Three-dimensional network-shaped silicon carbide and silicon nitride nanowire composite aerogel with high compression strength and preparation method of three-dimensional network-shaped silicon carbide and silicon nitride nanowire composite aerogel

Abstract

The invention discloses three-dimensional network-shaped silicon carbide and silicon nitride nanowire composite aerogel with high compression strength and a preparation method of the three-dimensional network-shaped silicon carbide and silicon nitride nanowire composite aerogel, and belongs to the technical field of composite aerogel. The preparation method comprises the following steps: uniformly mixing polysilazane, xylene and ferrocene to obtain a mixed solution; dipping melamine foam in the mixed solution, repeatedly extruding the melamine foam until the melamine foam is completely infiltrated by the mixed solution, and turning over and airing for many times until the mixed solution in the melamine foam is completely solidified to obtain a solidified sample; and carrying out heat treatment on the cured sample in a nitrogen atmosphere to prepare the three-dimensional network-shaped silicon carbide and silicon nitride nanowire composite aerogel with high compression strength. The three-dimensional network-shaped silicon carbide is uniformly distributed in the composite aerogel in a network shape, the silicon nitride nanowires are uniformly distributed in the three-dimensional network-shaped silicon carbide in an agglomerated shape, and the aerogel composite material with the structure has good compression strength and fire resistance and heat insulation performance.

Description

Technical Field

[0001] The invention belongs to the technical field of composite aerogels, and in particular relates to a three-dimensional network-shaped silicon carbide and silicon nitride nanowire composite aerogel with high compression strength and a preparation method thereof. Background Art

[0002] Aerogel has attracted wide attention due to its extremely high porosity, extremely low density, high specific surface area and good fire-resistant and heat-insulating properties. However, the compression strength of aerogel is generally low, and it is very easy to collapse the structure when facing external impact, which in turn affects its fire-resistant and heat-insulating effect and service life when facing external impact. Silicon carbide ceramics have excellent room temperature mechanical properties and good oxidation resistance, and its high-temperature mechanical properties are the best among known ceramic materials, and its high-temperature strength can be maintained up to 1600°C. One-dimensional silicon nitride nanomaterials have excellent properties such as good chemical stability, high temperature resistance, good flexibility, corrosion resistance, and good fire resistance. The one-dimensional silicon nitride nanomaterial stacked in a three-dimensional network has more micro-nano pores, which increases the phonon thermal vibration of the air during the heat transfer process, increases heat consumption, reduces heat transfer, and the silicon nitride material itself has a high melting point, so it has good fire-resistant and heat-insulating effects. The use of low thermal conductivity aerogels with high compression strength in practical applications is crucial to expand the application scenarios of aerogels and extend their service life.

[0003] Reference 1 “Zhi-Long, Yu, Bing, et al. Superelastic Hard Carbon Nanofiber Aerogels[J]. Advanced Materials, 2019.” reported the conversion of traditional rigid phenolic resin into superelastic hard carbon aerogel. The maximum compressive strength of the obtained carbon aerogel was about 30 kPa.

[0004] Reference 2 "Wu K, Cao J, Qian Z, et al. Monolithic carbon aerogels within foam framework for high-temperature thermal insulation and organic sabsorption [J]. Journal of Colloid and Interface Science, 2022, 618: 259-269." reported that phenolic resin was polymerized in melamine foam by a sol-gel method, followed by normal pressure drying and co-carbonization to prepare low-density, large-size monolithic carbon aerogels with a maximum compressive strength of 2.5 MPa.

[0005] Reference 3 “Peiying Hu, Xueyan Hu, Ling Liu, et al. Dimensional upgrading of 0D silica nanospheres to 3D networking toward robust aerogels for fire resistance and low-carbon applications, Materials Science and Engineering: R:Reports,Volume 161,2024,100842,ISSN 0927-796X,” reported poly(p-phenylene benzoxazole) nanofiber reinforced silica aerogels with a maximum compressive strength of 3.2 MPa.

[0006] However, the aerogel composite material with lower thermal conductivity prepared in the above literature has a maximum compression strength of 3.2 MPa. When facing external high-temperature flames and external force impacts, the low mechanical properties of aerogel limit its service life and affect its thermal insulation effect. Summary of the invention

[0007] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength and a preparation method thereof, wherein the three-dimensional network of silicon carbide is uniformly distributed in a network shape in the composite aerogel, and the silicon nitride nanowires are uniformly and agglomeratedly distributed inside the three-dimensional network of silicon carbide. The aerogel composite material having such a structure has good compressive strength and fire-resistant and thermal insulation properties.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for preparing a three-dimensional network-shaped silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength, comprising the following steps: uniformly mixing polysilazane, xylene and ferrocene to obtain a mixed solution; The melamine foam is immersed in the mixed solution, and the melamine foam is repeatedly squeezed until the melamine foam is completely soaked by the mixed solution, and then turned over and dried for many times until the mixed solution in the melamine foam is completely solidified to obtain a solidified sample; The cured samples were heat treated in a nitrogen atmosphere to produce a three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength.

[0009] In one embodiment, the mass ratio of the polysilazane to xylene is 1:3-1:5.

[0010] In one embodiment, the mass ratio of ferrocene to polysilazane is 1:3-1:5.

[0011] In one embodiment, the specific process of immersing the melamine foam in the mixed solution, repeatedly squeezing the melamine foam until the melamine foam is completely soaked by the mixed solution, and then turning it over and drying it several times until the mixed solution in the melamine foam is completely solidified to obtain a solidified sample is as follows: The melamine foam is immersed in the mixed solution for 12-24 hours, and the melamine foam is squeezed repeatedly to make the melamine foam completely soaked in the mixed solution, and the excess mixed solution is squeezed out, and it is dried at room temperature for 7-15 days. On the 6th to 8th day, the areas where the melamine foam is not fully soaked are soaked again, and the melamine foam is turned over every 1-2 days until the mixed solution in the melamine foam is completely solidified to obtain a cured sample.

[0012] In one embodiment, the nitrogen gas has an inlet flow rate of 1000-1200 ml / min.

[0013] In one embodiment, the heat treatment process is as follows: Keep at the set temperature of 1430-1480℃ for 3-4h and then cool naturally.

[0014] In one embodiment, the heat treatment is performed in a box-type atmosphere furnace.

[0015] The present invention also provides a three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength obtained by the method for preparing the three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength as described above, wherein the three-dimensional network of silicon carbide is uniformly distributed in a network shape in the composite aerogel, and the silicon nitride nanowires are uniformly and agglomeratedly distributed inside the three-dimensional network of silicon carbide.

[0016] In one embodiment, the three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength has a compressive strength of 13.8 MPa-14.5 MPa.

[0017] In one embodiment, the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength has no significant weight change in the temperature range of 25° C. to 1300° C. in air, and a thermal conductivity of 0.075-0.087 W / (m·K).

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing a three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength. The preparation method uses melamine foam as a precursor, and prepares a three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel in one step through impregnation, room temperature curing and heat treatment reaction. The melamine foam skeleton is converted into a three-dimensional network-like silicon carbide, and silicon nitride nanowires are introduced into the three-dimensional network-like silicon carbide, while maintaining the fire-resistant and heat-insulating properties of the aerogel composite material, the compressive strength of the aerogel is improved. By utilizing the precursor polymer cracking reaction, the melamine foam is converted into a three-dimensional network-like silicon carbide with a rich pore structure at high temperature, and a three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength is prepared in one step.

[0019] The present invention also provides a three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength obtained by the above-mentioned preparation method. The silicon nitride nanowires evenly distributed inside the three-dimensional network of silicon carbide increase the number of micro-nano pores and the frequency of phonon thermal vibrations in the air, so that the aerogel has excellent fire-resistant and heat-insulating properties. The presence of the three-dimensional network of silicon carbide improves the compressive strength of the composite aerogel, so that the compressive strength of the aerogel composite material is improved while maintaining the heat-insulating properties.

[0020] Furthermore, it has been calculated that the compressive strength of the three-dimensional network silicon carbide and silicon nitride nanowire composite aerogel is 14.5 MPa, which is 4.5 times higher than the maximum compressive stress in the relevant literature of the background technology, and has a high compressive strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the XRD result diagram of the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 1.

[0022] Figure 2 This is a scanning electron microscope photograph of silicon nitride nanowires in a three-dimensional silicon carbide skeleton of a three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 1.

[0023] Figure 3 This is a scanning electron microscope photograph of the hard silicon carbide skeleton and silicon nitride nanowires in the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 1.

[0024] Figure 4 This is a scanning electron microscope photograph of the hard silicon carbide skeleton and silicon nitride nanowires in the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 1.

[0025] Figure 5This is a compression test curve of the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 1.

[0026] Figure 6 This is a graph showing the thermogravimetric test results of the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 1 in the temperature range of 25°C-1300°C in air.

[0027] Figure 7 This is an infrared thermal imaging test photograph of a 1 cm thick three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 1 under ignition of a 600°C alcohol lamp.

[0028] Figure 8 This is an infrared thermal imaging test photograph of a 1 cm thick three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 1 under ignition of a butane torch at 1300°C.

[0029] Fig. 9 It is the original temperature rise curve of the thermal conductivity test of the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 2, Example 3 and Example 4 using the transient plane hot plate method at room temperature. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0031] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0032] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0033] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0034] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0035] In one aspect, the present invention provides a method for preparing a three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength, comprising the following steps: (1) Polysilazane, xylene and ferrocene are uniformly mixed, wherein the mass ratio of polysilazane to xylene is 1:3-1:5, and the mass ratio of ferrocene to polysilazane is 1:3-1:5, to obtain a mixed solution.

[0036] (2) Immerse the melamine foam in the mixed solution for 12-24 hours, repeatedly squeeze the melamine foam to make it completely soaked in the mixed solution, squeeze out the excess solution, and dry it at room temperature for 7-15 days. On the 6th to 8th day, soak the areas where the melamine foam is not fully soaked again, turn the melamine foam over every 1-2 days until the mixed solution in the melamine foam is completely solidified, thereby obtaining a cured sample A.

[0037] (3) Prepare a container, place the cured sample A in the container, place the container in a box-type atmosphere furnace, introduce nitrogen at a flow rate of 1000-1200 ml / min, keep the temperature at 1430-1480°C for 3-4 hours, and then cool naturally to obtain a three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength.

[0038] Preferably, the container is a graphite paper box.

[0039] On the other hand, the present invention provides a three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared by the above-mentioned preparation method, so that the aerogel has good fire-resistant and heat-insulating properties while the compressive strength is significantly improved. The present invention uses melamine foam as a silicon carbide skeleton precursor, a polymer solution as a room temperature curing agent for the melamine foam skeleton and a silicon nitride nanowire reaction precursor, and prepares a three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength through high-temperature heat treatment. Because the room temperature curing process of the precursor solution strengthens the melamine foam skeleton, the melamine foam is converted into a silicon carbide skeleton during the heating process, and the silicon nitride nanowires uniformly distributed inside the three-dimensional network-like silicon carbide increase the number of micro-nano pores, so that the aerogel composite material has good heat insulation properties while the compressive strength is improved.

[0040] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0041] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0042] Example 1 (1) Polysilazane, xylene and ferrocene are uniformly mixed, wherein the mass ratio of polysilazane to xylene is 1:5, and the mass ratio of ferrocene to polysilazane is 1:5, to obtain a mixed solution.

[0043] (2) The melamine foam was immersed in the mixed solution for 12 hours, and the melamine foam was squeezed repeatedly to make it completely soaked in the mixed solution, and the excess mixed solution was squeezed out. It was dried at room temperature for 7 days. On the 6th day, the areas where the melamine foam was not fully soaked were soaked again. The melamine foam was turned over every other day until the mixed solution in the melamine foam was completely solidified, thereby obtaining the cured sample A.

[0044] (3) Make a graphite paper box, place sample A in the graphite box, put it in a box-type atmosphere furnace, pass nitrogen at a flow rate of 1000 ml / min, keep it at 1430°C for 3 h, and then cool it naturally to obtain a three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel.

[0045] Example 1 A three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength was prepared, and the compressive strength was 14.5 MPa.

[0046] Example 2 (1) Polysilazane, xylene and ferrocene are uniformly mixed, wherein the mass ratio of polysilazane to xylene is 1:3, and the mass ratio of ferrocene to polysilazane is 1:3, to obtain a mixed solution.

[0047] (2) The melamine foam was immersed in the mixed solution for 24 hours, and the melamine foam was squeezed repeatedly to make it completely soaked in the mixed solution, and the excess mixed solution was squeezed out. It was dried at room temperature for 15 days, and the areas where the melamine foam was not fully soaked were soaked again on the 8th day. The melamine foam was turned over every 2 days until the mixed solution in the melamine foam was completely solidified, thereby obtaining the cured sample A.

[0048] (3) Make a graphite paper box, place sample A in the graphite box, put it in a box-type atmosphere furnace, pass nitrogen at a flow rate of 1200 ml / min, keep it at 1480°C for 4 h, and then cool it naturally to obtain a three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel.

[0049] Example 2: A three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength was prepared, and its compressive strength was 14.1 MPa.

[0050] Example 3 (1) Polysilazane, xylene and ferrocene are uniformly mixed, wherein the mass ratio of polysilazane to xylene is 1:4, and the mass ratio of ferrocene to polysilazane is 1:4, to obtain a mixed solution.

[0051] (2) The melamine foam was immersed in the mixed solution for 18 hours, and the melamine foam was squeezed repeatedly to make it completely soaked in the mixed solution, and the excess mixed solution was squeezed out. It was dried at room temperature for 10 days. On the 8th day, the areas where the melamine foam was not fully soaked were soaked again. The melamine foam was turned over every other day until the mixed solution in the melamine foam was completely solidified, thereby obtaining the cured sample A.

[0052] (3) Make a graphite paper box, place sample A in the graphite box, put it in a box-type atmosphere furnace, pass nitrogen at a flow rate of 1100 ml / min, keep it at 1450°C for 3.5 h, and then cool it naturally to obtain a three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel.

[0053] Example 3: A three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength was prepared, and the compressive strength was 14.3 MPa.

[0054] Example 4 (1) Polysilazane, xylene and ferrocene are uniformly mixed, wherein the mass ratio of polysilazane to xylene is 1:4, and the mass ratio of ferrocene to polysilazane is 1:3, to obtain a mixed solution.

[0055] (2) The melamine foam was immersed in the mixed solution for 16 hours, and the melamine foam was repeatedly squeezed to make it completely soaked in the mixed solution, and the excess mixed solution was squeezed out. It was dried at room temperature for 10 days. On the 7th day, the areas where the melamine foam was not fully soaked were soaked again. The melamine foam was turned over every 1.5 days until the mixed solution in the melamine foam was completely solidified, thereby obtaining the cured sample A.

[0056] (3) Make a graphite paper box, place sample A in the graphite box, put it in a box-type atmosphere furnace, pass nitrogen at a flow rate of 1200 ml / min, keep it at 1480°C for 3 h, and then cool it naturally to obtain a three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel.

[0057] Example 4 prepared a three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength, and its compressive strength was 13.8 MPa.

[0058] See also Figure 1 The XRD spectrum of the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel prepared in Example 1 is shown, where "♦" represents silicon carbide and "♥" represents silicon nitride, indicating that silicon carbide and silicon nitride were successfully prepared.

[0059] See also Figure 2 The surface of silicon nitride nanowires is smooth and evenly distributed inside the three-dimensional network-like silicon carbide skeleton. Figure 3 and Figure 4 , the three-dimensional network-like silicon carbide is evenly and continuously distributed, and the silicon nitride nanowires are filled inside the three-dimensional network-like silicon carbide skeleton.

[0060] like Figure 2-4 As shown, the three-dimensional network silicon carbide is evenly distributed in the composite aerogel in a network shape, and the silicon nitride nanowires are evenly and agglomeratedly distributed inside the three-dimensional network silicon carbide. Since the silicon carbide ceramic itself has high strength, the three-dimensional network silicon carbide provides good mechanical support for the composite aerogel. At the same time, the presence of silicon nitride nanowires inside the three-dimensional network silicon carbide skeleton increases the number of micro-nano pores in the composite aerogel. The aerogel composite material with this structure has good compressive strength and fire-resistant thermal insulation properties.

[0061] In order to verify the improvement of the mechanical properties and thermal insulation properties of aerogels by the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel, a compression test and a thermal conductivity test were performed on Example 1.

[0062] See also Figure 5 Compression test curve of the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 1. The material can withstand a maximum compression force of 2.72 kN, and the cross-sectional area of ​​the sample is 187.5 mm2 , the maximum compression strength is 14.5MPa.

[0063] See also Figure 6 The thermogravimetric test results of the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 1 in the temperature range of 25°C-1300°C in air are shown in FIG. The mass of the composite aerogel remains constant in the air at 25°C-1300°C, and the composite aerogel has good thermal stability in air.

[0064] See also Figure 7 The 1 cm thick three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 1 was ignited by an alcohol lamp at 600°C. Infrared thermal imaging test photos showed that the temperature on the back of the material was stable at around 97°C, which can isolate high temperatures of about 500°C. The composite aerogel has good thermal insulation and fire resistance.

[0065] See also Figure 8 The 1 cm thick three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength prepared in Example 1 was ignited by a butane torch at 1300°C. Infrared thermal imaging test photos showed that the temperature on the back of the material was stable at around 357°C, which can isolate high temperatures of about 900°C. The composite aerogel has good thermal insulation and fire resistance.

[0066] Compression test results are as follows Figure 5 As shown, the maximum compressive force that the three-dimensional network silicon carbide and silicon nitride nanowire composite aerogel can withstand is 2.72 kN, and the maximum compressive stress that it can withstand is 14.5 MPa. The thermal conductivity of Example 1 was tested using a hotdisk thermal conductivity meter, and its thermal conductivity was 0.08786 W / (m·K). Under the condition of low thermal conductivity (<0.1 W / (m·K)), the compressive stress was 4.5 times higher than the maximum compressive stress in the literature. It is proved that melamine is used as a three-dimensional network silicon carbide precursor, and three-dimensional network silicon carbide and silicon nitride nanowires are prepared in one step by pyrolysis of polymer precursors. The obtained three-dimensional network silicon carbide and silicon nitride nanowire composite aerogel has excellent compressive strength and thermal insulation properties. See Fig. 9 The original temperature rise curves of the thermal conductivity test of the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogels with high compressive strength prepared in Example 2, Example 3 and Example 4 were tested by the transient plane hot plate method at room temperature. The temperature rise curves were calculated by the Hotdisk thermal constant analyzer to obtain the thermal constants of Example 2, Example 3 and Example 4 to be 0.07513 W / (m·K), 0.07505 W / (m·K) and 0.07516 W / (m·K), respectively, and the thermal conductivities were low and less than 0.1 W / (m·K).

[0067] As shown Figure 5 and 9 As shown, the thermal conductivity of the three-dimensional network silicon carbide and silicon nitride nanowire composite aerogels is 0.075 W / (m·K)-0.087 W / (m·K), both of which have low thermal conductivity (<0.1 W / (m·K)).

[0068] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength, characterized in that: The following steps are involved: uniformly mixing polysilazane, xylene and ferrocene to obtain a mixed solution; The melamine foam is immersed in the mixed solution, and the melamine foam is repeatedly squeezed until the melamine foam is completely soaked by the mixed solution, and then turned over and dried for many times until the mixed solution in the melamine foam is completely solidified to obtain a solidified sample; The cured samples were heat treated in a nitrogen atmosphere to produce a three-dimensional network of silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength.

2. The method for preparing the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength according to claim 1, characterized in that: The mass ratio of the polysilazane to xylene is 1:3-1:

5.

3. The method for preparing the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength according to claim 1, characterized in that: The mass ratio of ferrocene to polysilazane is 1:3-1:

5.

4. The method for preparing a three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength according to claim 1, characterized in that: The specific process of immersing the melamine foam in the mixed solution, repeatedly squeezing the melamine foam until the melamine foam is completely soaked by the mixed solution, and then turning it over and drying it several times until the mixed solution in the melamine foam is completely solidified to obtain a solidified sample is as follows: The melamine foam is immersed in the mixed solution for 12-24 hours, and the melamine foam is squeezed repeatedly to make the melamine foam completely soaked in the mixed solution, and the excess mixed solution is squeezed out, and it is dried at room temperature for 7-15 days. On the 6th to 8th day, the areas where the melamine foam is not fully soaked are soaked again, and the melamine foam is turned over every 1-2 days until the mixed solution in the melamine foam is completely solidified to obtain a cured sample.

5. The method for preparing a three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength according to claim 1, characterized in that: The nitrogen gas flow rate is 1000-1200 ml / min.

6. The method for preparing the three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength according to claim 1, characterized in that: The heat treatment process is as follows: Keep at the set temperature of 1430-1480℃ for 3-4h and then cool naturally.

7. The method for preparing a three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength according to claim 1, characterized in that: The heat treatment is carried out in a box-type atmosphere furnace.

8. A three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength obtained by the method for preparing a three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength according to any one of claims 1 to 7, characterized in that: The three-dimensional network-like silicon carbide is evenly distributed in the composite aerogel in a network-like manner, and the silicon nitride nanowires are evenly and agglomeratedly distributed inside the three-dimensional network-like silicon carbide.

9. The three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength according to claim 8, characterized in that: The three-dimensional network-shaped silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength has a compressive strength of 13.8 MPa-14.5 MPa.

10. The three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength according to claim 8, characterized in that: The three-dimensional network-like silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength has a constant weight within a temperature range of 25° C. to 1300° C. in air; The thermal conductivity of the three-dimensional network-shaped silicon carbide and silicon nitride nanowire composite aerogel with high compressive strength is 0.075-0.087 W / (m·K).

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