JPS63103877A - Manufacture of mullite base porous body - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for producing a porous mullite body whose main structure is acicular crystals of mullite.

"Conventional technology" Conventionally, ceramic porous bodies (including mullite porous bodies) have been used.

) is a method in which the particle size structure of the raw material is adjusted to increase the porosity of the molding opening 1, and then the particles are bonded by sintering in the initial stage U, and the porous body 1' is formed.

A flammable pore-forming material such as cellulose or carbon material is mixed with ceramic raw material powder, molded, and fired to avoid sintering, and at the same time, combustible material 71 is burned to form pores. , methods of obtaining porous bodies, etc. (ceramics, 3.
168 [1985]).

``Problems to be solved by the invention'' However, these methods use amorphous or nearly spherical raw material powder and utilize the voids between particles, making it difficult to obtain a high porosity. is approximately 30-50
It's %. Furthermore, when the particles are bonded during the initial stage of sintering, the adhesive force between the two particles is weak, resulting in a decrease in the strength of the resulting porous body itself, and when sintering is performed to increase the primary strength. However, there were problems such as a decrease in porosity.

"Means for Solving the Problems" The present invention has been made to solve these problems, and is a method of molding and firing mullite-based porous material containing alumina and silica as main components. IjlE
Additives are added to the mullite to prevent unreacted or excessive silica and unavoidable impurities from transferring to the glass phase during C2 firing, suppress the formation of cristobalite, and at the same time act as a mineralizing agent for mullite. The glass phase in the sintered body is then eluted with acid to form a mullite porous body (7) whose main structure is acicular crystals of mullite.

As LFI materials containing alumina and silica as main components, phosphorus, sillimanite, silica, silica, feldspar, aluminum sulfate, water glass, etc. are used singly or in combination, but as long as they produce mullite by firing, It can be used regardless of whether it is natural or artificial.

Additives include metal oxides and halides.

Carbonates, etc. are used, but the types and types of additives used vary depending on the type and combination of starting materials.

However, in the case of any additive, the purpose of its addition is to serve as a mineralizing agent to improve the yield of mullite, or to prevent unreacted or excess silica from converting into grease 1 to pallite. It's about restraint. In other words, unreacted or excess silica present in the raw material changes into β-thuli heparite at temperatures above 100°C and becomes 2O during the cooling process.
At around 0°C, it changes from °αcris1 to palite, but at this time, a change in volume occurs. This causes the formation of microcracks in the sintered body, or even the destruction of the sintered body itself. Therefore, it is necessary to avoid residual grease 1 to pallite as much as possible after firing.

Additives are useful for this purpose.

After firing, the sintered body consists of mullite crystals, a glass phase surrounding them, and, in some cases, unreacted or excessive α-
Composed of alumina. By immersing this sintered body in an acid solution maintained at a predetermined concentration and temperature for a certain period of time, the glass phase in the sintered body is eluted. After elution, it becomes a porous body in which needle-shaped mullite crystals intersect three-dimensionally. Although hydrofluoric acid is often used as the acid solution used to elute the glass phase, other acid solutions can be used depending on the properties of the glass phase.

"Effect" The mullite 11 porous material obtained by this method has a large porosity because the main constituent elements of the structure are ε1-like crystals of mullite 1, and also has a three-dimensional intersecting structure, so the bending strength is also comparative. Strong to the point.

"Example" Examples of the present invention will be described below.

Example 1 Roxite with an average particle size of 1 μm and aluminum hydroxide of first class reagent were mixed at a ratio of A 12 O 3 : SI 02 of 3:2, and the additives shown in Table 1 (see below) were added to this mixture. Add 1% by external cutting. Furthermore, 0.5% of polycarboxylic acid anthinium was added as a peptizer by external cutting, and the moisture content was 40%.
It was made into a slurry. This was mixed in an alumina ball mill for 12 hours, dried, crushed, and granulated using an 80-mesh sieve. This powder was molded at a pressure of 300 K'1/cIi,
It was baked at 1400°C for 1 hour.

This sintered body was immersed in a hydrofluoric acid solution at a temperature of 0° C. and a permeability of 46% for 8 hours, and then taken out, thoroughly washed with water, and dried to obtain a porous body with a quality of 1 to 100 ml.

The crystalline phase constituting the sintered body and the properties of the porous body (7) are shown in Table 1 (see below). As a result of observation with an electron microscope, the size of II pores of the porous body obtained by this method is approximately 1
It was μm.゛No. 2 within the scope of the present invention
3.4.5, 6°7, 8.10.11.12.14.1
In No. 5, the crystal phase of α-cristobalite is not observed in the sintered body, or even if it is observed, it is in an extremely small amount, and its influence can be ignored. For No. 1.9 and 13.16 outside the range, α-Curi Example 2 Added 1% each of the additives listed in Table 2 (listed later) to halloysite with an average particle size of 1 μm, and the same as Example 1. A porous body was obtained using the method described above. The properties of the sintered body and the porous body 1q are as shown in Table 2. No. 17.2O within the scope of the present invention
．． In No. 21, the formation of α-cristobalite was suppressed, and as a result, a healthy porous body could be obtained. Samples outside this range will cause microcracks to form and the sintered body to break, making it impossible to obtain a perfectly porous body.

Example 3 Aluminum hydroxide and silica stone were mixed into A12O. , :SiO2
The mixture was mixed in a ratio of 1:2.1:1.3:2, 2:1.3:1, and v2O5 was added as an additive in a range of 1 to 5% at external v1. To this, 1% ammonium polycarboxylate was added externally as a peptizer to make a slurry with a moisture content of 40%, and a disk with a diameter of 30 mm was formed by molding. After baking this at 1400° C. for 10.1 hours, it was immersed in 46% hydrofluoric acid for 8 hours, taken out, and thoroughly washed with water. The properties of the sintered body and the porous body obtained are as shown in Table 3 (secondary part). As a result of electron microscopic observation of samples No. 36, 37, 38, and 39 within the scope of the invention, pores of about 1 μm were uniformly observed, and no cracks were observed. No. outside the scope of the invention;
In No. 33, No. 34, and No. 35, α-cristobalite was generated, so healthy tissues could not be obtained.

"Effects" The above two mullite porous materials according to the present invention have a fine porous structure and relatively high JJF resistance, and can be used for various industrial filters, bubble generators, bioreactor carriers, catalysts, etc. For the first time, 4J is effective (・Yes.

Table 2

Claims (1)

[Claims] Mullite (3
AL_2O_32SiO_2) In the method of obtaining a porous material, unreacted or excess silica is transferred to the glass phase during firing by adding additives to the raw material powder, and the formation of cristobalite is suppressed, and this glass phase is removed after firing. 1. A method for producing a mullite porous body, which comprises obtaining a porous body consisting of needle-like crystals of mullite by eluting the mullite with an acid.