JPH0218285B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing β-sialon powder. β-Sialon has the general formula Si _6-Z Al _Z O _Z N _8-Z (where Z represents a number greater than 0 and less than or equal to 4.2)
It is a compound represented by silicon nitride (Si ₃ N ₄ )
This is a solid solution of Al and O in a substitution type.

Since β-sialon has high oxidation resistance at high temperatures and excellent corrosion resistance against molten metal and slag, β-sialon powder is useful as a raw material for various refractories. Furthermore, the Sialon sintered body obtained by sintering this material has high high-temperature strength and hardness, so it is excellent as automobile engine parts and metal cutting tools.

Conventional methods for producing β-sialon powder include: (1) a method in which carbon is added to a clay mineral such as kaolinite, which is a natural silica-alumina mineral, and the mixture is heated in a nitrogen stream to perform reductive nitridation; .

(2) A method in which aluminum metal is added to silica raw materials such as whitebait and heated in a nitrogen stream.

(3) A method in which a co-precipitate of Al(OH) ₃ and silica gel is heated in an ammonia atmosphere.

It has been known.

However, since methods (1) and (2) use natural raw materials, they have the disadvantage of containing a large amount of impurities, and method (3) does not complete the reaction, leaving unreacted materials. There were some remaining flaws.

The present invention has been made to eliminate the drawbacks of the conventional methods, and its purpose is to provide a method for producing sialon powder having high purity, fineness, and uniform particle size.

As a result of intensive research to achieve the above object, the present inventors found that silica obtained by hydrolyzing a mixture of silicon alkoxide and aluminum alkoxide.
It was discovered that when an alumina mixture containing a smaller amount of carbon powder in a specific range than in conventional methods is heated in a nitrogen atmosphere, highly pure, uniformly fine β-SiAlON powder can be obtained. Based on this knowledge, the present invention was completed.

The gist of the present invention is as follows: (1) A precipitate obtained by hydrolyzing a mixed solution of silicon alkoxide and aluminum alkoxide is heated to produce 50 to 80 mol% of silica and 50% of alumina.
Make a silica-alumina mixed powder with a ratio of ~20 mol%, and add carbon powder to the mixed powder by 16~20 mol%.
1350~1550 in nitrogen atmosphere after mixing 25% by weight
A method for producing sialon powder, which comprises heating to ℃. and (2) heating the precipitate obtained by hydrolyzing a mixed solution of silicon alkoxide and aluminum alkoxide mixed with carbon powder to produce 50 to 80 mol% of silica, 50 to 20 mol% of alumina, silica and alumina. A method for producing β-sialon powder, which comprises preparing a mixed powder consisting of 16 to 25% by weight of carbon powder based on the total amount of carbon powder, and heating the mixed powder to 1350 to 1550°C in a nitrogen atmosphere. It is in.

Examples of the raw material silicon alkoxide include methyl silicate, ethyl silicate, propyl silicate, butyl silicate, and the like. Further, examples of the aluminum alkoxide include aluminum ethoxide, aluminum isopropoxide, aluminum-n-butoxide, and the like.

The mixing ratio of silicon alkoxide and aluminum alkoxide is an atomic ratio of Si and Al (Si/Al) of 0.5.
It is in the range of ~2. The molar ratio of SiO ₂ /Al ₂ O ₃ is 1
~4.

If the Si/Al atomic ratio is lower than 0.5, the amount of aluminum exceeds the solid solution range of SiAlON, so β-
Aluminum compounds are mixed into Sialon powder as impurities. On the other hand, if the atomic ratio exceeds 2, the reductive nitriding reaction becomes non-uniform and silicon nitride is also produced at the same time, making it impossible to obtain uniform sialon powder.

An alcohol such as isobutanol or isopropanol is added as a solvent to the alkoxide mixture mixed in such a ratio, and the mixture is dissolved when heated at about 80° C. for about 5 hours. After dissolving, 3~ of alkoxide
After adding 4 times (by weight) distilled water and dropping a small amount of aqueous ammonia, the mixture is heated at 80-90°C for about 8 hours, resulting in hydrolysis and a uniformly mixed precipitate. By heating this precipitate at 50 to 90°C under reduced pressure, the solvent, alcohol and water are separated and dried, and then heated at 500 to 700°C for 1 to 5 hours to obtain a silica-alumina mixed powder. . If the heating is lower than 500°C, components other than silica and alumina (mostly water) will remain, and if it exceeds 700°C, particle growth will occur, so it is preferable to heat at 500 to 700°C. The resulting mixed powder consists of uniformly dispersed particles of 0.01-0.1 micron. It is amorphous in terms of X-rays. According to chemical analysis, the Si/Al atomic ratio is within ±2% and matches the atomic ratio of the raw material. Carbon powder is added to the obtained silica-alumina mixture. The carbon powder is preferably a fine powder such as carbon black in order to disperse it uniformly.

Conventionally, the required amount of carbon was calculated assuming that the Si/Al atomic ratio did not change during reductive nitriding. For example, in a powder with silica:alumina=2:1 (molar ratio), it reacts with 3(2SiO ₂・Al ₂ O ₃ ) + 15CN ₂ -→ 2Si ₃ Al ₃ O ₃ N ₅ + 15CO...(1), resulting in β-sialon. 31.3% by weight for the synthesis of
of carbon is required, and this amount is the same as the raw material.
It was assumed that β-sialon with a Si/Al ratio could be obtained.

However, as a result of detailed analysis of the reaction and chemical analysis of the produced β-sialon powder, it was found that during reductive nitriding,
It was found that equation (1) does not hold true strictly because SiO is scattered and the Si/Al atomic ratio changes. The amount of SiO scattered depends on the raw material composition and reaction temperature. At around 1430℃, the reaction proceeds as follows.

4(2SiO ₂ .Al ₂ O ₃ ) + 18CN ₂ -→ Si ₆ Al ₈ O ₈ N ₁₁ + 2SiO + 18CO (1) As a result, β-sialon corresponding to the composition of Si _2.6 Al _3.4 O _3.4 N _4.7 is obtained. The Si/Al ratio in β-sialon is smaller than that in the raw material. The amount of carbon calculated from the reaction formula is 19.6
Weight%.

The amount of SiO scattered depends on the reaction temperature, and since it is a solid phase reaction, the optimal amount of carbon to mix is silica:
It changes depending on the mixing ratio of alumina. silica:
When the alumina molar ratio is 1:1, it is 16 to 20% by weight;
18-22% by weight for 2:1, 22 for 4:1
~25% by weight. If the amount is less than that, unreacted substances will remain, and if it is more than that, there will be a lot of unreacted carbon, and 15R-SiAlON, which has undergone further reduction and nitridation, will be produced, so the amount of carbon powder added should be between 16 and 25.
It is necessary to adjust the proportions as described above within the range of weight %. The carbon powder has a reducing effect on the silica-alumina powder, and may be mixed later, or may be mixed in advance with the alkoxide mixed solution. Pre-mixing allows the reduction reaction to occur uniformly, so there is an advantage that fine β-sialon can be obtained without post-treatment (treatment for decomposing secondary particles). After molding the mixture obtained in this way as necessary, the mixture is heated to 1350 ~
Heat to 1550°C for 0.5-24 hours. As a result, some of the oxygen in the silica-alumina is replaced with nitrogen, and β
- Sialon powder is obtained. Heating temperature is 1350℃
If the temperature is lower, the time to complete the reaction will be longer, and if it exceeds 1550°C, SiO will be scattered more frequently, resulting in the disadvantage that not only will the composition of β-sialon be greatly different from that of the raw material, but also 15R-sialon will be produced.

Therefore, it is necessary that the temperature is 1350-1550℃,
Preferably it is 1400-1500°C.

The lower the temperature, the longer the firing time is required. A suitable time is 3 to 10 hours at 1400°C, and 1 to 3 hours at 1500°C.

The resulting powder is fine and uniform with a particle size of 0.3 to 0.5 microns, and its purity is 0.1% impurity.
It has the following high purity.

Example 1 Add 300 cc of isobutanol to 30.6 g of ethyl silicate and 30.0 g of aluminum isopropoxide, and heat at 80°C.
The alkoxide was dissolved by heating in a water bath for 5 hours. After dissolution, 100 cc of distilled water was added dropwise, followed by 20 cc of aqueous ammonia solution (50%), and the mixture was heated at 85° C. for 8 hours to complete hydrolysis. This was heated from 50°C to 90°C under a reduced pressure of 200 mmHg to remove evaporated matter, and further heated to 600°C in air for 1 hour to obtain a white powder. The particle size of the powder is 0.01-0.1 micron,
It was X-ray amorphous. As a result of chemical analysis, the silica/alumina ratio was 2:1. 0.125 g of carbon black was added to 0.5 g of the powder and pressurized to 300 Kg/cm ² using a mold with a diameter of 12 mm to make pellets.

The pellets were placed in an alumina boat, transferred to an alumina furnace tube, the inside of the tube was replaced with nitrogen, and heated at 1430° C. for 2 hours while flowing nitrogen. The obtained powder contained a small amount of secondary particles of 1 to 10 microns, but most of the powder was fine particles of 1 micron or less. In order to decompose the secondary particles, the mixture was treated with a silicon nitride ball mill for 2 hours using n-hexane as a dispersion medium. As a result of measuring the particle size distribution of the powder, the average particle size was
It was found that the particle size was uniform, with about 85% by weight falling within the range of 0.4 microns and 0.4±0.1 microns, and about 4% by weight of secondary particles ranging from 1 to 5 microns. As a result of powder X-ray diffraction, the crystalline material was only β-sialon, and measurement of the lattice constant showed that the composition corresponded to z=3.3. The result of chemical analysis is Si:Al:O:N
=26.7:31.4:19.9:22.0 (weight ratio). This indicates that approximately 3% by weight of unreacted glass phase remained in approximately 97% by weight of β-sialon with z=3.3.

Example 2 61.2g of ethyl silicate and 120.0g of aluminum isopropoxide were dissolved in 500cc of isopropanol,
Add 50cc of ammonia solution and 300cc of distilled water to this,
In the same manner as in Example 1, silica: alumina = 1:
A mixed powder of No. 1 was obtained. 0.82 g of mixed powder and 0.18 g of carbon black were mixed to form pellets in the same manner as in Example 1, and heated at 1500° C. for 1 hour in a nitrogen atmosphere.

After the obtained powder was post-treated in the same manner as in Example 1, the particle size distribution was measured, and the average particle size was 0.5.
microns, about 80% by weight within the range of 0.5±0.2 microns, and about 6% by weight between 1 and 5 microns. As a result of powder X-ray diffraction, β-sialon and a very small amount of
15R- It was derived from Sialon. From the measurement of the lattice constant, the composition of β-sialon was found to be z=4.2. The result of chemical analysis is β-sialon with z = 4.2
The values corresponded to 97% by weight and 3% by weight of unreacted glass phase.

Example 3 15.2 g of methyl silicate and 24.6 g of aluminum-n-butoxide were added to 250 cc of isobutanol and dissolved in the same manner as in Example 1. To this was added 200 cc of distilled water,
Adding 30 cc of ammonia solution, the following procedure was repeated in the same manner as in Example 1 to obtain a mixed powder of silica:alumina=2:1. After mixing 0.8 g of powder and 0.2 g of carbon black, the mixture was molded and heated in the same manner as in Example 1.
Heating was carried out at 1470°C for 2 hours.

After the obtained powder was post-treated in the same manner as in Example 1, the particle size distribution was measured, and the average particle size was 0.4.
micron, about 70% by weight to 0.4±0.1 micron, 1~
It was 5 microns and 10% by weight. As a result of powder X-ray diffraction, the crystal phase was only β-sialon, and the measurement of the lattice constant showed that the composition corresponded to z=3.5. The result of chemical analysis is z=
This amount corresponded to 98% by weight of β-sialon of 3.5% and 2% by weight of unreacted glass phase.

Example 4 Using the same raw materials and method as in Example 1, a butanol solution of ethyl silicate and aluminum isopropoxide was prepared. After cooling this solution to room temperature, 4.2g
of carbon black was added and dispersed in the solution by applying ultrasonic vibration for 5 minutes. Distilled water and aqueous ammonia were added dropwise in the same manner as in Example 1, and then the evaporated matter was removed. Approximately 0.75 g of the obtained mixed powder was made into pellets in the same manner as in Example 1.

The pellets were heated in nitrogen as in Example 1. The resulting powder has an average particle size of 0.4 microns, approximately 80% by weight within the range of 0.4 ± microns, 1 to
about 5% by weight of secondary particles within a range of 5 microns;
A powder of uniform particle size was obtained without post-treatment. powder
According to line diffraction, only β-sialon was present, and the composition of sialon was found to be z=3.4 from the measurement of the lattice constant.
The chemical analysis results also agreed well with the X-ray diffraction results, indicating that the β-sialon content in the powder was 99% by weight or more, and the amount of unreacted glass phase was 1% by weight or less.

As described above, according to the method of the present invention, since the raw material is produced by hydrolysis of the alkoxide mixture,
It consists of pure, fine, uniform particles, and since the fine particles are mixed with an appropriate amount of carbon and subjected to reductive nitriding, it is easy to obtain a β-sialon composition with a ratio close to that of the raw material Si/Al. The resulting powder is extremely uniform and consists of fine particles, and has the excellent effect of being a β-sialon powder free of impurities.

Claims (1)

[Claims] 1. A precipitate obtained by hydrolyzing a mixed solution of silicon alkoxide and aluminum alkoxide is heated to produce 50 to 80 mol% silica and 50 to 20 mol% alumina.
A β-sialon powder characterized in that a silica-alumina mixed powder with a mol% ratio is prepared, 16 to 25% by weight of carbon powder is mixed with the mixed powder, and then heated to 1350 to 1550°C in a nitrogen atmosphere. manufacturing method. 2 The mixing amount of carbon powder is silica:alumina=
16 to 20% by weight for a 1:1 molar ratio, 18 to 22% by weight for a 2:1 molar ratio of silica:alumina, and 22 to 25% by weight for a 4:1 molar ratio of silica:alumina. A manufacturing method according to claim 1. 3 Heat the precipitate obtained by hydrolyzing a mixed solution of silicon alkoxide and aluminum alkoxide mixed with carbon powder to form silica 50
A mixed powder consisting of ~80 mol% carbon powder, 50-20 mol% alumina, and 16-25% by weight of carbon powder based on the total amount of silica and alumina is prepared, and the mixed powder is heated to 1350-1550°C in a nitrogen atmosphere. A method for producing β-sialon powder, characterized by: