JPS63233009A - Production of mullite powder and its sintered body - Google Patents

Abstract

PURPOSE:To obtain mullite powder having high purity, high strength and useful for material for high temp. furnace at low cost by dropping a specified raw material of Al and an aq. soln. of alkali silicate into water at the same time, agitating, bringing into reaction and then calcining the obtained product. CONSTITUTION:(D) Raw liquid material contg. Al is obtained by compounding (A) aq. soln. of Al salt such as AlCl3, (B) the A soln. and a soln. of alkali aluminate or (C) slurry of Al(OH)3 gel. Then, (E) a soln. of alkali silicate and the D component are compounded so that molar ratio of Al2O3/SiO2 in the D and E component expressed in terms of oxide become 1.1-2.4, is simultaneously dropped down into water of pH4.5-10 and brought into reaction at 10-80 deg.C for 3-6hr. Next, the mullite powder is obtained by calcining the obtained product at 900-1,600 deg.C after washing with water and drying. Then, the sintered body of mullite having >=3.00g/cm<3> bulk density, <=4% porosity and about 40kg/mm<2> bending strength is formed by molding the obtained powder, and then sintering at 1,500-1,800 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing mullite powder and a method for producing a mullite sintered body.

13 Mullite, which has a composition of Al2O, .2SiO2, is an oxide that has excellent properties such as low density, low coefficient of thermal expansion, and good creep properties at high temperatures. Tsukusu is becoming increasingly useful as a heat-resistant, high-strength material.

Mullite is generally produced by mixing clay material with alumina and firing the mixture. However, since such a method uses natural products as raw materials, the composition of the raw materials fluctuates widely and it is difficult to mix them completely uniformly, resulting in poor compositional uniformity of the resulting mullite. Furthermore, there is also the disadvantage that a high temperature of 1600° C. or higher is required to form mullite, and a large amount of energy is required. Furthermore, the strength of the nine mullite sintered body obtained by such a method is as low as about 10 gen/1 ut2, and a method for producing mullite with higher strength is required for industrial use.

Therefore, various methods for producing high-strength mullite have been investigated.
A method of reacting under high temperature and high pressure conditions of about IF/HIE2, ■ A method of reacting aluminum and silica with alkali, ■ A method of reacting a water-soluble aluminum salt and silica sol by mixing and adding an alkali, and As a precipitation method, a method in which an alkali silicate is reacted dropwise into a polybasic aluminum 1IISS solution, or a method in which a solution of an aluminum salt is reacted dropwise into an alkali silicate solution, etc., are newly being studied.

Problems to be Solved by the Invention However, among these methods for producing mullite, the above method (■) requires special equipment to carry out the reaction under high temperature and high pressure, and requires a large investment in equipment. In addition, the silica sol used as a raw material is an aggregate of silica, and the silica aggregate co-precipitates with aluminum, resulting in poor atomic compositional uniformity. , and its bondability with aluminum is weak, resulting in a high temperature at which it becomes mullite. In addition, in the above-mentioned method (2) using Alco beef shito, one raw material, Alco beef shito, is expensive, and heating is required for hydrolysis. For this reason,
The resulting mullite is expensive and is only used for very limited purposes.Also, the method described in (2) above, in which an alkali is added to a mixture of a water-soluble alkali salt and silica sol, is used to react with one alkali. By adding , the pH of the reaction solution changes, and the composition of the coprecipitate produced by the reaction is not constant, resulting in the formation of particles with poor uniformity. This also applies to the method of dropping an alkali silicate into an aqueous polybasic alkali salt solution or the method of dropping an aqueous aluminum salt solution into an alkali silicate solution as described in (2) above. Since the door B changes, the composition of the reaction product is not constant and the particles are not uniform. With mullite powder of such poor uniformity, it is difficult to remove impurities, and washing requires a large amount of water and labor. In addition, the mullite sintered body obtained using such mullite powder has uneven quality and inferior properties such as strength and creep properties. In view of the current situation, we have conducted extensive research to find a method to produce high-purity mullite powder at low cost, and a method to produce high-purity, dense, and high-strength mullite t-ramix through a simple process. Tekimaru. As a result, a liquid raw material containing a specific aluminum compound,
The product obtained by simultaneously dropping and reacting aqueous lII solution of alkali silicate into #H4, 5-10 water is 9
It has been found that it is possible to form mullite at a relatively low temperature of 00 to 1,600°C, and that the resulting mullite powder has high purity and excellent sintering activity.

In addition, the mullite T-ramix obtained by molding and firing this mullite powder has a uniform composition in which 1 mullite microcrystal is strongly sintered, and has excellent strength and creep properties at high temperatures. This finding led to the completion of the present invention.

That is, the present invention comprises: 1) an aluminum salt aqueous solution; b) an aluminum salt aqueous solution and an alkali aluminate aqueous solution; or C) an aluminum hydroxide gel slurry; and an alkali silicate aqueous solution are stirred. A method for producing mullite powder, characterized by simultaneously dropping it into water and reacting at 5 to 10 H4, washing the obtained product with water, drying, and then calcining at 900 to 1600 ° C., and d ) Aluminum salt aqueous solution, aluminum salt aqueous solution and alkali aluminate aqueous solution, or l) Aluminum-containing liquid raw material, which is aluminum hydroxide gel slurry 1, and an alkali silicate aqueous solution are simultaneously dropped into water with stirring, and fill 4 A mullite sintered body characterized by reacting at 5 to 10 degrees Celsius, washing the obtained product with water, drying, firing at 900 to 1600°C, then molding and firing at 1500 to 1800°C. A manufacturing method is provided.

In the method of the present invention, an aluminum-containing liquid raw material is used as the aluminum source, which is either: (1) an aqueous solution of an aluminum salt, (2) an aqueous solution of an aluminum salt and an alkali alkali phosphate, or (2) a slurry of an aluminum hydroxide gel. .

As the aluminum salt, for example, aluminum nitrate-aluminum sulfate, aluminum chloride, aluminum acetate, and their basic salts can be used. @As the alkali altriphosphate, sodium 1-aluminum triphosphate, potassium aluminate, etc. can be used. be able to.

It is appropriate to use the aluminum salt aqueous solution and the alkali aluminate aqueous solution each having a concentration of about 1 to 20% by weight as Al2O3.

As a slurry of aluminum hydroxide gel, X! li
It may be a slurry in which a diffractionally amorphous aluminum hydroxide gel is dispersed in water, preferably a slurry immediately after reaction generation, with a fiH of 5,0 to 7.0, more preferably In2. .0 to 6.0 can be used, and the concentration is suitably about 1 to 20% by weight.

In addition, in the above (2), it is appropriate to use an aluminum salt aqueous solution.

Further, in the method of the present invention, an aqueous alkali silicate solution is used as the silica source. As the alkali silicate, sodium silicate, potassium monosilicate, lithium silicate, etc. are preferably used. The aqueous alkali silicate solution is S t Oa
Approximately 5 to 80% of the weight is suitable for the company.

In the method of the present invention, first, the aluminum-containing liquid raw material and the aqueous alkali silicate solution are simultaneously dropped into water while stirring to cause the aluminum compound and the alkali silicate to react. The ratio of the dropped amount of aluminum compound and alkali silicate is A1203/5iO2 (in terms of oxide).
molar ratio) −1.1 to 2.4, preferably 1.25 to
It may be about 2.0.

The pM of water serving as a reaction medium is 4.5 to 10, preferably 6.0 to 7.5. If the ratio is less than 784.5, the aluminum compound will become a polybasic aluminum salt, and some of the silica will be liberated as lumps, making it difficult to obtain a uniform mullite composition.On the other hand, if the ratio is more than 10, the aluminum This is not preferable because the metal remains as an olide-like or dawsonite-like substance, making it difficult to remove the alkali metal oxide even if acid cleaning is performed in a subsequent step.

In addition, fluctuations in /)// during the dropping reaction will significantly affect the powder physical properties of the reaction product, causing variations in bulk density, specific surface area, mullite temperature, etc. It is desirable to minimize fluctuations in fiH during
Preferably, the fluctuation of -H is within ±0.25.

If fluctuations in /)// are likely to occur during the dropping reaction, fluctuations in sodium carbonate, potassium carbonate, and sodium hydroxide)H may be suppressed.

The liquid temperature during the reaction is preferably about 10 to 80°C.

A temperature of about 40 to 80''C is more preferable.The pressure during the reaction is
Normal pressure is sufficient.

The amount of water used as a reaction medium preferably varies from 2 to 20 times by weight, more preferably from 7 to 15 times the theoretical number iiK of hydrated aluminum silicate to be formed.

The reaction time may be about 8 to 6 hours.

After completion of the reaction, the obtained product is taken from house to house, washed with water, dehydrated, and dried with ventilation at about 60 to 100°C, thereby obtaining hydrated aluminum silicate.

According to the method described above, the aluminum compound and the alkali silicate are bonded uniformly and firmly (by reaction between ions or reaction between silicon ions and highly reactive aluminum hydroxide gel), resulting in good uniformity. An aluminum silicate minilum compound is obtained. Therefore, cleaning becomes easy, and alkali, potassium metals, anions, etc. produced by-products in the reaction are easily removed, and a high-purity product can be easily obtained. For example, normal hydrated aluminum silicate contains 2 to 8% of alkali metal as an impurity in terms of oxide, but in the above method, the alkali metal oxide jJi O , 05% or less, anion ("4, Cl %
Hydrous aluminum silicate with high purity of 0.5% or less (NO3, etc.) can be easily obtained. Additionally, this hydrated aluminum silicate can be cleaned using a single filter press.
Production efficiency is good and it is easy to make it a cost town. Furthermore,
In the resulting aluminum silicate, silicon and aluminum are strongly bonded, and it is easily converted into mullite by firing at low temperature for a short time.

In the present invention, the hydrous aluminum silicate obtained by the method described above is crushed and heat-treated at about 900-1600°C, preferably about 1100-1500°C, and then the average particle size is 6# or less, preferably 3 μm. Mullite powder is obtained by crushing to a certain degree or less. Appropriate heating time is about 0.5 to 50 hours. Heating temperature is 90
If the temperature is less than 0°C, mullite formation is insufficient44), 1600
If the temperature exceeds .degree. C., the fine mullite particles will become coarse, which is not preferable.

The obtained mullite powder is a high-purity product with very little contamination by impurities, precipitants, anions, etc., and contains almost no agglomerated secondary particles.・The above mullite powder is Na2
The amount of alkali metal oxides such as O, K2O, Lt20, etc. is 0.
It is preferably 1% by weight or less, more preferably 0.05% by weight or less. If the amount of alkali metal oxide exceeds 0.1% by weight, it is not preferable because it leads to deterioration of the high temperature characteristics of the obtained sintered body. Further, the mullite powder has a specific surface area of 878'/y to 100g/f.
It is preferable that it is in the range of . It is desirable for the specific surface area of the mullite powder to be high from the viewpoint of sintering activity, and it is desirable to have a low specific surface area from the viewpoint of increasing the formability and green density of the molded product. It is appropriate to round to within the above range. Especially 1 mold press, rubber press, extrusion, slip ten? In order to enable molding by various molding methods such as cast, injection, and sheet + cest, it is preferably 5 to 60 i/y.

In the present invention, the mullite powder obtained by the above method has 1
Add a molding aid such as polyvinyl alcohol and mold into a predetermined shape, and heat to about 1500-1800°C, preferably 155°C.
Therefore, t1! A dense and high-strength mullite sintered body with a buried theoretical density can be obtained. Firing temperature is 150
If the temperature is lower than 0°C, it is difficult to develop a structure of the fired body in which columnar, prism-shaped, rod-shaped, spherical, etc. mullite microcrystals are intertwined with each other, while if the temperature exceeds 1800°C, the particles will become coarse, which is not preferable.

In order for the obtained sintered body to consist mainly of mullite phase, the weight ratio of Al2O3/Siυ2 should be 65/
It is preferably in the range of 85 to 80/20, and 68/
More preferably, it is 82 to 78/22. Al2O
If 3/5in2 is below this range, the sintered body will contain a large amount of glass, which will lead to deterioration of the strength and creep resistance, and if it exceeds this range, the sintered body will contain a large amount of glass.
This is not preferable because the proportion of l2O particles increases, leading to a decrease in strength at high temperatures. In addition, Kume K, which obtains a sintered body consisting essentially of a single phase of mullite that does not contain glass or alumina particles, has an Al2O3/Sio2 weight ratio of 7.
The range is preferably 1/29 to 76/24.

Further, the bulk density of the sintered body is preferably 1.B,001/d or more, and more preferably 8.05 f/d or more. Further, the porosity is preferably 4% or less, more preferably 2% or less. If the bulk density or porosity is outside this range, the mechanical properties of the sintered body are likely to be poor. Here, porosity means true porosity, which is given by the following equation.

Porosity (%) - 100X (1 - bulk specific gravity + true specific gravity) In the method of manufacturing a mullite sintered body according to the method of the present invention, the sintering activity of the mullite powder used is extremely excellent, so a high strength sintered body can be produced. can get. For example, while the bending strength of conventional mullite sintered bodies was a maximum of Bghg7wa"m, the method of the present invention makes it possible to obtain sintered bodies with a high strength of about 40kg/l112. be.

Effects of the Invention As explained in detail above, the mullite powder obtained by the method of the present invention can be synthesized chemically, which is different from the conventional method of mixing alumina with clay raw materials. Good, it has excellent compositional uniformity and stable quality. In addition, low-cost materials such as aluminum salt, alkali aluminate, aluminum hydroxide gel, and alkali silicate are used as starting materials, and they can be used as raw materials for mullite without requiring special conditions such as high temperature and high pressure. Since it is possible to obtain hydrated aluminum silicate, the manufacturing cost of the raw material powder is low, making it suitable for industrial mass production.
It is economically very advantageous.

Moreover, the obtained hydrated aluminum silicate has a
The mullite powder obtained by converting into mullite at about 1600° C. contains extremely small amounts of impurities such as alkali metal components, has high purity, and has excellent sintering activity. Furthermore, the sintered body obtained by the method for producing a mullite sintered body of the present invention is a high-purity, bulk-density sintered body that is mainly composed of a mullite phase and has a structure in which mullite microcrystals are strongly sintered together. Therefore, compared to conventional mullite porcelain, it has much better mechanical properties such as strength and creep properties at room or high temperatures.

Due to its excellent mechanical properties, the mullite sintered body produced according to the present invention is suitable for use in crucibles, pots, shelves, protective tubes, and especially in fired O-Las, etc. Not only heat-resistant materials such as materials for high-temperature furnaces, but also blower fans for steel or heat treatment, wear-resistant pulp, chemical-resistant pumps, mechanical seals, precision measuring instruments, medical equipment parts, high-temperature burners, and diesel. It is useful as heat-resistant high-temperature structural products such as various parts of internal combustion engines such as engines and gas turbines, and as electronic ceramics including mullite substrates, and greatly contributes to improving their performance.

Examples of the present invention will be shown in detail below.

Example 1 Aluminum chloride aqueous solution (Al5O120% by weight) 80
0 kg, sodium aluminate aqueous solution (Al2032
0 weight M%) 598 kQ and sodium silicate aqueous solution (Sr 022011 [ffi%) 889 klj were stirred in 4 cups of water at a temperature of 40°C, and poured into doors H6 and 8.
Simultaneous dropping was carried out at ~6.5. fiH at the end of dripping is 6.4
, the liquid temperature was 40°C. 1 o'clock r#JJ8I! After the meal,
Filter the slurry using a filter press, wash with water,
The powder was dried at C and pulverized to an average particle size of about 7 μm to obtain a hydrated aluminum silicate powder. The analysis results of the obtained powder are shown in Table 1.

1st Table: It 8 9 7 kg"2'
3 Sx Oa 19.46% ignition reduction at 41.87
87.96% (40,10% 504 0.10% Na O, 028% In addition, Kono powder (1)
10 mA, CuKα) is shown in FIG.

As can be seen from FIG. 1, the obtained powder was hydrated aluminum silicate having an amorphous shape in terms of X@ diffraction. Figure 2 shows the results of xllA diffraction after heat-treating this powder at 1200"C. From Figure 2, it can be seen that simulite was generated by firing at 1200°C. Hydrous aluminum silicate, which is a raw material for mullite, is heat-treated at 1200"C in the air for 2 hours and crushed to produce a powder with an average particle diameter of 1 μm and a specific surface area of 80 doors/fSA1203/SiO
A mullite powder was obtained in which the weight ratio of N g 20 and N g 20 was 68.8/81.7, and the total amount of N g 20 and N g 20 contained in the powder was 0.044% by weight. The obtained mullite powder was 2.
Molded isotropically at a pressure of Q tos / cd and 1600
It was baked for 2 hours at a temperature of °C. The obtained sintered body is 8×4
Cut and polished to x40m+, density and room temperature, 1300
The bending strength at °C was measured. The density of the sintered body is 8.10 no/d, and the strength of 8-point bending at room temperature is 88 kgf/1yx.
2. As #//IEI2 at 1800°C, exhibiting excellent mechanical properties.

As a method for measuring each physical property, the bending strength at room temperature is determined by JIS
According to the standard, take a 8X4X40ff sample piece, span 8.
0jIl111 Crosshead speed 0.51fl/m
I found the 8-point bend K of #. Fossa temperature intensity is 1800
KflA was determined in an atmospheric furnace at room temperature in the same manner as at room temperature.The specific surface area was measured by the BET adsorption method.The density of the sintered body was determined by the Al + Medes method.

Example 2 Aluminum chloride aqueous solution (Al2O, 10% by weight) 9
20kg and sodium silicate aqueous solution (St 0220
While stirring 180 centimeters of heavy duty ff1%) into the water, pour it into the door H.
Sodium carbonate aqueous solution (Ha2c03
At the end of 90 drops, /H6,1, the liquid temperature was 89°C.

After soaking for 1 hour, the slurry was filtered using a filter press, washed with water, dried at 80° C., and ground to an average particle size of about 7 ttmK to obtain a powder of hydrous aluminum silicate.

The analysis results of the obtained powder are shown in Table 2.

2nd table collection jl 180&gH20
350,12% S* 02 19-50% ignition loss
29.86% CI 0.27% 5040.19% Ntl O. In addition, mullite powder with an average particle diameter of about 1 μm was obtained. A graph of the relationship between the heat treatment temperature and specific surface area of the mullite powder thus obtained is shown in FIG.

According to the curve in Figure 8, the heat treatment temperature is 900-1600℃.
It was confirmed that powder having a specific surface area of 100g/f to 8g/l was obtained in the range of 100g/f to 8g/l, and that the heat treatment temperature of hydrated aluminum silicate was desirably 900 to 1600°C. Incidentally, the total of N II 20 and Ni 20 contained in the mullite powder obtained after heating and firing according to this example is 0.01
It was heavy weight%.

Next, after heat treatment at each heat treatment temperature for 2 hours, a molded body was made using the crushed mullite powder in the same manner as in Example 1, and sintered at each sintering temperature to obtain a mullite sintered body. After
Physical properties were measured. The results are shown in Table 8.

It can be seen from Table 3 that within the firing temperature range of the present invention, a dense and high-strength mullite sintered body can be obtained. Also 1
When the surface of the sintered body of sample A5 sintered at 650°C was polished and etched, and the surface was observed using an electron microscope, it was found that a sintered body structure in which columnar or needle-shaped mullite crystals were entangled had developed. confirmed. Also, the porosity is all 4
% or less.

Example 8 Paste aluminum hydroxide gel (A
500 kg of g20310 weight ffi%) was added and stirred vigorously to obtain a uniform aluminum hydroxide gel slurry. The liquid property of this suspension was /'H5,6. A tank of water was prepared, the temperature of the liquid was raised to 50°C, and an aluminum hydroxide gel suspension and 94# of sodium silicate (SsO2 20% by weight) were simultaneously dropped into the tank while stirring. The liquid property at the end of simultaneous dropping was 11.1. 1
After stirring for a period of time, filter the slurry using a filter press.
It was washed with water, dried at 90°C, and ground to obtain hydrous aluminum silicate. Table 4 shows the analysis results of the obtained powder.

Table 4 Yield: 94 to 9”2’3
51.04%St O2 19-26% Loss on ignition 29.47% CI 0.008%So4
0.012%Ha
0.021% The obtained powder was subjected to X, IJ diffraction in the same manner as in Example 1, and as a result, it was found to be hydrated aluminum silicate having an amorphous shape. In addition, the obtained powder was
After heat treatment at .degree. C., X1s diffraction showed the formation of mullite.

Next, 1280% of the obtained hydrated aluminum silicate powder was
After heating and baking at ℃ for 2 hours and crushing, the average particle size was 0.8 μs.
, specific surface area 22M//fSAt203/Ss O2 weight ratio is 72.6/27.4, # contained in powder
A mullite powder was obtained in which the total amount of A20 and A20 was 0.02 weight mass. Also, 1.5 tons of this mullite powder
It was molded isotropically at a pressure of ag/ai and baked at a temperature of 1650 °C for 2 hours. The density of the sintered body is 8.12 f/d
The 8-point bending strength at room temperature is 87ktif/wx2.13.
86 kQf/I1M" at 00°C, and had excellent mechanical properties. Example 4 Except for using the amounts of aluminum chloride aqueous solution and sodium silicate aqueous solution shown in Table 6, A mullite sintered body was obtained in the same manner as in Example 2.

The measurement results of density and strength are shown in Table 6.

In addition, for comparison, a sample was cut out from a commercially available mullite porcelain whose main raw material is aluminum silicate clay mineral such as kaolin, and its density and strength were measured in the same manner as in Comparative Products A and B) 1. In addition, this mullite porcelain contains Al2O3, S
In addition to t and 2, several T t 02, Fe2O2, Cts
OSMyOSNg20. Includes K2O, etc.1 Retei fC
.

From Table 6, it can be seen that the mullite sintered body obtained by the method of the present invention has a higher density than commercially available mullite porcelain, and has high strength at room temperature and high temperature.

Furthermore, when the surface of the sintered body of products A1 and B of the present invention was polished and etched and observed under a scanning electron microscope, it was confirmed that the sintered body structure consisting of spherical mullite crystals had developed.

Table 5

[Brief explanation of the drawing]

Figure 1 shows the X-ray diffraction results of the hydrous aluminum silicate powder in Example 1, and Figure 2 shows the Xljl diffraction results of the mullite powder heat-treated at 1200°C in Example 1. FIG. 8 is a graph showing the relationship between the heat treatment temperature and the specific surface area of hydrated aluminum silicate as a raw material for mullite in Example 2. (Above) Figure 1 Figure 2 2e deg 7'LD heat quenched 2 degrees (℃)

Claims (2)

[Claims] (1) An aluminum-containing liquid raw material, which is a) aqueous aluminum salt solution, b) an aqueous aluminum salt solution and aqueous aluminate solution, or c) a slurry of aluminum hydroxide gel, and an aqueous alkali silicate solution are simultaneously dropped into water with stirring. A method for producing mullite powder, which comprises reacting at pH 4.5 to 10, washing the obtained product with water, drying, and then calcining at 900 to 1600°C. (2) An aluminum-containing liquid raw material, which is a) an aluminum salt aqueous solution, b) an aluminum salt aqueous solution and an alkali aluminate aqueous solution, or c) a slurry of an aluminum hydroxide gel, and an alkali silicate aqueous solution are simultaneously placed in water with stirring. Mullite is added dropwise and reacted at pH 4.5 to 10, and the resulting product is washed with water, dried, and then calcined at 900 to 1600°C, then molded and then calcined at 1500 to 1800°C. Manufacturing method of sintered body.