JPS61281081A - Manufacture of porous ceramics with fine layer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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, silicon nitride, silicon carbide,
So-called new ceramics, such as non-oxide ceramics such as sialon, aluminum oxide, and zirconium mide, 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, ceramic 2x, which is porous, has excellent properties in terms of heat insulation, sound absorption, light weight, etc., and is therefore expected to be used in a wide range of applications. Porous ceramics are produced by: 1. Normally, ceramic powder is press-molded to a low density and fired, or by a mixing method in which volatile or flammable substances are added during molding and fired, or during the firing process like Shirasu. 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 achieve a high 3D degree, for example, the pores on the surface of porous ceramics can be removed by bonding dense ceramics to the surface of pre-fabricated porous ceramics, or by vapor phase deposition, etc. Various 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, 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 producing porous ceramics having a dense layer, 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 to form a layer of composite particles. By laminating layers of powder and press-molding them, a composite compact of core material and ceramic powder is obtained, and then the composite compact 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 a porous ceramic 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 combustible substance is used as a core material 1, and a ceramic powder 2 is adhered 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 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.

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. In order to form a body, a predetermined amount of ceramic powder, composite particles, and ceramic powder are 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 the core material 1 to a temperature higher than the temperature at which it exhibits plasticity and apply pressure. It is effective to remove air bubbles from the viewpoint of improving the degree of densification of the ceramic part.

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

As the ceramic powder forming the ceramic powder layers 2 and 23, it is preferable to use 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 ceramic 20, with the core material 1 uniformly dispersed in the intermediate layer, having a cross-sectional shape as shown in FIG. 3 is obtained.

The composite green compact 4 obtained by pressure molding is then molded into a core material 1.
and sintering of the ceramic 20. The firing procedure involves first performing calcination to burn the core material l.

Although main firing may be performed to firmly sinter the ceramic 20, the ceramic 20 may be sintered in an oxygen-containing atmosphere.
The sintering of 0 and the oxidation removal of the core material 1 may be performed simultaneously. Alternatively, after the ceramic 20 is pre-sintered in a non-oxidizing atmosphere, it is heated in an oxygen-containing atmosphere to oxidize and remove the core material 1. Finally, main sintering may be performed in a non-oxidizing atmosphere or an oxygen-containing atmosphere.

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

In addition, in the above explanation, by forming three layers: a ceramic powder layer, a composite particle layer, and a ceramic layer.
The case of manufacturing porous ceramics with dense surfaces on both sides has been described, but as shown in FIG. 6(a), two layers, a ceramic powder layer 31 and a composite particle layer 32, are formed, and then pressure molding and firing are performed in the same manner. By carrying out this process, it is also possible to manufacture porous ceramics 7 that are dense on only one surface as shown in FIG. 6(b).

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 that, 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 possible to produce porous ceramics not only in the form of a plate but also in the shape of a cylinder as shown in FIGS. 9 and 10. (In addition, FIG. 9 and FIG. 10 each show a ceramic 40 having a dense layer 44 on one surface and a porous layer 42 in the center.
', and shows a ceramic 46 having a porous layer 42 on the surface and a dense layer 44 in the center) [Operation] Since a sinterable core material is used as a pore-forming agent, the particle size of the core material By changing the thickness of the coating layer of ceramic powder attached to the core material, the thickness of the ceramic powder layer filled in the mold for molding, and the thickness of the composite particle layer, desired pore size, porosity, and density can be achieved. Layer thickness.

A porous ceramic having a dense layer with a porous layer thickness can be easily produced.

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, and the extremely dense and high strength porous ceramic part of the ceramic part Become.

[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, and the particle size was 700! A granular core material was obtained. This core material was coated with ceramic powder (3 mo 1 e% Y 203 Zr02) using a pan coating device to obtain composite particles.

Into a cylindrical mold as shown in Fig. 1, first, the same ceramic powder that was used to coat 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 and then changing to 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/crn' (porosity about 60%), the pores are uniform and independent, and dense parts with a bulk density of 5.95 g/crrf are formed as a continuous integral body on both surfaces of the porous part. was.

The strength of this sintered body was significantly higher than that of conventional porous bodies, and it did not break easily.

[Effects of the Invention] As described above, the present invention forms a multilayer ceramic powder layer on a layer of particles in which a combustible core material is coated with ceramic powder, press-forms the layer, and then bakes it to form a dense layer. This method produces porous ceramics having layers.

According to the method of the present invention, however, (1) the pore diameter and pore distribution of the porous portion are extremely uniform;

(The ceramic phase of the porous part is extremely dense, and since it is a continuous and integral part of the dense part, it does not peel 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 range from extremely high porosity to low porosity. It can be adjusted to

(2) 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 produced.

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 the drawing]

FIG. 1 is a sectional view showing the core material and the ceramic powder coating layer, FIG. 2 is a sectional view illustrating the pressurizing process of the present invention,
Fig. 3 is a cross-sectional view of the composite green compact obtained by the pressure forming shown in Fig. 2, and Fig. 4 is a cross-sectional view of a porous ceramic having a dense layer obtained by firing the composite green compact of Fig. 3. It is. FIG. 5 is a diagram illustrating a pressurizing method using a rubber mold. Moreover, FIG. 6 is a sectional view explaining another embodiment of the present invention, FIG. 6(a) is a diagram showing an example of filling a mold, FIG.
b) shows the resulting porous ceramic with a dense layer; 7 to 10 are diagrams for explaining porous ceramics obtained by the method of the present invention, and FIGS. 7 and 8 are cross-sectional views. 9 and 10 are perspective views. ■...Nuclear material, 2...Ceramic powder, 3...Composite particles, 4...
Composite green compact, 5... Pores, 6.7.8, 9.40.46... Porous ceramics. 10.11...Mold, 16...Rubber mold. Figure 5 Figure 6 Figure 10

Claims (1)

[Claims] (1) By laminating a layer of ceramic powder on a layer of composite particles made by using a granular material made of a combustible material as a core material and adhering ceramic powder to the surface of the core material, and then press-molding this. , obtain a composite compact of core material and ceramic powder,
A method for producing porous ceramics having a dense layer, characterized in that the composite green compact is then heated to burn off the core material and sinter the ceramic powder.