Ceramic precursor and preparation method thereof

Abstract

The invention provides a ceramic precursor and a preparation method thereof, and relates to the technical field of ceramic materials.The preparation method comprises the steps that 1, a system containing metal lithium and a first organic solvent is placed in an ice salt bath, then dimethyl phenyl chlorosilane and methyl phenyl dichlorosilane are dropwise added into the system in sequence for a reaction, and a reaction product is obtained; adding triphenyl pentamethyl trisilane to obtain triphenyl pentamethyl trisilane; (2) triphenylpentamethyltrisilane and a chlorinating agent are added into a second organic solvent for a substitution reaction, and trichloropentamethyltrisilane is obtained; (3) adding trichloropentamethylpropyl silane into a second organic solvent, uniformly mixing, and then adding metal sodium to carry out coupling reaction, so as to obtain hyperbranched polysilane; and cracking the hyperbranched polysilane to obtain a ceramic precursor. The ceramic precursor provided by the scheme has a hyperbranched structure, is narrow in molecular weight distribution and excellent in solubility, does not need complex or expensive equipment, and is higher in yield.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, and in particular to a ceramic precursor and its preparation method. Background Technology

[0002] Ceramic precursors are crucial for the preparation of continuous ceramic fibers, and their properties play a decisive role in the quality of the ceramic fibers. Currently, in industry, ceramic precursors are mainly prepared through the cracking reaction of polysilanes under the action of a catalyst, and the properties of the ceramic precursors have a vital impact on the reaction efficiency and the quality of the products.

[0003] While traditional linear polysilanes can be used to prepare ceramic precursors, they suffer from inherent drawbacks: firstly, they are insoluble in hydrocarbon solvents, resulting in poor processability; secondly, they are prone to volatilization during pyrolysis, leading to low ceramic yields and affecting the properties of ceramic fibers. Chinese patent CN115466397A discloses a method for preparing polycarbosilane ceramic precursors. This method involves adding polydimethylsilane to a pyrolysis reactor, employing a high-temperature, high-pressure method, and using nitrogen and hydrogen for displacement while controlling the pressure to obtain polycarbosilane. However, this method requires sophisticated equipment and maintenance, resulting in high costs. Furthermore, the pyrolysis reactor exhibits significant temperature gradients at different locations, leading to severe coking of the reactor walls and consequently, low yields and a wide molecular weight distribution of the obtained polycarbosilane. Therefore, there is an urgent need for a ceramic precursor and its preparation method. Summary of the Invention

[0004] This invention provides a ceramic precursor and its preparation method. The ceramic precursor obtained by this preparation method has a hyperbranched structure, a narrow molecular weight distribution, excellent solubility, and does not require complex or expensive equipment, resulting in a higher yield.

[0005] In a first aspect, embodiments of the present invention provide a method for preparing a ceramic precursor, the method comprising: (1) The system containing lithium metal and the first organic solvent was placed in an ice-salt bath, and then dimethylphenylchlorosilane and methylphenyldichlorosilane were added dropwise to the system in sequence and reacted to obtain triphenylpentamethyltrisilane; (2) Triphenylpentamethyltrisilane and a chlorinating agent were added to a second organic solvent to carry out a substitution reaction to obtain trichloropentamethylpropane; (3) Trichloropentamethylpropylsilane is added to the second organic solvent and mixed well, and then sodium metal is added to carry out a coupling reaction to obtain hyperbranched polysilane; the hyperbranched polysilane is cracked to obtain the ceramic precursor.

[0006] Preferably, in step (1), the molar ratio of lithium metal to dimethylphenylchlorosilane is (2~3):1.

[0007] Preferably, in step (1), the molar ratio of dimethylphenylchlorosilane to methylphenyldichlorosilane is (2~3):1.

[0008] Preferably, in step (1): the temperature of the ice-salt bath is -5 to -20°C; the first organic solvent includes tetrahydrofuran, toluene, or diethyl ether.

[0009] Preferably, in step (1): the dripping rate is 1~2 mL / h.

[0010] Preferably, step (1) includes the following sub-steps: (11) Add dimethylphenylchlorosilane dropwise to the system. After the addition is complete, heat the system to 20-25°C and keep it at that temperature for 1-2 hours. Then, continue to place the system in the ice-salt bath and continue to add methylphenyldichlorosilane dropwise. After the addition is complete, react for 5-6 hours to obtain the initial product containing triphenylpentamethyltrisilane. (12) After adding a quencher to the initial product, extraction is performed. The extracted organic phase is then dried, filtered, and distilled under reduced pressure to obtain triphenylpentamethyltrisilane.

[0011] Preferably, in step (2): the chlorinating agent is acetyl chloride; the second organic solvent includes n-hexane, toluene or xylene.

[0012] Preferably, in step (2), the molar ratio of the chlorinating agent to triphenylpentamethyltrisilane is (6~8):1.

[0013] Preferably, step (2) includes the following sub-steps: (21) Triphenylpentamethyltrisilane was added to a second organic solvent and mixed well. Then, the chlorinating agent and catalyst were added at an initial temperature of 0-5°C to carry out a substitution reaction to obtain a reaction product containing trichloropentamethylpropane. (22) The reaction product was filtered, washed and distilled under reduced pressure to obtain trichloropentamethylpropane.

[0014] Preferably, in step (3), the molar ratio of sodium metal to trichloropentamethylpropylsilane is (3~4):1.

[0015] Preferably, in step (3): the temperature of the coupling reaction is 100~120℃ and the time is 2~4h.

[0016] Preferably, step (3) includes the following sub-steps: (31) Trichloropentamethylpropane was added to the second organic solvent and mixed well. Then, sodium metal was added to carry out a coupling reaction. After the reaction was completed, the reaction product was obtained. (32) The reaction product was subjected to vacuum distillation, dissolution, filtration, washing, addition of quencher, addition of terminator, and vacuum distillation in sequence to obtain hyperbranched polysilane.

[0017] Preferably, in step (3): the hyperbranched polysilane is cracked using a hollow catalyst to obtain the ceramic precursor; the amount of the hollow catalyst is 0.5wt%~1wt% of the amount of the hyperbranched polysilane; wherein, the hollow catalyst comprises, from the inside out, hollow titanium dioxide spheres, a silicon dioxide intermediate layer and an active outer layer; the mass ratio of the hollow titanium dioxide spheres to the silicon dioxide intermediate layer is (1~10):(1~10); the active outer layer comprises Pt and Ni; the active outer layer accounts for 1wt%~2wt% of the hollow catalyst.

[0018] In a second aspect, the present invention also provides a ceramic precursor, which is prepared by any of the methods for preparing ceramic precursors in the first aspect described above.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The hyperbranched polysilane of the present invention uses trichloropentamethylpropylsilane as a raw material to prepare a ceramic precursor containing tertiary silicon branched units and linear silicon units. In contrast, when monosilanes are used as raw materials, different chemical affinities are introduced into the polymer chain, which may lead to the formation of irregular, even linear or network structures, resulting in insoluble structures. The present invention uses a silane containing three silicon atoms as a raw material, which can form a polymer with high branching and high silicon content, breaking through the crystallinity limitation of linear polysilanes, thereby ensuring that the hyperbranched polysilane has excellent solubility in hydrocarbon solvents.

[0020] (2) The trichlorosubstituted propane monomer used in this invention contains pre-branched units, which form a regular hyperbranched structure after polymerization, resulting in a narrow molecular weight distribution and avoiding performance fluctuations caused by irregular copolymerization. At the same time, since the prepared hyperbranched polysilane has excellent solubility, its heat transfer performance in the liquid state is better than that of existing polydimethylsilane powder. Therefore, it can further reduce the pyrolysis reaction temperature and shorten the reaction time, making the pyrolysis reaction more uniform, reducing charring of the reactor wall, increasing the yield, and obtaining a ceramic precursor with a narrow molecular weight distribution. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The following is the concept of the present invention, which provides a method for preparing a ceramic precursor, comprising: (1) The system containing lithium metal and the first organic solvent was placed in an ice-salt bath, and then dimethylphenylchlorosilane and methylphenyldichlorosilane were added dropwise to the system in sequence and reacted to obtain triphenylpentamethyltrisilane; (2) Triphenylpentamethyltrisilane and a chlorinating agent were added to a second organic solvent to carry out a substitution reaction to obtain trichloropentamethylpropane; (3) Trichloropentamethylpropane was added to a second organic solvent and mixed well. Then sodium metal was added to carry out a coupling reaction to obtain hyperbranched polysilane. The hyperbranched polysilane was then cracked to obtain a ceramic precursor.

[0023] In this invention, triphenylpentamethyltrisilane was first prepared, and then subjected to a chlorination reaction to obtain trichloropentamethylpropane. Using trichloropentamethylpropane as a raw material, a ceramic precursor containing tertiary silicon branched units and linear silicon units was prepared. In contrast, when using monosilanes as raw materials, different chemical affinities are introduced into the polymer chain, which may lead to the formation of irregular, even linear or network structures, resulting in insoluble structures. This invention uses a silane containing three silicon atoms as a raw material, which can form polymers with high branching and high silicon content, overcoming the crystallinity limitations of linear polysilanes, thereby ensuring that the hyperbranched polysilane has excellent solubility in hydrocarbon solvents.

[0024] This invention utilizes trichlorosubstituted propane monomers pre-containing branched units, which, after polymerization, form a regular hyperbranched structure with a narrow molecular weight distribution, avoiding performance fluctuations caused by irregular copolymerization. Simultaneously, the prepared hyperbranched polysilane exhibits excellent solubility and superior heat transfer performance in the liquid state compared to existing polydimethylsilane powders. Therefore, it can further reduce the pyrolysis reaction temperature and shorten the reaction time, resulting in a more uniform pyrolysis reaction, reduced charring on the reactor wall, and increased yield, ultimately yielding a ceramic precursor with a narrow molecular weight distribution.

[0025] In a preferred embodiment, in step (1): the molar ratio of lithium metal to dimethylphenylchlorosilane is (2~3):1 (for example, it can be 2:1, 2.2:1, 2.5:1, 2.6:1, 2.8:1 or 3:1).

[0026] In a preferred embodiment, in step (1), the molar ratio of dimethylphenylchlorosilane to methylphenyldichlorosilane is (2~3):1 (for example, it can be 2:1, 2.2:1, 2.5:1, 2.6:1, 2.8:1 or 3:1).

[0027] It should be noted that the chemical structural formula of methylphenyldichlorosilane is as follows: .

[0028] Specifically, the chemical formula for the reaction between lithium metal and dimethylphenylchlorosilane is as follows: 2Li+C6H5-Si(CH3)2Cl→C6H5-Si(CH3)2Li+LiCl The chemical formula for the reaction between dimethylphenyllithium silane and methylphenyldichlorosilane is as follows: 2C6H5-Si(CH3)2Li+C6H5-Si(CH3)Cl2→C6H5-Si(CH3)2-Si(CH3)(C6H5)-Si(CH3)2-C6H5+2LiCl.

[0029] In this invention, adding an excess of lithium ensures that dimethylphenylchlorosilane reacts fully. Thus, adding a slightly excess of methylphenyldichlorosilane ensures that the obtained dimethylphenyllithium silane reacts fully, further improving the yield of triphenylpentamethyltrisilane.

[0030] In a preferred embodiment, in step (1): the temperature of the ice-salt bath is -5 to -20°C (for example, it can be -5°C, -8°C, -10°C, -12°C, -15°C, -18°C or -20°C); the first organic solvent includes tetrahydrofuran, toluene or diethyl ether.

[0031] It should be noted that the first organic solvent does not contain water to avoid a violent reaction between lithium and water.

[0032] In a preferred embodiment, in step (1): the dripping rate is 1~2 mL / h (for example, it can be 1 mL / h, 1.2 mL / h, 1.5 mL / h, 1.8 mL / h or 2 mL / h).

[0033] In a preferred embodiment, step (1) includes the following sub-steps: (11) Add dimethylphenylchlorosilane dropwise to the system. After the addition is complete, heat the system to 20-25°C (e.g., 20°C, 21°C, 22°C, 23°C, 24°C or 25°C) and keep it at that temperature for 1-2 hours (e.g., 1 hour, 1.2 hours, 1.5 hours, 1.6 hours, 1.8 hours or 2 hours). Then, continue to place the system in an ice-salt bath and continue to add dimethylphenylchlorosilane dropwise. After the addition is complete, react for 5-6 hours (e.g., 5 hours, 5.2 hours, 5.5 hours, 5.8 hours or 6 hours) to obtain the initial product containing triphenylpentamethyltrisilane. (12) After adding a quencher to the initial product, extraction was performed. The extracted organic phase was then dried, filtered, and distilled under reduced pressure to obtain triphenylpentamethyltrisilane.

[0034] Specifically, for step (12), the quencher is methanol. Excess methanol is added to the initial product to quench excess lithium until no bubbles are generated. Then, deionized water and n-hexane (the volume ratio of deionized water to n-hexane is 1:1) are added to the initial product. The organic phase and the aqueous phase are then separated and collected. The aqueous phase is extracted three times with n-hexane to obtain a secondary organic phase. After mixing all the organic phases, the organic phase is dried with anhydrous MgSO4 (the amount of anhydrous MgSO4 is 1 / 10 of the volume of the organic phase). After standing for 2 hours, the solution is filtered. Then, the filtrate is subjected to vacuum distillation at 40~60℃ and 0.07~0.09MPa to remove the solvent and collect the target fraction, which yields triphenylpentamethyltrisilane.

[0035] In this invention, by controlling the ambient temperature and the dropping rate of dimethylphenylchlorosilane, the reaction activity and rate can be controlled, side reactions can be avoided, and experimental safety can be improved. Simultaneously, the α-H of the lithium-efficiently deprotonated silane can be utilized to generate a silicon-based lithium intermediate. Controlling the reaction temperature at 20-25°C ensures the reaction rate of both the intermediate dimethylphenyllithium silane and methylphenyldichlorosilane, preventing decomposition of the intermediate due to excessive temperature. Furthermore, operating under conventional conditions further reduces energy consumption. Adding dimethylphenylchlorosilane at a rate of 1-2 mL / h avoids excessive addition leading to localized high concentrations and side reactions, while also maintaining uniform dispersion of the reactants and preventing excessive exothermic reactions that could cause system runaway.

[0036] In a preferred embodiment, in step (2): the chlorinating agent is acetyl chloride; the second organic solvent includes n-hexane, toluene or xylene.

[0037] In a preferred embodiment, in step (2): the molar ratio of chlorinating agent to triphenylpentamethyltrisilane is (6~8):1 (for example, it can be 6:1, 6.2:1, 6.5:1, 6.8:1, 7:1, 7.2:1, 7.5:1, 7.8:1 or 8:1).

[0038] In a preferred embodiment, step (2) includes the following sub-steps: (21) Triphenylpentamethyltrisilane is added to a second organic solvent and mixed well. Then, a chlorinating agent and a catalyst are added at an initial temperature of 0-5°C (for example, 0°C, 0.5°C, 1°C, 1.5°C, 2°C, 2.5°C, 3°C, 3.5°C, 4°C, 4.5°C or 5°C) to carry out a substitution reaction to obtain a reaction product containing trichloropentamethylpropane. (22) The reaction products were filtered, washed and distilled under reduced pressure to obtain trichloropentamethylpropane.

[0039] It should be noted that the second organic solvent includes toluene, n-hexane, and xylene.

[0040] Specifically, step (21) can be carried out by monitoring the reaction with gas chromatography until the raw material peak disappears and the target product peak stabilizes, at which point the reaction is terminated; alternatively, the chlorinating agent and catalyst can be added in multiple steps to carry out the substitution reaction. The catalyst is anhydrous aluminum chloride, and the molar ratio of anhydrous aluminum chloride to triphenylpentamethyltrisilane is (3~4):1. Anhydrous aluminum chloride is used to catalyze the activation of Si-benzene bonds. Step (22) includes: filtering the reaction product to obtain filtrate and filter residue, washing the filter residue with n-hexane to obtain a secondary filtrate, combining all the filtrates, and distilling the filtrate under reduced pressure at 86℃ and 0.0013MPa to obtain colorless liquid trichloropentamethylpropylsilane.

[0041] In this invention, the chlorinating agent is used to replace the phenyl group in trichloropentamethylpropane. If the molar ratio of the chlorinating agent to triphenylpentamethyltrisilane is less than 6:1, the amount of chlorinating agent used is too small, the substitution is incomplete, and the yield of trichloropentamethylpropane is low. However, if the molar ratio of the chlorinating agent to triphenylpentamethyltrisilane is greater than 8:1, the excessive amount of chlorinating agent used will increase the cost.

[0042] In a more preferred embodiment, the chlorinating agent is added dropwise at a rate of 1 to 2 mL / h.

[0043] In this invention, by controlling the dropping rate of the chlorinating agent, it is possible to avoid adding too much at once, which could lead to excessively high local concentrations and trigger side reactions. At the same time, it is also possible to maintain uniform dispersion of reactants and prevent excessive exothermic reactions that could cause the system to run out of control.

[0044] In a preferred embodiment, in step (3): the molar ratio of metallic sodium to trichloropentamethylpropylsilane is (3~4):1 (for example, it can be 3:1, 3.2:1, 3.5:1, 3.6:1, 3.8:1 or 4:1).

[0045] In a preferred embodiment, in step (3): the temperature of the coupling reaction is 100~120℃ (e.g., 100℃, 105℃, 110℃, 115℃ or 120℃), and the time is 2~4h (e.g., 2h, 2.5h, 3h, 3.5h or 4h).

[0046] In this invention, sodium metal is used as a catalyst. If the molar ratio of sodium metal to trichloropentamethylpropane is less than 3:1, the reducing coupling ability is insufficient, resulting in incomplete reaction and premature termination, leading to a lower molecular weight of the product. Furthermore, the incomplete reaction results in the presence of active Si-Cl groups at the product terminals, making the product more unstable. However, if the molar ratio of sodium metal to trichloropentamethylpropane is greater than 4:1, excessive reduction occurs, triggering severe degradation side reactions. This leads to a wider molecular weight distribution of the product, and excessive byproducts also make purification of the target product difficult, thus reducing yield and purity.

[0047] In a preferred embodiment, step (3) includes the following sub-steps: (31) Trichloropentamethylpropane was added to a second organic solvent and mixed well. Then sodium metal was added to carry out a coupling reaction. After the reaction was completed, the reaction product was obtained. (32) The reaction product was subjected to vacuum distillation, dissolution, filtration, washing, addition of quencher, addition of terminator, and vacuum distillation in sequence to obtain hyperbranched polysilane.

[0048] Specifically, in step (32): the reaction product containing hyperbranched polysilane is subjected to vacuum distillation to remove the second organic solvent and other volatile compounds. Subsequently, the remaining mixture is dissolved in the second organic solvent to obtain a turbid solution, which is then filtered to remove unreacted alkali metals and alkali metal salts generated during the reaction. The solid residue is then washed again with n-hexane, and the filtered filtrate containing hyperbranched polysilane is combined with the washings. The solution is then vacuum dried to obtain a solid product. To quench unreacted Si-Cl groups, a quencher (diethyl ether solution of methyl magnesium bromide) is added to the solid product until a neutral pH (e.g., 6.8–7.2) is measured after vigorous stirring of the hydrolyzed sample of the current reaction mixture. After stirring for 1 hour, trimethylchlorosilane is added as a terminator for the silane anion chain until a slightly acidic pH (e.g., 6–6.5) is measured after vigorous stirring of the hydrolyzed sample of the current reaction mixture for 30 minutes. Excess trimethylchlorosilane was quenched again by adding a solution of methyl magnesium bromide in diethyl ether to the stirred reaction mixture. All volatile compounds and solvents were removed by vacuum drying.

[0049] In a preferred embodiment, in step (3): the hyperbranched polysilane is cracked using a hollow catalyst to obtain the ceramic precursor; the amount of the hollow catalyst is 0.5wt% to 1wt% of the amount of the hyperbranched polysilane (for example, it can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, or 1wt%); wherein, the hollow catalyst comprises, from the inside out, hollow titanium dioxide spheres, a silica intermediate layer, and an active outer layer; the mass ratio of the hollow titanium dioxide spheres to the silica intermediate layer is (1~10):(1~10); the active outer layer comprises Pt and Ni; the active outer layer accounts for 1wt% to 2wt% of the hollow catalyst (for example, it can be 1wt%, 1.2wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.8wt%, or 2wt%).

[0050] Hollow catalysts are prepared by the following method: S1: Carbon nanospheres are dispersed in a solvent, and then tetrabutyl titanate and an aqueous ethanol solution are added and mixed to obtain titanium dioxide-coated carbon nanospheres; the titanium dioxide-coated carbon nanospheres are then calcined to obtain hollow titanium dioxide spheres. S2: Disperse titanium dioxide hollow spheres in a solvent and add silica nanoparticles to mix evenly to obtain silica-coated hollow spheres; calcine the silica-coated hollow spheres to obtain a carrier; the mass ratio of titanium dioxide hollow spheres to silica intermediate layer is (1~10):(1~10). S3: The support is impregnated in a mixed solution containing chloroplatinic acid and nickel nitrate to obtain a precursor solution; the precursor solution is filtered, dried and reduced in sequence to obtain a hollow catalyst; wherein the mass ratio of Pt to Ni in the mixed solution is (1~2):(1~2).

[0051] For (1~10): (1~10), it can be any value from 1:10 to 10:1, for example, it can be 1:10, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 2:3, 2:5, 2:7, 2:9, 3:1, 3:2, 3:4, 3:8, 4:1, 4:3, 4:7, 4:9, 5:1, 5:2, 5:3, 5:9, 6:1, 6:9, 7:1, 7:9, 8:1, 8:9, 9:1 or 10:1.

[0052] For (1~2): (1~2), it can be any value from 1:2 to 2:1, for example, it can be 1:1, 1:1.5, 1:2, 1.5:1, 1.5:2, 2:1.5 or 2:1.

[0053] The hollow catalyst provided by this invention is a TiO2-SiO2 bioxide support with a hollow structure and active components loaded on its surface. This hollow core-shell nanostructure exhibits better mass transfer and charge separation efficiency, a larger surface area, and a three-dimensional heterogeneous structure compared to the same weight of bulk spheres, thus improving the reactivity and efficiency of the pyrolysis reaction. SiO2, as a composite material for the TiO2 hollow spheres, further enhances the thermal stability, mechanical strength, and surface area of ​​the TiO2 hollow spheres. Furthermore, the synergistic effect between the Pt-Ni bimetal optimizes the catalytic activity towards the reactants. Thus, the combined action of the hollow TiO2-SiO2 bioxide support and the Pt-Ni bimetal enables rapid pyrolysis of polysilanes at temperatures lower than those required by traditional platinum-based catalysts, significantly shortening the reaction time and improving production efficiency.

[0054] In this invention, the hollow TiO2-SiO2 dual oxide support also has excellent thermal stability and anti-carbon deposition properties, which effectively inhibits the carbon deposition phenomenon of the hollow catalyst during the polysilane cracking process, maintains the activity of the hollow catalyst, and further ensures that the cracking reaction can continue to proceed efficiently, thereby improving the final yield of the ceramic precursor.

[0055] In this invention, experiments have confirmed that if the mass ratio of hollow titanium dioxide spheres to the silicon dioxide interlayer is greater than 10:1, grain sintering is likely to occur at 200-400℃, leading to the collapse of the hollow structure of the support. This results in a longer mass transfer path and a significant reduction in catalytic efficiency. Secondly, if the TiO2 content is too high, the SiO2 thickness becomes thinner or even partially absent, failing to effectively encapsulate TiO2. This causes the bimetallic particles to easily agglomerate at high temperatures, leading to a sharp decline in catalytic activity. If the mass ratio of hollow titanium dioxide spheres to the silicon dioxide interlayer is less than 1:10, the amount of hollow titanium dioxide spheres is too small, making it difficult to effectively weaken the Si-C bonds. This leads to an increase in the activation energy, requiring a higher reaction temperature or a longer reaction time, thus reducing catalytic efficiency.

[0056] In this invention, the process of preparing ceramic precursors by polysilane pyrolysis includes a multi-step reaction involving Si-H bond activation, C-Si bond breaking, and chain rearrangement. By limiting the ratio of Pt and Ni in the mixed solution during impregnation, the loading of Pt and Ni on the active outer layer of the hollow catalyst can be further determined, thereby achieving synergistic effects of the multi-step reaction. Experiments have shown that if the mass ratio of Pt to Ni in the mixed solution is less than 1:2, excessive Ni will result in too much Ni on the active outer layer of the catalyst. The C atoms generated by the pyrolysis of polysilane will adsorb onto the Ni surface, causing over-adsorption and affecting chain rearrangement. At the same time, it will also cause carbon deposition that obscures the metal active sites, leading to a decrease in catalytic efficiency. Moreover, Ni has a strong ability to break C-Si bonds, and excessive Ni may lead to excessive C-Si bond breaking, generating small molecule byproducts, reducing the yield and purity of the ceramic precursor. If the mass ratio of Pt to Ni in the mixed solution is greater than 2:1, insufficient Ni will result in too little Ni in the active outer layer of the catalyst, leading to insufficient active sites for C-Si bond breaking and reduced production efficiency. Conversely, a relatively high Pt content results in excessive Pt cost without a significant improvement in catalytic performance. Furthermore, a relatively high Pt content may cause activated Si-H bonds to form Si-Si bonds through self-coupling due to the lack of C-Si breaking fragments, which severely degrades the mechanical strength of the ceramic precursor. Therefore, this invention achieves functional synergy between Pt and Ni by controlling the mass ratio, ensuring effective C-Si bond breaking while avoiding excessive breaking and carbon deposition, thus guaranteeing the yield, purity, and thermal stability of the ceramic precursor. Compared to traditional single catalysts, this invention reduces the amount of precious metals used while maintaining catalytic performance, significantly lowering catalyst costs and meeting industrial application requirements.

[0057] In this embodiment of the invention, the content of the active outer layer is limited to 1wt%~2wt%, which can ensure high catalytic efficiency and high yield during polysilane pyrolysis, reduce pyrolysis temperature and shorten reaction time, avoid low efficiency when the amount of the active outer layer is too small, and avoid production cost due to excessive amount of the active outer layer.

[0058] The present invention also provides a ceramic precursor prepared by the above preparation method.

[0059] Unless otherwise specified, the raw materials used in this invention can be commercially available products or synthesized using existing methods.

[0060] In this invention, the use of "and / or" between multiple technical features indicates that these technical features are connected by an "and / or" relationship, meaning that it can be any one of these technical features, or any combination of two or more of these technical features.

[0061] The present invention will be further described below by way of examples, but the scope of protection of the present invention is not limited to these embodiments.

[0062] Example 1 (1) 45 mmol of lithium metal was added to 10 mL of anhydrous tetrahydrofuran in a glove box and then cooled to -10 °C using an ice-salt bath. 20 mmol of dimethylphenylchlorosilane was added dropwise at a rate of 1 mL / h. After the addition was complete, the temperature was slowly raised to room temperature (25 °C). After reacting for 1 h, the temperature was cooled to -10 °C and then 10 mmol of methylphenyldichlorosilane was added dropwise at a rate of 1 mL / h to avoid local overheating. The reaction was continued for 6 h. After the reaction was completed, the initial product containing triphenylpentamethyltrisilane was obtained. The initial product was placed in an ice-salt bath, and 10 mL of methanol was slowly added dropwise to quench excess lithium until no bubbles were generated. Then, 50 mL of deionized water and 50 mL of n-hexane were added for extraction. The organic phase and aqueous phase were collected separately. The aqueous phase was extracted three times with 30 mL of n-hexane each time to obtain a secondary organic phase. After mixing all the organic phases, the organic phase was dried with anhydrous MgSO4 (the amount of anhydrous MgSO4 was 1 / 10 of the volume of the organic phase). After standing for 2 hours, the mixture was filtered. Then, the filtrate was subjected to vacuum distillation at 40 °C and 0.08 MPa to remove the solvent and collect the target fraction, which yielded triphenylpentamethyltrisilane. (2) Add 55 mmol of triphenylpentamethyltrisilane and 100 mL of anhydrous n-hexane to a flask and stir until completely dissolved. Then add 165 mmol of anhydrous AlCl3 and add 330 mmol of acetyl chloride dropwise at a rate of 1 mL / h while cooling in an ice-water bath (0~5℃). Slowly heat the reaction mixture to room temperature and stir for 7 h at room temperature. Monitor the reaction in real time by gas chromatography. When the starting peak disappears and the target product peak is stable, terminate the reaction. Filter the obtained reaction product to obtain filtrate and residue. Wash the residue with n-hexane to obtain a secondary filtrate. Combine all filtrates and distill them under reduced pressure at 86℃ and 0.0013 MPa to obtain colorless liquid trichloropentamethylpropylsilane. (3) In a glove box, sodium metal (28.26 mmol) and trichloropentamethylpropylsilane (9.42 mmol) were added to a 20 mL toluene solution. The reaction mixture was then heated to 110 °C and stirred for 4 h. After the reaction was complete, a reaction product containing hyperbranched polysilane was obtained. The reaction product was then cooled to room temperature and subjected to vacuum distillation to remove toluene and other volatile compounds, resulting in a turbid solution. The turbid solution was filtered to remove unreacted alkali metals and alkali metal salts generated during the reaction. The solid residue was then washed again with n-hexane, and the filtrate containing hyperbranched polysilane was combined with the washing liquid. The solution was then dried under vacuum to obtain a solid product. The solid product was dissolved in 50 mL of n-hexane, and a diethyl ether solution of methyl magnesium bromide was added until the pH of the reaction system reached 6.8-7.2. After stirring for 1 h, a small amount of trimethylchlorosilane was added as a terminator for the silicon-based anionic chain until the pH of the reaction system reached 6. Then, after removing all volatile compounds and solvents by vacuum distillation, the reaction product was immediately dissolved in 10 mL of tetrahydrofuran, then added to 100 mL of methanol at room temperature, and finally the white precipitate was separated from the solution by filtration and vacuum drying to obtain hyperbranched polysilane. Under the protection of high-purity nitrogen, 100g of hyperbranched polysilane was dissolved in an atmospheric pressure pyrolysis reactor containing n-hexane. The mixture was then heated at 320℃ for 2 hours and then heated to 420℃ for 2 hours to carry out the reaction. After cooling, polycarbosilane suitable for spinning was obtained.

[0063] Example 2 Example 2 is basically the same as Example 1, except that the pyrolysis reaction in step (3) is different; Specifically, hyperbranched polysilane is dissolved in n-hexane, then heated at 360°C for 2 hours and then heated to 420°C for 2 hours to carry out the reaction. After cooling, polycarbosilane that can be used for spinning is obtained.

[0064] Example 3 Example 3 is basically the same as Example 1, except that the pyrolysis reaction in step (3) is different; Specifically, hyperbranched polysilane is dissolved in n-hexane, then heated at 400°C for 2 hours, and then heated to 420°C for 2 hours to carry out the reaction. After cooling, polycarbosilane that can be used for spinning is obtained.

[0065] Example 4 Example 4 is basically the same as Example 1, except that the preparation method of trichloropentamethylpropane is different. Specifically, (1) 60 mmol of lithium metal was added to 15 mL of anhydrous tetrahydrofuran in a glove box and then cooled to -10 °C using an ice-salt bath; 20 mmol of dimethylphenylchlorosilane was added dropwise at a rate of 2 mL / h. After the addition was completed, the temperature was slowly raised to room temperature (25 °C). After reacting for 2 h, the temperature was cooled to -10 °C and then 7 mmol of methylphenyldichlorosilane was added dropwise at a rate of 1 mL / h to avoid local overheating. The reaction was continued for 6 h. After the reaction was completed, an initial product containing triphenylpentamethyltrisilane was obtained. The initial product was placed in an ice-salt bath, and 20 mL of methanol was slowly added dropwise to quench excess lithium until no bubbles were generated. Then, 50 mL of deionized water and 50 mL of n-hexane were added for extraction. The organic phase and aqueous phase were collected separately. The aqueous phase was extracted three times with 30 mL of n-hexane each time to obtain a secondary organic phase. After mixing all the organic phases, the organic phase was dried with anhydrous MgSO4 (the amount of anhydrous MgSO4 was 1 / 10 of the volume of the organic phase). After standing for 2 hours, the solution was filtered. Then, the filtrate was subjected to vacuum distillation at 50 °C and 0.09 MPa to remove the solvent and collect the target fraction, which yielded triphenylpentamethyltrisilane. (2) Add 55 mmol of triphenylpentamethyltrisilane and 100 mL of anhydrous n-hexane to a flask and stir until completely dissolved. Then add 220 mmol of anhydrous AlCl3 and add 440 mmol of acetyl chloride dropwise at a rate of 2 mL / h while cooling in an ice-water bath (0~5℃). Slowly heat the reaction mixture to room temperature and stir for 6 h at room temperature. Monitor the reaction in real time by gas chromatography. When the starting peak disappears and the target product peak is stable, terminate the reaction. Filter the obtained reaction product to obtain filtrate and residue. Wash the residue with n-hexane to obtain a secondary filtrate. Combine all filtrates and distill them under reduced pressure at 86℃ and 0.0013 MPa to obtain colorless liquid trichloropentamethylpropylsilane.

[0066] Example 5 Example 5 is basically the same as Example 1, except that step (3) is different; (3) In a glove box, sodium metal (37.68 mmol) and trichloropentamethylpropylsilane (9.42 mmol) were added to a 20 mL toluene solution. The reaction mixture was then heated to 100 °C and stirred for 4 h. After the reaction was complete, a reaction product containing hyperbranched polysilane was obtained. The reaction product was then cooled to room temperature and subjected to vacuum distillation to remove toluene and other volatile compounds, resulting in a turbid solution. The turbid solution was filtered to remove unreacted alkali metals and alkali metal salts generated during the reaction. The solid residue was then washed again with n-hexane, and the filtrate containing hyperbranched polysilane was combined with the washing liquid. The solution was then vacuum dried to obtain a solid product. The solid product was dissolved in 50 mL of n-hexane, and a diethyl ether solution of methyl magnesium bromide was added until the pH of the reaction system reached 6.8-7.2. After stirring for 1 h, a small amount of trimethylchlorosilane was added as a terminator for the silicon-based anionic chain until the pH of the reaction system reached 6. Then, after removing all volatile compounds and solvents by vacuum distillation, the reaction product was immediately dissolved in 10 mL of tetrahydrofuran, then added to 100 mL of methanol at room temperature, and finally the white precipitate was separated from the solution by filtration and vacuum drying to obtain hyperbranched polysilane. Under the protection of high-purity nitrogen, 100g of hyperbranched polysilane was dissolved in an atmospheric pressure pyrolysis reactor containing n-hexane. The mixture was then heated at 320℃ for 2 hours and then heated to 420℃ for 2 hours to carry out the reaction. After cooling, polycarbosilane suitable for spinning was obtained.

[0067] Example 6 Example 6 is basically the same as Example 1, except that step (3) is different; (3) In a glove box, sodium metal (32.97 mmol) and trichloropentamethylpropylsilane (9.42 mmol) were added to a 20 mL toluene solution. The reaction mixture was then heated to 120 °C and stirred for 2 h. After the reaction was complete, a reaction product containing hyperbranched polysilane was obtained. The reaction product was then cooled to room temperature and subjected to vacuum distillation to remove toluene and other volatile compounds, resulting in a turbid solution. The turbid solution was filtered to remove unreacted alkali metals and alkali metal salts generated during the reaction. The solid residue was then washed again with n-hexane, and the filtrate containing hyperbranched polysilane was combined with the washing liquid. The solution was then vacuum dried to obtain a solid product. The solid product was dissolved in 50 mL of n-hexane, and a diethyl ether solution of methyl magnesium bromide was added until the pH of the reaction system reached 6.8-7.2. After stirring for 1 h, a small amount of trimethylchlorosilane was added as a terminator for the silicon-based anionic chain until the pH of the reaction system reached 6. Then, after removing all volatile compounds and solvents by vacuum distillation, the reaction product was immediately dissolved in 10 mL of tetrahydrofuran, then added to 100 mL of methanol at room temperature, and finally the white precipitate was separated from the solution by filtration and vacuum drying to obtain hyperbranched polysilane. Under the protection of high-purity nitrogen, 100g of hyperbranched polysilane was dissolved in an atmospheric pressure pyrolysis reactor containing n-hexane. The mixture was then heated at 320℃ for 2 hours and then heated to 420℃ for 2 hours to carry out the reaction. After cooling, polycarbosilane suitable for spinning was obtained.

[0068] Example 7 Example 7 is basically the same as Example 1, except that the pyrolysis reaction in step (3) is different; Under the protection of high-purity nitrogen, 100g of hyperbranched polysilane was dissolved in an atmospheric pressure cracking reactor containing n-hexane, and then 0.5g of hollow catalyst was added. The mixture was heated at 320℃ for 2 hours and then heated to 420℃ for 2 hours to carry out the reaction. After cooling, polycarbosilane suitable for spinning was obtained.

[0069] The hollow catalyst was prepared by the following method: S1. 100 mg of carbon nanospheres (particle size 100 nm) were dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed for 0.5 h. Then, after magnetic stirring for 1 h, 9 mL of tetrabutyl titanate (TBOT) was added dropwise at a rate of 3 mL / min while stirring. Then, 54 mL of an ethanol aqueous solution (composed of 9 mL of water and 45 mL of anhydrous ethanol) was added dropwise to the above system at a rate of 2 mL / min. Then, at 60 °C and 250 rpm, TBOT was adsorbed onto the surface of the carbon nanospheres and hydrolyzed to obtain a mixed liquid system containing titanium dioxide-coated carbon nanospheres. The mixed liquid system was filtered and dried at 80 °C to obtain titanium dioxide-coated carbon nanospheres. The titanium dioxide-coated carbon nanospheres were placed in a muffle furnace and calcined at 600 °C for 3 h to remove the core layer of the carbon spheres, obtaining hollow titanium dioxide spheres. S2. Take 0.1g of the titanium dioxide hollow spheres obtained in step S1, disperse them in 50mL of anhydrous ethanol, and sonicate them at a power density of 500W for 30min. Then, add 0.1g of silica nanoparticles (particle size of 20nm) to the system and continue to sonicate for 30min to mix them. Then, stir the above mixed solution at 250rpm at 60℃ for 1.5h, filter and dry (dry at 100℃ for 2h) to obtain silica-coated hollow spheres. Place the silica-coated hollow spheres in a muffle furnace and calcine them at 500℃ for 5h to form a complex hollow TiO2-SiO2 double oxide support. S3. Take 1g of the complexed hollow TiO2-SiO2 double oxide support obtained in step S2 and disperse it in deionized water. Then, add a mixed solution containing chloroplatinic acid H2PtCl6·6H2O and nickel nitrate Ni(NO3)2·6H2O (where the mass ratio of Pt to Ni is 1:1) to the above dispersion. The mixture was stirred at room temperature (25°C) for 1 hour to obtain a precursor solution. The precursor solution was then filtered and dried to obtain a precursor. The precursor was placed in a hydrogen atmosphere (a mixture of 20% hydrogen and 80% nitrogen) at 400°C for 1 hour to convert the precursor into metallic Pt and Ni, which were then loaded onto the support in step S2 to obtain a hollow catalyst. The hollow catalyst consists of hollow titanium dioxide spheres, a silica intermediate layer, and an active outer layer from the inside out. The mass ratio of the hollow titanium dioxide spheres to the silica intermediate layer is 1:1. The active outer layer is composed of Pt and Ni and accounts for approximately 1 wt% of the hollow catalyst.

[0070] Example 8 Example 8 is basically the same as Example 7, except that the mass ratio of titanium dioxide hollow spheres to silicon dioxide intermediate layer in the hollow catalyst is 5:1. Specifically, in step S2, 0.5g of the titanium dioxide hollow spheres obtained in step S1 are dispersed in 50mL of anhydrous ethanol and ultrasonically treated at a power density of 500W for 30min; then, 0.1g of silica nanoparticles (particle size of 20nm) are added to the system and ultrasonically mixed for another 30min. The mixture is then stirred at 250rpm for 1.5h at 60℃, filtered, and dried (drying at 100℃ for 2h) to obtain silica-coated hollow spheres; the silica-coated hollow spheres are then calcined in a muffle furnace at 500℃ for 5h to form a complexed hollow TiO2-SiO2 double oxide support.

[0071] Example 9 Example 9 is basically the same as Example 7, except that the mass ratio of Pt to Ni in step S3 of preparing the hollow catalyst is 2:1. Specifically, in step S3, 1g of the complexed hollow TiO2-SiO2 bioxide support obtained in step S2 is dispersed in deionized water. Then, a mixed solution containing chloroplatinic acid H2PtCl6·6H2O and nickel nitrate Ni(NO3)2·6H2O (where the mass ratio of Pt to Ni is 2:1) is added to the dispersion. The mixture is stirred at room temperature (25℃) for 1h to obtain a precursor solution. The precursor solution is then filtered and dried to obtain a precursor. The precursor is placed in a hydrogen atmosphere (a mixture of 20% hydrogen and 80% nitrogen) at 400℃ for 1h to convert the precursor into metallic Pt and Ni, which are then loaded onto the support obtained in step S2 to obtain a catalyst. The hollow catalyst comprises, from the inside out, hollow titanium dioxide spheres, a silica intermediate layer, and an active outer layer; the mass ratio of the hollow titanium dioxide spheres to the silica intermediate layer is 1:1; the active outer layer is composed of Pt and Ni; the active outer layer accounts for approximately 1 wt% of the hollow catalyst.

[0072] Comparative Example 1 Using polydimethylsilane as raw material, linear polydimethylsilane is placed in an atmospheric pressure pyrolysis reactor. Under the protection of high-purity nitrogen, the temperature is raised to 360°C to completely pyrolyze the linear polydimethylsilane into liquid polysilane (LPS). The temperature is then raised to 420°C and held for 8 hours. After natural cooling, polycarbosilane is obtained.

[0073] Comparative Example 2 Sodium metal (28.26 mmol) and 20 mL of toluene were loaded into a 6 L cylindrical glass reaction vessel, and the toluene was refluxed through a jacket using a circulating bath. A slightly positive pressure nitrogen atmosphere was maintained throughout the process. The molten sodium was then dispersed using a double-bladed impeller, and the jacket temperature was maintained at 110 °C. A mixture containing methylphenyldichlorosilane (1.46 g), diphenyldichlorosilane (508 mg), and methyltrichlorosilane (357 mg) was added dropwise to the reaction vessel over 60 min, and the mixture was kept at 110 °C for 16 h. After the reactants cooled to 40 °C, 2 g of methanol was slowly added to oxidize the remaining sodium metal. The salt was then separated by centrifugation, the toluene solution was filtered, and the remaining mixture was concentrated to 10 mL by vacuum evaporation. This mixture was slowly added to methanol to precipitate the product, which was then filtered and dried in a vacuum oven to obtain powdered hyperbranched polysilane. Under the protection of high-purity nitrogen, 100g of the hyperbranched polysilane was dissolved in an atmospheric pressure pyrolysis reactor containing n-hexane. The mixture was then heated at 400℃ for 2 hours and then heated to 420℃ for 2 hours to carry out the reaction. After cooling, polycarbosilane suitable for spinning was obtained.

[0074] Comparative Example 3 In a glove box, a solution of metallic sodium (39.9 mmol), 20 mL of toluene, and tetramethyldisilane (13.3 mmol) was added. The reaction mixture was then heated to 110 °C and stirred for 4 h. After the reaction was complete, a reaction product containing hyperbranched polysilane was obtained. The reaction product was then cooled to room temperature, and toluene and other volatile compounds were removed by vacuum distillation. The hyperbranched polysilane in the residue was dissolved in 50 mL of n-hexane, and then a diethyl ether solution of methyl magnesium bromide was added until the pH of the reaction system reached 6.8–7.2. After stirring for another 1 h, a small amount of trimethylchlorosilane was added as a terminator for the silane-based anionic chain until the pH of the reaction system reached 6. After removing all volatile compounds and solvents by vacuum distillation, the hyperbranched polysilane was immediately dissolved in 10 mL of tetrahydrofuran and then added to 100 mL of methanol at room temperature. Finally, the white precipitate was separated from the solution by filtration and vacuum drying to obtain the hyperbranched polysilane. Under the protection of high-purity nitrogen, 100g of hyperbranched polysilane was dissolved in an atmospheric pressure pyrolysis reactor containing n-hexane. The mixture was then heated at 400℃ for 2 hours, and then heated to 420℃ and held for 2 hours to carry out the reaction. After cooling, polycarbosilane suitable for spinning was obtained.

[0075] Comparative Example 4 Comparative Example 4 is basically the same as Example 7, except that the hollow catalyst is different and the cracking reaction in step (3) is different. Specifically, the hollow catalyst is prepared by the following method: S1. 100 mg of carbon nanospheres (particle size 100 nm) were dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed for 0.5 h. After mixing with magnetic stirring for 1 h, 9 mL of tetraethyl orthosilicate was slowly added dropwise while stirring. Then, 54 mL of an ethanol aqueous solution (composed of 9 mL of water and 45 mL of anhydrous ethanol) was added dropwise to the above system. At 60 °C and 250 rpm, tetraethyl orthosilicate was adsorbed onto the surface of the carbon nanospheres and hydrolyzed to obtain a mixed liquid system containing silica-coated carbon nanospheres. The mixed liquid system was filtered and dried at 80 °C to obtain silica-coated carbon nanospheres. The silica-coated carbon nanospheres were placed in a muffle furnace and calcined at 600 °C for 3 h to remove the core layer of the carbon spheres, obtaining hollow silica spheres. S2. Take 0.1g of the silica hollow spheres obtained in step S1, disperse them in 50mL of anhydrous ethanol, and sonicate them at a power density of 500W for 30min. Then, add 0.1g of titanium dioxide nanoparticles (particle size of 20nm) to the system and continue to sonicate for 30min to mix them. Then, stir the above mixed solution at 250rpm at 60℃ for 1.5h, filter and dry (dry at 100℃ for 2h) to obtain titanium dioxide coated hollow spheres. Place the titanium dioxide coated hollow spheres in a muffle furnace and calcine them at 500℃ for 5h to form a carrier. S3. Take 1g of the support obtained in step S2 and disperse it in deionized water. Then, add a mixed solution containing chloroplatinic acid H2PtCl6·6H2O and nickel nitrate Ni(NO3)2·6H2O (where the mass ratio of Pt to Ni is 1:1) to the above dispersion. Stir at room temperature (25℃) for 1h to obtain a precursor solution. Filter and dry the precursor solution to obtain a precursor. Place the precursor in a hydrogen atmosphere (a mixture of 20% hydrogen and 80% nitrogen) at 400℃ for 1h to convert the precursor into metallic Pt and Ni, which are then loaded onto the support in step S2 to obtain a hollow catalyst. The hollow catalyst consists of, from the inside out, hollow silica spheres, a titanium dioxide intermediate layer, and an active outer layer; the mass ratio of the hollow silica spheres to the titanium dioxide intermediate layer is 1:1; the active outer layer is composed of Pt and Ni; the active outer layer accounts for 1wt% of the hollow catalyst. In step (3), under the protection of high-purity nitrogen, 100g of hyperbranched polysilane is dissolved in an atmospheric pressure cracking reactor containing n-hexane. Then, it is heated at 380°C for 2 hours and then heated to 420°C for 2 hours to carry out the reaction. After cooling, polycarbosilane that can be used for spinning is obtained.

[0076] Comparative Example 5 Comparative Example 5 is basically the same as Example 7, except that the mass ratio of Pt to Ni in the mixed solution during the preparation of the hollow catalyst is 1:3, and the cracking reaction in step (3) is different. Specifically, in step S3, 1g of the support obtained in step S2 is dispersed in deionized water. Then, a mixed solution containing chloroplatinic acid H2PtCl6·6H2O and nickel nitrate Ni(NO3)2·6H2O (where the mass ratio of Pt to Ni is 1:3) is added to the dispersion. The mixture is stirred at room temperature (25°C) for 1 hour to obtain a precursor solution. The precursor solution is then filtered and dried to obtain a precursor. The precursor is placed in a hydrogen atmosphere (a mixture of 20% hydrogen and 80% nitrogen) at 400°C for 1 hour to convert the precursor into metallic Pt and Ni, which are then loaded onto the support from step S2 to obtain a hollow catalyst. This hollow catalyst consists of, from the inside out, hollow titanium dioxide spheres, a silica intermediate layer, and an active outer layer; the mass ratio of the hollow titanium dioxide spheres to the silica intermediate layer is 1:1; the active outer layer is composed of Pt and Ni; and the active outer layer accounts for approximately 1 wt% of the hollow catalyst. Step (3): Under the protection of high-purity nitrogen, 100g of hyperbranched polysilane is dissolved in an atmospheric pressure cracking reactor containing n-hexane. Then, it is heated at 380℃ for 2 hours and then heated to 420℃ for 2 hours to carry out the reaction. After cooling, polycarbosilane that can be used for spinning is obtained.

[0077] Comparative Example 6 Comparative Example 6 is basically the same as Example 7, except that the mass ratio of Pt to Ni in the mixed solution during the preparation of the hollow catalyst is 3:1, and the cracking reaction in step (3) is different. Specifically, in step S3, 1g of the support obtained in step S2 is dispersed in deionized water. Then, a mixed solution containing chloroplatinic acid H2PtCl6·6H2O and nickel nitrate Ni(NO3)2·6H2O (where the mass ratio of Pt to Ni is 3:1) is added to the dispersion. The mixture is stirred at room temperature (25°C) for 1 hour to obtain a precursor solution. The precursor solution is then filtered and dried to obtain a precursor. The precursor is placed in a hydrogen atmosphere (a mixture of 20% hydrogen and 80% nitrogen) at 400°C for 1 hour to convert the precursor into metallic Pt and Ni, which are then loaded onto the support from step S2 to obtain a hollow catalyst. This hollow catalyst consists of, from the inside out, hollow titanium dioxide spheres, a silica intermediate layer, and an active outer layer; the mass ratio of the hollow titanium dioxide spheres to the silica intermediate layer is 1:1; the active outer layer is composed of Pt and Ni; and the active outer layer accounts for approximately 1 wt% of the hollow catalyst. Step (3): Under the protection of high-purity nitrogen, 100g of hyperbranched polysilane is dissolved in an atmospheric pressure cracking reactor containing n-hexane. Then, it is heated at 380℃ for 2 hours and then heated to 420℃ for 2 hours to carry out the reaction. After cooling, polycarbosilane that can be used for spinning is obtained.

[0078] The present invention tested the molecular weight distribution coefficient of the polycarbosilanes prepared in each embodiment and each comparative example, and statistically analyzed the reaction temperature, reaction time and polycarbosilane yield in the pyrolysis process. The data results are shown in Table 1.

[0079] Table 1 As can be seen from the data in Table 1, the ceramic precursor (i.e., polycarbosilane) prepared in the embodiments of the present invention has a hyperbranched structure and a narrow molecular weight distribution, which can avoid performance fluctuations caused by irregular copolymerization. It also has excellent solubility, being soluble in hydrocarbon solvents. Therefore, polycarbosilane can be directly prepared by atmospheric pressure heating pyrolysis without the need for complex or expensive equipment, making it suitable for large-scale production. Compared with the linear polydimethylsilane of Comparative Example 1, the hyperbranched polysilane of Comparative Example 2, and the hyperbranched polysilane containing secondary silicon branches of Comparative Example 3, the hyperbranched polysilane containing tertiary silicon branch units and linear silicon units prepared in the embodiments of the present invention requires a lower pyrolysis temperature, and the resulting polycarbosilane has a narrower molecular weight distribution and a higher yield.

[0080] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a ceramic precursor, characterized in that, include: (1) The system containing lithium metal and the first organic solvent was placed in an ice-salt bath, and then dimethylphenylchlorosilane and methylphenyldichlorosilane were added dropwise to the system in sequence and reacted to obtain triphenylpentamethyltrisilane; (2) Triphenylpentamethyltrisilane and a chlorinating agent were added to a second organic solvent to carry out a substitution reaction to obtain trichloropentamethylpropane; (3) Trichloropentamethylpropylsilane is added to the second organic solvent and mixed well, and then sodium metal is added to carry out a coupling reaction to obtain hyperbranched polysilane; the hyperbranched polysilane is cracked to obtain the ceramic precursor.

2. The preparation method according to claim 1, characterized in that, In step (1): the molar ratio of lithium metal to dimethylphenylchlorosilane is (2~3):1; and / or, The molar ratio of dimethylphenylchlorosilane to methylphenyldichlorosilane is (2~3):

1.

3. The preparation method according to claim 1, characterized in that, In step (1): the temperature of the ice-salt bath is -5 to -20°C; the first organic solvent includes tetrahydrofuran, toluene, or diethyl ether; and / or, The dripping rate is 1~2 mL / h.

4. The preparation method according to claim 1, characterized in that, Step (1) includes the following sub-steps: (11) Add dimethylphenylchlorosilane dropwise to the system. After the addition is complete, heat the system to 20-25°C and keep it at that temperature for 1-2 hours. Then, continue to place the system in the ice-salt bath and continue to add methylphenyldichlorosilane dropwise. After the addition is complete, react for 5-6 hours to obtain the initial product containing triphenylpentamethyltrisilane. (12) After adding a quencher to the initial product, extraction is performed. The extracted organic phase is then dried, filtered, and distilled under reduced pressure to obtain triphenylpentamethyltrisilane.

5. The preparation method according to claim 1, characterized in that, In step (2): the chlorinating agent is acetyl chloride; the second organic solvent includes n-hexane, toluene, or xylene; and / or, The molar ratio of the chlorinating agent to triphenylpentamethyltrisilane is (6~8):

1.

6. The preparation method according to claim 1, characterized in that, Step (2) includes the following sub-steps: (21) Triphenylpentamethyltrisilane was added to a second organic solvent and mixed well. Then, the chlorinating agent and catalyst were added at an initial temperature of 0-5°C to carry out a substitution reaction to obtain a reaction product containing trichloropentamethylpropane. (22) The reaction product was filtered, washed and distilled under reduced pressure to obtain trichloropentamethylpropane.

7. The preparation method according to claim 1, characterized in that, In step (3): the molar ratio of metallic sodium to trichloropentamethylpropylsilane is (3~4):1; and / or, The coupling reaction is carried out at a temperature of 100-120°C for 2-4 hours.

8. The preparation method according to claim 1, characterized in that, Step (3) includes the following sub-steps: (31) Trichloropentamethylpropane was added to the second organic solvent and mixed well. Then, sodium metal was added to carry out a coupling reaction. After the reaction was completed, the reaction product was obtained. (32) The reaction product was subjected to vacuum distillation, dissolution, filtration, washing, addition of quencher, addition of terminator, and vacuum distillation in sequence to obtain hyperbranched polysilane.

9. The preparation method according to any one of claims 1 to 8, characterized in that, In step (3): the hyperbranched polysilane is cracked using a hollow catalyst to obtain the ceramic precursor, and the amount of the hollow catalyst is 0.5wt%~1wt% of the amount of the hyperbranched polysilane; wherein, the hollow catalyst comprises, from the inside out, hollow titanium dioxide spheres, a silica intermediate layer, and an active outer layer; the mass ratio of the hollow titanium dioxide spheres to the silica intermediate layer is (1~10):(1~10); the active outer layer comprises Pt and Ni; the active outer layer accounts for 1wt%~2wt% of the hollow catalyst; Hollow catalysts are prepared by the following method: Hollow titanium dioxide spheres were dispersed in a solvent and mixed with silica nanoparticles to obtain silica-coated hollow spheres. The silica-coated hollow spheres were then calcined to obtain a support. The support was then impregnated in a mixed solution containing chloroplatinic acid and nickel nitrate to obtain a precursor solution. The precursor solution was then filtered, dried, and reduced sequentially to obtain a hollow catalyst. The mass ratio of Pt to Ni in the mixed solution was (1~2):(1~2).

10. A ceramic precursor, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 9.

Images