JPH04209772A - Ceramic porous material - Google Patents

Abstract

PURPOSE:To provide a ceramic porous material capable of readily giving a ceramic containing different chemical components and having a different porous structure in response to an use purpose by successively laminating ceramic layers in order from a ceramic layer having a large pore diameter to a ceramic layer having a small pore diameter in the thickness direction. CONSTITUTION:Plural ceramic layers comprising ceramic layers having mutually different pores are laminated each other successively in order from a ceramic layer having a large pore diameter to a ceramic having a small pore diameter to provide the objective ceramic porous material. The porous material is produced, for example, as described below. Ceramic particles having a particle size distribution are first dispersed in water, and the produced slurry is slowly charged to water. Since the ceramic particles have different precipitation speeds in response to the sizes of the particles, the particles having large diameters first precipitate to from precipitation layers, tilted in response to the sizes of the particles. The precipitation layers are totally dried to provide a ceramic porous molded product having fine pores in the tilted fine pore size distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a ceramic porous body composed of a plurality of ceramic layers having different pore sizes.

[Prior Art] As is well known, porous ceramic bodies are used in fields such as ceramic filters that utilize continuous pores and heat insulating materials that utilize a structure that includes pores.

By the way, in order to reduce the permeation resistance of ceramic membranes such as ceramic filters, those having a so-called asymmetric structure have good characteristics and are often used. Furthermore, since the permeation resistance is high in the part with small pore diameter, an asymmetric structure is adopted to make this part as thin as possible. Here, in a ceramic membrane with an asymmetric structure, a first layer having a pore size smaller than that of the support is generally formed on a support having a large pore size, and a second layer having a small pore size is further formed on this. It has a structure of multiple layers formed and is asymmetrical in the film thickness direction.

On the other hand, as ceramic insulation materials, ceramic fiber molded materials and insulation bricks with pores formed by foaming are used, but none of them have pore size distribution that varies from part to part. Ta.

[Problems to be solved by the invention] However, in conventional ceramic porous bodies, supports,
Because it has an asymmetric structure in which the intermediate layer and membrane are formed in sequence, the manufacturing process is complicated and costs are high.

In addition, when creating a ceramic asymmetric membrane, the diameter of the ceramic particles forming the next layer is smaller than the pore diameter of the support, so in order to form the next layer on the support, it is necessary to prevent the next layer particles from penetrating into the support. This is one of the reasons why ceramic asymmetric membranes are expensive.

On the other hand, it must be said that porous ceramic heat insulating materials are insufficient in terms of heat conduction theory.

Regarding thermal conductivity, the conduction mechanism differs depending on the temperature, and heat transfer by radiation increases at high temperatures, so it is desirable to have a structure that minimizes thermal conductivity according to the temperature distribution. There was no such structure, and in reality, sufficient heat insulation effect was not achieved.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a ceramic porous body that can be easily manufactured with different chemical components and porous structures depending on the purpose of use, and that can reduce costs. shall be.

[Means for Solving the Problems] The present invention provides a method in which a plurality of ceramic layers composed of ceramics having different pore diameters are sequentially changed from a ceramic layer containing a ceramic layer having a large pore diameter to a ceramic layer containing a ceramic layer having a small pore diameter. This is a ceramic porous body characterized by being laminated in the thickness direction.

The ceramic porous body according to the present invention is characterized by a gradient distribution of pore diameters, and such a porous body can be manufactured by various methods.

For example, a ceramic filter (plate-shaped ceramic porous body) with pore diameters distributed in the thickness direction of the material is
It is made through each process of ~■. The pores of the filter are created by the voids between ceramic particles, and the pores are distributed in a gradient by filling and sintering ceramic particles of different sizes, creating a ceramic with continuous pores. A porous body is obtained.

■First, ceramic particles with a particle size distribution are dispersed in water to form a slurry. ■Next, this slurry is gently poured into water with ceramic particles at a certain depth.

The sedimentation speed of the ceramic particles in the slurry that has been added differs depending on their particle size, with particles with larger diameters settling first, forming a sedimentary layer in a gradient according to the particle size. (2) Thereafter, when this precipitated layer was dried, a molded ceramic porous body having a pore shape with a gradient pore distribution was obtained.

It is also possible to form a vib-shaped ceramic asymmetric membrane using the principle that the sedimentation rate in water is proportional to the particle size. For example, this asymmetric membrane is produced through the following steps. ■First, a plaster mold with a cylindrical space is filled with water. ■Next, a thin vibrator 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 stopper. ■Next, the plaster mold is rotated, and the centrifugal force moves the ceramic particles in the slurry toward the plaster mold and deposits them.

(2) Next, after forming the sediment layer, the water is drained, and after drying, the tube-shaped molded body is taken out of the plaster mold and sintered to form a ceramic asymmetric membrane.

Ceramic porous bodies used for insulation materials can be made by various methods, such as foaming, combustion removal of combustible materials, and blending of fibers and particles.Each manufacturing method involves introducing pore sizes in a gradient manner. Is possible. Here, when forming a ceramic porous body by the foaming method, the method of distributing the pore diameter in a gradient manner is as shown in (1) to (4) below. ■First, add a dispersant such as water to ceramic powder to form a slurry, add a foaming agent 2 binder, etc., and heat to decompose the foaming agent and generate gas, foaming the slurry. let ■Next, the foam is dried to remove moisture and solidify.

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 plasterboard.

As a result, the parts in contact with the plaster absorb water, and solidification progresses before the bubbles coalesce. In this way, a ceramic foam with a gradient distribution of bubble diameters can be molded. (2) Further, by sufficiently drying this foam and firing it, a foam-like ceramic porous body having a gradient distribution of bubble diameters is obtained. In addition, regarding the porous ceramic glass body in which pores are introduced by burning off combustible materials, the combustible material is first formed in an inclined manner, and the ceramic slurry is poured into the voids of the combustible material particles, in the same way as the inclined pore asymmetric membrane. It can be shaped by things.

[Function] According to the present invention, ceramic porous bodies can be obtained that can be easily manufactured with different chemical components and porous structures depending on the purpose of use, and that can reduce costs.

Examples of the present invention will be described below.

[Example 1] ■First, fused alumina particles with a maximum diameter of 20 μm, Bayer method alumina powder with an average particle diameter of 2 μm, and an average particle diameter of 0.5 μm
Alumina decomposed alumina powder was mixed to prepare alumina powder covering the range of 0.1 to 20 μm. Next, 100 parts of this powder, 30 parts of ion-exchanged water, and 065 parts of ammonium polyacrylate were mixed in a pot mill overnight to form a slurry.

■Meanwhile, a two-part plaster mold with a cavity with an inner diameter of 30 mm and a length of 100 sv is made in advance, and this plaster mold is filled with ion-exchanged water in which 5 parts of alum decomposed alumina powder is dispersed. The above slurry was gently injected into the center of the tube from a dropper made of a glass tube with an inner diameter of φ5 as.

Next, a plug is applied to the plaster mold, and the plaster mold is placed at 1100 Orp.
and rotated for 10 minutes. Subsequently, the stopper was opened and the water inside the plaster mold was gently poured out, and the mold was left indoors to dry the plaster mold with a thin layer of alumina powder adhered to its inner surface.

■Next, the plaster mold of the alumina tubular molded body was broken into two and taken out. The total thickness (H) was 1 .mu.m, and particles ranging from 20 .mu.m particles to 0.2 .mu.m powder were filled and sintered in a substantially gradient manner. Here, it was confirmed that the alum decomposed alumina powder, which had been previously dispersed in gypsum-type ion-exchanged water, had grown into particles and had a minimum particle size of 0.2 μm. Note that the alum decomposed alumina had grown into particles and had a particle size of 0.2 μm.

The tubular alumina porous body 1 obtained in this way is
As shown in the figure and Fig. 2, the particle size (L,) of the outermost layer
It has a structure in which multiple layers are stacked such that the particle size of each layer becomes smaller in order from the largest diameter layer 2 made of ceramics with a particle size of 20 μm to the innermost layer, the smallest diameter layer 3 made of ceramics with a particle size of 0.2 μm. .

In fact, when the fired body was cut and the microstructure was observed under a microscope, the layer thickness was approximately 1 ms, and the powder particles ranging from 20 μm particles to 0.2 μm powder were substantially slanted during filling and firing. It was tied. It was confirmed that the alum decomposed alumina powder, which was pre-dispersed in gypsum-type ion-exchanged water, contributed to the bonding of large particles. The alum decomposed alumina had grown to a minimum particle size of 0.2 μm.

When the pore size distribution of the above tubular alumina porous material was measured using a mercury intrusion boron simeter, the pore size ranged from 0.1 μm to 1 μm.
It was substantially distributed down to 0 μm.

It was also found that the ceramic tube had a pore size distribution that was gradient in the thickness direction. Furthermore, when the above ceramic tube was used as a filter, the pressure loss was small and it withstood vibration shock, etc., and could be used satisfactorily.

[Example 2] First, in the same manner as in Example 1, from 20 μm to 5 μm
A tubular molded body was obtained from carbon particles having a particle size of . Next, 80 yttria-stabilized zirconia powder with an average particle size of 0.2 μm
1 part, 20 parts of ion-exchanged water, and 2 parts of ammonium polyacrylate were mixed in a bot mill overnight to form a slurry.

Subsequently, this slurry was impregnated into the carbon molded body, and then left indoors to dry. Thereafter, this was fired in air at 1450" C for 12 hours to burn off the carbon and sinter it to obtain a tubular zirconia porous body with a diameter of 20 mm.

Although not shown, the tubular porous zirconia body obtained in this way has an outermost layer made of ceramics with a particle size of 15 μm, an innermost layer made of ceramics with a particle size of 3 μm, and the particle size of each layer becomes smaller in order from the outermost layer. It has a structure in which multiple layers are laminated.

[Example 3] First, 100 parts of silicon nitride powder with an average particle size of 0.8 μm.

5 parts of alumina powder with average particle size of 0.2 μm, average particle size of 0.5
5 parts of μm ittria, 30 parts of ion exchange water.

and 3 parts of ammonium polyacrylate were mixed in a bot mill overnight to prepare a slurry. Next, 2 parts of methyl cellulose as a binder and 2 parts of ammonium stearate as a foam stabilizer were added to this slurry, and the mixture was foamed using a foaming machine. Next, the foam was poured onto a dry plasterboard, and the foam was covered with a vinyl sheet to prevent drying and left indoors.

The water in the foam slurry was absorbed by the plaster mold, and solidification progressed from the bottom of the foam. At the same time, the bubbles began to coalesce little by little. - After being left to dry day and night, the dried foam molded body was degreased by heating in nitrogen gas at 600°C for 2 hours, and further fired in nitrogen gas at 1820°C for 2 hours to obtain foam silicon nitride ceramics. .

When the cell size was measured by cutting the foamed ceramic, it was found that the cell diameter was distributed gradiently from 100 μm to 300 μm in the drying direction.

When this ceramic porous body was used as a heat insulating material in a nitrogen atmosphere, the heat insulating effect was approximately twice that of conventional carbon fiber heat insulating materials.

[Effects of the Invention] As detailed above, the present invention provides a ceramic porous body that can be easily manufactured with different chemical components and porous structures depending on the purpose of use, and that can reduce costs. can.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a tubular alumina porous body according to an embodiment of the present invention, and FIG. 2 is a sectional view of a main part along line X-X+ in FIG. 1. 1... Tubular alumina porous body, 2... Maximum diameter layer, 3...
...Small diameter layer. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] A plurality of ceramic layers composed of ceramics having different pore diameters are sequentially laminated in the thickness direction from a ceramic layer composed of a ceramic layer with a large pore diameter to a ceramic layer composed of a ceramic layer with a small pore diameter. Ceramic porous body.