Silicon carbide thermal insulation aerogel and its preparation method and use by in-situ conversion of biomass

Abstract

The present invention belongs to the technical field of the preparation of silicon carbide aerogels, and specifically relates to a preparation method of a biomass in-situ transformed silicon carbide thermal insulation aerogel, the obtained silicon carbide thermal insulation aerogel, and the use of the silicon carbide thermal insulation aerogel as a high-temperature thermal insulation material. The present invention prepares a carbon template by carbonization after freeze-drying, immerses the carbon template in a mixed solution of tetraethyl orthosilicate, ethanol and deionized water, takes out the carbon template impregnated with the above mixed solution, dries it and then calcines it at high temperature to obtain a silicon carbide thermal insulation aerogel transformed by biomass in-situ. Due to the high-temperature stability of its ceramic components, it can maintain a stable structure for a long time under a butane flame; the silicon carbide thermal insulation aerogel has a certain thermal insulation performance in an aerobic environment due to its unique three-dimensional porous structure.

Description

Technical Field

[0001] The present invention relates to the technical field of high temperature resistant thermal insulation materials, and in particular to a method for preparing a biomass in-situ converted silicon carbide thermal insulation aerogel, the prepared silicon carbide thermal insulation aerogel, and use of the silicon carbide thermal insulation aerogel as a high temperature thermal insulation material. Background Art

[0002] When the aircraft flies at hypersonic speed, the static temperature of the airflow increases significantly, and the heat will be conducted to the inside of the aircraft in the form of thermal radiation and convective heat transfer, which seriously threatens the windward surface of the aircraft (such as the surface of the nose cone, the leading edge of the wing, the vertical tail, etc.), and the aerodynamic heating is extremely serious, and it is subjected to strong airflow impact. High-speed air and space aircraft have an urgent need for lightweight, non-ablative, high-temperature resistant, and highly efficient thermal insulation materials. Aerogel, as a type of high-performance lightweight nanoporous material, is an important "military and civilian dual-use" material in the field of thermal insulation protection. However, common carbon aerogels and polymer aerogels can only be used in oxygen-free environments or at low temperatures, and their performance will fail in oxygen environments or environments above 400°C. Aerogels with ceramic components still have excellent thermal insulation properties in oxygen-rich high-temperature environments and have a high temperature tolerance. Therefore, they have good development prospects as thermal insulation materials. However, in the prior art, the choice of precursors in the preparation process of silicon carbide or its composite aerogel as thermal insulation materials is limited, and the price of commonly used polycarbosilane is high, which inevitably leads to cost issues. Summary of the invention

[0003] One of the purposes of the present invention is to provide a method for preparing biomass in-situ converted silicon carbide thermal insulation aerogel, and the prepared silicon carbide thermal insulation aerogel realizes thermal insulation application in a high-temperature aerobic environment.

[0004] To achieve the above object, the present invention adopts the following technical scheme: a method for preparing biomass in-situ conversion of silicon carbide thermal insulation aerogel, comprising the following steps:

[0005] Step A, washing the biomass with deionized water, soaking it in a tert-butyl alcohol solution for replacement, and then freeze-drying it, and then placing it in a protective gas and carbonizing it at 700-1000° C. for 2-4 hours to obtain a carbon template;

[0006] Step B, tetraethyl orthosilicate and ethanol are mixed in a volume ratio of 1:1 to obtain a mixed solution, and then deionized water is added until the concentration of tetraethyl orthosilicate in the mixed solution is 0.4-2.0 mol / L, and hydrochloric acid is added dropwise after sufficient stirring to make the pH of the mixed solution 2-4, and the mixture is further sufficiently stirred to obtain a clear solution;

[0007] Step C, vacuum impregnating the carbon template prepared in step A in the clarified solution of step B for 3-6 hours, taking out the impregnated carbon template and drying it;

[0008] Step D: Place the dried product of Step C under a protective gas at a temperature of 1300 - 1500 °C for heat preservation for 3 - 5 h, and then naturally cool it to obtain silicon carbide thermal insulation aerogel;

[0009] Among them, Steps A and B have no sequential order.

[0010] As a further improvement to the preparation method of in-situ conversion of biomass into silicon carbide thermal insulation aerogel:

[0011] Preferably, the biomass in Step A is eggplant.

[0012] Preferably, the concentration of the tert-butanol solution in Step A is 60 - 80 wt%.

[0013] Preferably, the temperature of freeze-drying in Step A is -70 to -40 °C, and the time is 10 - 36 h.

[0014] Preferably, the protective gas in Steps A and D is high-purity argon.

[0015] Preferably, the carbonization in Step A is carried out in a high-temperature tube furnace, and the temperature is raised from room temperature to the carbonization temperature at a rate of 2 - 5 °C / min.

[0016] Preferably, the impregnated carbon template in Step C is dried at a temperature of 25 - 60 °C.

[0017] Preferably, the temperature is raised to the heat preservation temperature at a rate of 1 - 3 °C / min in Step D.

[0018] The second object of the invention is to provide a silicon carbide thermal insulation aerogel prepared by any of the above preparation methods.

[0019] The third object of the present invention is the use of the above silicon carbide thermal insulation aerogel as high-temperature heat insulation.

[0020] The beneficial effects of the present invention compared with the prior art are as follows:

[0021] 1) The preparation method of the silicon carbide thermal insulation aerogel provided by the present invention uses biomass as a carbon source, replaces it in a tert-butanol solution, maintains the structure of the original biomass after drying and carbonization; after impregnating with a silicon source, it is calcined at a high temperature under an argon atmosphere, thereby being transformed into a silicon carbide thermal insulation aerogel.

[0022] The selected biomass eggplant in Step A has a strong adsorption force due to its good porous structure, and can uniformly and abundantly fill the silicon source in the vesicular carbon structure of the eggplant during vacuum impregnation.

[0023] Step B is a typical TEOS hydrolysis process. With different concentrations of TEOS, the content of silica participating in subsequent reactions after hydrolysis is different. Excessive silicon can react with all carbon templates, while a small amount of silicon will leave some carbon vesicle walls remaining in the product morphology. The products with different components have different morphologies and different thermal conductivities.

[0024] In step C, under a vacuum atmosphere, the carbon template is placed in the silicon source. The bubbles in the carbon template will suck in the silicon source due to negative pressure, so that the silicon source is evenly present in the carbon template. After drying, it prepares for the subsequent high-temperature sintering experiment.

[0025] In step D, during the calcination of the precursor, the silica obtained after hydrolyzing TEOS will react with carbon to form silicon carbide. Taking eggplant as an example of biomass, silicon carbide nanowires are in-situ transformed at the carbon vesicle walls of the eggplant under the high-temperature condition of 1300 - 1500 °C, and 3 - 5 h is ensured to make the reaction proceed fully.

[0026] 2) The silicon carbide ceramic aerogel prepared by the in-situ transformation method of biomass of the present invention, as a high-temperature thermal insulation material, can achieve fireproof thermal insulation at a high temperature of 1300 °C. The multi-scale structure of one-dimensional silicon carbide nanowires can effectively inhibit the heat conduction of air, heat convection and phonon heat conduction of the solid skeleton, thus significantly improving the thermal insulation effect of the silicon carbide nanowire aerogel. Silicon carbide is a ceramic component, resistant to oxygen and high temperature, and can maintain good thermal stability and chemical stability in a high-temperature aerobic environment. At the same time, it has both light weight and high-efficiency thermal insulation performance. This preparation method only requires ordinary equipment commonly used in laboratories, does not require special equipment, nor special drugs. The process is simple and easy to operate, the reaction process is easy to control, the production cycle is short, the cost is low, and it can be mass-produced. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0028] Figure 1 Scanning electron microscope photos obtained by using a scanning electron microscope to detect the morphology of the silicon carbide thermal insulation aerogels prepared in Examples 1 - 5 and Comparative Example 1 of the present invention at a magnification of 20k.

[0029] Figure 2 XRD patterns obtained by using an X-ray diffraction analyzer to detect the substances of the silicon carbide thermal insulation aerogels prepared in Examples 1 - 5 and Comparative Example 1 of the present invention.

[0030] Figure 3Optical photograph of butane flame ablation of the silicon carbide thermal insulation aerogel prepared in Example 3 using a butane torch.

[0031] Figure 4 Thermal conductivity comparison chart of the silicon carbide thermal insulation aerogels prepared in Examples 1-5 and Comparative Example 1 from room temperature to 500 °C using a laser thermal conductivity meter. Detailed implementation mode

[0032] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0033] In order to more clearly show the technical solutions provided by the present invention and the technical effects produced, the following describes in detail a preparation method of a silicon carbide thermal insulation aerogel in-situ converted from biomass provided by an embodiment of the present invention with specific embodiments.

[0034] Example 1

[0035] A preparation method of a silicon carbide thermal insulation aerogel in-situ converted from biomass, comprising the following steps:

[0036] Step a1: After the eggplant is washed with deionized water, it is soaked in a 75 wt% tert-butanol solution for replacement, and then freeze-dried at -60 °C for 36 h until it is completely dry, thereby obtaining dry eggplant.

[0037] Step b1: Put the dry eggplant into an alumina crucible, place it in a high-temperature tube furnace, use high-purity argon as the protective gas, heat it to 800 °C at a rate of 5 °C / min, and keep it warm for 120 min, and finally cool it naturally to room temperature, thereby obtaining a carbon template, which is cut into 240 mg per small portion for use.

[0038] Step c1: Weigh 3.6 ml of tetraethyl orthosilicate and disperse it in 3.6 ml of ethanol, then add 2.8 ml of deionized water so that the concentration of tetraethyl orthosilicate in the mixed solution is 2.0 mol / L. After stirring for 7 h, add hydrochloric acid dropwise to the mixed solution until the pH = 3, and stir for another 3 h to obtain a clear solution.

[0039] Step d1: Vacuum impregnate the carbon template in the above-mentioned clear solution for 4 h and then take it out, and dry it at 30 degrees to obtain a dried carbon template impregnated with silica sol.

[0040] Step e1: Put the dried carbon template impregnated with silica sol into an alumina crucible, place it in a high-temperature tube furnace, use high-purity argon as the protective gas, heat from room temperature to 700 °C at a rate of 1 °C / min, then heat to 1500 °C at a rate of 2 °C / min, hold for 4 h, and finally cool naturally to room temperature to obtain silicon carbide thermal insulation aerogel.

[0041] Example 2

[0042] A preparation method of silicon carbide thermal insulation aerogel in-situ transformed from biomass, comprising the following steps:

[0043] Step a1: After washing the eggplant with deionized water, soak it in a 75 wt% tert-butanol solution for replacement, freeze-dry at -60 °C for 36 h to make it completely dry, thereby obtaining dry eggplant.

[0044] Step b1: Put the obtained dry eggplant into an alumina crucible, place it in a high-temperature tube furnace, use high-purity argon as the protective gas, heat to 800 °C at a rate of 5 °C / min, hold for 120 min, and finally cool naturally to room temperature to obtain a carbon template, cut it into 240 mg per small portion for use.

[0045] Step c1: Weigh 2.88 ml of tetraethyl orthosilicate and disperse it in 2.88 ml of ethanol, then add 4.24 ml of deionized water until the concentration of tetraethyl orthosilicate in the mixed solution is 1.6 mol / L. Stir for 7 h, then drop hydrochloric acid into it to make the pH of the mixed solution = 3, and stir for another 3 h to obtain a clear solution.

[0046] Step d1: Vacuum impregnate the carbon template in the above clear solution for 4 h, then take it out and dry it at 30 °C to obtain the dried carbon template impregnated with silica sol.

[0047] Step e1: Put the dried carbon template impregnated with silica sol into an alumina crucible, place it in a high-temperature tube furnace, use high-purity argon as the protective gas, heat from room temperature to 700 °C at a rate of 1 °C / min, then heat to 1500 °C at a rate of 2 °C / min, hold for 4 h, and finally cool naturally to room temperature to obtain silicon carbide thermal insulation aerogel.

[0048] Example 3

[0049] A preparation method of silicon carbide thermal insulation aerogel in-situ transformed from biomass, comprising the following steps:

[0050] Step a1: After washing the eggplant with deionized water, soak it in a 75 wt% tert-butanol solution for replacement, freeze-dry at -60 °C for 36 h to make it completely dry, thereby obtaining dry eggplant.

[0051] Step b1: Put the dried eggplants into an alumina crucible, place it in a high-temperature tube furnace, use high-purity argon as the protective gas, heat it to 800 °C at a rate of 5 °C / min, hold for 120 min, and finally cool it naturally to room temperature to obtain a carbon template, which is cut into 240 mg per small portion for use;

[0052] Step c1: Weigh 2.16 ml of tetraethyl orthosilicate and disperse it in 2.16 ml of ethanol, then add 5.68 ml of deionized water until the concentration of tetraethyl orthosilicate in the mixed solution is 1.2 mol / L. After stirring for 7 h, add hydrochloric acid dropwise to make the pH of the mixed solution = 3, and stir for another 3 h to obtain a clear solution;

[0053] Step d1: Immerse the carbon template in the above clear solution under vacuum for 4 h and then take it out, and dry it at 30 °C to obtain a dried carbon template impregnated with silica sol;

[0054] Step e1: Put the dried carbon template impregnated with silica sol into an alumina crucible, place it in a high-temperature tube furnace, use high-purity argon as the protective gas, heat it from room temperature to 700 °C at a rate of 1 °C / min, then heat it to 1500 °C at a rate of 2 °C / min, hold for 4 h, and finally cool it naturally to room temperature to obtain silicon carbide aerogel insulation.

[0055] Example 4

[0056] A preparation method of silicon carbide aerogel insulation in-situ converted from biomass, comprising the following steps:

[0057] Step a1: After washing the eggplants with deionized water, soak them in a 75 wt% tert-butanol solution for replacement, and freeze-dry them at -60 °C for 36 h to make them completely dry, thus obtaining dried eggplants;

[0058] Step b1: Put the dried eggplants into an alumina crucible, place it in a high-temperature tube furnace, use high-purity argon as the protective gas, heat it to 800 °C at a rate of 5 °C / min, hold for 120 min, and finally cool it naturally to room temperature to obtain a carbon template, which is cut into 240 mg per small portion for use;

[0059] Step c1: Weigh 1.44 ml of tetraethyl orthosilicate and disperse it in 1.44 ml of ethanol, then add 7.12 ml of deionized water until the concentration of tetraethyl orthosilicate in the mixed solution is 0.8 mol / L. After stirring for 7 h, add hydrochloric acid dropwise to make the pH of the mixed solution = 3, and stir for another 3 h to obtain a clear solution;

[0060] Step d1: Immerse the carbon template in the above clear solution under vacuum for 4 h and then take it out, and dry it at 30 °C to obtain a dried carbon template impregnated with silica sol;

[0061] Step e1: Put the dried carbon template impregnated with silica sol into an alumina crucible, place it in a high-temperature tube furnace, use high-purity argon as the protective gas, heat it from room temperature to 700 °C at a rate of 1 °C / min, then heat it to 1500 °C at a rate of 2 °C / min, hold for 4 h, and finally cool it to room temperature naturally to obtain silicon carbide thermal insulation aerogel.

[0062] Example 5

[0063] A preparation method of silicon carbide thermal insulation aerogel in-situ transformed from biomass, comprising the following steps:

[0064] Step a1: After washing the eggplant with deionized water, soak it in a 75 wt% tert-butanol solution for replacement, freeze-dry it at -60 °C for 36 h to make it completely dry, thus obtaining dry eggplant.

[0065] Step b1: Put the obtained dry eggplant into an alumina crucible, place it in a high-temperature tube furnace, use high-purity argon as the protective gas, heat it to 800 °C at a rate of 5 °C / min, hold for 120 min, and finally cool it to room temperature naturally to obtain a carbon template, cut it into 240 mg per small portion for use.

[0066] Step c1: Weigh 0.72 ml of tetraethyl orthosilicate and disperse it in 0.72 ml of ethanol, then add 8.56 ml of deionized water until the concentration of tetraethyl orthosilicate in the mixed solution is 0.4 mol / L, stir for 7 h, then drop hydrochloric acid into it until the pH of the mixed solution is 3, and stir for another 3 h to obtain a clear solution.

[0067] Step d1: Vacuum impregnate the carbon template in the above clear solution for 4 h, then take it out and dry it at 30 °C to obtain the dried carbon template impregnated with silica sol.

[0068] Step e1: Put the dried carbon template impregnated with silica sol into an alumina crucible, place it in a high-temperature tube furnace, use high-purity argon as the protective gas, heat it from room temperature to 700 °C at a rate of 1 °C / min, then heat it to 1500 °C at a rate of 2 °C / min, hold for 4 h, and finally cool it to room temperature naturally to obtain silicon carbide thermal insulation aerogel.

[0069] Comparative Example 1

[0070] A preparation method of silicon carbide thermal insulation aerogel in-situ transformed from biomass, comprising the following steps:

[0071] Step a1: After washing the eggplant with deionized water, soak it in a 75 wt% tert-butanol solution for replacement, freeze-dry it at -60 °C for 36 h to make it completely dry, thus obtaining dry eggplant.

[0072] Step b1: Put the dried eggplants into an alumina crucible, place it in a high-temperature tube furnace, use high-purity argon as the protective gas, heat it to 800 °C at a rate of 5 °C / min, hold for 120 min, and finally cool it naturally to room temperature to obtain a carbon template, which is cut into 240 mg per small portion for use.

[0073] Morphology observation and performance detection

[0074] Perform morphology observation and performance detection on the biomass-derived silicon carbide thermal insulation aerogels prepared in Examples 1-5 and Comparative Example 1 of the present invention, and the following results are obtained:

[0075] (1) Use an optical camera to take pictures of the intermediate product of the silicon carbide thermal insulation aerogel prepared in Example 3. By comparison, it can be seen that: in Example 3 of the present invention, when preparing a carbon template from dried eggplants, there is a certain shrinkage in volume, and the volume of the carbon template in-situ transformed into the silicon carbide thermal insulation aerogel remains basically unchanged.

[0076] (2) Use a scanning electron microscope to perform morphology detection on the silicon carbide thermal insulation aerogels prepared in Examples 1-5 and Comparative Example 1 of the present invention, and obtain the scanning electron microscope photos as shown in Figure 1 (a)-(f). Among them, Figure 1 (a)-(f) are the FESEM photos of the silicon carbide thermal insulation aerogels prepared in Examples 1-5 and Comparative Example 1 of the present invention at a magnification of 20k. Examples 1-5 are the cases where the carbon / silicon molar ratios are 1, 2, 3, 4, and 5 respectively, and Comparative Example is the case without adding silica sol. It can be seen that: as the carbon / silicon molar ratio gradually increases from 1 to 5, the prepared ceramic aerogel changes from a silicon carbide / silica composite aerogel to a silicon carbide thermal insulation aerogel and then to a silicon carbide / carbon composite aerogel. In Examples 1-5 of the present invention, as the C ratio increases, more of the carbon structure of the eggplant itself remains, and in Comparative Example 1, it is completely the morphology of the carbon template. Figure 1

[0077] (3) Use an X-ray diffractometer to perform substance detection on the silicon carbide thermal insulation aerogels and carbon templates prepared in Examples 1-5 and Comparative Example 1 of the present invention, and obtain the X-ray diffraction patterns as shown in Figure 2 ; It can be seen from Figure 2 that the silicon carbide thermal insulation aerogels prepared in Examples 1-5 of the present invention all show a pure β-SiC phase in the XRD pattern; while the carbon template prepared in Comparative Example 1 contains a large amount of amorphous carbon. The main component of the biomass material after carbonization in Comparative Example 1 is amorphous carbon. In Examples 1-5, the silica obtained by the hydrolysis of TEOS reacts with the carbon template to form β-SiC at 1300-1500 °C.

[0078] (4) The butane torch was used to conduct a butane flame ablation test on the silicon carbide thermal insulation aerogel prepared in Example 3, so as to obtain the optical photograph as shown in Figure 3 ; It can be seen from Figure 3 that the silicon carbide thermal insulation aerogel prepared in Example 3 of the present invention can resist the ablation of a butane flame at 1300 °C.

[0079] (5) A laser thermal conductivity meter was used to detect the thermal conductivity of the silicon carbide thermal insulation aerogel and the carbon template prepared in Examples 1-5 of the present invention and Comparative Example 1 respectively, so as to obtain the thermal conductivity spectrum as shown in Figure 4 ; It can be seen from Figure 4 that the silicon carbide thermal insulation aerogel prepared in Examples 1-5 of the present invention has a very low thermal conductivity from room temperature to 500 °C and has good thermal insulation performance; while the carbon template prepared in Comparative Example 1 shows poor thermal insulation because it contains a large number of macroscopic pore structures and microscopic vesicular carbon structures, which are denser than the silicon carbide nanowire network structure and have stronger heat conduction. Among them, Example 3 has the lowest thermal conductivity and the best thermal insulation performance.

[0080] In summary, the embodiments of the present invention not only have a simple preparation process, an easily controllable reaction process, a short production cycle, and low costs, but also the prepared silicon carbide thermal insulation aerogel has good high-temperature stability and good thermal insulation performance.

[0081] Those skilled in the art should understand that the above are only several specific embodiments of the present invention, rather than all embodiments. It should be pointed out that many modifications and improvements can be made for those of ordinary skill in the art. All modifications or improvements that do not exceed the scope of the claims should be regarded as the protection scope of the present invention.

Claims

1. A preparation method of biomass in-situ conversion silicon carbide thermal insulation aerogel, characterized in that, The steps include: Step A, washing the biomass eggplant with deionized water and then soaking it in a tert-butanol solution for replacement, wherein the concentration of the tert-butanol solution is 60-80wt%, and then freeze-drying it, and then placing it in a protective gas and carbonizing it at 700-1000° C. for 2-4 hours to obtain a carbon template; Step B, tetraethyl orthosilicate and ethanol are mixed in a volume ratio of 1:1, and then deionized water is added until the concentration of tetraethyl orthosilicate in the mixed solution is 0.4-2.0 mol / L, and hydrochloric acid is added dropwise after sufficient stirring to make the pH of the mixed solution 2-4, and the mixture is further sufficiently stirred to obtain a clear solution; Step C, vacuum impregnating the carbon template prepared in step A in the clarified solution of step B for 3-6 hours, taking out the impregnated carbon template and drying it; Step D, placing the dried product of step C in a protective gas, keeping it at 1300-1500° C. for 3-5 hours, and cooling it naturally to obtain silicon carbide thermal insulation aerogel; Among them, steps A and B are not performed in any particular order.

2. The preparation method of the biomass in-situ conversion silicon carbide thermal insulation aerogel according to claim 1, characterized in that, The freeze-drying temperature in step A is -70 to -40°C and the time is 10-36h.

3. The preparation method of the biomass in-situ conversion silicon carbide thermal insulation aerogel according to claim 1, characterized in that, The protective gas in step A and step D is high-purity argon.

4. The preparation method of the biomass in-situ conversion silicon carbide thermal insulation aerogel according to claim 1 or 3, characterized in that, In step A, the carbonization is carried out in a high temperature tube furnace, and the temperature is raised from room temperature to the carbonization temperature at a rate of 2-5°C / min.

5. The preparation method of the biomass in-situ conversion silicon carbide thermal insulation aerogel according to claim 1, characterized in that, The carbon template after impregnation in step C is placed at a temperature of 25-60° C. and dried.

6. The preparation method of the biomass in-situ conversion silicon carbide thermal insulation aerogel according to claim 1 or 3, characterized in that, In step D, the temperature is raised to the holding temperature at a rate of 1-3°C / min.

7. A biomass in-situ conversion silicon carbide thermal insulation aerogel prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the biomass in-situ converted silicon carbide thermal insulation aerogel according to claim 7 as a high temperature resistant thermal insulation material.

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