阅读说明：本技术 一种聚碳硅烷材料及其制备方法 (Polycarbosilane material and preparation method thereof ) 是由 黄清芊 陈智林 陈柏林 刘周东 陈杰华 谢丹松 于 2020-11-24 设计创作，主要内容包括：本发明公开了一种聚碳硅烷材料及其制备方法,制备步骤如下：取100份氯化钠进行电解并油浴加热,经过提纯成型,后再往熔融的金属钠中加入二甲基二氯硅烷进行反应,高温下搅拌熟化；在反应物中加入无水乙醇,控制温度并持续搅拌,提取氯化钠进行重新回收利用,后进行真空抽滤；在混合物中分别加入纯净水和无水乙醇进行多次清洗,以获得纯净的聚二甲基硅烷；将纯净的聚二甲基硅烷进行真空干燥；将真空干燥后的聚二甲基硅烷进行裂解反应,即得液态聚碳硅烷；再将液态聚碳硅烷在高温高压下进行合成得到聚碳硅烷；该聚碳硅烷材料的软化点为180℃～235℃,数均分子量为1000～1400,氧含量为：0.2％～0.5％,并且该聚碳硅烷在氮气中加热到1000℃的陶瓷产率为48％～60％。(The invention discloses a polycarbosilane material and a preparation method thereof, and the preparation method comprises the following steps: taking 100 parts of sodium chloride for electrolysis, heating in an oil bath, purifying and forming, then adding dimethyldichlorosilane into molten metal sodium for reaction, stirring and curing at high temperature; adding absolute ethyl alcohol into the reactant, controlling the temperature, continuously stirring, extracting sodium chloride for recycling, and then carrying out vacuum filtration; respectively adding purified water and absolute ethyl alcohol into the mixture for cleaning for multiple times to obtain pure polydimethylsilane; carrying out vacuum drying on the pure polydimethylsiloxane; carrying out cracking reaction on the vacuum-dried polydimethylsiloxane to obtain liquid polycarbosilane; then synthesizing liquid polycarbosilane at high temperature and high pressure to obtain polycarbosilane; the softening point of the polycarbosilane material is 180-235 ℃, the number average molecular weight is 1000-1400, and the oxygen content is as follows: 0.2-0.5%, and the yield of the ceramic when the polycarbosilane is heated to 1000 ℃ in nitrogen is 48-60%.)

1. The preparation method of the polycarbosilane material is characterized in that sodium chloride, dimethyldichlorosilane, absolute ethyl alcohol and purified water are used as raw materials, and the preparation method comprises the following steps:

(1) taking 100 parts of sodium chloride for electrolysis, heating in an oil bath, purifying and forming, adding 113 parts of dimethyldichlorosilane into molten metal sodium for reaction, stirring and curing at high temperature to obtain a reactant;

(2) adding 104 parts of absolute ethyl alcohol into the reactant obtained in the step (1), controlling the temperature, continuously stirring, extracting sodium chloride for recycling, and performing vacuum filtration on the mixture after reaction;

(3) respectively adding 705 parts of purified water and 222 parts of absolute ethyl alcohol into the mixture obtained in the step (2) for washing for multiple times to obtain pure polydimethylsilane;

(4) vacuum drying the pure polydimethylsiloxane obtained in the step (3);

(5) performing cracking reaction on the polydimethylsilane after vacuum drying in the step (4) to obtain liquid polycarbosilane;

(6) and (4) carrying out synthetic reaction on the liquid polycarbosilane obtained in the step (5) at high temperature and high pressure to obtain polycarbosilane.

2. The method of claim 1, wherein the polycarbosilane material is prepared by: the method for preparing the metal sodium by the electrolysis method in the step (1) comprises the specific steps of adopting a sodium chloride electrifying mode, arranging 40 electrolytic cells in one group, operating in a series connection mode, using graphite as an anode and iron as a cathode, generating the metal sodium on the cathode by electrolysis, and generating chlorine on the anode, wherein the working voltage is 7-8V, the working current is 24-40 KA, and the electrolysis temperature is 600 ℃.

3. The method of claim 1, wherein the polycarbosilane material is prepared by: in the step (1), under the protection of inert gas, dimethyldichlorosilane is dripped into molten sodium metal at a dripping speed of 1kg/min for reaction, in the process, stirring and curing are required to be carried out at a temperature of 110-120 ℃ for 24-36 hours, and the temperature is required to be controlled at 109-115 ℃ in the whole process.

4. The method of claim 1, wherein the polycarbosilane material is prepared by: in the step (2), in the process of dropwise adding absolute ethyl alcohol into the reactant obtained in the step (1) at a dropping speed of 110L/h for reaction, the temperature needs to be controlled to be 5-20 ℃, stirring is needed for 3-5 hours after the addition is finished, sodium chloride is extracted, and the whole process needs to be carried out in an inert gas environment.

5. The method of claim 1, wherein the polycarbosilane material is prepared by: in the step (3), the specific steps of the cleaning process are as follows: firstly, 222 parts of absolute ethyl alcohol is added into the mixture for cleaning, then 365 parts of purified water is added for secondary cleaning, and then 170 parts of purified water is added twice respectively for tertiary cleaning and quaternary cleaning to obtain pure polydimethylsilane; wherein, the whole cleaning process needs vacuum filtration, and the cleaning time is 0.3-0.8 h.

6. The method of claim 1, wherein the polycarbosilane material is prepared by: in the step (5), the cracking reaction comprises the following specific steps: opening a vacuum valve of the cracking kettle, starting a vacuum pump to vacuumize, keeping a certain pressure in the cracking kettle, and maintaining the pressure for 11-13 hours; and starting a stirring device and a heating device of the cracking kettle, heating to 200 ℃ for reduced pressure distillation, keeping the temperature for 1-3 hours, continuously stirring the polydimethylsilane in the cracking kettle at high temperature and low pressure, and heating again for cracking.

7. The method of claim 1, wherein the polycarbosilane material is prepared by: in the step (6), the specific steps adopted are as follows: heating to 300-500 ℃ under the pressure of 0.3-0.6 MPa to perform synthetic reaction, discharging the material after the reaction is finished to a material storage kettle to cool, sampling and testing the material in the cooling process to obtain the molecular weight of the material, vacuumizing the kettle by opening vacuum, removing 1-10% of low molecular substances, recovering the normal pressure, filtering by a filter, and discharging the material to a product receiving material storage tank.

8. The method of claim 3 or 4, wherein: the inert gas is nitrogen.

9. A polycarbosilane material prepared by the method of any one of claims 1 to 7, having a softening point of 180 ℃ to 235 ℃, a number average molecular weight of 1000 to 1400, and an oxygen content of: 0.2-0.5%, and the yield of the ceramic when the polycarbosilane is heated to 1000 ℃ in nitrogen is 48-60%.

Technical Field

The invention relates to the technical field of polycarbosilane, in particular to a polycarbosilane material and a preparation method thereof.

Background

At present, the preparation methods of polycarbosilane mainly comprise two methods, one method is a high-temperature high-pressure method invented by Yajima Japan, namely, dichlorodimethylsilane is used as a raw material, the condensation reaction is carried out to prepare the polydimethylsilane, then the polydimethylsilane is pyrolyzed in an autoclave, under the action of high temperature and high pressure, silicon-silicon bonds in a polymer undergo Kumada rearrangement to form Si-C bonds, and the polycarbosilane is further polymerized to obtain the polycarbosilane. The polycarbosilane prepared by the method has stable performance and good forming performance, and has been used for preparing continuous silicon carbide fibers by Nippon carbon company (Yajima, et al. Nature,1976,261: 683-685, US4110386, US 4100233). Another method is an atmospheric pressure catalytic synthesis method adopted by Ube corporation of Japan, which comprises reacting diphenyldichlorosilane with boric acid to obtain polyborosiloxane, adding the polyborosiloxane into the polydimethylsilane as a catalyst, and polymerizing at about 350 ℃ under atmospheric pressure to obtain polycarbosilane (Ishikawa, et al, U.S. Pat. No. 5,5948714).

However, the production technology of polycarbosilane has the defects of complex process, low actual production efficiency and the like because polydimethylsiloxane raw materials need to be produced by sections or purchased, and the whole process has high cost and low efficiency.

Disclosure of Invention

Aiming at the problems, the invention provides a polycarbosilane material and a preparation method thereof.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: the preparation method of the polycarbosilane material is characterized in that sodium chloride, dimethyldichlorosilane, absolute ethyl alcohol and purified water are used as raw materials, and the preparation method comprises the following steps:

(1) taking 100 parts of sodium chloride for electrolysis, heating in an oil bath, purifying and forming, adding 113 parts of dimethyldichlorosilane into molten metal sodium for reaction, stirring and curing at high temperature to obtain a reactant;

(2) adding 104 parts of absolute ethyl alcohol into the reactant obtained in the step (1), controlling the temperature, continuously stirring, extracting sodium chloride, and carrying out vacuum filtration on the mixture after reaction;

(3) adding 705 parts of purified water and 222 parts of absolute ethyl alcohol into the mixture obtained in the step (2) for washing for multiple times to obtain pure polydimethylsilane;

(4) vacuum drying the pure polydimethylsiloxane obtained in the step (3);

(5) performing cracking reaction on the polydimethylsilane after vacuum drying in the step (4) to obtain liquid polycarbosilane;

(6) and (4) carrying out synthetic reaction on the liquid polycarbosilane obtained in the step (5) at high temperature and high pressure to obtain polycarbosilane.

Preferably, the step (1) of preparing the metal sodium by an electrolysis method comprises the specific steps of adopting a sodium chloride electrifying mode, arranging 40 electrolytic cells in one group, operating in a series connection mode, taking graphite as an anode and iron as a cathode, generating the metal sodium on the cathode by electrolysis, and generating chlorine on the anode, wherein the working voltage is 7-8V, the working current is 24-40 KA, and the electrolysis temperature is 600 ℃.

Preferably, in the step (1), under the protection of inert gas, dimethyldichlorosilane is dropped into molten sodium metal at a dropping speed of 1kg/min for reaction, in the process, stirring and curing are required to be carried out at a temperature of 110-120 ℃ for 24-36 hours, and the temperature is required to be controlled at 109-115 ℃ in the whole process.

Preferably, in the step (2), in the process of dropwise adding absolute ethyl alcohol into the reactant obtained in the step (1) at a dropping speed of 110L/h for reaction, the temperature needs to be controlled at 5-20 ℃, stirring is needed for 3-5 hours after the addition is completed, sodium chloride is extracted, and the whole process needs to be carried out in an inert gas environment.

Preferably, in the step (3), the specific steps of the cleaning process are as follows: firstly, 222 parts of absolute ethyl alcohol is added into the mixture for cleaning, then 365 parts of purified water is added for secondary cleaning, and then 170 parts of purified water is added twice respectively for tertiary cleaning and quaternary cleaning to obtain pure polydimethylsilane; wherein, the whole cleaning process needs vacuum filtration, and the cleaning time is 0.3-0.8 h.

Preferably, in step (5), the cleavage reaction comprises the following specific steps: opening a vacuum valve of the cracking kettle, starting a vacuum pump to vacuumize to enable a certain pressure to exist in the cracking kettle, and maintaining the pressure for 11-13 hours; and starting a stirring device and a heating device of the cracking kettle, heating to 200 ℃ for reduced pressure distillation, keeping the temperature for 1-3 hours, continuously stirring the polydimethylsilane in the cracking kettle at high temperature and low pressure, and heating again for cracking.

Preferably, in the step (6), the specific steps adopted are as follows: heating to 300-500 ℃ under the pressure of 0.3-0.6 MPa to perform synthetic reaction, discharging the material after the reaction is finished to a material storage kettle to cool, sampling and testing the material in the cooling process to obtain the molecular weight of the material, vacuumizing the kettle by opening vacuum, removing 1-10% of low molecular substances, recovering the normal pressure, filtering by a filter, and discharging the material to a product receiving material storage tank.

Preferably, the inert gas is nitrogen.

The invention also provides a polycarbosilane material which is prepared by the method, the polycarbosilane material has a softening point of 180-235 ℃, a number average molecular weight of 1000-1400, and oxygen content of: 0.2-0.5%, and the yield of the ceramic when the polycarbosilane is heated to 1000 ℃ in nitrogen is 48-60%.

From the above description of the structure of the present invention, compared with the prior art, the present invention has the following advantages:

1. the invention adopts purified water and absolute ethyl alcohol to dissolve and remove impurities of the polydimethylsilane, namely, the sodium chloride in the polydimethylsilane is washed away by using the purified water, the water is removed by using the absolute ethyl alcohol to obtain the pure polydimethylsilane, then the polydimethylsilane is put into a cracking kettle, the kettle is subjected to pressure maintaining, vacuum pumping, heat preservation and temperature rising for cracking, then the kettle is transferred to a synthesis kettle for synthesis under high temperature and high pressure, and the synthesis process is subjected to desolventization according to different product requirements to obtain the polycarbosilane, so that the polycarbosilane with the softening point of 180-235 ℃, the number average molecular weight of 1000-1400 and the oxygen content of: 0.2 to 0.5 percent of polycarbosilane, and the yield of the ceramic heated to 1000 ℃ in nitrogen is 48 to 60 percent.

2. The invention has high production efficiency, high production efficiency and strong continuity in the whole process, and the production period of each batch is about one week.

3. The sodium chloride in the production process can be recycled, the cost is reduced, and the method is safe and environment-friendly and brings economic benefits to enterprises.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Example 1

A method for preparing polycarbosilane material adopts sodium chloride, dimethyldichlorosilane, absolute ethyl alcohol and purified water as raw materials, and comprises the following steps:

(1) 100 parts of sodium chloride is electrolyzed and heated in an oil bath, after purification and molding, 113 parts of dimethyldichlorosilane is dripped into molten metal sodium at the dripping speed of 1kg/min, and stirred and cured for 24 hours at the temperature of 110 ℃, thus obtaining a reactant; in the process, a sodium chloride electrifying mode is adopted, 40 electrolytic tanks are arranged in one group and operated in a series connection mode, the working voltage is 7-8V, the working current is 24-40 KA, the electrolysis temperature is 600 ℃, graphite is used as an anode, iron is used as a cathode, and the chemical formula is as follows: 2NaCL (melting) ═ 2Na + CL (electrical conduction)₂And ×) metallic sodium produced by the electrolysis method is electrolyzed and heated in an oil bath, and metallic sodium is produced at the cathode and chlorine gas is produced at the anode by electrolysis. Sodium chloride needs to be melted during electrolysis, and the melting point of sodium chloride is 801 ℃, which is technically difficult. The use of a low temperature eutectic (i.e. a mixture of two or more species with the lowest melting point) of 40% sodium chloride and 60% calcium chloride at a melting temperature of about 580 c reduces the temperature required for electrolysis and thus also the vapour pressure of sodium. During electrolysis, chlorine is released from the anode, and when current passes through the molten salt, metal sodium and metal calcium are simultaneously reduced and float above the cathodeOverflow from the pipeline. Cooling the molten metal mixture to 105 ℃, precipitating metal calcium as crystals, filtering to separate metal sodium from metal calcium, purifying and forming, and conveying the molten metal sodium to a reaction kettle in a heat conduction oil heating pipeline manner;

(2) reducing the temperature to 5 ℃, dripping 104 parts of absolute ethyl alcohol into the reactant obtained in the step (1) at a dripping speed of 100L/h, controlling the temperature to be 5 ℃, continuously stirring for 3 hours, extracting sodium chloride, and carrying out vacuum filtration on the mixture after reaction; the whole process needs to be carried out in an inert gas environment;

(3) respectively adding 705 parts of purified water and 222 parts of absolute ethyl alcohol into the mixture obtained in the step (2) for washing for multiple times to obtain pure polydimethylsilane; the cleaning process comprises the following specific steps: firstly, 222 parts of absolute ethyl alcohol is added into the mixture for cleaning, then 365 parts of purified water is added for secondary cleaning, and then 170 parts of purified water is added twice respectively for tertiary cleaning and quaternary cleaning to obtain pure polydimethylsilane; wherein, the whole cleaning process needs vacuum filtration, and the cleaning time is 0.3 hour;

(4) vacuum drying the pure polydimethylsiloxane obtained in the step (3);

(5) putting the polydimethylsilane after vacuum drying in the step (4) into a cracking kettle for cracking reaction to obtain liquid polycarbosilane; the cracking reaction comprises the following specific steps: opening a vacuum valve of the cracking kettle, starting a vacuum pump to vacuumize to enable the cracking kettle to have certain pressure, and maintaining the pressure for 11 hours; starting a stirring device and a heating device of the cracking kettle, heating to 200 ℃ for reduced pressure distillation, keeping the temperature for 1 hour, continuously stirring the polydimethylsilane in the cracking kettle at high temperature and low pressure, and heating again for cracking;

(6) transferring the liquid polycarbosilane obtained in the step (5) to a synthesis kettle, and carrying out synthesis reaction at high temperature and high pressure to obtain polycarbosilane; the specific steps of the synthesis reaction are as follows: heating to 300 ℃ under the pressure of 0.3MPa to carry out synthetic reaction, discharging the material after the reaction to a storage kettle to cool, sampling and testing the material in the cooling process, obtaining the molecular weight of the material, vacuumizing the kettle by opening vacuum, recovering the normal pressure after 1% of low molecular substances are pumped out, and discharging the material to a product receiving material storage tank after filtering by a filter.

The polycarbosilane material prepared by the method has the softening point of 180 ℃, the number average molecular weight of 1000, and the oxygen content: 0.2% and the yield of ceramic of the polycarbosilane heated to 1000 ℃ in nitrogen is 48%.

Example 2

A method for preparing polycarbosilane material adopts sodium chloride, dimethyldichlorosilane, absolute ethyl alcohol and purified water as raw materials, and comprises the following steps:

(1) 100 parts of sodium chloride is electrolyzed and heated in an oil bath, after purification and molding, 113 parts of dimethyldichlorosilane is dripped into molten metal sodium at the dripping speed of 1kg/min, and stirred and cured for 26 hours at the temperature of 112 ℃, thus obtaining a reactant; in the process, a sodium chloride electrifying mode is adopted, 40 electrolytic tanks are arranged in one group and operated in a series connection mode, the working voltage is 7-8V, the working current is 24-40 KA, the electrolysis temperature is 600 ℃, graphite is used as an anode, iron is used as a cathode, and the chemical formula is as follows: 2NaCL (melting) ═ 2Na + CL (electrical conduction)₂And ×) metallic sodium produced by the electrolysis method is electrolyzed and heated in an oil bath, and metallic sodium is produced at the cathode and chlorine gas is produced at the anode by electrolysis. Sodium chloride needs to be melted during electrolysis, and the melting point of sodium chloride is 801 ℃, which is technically difficult. The use of a low temperature eutectic (i.e. a mixture of two or more species with the lowest melting point) of 40% sodium chloride and 60% calcium chloride at a melting temperature of about 580 c reduces the temperature required for electrolysis and thus also the vapour pressure of sodium. During electrolysis, chlorine is discharged from the anode, and when current passes through the molten salt, the metal sodium and the metal calcium are simultaneously reduced, float on the molten salt above the cathode and overflow from the pipeline. Cooling the molten metal mixture to 105 ℃, precipitating metal calcium as crystals, filtering to separate metal sodium from metal calcium, purifying and forming, and conveying the molten metal sodium to a reaction kettle in a heat conduction oil heating pipeline manner;

(2) reducing the temperature to 12 ℃, dripping 104 parts of absolute ethyl alcohol into the reactant obtained in the step (1) at a dripping speed of 100L/h, controlling the temperature to 12 ℃, continuously stirring for 4 hours, extracting sodium chloride, and carrying out vacuum filtration on the mixture after reaction; the whole process needs to be carried out in an inert gas environment;

(3) respectively adding 705 parts of purified water and 222 parts of absolute ethyl alcohol into the mixture obtained in the step (2) for washing for multiple times to obtain pure polydimethylsilane; the cleaning process comprises the following specific steps: firstly, 222 parts of absolute ethyl alcohol is added into the mixture for cleaning, then 365 parts of purified water is added for secondary cleaning, and then 170 parts of purified water is added twice respectively for tertiary cleaning and quaternary cleaning to obtain pure polydimethylsilane; wherein, the whole cleaning process needs vacuum filtration, and the cleaning time is 0.4 hour;

(4) vacuum drying the pure polydimethylsiloxane obtained in the step (3);

(5) putting the polydimethylsilane after vacuum drying in the step (4) into a cracking kettle for cracking reaction to obtain liquid polycarbosilane; the cracking reaction comprises the following specific steps: opening a vacuum valve of the cracking kettle, starting a vacuum pump to vacuumize to enable the cracking kettle to have certain pressure, and maintaining the pressure for 11 hours; starting a stirring device and a heating device of the cracking kettle, heating to 200 ℃ for reduced pressure distillation, keeping the temperature for 1 hour, continuously stirring the polydimethylsilane in the cracking kettle at high temperature and low pressure, and heating again for cracking;

(6) transferring the liquid polycarbosilane obtained in the step (5) to a synthesis kettle, and carrying out synthesis reaction at high temperature and high pressure to obtain polycarbosilane; the specific steps of the synthesis reaction are as follows: heating to 300 ℃ under the pressure of 0.3MPa to carry out synthetic reaction, discharging the material after the reaction to a storage kettle to cool, sampling and testing the material in the cooling process, obtaining the molecular weight of the material, vacuumizing the kettle by opening vacuum, recovering the normal pressure after 2% of low molecular substances are pumped out, and discharging the material to a product receiving material storage tank after filtering by a filter.

The polycarbosilane material prepared by the method has the softening point of 180 ℃, the number average molecular weight of 1037, and the oxygen content of: 0.2% and the yield of ceramic of the polycarbosilane heated to 1000 ℃ in nitrogen is 48.5%.

Example 3

A method for preparing polycarbosilane material adopts sodium chloride, dimethyldichlorosilane, absolute ethyl alcohol and purified water as raw materials, and comprises the following steps:

(1) taking 100 parts of sodium chloride for electrolysis, heating in an oil bath, purifying and forming, then dripping 113 parts of dimethyldichlorosilane into molten metal sodium at the dripping speed of 1kg/min for reaction, and stirring and curing at the temperature of 115 ℃ for 24-36 hours to obtain a reactant; in the process, a sodium chloride electrifying mode is adopted, 40 electrolytic tanks are arranged in one group and operated in a series connection mode, the working voltage is 7-8V, the working current is 24-40 KA, the electrolysis temperature is 600 ℃, graphite is used as an anode, iron is used as a cathode, and the chemical formula is as follows: 2NaCL (melting) ═ 2Na + CL (electrical conduction)₂And ×) metallic sodium produced by the electrolysis method is electrolyzed and heated in an oil bath, and metallic sodium is produced at the cathode and chlorine gas is produced at the anode by electrolysis. Sodium chloride needs to be melted during electrolysis, and the melting point of sodium chloride is 801 ℃, which is technically difficult. The use of a low temperature eutectic (i.e. a mixture of two or more species with the lowest melting point) of 40% sodium chloride and 60% calcium chloride at a melting temperature of about 580 c reduces the temperature required for electrolysis and thus also the vapour pressure of sodium. During electrolysis, chlorine is discharged from the anode, and when current passes through the molten salt, the metal sodium and the metal calcium are simultaneously reduced, float on the molten salt above the cathode and overflow from the pipeline. Cooling the molten metal mixture to 108 ℃, separating out metallic calcium as crystals, filtering to separate metallic sodium from metallic calcium, purifying and forming, and conveying the molten metallic sodium to a reaction kettle in a heat conduction oil heating pipeline manner;

(2) reducing the temperature to 15 ℃, dripping 104 parts of absolute ethyl alcohol into the reactant obtained in the step (1) at a dripping speed of 100L/h, controlling the temperature to 15 ℃, continuously stirring for 4 hours, extracting sodium chloride, and carrying out vacuum filtration on the mixture after reaction; wherein, the whole process is carried out in an inert gas environment;

(3) respectively adding 705 parts of purified water and 222 parts of absolute ethyl alcohol into the mixture obtained in the step (2) for washing for multiple times to obtain pure polydimethylsilane; the cleaning process comprises the following specific steps: firstly, 222 parts of absolute ethyl alcohol is added into the mixture for cleaning, then 365 parts of purified water is added for secondary cleaning, and then 170 parts of purified water is added twice respectively for tertiary cleaning and quaternary cleaning to obtain pure polydimethylsilane; wherein, the whole cleaning process needs vacuum filtration, and the cleaning time is 0.5 hour;

(4) vacuum drying the pure polydimethylsiloxane obtained in the step (3);

(5) putting the polydimethylsilane after vacuum drying in the step (4) into a cracking kettle for cracking reaction to obtain liquid polycarbosilane; the cracking reaction comprises the following specific steps: opening a vacuum valve of the cracking kettle, starting a vacuum pump to vacuumize to ensure that a certain pressure is kept in the cracking kettle, and maintaining the pressure for 12 hours; starting a stirring device and a heating device of the cracking kettle, heating to 200 ℃ for reduced pressure distillation, keeping the temperature for 2 hours, continuously stirring the polydimethylsilane in the cracking kettle at high temperature and low pressure, and heating again for cracking;

(6) and (4) transferring the liquid polycarbosilane obtained in the step (5) to a synthesis kettle, and synthesizing at high temperature and high pressure to obtain the polycarbosilane. The specific steps of the synthesis reaction are as follows: heating to 400 ℃ under the pressure of 0.5MPa to carry out synthetic reaction, discharging the material after the reaction to a storage kettle to cool, sampling and testing the material in the cooling process, obtaining the molecular weight of the material, vacuumizing the kettle by opening vacuum, recovering the normal pressure after 5% of low molecular substances are pumped out, and discharging the material to a product receiving material storage tank after filtering by a filter.

The polycarbosilane material prepared by the method has the softening point of 215 ℃, the number average molecular weight of 1275 and the oxygen content of: 0.2% and the yield of ceramic of the polycarbosilane heated to 1000 ℃ in nitrogen is 53%.

Example 4

A method for preparing polycarbosilane material adopts sodium chloride, dimethyldichlorosilane, absolute ethyl alcohol and purified water as raw materials, and comprises the following steps:

(1) 100 parts of sodium chloride is electrolyzed and heated in an oil bath, after purification and molding, 113 parts of dimethyldichlorosilane is dripped into molten metal sodium at the dripping speed of 1kg/min for reaction, and stirred and cured for 34 hours at the temperature of 117 ℃ to obtain a reactant; in the process, a sodium chloride electrifying mode is adopted, 40 electrolytic tanks are arranged in one group and operated in a series connection mode, the working voltage is 7-8V, the working current is 24-40 KA, the electrolysis temperature is 600 ℃, graphite is used as an anode, iron is used as a cathode, and the chemical formula is as follows: 2NaCL (melting) ═ 2Na + CL (electrical conduction)₂And ×) metallic sodium produced by the electrolysis method is electrolyzed and heated in an oil bath, and metallic sodium is produced at the cathode and chlorine gas is produced at the anode by electrolysis. Sodium chloride needs to be melted during electrolysis, and the melting point of sodium chloride is 801 ℃, which is technically difficult. The use of a low temperature eutectic (i.e. a mixture of two or more species with the lowest melting point) of 40% sodium chloride and 60% calcium chloride at a melting temperature of about 580 c reduces the temperature required for electrolysis and thus also the vapour pressure of sodium. During electrolysis, chlorine is discharged from the anode, and when current passes through the molten salt, the metal sodium and the metal calcium are simultaneously reduced, float on the molten salt above the cathode and overflow from the pipeline. Cooling the molten metal mixture to 110 ℃, precipitating metal calcium as crystals, filtering to separate metal sodium from metal calcium, purifying and forming, conveying the molten metal sodium to a reaction kettle in a heat conduction oil heating pipeline mode, and dripping dimethyl dichlorosilane at a dripping speed of 1kg/min to participate in reaction;

(2) reducing the temperature to 17 ℃, dripping 104 parts of absolute ethyl alcohol into the reactant obtained in the step (1) at a dripping speed of 100L/h, controlling the temperature to be 17 ℃, continuously stirring for 5 hours, extracting sodium chloride, and carrying out vacuum filtration on the mixture after reaction; wherein, the whole process is carried out in an inert gas environment;

(3) respectively adding 705 parts of purified water and 222 parts of absolute ethyl alcohol into the mixture obtained in the step (2) for washing for multiple times to obtain pure polydimethylsilane; the cleaning process comprises the following specific steps: firstly, 222 parts of absolute ethyl alcohol is added into the mixture for cleaning, then 365 parts of purified water is added for secondary cleaning, and then 170 parts of purified water is added twice respectively for tertiary cleaning and quaternary cleaning to obtain pure polydimethylsilane; wherein, the whole cleaning process needs vacuum filtration, and the cleaning time is 0.7 hour;

(4) vacuum drying the pure polydimethylsiloxane obtained in the step (3);

(5) putting the polydimethylsilane after vacuum drying in the step (4) into a cracking kettle for cracking reaction to obtain liquid polycarbosilane; the cracking reaction comprises the following specific steps: opening a vacuum valve of the cracking kettle, starting a vacuum pump to vacuumize to enable the cracking kettle to have certain pressure, and maintaining the pressure for 13 hours; starting a stirring device and a heating device of the cracking kettle, heating to 200 ℃ for reduced pressure distillation, preserving heat for 3 hours to ensure that the polydimethylsilane in the cracking kettle is continuously stirred at high temperature and low pressure, and then heating for cracking;

(6) and (4) transferring the liquid polycarbosilane obtained in the step (5) to a synthesis kettle, and synthesizing at high temperature and high pressure to obtain the polycarbosilane. The specific steps of the synthesis reaction are as follows: heating to 500 ℃ under the pressure of 0.6MPa to carry out synthetic reaction, discharging the material after the reaction to a storage kettle to cool, sampling and testing the material in the cooling process, obtaining the molecular weight of the material, vacuumizing the kettle by opening vacuum, recovering the normal pressure after removing 10% of low molecular substances, and discharging the material to a product receiving material storage tank after filtering by a filter.

The polycarbosilane material prepared by the method has the softening point of 235 ℃, the number average molecular weight of 1342, and the oxygen content of: 0.2% and the yield of ceramic of the polycarbosilane heated to 1000 ℃ in nitrogen is 59%.

Example 5

A method for preparing polycarbosilane material adopts sodium chloride, dimethyldichlorosilane, absolute ethyl alcohol and purified water as raw materials, and comprises the following steps:

(1) 100 parts of sodium chloride is electrolyzed and heated in an oil bath, after purification and molding, 113 parts of dimethyldichlorosilane is dripped into molten metal sodium at the dripping speed of 1kg/min for reaction, and the reaction product is obtained after stirring and curing for 36 hours at the temperature of 117 ℃; in the process, a sodium chloride electrifying mode is adopted, 40 electrolytic tanks are arranged in one group and operated in a series connection mode, the working voltage is 7-8V, the working current is 24-40 KA, the electrolysis temperature is 600 ℃, graphite is used as an anode, iron is used as a cathode, and the chemical formula is as follows: 2NaCL (melting) ═ 2Na + CL (electrical conduction)₂And ×) metallic sodium produced by the electrolysis method is electrolyzed and heated in an oil bath, and metallic sodium is produced at the cathode and chlorine gas is produced at the anode by electrolysis. Sodium chloride needs to be melted during electrolysis, and the melting point of sodium chloride is 801 ℃, which is technically difficult. The use of a low temperature eutectic (i.e. a mixture of two or more species with the lowest melting point) of 40% sodium chloride and 60% calcium chloride at a melting temperature of about 580 c reduces the temperature required for electrolysis and thus also the vapour pressure of sodium. During electrolysis, chlorine is discharged from the anode, and when current passes through the molten salt, the metal sodium and the metal calcium are simultaneously reduced, float on the molten salt above the cathode and overflow from the pipeline. Cooling the molten metal mixture to 110 ℃, precipitating metal calcium as crystals, filtering to separate metal sodium from metal calcium, purifying and forming, conveying the molten metal sodium to a reaction kettle in a heat conduction oil heating pipeline mode, and dripping dimethyl dichlorosilane at a dripping speed of 1kg/min to participate in reaction;

(2) reducing the temperature to 20 ℃, dripping 104 parts of absolute ethyl alcohol into the reactant obtained in the step (1) at a dripping speed of 100L/h, controlling the temperature at 20 ℃, continuously stirring for 5 hours, extracting sodium chloride, and carrying out vacuum filtration on the mixture after reaction; wherein, the whole process is carried out in an inert gas environment;

(3) respectively adding 705 parts of purified water and 222 parts of absolute ethyl alcohol into the mixture obtained in the step (2) for washing for multiple times to obtain pure polydimethylsilane; the cleaning process comprises the following specific steps: firstly, 222 parts of absolute ethyl alcohol is added into the mixture for cleaning, then 365 parts of purified water is added for secondary cleaning, and then 170 parts of purified water is added twice respectively for tertiary cleaning and quaternary cleaning to obtain pure polydimethylsilane; wherein, the whole cleaning process needs vacuum filtration, and the cleaning time is 0.8 hour;

(4) vacuum drying the pure polydimethylsiloxane obtained in the step (3);

(5) putting the polydimethylsilane after vacuum drying in the step (4) into a cracking kettle for cracking reaction to obtain liquid polycarbosilane; the cracking reaction comprises the following specific steps: opening a vacuum valve of the cracking kettle, starting a vacuum pump to vacuumize to enable the cracking kettle to have certain pressure, and maintaining the pressure for 13 hours; starting a stirring device and a heating device of the cracking kettle, heating to 200 ℃ for reduced pressure distillation, preserving heat for 3 hours to ensure that the polydimethylsilane in the cracking kettle is continuously stirred at high temperature and low pressure, and then heating for cracking;

(6) and (4) transferring the liquid polycarbosilane obtained in the step (5) to a synthesis kettle, and synthesizing at high temperature and high pressure to obtain the polycarbosilane. The specific steps of the synthesis reaction are as follows: heating to 500 ℃ under the pressure of 0.6MPa to carry out synthetic reaction, discharging the material after the reaction to a storage kettle to cool, sampling and testing the material in the cooling process, obtaining the molecular weight of the material, vacuumizing the kettle by opening vacuum, recovering the normal pressure after removing 10% of low molecular substances, and discharging the material to a product receiving material storage tank after filtering by a filter.

The polycarbosilane material prepared by the method has the softening point of 235 ℃, the number average molecular weight of 1400 and the oxygen content of: 0.5% and the yield of ceramic of the polycarbosilane heated to 1000 ℃ in nitrogen is 60%.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.