JP2007112656A - Method for producing silicon fine particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple method for producing silicon fine particles. <P>SOLUTION: This method for producing silicon fine particles comprises (1) a step of heating and firing a mixture containing a silicon source and a carbon source under inert atmosphere, (2) a step of extracting the generated gas from the inert atmosphere, quenching the gas to solidify to obtain a powder mixture containing silicon fine particles, and (3) a step of extracting the silicon fine particles from the powder mixture. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing silicon fine particles.

With recent advances in nanotechnology, the size required for powders as raw materials is becoming smaller. Research and development targets are shifting from submicron particles to nanoparticles. In particular, it is known that nanoparticles of 20 nm or less have excellent characteristics that are not found in bulk materials due to the expression of a unique electromagnetic effect associated with changes in the electronic state and the increase in the proportion of surface atoms. Therefore, for example, silicon fine particles are expected to be applied as light emitting elements. Various methods for producing such silicon fine particles have been proposed (see, for example, Patent Document 1 and Non-Patent Document 1).
JP-A-6-279015 “Synthesis of Nanoparticles by Laser Ablation”, Akifumi Seto, Journal of Powder Technology (J. Soc. Powder Technology. Japan), Volume 42 (2005), pp. 39-44

  However, in the manufacturing methods disclosed in Patent Document 1 and Non-Patent Document 1, the handling of the manufacturing apparatus is complicated. Therefore, a simple method for producing silicon fine particles has been demanded.

That is, the present invention relates to the following items:
(1) A step of heating and baking a mixture containing a silicon source and a carbon source in an inert atmosphere, a step of extracting a product gas from the inert atmosphere and rapidly solidifying it to obtain a mixed powder containing silicon fine particles, and the above mixing And a step of extracting silicon fine particles from the powder.
(2) The method for producing silicon fine particles according to (1), wherein the silicon source produces silicon monoxide by heating.
(3) The method for producing silicon fine particles according to (2) above, wherein the silicon source is ethyl silicate.
(4) The method for producing silicon fine particles according to any one of (1) to (3), wherein the carbon source is a phenol resin.
(5) The method for producing silicon fine particles according to any one of (1) to (4), wherein silicon fine particles are extracted from a solution obtained by immersing the mixed powder in a hydrofluoric acid aqueous solution. .

  A simple method for producing silicon fine particles is provided.

Hereinafter, the present invention will be described with reference to embodiments, but it goes without saying that the present invention is not limited to the following embodiments.
In the silicon carbide powder manufacturing process, which is an intermediate process of the method for manufacturing a silicon carbide sintered body, for example, after mixing a silicon source and a carbon source, carbonization is performed by heating at a temperature of 1600 ° C. or higher in a non-oxidizing atmosphere. Silicon (SiC) powder is obtained. As this chemical reaction form, silicon monoxide (SiO) gas is first generated as an intermediate product as shown in the equation (1). When this silicon monoxide gas is continuously heated at a temperature of 1600 ° C. or higher, silicon carbide powder is obtained as shown in the equation (2). However, the present inventor has found that a mixture containing silicon (Si) fine particles can be obtained as shown in the formula (3) when cooled immediately at a temperature of less than 1600 ° C. after the production. The present invention is based on the above findings. Such knowledge is useful from the viewpoint that silicon fine particles can be easily produced and from the viewpoint that the by-product produced in the production process of the silicon carbide sintered body can be reused.

SiO ₂ + C → SiO + CO (1)
SiO + 2C → SiC + CO (2)
2SiO → Si + SiO ₂ (3)
(component)
As a component used for embodiment of this invention, the component used at the manufacturing process of the silicon carbide powder which is an intermediate process of the manufacturing method of a silicon carbide sintered compact can be used. The component used for embodiment of this invention is demonstrated through description of a silicon carbide powder.
Examples of the silicon carbide powder include α-type, β-type, amorphous, and mixtures thereof. In order to obtain a high-purity silicon carbide sintered body, it is preferable to use a high-purity silicon carbide powder as the raw material silicon carbide powder.
The grade of the β-type silicon carbide powder is not particularly limited, and for example, commercially available β-type silicon carbide can be used. The particle size of the silicon carbide powder is preferably small from the viewpoint of high density, specifically, about 0.01 μm to 10 μm, and more preferably 0.05 μm to 5 μm. If the particle size is less than 0.01 μm, handling in processing steps such as weighing and mixing tends to be difficult, and if it exceeds 10 μm, the specific surface area is small, that is, the contact area with the adjacent powder is small, and high This is not preferable because it is difficult to increase the density.

  The high-purity silicon carbide powder includes, for example, a silicon source containing at least one silicon compound, a carbon source containing an organic compound that generates carbon by heating at least one kind, and a polymerization or crosslinking catalyst. It can be obtained by a step of firing in a non-oxidizing atmosphere the powder obtained after being dissolved in and dried.

  As the silicon source containing the silicon compound (hereinafter referred to as “silicon source”), a liquid source and a solid source can be used in combination, but at least one of them must be selected from a liquid source. . As the liquid, a polymer of alkoxysilane (mono-, di-, tri-, tetra-) and tetraalkoxysilane is used. Among alkoxysilanes, tetraalkoxysilane is preferably used, and specific examples include methoxysilane, ethoxysilane, propoxysilane, butoxysilane, and the like. From the viewpoint of handling, ethoxysilane is preferable. Examples of the tetraalkoxysilane polymer include a low molecular weight polymer (oligomer) having a degree of polymerization of about 2 to 15 and a silicate polymer having a higher degree of polymerization, which are liquid. Examples of solid materials that can be used in combination with these include silicon oxide. In the above reaction sintering method, silicon oxide includes silica gel (colloidal ultrafine silica-containing liquid, containing OH group or alkoxyl group inside), silicon dioxide (silica gel, fine silica, quartz powder), etc. in addition to SiO. . These silicon sources may be used alone or in combination of two or more. Among these silicon sources, from the viewpoint of good homogeneity and handling properties, an oligomer of tetraethoxysilane, a mixture of an oligomer of tetraethoxysilane and fine powder silica, and the like are preferable. These silicon sources are high-purity substances, and the initial impurity content is preferably 20 ppm or less, more preferably 5 ppm or less. The silicon source is preferably one that generates silicon monoxide by heating, and specifically, ethyl silicate is preferred.

  The substance used as the carbon source is preferably a high-purity organic compound that contains oxygen in the molecule and remains carbon by heating. Specific examples include various sugars such as phenol resin, furan resin, epoxy resin, phenoxy resin, monosaccharides such as glucose, oligosaccharides such as sucrose, polysaccharides such as cellulose and starch. For the purpose of homogeneously mixing with the silicon source, these are mainly used in liquid form at room temperature, those that dissolve in a solvent, those that soften or become liquid when heated, such as thermoplasticity or heat melting properties. It is done. Of these, resol type phenol resins and novolac type phenol resins are preferred. In particular, a resol type phenol resin is preferably used.

  The polymerization and crosslinking catalyst used in the production of high-purity silicon carbide powder can be appropriately selected according to the carbon source. When the carbon source is a phenol resin or a furan resin, toluenesulfonic acid, toluenecarboxylic acid, acetic acid, oxalic acid And acids such as sulfuric acid. Among these, toluenesulfonic acid is preferably used.

  The ratio of carbon to silicon (hereinafter abbreviated as C / Si ratio) in the process of producing high-purity silicon carbide powder, which is a raw material powder used in the reaction sintering method, is obtained by carbonizing the mixture at 1000 ° C. The carbide intermediate is defined by elemental analysis. Stoichiometrically, the free carbon in the generated silicon carbide should be 0% when the C / Si ratio is 3.0, but in practice, the low C / Si is reduced due to volatilization of the SiO gas generated at the same time. Free carbon is generated in the ratio. It is important to determine the blending in advance so that the amount of free carbon in the generated silicon carbide powder does not become an amount that is not suitable for manufacturing applications such as sintered bodies. Usually, in firing at 1600 ° C. or more near 1 atm, free carbon can be suppressed when the C / Si ratio is set to 2.0 to 2.5, and this range can be suitably used. When the C / Si ratio is 2.55 or more, free carbon increases remarkably, but since this free carbon has an effect of suppressing crystal growth, the C / Si ratio is appropriately set according to the crystal growth size to be obtained. You may choose. However, when the atmospheric pressure is low or high, the C / Si ratio for obtaining pure silicon carbide varies, and in this case, the range is not necessarily limited to the above C / Si ratio.

  From the above, as a method for obtaining particularly high purity silicon carbide powder, the raw material powder production method described in the method for producing a single crystal in Japanese Patent Application Laid-Open No. 9-48605 previously filed by the applicant of the present application can be mentioned. That is, one or more selected from high-purity tetraalkoxysilane and tetraalkoxysilane polymer is used as a silicon source, and a high-purity organic compound that generates carbon by heating is used as a carbon source. A silicon carbide production step for obtaining a silicon carbide powder by heating and firing the obtained mixture in a non-oxidizing atmosphere; and maintaining the obtained silicon carbide powder at a temperature of 1700 ° C. or higher and lower than 2000 ° C. A post-treatment step of performing at least one treatment for 5 to 20 minutes at a temperature of 2000 ° C. to 2100 ° C., and by performing the above two steps, the content of each impurity element is 0.5 ppm or less A production method of high-purity silicon carbide powder to obtain a certain silicon carbide powder can be used. Since the silicon carbide powder obtained in this manner is non-uniform in size, it is preferable to treat the silicon carbide powder so as to meet the above particle size by pulverization and classification.

  In the case of introducing nitrogen in the process of producing silicon carbide powder, first, a silicon source, a carbon source, an organic substance composed of a nitrogen source, and a polymerization or crosslinking catalyst are homogeneously mixed. When dissolving an organic substance composed of a carbon source such as hexamethylenetetramine and a polymerization or crosslinking catalyst such as toluenesulfonic acid in a solvent such as ethanol, a silicon source such as an oligomer of tetraethoxysilane And thoroughly mixed.

(Silicon fine particle production equipment)
FIG. 3 shows a schematic diagram of the heating device 1 used for the production of silicon fine particles. The heating device 1
A heating container 2 containing a mixture containing a silicon source and a carbon source and forming a heating atmosphere;
A stage 6 for holding the heating container 2;
Heating bodies 10a and 10b for heating the mixture (sintered body) W;
A heat insulating material 12 covering the heating container 2 and the heating bodies 10a, 10b;
A blower 23 for sucking a reaction gas from the heating container 2 through a suction pipe 21, a dust collector 22 for containing the mixed powder, and a suction device 20 having a supply pipe 24 for supplying a gas are provided. The suction device 20 can suck SiO gas while maintaining a heated and inert atmosphere in the heating container 2. Argon gas is circulated in the suction device 20. In addition, an electromagnetic valve 25 that automatically opens and closes according to the set pressure is provided.

(Method for producing silicon fine particles)
A method for producing silicon fine particles according to an embodiment of the present invention includes:
(A) a step of heating and baking a mixture containing a silicon source and a carbon source in an inert atmosphere;
(B) extracting the generated gas from the inert atmosphere and rapidly solidifying it to obtain a mixed powder containing silicon fine particles;
(C) a step of extracting silicon fine particles from the mixed powder. Hereinafter, each process will be described in detail.

(I) Heating and firing step First, a mixture of ethyl silicate as a silicon source, a phenol resin as a carbon source, and maleic acid as a polymerization catalyst is placed in a heating vessel. The Si / C ratio is preferably 0.5 to 3.0. And the said mixture is heated and hardened at about 150 degreeC. Next, the cured product is heated at 800 to 1200 ° C. in a nitrogen atmosphere for 0.5 to 2 hours. Then, it heats at 1500-2000 degreeC under argon atmosphere.

(B) Rapid cooling and solidification step Next, the blower 23 is operated. Then, the generated gas is extracted from the inside of the heating container 2 through the suction pipe 21 by being put on an argon gas stream. Since the outside of the heat insulating material 12 is kept at room temperature, the generated gas is rapidly cooled to room temperature. A mixed powder composed of silicon (Si) and silica (SiO ₂ ) is obtained from the generated gas. The obtained mixed powder is collected in the dust collector 22. Further, an argon stream is sent into the heating container 2 through the supply pipe 24.

(C) Silicon extraction step A mixture of silicon and silica is added to a hydrofluoric acid aqueous solvent. Then, silicon dioxide is dissolved in a solvent. Thereafter, silicon is extracted from the solvent and appropriately dried to obtain silicon fine particles.

(Silicon fine particles)
The average particle diameter of the silicon fine particles according to this embodiment obtained by the above production method is 30 nm or less, preferably 20 to 30 nm. By providing such physical properties, it can be used, for example, as a light-emitting element material or an ultraviolet (UV) cut cosmetic.

Examples of the present invention will be shown below, but the present invention is not limited to these examples.
A mixed solution composed of 620 g of ethyl silicate as a silicon source, 288 g of phenol resin as a carbon source, and 92 g (35 wt%) of an aqueous maleic acid solution as a polymerization catalyst was placed in the heating container 2 of FIG. The mixed solution was heated at 150 ° C. to solidify. Next, the obtained solidified product was carbonized at 90 ° C. for 1 hour in a nitrogen atmosphere. The resulting carbide was heated at 1600 ° C. under an argon atmosphere.
Next, the by-product gas generated in the heating container 2 was conveyed out of the heating container 2 using the suction device 20 and a carrier gas of argon gas, and cooled at 1500 ° C. or less to obtain a powder.
As a result of transmission electron microscope (TEM) photographic analysis of the obtained powder, it was found that a powder containing silicon fine particles was obtained so as to be wrapped in silicon dioxide as shown in FIGS. Was confirmed.
Next, a powder containing silicon fine particles was added to a hydrofluoric acid aqueous solution to dissolve silicon dioxide, and then the silicon fine particles were recovered. The recovery rate was 11%. From the above, it was confirmed that silicon fine particles can be obtained simply and efficiently. When the particle size of each particle was measured for 200 silicon fine particles arbitrarily selected from a photograph taken with a transmission electron microscope (TEM), the average particle size of the silicon fine particles was 25 nm.

FIG. 1 shows a transmission electron micrograph of a mixed powder containing silicon fine particles. FIG. 2 shows a transmission electron micrograph of a mixed powder containing silicon fine particles. FIG. 3 shows an apparatus for producing silicon fine particles.

Explanation of symbols

1: Heating device 2: Heating vessel W: Mixture (sintered body)
6: Mixture 8: Stages 10a, 10b: Heating body 12: Insulating material

Claims (5)

Heating and baking a mixture containing a silicon source and a carbon source under an inert atmosphere;
Extracting the generated gas from the inert atmosphere and rapidly solidifying it to obtain a mixed powder containing silicon fine particles; and
Extracting silicon fine particles from the mixed powder;
A method for producing silicon fine particles, comprising:   The method for producing silicon fine particles according to claim 1, wherein the silicon source generates silicon monoxide by heating.   3. The method for producing silicon fine particles according to claim 2, wherein the silicon source is ethyl silicate.   The said carbon source is a phenol resin, The manufacturing method of the silicon particulates in any one of Claims 1-3 characterized by the above-mentioned.   5. The method for producing silicon fine particles according to claim 1, wherein silicon fine particles are extracted from a solution obtained by immersing the mixed powder in a hydrofluoric acid aqueous solution.