for the granular powder of the ceramic raw material, but when other dispersion medium is used. may be dissolved in the dispersion medium. Examples of polymeric substances that can be used include cellulose derivatives such as methylcellulose and carboxymethylcellulose, and multi-IJ! I, synthetic polymers such as polyvinyl alcohol, polyacrylic acid, polyacrylamide, and polyvinylpyrrolidone.

The amount of the polymeric substance blended varies depending on the type of polymeric substance used, but usually 0% is added to the slurry or fluid gel.
．． It is preferable to mix it so that it contains 1 to 10% of double stars. More specifically, in the case of methylcellulose, 0.2
~2% by weight, preferably 0.5-1% by weight, and in the case of polyvinyl alcohol, preferably 5-10ml%. If there is too much polymeric material, a degreasing step will be required before firing and sinterability will also deteriorate. Moreover, if it is too small, air bubbles in the slurry will not be retained.

The porous dried body produced by the method of the present invention is in a state in which ceramic particles are glued together with a polymer substance, and therefore has strength to withstand cutting. Therefore, in the method of the present invention, the dry product can be cut without performing temporary firing.

When carrying out the method of the present invention, especially when casting is performed using a mold whose inner wall is covered with a flexible water-resistant film, the film peels off from the mold as the ceramic shrinks during drying. Therefore, an excellent dried product can be obtained without causing the ceramic to crumble on the surface in contact with the mold or crack inside.

Further, the size and amount of air bubbles contained in the fluid gel or slurry can be controlled by stirring, and can be easily adjusted to a pore size of 3 nun or less.

The shaped rod obtained by processing the dried body can be fired as it is. In addition to the spherical macropores formed by the above-mentioned air bubbles, the sintered body contains three-dimensionally communicating micropores formed by the gaps between the raw material particles.

In addition, macropores made of air bubbles (enclosed air) are independent pores with a porosity of less than 40% and do not have continuity, but micropores are continuous pores, so low viscosity liquids can pass through them slowly. .

When the porosity is 40% or more, the macropores become communicating pores.

The method of the present invention can be applied to various types of ceramics such as calcium phosphate, alumina, silica, and zirconia, as well as artificial biomaterials, liquid chromatography packing materials, single catalysts, and various electrical - Can be applied to the manufacture of various products such as electronic materials, nuclear reactor materials, and ceramic heating elements.

"Examples of the Invention" Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Put 150 g of water into a 500 ml beaker and add methyl cellulose (hereinafter referred to as MC, manufactured by Wako Pure Chemical Industries, Ltd., molecular weight: 2% aqueous solution with a viscosity of 4000 c measured at 20'C).
ps) 2.7 g was added and stirred for 3 minutes with a Hunt mixer to prepare an aqueous solution of methylcellulose. Place this beaker in a constant temperature bath at 60"C and heat it at 40°C while stirring.
The mixture was heated to C and further stirred for 30 seconds to form a fluid gel containing air bubbles.

On the other hand, a hydroxyapatite slurry produced by a known wet synthesis method was granulated to an average particle size of 12 μm by spray drying, and further pulverized with a jet mill to obtain spherical powder with an average particle size of 10 μm and a spherical powder with an average particle size of 1 μm. Hydroxyapatite powder consisting of fine powder was prepared.

The beaker was taken out of the thermostatic bath, 50 g of the prepared granular hydroxyabatai was gradually mixed little by little, the viscosity was measured, and the mixture was poured into a 200 ml glass beaker. Place this beaker in a dryer at 90°C for 24 hours to gel and dry it, then use a hand saw to
It was cut into a rectangular parallelepiped of 30 x 10.4 mm, and fired in the following firing pattern.

The temperature was raised from room temperature to 600'C at a heating rate of 50'C/hour, then the temperature was raised to 1200°C at a heating rate of 100'C/hour, and after baking at this temperature for 4 hours, It was cooled to 600°C at a cooling rate of °C/hour, held at this temperature for 4 hours, and then cooled to room temperature at a cooling rate of 100°C/hour.The dimensions of the obtained sintered body were 28.5 x 20. 5 X
It was 7.1 mta.

In this experiment, the methylcellulose aqueous solution was heated to 45°C.
Drying and firing were carried out in exactly the same manner except for those heated to 50°C and those heated to 50°C to produce sintered bodies. Methylcellulose aqueous solution at 45°C
The dimensions of the dry rectangular parallelepiped obtained when the temperature was raised to . The dimensions of the dry rectangular parallelepiped obtained when a methylcellulose aqueous solution was heated to 50°C were 44.7
30.3 x 10.4, the dimensions of the sintered body are 30. I
It was 20.9 x 7.2 wm.

The porosity and three-point bending strength of the obtained sintered body were measured, and the results are shown in Table 1 below.

Table 1 Example 2 450 g of water and 8.1 g of the same MC used in Example 1 were placed in a 1000 Id beaker and stirred with a hand mixer to sufficiently dissolve the MC and foam it. When it became meringue-like, 50g of the hydroxyapatite powder prepared in Example 1 was added and mixed well.The slurry was poured into four 200ml beakers and placed in a dryer at 90°C for 3 hours. The slurry was gelled. Furthermore, it was dried in a dryer for 48 hours. After drying, the same operation as in Example 1 was added to obtain 44.6 x 2
30. IX
20. A sintered body of I x7.2 am was obtained. The porosity and three-point bending strength of this sintered body were measured.

Average porosity is 57.2%, average bending strength is 44.2kg
/ cIa.

Example 3 Carboxymethyl cellulose (Serva Peinb)
Manufactured by io-chemica GmbH & Co, hereinafter C
(denoted as MC) and 100 g of spherical powder of partially stabilized zirconia with 3 mol% ittria were mixed well, and 1 g of water was added.
Add 00g and stir well with a hand mixer to make a slurry of zirconia ceramics containing air bubbles.
The mixture was poured into a plastic beaker and placed in a dryer at 90°C for 24 hours to thicken and dry. 4. Dried body using hand saw
Cut into a rectangular parallelepiped of 4.6 x 30.6 x 8.7 mm, raise the temperature to 1550°C at a heating rate of 300''C/min, hold for 2 hours, and then lower to room temperature at a rate of 200°C/min. The porosity and 3-point bending strength were measured by firing method.

The obtained ceramic is a porous body with a continuous structure, and its average porosity is 43.8. %, average bending strength is 688
kg/cj. The dimensions of the sintered body are 30.6X21X
It was 6.1m.

Example 4 Polyvinyl alcohol (manufactured by Wako Pure Chemical Industries, Ltd., polymerization degree 20)
00, hereinafter referred to as PVA) and 100 g of a 5% aqueous solution of boric acid are placed in separate containers and heated in an 80°C water bath. When both reach a temperature of 70°C or higher, mix while stirring. and cooled while stirring. When the solution became a fluid gel containing air bubbles and became slightly cloudy, stirring was stopped and the mixture was mixed with 120 g of the hydroxyapatite powder prepared in Example 1. The mixture was placed in a 300 ml beaker and placed in a dryer at 50°C for 24 hours. After drying for several hours to form a gel, dry it in a dryer at 90°C for another 24 hours.
46. A dry rectangular parallelepiped measuring I x 31.5 x 11.7 m was prepared and processed, degreased, and fired in the same manner as in Example 1, and the average porosity was 54.1% and the average bending strength was 41 kg/a.
A porous body with spherical pores was obtained. The dimensions of this sintered body were 32.2 x 22.7 x 7.8 ml.

Example 5 A hydroxyapatite slurry synthesized by a wet method was granulated to an average particle size of 12 μm by spray drying. A part of the spherical hydroxyapatite powder thus obtained was ground in a ball mill to produce a fine powder with an average particle size of 1 μm.

2 g of MC was added to 150 g of water and stirred to dissolve and form an aqueous solution containing bubbles. 45 g of the above powder having an average particle size of 12 μm and 5 g of fine powder were added to this and mixed well.

The mixture was poured into a 300 ml beaker to gel, and then placed in a dryer at 80°C for 36 hours to gel and dry. Obtained 4 4.8 x 29.9 x 10.3
A dry rectangular parallelepiped of 30 mm in diameter was prepared in the same manner as in Example 1.
A sintered body measuring 5×20.4×7.3 m was obtained.

This sintered body had an average porosity of 57.2% and an average bending strength of 48.2 kg/c4.

Example 6 1.5 g of methylcellulose was dissolved in 100 g of water,
Whisk with a hand mixer, separate 3 mol% solid solution partially stabilized zirconia of Ittria prepared by coprecipitation method into 9 parts, add 50 g of the dried powder, stir further, and mix 200 m
ft glass beaker, placed in a dryer at 80''C for 24 hours to gel and dry, processed and burned under the same conditions as Example 3, porosity 58.2%, average bending strength 32
Porous zirconia ceramics weighing 1.7 kg/c+fl was obtained.

"Effects of the Invention" The porous ceramics according to the present invention have uniform macropores and three-dimensional communicating pores, and have excellent strength and machinability, and can be used as artificial biomaterials, fillers for liquid chromatography, catalyst supports, etc. It is useful as a material for a variety of products, including electrical and electronic materials, nuclear reactor materials, and ceramic heating elements.

According to the method of the present invention, shrinkage during drying proceeds almost isotropically, so porous ceramics can be easily produced without cracking or the like occurring during the drying process.

In addition, in the method of the present invention, the size and amount of bubbles contained in the fluid gel or slurry can be controlled by stirring, and can be easily aligned to macropores with a pore diameter of 3 mm or less, for example. Comparatively with macropores with a pore diameter of 1 mm or less? ! 1. You can create objects with rough shapes.

Furthermore, since the dried body is in a state in which ceramic particles are glued together with a polymer substance, it has strength to withstand cutting, and can be cut as it is without pre-firing.

In the present invention, ceramics with even higher strength can be obtained by allowing the fine powder to exist together with the secondary particles of the ceramic raw material powder.

Patent applicant: Asahi Optical Industry Co., Ltd.

Claims (1)

[Claims] 1. A porous ceramic having macropores with a pore diameter of 20 to 2000 μm and three-dimensional communicating pores consisting of interparticle gaps. 2. A porous ceramic characterized by being obtained by casting a slurry or fluid gel containing ceramic raw material powder, a polymeric substance, and air bubbles, thickening or gelling it to retain air bubbles, and drying it. Dry body for manufacturing. 3. Drying for producing porous ceramics according to claim 2, wherein the polymeric substance is a cellulose derivative such as methylcellulose, a polysaccharide such as curdlan, a synthetic polymer such as polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyvinylpyrrolidone, etc. body. 4. The polymer substance is present in the slurry or fluid gel from 0.1 to
The dry body for producing porous ceramics according to claim 2 or 3, which is blended to contain 10% by weight. 5. Dry product for producing porous ceramics, characterized in that a slurry or fluid gel containing ceramic raw material powder, a polymeric substance, and air bubbles is cast, thickened or gelled to retain air bubbles, and dried. manufacturing method. 6. A method for producing porous ceramics, which comprises firing the dried body for producing porous ceramics according to claim 2, 3, or 4, after shaping the dried body as required.