Carbon-silicon carbide nanofiber aerogel with 3D core-shell structure and preparation method of carbon-silicon carbide nanofiber aerogel

Abstract

The invention relates to the technical field of material synthesis, in particular to carbon-silicon carbide nanofiber aerogel with a 3D core-shell structure and a preparation method of the carbon-silicon carbide nanofiber aerogel. The preparation method provided by the invention comprises the following steps: (1) preparing a silicon carbide precursor spinning solution and a carbon precursor spinning solution, wherein the conductivity of the silicon carbide precursor spinning solution and the conductivity of the carbon precursor spinning solution are respectively and independently 10-100 [mu] S / cm; (2) the carbon precursor spinning is used as a core layer spinning solution, the silicon carbide precursor spinning solution is used as a shell layer spinning solution, coaxial electrostatic spinning is carried out, precursor nanofiber aerogel is obtained, and the environment humidity of coaxial electrostatic spinning is 5-60%; and (3) sequentially carrying out drying, thermocuring and thermal decomposition on the precursor nanofiber aerogel to obtain the carbon-coated silicon carbide nanofiber aerogel with the 3D core-shell structure. According to the method, the 3D core-shell structure carbon-coated silicon carbide nanofiber aerogel is prepared through the electrostatic spinning method, the process is simple, and the method is suitable for industrial application.

Description

Technical Field

[0001] This invention relates to the field of materials synthesis technology, and in particular to a 3D core-shell structured carbon@silicon carbide nanofiber aerogel and its preparation method. Background Technology

[0002] Carbon nanofiber aerogel, as a novel functional material, possesses ultra-lightweight properties, high porosity, and excellent thermal insulation. Its three-dimensional network structure endows the material with good adsorption and permeability, showing potential in environmental protection, energy, and other fields. Chinese patent CN119430152A discloses a carbon nanofiber aerogel and its preparation method, which uses a combination of freeze-drying and heat treatment to prepare a carbon nanofiber aerogel. However, this material still has the following technical problems: (1) The material has limited thermal stability. The carbon skeleton is prone to oxidation and decomposition above 400℃, resulting in insufficient reliability for long-term service in high-temperature environments; (2) The preparation of traditional carbon nanofiber aerogels (such as pure carbon and oxide nanofiber aerogels) suffers from defects such as easy structural collapse, poor mechanical properties, low porosity, and low yield, which limit its large-scale application.

[0003] Silicon carbide is an advanced ceramic material with excellent mechanical properties, high thermal conductivity, high dielectric constant, high temperature resistance, corrosion resistance, and wear resistance. Chinese patent CN119661180A discloses a silicon carbide nanofiber aerogel and its preparation method. The method involves forming an interpenetrating network aerogel in situ with aramid nanofibers and SiO2 sol, followed by high-temperature carbothermal reduction to prepare the silicon carbide nanofiber aerogel. This core-shell structured carbon@silicon carbide nanofiber aerogel possesses both the excellent properties of carbon nanofiber aerogels and the high-temperature resistance and oxidation resistance of silicon carbide.

[0004] However, core-shell nanofiber aerogels are usually produced by post-processing methods such as chemical vapor deposition, atomic layer deposition, and impregnation. However, these methods are all complicated in terms of preparation process and are not suitable for industrial application. Summary of the Invention

[0005] The purpose of this invention is to provide a 3D core-shell structured carbon@silicon carbide nanofiber aerogel and its preparation method. The preparation method provided by this invention is simple, easy to implement, and suitable for industrial application.

[0006] This invention provides a method for preparing 3D core-shell structured carbon@silicon carbide nanofiber aerogel, comprising the following steps: (1) Prepare silicon carbide precursor spinning solution and carbon precursor spinning solution, wherein the conductivity of the silicon carbide precursor spinning solution and the carbon precursor spinning solution is independently 10-100 μS / cm. (2) Using the carbon precursor spinning solution as the core spinning solution and the silicon carbide precursor spinning solution as the shell spinning solution, coaxial electrospinning is performed to obtain precursor nanofiber aerogel, wherein the ambient humidity for coaxial electrospinning is 5-60%. (3) The precursor nanofiber aerogel is dried, thermally cured and thermally decomposed in sequence to obtain 3D core-shell structured carbon@silicon carbide nanofiber aerogel.

[0007] Optionally, the silicon carbide precursor spinning solution includes a silicon carbide precursor and a first organic solvent. The silicon carbide precursor includes at least one of polycarbosilane, polysiloxane, polysilazane, polysiloxane, and polysilane, and the content of the silicon carbide precursor in the silicon carbide precursor spinning solution is 8-20 wt%. The first organic solvent includes at least one of N,N-dimethylformamide, tetrahydrofuran, xylene, chloroform, and dichloromethane.

[0008] Optionally, the carbon precursor spinning solution includes a carbon precursor and a second organic solvent. The carbon precursor includes at least one of polyacrylonitrile, polyimide, phenolic resin, cellulose, and chitosan, and the content of the carbon precursor in the carbon precursor spinning solution is 10-25 wt%. The second organic solvent includes at least one of N,N-dimethylformamide, tetrahydrofuran, xylene, chloroform, and dichloromethane.

[0009] Optionally, the silicon carbide precursor spinning solution includes a first inorganic salt, and the carbon precursor spinning solution includes a second inorganic salt. The first inorganic salt and the second inorganic salt each independently include at least one of inorganic aluminum salt, inorganic titanium salt, inorganic yttrium salt and inorganic iron salt.

[0010] Optionally, the silicon carbide precursor spinning solution further includes a spinning aid, which includes at least one of polyvinylidene fluoride, thermoplastic polyurethane and polyvinylpyrrolidone, and the content of the spinning aid is 1-10 wt%.

[0011] Optionally, the spinning voltage of the coaxial electrospinning is 15~30 kV.

[0012] Optionally, during the coaxial electrospinning process, the distance from the spinneret to the receiving plate is 15~25 cm, the propulsion speed of the core spinning solution is 0.015~0.03 mL / min, the propulsion speed of the shell spinning solution is 0.015~0.03 mL / min, the inner diameter of the spinneret's inner hole is 0.4 mm, the outer diameter of the inner hole is 0.7 mm, the inner diameter of the outer hole is 1.07 mm, and the outer diameter of the outer hole is 1.5 mm.

[0013] Optionally, the thermosetting temperature is 180-200℃ and the time is 5-7 h.

[0014] Optionally, the thermal decomposition is carried out in a protective atmosphere at a temperature of 1400-1600°C for 7-9 hours.

[0015] The present invention also provides a 3D core-shell structured carbon@silicon carbide nanofiber aerogel obtained by the preparation method described in any one of the above technical solutions.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention successfully prepared 3D core-shell carbon@silicon carbide precursor nanofiber aerogels directly via electrospinning by controlling the environmental humidity and the conductivity of the inner and outer spinning solutions during the electrospinning process. Specifically, this invention utilizes a highly conductive spinning solution for electrospinning. The high conductivity increases the surface charge density of the jet, and the resulting electrostatic repulsion prematurely triggers whiplash instability (i.e., accelerates fiber formation), facilitating the formation of a three-dimensional structure. Subsequently, through drying, thermal curing, and thermal decomposition, the 3D core-shell carbon@silicon carbide nanofiber aerogel was obtained. This method not only successfully overcomes the problems of complex preparation processes and poor high-temperature resistance of traditional carbon nanofiber aerogels, but also produces 3D core-shell carbon@silicon carbide nanofiber aerogels that are ultra-lightweight, have high porosity, and possess thermal insulation properties, making them highly applicable in the field of high-temperature insulation. Attached Figure Description

[0017] The above and other objects, features, and advantages of the invention will be apparent from the following description of preferred embodiments illustrating the gist of the invention and its use, and the accompanying drawings, in which: Figure 1 This is a physical image of the 3D core-shell structured carbon@silicon carbide nanofiber aerogel provided in Embodiment 1 of the present invention.

[0018] Figure 2 This is a scanning electron microscope image of the 3D core-shell structured carbon@silicon carbide nanofiber aerogel provided in Example 1 of the present invention.

[0019] Figure 3 This is a physical image of the 3D core-shell structured carbon@silicon carbide nanofiber aerogel after high-temperature treatment, as provided in Example 1 of this invention.

[0020] Figure 4 This is a scanning electron microscope image of the 3D core-shell structured carbon@silicon carbide nanofiber aerogel after high-temperature treatment, as provided in Example 1 of this invention.

[0021] Figure 5This is a scanning electron microscope image of the 3D structured carbon nanofiber aerogel after high-temperature treatment provided in Comparative Example 1 of the present invention.

[0022] Figure 6 This is a physical image of the 2D core-shell structured carbon@silicon carbide nanofiber aerogel provided in Comparative Example 2 of this invention.

[0023] Figure 7 This is a physical image of the 2D core-shell structured carbon@silicon carbide nanofiber aerogel provided in Comparative Example 3 of this invention. Detailed Implementation

[0024] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments described below are for illustrative purposes only and do not limit the scope of the invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the reagents and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the following embodiments, conditions and methods known in the art can be used for processing.

[0025] Electrospinning for the preparation of core-shell nanofibers has been widely used in existing technologies. However, in the process of preparing core-shell carbon@silicon carbide nanofiber aerogels using this method, there are problems such as insufficient adhesion between the silicon carbide and carbon precursors and poor compatibility at the core-shell interface, resulting in the inability to obtain a core-shell structure. Furthermore, the carbon@silicon carbide precursor nanofiber aerogel is prone to collapse during subsequent processing, failing to form a 3D structure. Therefore, there are currently no reports on the preparation of 3D core-shell carbon@silicon carbide nanofiber aerogels using electrospinning.

[0026] This invention provides a method for preparing 3D core-shell structured carbon@silicon carbide nanofiber aerogel, comprising the following steps: (1) Prepare silicon carbide precursor spinning solution and carbon precursor spinning solution, wherein the conductivity of the silicon carbide precursor spinning solution and the carbon precursor spinning solution is independently 10-100 μS / cm. (2) Using the carbon precursor spinning solution as the core spinning solution and the silicon carbide precursor spinning solution as the shell spinning solution, coaxial electrospinning is performed to obtain precursor nanofiber aerogel, wherein the ambient humidity for coaxial electrospinning is 5-60%. (3) The precursor nanofiber aerogel is dried, thermally cured and thermally decomposed in sequence to obtain 3D core-shell structured carbon@silicon carbide nanofiber aerogel.

[0027] The present invention first prepares a silicon carbide precursor spinning solution and a carbon precursor spinning solution, wherein the conductivity of the silicon carbide precursor spinning solution and the carbon precursor spinning solution is independently 10-100 μS / cm.

[0028] In some embodiments of the present invention, the silicon carbide precursor spinning solution comprises a silicon carbide precursor and a first organic solvent. The silicon carbide precursor comprises at least one of polycarbosilane (PCS), polycarbosilane, polysiloxane, polysiloxane, polysiloxane, and polysilane. The content of the silicon carbide precursor in the silicon carbide precursor spinning solution is 8-20 wt%, specifically 10 wt%, 11 wt%, 12 wt%, 14 wt%, 18 wt%, 20 wt%, etc. In the present invention, the above content ensures that the silicon carbide precursor is fully soluble in the solvent and that the electrospinning jet has good stability, thereby facilitating the obtaining of precursor nanofibers with good morphology.

[0029] The present invention does not specifically limit the type of the first organic solvent, as long as it can dissolve the silicon carbide precursor; in some embodiments of the present invention, the first organic solvent includes at least one of N,N-dimethylformamide (DMF), tetrahydrofuran (THF), xylene, chloroform and dichloromethane; specifically, the first organic solvent can be a mixture of DMF and acetone in a volume ratio of 4:6, or a mixture of DMF and THF in a volume ratio of 2:8.

[0030] In some embodiments of the present invention, the carbon precursor spinning solution includes a carbon precursor and a second organic solvent. The carbon precursor includes at least one selected from polyacrylonitrile (PAN), polyimide, phenolic resin, cellulose, and chitosan. The content of the carbon precursor in the carbon precursor spinning solution is 10-25 wt%, specifically 10 wt%, 15 wt%, 16 wt%, 20 wt%, 25 wt%, etc. In the present invention, the above content ensures that the carbon precursor can be fully dissolved in the solvent, and the electrospinning jet has good stability, which is beneficial to obtaining precursor nanofibers with good morphology.

[0031] The present invention does not have a particular limitation on the type of the second organic solvent, as long as it can dissolve the carbon precursor; in some embodiments of the present invention, the second organic solvent includes at least one of N,N-dimethylformamide, tetrahydrofuran, xylene, chloroform and dichloromethane.

[0032] In this invention, the electrical conductivity of the silicon carbide precursor spinning solution and the carbon precursor spinning solution can be adjusted by adding substances that improve conductivity. In some embodiments of this invention, the electrical conductivity of the silicon carbide precursor spinning solution and the carbon precursor spinning solution is adjusted by adding inorganic salts, and the amount of inorganic salt added is based on achieving the desired electrical conductivity. Specifically, in some embodiments of this invention, the silicon carbide precursor spinning solution includes a first inorganic salt, and the carbon precursor spinning solution includes a second inorganic salt. The first and second inorganic salts each independently include at least one of inorganic aluminum salts, inorganic titanium salts, inorganic yttrium salts, and inorganic iron salts, specifically ferric nitrate or its hydrate (such as ferric nitrate nonahydrate), aluminum nitrate or its hydrate (such as aluminum nitrate hydrate), yttrium nitrate or its hydrate (such as yttrium nitrate hexahydrate), titanium chloride, ferric chloride, basic aluminum chloride, etc. In some embodiments of the present invention, the amount of the first inorganic salt is 1-20 wt% of the mass of the silicon carbide precursor, specifically 7 wt%, 11 wt%, 15 wt%, etc.; the amount of the second inorganic salt is 1-20 wt% of the mass of the carbon precursor, specifically 5 wt%, 7 wt%, 9 wt%, 10 wt%, 15 wt%, etc.

[0033] In this invention, the conductivity of the silicon carbide precursor spinning solution and the carbon precursor spinning solution are each independently 10-100 μS / cm, specifically 25 μS / cm, 40 μS / cm, 55 μS / cm, 60 μS / cm, etc. The increased surface charge density of the jet formed by the silicon carbide precursor spinning solution and the carbon precursor spinning solution with the above-mentioned conductivity leads to an increased electrostatic repulsion force that prematurely triggers "whipping instability," thereby promoting the formation of the three-dimensional structure.

[0034] In some embodiments of the present invention, the silicon carbide precursor spinning solution further includes a spinning aid, which includes at least one of polyvinylidene fluoride (PVDF), thermoplastic polyurethane (TPU), and polyvinylpyrrolidone (PVP). The content of the spinning aid is 1-10 wt%, specifically 2 wt%, 5 wt%, 8 wt%, 10 wt%, etc. In the present invention, the spinning aid can be directly electrospun into fibers, which is beneficial to improving the overall viscosity or intermolecular entanglement of the spinning solution. If its content is too low, it will form beaded fibers, while if its content is too high, it will not be completely soluble in the solvent and will easily clog the needles during the spinning process.

[0035] Furthermore, in this invention, the selection of the silicon carbide precursor, carbon precursor, and solvent can further improve the mutual adhesion of the two spinning solutions and enhance the compatibility of the core-shell interface.

[0036] After obtaining the silicon carbide precursor spinning solution and the carbon precursor spinning solution, this invention uses the carbon precursor spinning solution as the core spinning solution and the silicon carbide precursor spinning solution as the shell spinning solution for coaxial electrospinning to obtain precursor nanofiber aerogels. The ambient humidity for the coaxial electrospinning is 5-60%. In this invention, a 3D core-shell structured carbon@silicon carbide precursor nanofiber aerogel, i.e., a silicon carbide precursor encapsulating a carbon precursor nanofiber aerogel, can be obtained through coaxial electrospinning.

[0037] In some embodiments of the present invention, the spinning voltage of the coaxial electrospinning is 15~30 kV, specifically 18 kV, 20 kV, 24 kV, 30 kV, etc. In the present invention, the above spinning voltage further ensures that the obtained precursor nanofibers are of uniform thickness.

[0038] In some embodiments of the present invention, during the coaxial electrospinning process, the distance from the spinneret to the receiving plate is 15-25 cm, specifically 18 cm, 20 cm, 22 cm, etc.; the propulsion speed of the core spinning solution is 0.015-0.03 mL / min, specifically 0.02 mL / min, 0.023 mL / min, 0.025 mL / min, etc.; the propulsion speed of the shell spinning solution is 0.015-0.03 mL / min, specifically 0.02 mL / min, 0.023 mL / min, 0.025 mL / min, etc.; the inner diameter of the spinneret's inner hole is 0.4 mm, the outer diameter of the inner hole is 0.7 mm, the inner diameter of the outer hole is 1.07 mm, and the outer diameter of the outer hole is 1.5 mm.

[0039] In this invention, the ambient humidity for coaxial electrospinning is 5-60%, specifically 13%, 20%, 30%, 50%, etc. In this invention, the combination of the above humidity and the conductivity of the spinning solution ensures the formation of a 3D core-shell structured carbon@silicon carbide precursor nanofiber aerogel. However, excessively low ambient humidity causes rapid solvent evaporation, leading to a shortened jet solidification time, increased fiber rigidity, and a tendency to form a discretely stacked three-dimensional porous structure. Conversely, excessively high ambient humidity hinders solvent evaporation in the jet, prolongs the stretching time of the jet in the electric field, and easily causes fiber adhesion or droplet aggregation, thereby disrupting the regularity of the three-dimensional structure.

[0040] After obtaining the precursor nanofiber aerogel, the present invention sequentially dries, thermally cures, and thermally decomposes the precursor nanofiber aerogel to obtain a 3D core-shell structured carbon@silicon carbide nanofiber aerogel. In the present invention, the curing and cross-linking process (i.e., cross-linking of the silicon carbide precursor and the carbon precursor with oxygen in the air) can be completed through the thermal curing process, and the silicon carbide precursor can be converted into silicon carbide and the carbon precursor into carbon through thermal decomposition.

[0041] The present invention does not have any particular limitation on the drying method, as long as a product with constant weight can be obtained; in the embodiments of the present invention, drying is completed by drying under vacuum conditions at 60°C for 2 hours.

[0042] In some embodiments of the present invention, the temperature for thermosetting is 180-200℃, specifically 180℃, 190℃, 200℃, etc.; the time is 5-7 h, specifically 5 h, 6 h, 7 h, etc.

[0043] In some embodiments of the present invention, the temperature of the thermal decomposition is 1400-1600℃, specifically 1400℃, 1450℃, 1500℃, 1550℃, 1600℃, etc.; the time is 7-9 h, specifically 7 h, 8 h, 9 h, etc.

[0044] In another aspect, the present invention provides a 3D core-shell structured carbon@silicon carbide nanofiber aerogel obtained by the preparation method described in any one of the foregoing technical solutions.

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. The embodiments of this application are only examples, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Example 1 (1) PCS, PVDF and inorganic iron salt (ferric nitrate nonahydrate) were dissolved in a mixed solvent of DMF and acetone (the volume ratio of DMF to acetone was 4:6) to obtain a silicon carbide precursor spinning solution, wherein the content of PCS was 12 wt%, the content of PVDF was 5 wt%, and the amount of inorganic iron salt was 7 wt% of PCS. The conductivity of the spinning solution was tested to be 25 μS / cm using a resistivity tester.

[0047] PAN and inorganic aluminum salt (hydrated aluminum nitrate) were dissolved in DMF to obtain a carbon precursor spinning solution, wherein the content of PAN was 16 wt% and the amount of inorganic aluminum salt was 5 wt% of PAN. The conductivity of the spinning solution was tested to be 25 μS / cm.

[0048] (2) Using carbon precursor spinning solution as core spinning solution and silicon carbide precursor spinning solution as shell spinning solution, coaxial electrospinning was carried out under an ambient humidity of 50% for 6 h to obtain precursor nanofiber aerogel. The spinning voltage of coaxial electrospinning was 20 kV, the propulsion speed of core spinning solution was 0.02 mL / min, the propulsion speed of shell spinning solution was 0.02 mL / min, the inner diameter of the spinneret was 0.4 mm, the outer diameter of the inner hole was 0.7 mm, the inner diameter of the outer hole was 1.07 mm, the outer diameter of the outer hole was 1.5 mm, and the distance from the spinneret to the receiving plate was 20 cm.

[0049] (3) The precursor nanofiber aerogel was dried in a vacuum oven at 60°C for 2 h, then placed in an air atmosphere at 190°C for 6 h for thermal curing, and then placed in a nitrogen atmosphere for thermal decomposition at 1500°C for 8 h to obtain 3D core-shell structure carbon@silicon carbide nanofiber aerogel.

[0050] The physical sample of the 3D core-shell structured carbon@silicon carbide nanofiber aerogel obtained in this embodiment is shown below. Figure 1 As shown, the prepared aerogel exhibits a distinct 3D structure. Its microstructure was characterized using scanning electron microscopy, as shown below. Figure 2 As shown in the figure, the nanofiber aerogel has a distinct core-shell structure and relatively uniform fiber diameter.

[0051] The 3D core-shell structured carbon@silicon carbide nanofiber aerogel prepared in this embodiment was sintered in air under a butane spray gun for 10 min, and its high-temperature resistance and oxidation resistance were tested. The actual image of the sintered aerogel is shown below. Figure 3 As shown, the microstructure is as follows Figure 4 As shown. By Figure 3 and Figure 4 and Figure 1 and Figure 2 The comparison shows that the 3D core-shell structured carbon@silicon carbide nanofiber aerogel prepared by the present invention still maintains good fiber morphology and 3D aerogel structure at high temperature, that is, it has good high temperature resistance.

[0052] Example 2 (1) PCS, TPU and inorganic yttrium salt (yttrium nitrate hexahydrate) were dissolved in a mixed solvent of DMF and tetrahydrofuran (in which the volume ratio of DMF and acetone was 2:8) to obtain a silicon carbide precursor spinning solution, wherein the content of PCS was 14 wt%, the content of TPU was 8 wt%, and the amount of inorganic yttrium salt was 11 wt% of PCS. The conductivity of the spinning solution was tested to be 40 μS / cm.

[0053] PAN and inorganic titanium salt (titanium chloride) were dissolved in DMF to obtain a carbon precursor spinning solution, wherein the content of PAN was 16 wt% and the amount of inorganic titanium salt was 7 wt% of PAN. The conductivity of the spinning solution was tested to be 25 μS / cm.

[0054] (2) Using carbon precursor spinning solution as core spinning solution and silicon carbide precursor spinning solution as shell spinning solution, coaxial electrospinning was carried out under an ambient humidity of 30% for 6 h to obtain precursor nanofiber aerogel. The spinning voltage of coaxial electrospinning was 24 kV, the propulsion speed of core spinning solution was 0.025 mL / min, the propulsion speed of shell spinning solution was 0.025 mL / min, the inner diameter of the spinneret was 0.4 mm, the outer diameter of the inner hole was 0.7 mm, the inner diameter of the outer hole was 1.07 mm, the outer diameter of the outer hole was 1.5 mm, and the distance from the spinneret to the receiving plate was 22 cm.

[0055] (3) The precursor nanofiber aerogel was dried, thermally cured and thermally decomposed in sequence using the method in step (3) of Example 1 to obtain 3D core-shell structure carbon@silicon carbide nanofiber aerogel.

[0056] Example 3 (1) PCS, PVP and inorganic titanium salt (titanium chloride) were dissolved in a mixed solvent of DMF and tetrahydrofuran (in which the volume ratio of DMF and acetone was 2:8) to obtain a silicon carbide precursor spinning solution, wherein the content of PCS was 10 wt%, the content of PVP was 5 wt%, and the amount of inorganic titanium salt was 15 wt% of PCS. The conductivity of the spinning solution was tested to be 55 μS / cm.

[0057] PAN and inorganic iron salt (ferric chloride) were dissolved in DMF to obtain a carbon precursor spinning solution, wherein the content of PAN was 16 wt% and the amount of inorganic iron salt was 9 wt% of PAN. The conductivity of the spinning solution was tested to be 55 μS / cm.

[0058] (2) Using carbon precursor spinning solution as core spinning solution and silicon carbide precursor spinning solution as shell spinning solution, coaxial electrospinning was carried out under an ambient humidity of 20% for 6 h to obtain precursor nanofiber aerogel. The spinning voltage of coaxial electrospinning was 18 kV, the propulsion speed of core spinning solution was 0.023 mL / min, the propulsion speed of shell spinning solution was 0.023 mL / min, the inner diameter of the spinneret was 0.4 mm, the outer diameter of the inner hole was 0.7 mm, the inner diameter of the outer hole was 1.07 mm, the outer diameter of the outer hole was 1.5 mm, and the distance from the spinneret to the receiving plate was 18 cm.

[0059] (3) The precursor nanofiber aerogel was dried, thermally cured and thermally decomposed in sequence using the method in step (3) of Example 1 to obtain 3D core-shell structure carbon@silicon carbide nanofiber aerogel.

[0060] Example 4 (1) PCS, PVP, TPU and inorganic aluminum salt (basic aluminum chloride) were dissolved in a mixed solvent of DMF and tetrahydrofuran (in which the volume ratio of DMF and acetone was 2:8) to obtain a silicon carbide precursor spinning solution, wherein the content of PCS was 11 wt%, the content of PVP was 2 wt%, the content of TPU was 4 wt%, and the amount of inorganic aluminum salt was 4 wt% of PCS. The conductivity of the spinning solution was tested to be 60 μS / cm.

[0061] PAN and inorganic yttrium salt (yttrium nitrate hexahydrate) were dissolved in DMF to obtain a carbon precursor spinning solution, wherein the content of PAN was 15 wt% and the amount of inorganic yttrium salt was 10 wt% of PAN. The conductivity of the spinning solution was tested to be 60 μS / cm.

[0062] (2) Using carbon precursor spinning solution as core spinning solution and silicon carbide precursor spinning solution as shell spinning solution, coaxial electrospinning was carried out under an ambient humidity of 13% for 6 h to obtain precursor nanofiber aerogel. The spinning voltage of coaxial electrospinning was 18 kV, the propulsion speed of core spinning solution was 0.02 mL / min, the propulsion speed of shell spinning solution was 0.02 mL / min, the inner diameter of the spinneret was 0.4 mm, the outer diameter of the inner hole was 0.7 mm, the inner diameter of the outer hole was 1.07 mm, the outer diameter of the outer hole was 1.5 mm, and the distance from the spinneret to the receiving plate was 20 cm.

[0063] (3) The precursor nanofiber aerogel was dried, thermally cured and thermally decomposed in sequence using the method in step (3) of Example 1 to obtain 3D core-shell structure carbon@silicon carbide nanofiber aerogel.

[0064] Comparative Example 1 (1) The spinning solution was prepared according to the method of core layer spinning solution preparation in Example 1. The obtained spinning solution was spun uniaxially under an ambient humidity of 50% for 6 h to obtain carbon precursor nanofiber aerosol. The spinning voltage was 20 kV, the spinning solution propulsion speed was 0.02 mL / min, the diameter of the spinneret was 0.8 mm, and the distance from the spinneret to the receiving plate was 20 cm.

[0065] (2) The precursor nanofiber aerogel was dried, thermally cured and thermally decomposed in sequence according to the method of step (3) in Example 1 to obtain 3D structured carbon nanofiber aerogel.

[0066] The 3D carbon nanofiber aerogel obtained in Comparative Example 1 was sintered in air under a butane spray gun for 10 min, and its high-temperature resistance and oxidation resistance were tested. The microstructure of the sintered aerogel is shown in the figure. Figure 5 As shown. Figure 5 and Figure 4 By comparison, it can be seen that the morphology of the 3D structured carbon nanofiber aerogel was destroyed after high-temperature treatment, indicating that its high-temperature resistance and antioxidant properties are poor.

[0067] Comparative Example 2 (1) PCS and PVDF were dissolved in a mixed solvent of DMF and acetone (the volume ratio of DMF and acetone was 4:6) to obtain a silicon carbide precursor spinning solution, wherein the content of PCS was 12 wt% and the content of PVDF was 5 wt%. The conductivity of the spinning solution was tested to be 9 μS / cm.

[0068] PAN was dissolved in DMF to obtain a carbon precursor spinning solution, in which the PAN content was 16 wt%, and the conductivity of the spinning solution was tested to be 10 μS / cm.

[0069] (2)-(3) Core-shell structured carbon@silicon carbide nanofiber aerogels were prepared by using steps (2)-(3) in Example 1.

[0070] The physical image of the core-shell structured carbon@silicon carbide nanofiber aerogel obtained in Comparative Example 2 is shown below. Figure 6 As shown, by Figure 6 It can be seen that when no inorganic metal salts are added to the spinning solution, the conductivity of the spinning solution is low. Electrospinning can only produce a thin nanofiber membrane structure, which is a 2D structure and has greater brittleness.

[0071] Comparative Example 3 Core-shell structured carbon@silicon carbide nanofiber aerogels were prepared using the method in Example 1, with the only difference being that the ambient humidity for coaxial electrospinning was 70%.

[0072] After obtaining core-shell structured carbon@silicon carbide nanofiber aerogels, their structural changes were observed and recorded. The results showed that spinning under excessively high humidity resulted in a core-shell structured carbon@silicon carbide nanofiber aerogel with a structure between 2D and 3D. However, after standing for a period of time, the aerogel structure easily collapsed into a 2D structure, ultimately leading to the preparation of 2D core-shell structured carbon@silicon carbide nanofibers. Figure 7 As shown.

[0073] In summary, without silicon carbide as the shell, carbon nanofiber aerogels exhibit poor high-temperature resistance and oxidation resistance. Furthermore, altering the conductivity of the core-shell spinning solution and increasing the humidity of the spinning environment prevents the formation of 3D core-shell structure precursor carbon@silicon carbide nanofiber aerogels. The preparation method of the 3D core-shell structured carbon@silicon carbide nanofiber aerogel provided in this invention has the advantage of simple operation, and the resulting 3D core-shell structured carbon@silicon carbide nanofiber aerogel possesses excellent properties such as ultra-lightweight, high porosity, high-temperature resistance, oxidation resistance, and thermal insulation, making it highly applicable and suitable for the aerospace field.

[0074] Although preferred embodiments of the invention have been shown and described, it is conceivable that those skilled in the art can devise various modifications to the invention within the spirit and scope of the appended claims.

Claims

1. A method for preparing a 3D core-shell structured carbon@silicon carbide nanofiber aerogel, comprising the following steps: (1) Prepare silicon carbide precursor spinning solution and carbon precursor spinning solution, wherein the conductivity of the silicon carbide precursor spinning solution and the carbon precursor spinning solution is independently 10-100 μS / cm. (2) Using the carbon precursor spinning solution as the core spinning solution and the silicon carbide precursor spinning solution as the shell spinning solution, coaxial electrospinning is performed to obtain precursor nanofiber aerogel, wherein the ambient humidity for coaxial electrospinning is 5-60%. (3) The precursor nanofiber aerogel is dried, thermally cured and thermally decomposed in sequence to obtain 3D core-shell structured carbon@silicon carbide nanofiber aerogel.

2. The preparation method according to claim 1, characterized in that, The silicon carbide precursor spinning solution comprises a silicon carbide precursor and a first organic solvent. The silicon carbide precursor comprises at least one of polycarbosilane, polysiloxane, polysilazane, polysiloxane, and polysilane. The content of the silicon carbide precursor in the silicon carbide precursor spinning solution is 8-20 wt%. The first organic solvent comprises at least one of N,N-dimethylformamide, tetrahydrofuran, xylene, chloroform, and dichloromethane.

3. The preparation method according to claim 1, characterized in that, The carbon precursor spinning solution includes a carbon precursor and a second organic solvent. The carbon precursor includes at least one of polyacrylonitrile, polyimide, phenolic resin, cellulose, and chitosan, and the content of the carbon precursor in the carbon precursor spinning solution is 10-25 wt%. The second organic solvent includes at least one of N,N-dimethylformamide, tetrahydrofuran, xylene, chloroform, and dichloromethane.

4. The preparation method according to any one of claims 1-3, characterized in that, The silicon carbide precursor spinning solution includes a first inorganic salt, and the carbon precursor spinning solution includes a second inorganic salt. The first inorganic salt and the second inorganic salt each independently include at least one of inorganic aluminum salt, inorganic titanium salt, inorganic yttrium salt and inorganic iron salt.

5. The preparation method according to claim 1 or 2, characterized in that, The silicon carbide precursor spinning solution further includes spinning aids, which include at least one of polyvinylidene fluoride, thermoplastic polyurethane, and polyvinylpyrrolidone, and the content of the spinning aids is 1-10 wt%.

6. The preparation method according to claim 1, characterized in that, The spinning voltage of the coaxial electrospinning is 15~30 kV.

7. The preparation method according to claim 1 or 6, characterized in that, During the coaxial electrospinning process, the distance from the spinneret to the receiving plate is 15~25 cm, the propulsion speed of the core spinning solution is 0.015~0.03 mL / min, the propulsion speed of the shell spinning solution is 0.015~0.03 mL / min, the inner diameter of the spinneret's inner hole is 0.4 mm, the outer diameter of the inner hole is 0.7 mm, the inner diameter of the outer hole is 1.07 mm, and the outer diameter of the outer hole is 1.5 mm.

8. The preparation method according to claim 1, characterized in that, The thermosetting temperature is 180-200℃, and the time is 5-7 h.

9. The preparation method according to claim 1, characterized in that, The thermal decomposition is carried out in a protective atmosphere at a temperature of 1400-1600℃ for 7-9 hours.

10. A 3D core-shell structured carbon@silicon carbide nanofiber aerogel obtained by the preparation method according to any one of claims 1-9.

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