JPH0465372A - Production of high strength porous ceramics - Google Patents

Abstract

PURPOSE:To obtain high strength porous ceramics constituting of three- dimensionally interlaced crystals and having continuous spaces at the inside of firing a molded body of acicular mullite powder extracted from a fired clay mineral. CONSTITUTION:A clay mineral contg. silicon dioxide and aluminum oxide as principal components is fired and a glass component is leached out with an acid and alkali to obtain acicular mullite powder. This mullite powder or a mixture of this powder or a mixture of this powder with an org. material is molded and this molded body is fired to obtain porous ceramics having freely controlled characteristics or pores.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to an oxidizing atmosphere at 1000 to 1700°C. (2) Mix ceramic powder with polymer powder, organic fiber, carbon powder, etc. as a pore-forming material, mold it, and then bake it to completely remove combustible substances. (3) A method of manufacturing by impregnating a polymeric foam material with a ceramic slurry and then manufacturing the polymeric foam material by causing it to disappear by heat treatment.

[Problem to be solved by the invention] In ceramic porous bodies manufactured using conventional techniques, when bonding individual ceramic particles, a glassy flux or a clay substance is used as a binder. The body's heat resistance and chemical resistance tend to decrease,
Porous bodies generally have low strength (curved strength), and most of the values reported so far are below 200 kgf/cm2.

Furthermore, under high temperatures, the binder softens, which tends to change the porosity and pore diameter, and furthermore, when the bonds between particles are weak, the strength tends to drop significantly.

[Means for Solving the Problems] The present inventors have discovered that acicular or whisker-like mullite, which is calcined and extracted from clay minerals, 1) has a low content of alkaline impurities that tend to form a glass phase; 2) It has been clarified so far that it is heat resistant up to about 1700 degrees Celsius in air, does not change its shape easily, and 3) has relatively low thermal expansion (Japan Ceramic Nox Association Academic Journal, No. 97). No. (1989). Focusing on the fact that when these crystals are tightly intertwined three-dimensionally through sintering, a continuous space is created inside, we developed a simple process in which only acicular mullite is molded into the desired shape and then fired. As a result, we have found a way to produce ceramics that have high strength and excellent porous properties (e.g., porosity and pore diameter) at high temperatures. That is, after forming only acicular mullite with a length of 1 to 20 μm and a thickness of 113 μm into a plate, pipe, or honeycomb shape by die press molding, casting molding, or extrusion molding, it is heated at 1500 to 1700°C. Burning in air for 1 to 5 hours, or mixing and molding acicular mullite with polymer powder such as acrylic resin or polyethylene, activated carbon, or carbon fiber powder to release flammable material in air. This is a method in which porous properties (porosity, pore distribution) can be freely controlled by vanishing, and high strength porous ceramics can be obtained.1500-1700°C
In this case, since the A1 or 81 components in mullite interdiffuse on the surfaces of individual crystals, sintering between crystals is likely to occur. Therefore, in the production of conventional porous bodies, binding aids or sintering aids were required to bond the constituent particles, but the method of the present invention does not require such aids at all. Furthermore, since mullite is an oxide with strong covalent bonding properties, once bonds are formed between crystals, the bonds at the interface become stronger, and the strength of the porous body composed of acicular mullite increases. Furthermore, the porosity and pore diameter can be freely controlled by changing the size and amount of the mixed combustible material.

[Example] Examples of the present invention will be described below.

Example 1 30 g of acicular mullite powder was placed in a mold with a diameter of 60 mm and subjected to primary molding at 200 kgf/cm2.

Alternatively, it is subjected to isostatic pressing at f&l~4 ton/cm2 and fired in air at 1500~1700°C for 1~5 hours. Table 1 shows the average three-point bending strength, porosity, pore diameter, and average coefficient of thermal expansion from room temperature to 1400°C of the porous bodies obtained under each condition.

In particular, porous bodies fired at temperatures of 1650°C or higher are
There is almost no change in the properties of the porous material even if it is reheated for several tens of hours at 00 to 1650°C.

Example 2 50 g of acicular mullite, 1 to 2 g of binder, and 3 g of deflocculant
After adding ~4 g and 12 to 13 g of pure water, mix thoroughly.
This slurry was cast into a plaster mold, and the length was 50 mm.
A plate-shaped molded body having a thickness of approximately 5 mm and a width of 30 mm was obtained. After drying, it was fired in air at 1500-1650°C for 1-5 hours. The average three-point curve of the porous material obtained under each condition was determined by the strength, porosity, pore diameter, and average coefficient of thermal expansion from room temperature to 1400°C as shown in Table 2. Because the distribution and orientation became easier, the strength increased compared to the porous body obtained by molding.

Example 3 Diameter: 10 μm, length: 100 μm for 20 g of acicular mullite
After adding 10 g of ~200 μm carbon fiber powder, 2 g of methyl cellulose, and 40 g of pure water and mixing thoroughly, a plate-shaped (5 x 20
x50mm). After drying 1600~]7
Bake at 00°C for 2 hours. At 1600°C, the average 3-point bending strength is 350-4. OOkgf/cm" and a porosity of 49 to 52%, but the pore diameters are sharply distributed between 0.7 to 0.8 μm and 6 to 7 μm as shown in Figure 1. This is acicular mullite. It means the distribution of pores formed by combustion and disappearance of carbon fibers. Also, at 1700°C, the average 3-point bending has a strength of 480
-530kgf/cm2. A porous body with a porosity of 36 to 41% can be obtained, and the pore diameter is 0.4 to 0.6 μm and 4 to 5 μm.
It is distributed in m.

As described above, the pore characteristics of the porous body made of acicular mullite can be controlled by adding the combustible substance (size, amount added).

[Brief explanation of tables and figures] Table 1 shows mold forming or subsequent 1 to 4 ton/cm2
These are the results of the average three-point bending strength, porosity, pore diameter, and coefficient of thermal expansion of a porous body of acicular mullite that was hydrostatically formed and fired at 1500 to 1700°C. Table 2 shows the results of various properties of porous bodies obtained by firing at 1500 to 1650°C after casting.

Figure 1 shows the pore distribution of a porous body obtained by adding carbon fiber powder to acicular mullite, mixing, casting, and firing at 1650°C.

Characteristics of various porous bodies Table 2: Characteristics of porous bodies obtained by casting and firing: 0.7
5 4.4 0.66 4.8 0.62 4.5 Procedural amendment (method) % formula % 1. Display of case 1990 Patent Application No. 173285 2. Name of invention Manufacture of high-strength porous ceramics Method Pore dian+eter (A) Figure 1 Pore distribution characteristics of acicular mullite 3, relation to the case of the person making the correction Address name Name

Claims (2)

[Claims] (1) Using acicular mullite powder obtained by sintering clay minerals mainly composed of silicon dioxide and aluminum oxide, and eluting the coexisting glassy components with acid or alkali, the acicular mullite powder is obtained by sintering after various moldings and sintering. A method for producing high-strength porous ceramics characterized by being composed only of mullite. (2) A method for producing high-strength porous ceramics, characterized in that the pore characteristics can be freely controlled by mixing the acicular mullite powder and an organic substance that is burnt out by combustion, followed by molding and firing.