KR20230171576A - Method and apparatus for synthesizing polycarbosilane for silicon carbide fiber precursor - Google Patents

Abstract

In the present invention, polycarbosilane synthesis is carried out at normal pressure, but the PDMS powder stays on the surface of the LPS liquid portion and suppresses the rise of gas volatilized from the LPS in the lower layer, causing a reaction like a closed system. This is similar to the principle that in high-pressure synthesis, volatile substances cannot escape to the outside due to a closed system reaction and instead participate in the reaction again, increasing the yield and reducing the synthesis time. Due to this, it has the feature of being able to shorten the reaction time by 30-60% compared to existing synthesis reactions, and controlling the molecular weight is easier than existing atmospheric pressure synthesis. Therefore, polycarbosilane synthesized in this way can reduce the diameter of polycarbosilane fibers and ultimately improve the strength of silicon carbide fibers synthesized therefrom.

Description

{Method and apparatus for synthesizing polycarbosilane for silicon carbide fiber precursor}

The present invention relates to an apparatus and method for synthesizing polycarbosilane for silicon carbide fiber precursors.

SiC _f /SiC composite, which uses silicon carbide (SiC fiber) as a reinforcement material and silicon carbide (SiC) as a matrix, has excellent high-temperature mechanical strength, is lightweight, has strong oxidation and corrosion resistance, and has radio wave shielding and absorption properties. Due to its unique characteristics, its use is gradually spreading in aircraft engines, power plant turbines, and defense industry parts. Here, the silicon carbide fibers that make up the SiC _f /SiC composite play an important role in contributing to thermal structural properties at high temperatures.

Silicon carbide fiber production is largely divided into methods obtained from polymer preceramic precursors and methods obtained by chemical vapor deposition. The former is the most widely used technology today. Polycarbosilane (PCS) is synthesized, polycarbosilane (PCS) fiber is spun from it, and then processed into infusible fiber by air or electron beam irradiation. , then silicon carbide fiber is manufactured through thermal decomposition at 1200~1800℃ in an inert atmosphere.

The strength of silicon carbide fibers greatly depends on the diameter of the fiber. According to a study by Wang et al., the strength of the fiber decreases by up to 50% as the diameter increases (Melt Spun of Continuous Polycarbosilane Fibers (Yingde Wang', Yanmo Chen, Meifang Zhu, 2000). Therefore, the diameter of silicon carbide fiber The smaller the better, but if the diameter of the polycarbosilane fiber is to be small, the silicon carbide fiber must be made thinner. If the diameter of the silicon carbide fiber is to be small, the polycarbosilane fiber must be made thinner first.

What affects the diameter of polycarbosilane fiber is, above all, the physical properties related to the molecular weight of polycarbosilane. Polycarbosilane fiber is obtained from melt spinning. If the melt strength of the molten polycarbosilane is high, it can withstand strong drawing and the diameter of the fiber can be made small. All these properties depend on the molecular weight, molecular structure, and molecular weight distribution of the polycarbosilane. Therefore, in order to increase the strength of silicon carbide fiber, the molecular weight of polycarbosilane, its raw material, must be controlled.

Meanwhile, polycarbosilane synthesis includes processes under high pressure and normal pressure conditions. The high-pressure process has the disadvantages of a limited amount of synthesis due to the high pressure conditions, the risk of high pressure, and the expensive synthesis equipment. However, since the high-pressure process is carried out in a closed system, the decomposed material cannot fly out and participates in the reaction again, so the yield is high at 50 to 60% and has the advantage of excellent control of molecular weight and molecular weight distribution.

On the other hand, the synthesis process at normal pressure is a technology that allows mass synthesis and has the advantage of low risk during synthesis and low equipment costs. However, normal pressure synthesis has the disadvantage of lower yield and longer reaction time compared to high pressure synthesis due to volatilization of low molecular weights that occur during the reaction. Additionally, it has the disadvantage that it is difficult to control molecular weight and molecular weight distribution.

Accordingly, there is a need for a polycarbosilane synthesis method that uses an atmospheric pressure process that allows mass synthesis while easily controlling the molecular weight and molecular weight distribution as in the high pressure process.

US registered patent (US 9815944 B2)

The purpose of the present invention is to provide an apparatus and method for synthesizing polycarbosilane for silicon carbide fiber precursors that can solve the above-mentioned problems.

A polycarbosilane synthesis device for silicon carbide fiber precursor to achieve the above object,

A reactor in which LPS (Liquid polysilane) is introduced and has an inert atmosphere;

A heater that heats the reactor to synthesize the LPS into polycarbosilane;

A PDMS chamber that stores PDMS powder and has an inert atmosphere;

A PDMS supply unit connected to the reactor and the PDMS chamber and spraying a set amount of the PDMS powder stored in the PDMS chamber on the surface of the LPS contained in the reactor;

A furnace connected to the upper part of the reactor, through which the PDMS powder sprinkled on the LPS surface is decomposed, gasified, and passes through it as it rises;

A condenser that condenses a portion of the PDMS gas whose molecular weight increases as it passes through the furnace and returns it to the reactor; and

It is characterized by including a gas exhaust pipe that discharges ultra-low molecular weight PDMS gas while passing through the furnace.

In addition, the above purpose is to

A first step of adding LPS to a reactor with an inert atmosphere and heating it;

A second step of spraying a set amount of PDMS powder on the LPS surface when the reactor reaches the set temperature;

A third step of heating the reactor to a set temperature and passing the PDMS gas, which decomposes and gasifies the PDMS powder and rises through the furnace, into a furnace to heat the reactor;

A fourth step of condensing some of the PDMS gas with an increased molecular weight while passing through the furnace, returning it to the reactor, and discharging PDMS gas with an ultra-low molecular weight while passing through the furnace; and

By a polycarbosilane synthesis method for a silicon carbide fiber precursor, comprising a fifth step of cooling the reactor to room temperature to obtain solid polycarbosilane, followed by filtering and vacuum distillation purification to obtain the final polycarbosilane. achieved.

In the present invention, polycarbosilane synthesis is carried out at normal pressure, but the PDMS powder stays on the surface of the LPS liquid portion and suppresses the rise of gas volatilized from the LPS in the lower layer, causing a reaction like a closed system. This is similar to the principle that in high-pressure synthesis, volatile substances cannot escape to the outside due to a closed system reaction and instead participate in the reaction again, increasing the yield and reducing the synthesis time. Due to this, it has the feature of being able to shorten the reaction time by 30-60% compared to existing synthesis reactions, and controlling the molecular weight is easier than existing atmospheric pressure synthesis. Therefore, polycarbosilane synthesized in this way can reduce the diameter of polycarbosilane fibers and ultimately improve the strength of silicon carbide fibers synthesized therefrom.

Figure 1 is a diagram showing a polycarbosilane synthesis apparatus for silicon carbide fiber precursor according to an embodiment of the present invention.
Figure 2 is a flowchart showing a method for synthesizing polycarbosilane for a silicon carbide fiber precursor according to an embodiment of the present invention.
Figure 3 shows the GPC chromatogram, GPC curve, and molecular weight distribution curve of polycarbosilane obtained in a comparative example (conventional method).
Figure 4 is an FT-IR spectrum of polycarbosilane obtained in Example 1.
Figure 5 is a GPC chromatogram and GPC curve of polycarbosilane obtained in Example 1.

Hereinafter, a polycarbosilane synthesis apparatus for silicon carbide fiber precursor according to an embodiment of the present invention will be described in detail.

As shown in FIG. 1, the polycarbosilane synthesis apparatus for silicon carbide fiber precursor according to an embodiment of the present invention includes a reactor 10, a heater 20, a PDMS chamber 30, a PDMS supply unit 40, It consists of a furnace (50), a condenser (60), and a gas exhaust pipe (70).

[Reactor (10), Heater (20)]

Liquid polysilane (LPS) is introduced into the reactor 10 and has an inert atmosphere. A vacuum and inert gas injector 11 is connected to the reactor 10 to control the inside of the reactor 10 to an inert atmosphere.

The heater 20 heats the reactor 10 so that LPS is synthesized into polycarbosilane. The heater 20 surrounds the outer surface of the reactor 10 and heats the reactants introduced into the reactor 10.

[PDMS chamber (30), PDMS supply unit (40)]

The PDMS chamber 30 stores PDMS (polydimethylsilane) powder and has an inert atmosphere. A vacuum and inert gas injector 31 is connected to the PDMS chamber 30 to control the inside of the PDMS chamber 30 to an inert atmosphere.

The PDMS supply unit 40 is connected to the reactor 10 and the PDMS chamber 30, and sprinkles a set amount of PDMS powder stored in the PDMS chamber 30 on the surface of the LPS contained in the reactor 10. The PDMS supply unit 40 sprinkles PDMS powder on the LPS surface in an amount of 10 to 100% of the weight of the LPS in order to control the amount and speed of polycarbosilane synthesis.

Meanwhile, the PDMS supply unit 40 may be further equipped with a blower. The blower blows air on the PDMS powder sprinkled on the LPS surface, spreading the PDMS powder evenly on the LPS surface. If PDMS powder is spread evenly on the LPS surface, low-molecular-weight polycarbosilane gas can be prevented from penetrating through the thinner PDMS powder. Because of this, many polycarbosilane synthesis reactions may occur within the reactor 10.

[furnace (50), condenser (60), gas exhaust pipe (70)]

The furnace 50 is connected to the upper part of the reactor 10, and the PDMS powder sprinkled on the LPS surface is decomposed, gasified, and passes as it rises. Since the furnace 50 is at a temperature of 400 to 500° C., the temperature of the PDMS gas increases as it passes through and the molecular weight increases.

The condenser 60 condenses some of the PDMS gas with increased molecular weight as it passes through the furnace 50 and returns it to the reactor 10. Some of the PDMS gas that has passed through the furnace 50, that is, the heavy PDMS gas, falls back into the reactor 10, and the gas with a molecular weight lower than the PDMS gas that fell rises and is condensed in the condenser 60. A plurality of condensers 60 may be connected depending on the length and reaction time.

The gas exhaust pipe 70 discharges ultra-low molecular weight PDMS gas while passing through the furnace 50. The gas exhaust pipe 70 is connected to the furnace 50 and the condenser 60, and is located above the furnace 50 and the condenser 60, so that the ultra-low molecular weight PDMS cannot branch from the furnace 50 to the condenser 60. Gas passes through. Among the PDMS gases that have passed through the furnace 50, ultra-low molecular weight PDMS gases are blown out through the gas exhaust pipe 70.

Meanwhile, a flow meter can be installed on the path through which the PDMS gas is refluxed from the condenser 60 to the reactor 10 to measure the flow rate of the PDMS gas condensed from the condenser 60 and refluxed into the reactor 10.

The PDMS gas refluxed into the reactor 10 reacts with the existing reactants and participates in increasing the molecular weight. At this time, by knowing the amount of PDMS gas refluxed, it is possible to know whether the amount of PDMS powder currently sprinkled on the LPS surface is appropriate. Additionally, it is possible to control the amount of PDMS powder sprinkled on the LPS surface in real time.

In other words, if the amount of refluxing PDMS gas is less than the standard, more PDMS powder is sprinkled on the LPS surface. If the amount of refluxing PDMS gas is more than the standard, less PDMS powder is sprinkled on the LPS surface. Because of this, the PDMS supply unit 40 can control the amount and speed of polycarbosilane synthesis more precisely by controlling the PDMS powder sprinkled on the LPS surface in real time.

Hereinafter, a method for synthesizing polycarbosilane for a silicon carbide fiber precursor according to an embodiment of the present invention will be described in detail. Reference is made primarily to Figure 1.

As shown in Figure 2, the polycarbosilane synthesis method for silicon carbide fiber precursor according to an embodiment of the present invention,

A first step (S11) of adding LPS to a reactor with an inert atmosphere and heating it;

A second step (S12) of spraying a set amount of PDMS powder on the surface of the LPS when the reactor reaches the set temperature;

A third step (S13) in which the reactor is heated to a set temperature, and the PDMS powder is decomposed and gasified by heating to pass the rising PDMS gas through a furnace.

A fourth step (S14) of condensing some of the PDMS gas with an increased molecular weight while passing through the furnace, returning it to the reactor, and discharging PDMS gas with an ultra-low molecular weight while passing through the furnace; and

The reactor is cooled to room temperature to obtain solid polycarbosilane, followed by filtering and vacuum distillation purification to obtain the final polycarbosilane (S15).

Hereinafter, the first step (S11) will be described.

Entering and removing nitrogen into the reactor 10 to create a vacuum is repeated several times to create an inert atmosphere inside the reactor 10.

Liquid polysilane (LPS) is introduced into the reactor 10 with an inert atmosphere.

LPS injection method

Dimethyldichlorosilane (DMDCS) and sodium metal are reacted in toluene or xylene solvent, then washed and dried to synthesize PDMS (polydimethylsilane).

PDMS is placed in a reactor (10) with an inert atmosphere, and the temperature is gradually raised to 360-420°C. During this process, PDMS decomposes and produces liquid polysilane (LPS) with the structure shown in the formula below. Meanwhile, the low molecular weight polysilane gas decomposed in the reactor 10 is condensed through the condenser 60 installed on the reactor 10 and collected into the reactor 10 to become liquid polysilane (LPS). The LPS collected in the reactor 10 is introduced into the reactor 10 in this manner.

[Chemical formula]

The reactor 10 is heated with a heater 20 to raise the temperature to 200°C at a rate of 0.5 to 2°C/min.

Hereinafter, the second step (S12) will be described.

When the reactor 10 reaches the set temperature, that is, 200°C, the PDMS supply unit 40 connected to the PDMS chamber 30 where the PDMS powder is stored sprinkles a set amount of PDMS powder on the LPS surface.

PDMS powder is sprinkled at 10 to 100% of the weight of LPS. PDMS has a low density of 0.5g/cm3, so it exists on the surface of LPS when mixed with LPS.

Hereinafter, the third step (S13) will be described.

Heat the reactor 10 to the set temperature.

As an example, heating involves raising the temperature of the reactor 10 to 300 to 380°C and allowing the reaction to proceed for more than 3 hours, then raising the temperature of the reactor 10 to 400 to 460°C and holding the reaction for more than 2 hours. It consists of

As the temperature rises, the molecular weight of the LPS inside the reactor 10 rapidly increases due to decomposition and recombination, and the viscosity increases. Polycarbosilane is synthesized. In this process, the low-molecular-weight polycarbosilane gas generated as LPS is converted to low-molecular-weight polycarbosilane becomes difficult to rise through the surface layer due to the PDMS present in the surface layer.

As a result, the volatilization of low molecular weight polycarbosilane gas is suppressed from rising to the condenser 60, and a large amount of polycarbosilane synthesis occurs within the reactor 10. In this way, the PDMS powder stays on the surface of the LPS liquid phase and suppresses the rise of gas volatilized from the LPS in the lower layer, causing a reaction like a closed system. In high-pressure synthesis, the volatile substances cannot fly out and participate in the reaction again due to a closed system reaction. It is similar to the principle that yield increases and synthesis time is shortened.

During polycarbosilane synthesis, the solid PDMS powder of the surface layer is converted to liquid LPS. Additionally, PDMS powder is decomposed and gasified by heating. The PDMS gas rises and passes into furnace 50 and is heated again while passing through furnace 50.

The temperature of the furnace 50 is 400 to 500°C. As the PDMS gas reaches the furnace 50 at 400-500°C together with nitrogen, the molecular weight increases.

Hereinafter, the fourth step (S14) will be described.

Some of the PDMS gas with increased molecular weight, that is, heavy PDMS gas, descends back into the reactor 10 to become LPS and participate in polycarbosilane synthesis.

In addition, some of the PDMS gas with an increased molecular weight as it passes through the furnace 50, that is, a gas with a lower molecular weight than the PDMS gas that descended into the reactor 10, rises and is condensed in the condenser 60 and returned to the reactor 10. . The refluxed PDMS gas becomes LPS and participates in polycarbosilane synthesis.

In addition, the PDMS gas that has an ultra-low molecular weight as it passes through the furnace 50, that is, the ultra-low molecular weight PDMS gas with a lower molecular weight than the condensed PDMS gas, flies out through the gas exhaust pipe 70.

Hereinafter, the fifth step (S15) will be described.

The reactor 10 is cooled to room temperature to obtain solid polycarbosilane, which is then filtered and purified by vacuum distillation.

As an example, solid polycarbosilane is dissolved in toluene solvent, filtered, and purified by vacuum distillation at 280°C in a vacuum atmosphere to obtain the final polycarbosilane.

The weight average molecular weight (hereinafter referred to as Mw) of the polycarbosilane obtained in this way is 2000 to 3000, the molecular index (hereinafter referred to as PDI) is 2.3 to 2.9, and the ratio of the high molecular weight to the middle molecular weight is 0.5 to 1.2. As polycarbosilane, when melt spinning, the diameter of polycarbosilane fibers can be obtained with a diameter of 12μm or less.

Comparative example (conventional method)

PDMS is obtained by reacting DMDCS and metallic sodium in toluene solvent. 1000 g of PDMS is placed in the reactor 10 and treated several times with nitrogen and vacuum. In a nitrogen atmosphere, the temperature of the reactor 10 is raised to 360°C at a rate of 1 to 5°C/min and maintained for 15 to 20 hours. Then, the temperature is raised to 450°C and maintained for 10 hours. Cool to room temperature to obtain solid polycarbosilane. Polycarbosilane is dissolved in toluene and filtered. The final polycarbosilane is obtained by vacuum distillation and purification at 280°C under a vacuum atmosphere.

Mw measured by GPC (Gel Permeation Chromatography) was 3104, number average molecular weight (hereinafter referred to as Mn) was 951, and PDI was 3.26. As shown in Figure 3, in the chromatogram curve of GPC, the area up to the effusion time of 27.850 min is the high molecular area (hereinafter referred to as AHM), and the area up to 28.686 min is the middle molecule area (hereinafter referred to as AMM). ), and the area after 30.117 min was calculated as the low molecule region (hereinafter referred to as ALM). The areas are 47.3, 38.3, and 14.4%, respectively. The ratio between high molecular weight and middle molecular weight is 1.27, so the high molecular weight exists more than the middle molecular weight. Polycarbosilane fiber was manufactured from the obtained polycarbosilane. In a mono-hole spinning equipment, 30 g of polycarbosilane is placed in a melting chamber, and the nitrogen-vacuum is replaced several times before creating a nitrogen atmosphere. The chamber temperature was raised to 280°C, and molten polycarbosilane was discharged through a 0.2 mm nozzle under a pressure of 1 bar and wound at 220 rpm. The average diameter of the obtained polycarbosilane fibers was 15 μm. It is difficult to make polycarbosilane fibers with a diameter of 15 μm or less using conventional methods.

Example 1

PDMS is obtained by reacting DMDCS and metallic sodium in toluene solvent. 1000 g of PDMS is placed in the reactor 10 and treated several times with nitrogen and vacuum. Nitrogen is added while the temperature of the reactor 10 is raised at a rate of 1 to 5°C/min, and placed in a vacuum state. The temperature of the final reactor (10) is 400°C, and the gas decomposed and volatilized in this process becomes liquid polysilane (LPS) through the condenser (60) and enters the reactor (10). The yield of liquid polysilane (LPS) reaches 80-90%. Molecular weight was measured by GPC. The molecular weight was 510 for Mw and 440 for Mn.

Only 500 g of the LPS synthesized in this way is left in the existing reactor (10) to synthesize polycarbosilane, or 500 g of LPS synthesized in this way is put into the reactor (10) dedicated for polycarbosilane synthesis to synthesize polycarbosilane. Hereinafter, the reactor 10 may be any.

The inside of the reactor (10) is purged several times with nitrogen and vacuum, and then nitrogen is supplied. While stirring, operate the heater 20 of the reactor 10 to raise the temperature to 200°C at a rate of 0.5 to 2°C/min, and 100g of PDMS (20wt% of LPS) is slowly introduced into the reactor 10 at this temperature. Stir while stirring. Raise the temperature to 300°C and maintain it for 6 hours. The temperature of the reactor (10) is raised to 410°C and maintained for 8 hours. Then cool to room temperature. Solid polycarbosilane is obtained. Polycarbosilane is dissolved in toluene and filtered. Then, polycarbosilane is obtained by vacuum distillation and purification at 280°C under a vacuum atmosphere. The yield at this time is 40%. As shown in Figure 4, the FT-IR spectrum confirmed that polycarbosilane bonds were formed.

The molecular weight of polycarbosilane was measured by GPC. Mw is 2391, Mn is 803, and PDI is 2.97. As shown in Figure 5, in the GPC chromatogram curve, the area up to the effusion time of 27.492 min is referred to as the high molecular area (AHM), the area up to 28.959 min is referred to as the intermediate molecular area (AMM), and 30.033 min. The area was calculated by considering the subsequent area as the low molecular area (ALM). The areas are 33.50, 48.11, and 18.37%, respectively. Approximately 18% of small molecules exist. The ratio of polymers and middle molecules is 0.69, which means that there is more middle molecular weight than high molecular weight.

Melt spinning was performed with the obtained polycarbosilane. Add 30 g of polycarbosilane to the melting chamber, and replace nitrogen and vacuum several times. The temperature is raised to 240°C in a nitrogen atmosphere to melt the polycarbosilane and maintained for 3 hours. Molten polycarbosilane was discharged with a 0.2 mm nozzle and polycarbosilane fibers were wound at 230 rpm. The diameter of the obtained polycarbosilane fibers is small, averaging 12 μm.

Example 2

LPS was prepared from PDMS as in Example 1.

Only 500 g of the LPS synthesized in this way is left in the existing reactor (10) to synthesize polycarbosilane, or 500 g of LPS synthesized in this way is put into the reactor (10) dedicated for polycarbosilane synthesis to synthesize polycarbosilane. Hereinafter, the reactor 10 may be any.

The inside of the reactor (10) is purged several times with nitrogen and vacuum, and then nitrogen is supplied. While stirring, operate the heater 20 of the reactor 10 to raise the temperature to 200°C at a rate of 0.5 to 2°C/min, and at this temperature, 200g of PDMS (40wt% of LPS) is slowly introduced into the reactor 10. Stir while stirring. Raise the temperature to 340°C and maintain it for 15 hours. The temperature is then raised to 430°C and maintained for 8 hours. Then cool to room temperature. Solid polycarbosilane is obtained. Polycarbosilane is dissolved in toluene and filtered. Then, polycarbosilane is obtained by vacuum distillation and purification at 280°C under a vacuum atmosphere.

Molecular weight was measured by GPC. Mw is 2278, Mn is 931, and PDI is 2.44. The molecular weight area was calculated from the GPC chromatogram. The high molecular area (AHM) is 32.55%, the medium molecular area (AMM) is 54.96%, and the low molecular area (ALM) is 12.47%. Low molecular weight exists at about 12%. The ratio of AHM/AMM is 0.59, which means that there are significantly more middle molecules than polymers. Polycarbosilane was melt-spun as in Example 1. Raise the temperature to 250℃, melt the polycarbosilane, and keep it for 3 hours. Molten polycarbosilane was discharged with a 0.2 mm nozzle and polycarbosilane fibers were wound at 240 rpm. The diameter of the obtained polycarbosilane fibers is small, averaging 12 μm.

10: reactor 20: heater
30: PDMS chamber 40: PDMS supply section
50: Furnace 60: Condenser
70: gas exhaust pipe

Claims (6)

A reactor in which LPS (Liquid polysilane) is introduced and has an inert atmosphere;
A heater that heats the reactor to synthesize the LPS into polycarbosilane;
A PDMS chamber that stores PDMS powder and has an inert atmosphere;
A PDMS supply unit connected to the reactor and the PDMS chamber and spraying a set amount of the PDMS powder stored in the PDMS chamber on the surface of the LPS contained in the reactor;
A furnace connected to the upper part of the reactor, through which the PDMS powder sprinkled on the LPS surface is decomposed, gasified, and passes through it as it rises;
A condenser that condenses a portion of the PDMS gas whose molecular weight increases as it passes through the furnace and returns it to the reactor; and
A polycarbosilane synthesis device for silicon carbide fiber precursor, comprising a gas exhaust pipe for discharging ultra-low molecular weight PDMS gas while passing through the furnace. A first step of adding LPS to a reactor with an inert atmosphere and heating it;
A second step of spraying a set amount of PDMS powder on the LPS surface when the reactor reaches the set temperature;
A third step of heating the reactor to a set temperature and heating the PDMS powder by decomposing and gasifying the PDMS gas, which rises by heating, by passing it through a furnace;
A fourth step of condensing some of the PDMS gas with an increased molecular weight while passing through the furnace, returning it to the reactor, and discharging PDMS gas with an ultra-low molecular weight while passing through the furnace; and
A method for synthesizing polycarbosilane for a silicon carbide fiber precursor, comprising a fifth step of cooling the reactor to room temperature to obtain solid polycarbosilane, followed by filtering and vacuum distillation purification to obtain final polycarbosilane. The method of claim 2, wherein in the first step,
The LPS is synthesized by reacting DMDCS and metallic sodium in toluene or xylene solvent, washing and drying to synthesize PDMS, and pyrolyzing the PDMS by raising the temperature to 360-420°C in a nitrogen atmosphere. Carbonization. Polycarbosilane synthesis method for silicon fiber precursor. The method of claim 2, wherein in the second step,
A polycarbosilane synthesis method for silicon carbide fiber precursor, characterized in that the PDMS powder is added up to 10 to 100% of the weight of the LPS. The method of claim 2, wherein in the second step,
A method for synthesizing polycarbosilane for a silicon carbide fiber precursor, characterized in that the reactor is heated to 200°C at a rate of 0.5 to 2°C/min. The method of claim 2, wherein in the third step,
The heating is characterized in that it consists of two steps: raising the temperature of the reactor to 300 to 380 ℃ and allowing the reaction to proceed for more than 3 hours, then raising the temperature of the reactor to 400 to 460 ℃ and holding the reaction for more than 2 hours. Polycarbosilane synthesis method for silicon carbide fiber precursor.