1. A preparation method of MarkIII type polycarbosilane is characterized by comprising the following steps: the method comprises the following steps: synthesizing polyborodiphenylsiloxane by using diphenylsilanediol and boric acid as raw materials; pyrolyzing polydimethylsiloxane powder to obtain liquid polysilane; and then adding polyborodiphenylsiloxane into the liquid polysilane to carry out pyrolysis rearrangement reaction to obtain the MarkIII type polycarbosilane.

2. The method for preparing MarkIII type polycarbosilane as claimed in claim 1, wherein the method comprises the following steps: adding diphenyl silanediol and boric acid into an organic solvent, carrying out reflux reaction for 15-25h at 80-110 ℃ under a protective atmosphere, then distilling to remove water and the organic solvent, heating to 300-400 ℃, preserving heat for 0.5-3h, and cooling to obtain the polyborodiphenyl siloxane.

3. The method for preparing MarkIII type polycarbosilane as claimed in claim 2, wherein the method comprises the following steps: the molar ratio of the diphenyl silanediol to the boric acid is 0.5-5: 1.

4. the method for preparing MarkIII type polycarbosilane as claimed in claim 2, wherein the method comprises the following steps: the organic solvent is selected from n-butyl ether.

5. The method for preparing MarkIII type polycarbosilane as claimed in claim 1, wherein the method comprises the following steps:

adding the polydimethylsiloxane powder into a reaction kettle, heating to 480 ℃ under the nitrogen atmosphere, and preserving heat for 1-10h to pyrolyze the polydimethylsiloxane powder to obtain the liquid polysilane.

6. The method for preparing MarkIII type polycarbosilane as claimed in claim 1, wherein the method comprises the following steps:

the adding amount of the polyborodiphenylsiloxane is 0.5-10% of the mass of the liquid polysilane.

7. The method for preparing MarkIII type polycarbosilane as claimed in claim 1, wherein the method comprises the following steps:

the temperature of the pyrolysis rearrangement reaction is 300-400 ℃, and the time of the pyrolysis rearrangement reaction is 3-15 h.

8. The MarkIII polycarbosilane prepared by the process of any one of claims 1 to 7.

Background

The silicon carbide-based composite material has a series of advantages of high temperature resistance, high strength, high modulus, low density, small thermal expansion coefficient and the like, and becomes a new generation of strategic thermal structural material. The method has key and wide application in the fields of aviation, aerospace, weaponry, ships, armor protection, high-speed braking and the like. The precursor conversion method is a mainstream method for preparing the silicon carbide fiber and mainly comprises four steps of precursor synthesis, spinning, infusible treatment and high-temperature sintering. There are two main types of continuous silicon carbide fibers currently produced, namely doped fibers and undoped fibers. The doped path utilizes the thinking of material compounding, and introduces high-temperature heterogeneous metal elements (such as metal titanium, zirconium, aluminum and the like) in the precursor synthesis stage, so that the doped SiC fiber has higher heat resistance. The undoped path is characterized in that no foreign impurities are introduced into the SiC fibers, and an electron beam irradiation technology is introduced through a non-melting link, so that the oxygen content is reduced, and the temperature resistance of the fibers is improved.

A typical representative of the undoped route is japan carbon company, and a successful representative of the doped route is japan division of japan company. In contrast, the doping route has the characteristics of small equipment investment, low cost and easy realization, and is the main development trend of the high-temperature resistant silicon carbide fiber. The technical route adopted by Yu corporation for synthesizing the precursor mainly comprises the following steps: firstly, dichlorodiphenylsilane and boric acid are used as raw materials to synthesize catalyst polyborodiphenylsiloxane (called Pinus for short), then the polyborodiphenylsiloxane is added into polydimethylsiloxane powder, cracking rearrangement is carried out by heating means to synthesize polycarbosilane precursor (called MarkIII PCS for short) (inorganic materials science report, 1986.12), and then organic metal compound containing heterogeneous elements is added into polycarbosilane to react under certain conditions to obtain the polycarbosilane precursor containing the heterogeneous elements. This route has the following drawbacks: 1. when the pimaric pine is synthesized, dichlorodiphenylsilane and boric acid are used as starting materials, acidic hydrogen chloride gas is generated in the reaction process, the environment is not protected, meanwhile, the dichlorodiphenylsilane is easy to hydrolyze, and the storage and operation process has higher requirements on the environment. 2. When MarkIII PCS is synthesized, the pimpines and the polydimethylsilane are mixed and heated, and the mixture of the pimpines and the polydimethylsilane is solid, so that the heat transfer is not facilitated, the uneven heat transfer of a reaction system is easily caused, and the control of the reaction and the uniformity of the performance of a product are not facilitated. The method has great influence on the synthesis, spinning, non-melting treatment and final ceramic fiber of the doped polycarbosilane.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide the MarkIII type polycarbosilane with uniform components and high ceramic yield and the preparation method thereof.

The purpose of the invention is realized by the following technical scheme:

the invention relates to a preparation method of MarkIII type polycarbosilane, which comprises the following steps: synthesizing polyborodiphenylsiloxane by using diphenylsilanediol and boric acid as raw materials; pyrolyzing polydimethylsiloxane powder to obtain liquid polysilane; then adding polyborodiphenylsiloxane into liquid polysilane for pyrolysis rearrangement reaction to obtain MarkIII type polycarbosilane

The preferable scheme is that diphenyl silanediol and boric acid are added into an organic solvent, reflux reaction is carried out for 15-25h at 80-110 ℃ under the protective atmosphere, then water and the organic solvent are removed by distillation, the temperature is raised to 300-400 ℃, the temperature is kept for 0.5-3h, and the polyborodiphenyl siloxane is obtained by cooling.

Further preferably, the molar ratio of the diphenyl silanediol to the boric acid is 0.5:1 to 5:1, preferably 1 to 2: 1.

Further preferably, the organic solvent is selected from n-butyl ether.

Further preferably, the protective atmosphere is a nitrogen atmosphere.

Further preferably, the reflux reaction is carried out under stirring.

Water removed by distillation is a reaction byproduct.

According to the preferable scheme, the polydimethylsiloxane powder is added into a metal reaction kettle, the temperature is increased to 480 ℃ under the nitrogen atmosphere, and the temperature is kept for 1-10h to pyrolyze the polydimethylsiloxane powder, so that the liquid polysilane is obtained.

In the actual operation process, adding the polydimethylsiloxane powder into a metal reaction kettle, vacuumizing and filling nitrogen for at least three times, keeping the nitrogen flowing at normal pressure, starting stirring, and heating the system to 360-480 ℃.

In a preferred scheme, the adding amount of the polyborodiphenylsiloxane is 0.5-10% of the mass of the liquid polysilane, and 2% -3% is preferred.

In a preferred embodiment, the pyrolytic rearrangement reaction is carried out under a protective atmosphere. The protective atmosphere is preferably a nitrogen atmosphere.

In a preferable scheme, the temperature of the pyrolysis rearrangement reaction is 300-400 ℃, and the time of the pyrolysis rearrangement reaction is 3-15 h.

The invention also provides the MarkIII type polycarbosilane prepared by the preparation method.

Principles and advantages

1) The method takes chlorine-free diphenyl silanediol as an initial raw material to synthesize polyborodiphenylsiloxane, the generated by-product is water, and the by-product is hydrogen chloride gas with high toxicity by using the traditional diphenyl dichlorosilane, so that the method avoids the toxicity and environmental pollution of the hydrogen chloride, and ensures that the reaction is milder, environment-friendly and easy to operate.

2) The hydrogen chloride by-product generated in the prior method has strong acidity and strong corrosivity to metal, and the traditional metal reaction kettle is not suitable any more, so the requirement on equipment is higher.

3) The MarkIII type polycarbosilane is synthesized by taking polyborodiphenylsiloxane and liquid polysilane instead of polydimethylsilane as reactants, wherein the polyborodiphenylsiloxane is a liquid phase reaction and a solid phase reaction, and the solid phase reaction is a solid-solid phase reaction.

4) The polyborodiphenylsiloxane synthesized by the method of the invention is used as a raw material to react with liquid polysilane, so that the synthesis yield is higher, and the yield of the finally obtained MarkIII polycarbosilane ceramic is high.

Drawings

FIG. 1 shows the appearance of Mark III polycarbosilane synthesized in example 1 of the present invention, and it can be seen that the Mark III polycarbosilane obtained in the present invention is a pale yellow or colorless transparent solid with high purity.

FIG. 2 shows the appearance of the MarkIII polycarbosilane obtained in comparative example 1, which is a dark brown opaque solid with more impurities and is not suitable for applications such as dope synthesis or spinning.

FIG. 3 is an IR spectrum of Mark III polycarbosilane synthesized in example 1 of the present invention.

FIG. 4 is an infrared spectrum of MarkIII polycarbosilane prepared in comparative example 1. 1355.13cm in the figure^-1The absorption peak at (A) corresponds to Si-CH in the structure₂The high or low content of chemical Si bonds reflects the degree of conversion of the Si-Si bonds, the higher the content, the higher the degree of conversion, the more advantageous the properties of the subsequent product. 2100.25cm^-1The higher the content of Si-H bond, the higher the reactivity of the Si-H bond, and the more favorable the subsequent doping reaction. The MarkIII polycarbosilane product obtained by the invention has higher Si-CH content₂Si content and higher Si-H content, which is very beneficial for the spinning of the subsequent precursor and the performance of the ceramic fiber.

Detailed Description

The invention is further illustrated by the following figures and examples.

Example 1

1. Putting diphenyl silanediol and boric acid into a metal reaction kettle which is added with n-butyl ether in advance according to the molar ratio of 3:2, introducing nitrogen, stirring, heating to 90 ℃, performing reflux reaction for 15 hours, then closing reflux, distilling to remove reaction by-product water and solvent n-butyl ether, heating to 300 ℃, preserving heat for 1 hour, and cooling to obtain the polyborodiphenyl siloxane.

2. Adding the polydimethylsiloxane powder into a metal reaction kettle, vacuumizing and filling nitrogen into the reaction kettle for at least three times, keeping the nitrogen flowing at normal pressure, starting stirring, heating the system to 400 ℃, and preserving the temperature for 2 hours to obtain a pyrolysis product liquid polysilane.

3. Adding polyborodiphenylsiloxane into liquid polysilane according to the weight ratio of 2%, heating to 350 ℃ in an inert atmosphere, preserving heat for 6 hours, and then cooling to obtain MarkIII polycarbosilane, wherein the appearance of the MarkIII polycarbosilane is light yellow solid, the melting point of the MarkIII polycarbosilane is 136.5 ℃, the synthetic yield of the markIII polycarbosilane is 63.6 wt%, and the ceramic yield of the markIII polycarbosilane in a nitrogen atmosphere at 1000 ℃ is 68.3 wt%.

Example 2

1. Putting diphenyl silanediol and boric acid into a reaction kettle which is added with n-butyl ether in advance according to the molar ratio of 3:2, introducing nitrogen, stirring, heating to 95 ℃, performing reflux reaction for 18 hours, closing reflux, distilling to remove reaction by-product water and solvent n-butyl ether, heating to 350 ℃, preserving heat for 1 hour, and cooling to obtain the polyborodiphenyl siloxane.

2. Adding the polydimethylsiloxane powder into a reaction kettle, vacuumizing and filling nitrogen into the reaction kettle, repeating for at least three times, keeping the nitrogen flowing at normal pressure, starting stirring, heating the system to 420 ℃, and preserving heat for 3 hours to obtain a pyrolysis product, namely the liquid polysilane.

3. Adding 3 wt% of polyborodiphenylsiloxane into liquid polysilane, heating to 360 ℃ in an inert atmosphere, preserving heat for 7 hours, and then cooling to obtain MarkIII type polycarbosilane, wherein the appearance of the product is a light yellow solid, the melting point of the product is 166.3 ℃, the synthetic yield of the product is 65.1 wt%, and the ceramic yield of the product is 71.3 wt% in a nitrogen atmosphere at 1000 ℃

Example 3

1. Putting diphenyl silanediol and boric acid into a reaction kettle which is added with n-butyl ether in advance according to the molar ratio of 3:2, introducing nitrogen, stirring, heating to 100 ℃, performing reflux reaction for 20 hours, then closing reflux, distilling to remove reaction by-product water and solvent n-butyl ether, heating to 350 ℃, preserving heat for 1 hour under a vacuum condition, and cooling to obtain the polyborodiphenyl siloxane.

2. Adding the polydimethylsiloxane powder into a reaction kettle, vacuumizing and filling nitrogen into the reaction kettle, repeating for at least three times, keeping the nitrogen flowing at normal pressure, starting stirring, heating the system to 420 ℃, and preserving the heat for 2 hours to obtain a pyrolysis product, namely the liquid polysilane.

3. Adding 3% polyborodiphenylsiloxane into liquid polysilane according to the weight ratio, heating to 370 ℃ in an inert atmosphere, preserving heat for 6 hours, and then cooling to obtain the MarkIII polycarbosilane with the appearance of light yellow solid and the melting point of 176.2 ℃. The synthetic yield was 62.1 wt%, and the ceramic yield of the product was 67.3 wt% in a nitrogen atmosphere at 1000 ℃.

Comparative example 1

1. Putting diphenyldichlorosilane and boric acid into a reaction kettle which is added with n-butyl ether in advance according to the molar ratio of 3:2, introducing nitrogen, stirring, heating to 90 ℃, carrying out reflux reaction for 15 hours, then closing reflux, distilling to remove reaction by-product water and solvent n-butyl ether, heating to 300 ℃, preserving heat for 1 hour, and cooling to obtain the polyborodiphenylsiloxane.

2. Adding polyborodiphenylsiloxane into polydimethylsilane according to the weight ratio of 2%, heating to 350 ℃ in an inert atmosphere, preserving heat for 6 hours, and then cooling to obtain MarkIII polycarbosilane. From FIG. 2, it can be seen that the resulting MarkIII type polycarbosilane was a dark brown opaque solid with a high impurity content, the calculated synthesis yield was 53%, and the ceramic yield of the product was 60.3% by weight at 1000 ℃ in a nitrogen atmosphere.