JPS5844608B2 - Method for producing cordierite composition powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing cordierite composition powders of desired proportions and highly homogeneous, finely divided powders.

In general, cordierite (2MgO.2A1203.5SiO2) exhibits very low thermal expansion over a wide temperature range and has excellent resistance to thermal shock when subjected to sudden temperature changes.

For this reason, cordierite is widely used as heat-resistant hot plates, bicam-shaped structures for purifying automobile exhaust gas, heat-resistant materials for physical and chemical applications, and the like.

Generally, cordierite is obtained by firing a combination of kaolin, talc, magnesite, aluminum oxide, magnesium hydroxide, clay, etc.

Theoretically MgO/3.7%, A1□0334.9%,
SiO251.4%, but generally MgO70~1
6%, Al2O333-41%, 5iO243-56%
range is used.

However, recently, cordierite has been synthesized using artificial raw materials rather than natural raw materials.

It has been confirmed that the presence of impurities, especially calcium oxide and alkali, increases the thermal expansion coefficient and adversely affects thermal shock resistance.

By using high-purity raw materials and the theoretical composition of cordierite, it has the lowest coefficient of thermal expansion and high thermal shock resistance, but because low-temperature 'liquid phase formation does not occur, the firing temperature can be increased This results in a narrow firing range, making sintering difficult and making the properties inconsistent.

According to the present invention, a fine powder can be obtained which is almost completely homogeneously mixed in a desired proportion, for example, the theoretical composition of cordierite exhibiting the smallest thermal expansion.

Its most distinctive feature is the method of adjusting silica and magnesium, which are important components of cordierite.

One method is to use a silicon organic compound as the silica, but this method is also expensive and requires complicated operating procedures.

Water drop is a method in which at least one selected from finely powdered silica, silica sol, and silica gel is added instead of a silicon organic compound.

Methanol, ethanol, propatool, acetone, ethylene glycol, etc. are used as water-soluble organic solvents, and their presence facilitates the formation of precipitates.

Furthermore, when adding ammonia alkaline ammonium carbonate to form a precipitate, a solution of ammonium carbonate dissolved in aqueous ammonia is used since the concentration of a normal aqueous solution of ammonium carbonate is insufficient.

6N-(NH4)2CO3 in the example is ammonia alkaline ammonium carbonate, and when this is added, the solubility of the magnesium component decreases and almost completely precipitates.

In the past, attempts have been made to produce high-purity cordierite, such as a method for producing cordierite by melting, but this is not common.

Also, a combination of high purity MgO, Al2O3, 5i02, 2Mg0+2A1203: 5Si02.2Mg
0+5Si02: 2A1203.2A1203 +
58in2:2Mg012Mg0+2A1203 +5
In combination with Si02, mineralizing agents (e.g. L
If there is no iFMgF2) 2Mg0+2A1203:
Spinel and silica, which is a combination of 5Si02, is said to be the most difficult to synthesize.

The best synthesis is achieved when a mineralizing agent is present, but currently fluorine is a pollutant, and lithium is an alkali, so it has drawbacks such as deterioration of electrical performance and fire resistance.

Although the cordierite composition prepared by this method is slightly less fine than when using a silicon organic compound,
A more uniform fine active powder can be obtained when the fine powders are mixed individually.

The cheapest silica source is finely divided silica powder, and the finer the powder, the better the results.

Also, when using what is currently available as silica sol or silica gel, if the SiO2 content is taken into account,
It can be formulated in the same manner as for finely divided silica powder, in which case a finer activated cordierite composition powder is obtained.

Theoretical composition from natural raw materials and general chemical powders,
During the synthesis process of cordierite by firing, various minerals such as enstatite, mullite, and gamma alumina appear in X-rays.1. At the same time as these disappear, it becomes cordierite.

It also tries to be easily converted into mullite.

Therefore, it is very difficult to adjust the cordierite formation.

On the other hand, in this method, spinel is generated during the synthesis process, and this turns into cordierite.

The difference from silicon organic compounds is that the disappearance of silica is slightly delayed during the synthesis process.

But in reality, there is no difference.

Therefore, it has heat resistance during the synthesis process, the shape of the molded body is well maintained, and cordierite can be synthesized easily.

In addition, it does not show the orientation that occurs when natural raw materials are used, and if necessary, trace components can be added easily and uniformly.

Next, the present invention will be explained in detail.

Example 1 Using high-purity reagents MgCl2・6H20, AlCl3・6H,,0 and reagent grade fine powder silica (particle size 2 μm), 201 was obtained with the theoretical composition of cordierite 2Mg0・2A1203・5SiO2 Therefore, first MgCl2・6H20 and AlCl3・6
H20, finely powdered silica and 500 cc of water were mixed and stirred, then 400 cc of ethanol was added, and the mixture was further mixed and stirred well.

Next, 6N-(NH4)2co3200CC was added, mixed, stirred, centrifuged, and dried by infrared rays to obtain a blended powder of cordierite.

This thing has MgO/3.6%, Al2O335.5%,
5in250.9%, which is almost the same as the theoretical composition, was compressed to a diameter of 281nm by applying a pressure of 500kg/crA.
It was molded into a disk with a thickness of about 3 mπ.

The sintered body that was fired at 1375°C for 1 hour in an electric furnace with a SiC heating element was found to be only cordierite by X-rays.
The coefficient of thermal expansion from room temperature to 960°C is 2. lX10-6
Met.

On the other hand, when ethanol is not used, cristobalite appears in X-rays by the same operation, and the coefficient of thermal expansion is 2.
．． 8XICl".

Example 2 Using reagent-grade MgCl2.6H20, AlCl3.6H20, and high-purity fine powder silica (manufactured by Mallinckroad, anhydrous), to obtain 21' with the composition of 2Mg0.2A1203.5Si02, first MgC1□. 6H20 and AlCl3・6H20 were dissolved in 500 cc of water, 500 cc of acetol (CHs COCH20H) was added and stirred, a predetermined amount of high-purity silica was added, mixed, and 6N-(
Add 200CC of NH4)2CO3, stir, centrifuge,
A mixed powder of cordierite was obtained by infrared drying.

This powder was pressurized at 500 kg/crti to a diameter of 28 m.
m.

Formed into a disk approximately 3 mm thick and heated at 1400°C for 1 hrS.
A sintered body was obtained by firing in an iC heating element electric furnace.

Only cordierite is fixed by X-ray diffraction, and the average coefficient of thermal expansion from room temperature to 960℃ is 2.0X.
10-6, the firing shrinkage in both the pressing direction and the direction perpendicular to this is as small as 5.3%, and the water absorption rate is 17%.
It was highly fire resistant.

Example 3 The same procedure was carried out when a sol with a 32% silica concentration hydrolyzed from ethyl silicate was used instead of the finely divided silica in Example 1, and when pulverized silica gel (containing 37.5% water) was used. Cordierite blend powder was obtained by the operation.

All of these were fired at 1200℃ and 1hr, and spinel and cordierite were identified by X-rays.
As the temperature rose, the spinel lines disappeared and the material became completely cordierite.

In the same manner as in Example 1, the coefficient of thermal expansion from room temperature to 960°C was in the range of 2.0 to 2.1X10-6, and the results were similar to those obtained when using silicon organic compounds or fine powder silica. No increase in thermal expansion due to cristobalite etc. was observed.

Claims (1)

[Claims] 1. To obtain the composition of cordierite, first add water-soluble organic A method for producing cordierite composition powder, which comprises adding a solvent and stirring, then adding an ammonia-alkaline ammonium carbonate solution to form a precipitate, and separating and drying this precipitate.