KR100477949B1 - SPHERICAL SiC-BASED PARTICLES AND METHODS FOR PREPARING THE SAME - Google Patents

Abstract

The present invention relates to a spherical silicon carbide compound and a method for producing the same, and in particular, to provide a spherical silicon carbide compound containing 10% by weight or more of spherical spherical particles satisfying the following formula (1) and a method for producing the same.

[Equation 1]

0.99 ≤ a / b ≤ 1

(Wherein a is the short diameter of the particle and b is the long diameter of the particle)

Description

Spherical Silicon Carbide-Based Compound and Method for Manufacturing the Same {SPHERICAL SiC-BASED PARTICLES AND METHODS FOR PREPARING THE SAME}

The present invention relates to a spherical silicon carbide-based compound and a method for producing the same, in particular, a silicon carbide-based compound which is a spherical silicon carbide (SiC) particles having a size of 0.1 ㎛ or more, or a spherical carbon particles coated with silicon carbide, and a method for producing the same. It is about.

[Prior art]

Since silicon carbide has high strength and stiffness and low electrical conductivity, spherical silicon carbide or silicon carbide coated spherical carbon is used as dispersed particles of electrorheological fluids, raw materials of composite materials, and tip of ballpoint pens. Or as a ball bearing.

There is a method of directly carbonizing silicon as a conventional method for producing the silicon carbide particles, but it is uneconomical because the price of silicon is expensive. As another method, there is a method of preparing silicon carbide powder by pyrolyzing a silane compound, but this method also has a problem in that a material to be handled is dangerous and expensive.

As another example, carbon thermal reduction is performed by coating fumed silica particles on carbon prepared by pyrolysis of propylene (C ₃ H ₆ ) and reacting at a temperature of 1,600 to 2,100 ° C. under an inert gas atmosphere. Has been reported to produce beta-silicon carbide (β-SiC) having a size of several tens of micrometers in number (J. Mater. Sci., 33 (1998) 2537). In the case of the above method, since the produced silicon carbide has to be pulverized in the form of agglomerates, the finally obtained silicon carbide particles are irregular, not spherical.

In recent years, a method for producing fibrous silicon carbide is known. Krishnarao et al. Described a method for producing SiC short fibers by reacting cotton fibers with silicon nitride at temperatures above 1300 ° C. (Krishnarao. RV; Mahajam, YR J. Mater. Sci. Lett ., 15 (1996) 232) and Okada and their co-workers produced SiC fibers by reacting activated carbon fibers with SiO gas (Okada, K .; Kata, H .; Nakajima, K. J. Am. Ceram. Soc., 77 ( 1994) 1691-1693), and Culter also produced SiC fibers from chaff (Culter, IB, US Pat. No. 3,745,076, 1970).

In addition, a method for producing SiC fibers from carbon fibers by a conversion method (also called 'pack-cementation') has been reported (Carbon Science 1 (2000), 12-16). That is, when a packed powder composed of a mixture of SiC, Si, and Al ₂ O ₃ is heat-treated at a temperature of 1,100 to 1,800 ° C. for 30 minutes to 4 hours to generate an unstable gaseous SiO, the gas is carbon-based. It diffuses to the surface and inside of, where it reacts with carbon to precipitate SiC and release gaseous CO, so that the substrate is converted to SiC, and CO is diffused into the packed powder and reacted with Si to react with Si in a chain reaction of 1 to 10 ㎛. SiC is manufactured. However, in the above method, since the reaction rate with carbon constituting the fiber is faster than the rate at which SiO gas diffuses into the fiber at 1800 ° C., only a predetermined thickness of the fiber is converted into SiC and the inside of the carbon remains intact. There is a problem of having a shell structure, and also an arrangement of crystals grows perpendicularly to the axial direction of the fiber, thereby causing a problem in the mechanical strength of the fiber.

In addition, Korean Patent Registration No. 115794 mixes 1 mole of silica or less with 200 mesh and 1.5 to 3 moles of carbon source and 2.0 to 2.7 moles of magnesium (MgO) of 50 mesh or less to make a molded product, and then ignites the molded product to self-heat the chemical. Reaction, washing with acid, washing, filtration, drying and roasting to remove free carbon, heating by adding nitric acid and hydrofluoric acid mixed solution, filtration, washing, drying and pulverizing silicon carbide (SiC) ) Is described. In addition, Korean Patent Publication No. 1991-700198 discloses amorphous granular silica, fumed silica, aqueous colloidal silica, silica gel, precipitated silica, and mixtures thereof in a device consisting of a reactant transport engine, a reaction chamber, a heating means, a cooling chamber, and the like. And a carbon source selected from hydrocarbons, carbohydrates, starches, celluloses, other carbon-containing compounds, and mixtures thereof, with a molar ratio of carbon to silica of less than 3.5, to a particulate reactive mixture of the silica source and the carbon source. Substantially all of the particles of the reactive mixture are heated individually at a temperature of 1,400 to 2,400 ° C. at a heating rate of at least about 100 ° C./sec and passed through a heating zone maintained for 0.2 to 10 seconds, at least a portion of the excess carbon and oxygen At least 50% by weight of the silicon carbide crystals A method for producing fine silicon carbide ceramic powders using carbon thermal reduction that results in silicon carbide crystals having a size distribution of 0.4 to 1.6 times the crystal size of at least about 80% by weight is described. However, the above methods can produce silicon carbide of a fine size, but there are problems in that the process is complicated or that the shape of the manufactured silicon carbide particles is irregular rather than spherical.

Accordingly, an object of the present invention is to provide a spherical silicon carbide-based compound having a spherical shape of 0.1 μm or more by a simple method using a carbon precursor and hydrophobic silica.

Another object of the present invention is to adjust the mixing ratio of the carbon precursor and silica, and the firing temperature and time in the production of the spherical silicon carbide-based compound to produce spherical silicon carbide or spherical carbide to produce carbon carbide coated carbon particles It is to provide a method for producing a silicon compound.

In order to achieve the above object, the present invention provides a spherical silicon carbide compound,

It provides a spherical silicon carbide compound containing 10% by weight or more of spherical spherical particles satisfying the following formula (1).

[Equation 1]

0.99 ≤ a / b ≤ 1

Wherein a is the short diameter of the particle and b is the long diameter of the particle.

In addition, the present invention provides a method for producing a spherical silicon carbide compound,

a) iii) a carbon precursor; And

   Ii) silica with hydrophobic surface

   Mixing; And

b) calcining the mixture of step a)

It provides a manufacturing method comprising a.

Hereinafter, the present invention will be described in detail.

The present invention is a spherical silicon carbide which is a resin, pitch, spherical carbon or a mixture thereof, is added to the surface treated to have a hydrophobic (silica) hydrophobic (silica), and then mixed and heat-treated at a temperature of 1400 ℃ or more in an inert gas atmosphere It is to provide a sub-compound and a method for producing the same. According to this method, it is possible to produce spherical particles having a size of 0.1 μm or more by only one heat treatment after mixing raw materials.

Such spherical silicon carbide compound of the present invention preferably contains 10% by weight or more of spherical spherical particles satisfying the following formula (1).

In addition, the remaining particles of the spherical silicon carbide-based compound preferably includes spherical spherical particles satisfying the following formula (2).

[Equation 1]

0.99 ≤ a / b ≤ 1

[Equation 2]

0.1 ≤ a / b ≤ 0.99

Wherein a is the short diameter of the particle and b is the long diameter of the particle.

The spherical silicon carbide compound of the present invention has an average particle diameter of 0.1 µm or more, preferably 0.1 to 500 µm.

In the present invention, the spherical silicon carbide compound is preferably spherical silicon carbide particles or spherical carbon particles coated with silicon carbide.

In addition, the spherical silicon carbide compound of the present invention can be prepared by a simple method as follows. In detail, the present invention performs a step of a) mixing the carbon precursor and the surface treated hydrophobic silica, and b) calcining the mixture to prepare a spherical silicon carbide-based compound.

In the present invention, by adjusting the mixing ratio, firing temperature and time of the carbon precursor and silica, there is a feature that can produce a silicon carbide having a spherical shape, or to produce a carbon carbide coated carbon particles.

The mixing ratio of the carbon precursor and the surface-treated silica is preferably mixed in a weight ratio of 100: 0.1 to 1000, wherein the amount of the silica-treated surface hydrophobic is 0.1 weight based on 100 parts by weight of the carbon precursor. If it is less than parts, the production of spherical particles is difficult, and if it is more than 1000 parts by weight, it is difficult to obtain the effect as much as the added amount. However, as the amount of silica added increases, the thickness of the silicon carbide coating layer on the carbon surface increases, so it is necessary to adjust the amount of silica to suit the thickness of the desired silicon carbide layer. That is, in order to obtain spherical silicon carbide particles, the weight ratio of silica to carbon precursor should be 50% or more.

Therefore, in the present invention, when producing the spherical silicon carbide a) after mixing the carbon precursor and the surface-treated hydrophobic silica in a weight ratio of 100: 50 to 1000, 700 to a temperature increase rate of 1 to 100 ℃ / min After firing for 1 to 10 hours at a temperature of 1000 ℃, it is preferable to heat again at a temperature increase rate of 1 to 100 ℃ / min and refire for 1 to 10 hours at a temperature of 1400 to 2000 ℃.

In the present invention, when preparing carbon carbide-coated carbon particles, a) a carbon precursor and a surface-treated hydrophobic silica are mixed at a weight ratio of 100: 0.1 to 1000, and then heated to 1 to 100 ° C / min. It is preferable to bake for 1 to 10 hours at a temperature of 700 to 1000 ° C at a rate, and then to again heat at a temperature rising rate of 1 to 100 ° C / min for 30 minutes to 10 hours at a temperature of 1400 to 2000 ° C. .

The mixing may be performed in a mortar, ball mill, or the like to coat hydrophobic silica particles on the surface of the carbon precursor, or to prepare a slurry by dispersing the hydrophobic silica and the polymer binder in a solvent, and then coating the slurry on the surface of the carbon precursor. However, the method of coating the hydrophobic silica on the surface of the carbon precursor in the present invention is not limited to the above method.

Since the carbon precursor used in the present invention may be a solid powder that can be mixed with silica, there is no particular limitation on the kind of precursor, and spherical carbon, resin, pitch, or a mixture thereof is preferably used. In addition, the particle size of the precursor powder is not limited.

In the present invention, the resin used as the carbon precursor is preferably a thermosetting synthetic resin, and the thermosetting synthetic resin is a phenolics resin, a furan resin, an epoxy resin, a polyacrylonitrile resin, From the group consisting of polyimide resin, polybenzimidazoloe resin, polyphenylene resin, and biphenol resin, divinylbenzene styrene copolymer, and cellulose It is preferable that 1 or more types are selected.

In addition, the pitch used as the carbon precursor in the present invention may be used such as petroleum pitch or coal pitch.

The present invention can be converted into spherical particles by adding a hydrophobically treated silica to the carbon precursor. The hydrophobic silica used in the present invention surrounds the surface of the carbon precursor powder to prevent agglomeration of carbon particles from each other in the carbonization process, and also provides a high surface tension when the particles shrink in the carbonization process so that the particles are spherical. Induce as much as possible. When the carbon precursor is not introduced into the carbon precursor or carbonized by introduction of silica that has not been hydrophobized on the surface, agglomerated particles are obtained. Therefore, in the present invention, the use of silica whose surface is hydrophobically treated is very important for the production of spherical particles. To be an element.

Specific examples of silica whose surface is hydrophobicly treated in the present invention include Cabosil (Cab-O-SIL TS-720, TS-610, TS-530, TS-500, TG-308F, TG-810G530, etc.) and Deggusa's Aerosil (AEROSIL R972, R974, R812, R812S, R202). These inorganic substances may use a commercialized product, and may also use it synthetically.

The method of synthesizing the hydrophobized silica specifically includes adding an organosilane surface treatment agent such as fumed silica and trimethyl chlorosilane whose surface is non-hydrophobic to a solvent such as toluene. By refluxing with stirring, the surface-treated hydrophobic silica can be easily obtained.

In the present invention, the mixture is calcined under an inert gas (eg, argon, nitrogen, helium, etc.) atmosphere, thereby obtaining carbon spheres coated with silicon carbide or silicon carbide having a spherical shape. In this case, as described above, the thickness of the coated silicon carbide layer increases as the silicon content of the silica increases as compared to the carbon content of the carbon precursor, and the thickness of the silicon carbide coating layer increases as the firing temperature and time increase. If the content of one silica is sufficient and the firing temperature and time are long, spherical pure silicon carbide particles are obtained.

Hereinafter, the present invention will be described with reference to the following Examples and Comparative Examples. However, these examples are only for illustrating the present invention, and the present invention is not limited thereto.

Example 1

Phenol resin (CAB-O-SIL) TS-530 silica treated with hexamethyldisilazane hydrophobic surface was induced in phenolic resin, a carbon precursor, in a weight ratio of 1: 1. After mixing at, the mixture was heated at an elevated temperature rate of 10 ° C./min in an argon gas atmosphere and maintained at 1000 ° C. for 1 hour. Spherical silicon carbide-coated carbon particles were prepared by heating at a temperature increase rate of 10 ° C./min and heat-treating at 1400 ° C. for 3 hours. The thickness of the silicon carbide layer coated on the carbon surface of the spherical particles thus prepared was about 2 μm. Scanning electron micrograph (8,000 times) thereof was taken and shown in FIG. 1. 2 shows the magnification of the scanning electron micrograph of the carbon particles obtained above by 1,000 times. 2, the ratio (a / b) of the short diameter a and the long diameter b of most spherical carbon particles coated with silicon carbide was 0.99 or more, and the average particle diameter was 22 μm. 3 is a scanning micrograph (6,000 times) of the cross-section of the carbon carbide coated carbon particles made by the above method was heated at a temperature increase rate of 10 ℃ / min in air and maintained at 800 ℃ for 15 hours to remove the carbon inside )to be. 6 shows its thermogravimetric analysis (in air, 10 ° C./min). In Figure 6, it can be seen that the content of silicon carbide is approximately 81% by weight.

Example 2

Spherical carbon particles coated with silicon carbide were prepared in the same manner as in Example 1, except that the firing temperature was 1500 ° C. and the temperature increase rate was 5 ° C./min. The thickness of the silicon carbide layer coated on the carbon surface of the spherical particles thus prepared was about 4 μm. Its scanning electron microscope cross section (2,300 times) is shown in FIG. 6 shows the result of thermogravimetric analysis thereof (in air, 10 ° C / min). In Figure 6, it can be seen that the content of silicon carbide is about 83% by weight. The ratio (a / b) of the short diameter a and the long diameter b of the silicon carbide-coated spherical carbon particles was 0.99, and the average particle diameter was 20 µm.

Example 3

Pure spherical silicon carbide was prepared in the same manner as in Example 1 except that the firing temperature was 1600 ° C and the temperature increase rate was 5 ° C / min. Its scanning electron microscope cross section (2,000 times) is shown in FIG. 6 shows its thermogravimetric analysis (in air, 10 ° C./min). In Figure 6 it can be seen that the particles produced are almost pure silicon carbide. The ratio (a / b) of the short diameter a and the long diameter b of the said spherical silicon carbide particles was 0.99, and the average particle diameter was 18 micrometers.

7 shows an X-ray diffraction pattern. In Figure 7 it can be seen that the same as the diffraction pattern of the beta-silicon carbide (β-SiC), the resulting material is beta-silicon carbide (β-SiC).

Example 4

Spherical silicon carbide particles were prepared in the same manner as in Example 3, except that the calcination temperature was maintained at 1600 ° C. for 1 hour. The ratio (a / b) of the short diameter a and the long diameter b of the said spherical silicon carbide particles was 0.99, and the average particle diameter was 19 micrometers.

6 shows the results of thermogravimetric analysis (in air, 10 ° C./min). In Figure 6, it can be seen that the content of silicon carbide is about 96% by weight.

Example 5

Spherical carbon particles coated with silicon carbide were prepared in the same manner as in Example 1, except that the carbon precursor and the silica were mixed in a weight ratio of 1: 1.5. The ratio (a / b) of the short diameter a and the long diameter b of the silicon carbide-coated spherical carbon particles was 0.99, and the average particle diameter was 20 µm.

Example 6

Spherical carbon particles coated with silicon carbide in the same manner as in Example 1, except that Carbosil (CAB-O-SIL) TS-720 dry silica treated with polydimethylsiloxane was used. Was prepared. The ratio (a / b) of the short diameter a and the long diameter b of the silicon carbide coated spherical carbon particles was 0.99, and the average particle diameter was 23 μm.

Example 7

Spherical carbon particles coated with silicon carbide were prepared in the same manner as in Example 1, except that naphthalene isotropic pitch was used as a carbon precursor. The ratio (a / b) of the short diameter a and the long diameter b of the silicon carbide coated spherical carbon particles was 0.99, and the average particle diameter was 30 μm.

As described above, according to the present invention, by adjusting the mixing ratio of the carbon precursor and silica, and the calcination temperature and time, the thickness of the silicon carbide layer coated on the carbon surface is controlled to produce spherical carbon particles coated with silicon carbide or Pure silicon carbide particles can be prepared. In addition, the present invention does not require a pulverization process because the resin, pitch, or a mixture thereof is used as a carbon precursor and the surface is hydrophobicly treated and not formed in the form of agglomerates as in the prior art. In order to prepare a spherical carbon particles coated with silicon carbide or silicon carbide having a size of 0.1 ㎛ or more. Since the silicon carbide produced in the present invention has high strength and rigidity and low electrical conductivity, the spherical silicon carbide or silicon carbide coated spherical carbon is used as dispersed particles of electrorheological fluids or of composite materials. It can be used as a raw material, a tip of a ballpoint pen, or a ball bearing.

1 is a scanning electron micrograph at 8,000 magnification of spherical carbon coated with silicon carbide of Example 1 prepared in the present invention,

2 is a scanning electron micrograph at 1,000 magnification of the spherical carbon coated with silicon carbide of Example 1 prepared in the present invention,

Figure 3 is a scanning electron micrograph of 6,000 magnification of the cross section of the carbon-carburized silicon carbide shell of the center of Example 1 prepared in the present invention,

4 is a scanning microscope photograph of 2,300 magnification of the spherical carbon cross-section coated with silicon carbide of Example 2 prepared in the present invention,

5 is a scanning electron micrograph at 2,000 magnification of the cross-section of spherical silicon carbide particles of Example 3 prepared in the present invention,

6 is a thermogravimetric analysis result showing the content of silicon carbide in the spherical silicon carbide or silicon carbide coated carbon of Examples 1, 2, 3, and 4 prepared in the present invention,

7 is an X-ray diffraction pattern of the spherical silicon carbide particles of Example 3 prepared in the present invention.

Claims (12)

delete delete delete delete delete In the method for producing a spherical silicon carbide compound, a) iii) a carbon precursor; And    Ii) silica with hydrophobic surface    Mixing; And b) calcining the mixture of step a) Manufacturing method comprising a. The method of claim 6, a) iii) a carbon precursor; And    Ii) silica with hydrophobic surface    Mixing 100 to 50: 1000 by weight; And b) the mixture of step a)    After firing for 1 to 10 hours at a temperature of 700 to 1000 ℃ at a temperature rising rate of 1 to 100 ℃ / min, and then heated at a temperature rising rate of 1 to 100 ℃ / min 1 to 10 hours at a temperature of 1400 to 2000 ℃ Refired to produce spherical silicon carbide particles Manufacturing method comprising a. The method of claim 6, a) iii) a carbon precursor; And    Ii) silica with hydrophobic surface    Mixing 100 at a weight ratio of 0.1: 1000; And b) the mixture of step a)    It is calcined for 1 to 10 hours at a temperature of 700 to 1000 ℃ at a temperature rising rate of 1 to 100 ℃ / min, then heated at a temperature rising rate of 1 to 100 ℃ / min and 30 minutes to 10 at a temperature of 1400 to 2000 ℃ Refiring for a time to produce spherical carbon particles coated with silicon carbide particles Manufacturing method comprising a. The method of claim 6, The carbon precursor of step a) iii) is a resin, pitch, spherical carbon or a mixture thereof. The method of claim 9, The resin may be a phenol resin, furan resin, epoxy resin, polyacrylonitrile resin, polyimide resin, polybenzimidazoloe resin, polyphenylene ( A polyphenylene resin, and a thermosetting synthetic resin containing a biphenol resin, a divinylbenzene styrene copolymer, and a manufacturing method selected from the group consisting of cellulose. The method of claim 9, The pitch is coal pitch or petroleum pitch. The method of claim 6, The a) silica of the surface of step a) step ii) hydrophobic is prepared by refluxing the hydrophilic silica and the organosilane solution.