JP2008081365A - Method of manufacturing silicon carbide powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing silicon carbide powder having high electric resistance and thermal conductivity and suitable as filler for obtaining a plastic-SiC composite having excellent strength characteristic. <P>SOLUTION: The method of manufacturing the silicon carbide powder includes: mixing alcohol with silicon alkoxide; adding a thermosetting resin and stirring and mixing; hydrolyzing the liquid mixture by adjusting pH to 1-7; applying heat-treatment to the resultant thermosetting resin-silica composite gel at 800-1,000°C in a non-oxidizing atmosphere; adjusting the molar ratio (C/SiO<SB>2</SB>) of carbon/silica composite obtained by carbonizing the resin component to 2-5; heating the composite at the temperature of 1,400-2,300°C in a non-oxidizing atmosphere; and reducing silica of the carbon/silica composite by carbon to convert it to SiC. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing silicon carbide powder having a high agglomerated structure (structure) in which powder particles are secondarily bonded, and in particular, a plastic having high electrical resistance and high thermal conductivity and excellent strength properties. The present invention relates to a method for producing silicon carbide powder suitable as a filler for producing a SiC composite.

  Pure silicon carbide has a high thermal conductivity while having a band gap of approximately 3.2 eV and is substantially non-conductive. For example, if silicon carbide powder is combined with plastic such as resin, high electrical resistance and A highly thermally conductive plastic-SiC composite material is obtained.

  However, simply mixing silicon carbide powder with plastic cannot improve the strength of the plastic-SiC composite, but rather has a drawback of lowering. Therefore, silicon carbide suitable for the production of a plastic-SiC composite that does not cause a decrease in strength even when composited with plastic, further improves strength, and can impart high electrical insulation and thermal conductivity. The development of powder is desired.

  A method of pulverizing and classifying bulk SiC produced by the Atchison method has long been known as a method for producing silicon carbide powder, but since SiC is an extremely hard substance, it is pulverized into fine spherical powder particles. In addition, impurities are easily mixed in the pulverization and classification processes, and it is difficult to obtain a high-purity product.

  Therefore, a technique for producing fine SiC fine powder of submicron grade by a vapor phase process has been developed. For example, Patent Document 1 discloses that the average particle diameter of SiC powder obtained by thermally decomposing halogenated silane is 0. An easily sinterable β-type SiC powder having an average ratio between the maximum particle size and the minimum particle size of 1.1 to 1.4 at 2 to 0.7 μm is disclosed.

  Patent Document 2 discloses a spherical monodispersed β that hydrolyzes a mixture of silicon alkoxide and an alkoxysilane having at least one hydrocarbon group to form a spherical monodispersed gel particle, which is then fired to form β-SiC. -A method for producing SiC fine particles is disclosed.

Further, in Patent Document 3, a mixed solution of silicon alkoxide and resin is dropped into an aqueous base solution and hydrolyzed to prepare silica / resin composite fine particles. The obtained silica / resin composite fine particles are obtained at 1450 ° C. in an oxygen-free atmosphere. The manufacturing method of the SiC powder heated to SiC and having been described above is disclosed.
JP 59-102809 Japanese Patent Laid-Open No. 03-199115 JP 09-208210 A

  Accordingly, the present inventor has developed a silicon carbide powder for obtaining a plastic-SiC composite having high strength characteristics when composited with plastic, and having high electrical resistance and non-conductivity, and good thermal conductivity. We conducted intensive research on the development of.

  As a result, when silicon carbide powder with a high agglomeration structure (structure) in which silicon carbide powder particles are secondarily bonded is combined with plastic, the plastic has high electrical resistance and thermal conductivity, and excellent strength characteristics. It was found that a SiC composite can be obtained.

  That is, the present invention has been developed based on the above findings, and an object thereof is to provide a method for producing silicon carbide powder suitable as a filler for obtaining a plastic-SiC composite having these characteristics. .

In order to achieve the above object, the method for producing silicon carbide powder according to the present invention comprises mixing silicon alkoxide with alcohol, adding a thermosetting resin, stirring and mixing, and then adjusting the pH of the mixed solution to 1-7. The resulting thermosetting resin / silica composite gel was heat-treated at a temperature of 800 to 1000 ° C. in a non-oxidizing atmosphere to carbonize the resin component (C / silica (C / After adjusting the C / SiO ₂ molar ratio of the SiO ₂ ) composite to 2 to 5, heat treatment is performed at a temperature of 1400 to 2300 ° C. in a non-oxidizing atmosphere to reduce the silica of the carbon / silica composite with carbon. It is characterized by being converted to SiC.

In the above production method, the C / SiO ₂ molar ratio of the carbon / silica (C / SiO ₂ ) composite is adjusted to 2 to 5 by controlling the addition amount of the thermosetting resin. Is done.

  According to the present invention, there is provided a method for producing a silicon carbide powder having a high agglomerated structure (structure) in which powder particles are secondarily bonded, and the silicon carbide powder produced according to the present invention is blended into a plastic such as a resin as a filler. By doing so, it becomes possible to obtain a plastic-SiC composite having high electrical resistance and thermal conductivity and excellent strength properties.

[1] Synthesis of thermosetting resin / silica composite gel;
First, alcohol is mixed with silicon alkoxide which is a silica source to prepare a mixed solution. Examples of silicon alkoxides include alkyl silicates, (mono-, di-, tri-, tetra-) alkoxysilanes, tetraalkoxysilane polymers, etc., and examples of alkyl silicates include methyl silicate, ethyl silicate, butyl silicate, and the like. However, ethyl silicate is preferred from the viewpoints of handleability and reactivity. Further, as the alkoxysilane, tetraalkoxysilane is preferable, and as the polymer of tetraalkoxysilane, a low molecular weight polymer having a polymerization degree of about 2 to 15 is preferable.

  The alcohol mixed with the silicon alkoxide is not particularly limited and any alcohol can be used, but ethanol is preferably used. In addition, the amount of alcohol to be mixed is preferably 0.5 times or more with respect to silicon alkoxide by volume so that the next-added thermosetting resin can be easily mixed. It is necessary to remove excess alcohol, and the amount is preferably 3 times or less.

  To this mixed solution of silicon alkoxide and alcohol, a thermosetting resin is added and mixed by stirring. Then, an aqueous acid solution or water is added to the mixed solution and mixed by stirring to adjust the pH of the mixed solution to 1 to 7. To hydrolyze. Hydrolysis is performed by adjusting the pH of the mixed solution and leaving it to stand for about 1 hour to 3 days to obtain a thermosetting resin / silica composite gel.

  If the pH of the mixed solution is less than 1, the hydrolysis reaction of the silicon alkoxide may proceed remarkably fast and cause a reaction runaway. On the other hand, if the pH exceeds 7, the progress of the hydrolysis reaction becomes extremely slow and becomes impractical.

  The thermosetting resin / silica composite gel thus obtained is dried and then pulverized to obtain a precursor for producing silicon carbide powder.

[2] Carbonization;
The thermosetting resin / silica composite gel, which is a precursor for producing silicon carbide powder thus obtained, is heat-treated at a temperature of 800 to 1000 ° C. in a non-oxidizing atmosphere such as an inert gas or nitrogen gas. The components are carbonized to produce a carbon / silica (C / SiO ₂ ) composite.

In this case, the molar ratio C / SiO ₂ of carbon (C) obtained by carbonizing the resin component and silica (SiO ₂ ) generated by hydrolysis of silicon alkoxide is adjusted to 2-5.

When the C / SiO ₂ molar ratio of the carbon / silica (C / SiO ₂ ) composite is less than 2, the production yield of the produced silicon carbide powder is lowered, and the particles of the silicon carbide powder are secondary. The combined agglomerated structure (structure) becomes too high, and the kneadability at the time of compounding with plastic is remarkably lowered. However, if the molar ratio of C / SiO ₂ exceeds 5, the development of an agglomerated structure (structure) in which the particles of silicon carbide powder are secondarily bonded becomes small.

The C / SiO ₂ molar ratio of the carbon / silica (C / SiO ₂ ) composite is controlled by adjusting the amount of carbon produced by carbonization of the thermosetting resin relative to silica produced by hydrolysis of silicon alkoxide. It can be adjusted and controlled by the amount of thermosetting resin added to the mixed solution of silicon alkoxide and alcohol.

The thermosetting resin / silica composite gel is heat-treated at a temperature of 800 to 1000 ° C. in a non-oxidizing atmosphere to carbonize the resin component to produce a carbon / silica (C / SiO ₂ ) composite. If the temperature is less than 800 ° C., the resin component is not sufficiently carbonized. On the other hand, if the heat treatment temperature exceeds 1000 ° C., the carbonization is already completed, which is unnecessary.

[3] Production of silicon carbide powder;
The carbon / silica (C / SiO ₂ ) composite thus obtained is heat-treated at a temperature of 1400 to 2300 ° C. in a non-oxidizing atmosphere, whereby silica (SiO ₂ ) in the carbon / silica composite is obtained. Is reduced with carbon (C), and a reaction of SiO ₂ + 3C → SiC + 2CO occurs to produce silicon carbide powder.

  In this case, the reason why the heat treatment temperature is set to 1400 to 2300 ° C. is that this reaction does not proceed sufficiently when the heat treatment temperature is lower than 1400 ° C., whereas the generated silicon carbide is decomposed when the heat treatment temperature is higher than 2300 ° C. .

In the silicon carbide powder produced by heat-treating the carbon / silica (C / SiO ₂ ) composite in a non-oxidizing atmosphere in this way, unreacted carbon is likely to remain, and thus it is necessary to remove this. . The removal of the carbon content is simple and preferable by heating to a temperature of about 700 to 1000 ° C. in an atmosphere such as air where oxygen is present to burn and remove the carbon. When the heating temperature is 700 ° C. or lower, the treatment time becomes long, and when it is 1000 ° C. or higher, the generated silicon carbide powder is oxidized, which is not preferable.

  Thus, a silicon carbide powder having a large aggregate structure (structure) in which powder particles are secondarily bonded can be produced. For example, the DBP absorption amount, which is an index indicating the size of the structure of carbon black, is 70. High structure silicon carbide powder of about ~ 200ml / 100g can be produced. The DBP absorption is a value measured according to JIS K6217 “Testing method for basic performance of carbon black for rubber”.

Example 1
Ethyl silicate 40 (manufactured by Colcoat Co.) as a silicon alkoxide is mixed with an equal volume of ethanol in a volume ratio, and a resol type phenol resin (manufactured by Dainippon Ink & Chemicals, J-325) is used as a thermosetting resin in the mixed solution. The carbon / silica (C / SiO ₂ ) composite obtained by carbonizing the resin component is mixed so that the C / SiO ₂ molar ratio is 3, and hydrochloric acid is added so that the pH is 3. After adding and allowing to stand overnight, the ethyl silicate 40 was hydrolyzed and converted to silica, and then dried and pulverized to prepare a phenol resin / silica composite gel to be a precursor for producing silicon carbide powder.

The phenol resin / silica composite gel thus obtained was heat-treated in a nitrogen gas atmosphere at a temperature of 800 ° C., and the phenol resin was calcined to produce a carbon / silica (C / SiO ₂ ) composite. Next, the silica (SiO ₂ ) in the composite is reduced by carbon (C) to be converted into silicon carbide by heat treatment at a temperature of 1650 ° C. in an argon atmosphere, and then heated to a temperature of 800 ° C. in air to remain. The carbon content was burned and removed to produce silicon carbide powder.

  This silicon carbide powder and a resol type phenol resin (manufactured by Dainippon Ink Chemical Co., Ltd., J-325) are mixed so that the weight ratio of the solid content after curing is 4: 6, and a phenol resin-SiC composite The body was manufactured.

Comparative Example 1
A phenol resin-SiC composite was produced in the same manner as in Example 1 using a commercially available product (OY-15 manufactured by Yakushima Electric Works) as silicon carbide powder.

Comparative Example 2
In Example 1, the phenol resin was mixed by adjusting so that the C / SiO ₂ molar ratio of the carbon / silica (C / SiO ₂ ) composite was 1.5. Silicon carbide powder was produced, and a phenol resin-SiC composite was produced.

Comparative Example 3
In Example 1, silicon carbide was prepared in the same manner as in Example 1 except that the phenol resin was mixed so that the C / SiO ₂ molar ratio of the carbon / silica (C / SiO ₂ ) composite was 8. Powder was produced and a phenol resin-SiC composite was produced.

  Table 1 shows the DBP absorption amount of the silicon carbide powder thus produced, the kneadability with the resin, and the bending strength of the phenol resin-SiC composite.

Claims (2)

After mixing alcohol with silicon alkoxide, then adding thermosetting resin, stirring and mixing, adjusting the pH of the mixture to 1-7 to hydrolyze, and the resulting thermosetting resin / silica composite gel The carbon / silica (C / SiO ₂ ) composite C / SiO ₂ molar ratio of carbon / silica (C / SiO ₂ ) composite obtained by heat treating the resin component at a temperature of 800 to 1000 ° C. in a non-oxidizing atmosphere is adjusted to 2 to 5. Then, heat treatment is performed at a temperature of 1400 to 2300 ° C. in a non-oxidizing atmosphere, and the silica of the carbon / silica composite is reduced with carbon and converted to SiC. The silicon carbide according to claim 1, wherein the addition amount of the thermosetting resin is adjusted so that the molar ratio between the amount of SiO ₂ generated from silicon alkoxide and the amount of C formed by carbonization of the resin component is 2 to 5. Powder manufacturing method.