JPH03257081A - Production of porous ceramics - Google Patents

Abstract

PURPOSE:To obtain the porous ceramics having desired porosity and pore distribution by nonuniformly forming a slurry contg. a ceramic core material coated with a ceramic powder and a ceramic grain and calcining the formed body. CONSTITUTION:A ceramic powder 2 (e.g. alumina) is deposited on the surface of a core material 1 consisting of a globular combustible material (e.g. graphite) to obtain a composite grain 3. The composite grain 3 and a granular ceramic grain 6 are suspended in a dispersion medium such as an aq. 2.5% PVA soln., the obtained slurry 4 is poured into a casting mold 5 of gypsum, etc., having high liq. absorptivity and cast to obtain a nonuniform cast body 7 in which there are many composite grains 3 in the lower layer and the ceramic grains 6 are progressively increased toward the upper layer. The cast body 7 is dried, calcined to burn off the core material 1 and then sintered to sinter the ceramic grain 6 to obtain a porous ceramics 9 having many pores 8 in its lower layer.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing porous ceramics, and in particular, a method for manufacturing porous ceramics, in which porous ceramics having a dense portion and a porous portion are formed into an arbitrary shape and a desired porosity. The present invention relates to a method for manufacturing porous ceramics that can be easily and efficiently manufactured to have a pore distribution.

[Prior art] In recent years, silicon nitride and carbon (1jI) have been used as high-temperature, high-strength structural materials.
So-called new ceramics, such as non-oxide ceramics such as lK and '+ iron, or aluminum oxide and zirconium oxide, are rapidly attracting attention, and much research and development is being carried out. These ceramics have many uses as gas turbine blades and combustors, diesel engine cylinders and pistons, and other high-temperature mechanical parts.

Among ceramics, porous ceramics have insulation properties,
It is expected to be used in a wide range of applications because it has excellent properties such as sound absorption and light weight. Porous ceramics are usually produced using a mixing method in which ceramic powder is pressed to a low density and then fired, or a volatile or flammable substance is added during molding and then fired, or as in Shirasu, during the firing process. It is manufactured by a method such as a foaming method using foamable materials.

[Problems to be Solved by the Invention] However, although porous ceramics have excellent properties, they have a drawback in that they have poor strength and cannot be used in applications that require high strength.

For this reason, in order to increase the strength, for example, there is a method of adhering dense ceramics to the surface of pre-manufactured porous ceramics, or filling the pores on the surface of porous ceramics by vapor phase deposition, etc. Methods are being considered.

However, the method of bonding dense ceramics to the surface of porous ceramics has problems such as low bonding strength, thermal stress due to the difference in thermal expansion at the bonding interface, and insufficient strength of the bonding layer. may cause peeling or cracking. Furthermore, the method of filling the pores by vapor phase deposition has the disadvantage that it is difficult to completely fill the pores and that the processing time is long.

The present invention solves the above-mentioned problems of the prior art, and enables porous ceramics to be formed into any shape, which has a porous layer and a dense layer, and has almost no cracking caused by thermal stress between the two layers. It is an object of the present invention to provide a method for manufacturing porous ceramics that can be easily and efficiently manufactured to have desired porosity and pore distribution.

[Means for Solving the Problems] The method for producing porous ceramics of the present invention includes composite particles in which a granular material made of a combustible substance is used as a core material, and a ceramic powder is attached to the surface of the core material; A slurry obtained by suspending ceramic particles is formed into a non-uniform top and bottom part using a slurry casting method, and the obtained formed body is fired to burn off the core material and sinter the ceramic. This method is characterized by producing porous ceramics whose porosity changes continuously.

The present invention will be explained in detail below with reference to the drawings.

1 to 344 are schematic cross-sectional views illustrating the manufacturing process of porous ceramics according to an embodiment of the present invention.

In the present invention, first, as shown in FIG. As the core material, granular materials, preferably spherical materials, of substances that oxidize and burn at high temperatures are used. Specifically, oxidizing and combustible substances such as carbon and graphite, and organic polymeric thermoplastics such as polyethylene, polypropylene, and polystyrene are used. Resin granules or granulated resin particles with a suitable combustible binder are used. The particle size of the core material 1 is determined by the pore size of the intended porous portion.

It is preferable to adhere (coat) the ceramic raw material powder 2 to the surface of the core material 1 as uniformly as possible.

Various commonly used coating methods can be used, such as a method in which a ceramic pigment powder solution containing an appropriate binder is applied to the core material in a fluidized bed state by spraying, or a method in which the core material is coated with a ceramic raw material. A suitable method is to immerse the powder in a suspension (or a solution if the substance to be coated is soluble) and then dry it.

Ceramic powders are not particularly limited, and include zirconia,
Various ceramic powders such as alumina, silicon carbide, silicon nitride, sialon, and silica can be used.

Separately, ceramic powder is granulated according to a conventional method to obtain ceramic particles. As the ceramic powder used for granulation, it is advantageous to use one made of the same material as the ceramic powder used for manufacturing the composite particles.

The composite particles and ceramic particles thus obtained are placed in a suitable dispersion medium such as water or a 2.5% aqueous solution of PVA.
Sufficient mixing and agitation is performed to suspend and form a slurry. In this case, if necessary, a binder such as CMC is added in an amount of about 1% by weight based on the total weight of the slurry.

Next, as shown in FIG. 2, the obtained slurry 4 is poured into a casting mold with high liquid absorption properties, such as a plaster mold 5, to perform slurry casting. During molding, while the dispersion medium of the slurry 4 such as water is absorbed into a mold such as a plaster mold 5, the composite particles 3 and ceramic particles 6 in the slurry 4 settle.
At this time, because the rain particles 3.6 have different settling speeds due to the difference in specific gravity, the heavier particles settle first and the lighter particles settle later. When particles 3 are heavier and have a faster sedimentation rate, as shown in Figure 3, there are many composite particles 3 in the lower layer, and ceramic particles 6 gradually increase toward the upper layer, and in the top layer, most of the composite particles 3 are ceramic particles 6. Deposit as desired.

Next, after sufficiently drying the molded body 7 obtained in this way, it is released from the mold, and after further drying, the core material 1 of the composite particles 3 is burned and removed, and the ceramic particles 6 are sintered. Fire. As a procedure for this firing, it is also possible to first perform calcination to burn the core material 1, and then perform main firing to firmly sinter the ceramic particles 6. Sintering and oxidation removal of the core material 1 may be performed simultaneously. Further, after preliminary sintering of the ceramic particles 6 in a non-oxidizing atmosphere, heating is performed in an oxygen-containing atmosphere to oxidize and remove the core material 1, and finally, main sintering is performed in a non-oxidizing atmosphere or an oxygen-containing atmosphere. You can do it.

After firing, as shown in Figure 4, the area where the core material 1 was present becomes pores 8, the lower layer has many pores, that is, the porosity is high, and the porosity decreases as it goes to the upper layer, and the surface of the top layer Porous ceramics 9 having dense layers is obtained.

Note that during firing, the degree of densification of the ceramic portion of the porous ceramic obtained can be improved by applying pressure to the dried molded body using a rubber press or the like and then performing firing treatment.

The example shown in FIGS. 1 to 4 is an embodiment of the present invention,
The present invention is not limited to what is shown in the drawings. For example, casting molds with other irregular shapes can be used, and composite particles and ceramic particles of several sizes and specific gravity can be used to adjust the sedimentation rate of these particles. It is also possible to obtain porous ceramics in which porous layers and dense layers are alternately formed by adjusting the .

[Function] Since a combustible core material is used as a pore-forming material, the desired value can be obtained by changing the grain size of the core material, the thickness of the coating layer of ceramic powder attached to the core material, and the amount of particles added to the slurry. Porous ceramics with pore diameter, porosity, and pore distribution can be easily produced. Furthermore, by adjusting the size and specific gravity of the composite particles and the size and specific gravity of the ceramic particles to adjust the settling speed of each, dense and porous areas can be formed in any location and in any ratio. .

In addition, the ceramic in the dense part and the ceramic in the porous part are continuous and integrated, and the porosity of the formed porous part and dense part does not change suddenly, but continuously. Therefore, cracking or peeling due to thermal stress hardly occurs, and the ceramic portion becomes an extremely dense and high-strength porous ceramic.

Furthermore, since the molding is performed by slurry casting, it is possible to easily mold products with complex irregular shapes.

[Examples] The present invention will be explained in more detail by Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

Example 1 As a core material, commercially available carbon powder was granulated using a fluidized bed method to obtain a granular core material with a particle size of about 200 μm. This core material was coated with ceramic powder (3 mo1% Zr02 containing Y203) using a pan coating device to obtain a particle size of 300μ.
, composite particles with a specific gravity of 1.3 were obtained.

Separately, the same ceramic powder as above was granulated using a spray dryer to obtain ceramic particles having a particle size of 50 μm and a specific gravity of 1.2.

35g of the obtained composite particles and 5g of ceramic particles were placed in a 70m
Pour into J2 water and add 10% CMC as a binder.
10g of aqueous solution was added and thoroughly mixed and stirred. The obtained slurry was poured into a plaster mold as shown in FIG. 2, slurry casting was performed, and the mold was removed after drying.

The obtained molded body was heated to 3000 kg/c rri'
After rubber pressing for 2 minutes, the core material was burned off at 800°C in the atmosphere, and then fired at 1400°C for 5 hours.

As a result, the bulk density of the lower porous portion of the obtained sintered body was 1.7 g/crr? (porosity is approximately 28%), and the pores are uniform independent pores, and the porosity decreases toward the upper layer, and the surface has a bulk density of 5.95 g/crn.
The dense partial force (formed as a continuous unit).

This sintered body was superior in strength to conventional porous bodies by several orders of magnitude, and did not break easily.

[Effects of the Invention] As detailed above, according to the method for manufacturing porous ceramics of the present invention, (1) Dense portions and porous portions can be formed at desired locations and in desired ratios.

■ Porosity and pore diameter can be set arbitrarily, and can be freely adjusted from extremely high porosity to low porosity.

■ The pore size and pore distribution of the porous part are extremely uniform.

■ The ceramic layer in the porous part is extremely dense and continuous with the dense part, and the porosity changes continuously between the porous part and the dense part, so there is no risk of peeling or cracking due to thermal stress. It does not occur and has extremely high strength.

■ Since it is a slurry casting method, even complex irregular shapes can be easily molded.

etc. effects are deepened.

Therefore, according to the method of the present invention, excellent porous ceramics useful as various structures can be provided, which is extremely advantageous industrially.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the core material and the ceramic powder coating layer, FIG. 342 and FIG. 3 are cross-sectional views explaining the molding process of the present invention, and FIG. 4 is a cross-sectional view of the porous ceramic obtained. 1... Core material, 2... Ceramic powder, 3... Composite particles, 4... Slurry 5
...Gypsum mold, 6.Ceramic particles, 9.
...Porous, ceramic. Figure 1 fIA2 Figure

Claims (1)

[Claims] (1) Composite particles made of a granular material made of a flammable substance as a core material and ceramic powder attached to the surface of the core material;
A slurry obtained by suspending ceramic particles is formed into a non-uniform top and bottom part using a slurry casting method, and the obtained formed body is fired to burn off the core material and sinter the ceramic. A method for producing porous ceramics with continuously changing porosity, characterized by: