JP2997542B2 - Ceramic porous body - Google Patents

Description

The present invention relates to a porous ceramic body composed of a plurality of ceramic layers having different pore diameters.

[Prior Art] As is well known, a porous ceramic body is used in fields such as a ceramic filter using continuous pores and a heat insulating material using a structure including pores.

Incidentally, a ceramic film such as a ceramic filter having a so-called asymmetric structure has good characteristics and is often used in order to reduce transmission resistance. In addition, since a portion having a small pore diameter has a large transmission resistance, an asymmetric structure is adopted to make this portion as thin as possible. Here, the ceramic film having an asymmetric structure generally forms a first layer having a pore size smaller than the support pore size on a support having a large pore size, and further forms a second layer having a small pore size thereon. It has a configuration of a plurality of layers formed and is asymmetric in the film thickness direction.

On the other hand, as the ceramic heat insulating material, a ceramic fiber molded material or a heat insulating brick having pores formed by foaming is used, but as one product, the distribution of the pore diameter is not changed by part. Was.

[Problems to be Solved by the Invention] However, the conventional ceramic porous body has an asymmetric structure in which a support, an intermediate layer, and a film are sequentially formed, so that the manufacturing process is complicated and the cost is high. .

In addition, in making a ceramic asymmetric membrane, since the diameter of the ceramic particles forming the next layer is smaller than the pore diameter of the support,
In order to form the next layer on the support, it is necessary to take measures to prevent the particles of the next layer from entering the support, and this is one of the reasons why the ceramic asymmetric membrane is expensive.

On the other hand, the porous ceramic heat insulating material cannot be said to be insufficient according to the theory of heat conduction. The thermal conductivity has a different conduction mechanism depending on the temperature, and heat transfer by radiation increases at high temperatures.Therefore, it is desirable to have a structure that minimizes the thermal conductivity according to the temperature distribution. None had such a structure, and a sufficient heat insulating effect was not actually exhibited.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a ceramic porous body that can easily produce a substance having a different chemical component or a porous structure according to the purpose of use and can reduce the cost. And

Means for Solving the Problems According to the present invention, a plurality of ceramic layers composed of ceramics having different pore diameters are formed as ceramic layers having a large pore diameter on the outermost side and ceramics having a small pore diameter on the innermost side. The ceramic porous body is characterized in that it is a ceramic layer composed of:

The ceramic porous body according to the present invention is characterized in that the pore diameter is distributed with a gradient, and such a porous body is manufactured by various methods.

For example, a ceramic filter (porous ceramic body having a plate shape) in which pore diameters are distributed in the thickness direction of the material is produced through the following steps (1) to (4). The pores of the filter are created by the gaps between the ceramic particles, and the ceramic particles having different sizes are gradually filled by sintering and sintering the ceramic particles of different sizes, and the ceramics have continuous pores. A porous body is obtained.

First, ceramic particles having a particle size distribution are dispersed in water to form a slurry. Next, ceramic particles having a certain depth of water in the slurry are statically poured into water. The sedimentation speed of the ceramic particles in the supplied slurry varies depending on the particle size, and particles having a large diameter settle first, and a sedimentation layer is formed with a gradient according to the particle size. Thereafter, when the sedimented layer was dried, a molded body of a porous ceramic body having pores having a gradient pore distribution was obtained.

It is also possible to form a pipe-shaped ceramic asymmetric membrane utilizing the principle that the sedimentation velocity in water is proportional to the particle size. For example, this asymmetric membrane is made through the following steps. First, water is filled in a gypsum mold having a cylindrical space. Next, a thin pipe filled with slurry is introduced into the center of the water column, and the slurry is introduced into the center of the water column by removing the plug. Subsequently, the gypsum mold is rotated, and the ceramic particles in the slurry are moved by the centrifugal force in the gypsum mold direction and deposited. Then
After the sedimentation layer is formed, water is drained, and after drying, the pipe-shaped molded product is taken out of the gypsum mold and sintered to form a ceramic asymmetric membrane.

The ceramic porous body used for heat insulation etc.
It can be made by various methods such as combustion removal of combustibles and blending of fibers and particles. In each of the production methods, it is possible to introduce a pore diameter with a gradient. Here, a method of distributing the pore diameter in a gradient manner when forming the ceramic porous body by the foaming method is as described below.
First, a dispersing agent such as water is added to the ceramic powder to form a slurry, which is then added with a foaming agent, a binder, and the like.
The foaming agent is decomposed by heating or the like to generate gas, and the slurry is foamed. Next, the foam is dried and solidified by removing moisture. However, since the foam has a large surface area, the bubbles coalesce and grow into large bubbles before solidifying. Therefore, the foam is placed on an absorbent material such as gypsum board. As a result, the portion in contact with the gypsum is absorbed, and the solidification proceeds before the bubbles coalesce. In this way, a ceramic foam in which the foam diameter is distributed with a gradient can be formed. Furthermore, the foamed body is sufficiently dried and then fired to obtain a foamed ceramic porous body in which the bubble diameter is distributed in a gradient. In addition, as for the ceramic porous body which introduces pores by burning and removing combustibles, similarly to the inclined pore asymmetric membrane, the combustibles are first formed obliquely, and the ceramic slurry is poured into the voids of the combustible particles. Can be molded.

[Operation] According to the present invention, it is possible to easily produce one having different chemical components and porous structures according to the purpose of use, and to obtain a ceramic porous body capable of reducing costs.

 Hereinafter, examples of the present invention will be described.

Example 1 First, fused alumina particles having a maximum diameter of 20 μm and an average diameter of 2
The Bayer method alumina powder having an average particle size of 0.5 μm and the alum-decomposed alumina powder having an average particle size of 0.5 μm were mixed to prepare alumina powder particles covering a range of 0.1 to 20 μm. Next, this powder
100 parts, 30 parts of ion-exchanged water, and 0.5 part of ammonium polyacrylate were mixed in a pot mill for 24 hours to form a slurry.

On the other hand, a two-piece gypsum mold having an inner diameter of φ30 mm and a length of 100 mm was prepared in advance, and the gypsum mold was filled with ion exchange water in which 5 parts of alum-decomposed alumina powder were dispersed. The slurry was gently poured into the center of a dropper made of a glass tube having an inner diameter of 5 mm. Next, the gypsum mold was plugged, and the gypsum mold was rotated at 1000 rpm for 10 minutes. Subsequently, the stopper was opened and the water in the gypsum mold was allowed to flow out gently, and then left in a room to dry the gypsum mold having a thin layer of alumina powder adhered to the inner surface.

Next, the plaster mold was split into two and the alumina tubular molded body was taken out. The total thickness (H) was 1 mm, and the particles ranging from 20 μm particles to 0.2 μm powder were filled and sintered substantially obliquely. Here, the alum-dispersed alumina powder previously dispersed in the gypsum-type ion-exchanged water grows to have a minimum particle size.
It was confirmed that the thickness was 0.2 μm. The alum-decomposed alumina was grown to have a particle size of 0.2 μm.

As shown in FIG. 1 and FIG. 2, the tubular alumina porous body 1 thus obtained has a particle diameter (L ₁ ) as an outermost layer.
A plurality of layers are laminated so that the particle diameter of each layer becomes smaller in order from the largest diameter layer 2 made of ceramics of 20 μm to the smallest inner diameter layer 3 made of ceramics having a particle diameter of 0.2 μm.

In fact, when cutting the fired body and observing the microstructure with a microscope, the layer thickness was about 1 mm, and the powder from 20 μm to 0.2 μm powder was substantially inclined and filled and sintered. It had been. It was confirmed that alum-decomposed alumina powder previously dispersed in gypsum-type ion-exchanged water contributed to the binding of large particles. The alum-dissolved alumina grew to have a minimum particle size of 0.2 μm.

When the pore size distribution of the tubular alumina porous body was measured by a mercury intrusion boron simeter, the pore size was 0.1 μm to 10 μm.
It was substantially distributed down to μm. It was also found that the ceramic tube was a tube having a pore size distribution inclined in the thickness direction. Furthermore, when the above-mentioned ceramic tube was used as a filter, the pressure loss was small, the device was resistant to vibrations and the like, and it could be used well.

Example 2 First, in the same manner as in Example 1, 20 μm to 5 μm
A tubular molded body was obtained from carbon particles having a particle size of Next, 80 parts of yttria-stabilized zirconia powder having an average particle size of 0.2 μm,
20 parts of ion-exchanged water and 2 parts of ammonium polyacrylate were mixed in a pot mill for 24 hours to form a slurry. Subsequently, the slurry was impregnated into the carbon molded body, and then left to dry in a room. After this, put it in air 14
The resultant was fired at 50 ° C. for 2 hours, fired to remove carbon, and sintered to obtain a tubular zirconia porous body having a diameter of 20 mm.

Although the tubular zirconia porous body thus obtained is not shown, the outermost layer is made of a ceramic having a particle diameter of 15 μm, the innermost layer is made of a ceramic having a particle diameter of 3 μm, and the particle diameter of each layer is gradually reduced from the outermost layer. It has a configuration in which a plurality of layers are stacked.

Example 3 First, 100 parts of silicon nitride powder having an average particle size of 0.8 μm, average particle size
5 parts of 0.2 μm alumina powder, 5 parts of yttria having an average particle size of 0.5 μm, 30 parts of ion-exchanged water, and 3 parts of ammonium polyacrylate were mixed in a pot mill for 24 hours to prepare a slurry. Next, 2 parts of methylcellulose as a binder and 2 parts of ammonium stearate as a foam stabilizer were added to the slurry, and foaming was performed with a whisk. Subsequently, the foam was poured on a dried gypsum board, and further, the foam was covered with a vinyl sheet to prevent drying, and left indoors. The moisture in the foam slurry was absorbed by the gypsum mold, and solidification proceeded from the lower surface of the foam. At the same time, the bubbles gradually coalesced. After leaving to dry all day and night, the dried foamed body was heated at 600 ° C in nitrogen gas.
Degreasing by heating for 2 hours, then 1820 ℃ in nitrogen gas
For 2 hours to obtain a foamed silicon nitride ceramic.

When the cell size was measured by cutting the foamed ceramic, the cell diameter was distributed in a gradient of 100 μm to 300 μm in the drying direction. When this ceramic porous body was used as a heat insulator in a nitrogen atmosphere,
About twice the heat insulating effect was obtained as compared with the heat insulating material using the conventional carbon fiber.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to provide a porous ceramic body that can easily produce a substance having a different chemical component or porous structure according to the purpose of use and can reduce the cost. .

[Brief description of the drawings]

FIG. 1 is an explanatory view of a tubular porous alumina body according to one embodiment of the present invention, and FIG. 2 is a cross-sectional view of a main part along XX of FIG. 1 ... tubular alumina porous body, 2 ... maximum diameter layer, 3 ... small diameter layer.

Continued on the front page (72) Inventor Koichi Shiraishi 30 Soya, Hadano-shi, Kanagawa Prefecture, Central Research Laboratory Toshiba Ceramics Co., Ltd. (72) Inventor Kuniko Ando 30 Soya, Hadano-shi, Kanagawa Prefecture, Central Research Laboratory Toshiba Ceramics ( 56) References JP-A-63-291881 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 38/00

Claims (1)

(57) [Claims] A ceramic layer composed of ceramics having different pore diameters, a ceramic layer composed of ceramics having a large pore diameter at the outermost part, and a ceramic layer composed of ceramics having a small pore diameter at the outermost part. A ceramic porous body characterized in that it is laminated obliquely in the vertical direction.