KR20200121269A - Method for producing silicon carbide fiber and the silicon carbide fiber manufactured by using the same - Google Patents

Abstract

The present invention relates to a method for manufacturing silicon carbide fiber comprising a step of heating mixed powder including carbon fiber, silicon (Si) powder, and silicon dioxide (SiO_2) powder in a high-temperature vacuum furnace. The manufacturing method completely converts the carbon fiber into the silicon carbide fiber, and provides the silicon carbide fiber with excellent thermal properties, excellent electrical properties, and excellent mechanical properties.

Description

TECHNICAL FIELD The manufacturing method of silicon carbide fiber and silicon carbide fiber manufactured by the above manufacturing method TECHNICAL FIELD [METHOD FOR PRODUCING SILICON CARBIDE FIBER AND THE SILICON CARBIDE FIBER MANUFACTURED BY USING THE SAME}

The present invention relates to a method of manufacturing a silicon carbide fiber and a silicon carbide fiber manufactured by the method.

Silicon carbide (SiC) has excellent chemical stability at high temperature, high thermal conductivity and low coefficient of thermal expansion, so it has good heat resistance and thermal stability, and has excellent mechanical strength and high wear resistance. Because of these excellent properties, researches are actively being applied to high-temperature materials, high-temperature semiconductors, fixtures for semiconductors, wear-resistant materials, automobile parts, corrosion-resistant or chemical-resistant parts of chemical factories, or electronic parts.

Among them, silicon carbide fibers are generally cylindrical in diameter of about tens to several tens of nm, and have a length of tens to hundreds of μm, and the main components are carbon and silicon in an atomic ratio of 1:1. Depending on the manufacturing method, amorphous silicon oxide may be covered with a thickness of several to tens of nm. Silicon carbide fiber is a material having high strength, excellent chemical stability, and excellent electrical properties, like the general silicon carbide (bulk type, etc.) described above. Field emission device FETs (field emission tips) using nanomaterials, which have been recently researched and developed, require stability at high temperatures during the operation process, and in this respect, silicon carbide nanorods show more stable structural characteristics than carbon nanotubes. It is attracting attention as a field emission device material. Such silicon carbide fibers are manufactured by various methods. Conventionally known methods of manufacturing silicon carbide fibers include Chemical Vapor Infiltration (CVI), Polymer Impregnation and Pyrolysis (PIP), Liquid Silicon Infiltration (LSI), and high temperature. Pressure sintering (HP, Hot Press), and the like. The chemical vapor deposition method is a method of producing a silicon carbide matrix by infiltrating a gaseous metal-organic compound through fibers and thermally decomposing them to deposit silicon carbide around the fibers, and the polymer penetration and pyrolysis method is an organic compound such as polycarbosilane. This is a method of obtaining a silicon carbide matrix phase by mixing with silicon carbide powder to make a slurry, and then penetrating the slurry into a silicon carbide fiber preform and thermally decomposing. In addition, the molten silicon penetration method is to prepare a silicon carbide matrix by filling the preform with carbon and silicon carbide powder and melting and penetrating the silicon to react with carbon.The high-temperature pressurization sintering method is to prepare a slurry of silicon carbide powder and a sintering aid. It is a method of sintering under high temperature pressure after penetrating into the preform.

However, the chemical vapor deposition method has the disadvantages that the process time is long, there are residual pores, and the manufacturing cost is high, and the polymer penetration and thermal decomposition method is difficult to obtain crystalline silicon carbide consisting of a chemical quantitative ratio, and the thermal conductivity is low. Because cracking occurs, several iterations are required. In addition, the molten silicon penetration method can produce a composite with few pores and excellent thermal conductivity, but has a disadvantage of relatively poor heat resistance and radiation resistance due to the residual unreacted silicon. There is a disadvantage of being damaged.

In recent years, many studies have been conducted to improve the disadvantages of the methods as described above. As a specific example, Korean Patent Registration No. 1103649 (registered on Feb. 2012) introduced a method of electrospinning a polymer solution prepared by mixing an organosilicon compound, a polymer precursor, and a solvent. This method has a simple manufacturing process and It was introduced that the manufactured silicon carbide nanofiber has the advantage of having electrical conductivity. In addition, Korean Patent Registration No. 0561701 (registered on March 9, 2006) introduced a method of coating the surface of a carbon structure using a transition metal as a metal catalyst, and then reacting the coated carbon structure with a mixture of silicon and silicon dioxide powder. It was introduced that it has the advantage of being able to manufacture a large amount of carbon nanofibers at low temperatures.

However, the processes for manufacturing silicon carbide fibers as described above have disadvantages in that expensive high-purity raw materials are used, the process and process equipment are complex, and the processing is difficult, resulting in high manufacturing cost.

Accordingly, the present inventors have developed a method for producing silicon carbide fibers by reacting silicon oxide with carbon fibers and efficiently converting carbon fibers into silicon carbide fibers.

Thus, as a first embodiment of the present invention, a method for producing a silicon carbide fiber comprising the step of placing and heating a mixed powder including carbon fiber, silicon (Si) powder and silicon dioxide (SiO ₂ ) powder in a high-temperature vacuum furnace. To provide.

Heating according to the above embodiment is characterized in that it is performed at 1400 to 2200 ℃.

Heating according to the above embodiment is characterized in that it is performed for 1 minute to 6 hours.

The mixed powder according to the embodiment is characterized in that 150 to 7000 parts by weight is used based on 100 parts by weight of carbon fiber.

The mixed powder according to the embodiment is characterized in that the silicon powder and the silicon dioxide powder are mixed in a weight ratio of 1:1 to 1:4.

The manufacturing method according to the above embodiment is characterized in that silicon oxide gas generated by heating the silicon powder and the silicon dioxide powder reacts with the carbon fibers to convert the carbon fibers into silicon carbide fibers.

In addition, the present invention provides a silicon carbide fiber manufactured by the above manufacturing method as a second embodiment.

The fiber according to the second embodiment is characterized in that the diameter is 5㎛ to 20㎛.

In the method for producing a silicon carbide fiber of the present invention, the carbon fiber is reacted with silicon oxide gas generated in a mixed powder of silicon and silicon dioxide powder, so that hydrocarbon (C) can be completely converted to silicon carbide fiber (SiC). have. The silicon carbide fiber according to the above manufacturing method is completely converted to silicon carbide up to the core, and has excellent thermal properties and mechanical properties, and thus can be usefully used as a wire material.

In addition, the thickness of silicon carbide can be adjusted according to the reaction conditions, so that carbon fibers on the inside and fibers coated with silicon carbide on the outside can be obtained.The properties of the carbon fiber plus the properties of silicon carbide are used for various industrial purposes. Is expected.

1 is a view showing a graphite crucible entering a vacuum furnace performing the reaction of the present invention.
2 is a view showing the result of confirming the amount of silicon oxide generated according to the highest temperature and the amount of silicon oxide generated according to the holding time at the highest temperature of 1600°C.
3 is a view showing the appearance of the fibers prepared according to Example 1.
4 is a view showing the appearance of the fibers prepared according to Example 2.
5 is a view showing the appearance of the fibers prepared according to Example 3.
6 is a view showing the appearance of the fiber prepared according to Example 4.
7 is a view showing the appearance of the fiber prepared according to Example 5.
8 is a view showing the appearance of the fiber prepared according to Example 6.
9 is a view showing the appearance of the fiber prepared according to Example 7.
10 is a view showing a result of confirming the shape of the fiber prepared in Example 1 by SEM and EDS analysis.
11 is a view showing the result of confirming the shape of the fiber prepared in Example 2 by SEM and EDS analysis.
12 is a view showing the result of confirming the shape of the fiber prepared in Example 3 by SEM and EDS analysis.
13 is a view showing the result of confirming the shape of the fiber prepared in Example 4 by SEM and EDS analysis.
14 is a view showing the result of confirming the shape of the fiber prepared in Example 5 by SEM and EDS analysis.
15 is a view showing the result of confirming the shape of the fiber prepared in Example 6 by SEM and EDS analysis.
16 is a view showing the result of confirming the shape of the fiber prepared in Example 7 by SEM and EDS analysis.
17 and 18 are diagrams showing the results of confirming the crystal form of the prepared fiber by XRD analysis.

The present invention provides a method for producing silicon carbide fibers, and the present invention completes the present invention by confirming conditions showing excellent conversion rates as a result of a study to develop manufacturing conditions capable of completely converting carbon fibers into silicon carbide fibers. I did.

Accordingly, the present invention provides a method for producing a silicon carbide fiber, including the step of heating a mixed powder including carbon fiber and silicon (Si) powder and silicon dioxide (SiO ₂ ) powder in a high-temperature vacuum furnace.

In the above manufacturing method, heating is characterized by heating at 1400 to 2200°C for 1 minute to 6 hours in an inert gas atmosphere such as 1 to 10 ^-2 Torr or argon (Ar).

Preferably, the heating may be 1500 to 2000 °C. When heated to a temperature of less than 1500 °C during heating, only the surface of the carbon fiber may be converted to silicon carbide, and when heated to a temperature exceeding 2000 °C, cracks may be formed on the surface of the silicon carbide fiber.

In addition, preferably, the heating may be heated for 50 minutes to 4 hours. When the heating is performed for less than 50 minutes, the carbon fiber core may not be converted to silicon carbide, and when the heating is performed for more than 4 hours, cracks may be formed on the surface of the silicon carbide fiber.

The manufacturing method is that the silicon oxide gas generated by heating the silicon powder and the silicon dioxide powder reacts with the carbon fiber to convert the carbon fiber into silicon carbide fiber, and the mixed powder is 150 to 7000 per 100 parts by weight of the carbon fiber. It is preferable to use it in parts by weight. If the mixed powder is used in an amount of less than 150 parts by weight, carbon fibers may be insufficient to be completely converted to silicon carbide fibers, and if it exceeds 7000 parts by weight, raw materials may be wasted due to an increase in unreacted silicon oxide gas, which may become inefficient. .

In another embodiment of the present invention, when the heating is performed, the heating may be performed while applying tension to the carbon fiber. There is no limitation on the method of applying the tension, and when heating is performed while applying tension, cracks occurring on the surface of the silicon carbide fiber can be prevented.

The mixed powder serves as a source of silicon monoxide gas, and the silicon powder and silicon dioxide of the mixed powder react according to the following reaction equation upon heating to generate silicon monoxide gas.

[Formula 1]

Si(s) + SiO ₂ (s) → 2SiO(g)

The mixed powder may be obtained by mixing silicon powder and silicon dioxide powder in a weight ratio of 1:1 to 1:4. If the silicon dioxide powder is used in an amount of less than 1 part by weight or more than 4 parts by weight based on 1 part by weight of the silicon powder, the amount of silicon oxide gas generated is small compared to the amount of the mixed powder added, and the mixed powder is wasted, making it inefficient. I can.

In addition, the present invention can provide a silicon carbide fiber manufactured by the above manufacturing method.

The silicon carbide fiber may have a diameter of 5 μm to 20 μm, and carbon may be partially converted to silicon carbide or completely converted to silicon carbide.

Hereinafter, the present invention will be described in more detail through examples. These examples are for illustrative purposes only, and it will be apparent to those of ordinary skill in the art that the scope of the present invention is not limited by these examples.

[Example]

1. Confirmation of silicon oxide gas conversion rate of mixed powder

In this preparation example, a mixed powder including silicon (Si) powder and silicon dioxide (SiO ₂ ) powder was placed in a high-temperature vacuum furnace, and heated at 1400 to 1600° C. for 10 minutes to 3 hours in an argon (Ar) atmosphere (Fig. One).

The mixing ratio of the silicon powder and the silicon dioxide powder contained in the mixed powder is shown in Table 1 below.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Mixed powder (g) 100g 30.0 30.0 30 29.5 30.1 30.1 Si: SiO ₂ mixing weight ratio
(Mixed molar ratio) 28:60 (1:1) Silicon oxide gas
Conversion rate (%) 2.7 17.3 24.3 15.7 13.2 11.3 6.6 Temperature(℃) 1400 1500 1600 Maximum temperature
Holding time(hr) 3 3 3 2 One 0.5 0.17

Preparation conditions for each of the examples are shown in Table 2 below.

Test Maximum temperature Holding time Heating rate Total Time Example 1 1,400℃ 3 hours 10℃/min 460 minutes Example 2 1,500℃ 3 hours 10℃/min 480 minutes Example 3 1,600℃ 3 hours 10℃/min 500 minutes Example 4 1,600℃ 2 hours 10℃/min 440 minutes Example 5 1,600℃ 1 hours 10℃/min 380 minutes Example 6 1,600℃ 30 minutes 10℃/min 350 minutes Example 7 1,600℃ 10 minutes 10℃/min 330 minutes

By measuring the weight of the graphite crucible before and after the reaction by the above heating, the weight of the unreacted mixed powder which reacted with each other and was blown away as the silicon oxide gas was checked to confirm the conversion rate. Conversion rate (%) = (( weight before reaction-weight after reaction) / (weight before reaction )) X 100

Weight before reaction = weight of graphite crucible + weight of mixed powder

Weight after reaction = weight of graphite crucible + weight of residual mixed powder

The results of confirming the conversion rate are shown in FIG. 2, and Example 1, which maintained the highest temperature at 1400°C, showed a conversion rate of 2.7%, and Example 3, which maintained the highest temperature at 1600°C, showed a conversion rate of 24.3%. In addition, even if the maximum temperature was maintained at 1600°C, the conversion rates were 11.3% and 6.6% as in Examples 6 and 7 when maintained for less than 1 hour. From the above results, it was confirmed that the higher the maximum temperature and the longer the holding time at the maximum temperature, the higher the conversion rate.

2. Appearance check

Under the conditions described in Examples 1 to 7 above, carbon fibers were placed in a high-temperature vacuum furnace and reacted to prepare silicon carbide fibers. About 4g of carbon fiber was used.

After the reaction was completed, the appearances of the silicon carbide fibers prepared as a result of Examples 1 to 7 are shown in Figs. 3 to 9 compared with the carbon fibers.

In the case of Fig. 3, it has a slightly bluish gray color compared to the carbon fiber, and in Fig. 4, the surface of the fiber is iridescent, and in Fig. 5, it is confirmed that the fiber has a slightly light green color, and the bottom part of the graphite crucible is coated with a light green color. Became. The fiber of FIG. 6 showed a slightly pale greenish bluish gray color, and the fiber of FIG. 7 showed a bluish gray color. In addition, both the fiber of FIG. 8 and the fiber of FIG. 9 showed bluish gray light.

3. SEM and EDS analysis

SEM analysis (FE-SEM (JSM-7610F) manufactured by JEOL, Japan) and EDS analysis (FE-SEM (JSM-7610F) manufactured by JEOL Japan) were performed to confirm the shape of the prepared fiber.

As shown in FIG. 10, the fiber of Example 1 had a diameter of 7 to 7.5 µm, and only the outer surface of the fiber was visible, and it was confirmed that the silicon carbamide was not converted to the core, and as shown in FIG. The fiber of Example 2 had a diameter of 7 to 7.5 µm, and a fine short fiber like a whisker was attached to the surface of the fiber. As in Example 1, only the outer surface of the silicon was seen, and it was confirmed that silicon carbamide was not converted to the core.

On the other hand, as shown in FIG. 12, the fiber of Example 3 had a fiber diameter of about 8.1 μm, and Si was visible to the inside of the fiber, and the carbon fiber (C) was completely converted to silicon carbamide. Confirmed. This is different from the conventional products showing the Hollow Fiber type.

In addition, as shown in FIG. 13, the fiber of Example 4 also had a larger fiber diameter of about 8.4 µm, and silicon was visible to the inside of the fiber, so that the carbon fiber (C) was completely converted to silicon carbamide. As shown in Fig. 14, in the case of Example 5, the fiber diameter was large at about 8.4 µm, and silicon was seen up to the inside of the fiber, confirming that the carbon fiber (C) was completely converted to silicon carbamide. Became.

However, as shown in FIG. 15, in the case of Example 6, since carbon fibers remained in the core portion, it was confirmed that the interface between the carbon fibers and the converted silicon carbamide was cracked, and the fiber surface was also cracked a lot.

In addition, as shown in FIG. 16, in the case of Example 7, the carbon fiber remained, but unlike Test 6 (1.600° C., 30 minutes), the interface between the carbon fiber and the converted SiC was not separated and was continuously seen, and the surface was similarly A lot of cracks were confirmed.

4. XRD analysis

XRD analysis (D/MAX 2500 manufactured by RIGAKU, Japan) was performed to confirm the crystal form of the prepared fiber.

The results are shown in FIGS. 17 and 18.

As shown in FIGS. 17 and 18, it was confirmed that silicon carbide (SiC) peak appeared, indicating that silicon carbide was generated. As in Example 1 and Example 2, at 1400°C and 1500°C, the peak of unreacted carbon (C) and the peak of silicon carbide (SiC) were also large, but as in Examples 3 to 7, the peak of unreacted carbon was As the holding time increased, it almost disappeared and only the silicon carbide (SiC) peak remained, indicating that the conversion to silicon carbide (SiC) became high.

As the specific parts of the present invention have been described in detail above, it will be apparent to those of ordinary skill in the art that these specific descriptions are only preferred embodiments, and the scope of the present invention is not limited thereby. will be. Accordingly, it will be said that the substantial scope of the present invention is defined by the appended claims and their equivalents.

Claims (4)

Including the step of heating the mixed powder containing carbon fiber and silicon (Si) powder and silicon dioxide (SiO ₂ ) powder in a vacuum furnace,
The heating is performed at 1400 to 2200°C,
The maximum temperature of the vacuum furnace is 1,600 °C or more, and the holding time at the maximum temperature is 1 to 3 hours,
The mixed powder of the silicon powder and the silicon dioxide is used in an amount of 150 to 7000 parts by weight based on 100 parts by weight of carbon fiber, the silicon powder and the silicon dioxide powder are mixed in a weight ratio of 1:1 to 1:4,
The silicon oxide gas generated by heating the silicon powder and the silicon dioxide powder reacts with the carbon fiber to convert the carbon fiber into silicon carbide fiber, so that the silicon oxide gas conversion rate is 13.2 to 24.3%, and the fiber diameter is 8.1 to 8.4 μm. A method for producing silicon carbide fibers, characterized in that.
The method of claim 1,
The heating is characterized in that heating for 1 minute to 6 hours, the method of producing a silicon carbide fiber.
Silicon carbide fibers manufactured by the manufacturing method of claim 1.
The method of claim 3,
The fiber is characterized in that the diameter of 5㎛ 20㎛, silicon carbide fiber.

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