JPH0218367A - Production of porous ceramics - Google Patents

Abstract

PURPOSE:To obtain the porous ceramics which has excellent mechanical strength and thermal impact resistance and does not require a holding material at the time of use by adding and dispersing a foaming agent having the sp. gr. different from the sp. gr. of a sol into the sol, then solidifying and drying the sol in the stage when the concn. of the foaming agent in the sol is inclined by the difference in the sp. gr. CONSTITUTION:The following structure is adopted in the production of ceramics by a sol-gel method: The foaming agent having the sp. gr. difference from the sol is added into the formed sol and thereafter, the sol is cast into a mold of an arbitrary shape. The dry gel is then formed by solidifying and drying the sol in the stage when the concn. of the foaming agent in the sol is inclined by the difference in the sp. gr. This gel is heated to the decomposition temp. of the foaming agent or above to decompose the foaming agent incorporated therein and further, this mixture is calcined. The foaming agent to be used is exemplified by org. foaming agents of an azo system, hydrazine system, N-nitron system, etc., org. resins such as polystyrene and polyethylene and inorg. materials such as carbon and CaCO3 and all these compds. may be usable.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to porous ceramics used for gas separation under high pressure and high temperature, catalysts for desalination of seawater, and supports for immobilized enzymes and inorganic catalysts. Relating to a manufacturing method. [Prior art] Figure 5 shows the simple manufacturing method for porous glass, which is the most famous conventional porous ceramic.
After preparing the raw material consisting of ano-B*0s-SiOx, it is melted at a high temperature of about 1500°C, and further heated at a temperature of 800°C to 110°C.
It is molded into shapes such as tubes and roots at a temperature of 0°C. Since the borosilicate glass obtained at this time is unseparated, the temperature at 500°C
Phase separation treatment is performed in the temperature range of ~650°C, and N a *
O-B O0. It is separated into two phases: phase and S i O* phase. When this split-phase glass is acid-treated with nitric acid or hydrochloric acid,
The N a *O-B□O1 phase, which is easily soluble in acid, is eluted, and only the S i O* phase remains. NagO-B
Since the *O* phase and 51b are intertwined, the remaining SiO* glass is a porous glass having countless continuous pores. In addition, ceramics can be manufactured using the sol-gel method (see Japanese Patent Laid-Open No. 59-92924). In this case, the sintering conditions can be controlled by taking advantage of the fact that the resulting ceramics tend to have pores. A method of making porous ceramics by doing so is also being considered. Furthermore, there is also a method for producing foam glass, in which a glass raw material and a foaming agent are mixed and then treated at high temperature to perform fusing and foaming at the same time. [Problem to be solved by the invention] However, with the conventional manufacturing method, only porous ceramics can be created in which the porosity of the ceramic is constant regardless of the location. In normal use, porous ceramics are difficult to use alone and require a retainer, and porous materials lose strength at the interface when joining/adhering with other parts, so they cannot be used at high temperatures. The problem is that it is difficult to use under such harsh conditions. The present invention aims to solve these problems5.The purpose of the present invention is to improve mechanical strength and heat resistance by having two different characteristics, porosity and denseness, in a single ceramic. It is an object of the present invention to provide a method for producing porous ceramics that has excellent impact resistance and does not require a holding material during use. [Means for Solving the Problems] The method for producing porous ceramics of the present invention involves adding and dispersing a blowing agent having a specific gravity different from that of the sol in the produced sol in producing ceramics by the sol-gel method. After that, this sol is poured into a mold of any shape, and when the concentration of the blowing agent in the sol slopes due to the difference in specific gravity, it solidifies and dries to form a dry gel, and this gel is heated above the decomposition temperature of the blowing agent. , the foaming agent contained therein is decomposed, and the mixture is then fired. [Function] According to the present invention, foaming agents with different specific gravities are added to the sol.
After dispersion, the sol is solidified and dried at a stage where the concentration of the blowing agent in the sol is tilted due to the difference in specific gravity, so that the porosity distribution of the resulting porous ceramic is tilted. [Example 1 (Example 1) The manufacturing process of porous ceramics of the present invention is shown in FIG. 4. Ethyl silicate was hydrolyzed under acidic conditions, and SiO fine particles with an average particle size of 0.05 to 0.4 (um) were added thereto, and azodicarbonamide was added as a foaming material to the solution.
After adding 1 (wt%), ammonia water was added to adjust the pH to 4.
．． Adjust the sol to 0. This sol is placed in a polypropylene container and stored in a sealed state for 48 hours to prevent gelation. At the stage when the concentration of the blowing agent in the sol becomes gradient due to the difference in specific gravity, a wet gel is created. Thereafter, the wet gel is taken out from the sealed container and dried for two weeks to create a dry gel. Put this dry gel in a firing furnace for 30 ('C/hour)
Heat to 200°C at a heating rate of 200°C and hold at the same temperature for 5 hours, then further heat to 300°C and hold at the same temperature for 5 hours to completely decompose the added azodicarbonamide and perform desorption water treatment. . The dry gel is further heated to 1000°C at a heating rate of 30 ('C/hour), and fired by holding at the same temperature for 20 hours to obtain porous ceramics. Firing is performed in a nitrogen atmosphere or in a vacuum, but it is desirable to perform the foaming and degassing steps in a vacuum until the foamed material is completely decomposed. The foaming materials used are typified by azo-based materials such as azodicarbonamide, hydrazine-based materials such as diphenylsulfone-3,3° disulfohydrazine, and N-nitroso-based materials such as N,N'-dinitrosopentamethylenetetramine. Any of organic foaming agents, organic resins such as polystyrene and polyethylene, and inorganic materials such as carbon and CaCOs may be used. The shape of the created ceramic is φ80×t20(+n
m) is disc-shaped. This ceramic was divided into 10 equal parts in the thickness direction, and the porosity of each sample was measured. Regarding this ceramic, the relationship between the distance from the base and the porosity is shown in Figure 1, and a schematic diagram of the cross section of the sample is shown in Figure 4.
1 is the top, 2 is the hole, and 3 is the bottom part. Since the specific gravity of the blowing agent azodicarbonamide used in this example is lower than the specific gravity of the sol, the blowing agent gathers in the upper part. When this is gelled at an appropriate stage, it solidifies with a gradient in the concentration of the foaming agent, and when foamed and fired, a porous ceramic with a gradient in void efficiency is obtained. (Example 2) In Example 1, the amount of blowing agent and firing temperature were changed as shown in Table 1 under the manufacturing conditions to create porous ceramics with various porosity distributions. . Table 1 The prepared sample was divided into 10 equal parts in the thickness direction as in Example 1, and the porosity of each was measured. FIG. 2 shows the relationship between the distance from the base and the porosity for each ceramic. By changing the manufacturing conditions, the porosity distribution can be changed. It is also possible to control the pore size in ceramics in the same way, and in experiments it is possible to control the pore size in the range of tens (people) to hundreds (μm).
A range of pores was obtained. (Example 3) Hydrolyzing aluminum isopropoxide under acidic conditions,
To this, Al with an average particle diameter of 0.05 to 0.08 (μm)
After adding mOs fine particles and further adding 0.1 (wt%) of azodicarbonamide as a foaming material, ammonia water was added to adjust the pt-t to 4.0 to prepare a sol. This sol is placed in a polypropylene container and stored in a sealed state for 48 hours to prevent gelation. A wet gel is created at the stage where the concentrations of the sol and the foaming agent become gradient due to the difference in specific gravity. Thereafter, the wet gel is taken out from the sealed container and dried for two weeks to prepare a dry gel. Put it in this dry gel sintering furnace and heat it at 30℃/℃ in vacuum.
Heating to 200℃ at a temperature increase rate of 2 hours) and storing at the same temperature for 5 hours, further heating to 300℃ and keeping at the same temperature for 5 hours to completely decompose the added azodicarbonamide and treat the desorbed water. Do this. The dry gel was further heated under a nitrogen atmosphere at a heating rate of 30 ('C/hr) for 12
The sample is heated to 00°C and kept at the same temperature for 20 hours for firing to obtain porous ceramics. The shape of this porous ceramic is (outer diameter) 100X (inner diameter) 70Xt20 (+
n+n), and similarly to Example 1, this ceramic is divided into 10 equal parts in the thickness direction, and the porosity of each sample is measured. Regarding this porous ceramic, the relationship between the distance from the base and the porosity is shown in FIG. 3, and its external view is shown in FIG. 4. The method for producing porous ceramics of the present invention includes the above-mentioned S t
In addition to Ox-based and A 1 s Os-based materials, ZnO-based and S
It is effective for all ceramic materials such as nOs type and V x Os type. Furthermore, as shown in this embodiment, by conventional manufacturing methods such as ring shapes, complex shapes that require secondary processing can be easily created. [Effects of the Invention] As described above, according to the present invention, after dispersing a foaming agent having a specific gravity different from that of a sol into a sol, the gel is formed by using the difference in specific gravity at a stage where the concentration of the foaming agent is inclined. foaming and
By firing, it is possible to produce porous ceramics that have two contradictory properties: porosity and density. Further, the porosity distribution of the obtained porous ceramic can be changed depending on the manufacturing conditions, so that ceramics having any desired porosity distribution can be easily manufactured. Furthermore, the manufacturing method of the present invention takes advantage of the characteristics of the ceramic manufacturing method using the sol-gel method. This has the effect that samples with complex shapes can be easily manufactured.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the porosity distribution of SiO3-based porous ceramics produced by the manufacturing method of the present invention. FIG. 2 is an external view of a cross section of porous ceramics prepared under different manufacturing conditions. FIG. 3 shows A 1 x03 manufactured by the manufacturing method of the present invention.
A diagram showing the porosity distribution of the porous ceramics of the system. FIG. 4 is a schematic diagram of a cross section of porous ceramics produced by the manufacturing method of the present invention. FIG. 5 is a process diagram showing the method for manufacturing porous ceramics of the present invention. FIG. 6 is a process diagram showing a conventional method for manufacturing porous ceramics. Applicant Seiko Epson Co., Ltd. Agent Patent Attorney Kizobe Suzuki (and 1 other person) Figure 2 Rhythm =) / IX Sono ¥F Kame 1 (1~) Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] In the production of ceramics by the sol-gel method, a blowing agent with a specific gravity different from that of the sol is added and dispersed in the created sol, and then this sol is poured into a mold of any shape, and then the sol is expanded due to the difference in specific gravity. When the concentration of the foaming agent in the gel reaches a gradient, it solidifies and dries to form a dry gel, and this gel is heated above the decomposition temperature of the foaming agent to decompose the foaming agent contained therein.
A method for producing porous ceramics, which further comprises firing this mixture.