JPH0155226B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing porous ceramics having a dense layer, and in particular a method for producing porous ceramics with high strength and uniform pores in the porous portion. Regarding.

[Prior art] In recent years, non-oxide ceramics such as silicon nitride, silicon carbide, and sialon have been used as high-temperature, high-strength structural materials.
In addition, so-called new ceramics such as aluminum oxide and zirconium oxide are rapidly becoming popular, 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 are expected to be used in a wide range of applications because they have excellent properties such as heat insulation, sound absorption, and light weight. Porous ceramics are usually produced using a mixing method in which ceramic powder is pressure-molded to a low density and then fired, or a volatile or combustible substance is added during molding and then fired, or as in the case of Shirasu, the firing process is performed. 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 the disadvantage 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 porous ceramics manufactured in advance, or filling the pores on the surface of porous ceramics by vapor phase deposition. 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 thermal expansion difference at the bonding interface, and insufficient strength of the bonding layer. In some cases, peeling or cracking may occur. In addition, it is difficult to completely fill the pores with the method of filling the pores by vapor phase deposition.
Moreover, it has the disadvantage that the processing time is long.

[Means for Solving the Problems] The present invention solves the problems of the prior art described above, and has a porous layer and a dense layer, and there is almost no occurrence of cracks or the like due to thermal stress between the two layers. , provides a method for manufacturing porous ceramics having a dense layer, in which a granular material made of a combustible substance is used as a core material, and ceramic powder is attached to the surface of the core material to form a layer of composite particles. By laminating powder layers and press-molding them, a composite green body of core material and ceramic powder is obtained, and then the composite green body is heated to burn and remove the core material. The gist of the present invention is a method for producing porous ceramics having a dense layer, which comprises firing and sintering ceramic powder.

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

1 to 4 are schematic cross-sectional views illustrating the manufacturing process of porous ceramics having a dense layer according to an embodiment of the present invention.

In the present invention, first, as shown in FIG. 1, a granular material made of a flammable substance is used as a core material 1, and a ceramic powder 2 is attached to the surface of this core material 1 to obtain composite particles 3. 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. When a plastic core material is used, the core material 1 is deformed by pressure molding in the post-process, and a denser molded body can be obtained.

The particle size of the core material 1 is determined by the pore size of the intended porous portion. When using a plastic core material, it is sufficient to use a core material having a particle size slightly larger than the intended pore diameter.

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

Various commonly used coating methods can be employed, such as a method in which a ceramic pigment powder solution containing an appropriate binder is applied by spraying to a core material in a fluidized bed state, or a method in which a ceramic pigment powder solution containing a suitable binder is applied to a core material in a fluidized bed state, or a method in which a ceramic pigment powder solution containing a suitable binder is applied to a core material in a fluidized bed state; 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.

The ceramic powder is not particularly limited, and various ceramic powders such as zirconia, alumina, silicon carbide, silicon nitride, sialon, and silica can be used.

The composite particles 3 to which the ceramic powder has been adhered in this way are then stacked in a press mold 10, 11, etc., with a ceramic powder layer 21, a layer 22 of the composite particles 3, and a ceramic powder layer 23, as shown in FIG. Ceramic powder, composite particles,
A predetermined amount of ceramic powder is filled in this order and pressure molded. When performing pressure molding, if the core material 1 is a thermoplastic material, it is preferable to heat and press the core material 1 to a temperature higher than the temperature at which the core material 1 exhibits plasticity. Furthermore, during pressure molding, reducing the pressure in the mold to remove air bubbles is effective in improving the degree of densification of the ceramic portion.

As the pressure molding method, in addition to the above-mentioned method using a mold, a hydrostatic press method using a rubber mold 16 as shown in FIG. 5 can also be adopted.

The ceramic powder forming the ceramic powder layers 21 and 23 is preferably made of the same material as the ceramic powder coated on the composite particles 3, but it is also possible to use a different material.

In this way, a composite green compact 4 of the core material 1 and the ceramics 20 with the core material 1 uniformly dispersed in the intermediate layer and having a cross-sectional shape as shown in FIG. 3 is obtained.

The composite compact 4 obtained by pressure molding is then fired to burn off the core material 1 and sinter the ceramic 20. The firing procedure involves first performing calcination to burn the core material 1, then
Although main firing may be performed to firmly sinter the ceramics 20, the sintering of the ceramics 20 and the oxidation removal of the core material 1 may be performed simultaneously in an oxygen-containing atmosphere. Further, after preliminary sintering of the ceramics 20 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. It's okay to get old.

By firing, as shown in FIG. 4, the areas where the core material 1 was present become pores 5, and a porous ceramic 6 with a dense surface is obtained.

In the above explanation, a case was described in which porous ceramics with dense surfaces on both surfaces were manufactured by forming three layers: a ceramic powder layer, a composite particle layer, and a ceramic layer. By forming two layers, a ceramic powder layer 31 and a composite particle layer 32, and performing pressure molding and firing in the same manner, a porous ceramic 7 with only one surface dense as shown in FIG. 6b can be manufactured. You can also do it.

In the present invention, a porous ceramic 8 having a dense layer inside and porous on both surfaces as shown in FIG. 7, or a laminate of a dense layer and a porous layer as shown in FIG. It is also possible to produce porous ceramics 9.

In the example shown in FIG. 7, first a composite particle layer is filled in a mold, a ceramic powder layer is filled on top of the composite particle layer, and a composite particle layer is further filled on top of the ceramic powder layer, followed by pressure molding and firing.

In the example shown in FIG. 8, ceramic powder layers and composite particle layers are alternately filled, and after finally filling the ceramic powder layer, pressure molding and firing are performed.

Furthermore, by appropriately selecting the shape of the mold for molding, it is also possible to manufacture not only plate-shaped porous ceramics but also column-shaped porous ceramics as shown in FIGS. 9 and 10. (In addition, Figures 9 and 10 are
A ceramic 40 having a dense layer 44 on the surface and a porous layer 42 in the center, and a ceramic 46 having a porous layer 42 on the surface and a dense layer 44 in the center are shown, respectively. ) [Function] Since a combustible core material is used as a pore-forming agent, the particle size of the core material, the thickness of the coating layer of ceramic powder attached to the core material, and the thickness of the ceramic powder layer filled in the mold for molding are controlled. By changing the thickness of the composite particle layer, it is possible to easily produce a porous ceramic having a dense layer having a desired pore diameter, porosity, dense layer thickness, and porous layer thickness.

In addition, since the ceramic part of the dense layer and the ceramic part of the porous layer are continuous and integrated, cracking or peeling due to thermal stress hardly occurs.
The ceramic part becomes extremely dense and highly strong porous ceramic.

[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 bulk core material with a particle size of about 700 μm. This core material was coated with ceramic powder (ZrO ₂ containing 3 mole% Y ₂ O ₃ ) using a pan coating device to obtain composite particles.

Into a cylindrical mold as shown in Fig. 1, first, the same ceramic powder as that coated on the core material is placed to form a ceramic powder layer, and then the composite particles obtained above are placed to form a composite particle layer. Finally, a ceramic powder layer was formed again to obtain a three-layer structure, which was then dry pressed at room temperature. The obtained composite powder compact was fired under the conditions of holding at 750°C → 1450°C. Further, this firing was performed in an air atmosphere.

As a result, the bulk density of the porous part of the obtained sintered body was 2.37 g/cm ³ (porosity approximately 60%), the pores were uniform, closed pores, and both surfaces of the porous part were A dense part with a bulk density of 5.95 g/cm ³ was formed as a continuous unit.

This sintered body was far superior in strength to conventional porous bodies and did not break easily.

[Effects of the Invention] As described above, the present invention forms a multi-layered ceramic powder layer on a layer of particles made of a combustible core material coated with ceramic powder, press-forms this, and then bakes it to create a dense structure. This method produces porous ceramics having layers.

According to the method of the present invention, however, the pore diameter and pore distribution of the porous portion are extremely uniform.

The ceramic phase in the porous part is extremely dense,
Moreover, since it is an integral part that is continuous with the dense part, it does not peel off or crack due to thermal stress, and has extremely high strength.

The pore size and porosity of the porous part can be changed arbitrarily by selecting the particle size of the core material or the coating layer thickness of the ceramic powder, and can be freely varied from extremely high porosity to low porosity. Can be adjusted.

The layer thickness of the dense portion can be arbitrarily changed by changing the layer thickness of the ceramic powder filled into the mold (rubber mold, metal mold).

Effects such as this are achieved.

Therefore, according to the method of the present invention, porous ceramics having an excellent dense layer 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. 2 is a cross-sectional view illustrating the pressing process of the present invention, and FIG. 3 is a composite green compact obtained by the pressure forming shown in FIG. 2. FIG. 4 is a cross-sectional view of porous ceramics having a dense layer obtained by firing the composite powder compact of FIG. 3. FIG. 5 is a diagram illustrating a method of applying pressure using a rubber mold. Further, FIG. 6 is a cross-sectional view for explaining another embodiment of the present invention, FIG. 6 a is a diagram showing an example of filling a mold, and FIG. FIG. 7 to 10 are views for explaining porous ceramics obtained by the method of the present invention, in which FIGS. 7 and 8 are cross-sectional views, and FIGS. 9 and 10 are perspective views. DESCRIPTION OF SYMBOLS 1... Core material, 2... Ceramic powder, 3... Composite particle, 4... Composite green compact, 5... Pore, 6,
7, 8, 9, 40, 46... Porous ceramics, 10, 11... Mold, 16... Rubber mold.

Claims (1)

[Claims] 1 A layer of ceramic powder is laminated on a layer of composite particles made by using a granular material made of a combustible material as a core material and ceramic powder is attached to the surface of the core material, and this is pressure-molded to form a core. A composite green compact of material and ceramic powder is obtained, and then the composite green compact is heated to burn off the core material and sinter the ceramic powder. A method for producing porous ceramics.