A ceramic precursor and a method for preparing the same

Abstract

The application provides a ceramic precursor and a preparation method thereof, and relates to the technical field of ceramic materials, and the preparation method comprises the following steps: (1) placing a system containing metallic lithium and a first organic solvent in an ice-salt bath, then adding dimethylphenylchlorosilane and methylphenyldichlorosilane into the system in sequence, and performing reaction to obtain triphenylpentamethyltrisilane; (2) adding triphenylpentamethyltrisilane and a chlorinating agent into a second organic solvent to perform a substitution reaction, so as to obtain trichloropentamethylpropylsilane; (3) adding trichloropentamethylpropylsilane into the second organic solvent and uniformly mixing, then adding metallic sodium to perform a coupling reaction, so as to obtain hyperbranched polysilane; and the hyperbranched polysilane is cracked to obtain the ceramic precursor. The ceramic precursor provided by the scheme has a hyperbranched structure, a narrow molecular weight distribution, excellent solubility, and higher yield without the need of complex or expensive equipment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic materials, in particular to a ceramic precursor and a preparation method thereof. BACKGROUND

[0002] The ceramic precursor is a key precursor for preparing continuous ceramic fibers, and its performance plays a decisive role in the quality of the ceramic fibers. At present, the ceramic precursor is mainly prepared by the cracking reaction of polysilane under the action of a catalyst in the industry, and the performance of the ceramic precursor has a crucial influence on the efficiency of the reaction and the quality of the product.

[0003] Although the traditional linear polysilane can prepare the ceramic precursor, it has the following inherent defects: first, it is insoluble in hydrocarbon solvents and has poor processability; second, it is easy to volatilize in the pyrolysis process, which affects the performance of the ceramic fibers. Chinese Patent CN115466397A discloses a preparation method of a polycarbosilane ceramic precursor. In the method, polydimethylsilane is put into a cracking kettle, a high-temperature and high-pressure method is adopted, nitrogen and hydrogen are used for displacement, and a certain pressure is controlled to prepare polycarbosilane. However, the method has high requirements for equipment and device maintenance, and has high cost; in addition, there is a large temperature gradient field at different positions of the cracking kettle, and the kettle wall is seriously coked, which results in low yield and wide molecular weight distribution of the prepared polycarbosilane. Therefore, there is an urgent need for a ceramic precursor and a preparation method thereof. SUMMARY

[0004] The present application provides a ceramic precursor and a preparation method thereof. The ceramic precursor obtained by the preparation method has a hyperbranched structure, a narrow molecular weight distribution, excellent solubility, and higher yield without complex or expensive equipment.

[0005] In a first aspect, the present application provides a preparation method of a ceramic precursor, which comprises:

[0006] (1) placing a system containing metallic lithium and a first organic solvent in an ice-salt bath, then sequentially adding dimethylphenylchlorosilane and methylphenyldichlorosilane to the system dropwise and performing a reaction to obtain triphenylpentamethyltrisilane;

[0007] (2) adding triphenylpentamethyltrisilane and a chlorinating agent to a second organic solvent to perform a substitution reaction to obtain trichloropentamethylpropylsilane;

[0008] (3) mixing trichloropentamethylpropylsilane in the second organic solvent, then adding metallic sodium to perform a coupling reaction to obtain hyperbranched polysilane; and performing a cracking of the hyperbranched polysilane to obtain the ceramic precursor.

[0009] Preferably, in step (1): the molar ratio of lithium metal to dimethylphenylchlorosilane is (2-3):1.

[0010] Preferably, in step (1): the molar ratio of dimethylphenylchlorosilane to methylphenyldichlorosilane is (2-3):1.

[0011] Preferably, in step (1): the temperature of the ice-salt bath is -5 to -20℃; the first organic solvent comprises tetrahydrofuran, toluene or diethyl ether.

[0012] Preferably, in step (1): the rate of dropwise addition is 1-2 mL / h.

[0013] Preferably, the step (1) comprises the following sub-steps:

[0014] (11) dimethylphenylchlorosilane is added dropwise to the system, after the dropwise addition is completed, the temperature is raised to 20-25℃ and kept for 1-2 h, then the system is continuously placed in the ice-salt bath and methylphenyldichlorosilane is continuously added dropwise, after the dropwise addition is completed, the reaction is continued for 5-6 h to obtain an initial product comprising triphenylpentamethyltrisilane;

[0015] (12) after the quenching agent is added to the initial product, extraction is carried out, and after extraction, the organic phase is sequentially subjected to drying, filtration and reduced pressure distillation to obtain triphenylpentamethyltrisilane.

[0016] Preferably, in step (2): the chlorinating agent is acetyl chloride; the second organic solvent comprises n-hexane, toluene or xylene.

[0017] Preferably, in step (2): the molar ratio of the chlorinating agent to triphenylpentamethyltrisilane is (6-8):1.

[0018] Preferably, the step (2) comprises the following sub-steps:

[0019] (21) triphenylpentamethyltrisilane is added to the second organic solvent and mixed, then the chlorinating agent and the catalyst are added at an initial temperature of 0-5℃ to carry out substitution reaction to obtain a reaction product comprising trichloropentamethyltrisilane;

[0020] (22) the reaction product is sequentially subjected to filtration, washing and reduced pressure distillation to obtain trichloropentamethyltrisilane.

[0021] Preferably, in step (3): the molar ratio of sodium metal to trichloropentamethyltrisilane is (3-4):1.

[0022] Preferably, in step (3): the temperature of the coupling reaction is 100-120℃ and the time is 2-4 h.

[0023] Preferably, the step (3) comprises the following sub-steps:

[0024] (31) adding trichloropentamethyltrisilane into the second organic solvent and mixing, then adding sodium metal to perform coupling reaction, and obtaining reaction product after the reaction is completed;

[0025] (32) sequentially performing vacuum distillation, dissolving, filtering, washing, adding quenching agent, adding terminating agent, and vacuum distillation on the reaction product, to obtain hyperbranched polysilane.

[0026] Preferably, in the step (3), the hyperbranched polysilane is cracked by using a hollow catalyst to obtain the ceramic precursor; the hollow catalyst is used in an amount of 0.5wt%-1wt% of the amount of the hyperbranched polysilane; the hollow catalyst comprises, from inside to outside, titania hollow spheres, a silica intermediate layer, and an active outer layer; the mass ratio of the titania hollow spheres to the silica intermediate layer is (1-10):(1-10); the active outer layer comprises Pt and Ni; and the active outer layer accounts for 1wt%-2wt% of the hollow catalyst.

[0027] In a second aspect, the application further provides a ceramic precursor prepared by using the preparation method of the ceramic precursor in any one of the above first aspect.

[0028] Compared with the prior art, the application has at least the following beneficial effects:

[0029] (1) The hyperbranched polysilane of the application uses trichloropentamethyltrisilane as raw material, and a ceramic precursor containing tertiary silicon branched unit and linear silicon unit is prepared. In comparison, when monosilane is used as raw material, different chemical affinities will be introduced into the polymer chain, which may form irregular structures, even linear or network structures, thereby leading to the formation of insoluble structures. In the application, silane containing three silicon atoms is used as raw material, which can form a polymer with high branching and high silicon content, thereby breaking through the crystallinity limitation of linear polysilane, and ensuring excellent solubility of the hyperbranched polysilane in hydrocarbon solvents.

[0030] (2) The trichloro-substituted propylsilane monomer used in the application contains branched units in advance, and forms a regular hyperbranched structure after polymerization, with narrow molecular weight distribution, avoiding performance fluctuations caused by irregular copolymerization. At the same time, the hyperbranched polysilane prepared has excellent solubility, and its heat transfer performance in liquid state is better than that of existing polydimethylsilane powder, so that the cracking reaction temperature can be further reduced, the reaction time can be shortened, the cracking reaction can be uniform, the coking of the kettle wall can be reduced, the yield can be improved, and a ceramic precursor with narrow molecular weight distribution can be obtained. DETAILED DESCRIPTION

[0031] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are some of the embodiments of the present application but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the protection scope of the present application.

[0032] The present application provides a preparation method of ceramic precursor, comprising:

[0033] (1) placing a system containing metallic lithium and a first organic solvent in an ice-salt bath, then adding dimethylphenylchlorosilane, methylphenyldichlorosilane to the system in sequence and performing a reaction to obtain triphenylpentamethyltrisilane;

[0034] (2) adding triphenylpentamethyltrisilane, a chlorinating agent to a second organic solvent to perform a substitution reaction to obtain trichloropentamethylpropylsilane;

[0035] (3) adding trichloropentamethylpropylsilane to the second organic solvent and mixing, then adding metallic sodium to perform a coupling reaction to obtain hyperbranched polysilane; and performing cleavage on the hyperbranched polysilane to obtain the ceramic precursor.

[0036] In the present application, triphenylpentamethyltrisilane is first prepared, then a chloro-substitution reaction is performed on the triphenylpentamethyltrisilane to obtain trichloropentamethylpropylsilane, and the ceramic precursor containing tertiary silicon branched units and linear silicon units is prepared by using the trichloropentamethylpropylsilane as a raw material. In comparison, when monosilane is used as a raw material, different chemical affinities will be introduced into the polymer chain, which may form irregular structures, even linear or network structures, thus leading to the formation of insoluble structures. In the present application, the silane containing three silicon atoms is used as a raw material, which can form a polymer with high branching and high silicon content, thus breaking through the crystallinity limitation of linear polysilane, and ensuring that the hyperbranched polysilane has excellent solubility in hydrocarbon solvents.

[0037] The trichloro-substituted propylsilane monomer used in the present application contains branched units in advance, and after polymerization, a regular hyperbranched structure is formed, the molecular weight distribution is narrow, and the performance fluctuation caused by irregular copolymerization is avoided. At the same time, the hyperbranched polysilane prepared has excellent solubility, and its heat transfer performance in a liquid state is better than that of the existing polydimethylsilane powder, so that the cleavage reaction temperature can be further reduced, the reaction time can be shortened, the cleavage reaction can be uniform, the coking of the kettle wall can be reduced, the yield can be improved, and the ceramic precursor with narrow molecular weight distribution can be obtained.

[0038] 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).

[0039] 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).

[0040] It should be noted that the chemical structure of methylphenyldichlorosilane is as follows: .

[0041] Specifically, the chemical reaction formula of the reaction between lithium metal and dimethylphenylchlorosilane is as follows:

[0042] 2Li + C6H5-Si(CH3)2Cl → C6H5-Si(CH3)2Li + LiCl

[0043] The chemical reaction formula of the reaction between dimethylphenylsilyllithium and methylphenyldichlorosilane is as follows:

[0044] 2C6H5-Si(CH3)2Li + C6H5-Si(CH3)Cl2 → C6H5-Si(CH3)2-Si(CH3)(C6H5)-Si(CH3)2-C6H5 + 2LiCl.

[0045] In the present application, by adding excess lithium, it can be ensured that dimethylphenylchlorosilane is fully reacted, and thus, by further adding a slight excess of methylphenyldichlorosilane, it can be ensured that the obtained dimethylphenylsilyllithium is fully reacted, thereby further improving the yield of triphenylpentamethyltrisilane.

[0046] In a preferred embodiment, in step (1), the temperature of the ice-salt bath is -5 to -20℃ (for example, it can be -5℃, -8℃, -10℃, -12℃, -15℃, -18℃ or -20℃); the first organic solvent comprises tetrahydrofuran, toluene or diethyl ether.

[0047] It should be noted that the first organic solvent does not contain water, so as to avoid the violent reaction of lithium with water.

[0048] In a preferred embodiment, in step (1), the rate of dropwise addition is 1 to 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).

[0049] In a preferred embodiment, step (1) comprises the following sub-steps:

[0050] (11) Dimethylphenylchlorosilane is added dropwise to the system, after the dropwise addition is completed, the temperature is raised to 20-25°C (for example, it can be 20°C, 21°C, 22°C, 23°C, 24°C or 25°C) and is kept for 1-2h (for example, it can be 1h, 1.2h, 1.5h, 1.6h, 1.8h or 2h), then it is continuously placed in the ice-salt bath and methylphenyldichlorosilane is continuously added dropwise, after the dropwise addition is completed, the reaction is continued for 5-6h (for example, it can be 5h, 5.2h, 5.5h, 5.8h or 6h), to obtain an initial product containing triphenylpentamethyltrisilane;

[0051] (12) After the initial product is added with a quenching agent, extraction is carried out, the organic phase after extraction is sequentially subjected to drying, filtration and reduced pressure distillation, to obtain triphenylpentamethyltrisilane.

[0052] Specifically, for step (12), the quenching agent is methanol, excess methanol is added to the initial product to quench the 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, then the organic phase and the aqueous phase are collected by liquid separation, the aqueous phase is extracted with n-hexane for 3 times to obtain secondary organic phases, after the organic phases are mixed, anhydrous MgSO4 is used to dry the organic phases (the amount of anhydrous MgSO4 is 1 / 10 of the volume of the organic phases), after standing for 2h, filtration is carried out, then the filtrate is subjected to reduced pressure distillation under the conditions of 40-60°C and 0.07-0.09MPa, to evaporate the solvent to collect a target fraction, i.e. to obtain triphenylpentamethyltrisilane.

[0053] In the present application, by controlling the environmental temperature of the system and the dropwise addition rate of dimethylphenylchlorosilane, the reaction activity and the reaction rate can be controlled, the occurrence of side reactions can be avoided, the experimental safety can be improved, the α-H of lithium efficiently deprotonated silane can be utilized to generate a silicon-based lithium intermediate. The reaction temperature is controlled at 20-25°C, which can ensure the reaction rates of both the intermediate dimethylphenyl lithium silane and methylphenyldichlorosilane, avoid the decomposition of the intermediate due to excessively high temperature, and further reduce the energy consumption under conventional conditions. By adding dimethylphenylchlorosilane at a rate of 1-2mL / h, the occurrence of side reactions caused by excessively high local concentration due to excessive one-time addition can be avoided, and the uniform dispersion of reactants can be maintained to prevent excessive heat release from causing the system to be out of control.

[0054] In a preferred embodiment, in step (2): the chlorinating agent is acetyl chloride; the second organic solvent includes n-hexane, toluene or xylene.

[0055] In a preferred embodiment, in step (2), the molar ratio of the 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).

[0056] In a preferred embodiment, step (2) comprises the following sub-steps:

[0057] (21) triphenylpentamethyltrisilane is added to the second organic solvent, and then the chlorinating agent and the catalyst are added at a starting temperature of 0-5°C (for example, it can be 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 the substitution reaction, to obtain a reaction product comprising trichloropentamethyltrisilane;

[0058] (22) the reaction product is sequentially subjected to filtration, washing and reduced-pressure distillation, to obtain trichloropentamethyltrisilane.

[0059] It should be noted that the second organic solvent includes toluene, n-hexane and xylene.

[0060] Specifically, step (21) can be monitored by gas chromatography until the raw material peak disappears and the target product peak is stable, and then the reaction is terminated; or the chlorinating agent and the catalyst can be added in multiple times to carry out the substitution reaction. The catalyst is anhydrous aluminum chloride, and the molar ratio of the anhydrous aluminum chloride to triphenylpentamethyltrisilane is (3-4):1, and the anhydrous aluminum chloride is used to catalyze the activation of the Si-phenyl bond. Step (22) comprises: filtering the reaction product to obtain a filtrate and a residue, washing the residue with n-hexane to obtain a secondary filtrate, and combining all the filtrates, and then subjecting the combined filtrate to reduced-pressure distillation at 86°C and 0.0013 MPa, to obtain colorless liquid trichloropentamethyltrisilane.

[0061] In the present application, the chlorinating agent is used to replace the phenyl group in trichloropentamethyltrisilane. If the molar ratio of the chlorinating agent to triphenylpentamethyltrisilane is less than 6:1, the amount of the chlorinating agent is too small, the replacement is not complete, and the yield of trichloropentamethyltrisilane is low. However, if the molar ratio of the chlorinating agent to triphenylpentamethyltrisilane is higher than 8:1, the amount of the chlorinating agent is too large, which increases the cost.

[0062] In a more preferred embodiment, the chlorinating agent is added at a rate of 1-2 mL / h.

[0063] In the present application, by controlling the dropping rate of the chlorinating agent, it can avoid the local high concentration caused by adding too much at one time, which can cause side reactions, and at the same time, it can also maintain the uniform dispersion of the reactants, and prevent the system from being out of control due to excessive heat release.

[0064] In a preferred embodiment, in step (3), the molar ratio of sodium metal to trichloropentamethyltrisilane 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).

[0065] In a preferred embodiment, in step (3), the temperature of the coupling reaction is 100-120°C (for example, it can be 100°C, 105°C, 110°C, 115°C or 120°C) and the time is 2-4h (for example, it can be 2h, 2.5h, 3h, 3.5h or 4h).

[0066] In the present application, sodium metal is used as a catalyst. If the molar ratio of sodium metal to trichloropentamethyltrisilane is less than 3:1, the reduction coupling ability is insufficient, the reaction is incomplete, and the reaction is prone to premature termination, resulting in a low molecular weight of the product. At the same time, due to incomplete reaction, the product still has active Si-Cl groups at the end, making the product more unstable. However, if the molar ratio of sodium metal to trichloropentamethyltrisilane is higher than 4:1, excessive reduction will occur, which will trigger serious degradation side reactions, resulting in a wide molecular weight distribution of the product. Moreover, too many by-products will also make it difficult to purify the target product, thereby reducing the yield and purity.

[0067] In a preferred embodiment, step (3) comprises the following sub-steps:

[0068] (31) trichloropentamethyltrisilane is added to the second organic solvent and mixed, then sodium metal is added for coupling reaction, and after the reaction is completed, a reaction product is obtained;

[0069] (32) the reaction product is subjected to vacuum distillation, dissolution, filtration, washing, addition of a quenching agent, addition of a terminating agent, and vacuum distillation in sequence to obtain a hyperbranched polysilane.

[0070] Specifically, in step (32): the reaction product containing the 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 filtered to remove unreacted alkali metal and alkali metal salts generated during the reaction. The solid residue is then washed again with n-hexane, and the hyperbranched polysilane-containing filtrate after filtration is combined with the washing liquid, and then the solution is vacuum dried to obtain a solid product. In order to quench the unreacted Si-Cl groups, a quenching agent (methyl magnesium bromide diethyl ether solution) is added to the solid product until the hydrolyzed sample of the current reaction mixture is measured to be neutral (for example, 6.8~7.2) after vigorous stirring. After continuing to stir for 1h, trimethylchlorosilane is added as a terminator of the silane anion chain end until the hydrolyzed sample of the current reaction mixture is measured to be slightly acidic (for example, 6~6.5) after vigorous stirring for 30min. The excess trimethylchlorosilane is again quenched by adding an ethyl ether solution of methyl magnesium bromide to the stirred reaction mixture. All volatile compounds and solvents are removed under vacuum drying.

[0071] In a preferred embodiment, in step (3): the hyperbranched polysilane is subjected to cracking to obtain the ceramic precursor by using a hollow catalyst; the amount of the hollow catalyst is 0.5wt%~1wt% (for example, it can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% or 1wt%) of the amount of the hyperbranched polysilane; wherein the hollow catalyst comprises, from inside to outside, a titanium dioxide hollow sphere, a silica intermediate layer and an active outer layer; the mass ratio of the titanium dioxide hollow sphere 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% (for example, it can be 1wt%, 1.2wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.8wt% or 2wt%) of the hollow catalyst.

[0072] The hollow catalyst is prepared by the following method:

[0073] S1: dispersing carbon nanospheres in a solvent, then adding tetrabutyl titanate and an aqueous ethanol solution to mix, to obtain titanium dioxide coated carbon nanospheres; and calcining the titanium dioxide coated carbon nanospheres to obtain titanium dioxide hollow spheres;

[0074] S2: dispersing the titanium dioxide hollow spheres in a solvent, and adding silica nanoparticles to mix, to obtain silica coated hollow spheres; and calcining the silica coated hollow spheres to obtain a carrier; the mass ratio of the titanium dioxide hollow spheres to the silica intermediate layer is (1~10):(1~10);

[0075] S3: dipping the carrier into a mixed solution containing chloroplatinic acid and nickel nitrate to obtain a precursor solution; and obtaining the hollow catalyst after sequentially filtering, drying and reducing the precursor solution; wherein the mass ratio of Pt to Ni in the mixed solution is (1-2):(1-2).

[0076] For (1-10):(1-10), it can be any value between 1:10 and 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.

[0077] For (1-2):(1-2), it can be any value between 1:2 and 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.

[0078] The hollow catalyst provided by the application is a TiO2-SiO2 double oxide carrier with a hollow structure, and the surface is loaded with active ingredients. The nanostructure form of the hollow core-shell structure has better mass transfer and charge separation efficiency, larger surface area than the same weight of bulk form, and has a three-dimensional heterogeneous structure, thereby improving the reaction activity and efficiency of cracking. Among them, SiO2 as a composite material of TiO2 hollow sphere further improves the thermal stability, mechanical strength and surface area of TiO2 hollow sphere. On the other hand, the synergistic effect between Pt-Ni bimetal optimizes the catalytic ability to the reactants, so that the hollow TiO2-SiO2 double oxide carrier and Pt-Ni bimetal jointly act, so that polysilane is rapidly cracked at a temperature lower than that required by the traditional platinum-based catalyst, greatly shortening the reaction time and improving the production efficiency.

[0079] In the application, the hollow TiO2-SiO2 double oxide carrier also has excellent thermal stability and anti-coking performance, effectively inhibiting the coking phenomenon of the hollow catalyst during the polysilane cracking process, maintaining the activity of the hollow catalyst, and further ensuring that the cracking reaction can continue efficiently, thereby improving the final yield of the ceramic precursor.

[0080] In the present application, experiments have proved that if the mass ratio of the hollow TiO2 sphere and the intermediate layer of SiO2 is greater than 10:1, the grain sintering occurs easily at 200-400 DEG C, which leads to the collapse of the hollow structure of the carrier, and further leads to the lengthening of the mass transfer path, and significantly reduces the catalytic efficiency; secondly, if the proportion of TiO2 is too high, the thickness of SiO2 becomes thin or even locally missing, which cannot effectively wrap TiO2, leading to the easy agglomeration of bimetallic particles at high temperature, and further leading to the sharp decay of catalytic activity. If the mass ratio of the hollow TiO2 sphere and the intermediate layer of SiO2 is less than 1:10, the amount of the hollow TiO2 sphere is too small, which is difficult to effectively weaken the Si-C bond, leading to the increase of the reaction activation energy, and the need for higher reaction temperature or longer reaction time, and further leading to the reduction of catalytic efficiency.

[0081] In the present application, the process of preparing ceramic precursor by polysilane cracking includes Si-H bond activation, C-Si bond breaking-chain rearrangement multi-step reaction, and by limiting the ratio between Pt and Ni in the mixed solution during impregnation, the Pt and Ni loadings of the active outer layer of the hollow catalyst can be further determined, and the synergy of the multi-step reaction is realized. Experiments have proved that if the mass ratio of Pt and Ni in the mixed solution is less than 1:2, the amount of Ni is too much, the Ni of the active outer layer of the catalyst is too much, the C atoms generated by the cracking of polysilane are adsorbed on the surface of Ni, which causes excessive adsorption and affects chain rearrangement, and also causes carbon deposition to shield the metal active sites, leading to the reduction of catalytic efficiency; and the breaking ability of Ni to C-Si bond is strong, and too much Ni or leads to excessive breaking of C-Si bond to generate small molecule byproducts, reducing the yield and purity of the ceramic precursor. If the mass ratio of Pt and Ni in the mixed solution is greater than 2:1, the amount of Ni is too small, the Ni of the active outer layer of the catalyst is too small, and the active sites for C-Si bond breaking are insufficient, leading to the reduction of production efficiency; at this time, the amount of Pt is relatively large, the cost of Pt is too high, but the catalytic performance does not improve significantly; at the same time, the amount of Pt is relatively large, the activated Si-H bond may form Si-Si bond through self-coupling due to the lack of C-Si breaking fragments, and the existence of Si-Si bond will seriously deteriorate the mechanical strength of the ceramic precursor. Thus, the present application realizes the functional synergy of Pt and Ni by controlling the mass ratio of Pt and Ni, which can not only ensure the effective breaking of C-Si bond, but also avoid excessive breaking and carbon deposition, and ensure the yield, purity and thermal stability of the ceramic precursor. Compared with the traditional single catalyst, the amount of noble metal is reduced under the premise of ensuring the catalytic performance, thereby significantly reducing the cost of the catalyst, and meeting the industrial application requirements.

[0082] In the embodiments of the present application, the content of the active outer layer is limited to 1wt%-2wt%, which can not only ensure the high catalytic efficiency and high yield of polysilane cracking, but also reduce the cracking temperature, shorten the reaction time, and avoid the low efficiency when the amount of the active outer layer is too small, and avoid the high production cost when the amount of the active outer layer is too much.

[0083] The application also provides a ceramic precursor prepared by the above preparation method.

[0084] In the application, each raw material used in the absence of special instructions can be a product directly purchased on the market or synthesized by an existing method.

[0085] In the application, "and / or" appearing between multiple technical features means that these technical features are connected in a "and / or" relationship, indicating that it can be any one of these technical features, or a combination of any two or more of these technical features.

[0086] The application will be further described below by way of examples, but the protection scope of the application is not limited to these examples.

[0087] Example 1

[0088] (1) In a glove box, 45 mmol of lithium metal was added to 10 mL of anhydrous tetrahydrofuran, and then cooled to -10°C using an ice-salt bath; 20 mmol of dimethylphenylchlorosilane was added at a rate of 1 mL / h, after the addition was completed, it was slowly warmed to room temperature (25°C), and after 1 h of reaction, it was cooled to -10°C, and then 10 mmol of methylphenyldichlorosilane was added at a rate of 1 mL / h to avoid local overheating, and then 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 to quench the excess lithium until no bubbles were generated; then 50 mL of deionized water and 50 mL of n-hexane were added for extraction, and the organic phase and the aqueous phase were collected by liquid separation, and 30 mL of n-hexane was used for each aqueous phase for a total of 3 times to obtain secondary organic phase, after the organic phase was mixed, anhydrous MgSO4 was used to dry the organic phase (the amount of anhydrous MgSO4 was 1 / 10 of the volume of the organic phase), after 2 h of standing, the filtrate was filtered, and then the filtrate was distilled under reduced pressure at 40°C and 0.08 MPa to remove the solvent to collect the target fraction, i.e., triphenylpentamethyltrisilane;

[0089] (2) 55 mmol of triphenylpentamethyltrisilane and 100 mL of anhydrous n-hexane were added to a flask, and stirred to completely dissolve. Then 165 mmol of anhydrous AlCl3 was added, and 330 mmol of acetyl chloride was added dropwise at a rate of 1 mL / h under cooling with an ice water bath (0-5°C). The reaction mixture was slowly warmed to room temperature and stirred at room temperature for 7 h. The reaction was monitored in real time by gas chromatography, and when the starting material peak disappeared and the target product peak was stable, the reaction was terminated. The obtained reaction product was filtered to obtain a filtrate and a filter residue, and the filter residue was washed with n-hexane to obtain a second filtrate. All the filtrates were combined, and the filtrate was subjected to vacuum distillation at 86°C and 0.0013 MPa to obtain colorless liquid trichloropentamethylpropylsilane;

[0090] (3) In a glove box, sodium metal (28.26 mmol) and trichloropentamethylpropylsilane (9.42 mmol) were added to a solution of 20 mL of toluene, and then the reaction mixture was heated to 110°C and stirred for 4 h. After the reaction was completed, a reaction product containing hyperbranched polysilane was obtained, and then the reaction product was cooled to room temperature, followed by vacuum distillation to remove toluene and other volatile compounds to obtain a turbid solution. The turbid solution was filtered to remove unreacted alkali metal and alkali metal salts generated during the reaction. Then the solid residue was washed again with n-hexane, and the filtered hyperbranched polysilane-containing filtrate was combined with the washing liquid, and then the solution was vacuum dried to obtain a solid product. The solid product was dissolved in 50 mL of n-hexane, and a methylmagnesium bromide diethyl ether solution was added until the pH of the reaction system reached 6.8-7.2. After continuing to stir for 1 h, a small amount of trimethylchlorosilane was added as a terminator for the end of the silicon-based anion 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, and then added to 100 mL of methanol at room temperature. Finally, a white precipitate was separated from the solution by filtration and vacuum drying to obtain hyperbranched polysilane;

[0091] Under the protection of high-purity nitrogen, 100 g of hyperbranched polysilane was dissolved in a normal-pressure cracking reaction kettle containing n-hexane, and then heated at 320°C for 2 h and then heated at 420°C for 2 h to react. After cooling, a polycarbosilane capable of being used for spinning was obtained.

[0092] Example 2

[0093] Example 2 is basically the same as Example 1, except that the cracking reaction in step (3) is different.

[0094] Specifically, the hyperbranched polysilane was dissolved in n-hexane, and then heated at 360°C for 2 h and then heated at 420°C for 2 h to react. After cooling, a polycarbosilane capable of being used for spinning was obtained.

[0095] Example 3

[0096] Example 3 is basically the same as Example 1, except that the cleavage reaction in step (3) is different.

[0097] Specifically, the hyperbranched polysilane is dissolved in n-hexane, then heated at 400℃ for 2h, and then heated at 420℃ for 2h to perform the reaction, and after cooling, a polycarbosilane capable of being used for spinning is obtained.

[0098] Example 4

[0099] Example 4 is basically the same as Example 1, except that the preparation method of trichloropentamethylpropylsilane is different.

[0100] Specifically, (1) in a glove box, 60 mmol of lithium metal is added to 15 mL of anhydrous tetrahydrofuran, and then cooled to -10℃ using an ice-salt bath; 20 mmol of dimethylphenylchlorosilane is added dropwise at a rate of 2 mL / h, after the dropwise addition is completed, it is slowly warmed to room temperature (25℃), and after reacting for 2h, it is cooled to -10℃, and then 7 mmol of methylphenyldichlorosilane is added dropwise at a rate of 1 mL / h to avoid local overheating, and then continues to react for 6h, after the reaction is completed, the initial product containing triphenylpentamethyltrisilane is obtained. The initial product is placed in an ice-salt bath, and 20 mL of methanol is slowly added dropwise to quench the excess lithium until no bubbles are generated; then 50 mL of deionized water and 50 mL of n-hexane are added for extraction, and the organic phase and the aqueous phase are collected by liquid-liquid separation, and 30 mL of n-hexane is used for each time to extract the aqueous phase for a total of 3 times to obtain secondary organic phase, and after all the organic phases are mixed, the organic phase is dried using anhydrous MgSO4 (the amount of anhydrous MgSO4 is 1 / 10 of the volume of the organic phase), and after standing for 2h, it is filtered, and then the filtrate is subjected to vacuum distillation at 50℃ and 0.09 MPa to remove the solvent to collect the target fraction, i.e. to obtain triphenylpentamethyltrisilane;

[0101] (2) 55 mmol of triphenylpentamethyltrisilane and 100 mL of anhydrous n-hexane are added to a flask, and stirred to completely dissolve. Then 220 mmol of anhydrous AlCl3 is added, and under ice water bath (0~5℃) cooling, 440 mmol of acetyl chloride is added dropwise at a rate of 2 mL / h, and the reaction mixture is slowly warmed to room temperature and stirred at room temperature for 6h. The reaction is terminated when the raw material peak disappears and the target product peak is stable by real-time monitoring of the reaction by gas chromatography. The obtained reaction product is filtered to obtain a filtrate and a filter residue, and the filter residue is washed with n-hexane to obtain a secondary filtrate, and after all the filtrates are combined, the filtrate is subjected to vacuum distillation at 86℃ and 0.0013 MPa to obtain colorless liquid trichloropentamethylpropylsilane.

[0102] Example 5

[0103] Example 5 is substantially identical to Example 1, except that step (3) is different;

[0104] (3) In a glove box, sodium metal (37.68 mmol) and trichloropentamethylsilane (9.42 mmol) were added to a solution of 20 mL of toluene, and then the reaction mixture was heated to 100°C and stirred for 4 h. After the reaction was completed, a reaction product containing a hyperbranched polysilane was obtained, and then the reaction product was cooled to room temperature. The toluene and other volatile compounds were removed by distillation under reduced pressure to obtain a turbid solution. The turbid solution was filtered to remove unreacted alkali metal and alkali metal salts generated during the reaction. The solid residue was then washed again with n-hexane, and the filtered hyperbranched polysilane-containing filtrate and the washing liquid were combined. The solution was then vacuum dried to obtain a solid product. The solid product was dissolved in 50 mL of n-hexane, and a methylmagnesium bromide diethyl ether solution 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 anion chain end, until the pH of the reaction system reached 6. Then, after removing all volatile compounds and solvents by distillation under reduced pressure, the reaction product was immediately dissolved in 10 mL of tetrahydrofuran, and then added to 100 mL of methanol at room temperature. Finally, a white precipitate was separated from the solution by filtration and vacuum drying, to obtain a hyperbranched polysilane;

[0105] Under the protection of high-purity nitrogen, 100 g of the hyperbranched polysilane was dissolved in a normal-pressure pyrolysis reactor containing n-hexane, and then heated at 320°C for 2 h and then heated at 420°C for 2 h to perform the reaction. After cooling, a polycarbosilane that can be used for spinning was obtained.

[0106] Example 6

[0107] Example 6 is substantially identical to Example 1, except that step (3) is different;

[0108] (3) In a glove box, sodium metal (32.97 mmol) and trichloropentamethylsilane (9.42 mmol) were added to a solution of 20 mL of toluene, and then the reaction mixture was heated to 120°C and stirred for 2 h. After the reaction was completed, a reaction product containing hyperbranched polysilane was obtained. Then the reaction product was cooled to room temperature, and then vacuum distillation was performed to remove toluene and other volatile compounds to obtain a turbid solution. The turbid solution was filtered to remove unreacted alkali metal and alkali metal salts generated during the reaction. Then the solid residue was washed again with n-hexane, and the hyperbranched polysilane-containing filtrate after filtration was combined with the washing liquid, and then the solution was vacuum dried to obtain a solid product. The solid product was dissolved in 50 mL of n-hexane, and a methylmagnesium bromide diethyl ether solution was added until the pH of the reaction system reached 6.8-7.2. After continuing to stir for 1 h, a small amount of trimethylchlorosilane was added as a terminator for the end of the silicon-based anion 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, and then added to 100 mL of methanol at room temperature. Finally, a white precipitate was separated from the solution by filtration and vacuum drying to obtain hyperbranched polysilane;

[0109] Under the protection of high-purity nitrogen, 100 g of hyperbranched polysilane was dissolved in a normal-pressure cracking reaction kettle containing n-hexane, and then heated at 320°C for 2 h and then heated to 420°C for 2 h to react. After cooling, a polycarbosilane that can be used for spinning was obtained.

[0110] Example 7

[0111] Example 7 is basically the same as Example 1, except that the difference lies in the cracking reaction in step (3);

[0112] Under the protection of high-purity nitrogen, 100 g of hyperbranched polysilane was dissolved in a normal-pressure cracking reaction kettle containing n-hexane, and then 0.5 g of hollow catalyst was added. After heating at 320°C for 2 h and then heating to 420°C for 2 h to react, a polycarbosilane that can be used for spinning was obtained after cooling.

[0113] The hollow catalyst is prepared by the following method:

[0114] S1, 100 mg of carbon nanospheres (100 nm in diameter) were dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed for 0.5 h. Then, 9 mL of tetrabutyl titanate (TBOT) was added dropwise to the above system at a rate of 3 mL / min under magnetic stirring for 1 h. Then, 54 mL of an ethanol aqueous solution (consisting 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, the TBOT was allowed to adsorb on the surface of the carbon nanospheres and hydrolyze at 60°C under stirring at 250 rpm to obtain a mixed solution system containing titanium dioxide-coated carbon nanospheres. The mixed solution system was filtered and dried at 80°C to obtain titanium dioxide-coated carbon nanospheres. The titanium dioxide-coated carbon nanospheres were calcined in a muffle furnace at 600°C for 3 h to remove the core layer of the carbon spheres, thereby obtaining titanium dioxide hollow spheres.

[0115] S2, 0.1 g of the titanium dioxide hollow spheres obtained in step S1 were dispersed in 50 mL of anhydrous ethanol and ultrasonically treated at a power density of 500 w for 30 min. Then, 0.1 g of silica nanoparticles (20 nm in diameter) was added to the above system and ultrasonically mixed for 30 min. Then, the above mixed solution was stirred at 60°C at 250 rpm for 1.5 h. After filtration and drying (dried at 100°C for 2 h), silica-coated hollow spheres were obtained. The silica-coated hollow spheres were calcined in a muffle furnace at 500°C for 5 h to form a complex hollow TiO2-SiO2 double oxide carrier.

[0116] S3, 1 g of the complex hollow TiO2-SiO2 double oxide carrier obtained in step S2 was dispersed in deionized water. Then, a mixed solution containing chloroplatinic acid H2PtCl6·6H2O and nickel nitrate Ni(NO3)2·6H2O (wherein the mass ratio of Pt to Ni was 1:1) was added to the above dispersion. The mixture was stirred at room temperature (25°C) for 1 h to obtain a precursor solution. The precursor solution was sequentially filtered and dried to obtain a precursor. The precursor was placed in a hydrogen atmosphere (a mixed gas consisting of 20% hydrogen and 80% nitrogen) at 400°C and reacted for 1 h, so that the precursor was converted into metal Pt and Ni and loaded on the carrier of step S2 to obtain a hollow catalyst. The hollow catalyst sequentially comprises a titanium dioxide hollow sphere, a silica intermediate layer and an active outer layer from the inside to the outside. The mass ratio of the titanium dioxide hollow sphere to the silica intermediate layer is 1:1. The active outer layer is composed of Pt and Ni. The active outer layer accounts for about 1 wt% of the hollow catalyst.

[0117] Example 8

[0118] Example 8 is basically the same as Example 7, except that the mass ratio of the titanium dioxide hollow sphere to the silica intermediate layer in the hollow catalyst is 5:1.

[0119] Specifically, in step S2, 0.5 g of the titanium dioxide hollow spheres obtained in step S1 were dispersed in 50 mL of anhydrous ethanol and ultrasonically treated for 30 min at a power density of 500 w; then, 0.1 g of silica nanoparticles (with a particle size of 20 nm) were added to the system and ultrasonically treated for 30 min to mix, and then the mixed solution was stirred at 250 rpm at 60 °C for 1.5 h, and then filtered and dried (dried at 100 °C for 2 h) to obtain silica-coated hollow spheres; and the silica-coated hollow spheres were calcined in a muffle furnace at 500 °C for 5 h to form a complex hollow TiO2-SiO2 double oxide carrier.

[0120] Example 9

[0121] Example 9 is basically the same as Example 7, except that the mass ratio of Pt to Ni in step S3 for preparing the hollow catalyst is 2:1.

[0122] Specifically, in step S3, 1 g of the complex hollow TiO2-SiO2 double oxide carrier obtained in step S2 was dispersed in deionized water, and then a mixed solution containing chloroplatinic acid H2PtCl6·6H2O and nickel nitrate Ni(NO3)2·6H2O (with a mass ratio of Pt to Ni of 2:1) was added to the dispersion. The mixture was stirred at room temperature (25 °C) for 1 h to obtain a precursor solution; the precursor solution was sequentially filtered and dried to obtain a precursor; and the precursor was placed in a hydrogen atmosphere (a mixed gas composed of 20% hydrogen and 80% nitrogen) at 400 °C for 1 h to convert the precursor into metal Pt and Ni and load them on the carrier of step S2 to obtain a catalyst. The hollow catalyst comprises, from the inside out, titanium dioxide hollow spheres, a silica intermediate layer, and an active outer layer; the mass ratio of the titanium dioxide hollow 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 about 1 wt% of the hollow catalyst.

[0123] Comparative Example 1

[0124] Linear polydimethylsilane was placed in a normal-pressure cracking reactor under the protection of high-purity nitrogen, and then heated to 360 °C to completely crack the linear polydimethylsilane into liquid polysilane (LPS); then the temperature was raised to 420 °C, and the system was kept at this temperature for 8 h; and after natural cooling, polycarbosilane was obtained.

[0125] Comparative Example 2

[0126] Sodium metal (28.26 mmol) and 20 mL of toluene were loaded into a 6 L cylindrical glass reaction vessel, then the toluene was refluxed by jacket using a circulation bath. A slightly positive pressure of nitrogen atmosphere was maintained throughout the process, then the molten sodium was dispersed using a double inclined blade impeller, and the jacket temperature was maintained at 110°C, then a mixture containing methylphenyldichlorosilane (1.46 g), diphenyldichlorosilane (508 mg) and methyltrichlorosilane (357 mg) was added dropwise into the reaction vessel within 60 min, and incubated at 110°C for 16 h, after the reaction was cooled to 40°C, 2 g of methanol was slowly added to oxidize the residual sodium metal. Then the salt was separated by centrifugation, the toluene solution was filtered, and then the remaining mixture was concentrated to 10 mL by vacuum evaporation. The mixed solution was slowly added to methanol to precipitate the product, then after filtration, it was dried in a vacuum oven to obtain a powder of hyperbranched polysilane;

[0127] Under the protection of high-purity nitrogen, 100 g of the hyperbranched polysilane was dissolved in a normal-pressure pyrolysis reactor containing n-hexane, then heated to 400°C for 2 h and then heated to 420°C for 2 h to react, and after cooling, a polycarbosilane capable of being used for spinning was obtained.

[0128] Comparative Example 3

[0129] In a glove box, a solution of sodium metal (39.9 mmol), 20 mL of toluene and dichlorotetramethyldisilane (13.3 mmol) was prepared, then the reaction mixture was heated to 110°C and stirred for 4 h, after the reaction was completed, a reaction product containing hyperbranched polysilane was obtained, then the reaction product was cooled to room temperature, and the toluene and other volatile compounds were removed by reduced pressure distillation. The hyperbranched polysilane in the residue was dissolved in 50 mL of n-hexane, then a solution of methylmagnesium bromide in diethyl ether was added until the pH of the reaction system reached 6.8-7.2, and then the stirring was continued for 1 h, and a small amount of trimethylchlorosilane was added as a terminator for the anionic chain end of silicon, until the pH of the reaction system reached 6. Then after removing all volatile compounds and solvents by reduced pressure distillation, the hyperbranched polysilane was immediately dissolved in 10 mL of tetrahydrofuran, and 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 the hyperbranched polysilane;

[0130] Under the protection of high-purity nitrogen, 100 g of the hyperbranched polysilane was dissolved in a normal-pressure pyrolysis reactor containing n-hexane, then heated to 400°C for 2 h and then heated to 420°C for 2 h to react, and after cooling, a polycarbosilane capable of being used for spinning was obtained.

[0131] Comparative Example 4

[0132] Comparative Example 4 is substantially the same as Example 7, except that the hollow catalyst is different and the cracking reaction of Step (3) is different.

[0133] In particular, the hollow catalyst is prepared by the following method:

[0134] S1, 100 mg of carbon nanospheres (particle size of 100 nm) were dispersed in 100 mL of anhydrous ethanol and ultrasonically dispersed for 0.5 h. Then, after magnetic stirring and mixing for 1 h, 9 mL of tetraethyl orthosilicate was slowly added dropwise while stirring was continued. Then, 54 mL of an aqueous ethanol solution (consisting of 9 mL of water and 45 mL of anhydrous ethanol) was added dropwise to the above system, and then, at 60°C, the tetraethyl orthosilicate was allowed to adsorb on the surface of the carbon nanospheres and hydrolyze at 250 rpm, to obtain a mixed solution system containing silica-coated carbon nanospheres. The mixed solution system was filtered and dried at 80°C to obtain silica-coated carbon nanospheres. The silica-coated carbon nanospheres were calcined in a muffle furnace at 600°C for 3 h to remove the core layer of the carbon spheres, to obtain silica hollow spheres;

[0135] S2, 0.1 g of the silica hollow spheres obtained in Step S1 were dispersed in 50 mL of anhydrous ethanol and ultrasonically treated at a power density of 500 w for 30 min. Then, 0.1 g of titanium dioxide nanoparticles (particle size of 20 nm) was added to the system and ultrasonically mixed for 30 min. Then, the above mixed solution was stirred at 60°C at 250 rpm for 1.5 h, and then, after filtration and drying (drying at 100°C for 2 h), titanium dioxide-coated hollow spheres were obtained. The titanium dioxide-coated hollow spheres were calcined in a muffle furnace at 500°C for 5 h to form a carrier;

[0136] S3, 1 g of the carrier obtained in Step S2 was dispersed in deionized water, and then a mixed solution containing chloroplatinic acid H2PtCl6·6H2O and nickel nitrate Ni(NO3)2·6H2O (wherein the mass ratio of Pt to Ni is 1:1) was added to the above dispersion. The precursor solution was obtained after stirring at room temperature (25°C) for 1 h. The precursor solution was sequentially filtered and dried to obtain a precursor. The precursor was placed in a hydrogen atmosphere (a mixed gas consisting of 20% hydrogen and 80% nitrogen) at 400°C for 1 h, to convert the precursor into metal Pt and Ni and load them on the carrier of Step S2, to obtain a hollow catalyst. The hollow catalyst comprises, from the inside out, silica hollow spheres, a titanium dioxide intermediate layer, and an active outer layer. The mass ratio of the silica hollow 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 1 wt% of the hollow catalyst;

[0137] Step (3), under the protection of high-purity nitrogen, 100 g of the hyperbranched polysilane was dissolved in a normal-pressure pyrolysis reactor containing n-hexane, and then heated at 380°C for 2 h, and then heated at 420°C for 2 h to perform the reaction. After cooling, poly (carbosilane) capable of being used for spinning was obtained.

[0138] Comparative Example 5

[0139] Comparative Example 5 is basically the same as Example 7, except that the mass ratio of Pt to Ni in the mixed solution in the preparation process of the hollow catalyst is 1:3, and the pyrolysis reaction in step (3) is different.

[0140] Specifically, S3, 1 g of the carrier obtained in step S2 was dispersed in deionized water, and then a mixed solution containing chloroplatinic acid H2PtCl6·6H2O and nickel nitrate Ni(NO3)2·6H2O (wherein the mass ratio of Pt to Ni is 1:3) was added to the above dispersion. And stirred at room temperature (25°C) for 1 h to obtain a precursor solution; the precursor solution was sequentially filtered, dried to obtain a precursor; the precursor was placed in a hydrogen atmosphere (a mixed gas composed of 20% hydrogen and 80% nitrogen) at 400°C for 1 h to convert the precursor into metal Pt, Ni and load them on the carrier of step S2 to obtain a hollow catalyst. The hollow catalyst comprises, from the inside out, a titanium dioxide hollow sphere, a silica intermediate layer and an active outer layer; the mass ratio of the titanium dioxide hollow sphere to the silica intermediate layer is 1:1; the active outer layer is composed of Pt and Ni; the active outer layer accounts for about 1 wt% of the hollow catalyst;

[0141] Step (3), under the protection of high-purity nitrogen, 100 g of the hyperbranched polysilane was dissolved in a normal-pressure pyrolysis reactor containing n-hexane, and then heated at 380°C for 2 h, and then heated at 420°C for 2 h to perform the reaction. After cooling, poly (carbosilane) capable of being used for spinning was obtained.

[0142] Comparative Example 6

[0143] Comparative Example 6 is basically the same as Example 7, except that the mass ratio of Pt to Ni in the mixed solution in the preparation process of the hollow catalyst is 3:1, and the pyrolysis reaction in step (3) is different.

[0144] Specifically, 1 g of the carrier obtained in step S2 is dispersed in deionized water, and then a mixed solution containing chloroplatinic acid H2PtCl6·6H2O and nickel nitrate Ni(NO3)2·6H2O (wherein the mass ratio of Pt to Ni is 3:1) is added to the dispersion. The precursor solution is obtained by stirring at room temperature (25℃) for 1 h. The precursor solution is filtered and dried in sequence to obtain a precursor. The precursor is placed in a hydrogen atmosphere (a mixed gas composed of 20% hydrogen and 80% nitrogen) at 400℃ for 1 h, so that the precursor is converted into metal Pt and Ni and loaded on the carrier of step S2 to obtain a hollow catalyst. The hollow catalyst comprises, from the inside to the outside, a titanium dioxide hollow sphere, a silica intermediate layer and an active outer layer; the mass ratio of the titanium dioxide hollow sphere to the silica intermediate layer is 1:1; the active outer layer is composed of Pt and Ni; the active outer layer accounts for about 1 wt% of the hollow catalyst;

[0145] Step (3), under the protection of high-purity nitrogen, 100 g of the hyperbranched polysilane is dissolved in a normal-pressure pyrolysis reactor containing n-hexane, and then heated at 380℃ for 2 h, and then heated at 420℃ for 2 h to perform the reaction. After cooling, a polycarbosilane capable of being used for spinning is obtained.

[0146] The present application tests the molecular weight distribution coefficient of the polycarbosilane prepared in each example and each comparative example, and the reaction temperature, reaction time and polycarbosilane yield in the pyrolysis process are counted, and the data results are shown in Table 1.

[0147] Table 1

[0148]

[0149] As can be seen from the data in Table 1, the ceramic precursor (i.e. polycarbosilane) prepared in the examples of the present application has a hyperbranched structure, a narrow molecular weight distribution, can avoid performance fluctuations caused by irregular copolymerization, and has excellent solubility, capable of being dissolved in hydrocarbon solvents, so that the polycarbosilane can be directly prepared by normal-pressure heating pyrolysis, without the need for complex or expensive equipment, 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 branched units of Comparative Example 3, the hyperbranched polysilane containing tertiary silicon branched unit and linear silicon unit prepared in the examples of the present application has a lower pyrolysis temperature, a narrower molecular weight distribution of the prepared polycarbosilane and a higher yield.

[0150] The part of the present application not described in detail is the technology known to those skilled in the art.

[0151] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

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 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 to the outside, 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 includes 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).

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.

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

1.

4. 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.

5. The preparation method according to claim 1, characterized in that, In step (1): The dripping rate is 1~2 mL / h.

6. 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.

7. 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.

8. The preparation method according to claim 1, characterized in that, In step (2): the molar ratio of the chlorinating agent to triphenylpentamethyltrisilane is (6~8):

1.

9. 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.

10. The preparation method according to claim 1, characterized in that, In step (3): the molar ratio of sodium metal to trichloropentamethylpropylsilane is (3~4):

1.

11. The preparation method according to claim 1, characterized in that, In step (3): the temperature of the coupling reaction is 100~120℃ and the time is 2~4h.

12. 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.

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