JPH01224282A - Thermal shock-resistant porous ceramic and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title ceramic with uniformized pore size by calcination of mullite aggregate incorporated with a specified proportion of cordierite at the melting temperature of cordierite. CONSTITUTION:Firstly, mullite (3Al2O3.2SiO2) aggregate with a mean granular size of >=3mum is incorporated with 3-50wt.% of cordierite (2MgO.2Al2O3.5SiO2) to make a form. The resulting formed product is calcined at the melting temperature of cordierite to effect binding the mullite aggregate with the melted cordierite as the binder.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention provides a filter for separating ducts in high-temperature exhaust gas;
The present invention relates to porous ceramics having thermal shock resistance that can be used as carriers for combustion catalysts, etc., and a method for producing the same.

(Prior art and its problems) Conventionally, materials that require thermal shock resistance, such as ceramic carriers for purifying automobile exhaust gas and ceramic carriers for separating solid particles in high-temperature exhaust gas, have been required to have heat resistance, thermal shock resistance, and Cordierite (2), which has excellent chemical stability etc.
MgO・zAt*os・5S i Ox), silicon carbide (SiC), mullite (3A 12O3” 2S
i O2) Mainly used.

Here, in ceramic carriers for exhaust gas purification that particularly require heat resistance, those made of the cordierite material have problems in heat resistance due to the low melting point of cordierite, and have poor heat resistance and thermal shock resistance. Mullite is superior in terms of properties, and when trying to form a ceramic carrier using this mullite as a main component, for example, in order to uniformly form good pores inside, the average particle size is about 3 μm.
If mullite with a particle size of about 3 μm or more is to be strongly bonded as an aggregate, it must be fired at a high temperature of 1700°C or more, which causes problems with the fire resistance of kilns, etc. However, there was a problem in that it was naturally expensive.

(Means for Solving the Problems) The present invention was devised in view of the above-mentioned conventional problems, and aims to provide porous ceramics having thermal shock resistance that can be molded at low temperatures. The gist is that mullite (3A l*Os-2S tOx) aggregate is
50% by weight cordierite (2M g O.2A
1 * Os ・5 S s O! ) is added, fired at a firing temperature that can melt cordierite, and the mullite aggregate is bonded with the molten cordierite.

In addition, the gist of the manufacturing method is that 3 to 50% by weight of hoop yelite (2M = 0.2A1
．． 03.5SiOx) and firing at a temperature higher than that at which cordierite can be melted.

(Function) By adding cordierite to mullite aggregate, which has excellent heat resistance, this cordierite has a lower melting point than mullite (approximately 1460°C). If fired at a certain firing temperature, the cordierite will melt during firing, and this molten cordierite will firmly bind the mullite particles, so the mullite particles will be well bound, creating a ceramic with excellent mechanical strength. It is possible to obtain uniform pores between the mullite particles, and by appropriately selecting the particle size of the mullite that is the aggregate, it is possible to easily adjust the pore size formed in the fired body. Can be changed.

Also, since cordierite has a lower melting point than mullite, it is only necessary to fire at a temperature that can melt this cordierite, and there is no need to melt mullite itself, so it is necessary to fire at a temperature of about 1400°C to 16000°C. It can be manufactured at low cost.

Furthermore, since molten cordierite exists in the joints of each particle of mullite, which is the aggregate, this cordierite has a smaller coefficient of thermal expansion than mullite, and is a porous ceramic with excellent thermal shock resistance. can be obtained.

(Examples) The following examples relate to porous ceramics for use in applications such as filters for separating dust in high-temperature exhaust gas, carriers for combustion catalysts, porous bodies for combustion, and setters for firing.

Average particle diameter 20μm (7)'f4 fused Muram 24880
When 20% by weight of cordierite is mixed and fired, the physical properties are that when the firing temperature is 1300°C, the pore diameter is 2.1 μm and the porosity is 43.4%.
The density is 1.7g/am” and the bending strength is 13kg.
f/am”.

In addition, when fired at a firing temperature of 1400°C, the pore diameter was 2.9 μm and the porosity was 42°3%.
The density is 1.7 g 7cm" and the bending strength is 63
kgf/cm'Teatsuta.

In addition, in the case of the one fired at a firing temperature of 1500°C, the pore diameter was 8 μm, the porosity was 34.6%, and the density was 2. Qg/Cm", and the bending strength is 526 kgf
/ cm” was there.

Furthermore, for those fired at a firing temperature of 1600°C, the pore diameter was 10 μm, the porosity was 25.1%, the density was 2.3 g/cm'', and the bending strength was 7.
58 kgf/Cm".

Moreover, the pore size distribution at each of the above firing temperatures was as shown in FIG.

In this way, for cordierite fired at a firing temperature of 1400"C or lower, the melting point of cordierite is 1460"C, and since cordierite has not yet melted at this temperature, although the porosity is large, it is It has a structure in which cordierite particles exist in the gaps between the mullite particles that make up the material, and it has very little strength and pore size that is a combination of mullite and cordierite.

In addition, in those fired at 1500℃ or higher, the hoop yerite is molten, so the cordierite becomes a liquid phase and covers the surface of the mullite particles, and the cordierite binds the mullite particles together and makes them strong. It has a strong structure, and its strength increases rapidly. Moreover, the pore diameter is also large due to the gaps between the mullite particles.

In this way, it was confirmed that when fired at a temperature above the melting point of cordierite, the mechanical strength such as bending strength increases rapidly, and the pore diameter becomes larger. It can be confirmed that the mullite particles are firmly bound together.

In addition, Fig. 2 shows that after firing at 1600℃, this was heated to 11℃.
It shows the powder diffraction X-ray pattern when reheated at 00°C for about 1 hour.

As is clear from the figure, the molten cordierite is crystallized by reheating, and the crystallized cordierite is placed on the surface of the mullite particles, solidifying the mullite through the cordierite. The particles form a bonded structure.

Even when cordierite is reheated and crystallized in this way, the pore diameter does not change, and a porous ceramic with excellent thermal shock resistance is produced.

The coefficient of thermal expansion of this reheated fired body is 5.6X10-'/
``C, it was able to withstand rapid cooling in water from 1000℃ more than 10 times.

The pore size can be selected by selecting the particles and diameter of mullite, which is the aggregate, and the narrower the mullite particle size distribution, the more uniform the pore size can be obtained.

Further, examples of mullite include fused mullite and crushed mullite porcelain, and in any case, the higher the mullite content, the better the fired product can be obtained.

Cordierite can be synthesized cordierite (magnetic pulverized cordierite) or cordierite composition mixture (talc, magnesium hydroxide, magnesium oxide, magnesium carbonate.

Cordierite compositions prepared using olivine, silica, kaolin, alumina, alumina hydroxide, clay, etc. may also be used.

In addition, the particle size of cordierite should be as small as possible in order to improve dispersion and make the pore size uniform, and should be about the average particle size of mullite, which is the aggregate, or less.

Furthermore, the strength increases as the amount of cordierite added increases, but the porosity decreases as the amount added increases, so the amount added is preferably 3 to 50% by weight.

For example, the average particle size of mullite, which is aggregate, is 200 to 40.
When the temperature is 0ttm, the amount of cordierite added is 2
0 to 40% by weight is appropriate, and when the average particle size of mullite is 20 to 100 μm, 5 to 30% by weight is appropriate, and when the average particle size of mullite is 3 to 10 μm, 3% by weight is appropriate.
Approximately 20% by weight is appropriate.

In addition, when the particle size of mullite, which is the aggregate, is about 3 μm or less, the mullite particles themselves sinter during firing, so it is not necessary to add hoop yerite, and this reduces the porosity. It is better not to add cordierite when the particle size is 3 μm or less.

Note that the above-mentioned crystallization of cordierite can also be carried out not by reheating but by maintaining the temperature at about 1000° C. or higher during cooling during the -th firing process.

Specific examples will be described below: fused mullite beads (100 mesh, average particle diameter 200 μm) manufactured by Pacific Random Co., Ltd., pulverized molten mullite 80F (average particle diameter 40 μm), 325F pulverized mullite (average particle diameter 2011 m) etc. can be used as an aggregate, and as cordierite 5 manufactured by Marusu Glaze Co., Ltd.
S-200 (average particle size 3 μm) can be used, and 2MgO・2A1.0.・5
S i O, such as talc 4
1.8% by weight, kaolin 43.9% by weight, alumina 14
．． 3% by weight of raw material can be used.

Using the above raw materials, mix 80% by weight of mullite as aggregate and hoop yerite or cordierite composition 2
After dry mixing 0% by weight, PVA as a binder.
12 (H1!
Press-formed into a 1×30uta plate shape, held and fired at 1500°C for 1 hour at a heating rate of about 6°C/min in an electric furnace, and then left to cool naturally in the furnace to produce a fired body, Further, it was heat-treated by maintaining it at 1300° C. for 5 hours in an electric furnace to obtain porous ceramics.

The physical properties of the obtained porous ceramics are shown in Table 1 below.
Shown below. In addition, when the porous ceramic thus obtained was rapidly cooled in water from 1000°C, it did not break even after the cooling was repeated 10 times or more.

Table 1 Various physical properties of the fired body of the example Coefficient of thermal expansion 56 to 57X10-'/'C (effect of the invention) The porous ceramic having thermal shock resistance of the present invention is composed of mullite (3At*os・2SiO2) bone 3~ for wood
50% by weight hoop yellowite (2MgO・2A1.O
,・5 SiO2) is added, fired at a firing temperature that can melt cordierite, and the mullite aggregate is bonded with the molten cordierite.It has high heat resistance and is easy to machine. It also has high mechanical strength, can make the pore diameter uniform, can be used in high-temperature atmospheres, and has the effect of expanding the range of use in high-temperature ranges compared to conventional materials.

In addition, the manufacturing method involves adding 3 to 50% by weight of cordierite (2MgO.2Al, 0..5S) to mullite (3A1.O,.2SiO*) aggregate with an average particle diameter of about 3 μm or more
By adding O2) and firing at a temperature higher than that at which cordierite can melt, it is possible to melt cordierite and firmly bond mullite, which is an aggregate, and to reduce manufacturing costs. This has the effect that porous ceramics that are strong and heat resistant can be easily obtained in an oxidized state.

[Brief explanation of the drawing]

Figure 1 is a pore size distribution diagram at various firing temperatures when 80% by weight of fused mullite with an average particle diameter of 20 μm and 20% by weight of synthetic cordierite is mixed and fired, and Figure 2 is a pore size distribution diagram of 160% by weight of fused mullite with an average particle diameter of 20 μm.
This is a powder diffraction X-ray pattern diagram when fired at 0°C and then reheated at 1100″C for about 1 hour. Patent applicant Inax Co., Ltd. Agent
Patent Attorney Yoshihisa Shimizu 04
/Q 10 more (4th colonel, /A
4f% Figure 1 10 2ri meku
+, r rim -, 2ρ (dt2.) Fig. 2

Claims (2)

[Claims] (1) Mullite (3Al_2O_3・2SiO_2) aggregate with 3 to 50% by weight of cordierite (2MgO・2
A porous ceramic having thermal shock resistance, which is made by adding Al_2O_3・5SiO_2), firing at a firing temperature that can melt cordierite, and bonding the mullite aggregate with the molten cordierite. (2) Mullite (3Al_2
O_2・2SiO_2) 3-50% by weight of cordierite (2MgO・2Al_2O_3・5SiO_
2) and firing at a temperature higher than that at which cordierite can be melted.