JPH0352439B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Technical field of the invention The present invention relates to a method for producing a fibrous crystal (including whiskers) aggregate made of silicon nitride and silicon oxynitride;
More specifically, by combining silicon with specific metals such as magnesium, aluminum, and copper to form an alloy on the surface layer of silicon, and by adding silicon dioxide to silicon nitride seed crystals and mixing or granulating and reacting, crystallization is achieved. The present invention also relates to a method for producing fibrous aggregates of silicon nitride and silicon oxynitride with excellent fineness in high yield. (b) Prior art and problems Silicon oxynitride, especially silicon nitride, has good properties such as heat resistance and mechanical strength, so its fibers are also important as heat-resistant, heat-insulating materials or composite reinforcing materials, and various methods have been proposed. ing. In other words, conventional methods for producing silicon nitride fibers generally involve reacting silicon or silicon monoxide vapor obtained by heating silicon, reducing silicon compounds or oxides such as silicon dioxide, or reacting silicon and silicon dioxide with nitrogen. However, the yield is low in all of these methods, and there is also a method of manufacturing from rice husks, but the fibers are fine. In addition, regardless of the method, the crystals that are formed are not deposited in the raw material but on a distant substrate or the inner wall of the furnace, so it is difficult to separate and recover them as silicon nitride, and they are used as insulation materials or aggregates for composite materials such as glass and metal. No easy aggregates were obtained. The present inventors previously filed a patent application for the production of silicon oxynitride fibrous crystals in 1972.
-156827, but it had the drawback that a fibrous structure of silicon nitride could not be obtained and the aggregate was easily fragile and difficult to handle. (c) Problems to be Solved The inventors of the present invention have conducted intensive research to obtain a fibrous aggregate made of silicon nitride and silicon oxynitride. A molded product is created by combining metals such as metals or their salts, heating them in an inert or reducing atmosphere to form an alloy with the added metal on the surface layer of silicon, and nitriding the molded product with silicon dioxide mixed therein. A silicon nitride and silicon oxynitride fibrous structure with excellent crystallinity and fineness was produced from the surface layer to the inside (first method). Furthermore, by granulating the silicon alloy and silicon dioxide in the first method described above, an aggregate having a thin and long fibrous structure with good shape retention was produced (second method). (d) Means for Solving the Problems of the Invention In the present invention, in order to obtain a fibrous aggregate made of silicon nitride and silicon oxynitride, carbon is added to various metals in advance and heated to form an alloy on the surface layer of silicon and the mixture is mixed. This can lead to the reaction of silicon-containing alloys with silicon dioxide with high activity.
In other words, this method produces silicon oxynitride fibrous crystals with well-defined crystallinity and fineness by suppressing the dissolution of catalyst metals such as magnesium, aluminum, or copper into silicon dioxide until the temperature at which silicon oxynitride begins to form (1050°C). is produced by the reaction equations shown in (1) and (2), and silicon nitride whiskers are obtained with good reproducibility from silicon-containing alloys or silicon monoxide vapor by steps (3), (4), and (5). This is the manufacturing method that made this possible. Si ^(s) +SiO ₂ ^(s) →2SiO(g) (1) 2SiO(g)＋2Si+2N ₂ →2Si ₂ ON ₂ ^(s) (2) 3Si ^(s) +2N ₂ →Si ₃ N ₄ ^(s) (3 ) 3SiO(g)+3C→3Si ^(s) +3CO (4) 3Si(g)+2N ₂ →Si ₃ N ₄ ^(s) (5) In connection with the above reaction, the formation with silicon alloy particles and silicon dioxide The effect of grains will be explained in more detail. (e) Effect of the invention (1) Magnesium, aluminum, and a single or multi-component metal or salt thereof among copper, manganese, iron, and nickel as a catalyst are added to silicon, and the mixture is heated in an inert or reducing atmosphere. , an alloy phase is formed in advance on the surface layer of silicon. According to these preparation methods, it is combined with silicon at a relatively low temperature, but the melting point of silicon is 1420℃.
It is advantageous to do this in such a way that it reaches (2) Magnesium easily combines with oxygen and moisture in the air to form an oxide film, sometimes forming Mg(OH) ₂
produces fibers. When an oxide film is formed on the surface of magnesium, it becomes difficult to form an alloy with a catalyst such as silicon or copper, but it tends to react with silicon dioxide to form a magnesium-silica melt. Therefore, in order to obtain an active magnesium component, in the present invention, magnesium is heated with silicon and various metals to form alloy particles.
This provides alloy particles with little change over time due to oxidation of magnesium or aluminum components and with little contamination on the main silicon metal surface. (3) Adding aluminum increases the viscosity of the liquid phase, making it homogeneous and making it possible to obtain a stable liquid phase. Therefore, adding aluminum as a stable liquid phase forming agent increased the yield of long fibrous structures. (4) Furthermore, in the process of forming alloy particles, the corners of the silicon particles, which make up the majority of them, become rounded and uniform, so that the reaction with silicon dioxide proceeds uniformly in the next step. Furthermore, the advantage of alloy formation is not only the uniformity of the metal composition, but also the ability to mix fine metal particles,
Contamination by dust generated during molding or dissipation into equipment can be easily prevented. (5) To granulate alloy particles and silicon dioxide, binder and water are added, mixed, dried, and then crushed.
Granulate to a roughness of 0.07 to 2 mm using a sieve. As the binder, carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol, etc. are used as a solution of 3 to 10% by weight. These binders account for 2% of the total amount of the powder mixture.
Add at a rate of ~10% by weight. In the present invention, it is considered that by granulating the mixed powder, contact between the reactants becomes better, so that the reaction progresses evenly. (6) When the above granular material is molded and heated in a nitrogen atmosphere, the multi-component alloy particles and silicon dioxide gradually react, forming a liquid phase made of silicon dioxide and countless silicon spherules inside the molded material. the above
As a result of the reactions (1) and (2) proceeding slowly and uniformly, silicon oxynitride crystals with less unreacted substances and molten silicate are formed inside the molded body than in the prior application. Furthermore, if carbon is dissolved into the alloy,
(2), (3), (4) Since the solubility of nitrogen increases in the alloy liquid phase in the reaction, the formation of crystalline silicon oxynitride and silicon nitride is promoted. (7) Adding a silicon nitride seed crystal causes silicon nitride-type structural ions to be generated in the metal droplets that combine with nitrogen, contributing to the formation of crystal nuclei, and playing a role in controlling the direction of crystal growth, resulting in the formation of silicon nitride fibers. It promoted the growth of crystals. Since silicon nitride crystals are thin and have a Karami effect, the shape retention of the obtained fibrous aggregate increases, and furthermore, when pressed with a finger, it provides multiplicity. The above action is reliable and complete, and the effect is very large, resulting in the formation of an alloy phase in the silicon surface layer,
This demonstrates the effectiveness of granulating the reactants. The invention will be explained in further detail by the following examples. (f) Examples of the invention Example 1 2.81g of silicon (molar ratio 10) and 0.07g of magnesium
After mixing 0.05 g of carbon (molar ratio 0.2) with fine metal powders of 1.5 g (molar ratio 0.3), 0.02 g copper (molar ratio 0.03), and 0.02 g aluminum (molar ratio 0.1), 15 mm
Form into a cylindrical shape of φ x 10 mm. The compact is placed in a silicon nitride boat, covered with a lid, and loaded into the center of a high alumina combustion tube. 30ml of argon/
The sample was heated in a resistance heating furnace while flowing hydrogen at 5 ml/min, and the temperature was raised at a rate of 10°C per minute and held at 1420°C for 30 minutes. As a result of X-ray diffraction, it was found that aluminum and magnesium, silicon and magnesium, and magnesium and copper alloys were formed in the silicon surface layer by this process. Next, add 0.35 g of α-type silicon nitride (10% by weight of the total amount) to 0.6006 g of silicon dioxide (mole ratio 1) to the alloy particles, mix well, form into a cylinder of 10 mmφ x 7 mm, and place in a silicon nitride container. Nitrogen gas 30ml/min, hydrogen gas 3
1470°C at a rate of 8°C/min.
Raise the temperature to The molded body begins to swell after 5 minutes have elapsed, gradually rises, and swells continuously until about 2 hours have elapsed, and the fibrous crystals grow. The operating holding temperature is 1470°C for 4 hours. Through this step, the compact becomes 10 to 12 times bulkier, and an aggregate of silicon nitride and silicon oxynitride, which is mainly cocoon-like α-type, is obtained. The bulk specific gravity of this thing is
It is 0.3. As a result of measuring a part of the aggregate with a microscope, the silicon oxynitride is 1-3 μm thick and 50-50 μm long.
It is a relatively uniform fibrous crystal with a diameter of 300 μm and an average length of 100 μm. Silicon nitride solidifies with a thickness of 0.5 to 1 μm and is uniformly distributed from the surface to the inside of the aggregate. Results of powder X-ray diffraction using the internal standard method
Si ₂ ON ₂ is 18%, α-Si ₃ N ₄ 47%, β-Si ₃ N ₄ 12
%was gotten. During the reaction process, the growth of silicon oxynitride fibrous crystals begins at 1400°C and is maintained at 1470°C for 30 minutes, but as the silicon alloy in the liquid phase becomes gaseous and grows inside the compact, α-type silicon nitride crystals continue to grow. Be looked at. Incidentally, the remaining amorphous silica phase is formed as the molded product rapidly expands, most of it is in the form of fibers, and some of it serves as a link between the fibers. In this way, most of the aggregates obtained by heat-treating a green compact made of alloy-forming particles of silicon, copper, magnesium, and aluminum plus carbon plus silicon dioxide and α-type silicon nitride in nitrogen. can be converted into a fibrous structure of silicon nitride and silicon oxynitride with good crystallinity. Example 2 Manganese 0.02g instead of copper in Example 1
(molar ratio 0.03), silicon 2.24g (molar ratio 8)
Magnesium 0.07g (molar ratio 0.3), aluminum 0.02g (molar ratio 0.1), carbon 0.05g (molar ratio
0.2) Mix and mold each fine powder. Next, 0.6006 g of silicon dioxide (molar ratio 1), 10% by weight of the total amount, and 0.3 g of α-type silicon nitride were added to the alloy forming particles obtained by heat-treating this compact in the same manner as in Example 1.
The fibrous aggregate produced by the treatment under the same conditions as in Example 1 was otherwise composed of 19% Si ₂ ON ₂ , 33% α-Si ₃ N ₄ ,
β-Si ₃ N ₄ was 18%. Example 3 Using 0.011 g of manganese (molar ratio 0.02) and 0.011 g of nickel (molar ratio 0.02) in place of copper in Example 1,
Magnesium 0.07 to silicon 2.24g (molar ratio 0.8)
(molar ratio 0.3), aluminum 0.02 (molar ratio 0.1), and carbon 0.05g (molar ratio 0.2) are mixed and molded. Next, this molded body was heat-treated in the same manner as in Example 1, and silicon dioxide 0.6006 was added to the alloy-forming particles obtained.
g (mole ratio 1), 10% by weight of the total amount, and 0.3 g of α-type silicon nitride were added, and while supplying nitrogen and hydrogen gas, the heating rate was slow to 7°C/min, and the operating temperature was maintained at 1460°C. When the temperature was lowered to 1490°C for 30 minutes and 3 hours, a fibrous aggregate with good entanglement properties was obtained, mainly consisting of silicon nitride and silicon oxynitride. The generated phase is
Si ₂ ON ₂ 21%, α-Si ₃ N ₄ 25%, β-Si ₃ N ₄ 25%
It was hot. In this example, the combination and type of the heavy metal fine powders used as the contact can be varied. Example 4 Cuprous chloride 0.03 instead of copper in Example 1
g, 0.02 g (molar ratio 0.03) as copper is used, but the crystal water is sufficiently removed to form an alloy. Further, Table 1 shows the results of fibrous aggregates obtained by processing under the same conditions as in Example 1 except that the blending ratio of silicon and silicon dioxide was changed. Example 5 In place of copper in Example 1, one or more salts were used, namely copper carbonate 0.03 g (0.01 g as metal, molar ratio 0.015), manganese nitrate 0.01 g (0.008 g as metal).
g, molar ratio 0.015) to sufficiently dry and remove crystallization water, and then prepare alloy-forming particles for use. Further, the results of the formed phase of the fibrous aggregate obtained by setting the silicon/silicon dioxide molar ratio to 8 and performing the treatment under the same heating conditions as in Example 3 are shown in the table. Example 6 2.24 g of silicon (molar ratio 8) and 0.02 g of copper (molar ratio
0.03), magnesium 0.07g (molar ratio 0.3), aluminum 0.02g (molar ratio 0.1), carbon 0.05 (molar ratio
0.1) Mix each fine powder. This mixture was applied to the surface layer of silicon in the same manner as in Example ₁ .
Forms alloy phases such as AlMg and MgSi ₂ . Next, 0.6006 g of silicon dioxide (molar ratio 1) and α-type silicon nitride crystals of 10% by weight of the total amount were added to the alloy particles, and 1 ml of a 3% methyl cellulose solution was added and molded.
The molded body was dried at 80℃ for 20 hours and then crushed in a mortar.
Adjust the particle size between 70mesh (0.2mm) and 200mesh (0.07mm). Take 2.5g of the granulated material and make 200Kg/ ^cm2 for 10
It was formed into a cylinder shape of mmφ x 7mm, placed in a silicon nitride container, nitrogen gas was introduced at a rate of 30ml/min, and the temperature was raised to 1470°C at a rate of 7°C/min, and then heated to 1500°C for 30 minutes.
It was held for 3.5 hours. Through this process, the molded body becomes 10 times bulkier, and a fluffy and hard-to-collapse cocoon-like α-type aggregate of silicon nitride and silicon oxynitride is obtained. The silicon oxynitride crystals were the same as in Example 1, but the yield of silicon nitride crystals was increased. The results of the generated phases are shown in Tables 1 and 2. Example 7 3.37g silicon (mole ratio 12) and increased manganese
0.04 (molar ratio 0.5), magnesium 0.07g (molar ratio
After mixing fine powders of 0.3) and 0.02 g of aluminum (molar ratio 0.1), an alloy phase is formed on the silicon surface layer under the same conditions as in Example 1. This alloy particle
Weigh 2.01g (molar ratio 12) and 0.36g silicon dioxide (molar ratio 1), and add the β-type silicon nitride crystals to the total amount.
After adding 0.23g of 10% by weight and mixing, the mixture was formed into a cylindrical shape with a diameter of 7mm. This was put into the combustion tube again, and while nitrogen was being supplied at 30 ml/min and hydrogen was being supplied at 5 ml/min,
Raise the temperature to 1470℃ at a heating rate of ℃ and hold for 30 minutes.
It was held at 1510°C for 3 hours. Through this step, the molded body becomes 8 times bulkier and is obtained as a grayish-black aggregate of β-type silicon nitride and silicon oxynitride.
Among the fibrous aggregates, silicon oxynitride has a thickness of 1~
3 μm, length 20-100 μm, average length 70 μm, and silicon nitride crystal structure became shorter with thickness 0.5-1 μm and length 100-200 μm. As in Examples 1 to 6, by using copper, iron, manganese, nickel or a salt thereof, or by granulating with methyl cellulose, etc., it is made of silicon oxynitride with good crystallinity and silicon nitride with many β-types. A fibrous aggregate was obtained. The results of the generated phase at that time are shown in Table 2 and Example 22. Furthermore, when the silicon/silicon dioxide ratio (mole) was increased to 15 and 18, the bulk of the molded product was 6 times, respectively.
4 times, the fibrous tissue showed a tendency to shorten and harden. When the silicon/silicon dioxide ratio (mole) was decreased to 8 or less, the production of silicon nitride was sharply reduced. Therefore, the upper limit of the molar ratio of silicon and silicon dioxide to obtain a fibrous aggregate composed of silicon oxynitride and α- and β-type silicon nitrides with good crystallinity is preferably 12 and the lower limit is 8. The results of the generated phases are shown in Tables 1 and 2.

【table】

【table】

[Table] (g) Effects of the Invention As described above, according to the method of the present invention, a nitride-based fibrous aggregate with good performance can be produced relatively easily. The fibrous aggregate made of silicon nitride and silicon oxynitride obtained by the present invention is a heat-resistant and heat-insulating material used in space, ocean, and environmental chemical materials, light alloys, ceramics, high-temperature electricity, etc., and nuclear, petrochemical, and other plants. It can be used as a composite reinforcing material for metals, plastics, and glass to improve its performance, and it can also be used in filters and the like.

[Brief explanation of drawings]

The drawing is a scanning electron microscope photograph of silicon nitride and silicon oxynitride crystals. (×200)

Claims (1)

[Claims] 1. A mixture of magnesium and at least one of metals selected from copper, iron, manganese, and nickel, and aluminum and carbon are added to silicon powder in an inert or reducing atmosphere. Heated to below 1450℃, without alloy forming powder,
A fibrous aggregate made of silicon nitride and silicon oxynitride, which is characterized by adding silicon dioxide and silicon nitride to this alloy powder, mixing it, molding it, and heating the molded product to 1380°C or higher in a nitrogen or reducing gas flow. manufacturing method. 2. The method according to claim 1, wherein a metal or a salt thereof is added to silicon and heated to alloy the silicon. 3. The method according to claim 1, wherein a mixture of silicon dioxide in which silicon nitride is added to silicon alloy-forming powder is granulated to a particle size of 0.07 to 2 mm.