CN115197430A - Novel polycarbosilane ceramic precursor material and preparation method thereof - Google Patents
Novel polycarbosilane ceramic precursor material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a novel polycarbosilane ceramic precursor material and a preparation method thereof, which comprises the steps of firstly respectively synthesizing polydimethylsilane and polydiphenylsilane as raw materials, then respectively carrying out pyrolysis on the polydimethylsilane and the polydiphenylsilane to collect corresponding small molecular mixed liquid, then putting the mixture into a synthesis kettle according to a certain proportion, more effectively controlling the content of phenyl in the polycarbosilane, enabling the silicon-carbon ratio to be adjustable, optimizing the composition structure of PCS, and finally obtaining the novel polycarbosilane containing phenyl, wherein the softening point of the polycarbosilane containing phenyl is 200-250 ℃, the molecular weight is 1100-1600, the PCS fiber can be continuously spun, the surface of the fiber is smooth, the broken ends are few, the non-melting uniformity is good, the free carbon is few after high-temperature sintering, the interior and the surface of the fiber are also smooth, the fiber diameter is thinner, and the mechanical property of the SiC fiber is improved.
Description
Technical Field
The invention relates to the technical field of ceramic precursor materials, in particular to a novel polycarbosilane ceramic precursor material and a preparation method thereof.
Background
As a novel structural material, silicon carbide (SiC) fiber is widely applied to the high-tech fields of space navigation, ships, nuclear energy and the like due to the characteristics of high temperature resistance, oxidation resistance, corrosion resistance, aging resistance, excellent mechanical property and the like.
The precursor conversion method is the most successful method for preparing SiC fibers at present. The method comprises four major procedures of synthesis of precursor Polycarbosilane (PCS), melt spinning of PCS, non-melting treatment of PCS fibril, high-temperature sintering of SiC fiber and the like. Research shows that the lower performance of SiC fiber is caused by the imperfect composition structure of the fiber, which is mainly reflected by high oxygen content, high surface carbon content, incomplete mineralization and low crystallinity in the fiber. The main reason for the imperfect composition and structure of the fiber is the imperfect composition structure of PCS, which is the raw material for preparing SiC fiber. The composition, structure and performance of PCS have a decisive effect on the performance of SiC fibers, and the performance of the PCS not only directly influences the melt spinning process and the quality of PCS fibrils, but also influences the non-melting process of the fibrils, so that the PCS fibers have large damage, more broken ends, poorer non-melting uniformity and more defects in the fiber and on the surface, and finally the mechanical property of the SiC fibers is reduced.
The molecular structure of PCS directly influences the quality of SiC fibers. Oxygen and free carbon in the SiC fiber are main factors influencing the performance of the fiber, the impurities directly or indirectly come from a precursor PCS, such as Si-H and the like, have low active group content, high carbon element content and the like. Therefore, perfecting the composition structure of PCS and improving the synthesis yield become one of the research directions for synthesizing PCS precursors. The ideal precursor PCS should have several characteristics: (1) good spinnability and easy treatment after filamentation; (2) Has certain active groups and can react to obtain a stable structure or a cross-linked structure; (3) The composition has less non-target elements, basically no impurities after cracking and high ceramic yield.
Common methods for synthesizing PCS are: (1) a pyrolytic rearrangement of polysilanes; (2) a cyclic carbosilane ring-opening polymerization method; and (3) hydrosilation of unsaturated chlorosilane. Pyrolytic rearrangement is currently the most desirable process. The method comprises the steps of taking dichlorodimethylsilane as a raw material, carrying out Wurtz coupling reaction on the dichlorodimethylsilane and metal sodium to generate polydimethylsilane, and carrying out pyrolysis rearrangement to obtain Mark I type PCS. The structure is a linear structure, the spinnability is excellent, the strength of the protofilament is larger, but the molecular weight is not high because the protofilament still contains a large amount of branched chains and annular structures, and the spinning performance is very limited. In order to further improve the spinning performance of Mark I type PCS, diphenyl dichlorosilane is introduced into the original production route, and the Mark II type PCS containing phenyl is synthesized by the same method. The synthesis of Mark II type PCS is carried out by two steps: firstly, dichlorodimethylsilane and diphenyldichlorosilane are subjected to Wurtz coupling reaction with metal sodium to synthesize the dimethylsilane-diphenylsilane copolymer. And secondly, cracking and rearranging the dimethylsilane-diphenylsilane copolymer at high temperature to finally synthesize the phenyl-containing polycarbosilane.
The first step of the Mark II type PCS synthesis is a Wurtz coupling reaction of dichlorodimethylsilane and a small amount of diphenyldichlorosilane and metal sodium. The Wurtz coupling reaction mechanism is a free radical copolymerization mechanism, metal sodium is used as an initiator to replace chloride ions of dimethyl dichlorosilane (diphenyl dichlorosilane) to form NaCl, the dimethyl dichlorosilane (diphenyl dichlorosilane) loses one electron and becomes silicon anions (R1R 2Si-Na +) with negative charge, the formed silicon anions attack another monomer molecule to form Si-Si covalent bonds, and thus, the polymerized chain growth is generated, and finally, the dimethylsilane-diphenyl silane copolymer is formed.
According to the free radical copolymerization mechanism, as the reactivity ratios of the dimethyldichlorosilane and the diphenyldichlorosilane are different, in the polymerization process, the viscosity of the system is gradually increased when the chain of the system is increased, and a small amount of diphenyldichlorosilane is difficult to completely generate chain growth reaction, so that the content of the polydiphenylsilane in the copolymer is uncontrollable.
The spinning performance of Mark II type PCS synthesized by the dimethyl silane-diphenyl silane copolymer through high-temperature cracking rearrangement is greatly improved compared with that of Mark I type PCS, and the mechanical property is improved, but the PCS fiber is greatly damaged and has more broken ends, and further improvement of the mechanical property of the SiC fiber is hindered.
Disclosure of Invention
Aiming at the problems, the invention provides a novel polycarbosilane ceramic precursor material and a preparation method thereof.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a novel polycarbosilane ceramic precursor material has a chemical structural formula as follows:
wherein m1, m2, m3 and m4 are positive integers, and m is more than or equal to 1.
Preferably, the ratio of (m 1+ m2+ m 4) to m3 is 10: 1 to 100: 1.
The invention also provides a preparation method of the novel polycarbosilane ceramic precursor material, which comprises the following steps:
(1) Melting metal sodium in a xylene solvent, and adding dimethyldichlorosilane into the xylene solvent for synthesis to obtain polydimethylsilane;
(2) Melting metal sodium in a xylene solvent, and adding diphenyl dichlorosilane into the xylene solvent for synthesis to obtain poly diphenyl silane;
(3) Performing pyrolysis on the polydimethylsiloxane synthesized in the step (1) to collect first small molecule mixed liquid;
(4) Performing pyrolysis on the poly-diphenylsilane synthesized in the step (2) to collect second small molecule mixed solution;
(5) And (4) carrying out high-temperature high-pressure rearrangement synthesis on the first small molecule mixed solution obtained in the step (3) and the second small molecule mixed solution obtained in the step (4) according to a certain mass ratio to obtain the phenyl-containing polycarbosilane, wherein the softening point of the phenyl-containing polycarbosilane is 200-250 ℃, and the molecular weight of the phenyl-containing polycarbosilane is 1100-1600.
Preferably, in the step (1), the temperature of the xylene solvent is controlled to be between 100 and 120 ℃, the dripping time of the dimethyldichlorosilane is 10 to 20 hours, the reaction temperature is controlled to be between 110 and 140 ℃ after the dripping is finished, the total time from the dripping to the reaction is 24 to 50 hours, the polydimethylsilane is obtained, and the product is sequentially subjected to solvent removal, water washing and vacuum drying to obtain white powdery polydimethylsilane.
Preferably, in the step (1), the molar ratio of the metal sodium to the dimethyldichlorosilane is 2: 1-3: 1; the mass ratio of the metal sodium to the dimethylbenzene is 1: 1-1: 3.
Preferably, in the step (2), the temperature of the xylene solvent is controlled to be between 100 and 120 ℃, the dripping time of the diphenyldichlorosilane is 10 to 20 hours, the reaction temperature is controlled to be between 110 and 140 ℃ after the dripping is finished, the total time from the dripping to the reaction is 24 to 50 hours, the poly diphenylsilane is obtained, and the product is sequentially subjected to solvent removal, water washing and vacuum drying to obtain white powdery poly diphenylsilane.
Preferably, in the step (2), the molar ratio of the sodium metal to the diphenyldichlorosilane is 2: 1-3: 1; the mass ratio of the metal sodium to the dimethylbenzene is 1: 1-1: 3.
Preferably, in the step (3), the polydimethylsilane synthesized in the step (1) is firstly put into a cracking kettle to be vacuumized, a vacuum valve of the cracking kettle is closed after the polydimethylsilane is vacuumized to-0.08 MPa to-0.10 MPa, then nitrogen is introduced into the cracking kettle, the pressure of the cracking kettle is maintained for 15 to 24 hours when the pressure is 0.02 to 0.04MPa, then the cracking kettle is heated and stirred after the pyrolysis kettle is vacuumized to less than-0.09 MPa, and the temperature is kept for 1 to 2 hours when the temperature of the cracking kettle is heated to 200 ℃ for removing the residual solvent of the polydimethylsilane; and finally, introducing nitrogen into the cracking kettle to ensure that the pressure in the cracking kettle is 0.02Mpa, condensing gas generated by cracking in the cracking kettle, and finally collecting the first micromolecule mixed liquid through a first micromolecule liquid tank.
Preferably, in the step (4), the poly diphenylsilane synthesized in the step (2) is firstly put into a cracking kettle for vacuumizing, when the vacuum degree is between-0.08 and-0.10 MPa, a vacuum valve of the cracking kettle is closed, then nitrogen is introduced into the cracking kettle, when the pressure in the cracking kettle is between 0.02 and 0.04MPa, the pressure is maintained for 15 to 24 hours, then the cracking kettle is vacuumized to less than-0.09 MPa, the cracking kettle is heated and stirred, and when the temperature of the cracking kettle is heated to 200 ℃, the temperature is kept for 1 to 2 hours for removing the residual solvent of the poly diphenylsilane; and finally, introducing nitrogen into the cracking kettle to ensure that the pressure in the cracking kettle is 0.02Mpa, condensing gas generated by cracking in the cracking kettle, and finally collecting second micromolecule mixed liquid through a second micromolecule liquid tank.
Preferably, in the step (5), the first small molecule mixed solution and the second small molecule mixed solution are put into a synthesis kettle according to the mass ratio of 10: 1-100: 1, then nitrogen is introduced to adjust the pressure in the synthesis kettle to 0.2-0.8 Mpa, then the nitrogen introduction is stopped, the pressure in the synthesis kettle 3 is kept to 0.2-0.8 Mpa, then the synthesis kettle is heated and stirred, when the temperature in the synthesis kettle reaches 300 ℃, a reflux device is started, when the temperature in the synthesis kettle reaches 350 ℃, the reflux device is closed after the temperature is kept for 2-3 hours, when the temperature in the synthesis kettle is increased to 400-600 ℃, the liquid in the synthesis kettle is filtered and cooled for 48 hours in sequence after the temperature is kept for 20-80 hours, and the polycarbosilane containing phenyl is obtained.
From the above description of the structure of the present invention, compared with the prior art, the present invention has the following advantages:
the invention firstly synthesizes polydimethylsilane and polydiphenylsilane respectively as raw materials, then carries out pyrolysis on the polydimethylsilane and polydiphenylsilane respectively to collect corresponding micromolecule mixed liquid, then puts the mixture into a synthesis kettle according to a certain proportion, more effectively controls the content of phenyl in polycarbosilane, enables the ratio of silicon to carbon to be adjustable, optimizes the composition structure of PCS, finally obtains novel polycarbosilane containing phenyl with better spinnability (wherein the softening point of the polycarbosilane containing phenyl is 200-250 ℃, the molecular weight is 1100-1600, continuous SiC fiber with the tensile strength of 3.48GPa can be obtained through melt spinning, non-melt processing and high-temperature sintering), PCS fiber can be continuously spun, the surface of the fiber is smooth, the broken ends are few, the non-melt uniformity is good, the free carbon is few after high-temperature sintering, the inner part and the surface of the fiber are also smooth, the fiber diameter is thinner, thereby further improving the mechanical property of SiC of the fiber.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a chemical structural formula of a novel polycarbosilane ceramic precursor material of the invention;
FIG. 2 is a synthetic route diagram according to the present invention;
FIG. 3 is a process flow diagram of the present invention;
FIG. 4 is a graph of the tensile strength of the novel phenyl-containing polycarbosilane synthesized by the method provided by the invention;
FIG. 5 is a chart showing the tensile strength of Mark type II PCS of the prior art in Table 2.
In the figure: 1. a cracking kettle; 2. a cracking kettle; 3. a synthesis kettle; 4 small molecule liquid tank; 5. a small molecule liquid tank; 6. a reflux tank; 7. a buffer tank; 8. a finished product tank; 9. a constant pressure device; 10. a vacuum pump; 11. a nitrogen tank; 12, a vacuum pump; 13. a nitrogen tank; 14. a nitrogen tank; 15. a condenser; 16. a condenser; 17. a condenser; 18. a filter; 19. a vacuum valve of the cracking kettle; 20. a nitrogen valve of the cracking kettle; 21. a vacuum valve of the cracking kettle; 22. a nitrogen valve of the cracking kettle; 23. a metering pump valve; 24. a metering pump valve; 25. a constant pressure valve; 26. nitrogen valve of synthesis kettle.
Detailed Description
The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
Example 1
Referring to fig. 1, 2 and 3, a novel polycarbosilane ceramic precursor material has a chemical structural formula:
wherein m1, m2, m3 and m4 are positive integers, m is more than or equal to 1, and the ratio of (m 1+ m2+ m 4) to m3 is 10: 1-100: 1.
A process flow chart of the preparation method of the novel polycarbosilane ceramic precursor material is shown in figure 2, and the preparation method comprises the following steps:
(1) Synthesis of polydimethylsilane
Melting metal sodium in a xylene solvent at 100 ℃, then dropwise adding dimethyl dichlorosilane into a reaction kettle at a certain speed, starting to perform Wurtz coupling reaction, wherein the dropwise adding time is 10 hours, controlling the reaction temperature to be 110 ℃ after the dropwise adding of dichlorodimethylsilane is finished, obtaining polydimethylsiloxane after the total time from the dropwise adding to the reaction is 24 hours, removing a product by using the solvent, washing with water and performing vacuum drying to obtain white powdery polydimethylsiloxane; the reaction equation is shown as follows:
(2) Synthesis of polydiphenylsilane
Melting metal sodium in a xylene solvent at 100 ℃, then dropwise adding diphenyldichlorosilane into a reaction kettle at a certain speed, beginning to perform Wurtz coupling reaction, wherein the dropwise adding time is 10 hours, controlling the reaction temperature to be 110 ℃ after the dropwise adding of the diphenyldichlorosilane is finished, obtaining polydiphenylsilane after the total time from the dropwise adding to the reaction is 24 hours, removing the product by using the solvent, washing with water and drying in vacuum to obtain white powdery polydiphenylsilane; the reaction equation is shown as follows:
(3) Pyrolysis of polydimethylsilanes
Adding the polydimethylsilane into a cracking kettle 1, opening a vacuum valve 19 of the cracking kettle, starting a vacuum pump 10, vacuumizing to-0.08 MPa, closing the vacuum valve 19 of the cracking kettle, opening a nitrogen valve 20 of the cracking kettle, introducing nitrogen, keeping the pressure in the cracking kettle 1 at 0.02MPa, and maintaining the pressure for 15 hours. Then, vacuumizing the cracking kettle 1 to be less than-0.09 MPa, starting a stirring device and a heating device of the cracking kettle 1, and keeping the temperature for 1h when the temperature in the cracking kettle 1 is heated to 200 ℃, so that the polydimethylsilane in the cracking kettle 1 is continuously stirred at high temperature and low pressure for removing the residual solvent of the polydimethylsilane;
closing a vacuum valve 19 of the cracking kettle, closing a vacuum pump 10, opening a nitrogen valve 20 of the cracking kettle, introducing nitrogen, enabling the pressure in the cracking kettle 1 to be 0.02Mpa, condensing gas generated by cracking in the cracking kettle 1 through a condenser 15, collecting the gas into the micromolecule liquid tank 4, heating the temperature in the cracking kettle 1 to 250 ℃ in the process, recording the liquid level of the micromolecule liquid tank 4 in every 20min, and closing a heating device and a stirring device of the cracking kettle 1 when the three recorded values of the micromolecule liquid tank 4 are the same so as to obtain a first micromolecule mixed liquid;
(4) Pyrolysis of polydiphenylsilane
Putting polydiphenylsilane into a cracking kettle 2, opening a vacuum valve 21 of the cracking kettle, starting a vacuum pump 12, vacuumizing to-0.08 MPaMPa, closing the vacuum valve 21 of the cracking kettle, opening a nitrogen valve 22 of the cracking kettle, introducing nitrogen to ensure that the pressure in the cracking kettle 2 is 0.02MPa, and maintaining the pressure for 15h. Then, after the cracking kettle 2 is vacuumized to less than-0.09 MPa, a stirring device and a heating device of the cracking kettle 2 are started, when the temperature in the cracking kettle 2 is heated to 200 ℃, the temperature is kept for 1h, so that the poly diphenyl silane in the cracking kettle 2 is continuously stirred at high temperature and low pressure for removing the residual solvent of the poly diphenyl silane;
closing a vacuum valve 21 of the cracking kettle, closing a vacuum pump 12, opening a nitrogen valve 22 of the cracking kettle, introducing nitrogen, enabling the pressure in the cracking kettle 2 to be 0.02Mpa, condensing gas generated by cracking in the cracking kettle 2 through a condenser 17, collecting the gas into the micromolecule liquid tank 5, heating the temperature in the cracking kettle 2 to 250 ℃ in the process, recording the liquid level of the micromolecule liquid tank 5 in every 20min, and closing a heating device and a stirring device of the cracking kettle 2 when the three recorded values of the micromolecule liquid tank 5 are the same so as to obtain a second micromolecule mixed liquid;
(5) Synthesis of first small molecule mixed solution and second small molecule mixed solution
Putting the first small molecule mixed solution and the second small molecule mixed solution into a synthesis kettle 3 through a metering pump according to the mass ratio of 10: 1-100: 1, opening a nitrogen valve 26 of the synthesis kettle, introducing nitrogen, adjusting the pressure in the synthesis kettle 3 to 0.2Mpa, closing the nitrogen valve 26 of the synthesis kettle, and keeping the pressure in the synthesis kettle 3 to be 0.2Mpa; and then, starting a stirring device and a heating device of the synthesis kettle 3, controlling the temperature in the synthesis kettle 3 to be 300 ℃, starting a reflux device, preserving heat for 2 hours when the temperature in the synthesis kettle 3 is raised to 350 ℃, closing the reflux device, discharging the liquid in the synthesis kettle 3 into a buffer tank 7 through a filter 18 after the temperature in the synthesis kettle 3 is raised to 400 ℃ and preserved for 20 hours, and then discharging into a finished product tank 8, so that the polycarbosilane containing phenyl is obtained after the polycarbosilane high-temperature fluid material is cooled for 48 hours in the finished product tank.
Example 2
Referring to fig. 1, 2 and 3, a novel polycarbosilane ceramic precursor material has a chemical structural formula:
wherein m1, m2, m3 and m4 are positive integers, and m is more than or equal to 1, wherein the ratio of (m 1+ m2+ m 4) to m3 is 10: 1-100: 1.
A process flow chart of the preparation method of the novel polycarbosilane ceramic precursor material is shown in figure 2, and the preparation method comprises the following steps:
(1) Synthesis of polydimethylsilane
Melting metal sodium in a xylene solvent at 110 ℃, then dropwise adding dimethyldichlorosilane into a reaction kettle at a certain speed, starting to perform Wurtz coupling reaction, wherein the dropwise adding time is 15h, controlling the reaction temperature to be 120 ℃ after the dropwise adding of dichlorodimethylsilane is finished, obtaining polydimethylsilane after the total time from the dropwise adding to the reaction is 37h, removing a product through the solvent, washing and performing vacuum drying to obtain white powdery polydimethylsilane; the reaction equation is shown as follows:
(2) Synthesis of polydiphenylsilane
Melting metal sodium in a xylene solvent at 110 ℃, then dropwise adding diphenyldichlorosilane into a reaction kettle at a certain speed, beginning to perform Wurtz coupling reaction, wherein the dropwise adding time is 15 hours, controlling the reaction temperature to be 130 ℃ after the dropwise adding of the diphenyldichlorosilane is finished, obtaining polydiphenylsilane after the total time from the dropwise adding to the reaction is 37 hours, removing the product by using the solvent, washing with water and drying in vacuum to obtain white powdery polydiphenylsilane; the reaction equation is shown as follows:
(3) Pyrolysis of polydimethylsilanes
Adding polydimethyl silane into cracking kettle 1, opening vacuum valve 19, starting vacuum pump 10, vacuumizing to-0.08 MPa-0.10 MPa, closing vacuum valve 19, opening nitrogen valve 20, introducing nitrogen to make pressure in cracking kettle 1 be 0.03MPa, and maintaining pressure for 20 hr. Then, vacuumizing the cracking kettle 1 to be less than-0.09 MPa, starting a stirring device and a heating device of the cracking kettle 1, and keeping the temperature for 1.5 hours when the temperature in the cracking kettle 1 is heated to 200 ℃, so that the polydimethylsilane in the cracking kettle 1 is continuously stirred at high temperature and low pressure for removing the residual solvent of the polydimethylsilane;
closing a vacuum valve 19 of the cracking kettle, closing a vacuum pump 10, opening a nitrogen valve 20 of the cracking kettle, introducing nitrogen, enabling the pressure in the cracking kettle 1 to be 0.02Mpa, condensing gas generated by cracking in the cracking kettle 1 through a condenser 15, collecting the gas into the micromolecule liquid tank 4, heating the temperature in the cracking kettle 1 to 335 ℃ in the process, recording the liquid level of the micromolecule liquid tank 4 every 20min, and closing a heating device and a stirring device of the cracking kettle 1 when the three recorded values of the micromolecule liquid tank 4 are the same to obtain a first micromolecule mixed solution;
(4) Pyrolysis of polydiphenylsilane
Putting polydiphenylsilane into a cracking kettle 2, opening a vacuum valve 21 of the cracking kettle, starting a vacuum pump 12, vacuumizing to-0.09 MPa, closing the vacuum valve 21 of the cracking kettle, opening a nitrogen valve 22 of the cracking kettle, introducing nitrogen to ensure that the pressure in the cracking kettle 2 is 0.03MPa, and maintaining the pressure for 19 hours. Then, after the cracking kettle 2 is vacuumized to be less than-0.09 MPa, a stirring device and a heating device of the cracking kettle 2 are started, when the temperature in the cracking kettle 2 is heated to 200 ℃, the temperature is kept for 1.5h, and the poly-diphenylsilane in the cracking kettle 2 is continuously stirred at high temperature and low pressure for removing the residual solvent of the poly-diphenylsilane;
closing a vacuum valve 21 of the cracking kettle, closing a vacuum pump 12, opening a nitrogen valve 22 of the cracking kettle, introducing nitrogen, enabling the pressure in the cracking kettle 2 to be 0.02Mpa, condensing gas generated by cracking in the cracking kettle 2 through a condenser 17, collecting the gas into the micromolecule liquid tank 5, heating the temperature in the cracking kettle 2 to 335 ℃ in the process, recording the liquid level of the micromolecule liquid tank 5 in every 20min, and closing a heating device and a stirring device of the cracking kettle 2 when the three recorded values of the micromolecule liquid tank 5 are the same so as to obtain a second micromolecule mixed liquid;
(5) Synthesis of first small molecule mixed solution and second small molecule mixed solution
Putting the first small molecule mixed solution and the second small molecule mixed solution into a synthesis kettle 3 through a metering pump according to the mass ratio of 10: 1-100: 1, opening a nitrogen valve 26 of the synthesis kettle, introducing nitrogen, adjusting the pressure in the synthesis kettle 3 to 0.5Mpa, closing the nitrogen valve 26 of the synthesis kettle, and keeping the pressure in the synthesis kettle 3 to be 0.5Mpa; and then, starting a stirring device and a heating device of the synthesis kettle 3, controlling the temperature in the synthesis kettle 3 to be 300 ℃, starting a reflux device, keeping the temperature for 2.5 hours when the temperature in the synthesis kettle 3 is raised to 350 ℃, closing the reflux device, discharging the liquid in the synthesis kettle 3 into a buffer tank 7 through a filter 18 after the temperature in the synthesis kettle 3 is raised to 500 ℃ and kept for 50 hours, and discharging into a finished product tank 8 to obtain the polycarbosilane containing phenyl after the polycarbosilane high-temperature fluid material is cooled for 48 hours in the finished product tank.
Example 3
Referring to fig. 1, fig. 2 and fig. 3, a novel polycarbosilane ceramic precursor material has a chemical structural formula:
wherein m1, m2, m3 and m4 are positive integers, and m is more than or equal to 1, wherein the ratio of (m 1+ m2+ m 4) to m3 is 10: 1-100: 1.
A process flow chart of the preparation method of the novel polycarbosilane ceramic precursor material is shown in figure 2, and the preparation method comprises the following steps:
(1) Synthesis of polydimethylsilane
Melting metal sodium in a xylene solvent at 120 ℃, then dropwise adding dimethyl dichlorosilane into a reaction kettle at a certain speed, starting to perform Wurtz coupling reaction, wherein the dropwise adding time is 20 hours, controlling the reaction temperature to be 140 ℃ after the dropwise adding of dichlorodimethylsilane is finished, obtaining polydimethylsiloxane after the total time from the dropwise adding to the reaction is 50 hours, removing a product by using the solvent, washing with water and performing vacuum drying to obtain white powdery polydimethylsiloxane; the reaction equation is shown as follows:
(2) Synthesis of polydiphenylsilane
Melting metal sodium in a xylene solvent at 120 ℃, then dropwise adding diphenyl dichlorosilane into a reaction kettle at a certain speed, starting to perform a Wurtz coupling reaction, wherein the dropwise adding time is 20h, controlling the reaction temperature to be 150 ℃ after the dropwise adding of the diphenyl dichlorosilane is finished, obtaining poly (diphenyl silane) after the total time from the dropwise adding to the reaction is 50h, removing a product through the solvent, washing and drying in vacuum to obtain white powdery poly (diphenyl silane); the reaction equation is shown as follows:
(3) Pyrolysis of polydimethylsilanes
Adding the polydimethylsilane into a cracking kettle 1, opening a vacuum valve 19 of the cracking kettle, starting a vacuum pump 10, vacuumizing to-0.10 MPa, closing the vacuum valve 19 of the cracking kettle, opening a nitrogen valve 20 of the cracking kettle, introducing nitrogen, keeping the pressure in the cracking kettle 1 at 0.04MPa, and maintaining the pressure for 24 hours. Then, vacuumizing the cracking kettle 1 to be less than-0.09 MPa, starting a stirring device and a heating device of the cracking kettle 1, and keeping the temperature for 2 hours when the temperature in the cracking kettle 1 is heated to 200 ℃, so that the polydimethylsilane in the cracking kettle 1 is continuously stirred at high temperature and low pressure for removing the residual solvent of the polydimethylsilane;
closing a vacuum valve 19 of the cracking kettle, closing a vacuum pump 10, opening a nitrogen valve 20 of the cracking kettle, introducing nitrogen, enabling the pressure in the cracking kettle 1 to be 0.02Mpa, condensing gas generated by cracking in the cracking kettle 1 through a condenser 15, collecting the gas into the micromolecule liquid tank 4, heating the temperature in the cracking kettle 1 to 420 ℃ in the process, recording the liquid level of the micromolecule liquid tank 4 in every 20min, and closing a heating device and a stirring device of the cracking kettle 1 when the three recorded values of the micromolecule liquid tank 4 are the same so as to obtain a first micromolecule mixed liquid;
(4) Pyrolysis of polydiphenylsilane
Putting polydiphenylsilane into a cracking kettle 2, opening a vacuum valve 21 of the cracking kettle, starting a vacuum pump 12, vacuumizing to-0.10 MPa, closing the vacuum valve 21 of the cracking kettle, opening a nitrogen valve 22 of the cracking kettle, introducing nitrogen to ensure that the pressure in the cracking kettle 2 is 0.04MPa, and maintaining the pressure for 24 hours. Then, after the cracking kettle 2 is vacuumized to be less than-0.09 MPa, a stirring device and a heating device of the cracking kettle 2 are started, when the temperature in the cracking kettle 2 is heated to 200 ℃, the temperature is kept for 2 hours, so that the poly-diphenylsilane in the cracking kettle 2 is continuously stirred at high temperature and low pressure for removing the residual solvent of the poly-diphenylsilane;
closing a vacuum valve 21 of the cracking kettle, closing a vacuum pump 12, opening a nitrogen valve 22 of the cracking kettle, introducing nitrogen, enabling the pressure in the cracking kettle 2 to be 0.02Mpa, condensing gas generated by cracking in the cracking kettle 2 through a condenser 17, collecting the gas into the micromolecule liquid tank 5, heating the temperature in the cracking kettle 2 to 420 ℃ in the process, recording the liquid level of the micromolecule liquid tank 5 in every 20min, and closing a heating device and a stirring device of the cracking kettle 2 when the three recorded values of the micromolecule liquid tank 5 are the same so as to obtain a second micromolecule mixed liquid;
(5) Synthesis of first small molecule mixed solution and second small molecule mixed solution
The first micromolecule mixed liquid and the second micromolecule mixed liquid are put into a synthesis kettle 3 through a metering pump according to the mass ratio of 10: 1-100: 1, a nitrogen valve 26 of the synthesis kettle is opened, nitrogen is introduced, when the pressure in the synthesis kettle 3 is adjusted to 0.8Mpa, the nitrogen valve 26 of the synthesis kettle is closed, and the pressure in the synthesis kettle 3 is kept to be 0.8Mpa; and then, starting a stirring device and a heating device of the synthesis kettle 3, controlling the temperature in the synthesis kettle 3 to be 300 ℃, starting a reflux device, keeping the temperature for 3 hours when the temperature in the synthesis kettle 3 is raised to 350 ℃, closing the reflux device, discharging the liquid in the synthesis kettle 3 into a buffer tank 7 through a filter 18 after the temperature in the synthesis kettle 3 is raised to 600 ℃ and kept for 80 hours, and discharging into a finished product tank 8 to obtain the polycarbosilane containing phenyl after the polycarbosilane high-temperature fluid material is cooled for 48 hours in the finished product tank.
According to the invention, polydimethylsilane and polydiphenylsilane are subjected to pyrolysis respectively to collect corresponding small-molecule mixed liquid, and then the small-molecule mixed liquid is put into a synthesis kettle according to a certain proportion, so that the content of phenyl in polycarbosilane can be controlled more effectively, the silicon-carbon ratio is adjustable, and the composition structure of PCS is optimized. The finally obtained novel phenyl-containing polycarbosilane has better spinnability (wherein the softening point of the phenyl-containing polycarbosilane is 200-250 ℃, the molecular weight is 1100-1600, continuous SiC fibers with the tensile strength of 3.48GPa can be obtained through melt spinning, non-melting treatment and high-temperature sintering), PCS fibers can be continuously spun, the surfaces of the fibers are smooth, the broken ends are few, the non-melting uniformity is good, free carbon is few after high-temperature sintering, the inner and the surfaces of the fibers are also smooth, the fiber diameter is thinner, and therefore the mechanical property of the SiC fibers is further improved and the obtained SiC fibers can be obtained.
Table 1 shows the mechanical properties values measured by and respectively for the present application (samples 2 to 13), and table 2 shows the mechanical properties values measured respectively for the prior art Mark type ii PCS (samples 1 to 15).
TABLE 1
TABLE 2
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.
Claims (10)
1. A novel polycarbosilane ceramic precursor material is characterized in that the chemical structural formula is as follows:
wherein m1, m2, m3 and m4 are positive integers, and m is more than or equal to 1.
2. The novel polycarbosilane ceramic precursor material as set forth in claim 1, wherein: the ratio of (m 1+ m2+ m 4) to m3 is 10: 1-100: 1.
3. The preparation method of the novel polycarbosilane ceramic precursor material as claimed in any one of claims 1 to 2, comprising the following steps:
(1) Melting metal sodium in a xylene solvent, and adding dimethyldichlorosilane into the xylene solvent for synthesis to obtain polydimethylsilane;
(2) Melting metal sodium in a xylene solvent, and adding diphenyl dichlorosilane into the xylene solvent for synthesis to obtain poly diphenyl silane;
(3) Performing pyrolysis on the polydimethylsiloxane synthesized in the step (1) to collect first small molecule mixed liquid;
(4) Performing pyrolysis on the poly-diphenylsilane synthesized in the step (2) to collect second small molecule mixed solution;
(5) And (4) carrying out high-temperature high-pressure rearrangement synthesis on the first small molecule mixed solution obtained in the step (3) and the second small molecule mixed solution obtained in the step (4) according to a certain mass ratio to obtain the phenyl-containing polycarbosilane, wherein the softening point of the phenyl-containing polycarbosilane is 200-250 ℃, and the molecular weight of the phenyl-containing polycarbosilane is 1100-1600.
4. The method for preparing a novel polycarbosilane ceramic precursor material as claimed in claim 3, wherein the method comprises the following steps: in the step (1), the temperature of a xylene solvent is controlled to be between 100 and 120 ℃, the dripping time of the dimethyldichlorosilane is 10 to 20 hours, the reaction temperature is controlled to be between 110 and 140 ℃ after the dripping is finished, the total time from the dripping to the reaction is 24 to 50 hours, the polydimethylsilane is obtained, and the product is sequentially subjected to solvent removal, water washing and vacuum drying to obtain white powdery polydimethylsilane.
5. The method for preparing a novel polycarbosilane ceramic precursor material as claimed in claim 3, wherein the method comprises the following steps: in the step (1), the molar ratio of the metal sodium to the dimethyldichlorosilane is 2: 1-3: 1; the mass ratio of the metal sodium to the dimethylbenzene is 1: 1-1: 3.
6. The method for preparing a novel polycarbosilane ceramic precursor material as claimed in claim 3, wherein the method comprises the following steps: in the step (2), the temperature of the xylene solvent is controlled between 100 ℃ and 120 ℃, the dripping time of the diphenyl dichlorosilane is 10 to 20 hours, the reaction temperature is controlled between 110 ℃ and 140 ℃ after the dripping is finished, the total time from the dripping to the reaction is 24 to 50 hours, the poly diphenyl silane is obtained, and the product is sequentially subjected to solvent removal, water washing and vacuum drying to obtain white powdery poly diphenyl silane.
7. The preparation method of the novel polycarbosilane ceramic precursor material as claimed in claim 3, wherein the preparation method comprises the following steps: in the step (2), the molar ratio of the metal sodium to the diphenyl dichlorosilane is 2: 1-3: 1; the mass ratio of the metal sodium to the dimethylbenzene is 1: 1-1: 3.
8. The method for preparing a novel polycarbosilane ceramic precursor material as claimed in claim 3, wherein the method comprises the following steps: in the step (3), firstly putting the polydimethylsilane synthesized in the step (1) into a cracking kettle for vacuumizing, closing a vacuum valve of the cracking kettle after vacuumizing to-0.08 MPa to-0.10 MPa, then introducing nitrogen into the cracking kettle, keeping the pressure of the cracking kettle for 15-24 hours when the pressure of the cracking kettle is 0.02-0.04 MPa, then vacuumizing the cracking kettle to less than-0.09 MPa, heating and stirring the cracking kettle, and keeping the temperature for 1-2 hours when the temperature of the cracking kettle is heated to 200 ℃ for removing the residual solvent of the polydimethylsilane; and finally, introducing nitrogen into the cracking kettle to ensure that the pressure in the cracking kettle is 0.02Mpa, condensing gas generated by cracking in the cracking kettle, and finally collecting the first micromolecule mixed liquid through a first micromolecule liquid tank.
9. The method for preparing a novel polycarbosilane ceramic precursor material as claimed in claim 3, wherein the method comprises the following steps: in the step (4), the poly diphenylsilane synthesized in the step (2) is firstly put into a cracking kettle for vacuumizing, when the vacuum is vacuumized to-0.08 MPa to-0.10 MPa, a vacuum valve of the cracking kettle is closed, then nitrogen is introduced into the cracking kettle, when the pressure in the cracking kettle is 0.02 to 0.04MPa, the pressure is maintained for 15 to 24 hours, then the cracking kettle is vacuumized to less than-0.09 MPa, the cracking kettle is heated and stirred, and when the temperature of the cracking kettle is heated to 200 ℃, the temperature is maintained for 1 to 2 hours for removing the residual solvent of the poly diphenylsilane; and finally, introducing nitrogen into the cracking kettle to ensure that the pressure in the cracking kettle is 0.02Mpa, condensing gas generated by cracking in the cracking kettle, and finally collecting second micromolecule mixed liquid through a second micromolecule liquid tank.
10. The method for preparing a novel polycarbosilane ceramic precursor material as claimed in claim 3, wherein the method comprises the following steps: in the step (5), the first small molecule mixed liquid and the second small molecule mixed liquid are put into a synthesis kettle according to the mass ratio of 10: 1-100: 1, then nitrogen is introduced to adjust the pressure in the synthesis kettle to 0.2-0.8 Mpa, the nitrogen introduction is stopped, the pressure in the synthesis kettle 3 is kept to 0.2-0.8 Mpa, then the synthesis kettle is heated and stirred, when the temperature in the synthesis kettle reaches 300 ℃, a reflux device is started, when the temperature in the synthesis kettle reaches 350 ℃, the reflux device is closed after the temperature is kept for 2-3 hours, when the temperature in the synthesis kettle is raised to 400-600 ℃, the liquid in the synthesis kettle is filtered and cooled for 48 hours in sequence after the temperature is kept for 20-80 hours, and the phenyl-containing polycarbosilane is obtained.
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