KR20170093478A - Manufacturing Method of Silicon Carbide Nano Powder using Polycarbosilane - Google Patents
Manufacturing Method of Silicon Carbide Nano Powder using Polycarbosilane Download PDFInfo
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- KR20170093478A KR20170093478A KR1020160014925A KR20160014925A KR20170093478A KR 20170093478 A KR20170093478 A KR 20170093478A KR 1020160014925 A KR1020160014925 A KR 1020160014925A KR 20160014925 A KR20160014925 A KR 20160014925A KR 20170093478 A KR20170093478 A KR 20170093478A
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- silicon carbide
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- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
Abstract
The present invention relates to a method for producing silicon carbide nanopowder using polycarbosilane, and the silicon carbide nanopowder produced by the method according to the present invention uses a high molecular weight polycarbosilane having a high thermal stability and a high thermal decomposition yield , High-molecular-weight polycarbosilane is oxidized at a low temperature and heat-treated at a high temperature to remove excess carbon, thereby exhibiting high yield, high purity and high crystallinity.
Description
The present invention relates to a process for producing silicon carbide powder using polycarbosilane, and more particularly, to a process for producing silicon carbide powder using polycarbosilane, which comprises separating and purifying a high molecular weight region of polycarbosilane, and oxidizing and heat- SiC) nano powders.
BACKGROUND ART Polycarbosilane (PCS) is a silicon-based compound having a basic skeleton of a covalent bond of silicon and carbon as shown in Chemical Formula 1, and is widely used as a silicon carbide (SiC) ceramic precursor.
[Chemical Formula 1]
Polycarbosilane has the advantage of being able to form silicon carbide crystals even at a relatively low temperature of 1,200 ° C. due to the above covalent bond, and it is possible to produce a shape which is impossible to be a powder such as a fiber or a thin film because of its polymer properties.
However, since the polycarbosilane of Formula 1 has a high carbon content, it is difficult for excess carbon to inhibit the growth of silicon carbide crystals to form highly crystalline beta-SiC, and the purity of the silicon carbide powder (Bunsell et al., Journal of material science 41 (2006) 823).
In addition, the polycarbosilane is a silicon-based compound and easily oxidized at a high temperature. In order to produce silicon carbide, it is necessary to perform heat treatment in an inert atmosphere. In such an inert atmosphere, the polycarbosilane melts and it is difficult to produce powder. In order to solve this problem, there is a curing step using oxygen prior to the heat treatment step.
In particular, ISHIHARA et al. Prepared a polycarbosilane powder by dissolving polycarbosilane in a solvent such as toluene or hexane (good solvent) and then performing supersaturation precipitation in a solvent such as alcohol or acetone (poor solvent) Followed by post-heat treatment. This is one of the methods for obtaining the bulk polycarbosilane as a powder. As described above, in order to prevent melting of the polymer powder during the heat treatment, it is cured by maintaining it in an oxidation atmosphere (usually air atmosphere) at 150 to 250 DEG C for a long time. At this time, the atmospheric oxygen breaks the Si-H bond, which is a weak bond in the molecular bond of the polycarbosilane, to form Si-O-Si crosslinking. Such excessive oxygen incorporation greatly decreases the purity of the silicon carbide powder It is known that it is not a suitable method for producing ultra-high purity silicon carbide powder because it inhibits crystallization of silicon carbide (Ishihara et al., Journal of the Ceramic Society of Japan 114 (2006) 507-510).
Therefore, there is a need to develop a method for manufacturing a high purity silicon carbide nano powder by preventing the melting of the polymer to maintain the powder shape and minimizing the influence of impurities such as oxygen and carbon in the process.
In order to solve the above problems in the process for producing silicon carbide nano powder using the polycarbosilane of the present invention,
Although the polycarbosilane has a small molecular weight, it has a wide molecular weight distribution. Therefore, the polycarbosilane contains a low molecular weight region due to its broad molecular weight distribution. Such a low molecular weight polycarbosilane melts in the heat treatment step Which is not only a main factor for the formation of silicon carbide but also fails to secure thermal stability, resulting in a problem of lowering the silicon carbide yield.
Further, it has been found that when the polycarbosilane in the high molecular weight region separated from the low molecular weight region is oxidized at a low temperature and heat-treated at a high temperature, surplus carbon can be removed. In addition, no oxygen remained, and it was confirmed that high purity silicon carbide crystals were formed.
Accordingly, an object of the present invention is to provide a method for preparing beta-phase silicon carbide nanopowder of high yield, high purity and high crystallinity by oxidizing and heat-treating separated and purified high molecular weight polycarbosilane at a predetermined temperature.
On the other hand,
Dissolving the polycarbosilane in an organic solvent to prepare a polycarbosilane solution;
Adding the polycarbosilane solution to methanol, ethanol, propanol, 2-propanol, acetonitrile or acetone under agitation to form a precipitate;
Oxidizing the precipitate at 150 to 300 占 폚; And
And heat-treating the oxidized precipitate at 1600 to 1800 ° C to produce silicon carbide powder. The present invention also provides a method for producing silicon carbide powder using the polycarbosilane.
In one embodiment of the present invention, the organic solvent is one selected from the group consisting of a normal nucleic acid, a cyclic nucleic acid, a heptane, a toluene, a tetrahydrofuran, xylene, chloroform and methylene chloride.
In one embodiment of the present invention, a high molecular weight region is separated and purified by using methanol, ethanol, propanol, 2-propanol, acetonitrile or acetone when the precipitate is formed from the polycarbosilane solution.
In an embodiment of the present invention, the step of forming the precipitate into spherical fine powder is further carried out by increasing the stirring speed after forming the precipitate.
In one embodiment of the present invention, the step of filtering and drying the precipitate after the formation of the precipitate is further carried out.
In one embodiment of the present invention, the average particle size of the silicon carbide powder is 5 to 700 nm.
The silicon carbide nano powder produced by the production method according to the present invention can be obtained by using a high molecular weight polycarbosilane having a high thermal stability and a high thermal decomposition yield, oxidizing the high molecular weight polycarbosilane at a low temperature, High yield and high crystallinity can be obtained by removing excess carbon.
1 is a graph showing the thermal stability and the thermal decomposition yield of polycarbosilane according to an embodiment of the present invention.
2 is a photograph showing a silicon carbide powder according to an embodiment of the present invention.
3 is a graph showing the results of X-ray diffraction analysis of the silicon carbide powder according to one embodiment of the present invention.
4 is a graph showing the results of Raman analysis of silicon carbide powder according to an embodiment of the present invention.
5 is a photograph showing a high magnification TEM image of a silicon carbide powder according to an embodiment of the present invention.
6 is a photograph showing a high magnification TEM image and a diffraction pattern of the silicon carbide powder according to one embodiment of the present invention.
Hereinafter, the present invention will be described in more detail.
One embodiment of the present invention
Dissolving the polycarbosilane in an organic solvent to prepare a polycarbosilane solution;
Adding the polycarbosilane solution to methanol, ethanol, propanol, 2-propanol, acetonitrile or acetone under agitation to form a precipitate;
Oxidizing the precipitate at 150 to 300 占 폚; And
And heat-treating the oxidized precipitate at 1600 to 1800 ° C to produce silicon carbide powder. The present invention also relates to a method for producing silicon carbide nanopowder using polycarbosilane.
In one embodiment of the present invention, a polycarbosilane solution can be prepared by dissolving polycarbosilane in an organic solvent.
The polycarbosilane may be contained in an amount of 20 to 50% by weight based on 100% by weight of the organic solvent.
Examples of the organic solvent include n-hexane, cyclohexane, heptane, toluene, tetrahydrofuran, xylene, chloroform, methylene chloride methylene chloride) can be used.
In one embodiment of the present invention, when a precipitate is formed from a polycarbosilane solution, it is preferable to use methanol, ethanol, propanol, 2-propanol, acetonitrile or acetone (acetone), preferably methanol, ethanol, or acetone.
The polycarbosilane has a different solubility in an organic solvent depending on a molecular weight distribution like a general polymer. It can be separated according to the molecular weight size by using it, and thermal stability and pyrolysis yield are different according to molecular weight size. Therefore, when a region having a high molecular weight is separated and heat-treated, the fine-powder silicon carbide can be produced in a high yield by pyrolyzing without passing through a melting point.
In one embodiment of the present invention, the oxidation step is performed at 150 to 300 ° C, preferably 200 to 250 ° C, and the heat treatment step is performed at 1600 to 1800 ° C, preferably 1600 to 1700 ° C.
During the heat treatment process, silicon and carbon form silicon carbide crystals, and graphitization of carbon occurs. Such graphitized carbon surrounds silicon carbide crystals, which hinders crystal growth of silicon carbide.
In order to remove such surplus carbon, when the separated high molecular weight region of the polycarbosilane is subjected to an oxidation treatment at a temperature of 150 to 300 ° C, some silicon atoms are oxidized to form Si-O bonds, Lt; RTI ID = 0.0 > C, < / RTI > and is lost to carbon monoxide (CO). At the same time, the silicon carbide crystal starts to be formed. At this temperature, the reaction is not completely completed. According to the embodiment of the present invention, the reaction is completely completed at 1600 ° C., and the high- .
Therefore, it is possible not only to prevent the carbon from remaining through the oxidation step of the present invention, but also to produce silicon carbide particles of high purity and high purity in the heat treatment step performed after the oxidation step.
In one embodiment of the present invention, a step of preparing the precipitate as a spherical fine powder by increasing the stirring speed after forming the precipitate may be further performed.
In general, polycarbosilane commercial products are provided in a bulk state or are pulverized and supplied as powder, which is characterized by being amorphous. Such commercial products are difficult to produce nano-sized silicon carbide having excellent dispersibility because the crystals formed in the heat treatment process are aggregated. Therefore, by making the precipitate into a spherical fine powder, it is possible to prevent nanocrystalline particles from being agglomerated in the heat treatment step, thereby effectively producing nano-sized particles.
In one embodiment of the present invention, the step of filtering and drying the precipitate after forming the precipitate can be further carried out.
The drying temperature is preferably 40 to 80 ° C.
In one embodiment of the present invention, the average particle size of the silicon carbide powder is preferably 5 to 700 nm. Silicon carbide is known to be difficult to sinter with typical high temperature structural ceramic materials. When the average particle size of the silicon carbide powder is within the above range, it has a large specific surface area of uniform particle size, and can be used for a catalyst carrier, a raw material for manufacturing a single crystal, and the like.
Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are for illustrative purpose only and that the scope of the present invention is not limited to these embodiments.
Manufacturing example One:
A polycarbosilane solution in which polycarbosilane was dissolved in cyclohexane was added dropwise to ethanol under stirring to form a precipitate. At this time, the stirring speed was increased so that the precipitate became a spherical fine powder. The resulting spherical fine powder precipitate was filtered and dried in an oven at 60 ° C to prepare a precipitated polycarbosilane powder.
Experimental Example One:
Thermal analysis was performed in an inert atmosphere to confirm the thermal stability and pyrolysis yield of polycarbosilane (Separated PCS) after precipitation separation with polycarbosilane (PCS as purchased) before precipitation separation. The results were shown in FIG. 1 .
Referring to FIG. 1, it was confirmed that the polycarbosilane precipitated and separated had a thermal stability of up to 500 ° C. and a thermal decomposition yield of 90%.
Example One:
Precipitation of Production Example 1 The separated polycarbosilane powder was oxidized in an oven at 200 ° C for 12 hours. Then, the oxidized polycarbosilane powder was heat-treated at 1800 캜 for 2 hours to prepare silicon carbide powder.
Example 2:
Precipitation of Production Example 1 The separated polycarbosilane powder was oxidized in an oven at 200 ° C for 12 hours. Then, the oxidized polycarbosilane powder was heat-treated at 1600 ° C for 2 hours to prepare silicon carbide powder.
Comparative Example One:
Polycarbosilane (PCS as purchased) before precipitation separation was heat-treated at 1800 캜 for 2 hours to prepare silicon carbide powder.
Comparative Example 2:
Polycarbosilane (PCS as purchased) before precipitation separation was oxidized in an oven at 200 ° C for 12 hours. Then, the oxidized polycarbosilane powder was heat-treated at 1800 캜 for 2 hours to prepare silicon carbide powder.
Comparative Example 3 :
Precipitation of Production Example 1 The separated polycarbosilane powder was oxidized in an oven at 200 ° C for 12 hours. Then, the oxidized polycarbosilane powder was heat-treated at 1400 ° C for 2 hours to prepare silicon carbide powder.
Comparative Example 4:
The precipitated polycarbosilane powder of Preparation Example 1 was heat-treated at 1800 캜 for 2 hours to prepare silicon carbide powder.
Comparative Example 5:
The precipitated polycarbosilane powder of Preparation Example 1 was heat-treated at 1400 ° C for 2 hours to prepare silicon carbide powder.
Experimental Example 2:
Fig. 2 is a photograph showing the silicon carbide powder of Example 1, Comparative Example 1 and Comparative Example 2. Specifically, Fig. 2 (a) shows the results of Example 1, (b) This is a photograph showing a silicon carbide powder.
2, the silicon carbide powders of Comparative Examples 1 and 2 were all obtained by heat-treating polycarbosilane not subjected to precipitation separation and purification, and in the case of hydrocarbons of Comparative Examples 1 and 2 containing a low molecular weight, It was confirmed that the molten mixture was obtained as a lump even after the thermal decomposition by melting in the heat treatment step regardless of the step. In this case, it was difficult to obtain powder, and in the case of powder, particle diameter was large due to agglomeration of particles. In particular, pyrolysis yield of silicon carbide of Comparative Example 2 was less than 30%.
Experimental Example 3:
3 is a graph showing the results of X-ray diffraction analysis of the silicon carbide powders of Examples 1 and 2, Comparative Example 3 and Comparative Examples 4 and 5. Specifically, (a) shows the results of Examples 1 and 2 and Comparative Example 3 (B) is a graph showing the results of X-ray diffraction analysis of the silicon carbide powder of Comparative Examples 4 and 5. FIG.
3, the silicon carbide powders of Examples 1 and 2 and Comparative Example 3 were subjected to precipitation separation, purification of the purified polycarbosilane powder, and heat treatment at 1,800 ° C, 1,600 ° C, and 1,400 ° C, respectively, It was confirmed that the silicon carbide powder was formed even under the temperature condition. However, in the X-ray diffraction analysis graph of the silicon carbide powder of Example 2, a small peak appears at 34 °, which is attributable to an α-SiC or a stacking fault. As in Example 1, , It is confirmed that the structural defects disappear and silicon carbide of high purity and high crystallinity can be obtained.
It was confirmed that the silicon carbide powder of Comparative Examples 4 and 5 was formed by heat-treating the non-oxidized polycarbosilane, and in Comparative Example 5, the silicon carbide powder was formed even at a low heat treatment temperature of 1400 ° C. However, in the case of the silicon carbide powder of Comparative Example 5 produced at 1800 ° C under the same condition as Example 1, a small peak was observed at 34 °, confirming that structural defects still existed
Experimental Example 4:
The Raman analysis was evaluated to confirm the behavior of the graphitized carbon which was not shown in the X-ray diffraction analysis results of Experimental Example 3. [
4 is a graph showing the results of Raman analysis of the silicon carbide powders of Examples 1 and 2, Comparative Example 3 and Comparative Examples 4 and 5. Specifically, FIG. 4 (a) is a graph showing the results of Raman analysis of silicon carbide powder of Examples 1 and 2 and Comparative Example 3 (B) is a graph showing the results of Raman analysis of the silicon carbide powder of Comparative Examples 4 and 5. FIG.
4, graphitized carbon peaks of the silicon carbide powders of Examples 1 and 2 and Comparative Example 3 are very small, whereas in Example 1 which is a high temperature synthesis condition, 970 cm < -1 > and 795 cm < -1 > shows a very distinct peak.
However, Comparative Examples 4 and 5 of the silicon carbide powder is a peak resulting from a silicon carbide on the beta does not appear very small while, graphitized carbon peak of 1350 cm - was confirmed that a peak appears clearly from 1 and 1600 cm -1 region .
Experimental Example 5:
In order to confirm the microstructure of the silicon carbide powder prepared in the above Examples and Comparative Examples, TEM observation was carried out.
5 is a photograph showing TEM images of silicon carbide powders of Examples 1 and 2 and Comparative Example 4. Specifically, (a) shows Example 1, (b) shows Example 2, and (c) Of TEM images of the silicon carbide powder.
Referring to FIG. 5, it was confirmed that the silicon carbide powder (a) of Example 1 grew about 700 nm in size of silicon carbide particles, and the surface of the particles was very clean and crystal state was very good. In addition, the silicon carbide powder (b) of Example 2 showed that silicon carbide particles having a size of less than about 50 nm were produced, and in both cases, no graphitized carbon was confirmed.
However, it was confirmed that the silicon carbide powder (c) of Comparative Example 4 exhibited not only amorphous silicon carbide particles but also low crystallinity and a wide distribution of graphitized carbon. This was confirmed by the fact that the excess carbon not only lowered the purity of the silicon carbide powder but also interfered with the growth of the silicon carbide crystal.
6 is a TEM analysis of a silicon carbide powder of Example 2 at a high magnification, in which (a) is a TEM image and (b) is a diffraction pattern thereof.
Referring to Fig. 6, it was confirmed that the silicon carbide powder particles of Example 2 were formed into a single phase. It was confirmed by X-ray diffraction analysis that structural defects were partially observed, but individual particles were highly crystalline in a single phase.
Thus, according to the above results, silicon carbide (SiC) formed through oxidation and heat treatment steps after separation and purification is highly crystalline nanoparticles. The silicon carbide particles formed by heat treatment at 1600 to 1800 ° C showed high purity and no crystal defects were found. Particularly, the silicon carbide particles formed at 1600 ° C had structure defects due to the interface between the particles, It was formed on a daily basis. Therefore, in this case, it is possible to grow particles having excellent crystallinity even at a low temperature of 1800 to 2000 ° C in an additional step such as a sintering step, and it is also possible to obtain a sintered body having excellent crystallinity under the above low temperature conditions.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Do. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Accordingly, the actual scope of the invention is defined by the appended claims and their equivalents.
Claims (6)
Adding the polycarbosilane solution to methanol, ethanol, propanol, 2-propanol, acetonitrile or acetone under agitation to form a precipitate;
Oxidizing the precipitate at 150 to 300 占 폚; And
And heat-treating the oxidized precipitate at 1600 to 1800 占 폚 to produce silicon carbide powder. The method of producing silicon carbide nano powder using polycarbosilane.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109354691A (en) * | 2018-11-14 | 2019-02-19 | 中国科学院宁波材料技术与工程研究所 | A kind of preparation method of high ceramic yield Polycarbosilane |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN109354691A (en) * | 2018-11-14 | 2019-02-19 | 中国科学院宁波材料技术与工程研究所 | A kind of preparation method of high ceramic yield Polycarbosilane |
| CN109354691B (en) * | 2018-11-14 | 2021-03-09 | 中国科学院宁波材料技术与工程研究所 | Preparation method of polycarbosilane with high ceramic yield |
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