Biomass-derived silicon carbide fiber aerogels and methods of making and using the same

Abstract

The application discloses a biomass-derived silicon carbide fiber aerogel and a preparation method and application thereof. In the application, kapok hollow fibers are subjected to degreasing and cleaning, and then subjected to high-temperature carbonization to obtain carbon micrometer tube fibers; the carbon micrometer tube fibers are taken as basic component units, subjected to freeze forming and freeze drying to obtain carbon micrometer tube fiber aerogel blanks; and finally, high-temperature carbothermal reduction reaction is performed to in-situ convert the carbon micrometer tube into silicon carbide micrometer tube, so as to obtain a silicon carbide micrometer tube / silicon carbide nanowire composite aerogel wave-absorbing material with silicon carbide nanowires growing inside the aerogel. The material is light in mass, high in high-temperature resistance and mechanical performance, and has good electromagnetic wave absorption performance when used as a wave-absorbing material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wave-absorbing materials, and particularly relates to a biomass-derived silicon carbide fiber aerogel and a preparation method and application thereof. BACKGROUND

[0002] With the vigorous development of science and technology, various electronic products have sprung up like mushrooms, leading to increasingly serious electromagnetic pollution problems. Electromagnetic wave absorbing materials can consume electromagnetic wave energy through various attenuation mechanisms, and are an effective way to solve this problem. Therefore, the research on wave-absorbing materials with high-efficiency electromagnetic wave absorption capacity has attracted much attention in recent years.

[0003] Silicon carbide fibers are a typical wave-absorbing material, but a single electromagnetic wave loss mechanism makes it increasingly unable to meet the actual application requirements. Aerogel is a porous structure material with extremely high porosity, and the rich pore structure helps to optimize the impedance matching of the material and enhance the multiple reflection effect of electromagnetic waves and the interface polarization effect of the material, thereby effectively improving the wave-absorbing performance of the material. Therefore, the silicon carbide fiber aerogel assembled by silicon carbide fibers has broad application prospects in the field of wave-absorbing.

[0004] At present, the preparation of silicon carbide fibers mostly uses polycarbosilane as a precursor to obtain silicon carbide fibers through a spinning method, which not only has high cost, but also has a relatively complicated process flow, and is mostly used in high-end aerospace or military weapon equipment fields. Therefore, it is particularly important to explore a preparation method of silicon carbide fiber aerogel wave-absorbing materials with low cost and simple process, so as to promote its popularization and application in civilian fields. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art, and provides a biomass-derived silicon carbide fiber aerogel and a preparation method and application thereof, which solve the problems in the background art.

[0006] One of the technical solutions adopted by the present application to solve the technical problems is to provide a preparation method of a biomass-derived silicon carbide fiber aerogel, which comprises the following steps:

[0007] (1) defatting and cleaning cotton fiber and drying to obtain hollow cotton fiber;

[0008] (2) high-temperature carbonization of the defatted and cleaned hollow cotton fiber to obtain carbon microporous tube fiber;

[0009] (3) uniformly dispersing the carbon microporous tube fiber into distilled water at a concentration of 5-55 mg / mL at 25-60 DEG C, freezing for 2-8 h at-18 DEG C to-196 DEG C, and then placing in a freeze dryer to vacuumize for 24-48 h to obtain a carbon microporous tube fiber aerogel blank;

[0010] (4) Mix silicon powder and silicon dioxide powder at a mass ratio of 7:15 and ball mill for 3-8 hours to obtain mixed powder; place the carbon microtube fiber aerogel preform above the mixed powder and place it in a tube furnace according to a silicon to carbon molar ratio of 4:1, and carry out a high-temperature carbothermic reduction reaction under a protective atmosphere to obtain silicon carbide microtube fiber aerogel material.

[0011] In a preferred embodiment of the present invention, in step (1), sodium chlorite is dissolved in deionized water, and the pH of the solution is adjusted to 3.5-5.0 with acid. Then, kapok fibers are added to the sodium chlorite aqueous solution and placed in an oven at 80-90°C for 4-8 hours. Then, the mixture is cooled naturally, and the fiber mixture is washed repeatedly with deionized water 3-5 times. Finally, it is placed in a forced-air drying oven at 60-90°C for 3-24 hours to obtain the kapok fibers.

[0012] In a preferred embodiment of the present invention, the mass fraction of sodium chlorite in the sodium chlorite aqueous solution is 0.5-5 wt%.

[0013] In a preferred embodiment of the present invention, the acid includes acetic acid, phosphoric acid, and hydrochloric acid.

[0014] In a preferred embodiment of the present invention, in step (2), the cleaned and degreased kapok fibers are placed in a tube furnace, and the heating rate is 1-5℃ / min under a protective atmosphere, the carbonization temperature is 650℃-900℃, and the holding time is 2-6h to obtain carbon micron tube fibers.

[0015] In a preferred embodiment of the present invention, in step (3), the carbon microtube fibers are uniformly dispersed in distilled water by vigorous magnetic stirring at 25°C to 60°C for 1 to 3 hours.

[0016] In a preferred embodiment of the present invention, in step (3), the vacuum degree of the freeze dryer is always below 25 Pa during the freeze drying process.

[0017] In a preferred embodiment of the present invention, in step (4), the heating rate of the high-temperature carbothermic reduction reaction is 1-5℃ / min, and the temperature is maintained at 1400℃-1500℃ for 2-6 hours.

[0018] In a preferred embodiment of the present invention, the protective atmosphere is nitrogen, argon or helium.

[0019] In a preferred embodiment of the present invention, the freezing device is one of a refrigerator, a freeze dryer, and liquid nitrogen.

[0020] The second technical solution adopted by the present invention to solve its technical problem is: a biomass-derived silicon carbide fiber aerogel is provided, which is prepared by the above method. The aerogel contains silicon carbide microtube fibers, which have a hollow structure; or the aerogel contains silicon carbide microtubes and silicon carbide nanowires, which have a hollow structure. Silicon carbide nanowires are grown around the silicon carbide microtubes, and the silicon carbide microtubes and silicon carbide nanowires are interleaved in the aerogel.

[0021] The third technical solution adopted by the present invention to solve its technical problem is: to provide the application of the above-mentioned biomass-derived silicon carbide fiber aerogel for use as an electromagnetic wave absorbing material.

[0022] Compared with the prior art, this technical solution has the following advantages:

[0023] 1. This invention uses naturally renewable biomass kapok hollow fiber as raw material to prepare silicon carbide fiber aerogel microwave absorbing material, which is low in cost; it does not require polycarbosilane as a precursor, nor does it require large-scale spinning equipment. The preparation process is simple, low in cost, and has good industrial applicability.

[0024] 2. The silicon carbide fiber aerogel prepared by the present invention has a large number of silicon carbide fibers distributed inside, including silicon carbide microtubes, or silicon carbide microtubes and silicon carbide nanowires grown around them with silicon carbide microtubes as the matrix fibers. The fibers are intertwined and crisscrossed, which can promote more electromagnetic wave loss and enhance its electromagnetic wave absorption effect.

[0025] 3. The silicon carbide microtube fibers of the present invention have a hollow structure, which helps to optimize the impedance matching of the material and enhance the electromagnetic wave multiple reflection effect and interface polarization effect, thereby effectively improving the wave absorption performance of the material; and the fibers themselves have high toughness, which helps to improve the mechanical properties of silicon carbide fiber aerogel.

[0026] 4. According to the test, the silicon carbide microtube fiber aerogel material prepared by the present invention has a minimum reflection loss of -53.3dB and an effective absorption bandwidth of 4.68GHz under a thickness of 2.8mm; at the same time, the compressive strength under 10% strain is greater than 0.56MPa. Attached Figure Description

[0027] Figure 1 The image shows a physical picture of the biomass-derived silicon carbide microtube fiber aerogel microwave absorbing material prepared in Example 1.

[0028] Figure 2 Here is a SEM image of the carbon microtube fibers during the preparation process in Example 1;

[0029] Figure 3SEM image of the biomass-derived silicon carbide microtube fiber aerogel microwave absorbing material prepared in Example 2;

[0030] Figure 4 The image shows the XRD pattern of the biomass-derived silicon carbide microtube fiber aerogel microwave absorbing material prepared in Example 2.

[0031] Figure 5 The compressive stress-strain curve of the biomass-derived silicon carbide microtube fiber aerogel microwave absorbing material prepared in Example 3 is shown.

[0032] Figure 6 The electromagnetic wave reflection loss diagram is shown for the biomass-derived silicon carbide microtube fiber aerogel absorbing material prepared in Example 4. Detailed Implementation

[0033] The present invention will be further described below with reference to embodiments.

[0034] Example 1

[0035] This embodiment describes a method for preparing a biomass-derived silicon carbide fiber aerogel microwave absorbing material, comprising the following steps:

[0036] (1) Dissolve sodium chlorite in deionized water and adjust the pH of the sodium chlorite solution to 4.0 with acetic acid. Then add the original hollow kapok fibers to the solution and keep it in an oven at 85°C for 8 hours. Then cool naturally and wash the fiber mixture three times with deionized water. Finally, dry it in a 60°C forced-air drying oven for 20 hours to obtain cleaned and degreased hollow kapok fibers.

[0037] (2) The cleaned and degreased kapok hollow fibers are placed in a tube furnace and heated to 800°C at a rate of 1°C / min under argon atmosphere protection. The temperature is maintained for 2 hours to obtain carbon micron tube fibers.

[0038] (3) Disperse carbon microtube fibers in distilled water at a concentration of 35 mg / mL and stir vigorously with a magnetic force at 25°C for 2 hours to ensure uniform dispersion. Pour the fiber dispersion into a polytetrafluoroethylene mold and freeze it in a refrigerator for 6 hours. Then place the sample in a freeze dryer and vacuum it for 48 hours to obtain a carbon microtube fiber aerogel preform.

[0039] (4) Silicon powder and silica powder were ball-milled at a mass ratio of 7:15 for 5 hours to mix them evenly. Then, the mass of the carbon microtube fiber aerogel preform was weighed. The mass of the mixed powder was determined according to a silicon to carbon molar ratio of 4:1, using the mixed powder of silicon powder and silica powder as the silicon source and the carbon microtube fiber aerogel preform as the carbon source. The mixed powder was transferred to a silica crucible, with the carbon microtube fiber aerogel preform placed on top of the mixed powder. Finally, the aerogel preform and the mixed powder were placed in a tube furnace and heated to 1450°C at a heating rate of 5°C / min under argon atmosphere protection, and held for 2 hours to carry out a high-temperature carbothermic reduction reaction to obtain silicon carbide microtube fiber aerogel microwave absorbing material.

[0040] A physical image of the silicon carbide fiber aerogel microwave absorbing material prepared in this embodiment is attached. Figure 1 As shown, the aerogel contains a large number of silicon carbide fibers; these silicon carbide fibers include silicon carbide microtubes made from hollow kapok fibers, with the fibers intertwined and crisscrossed. The SEM image of the carbon microtube fibers obtained by high-temperature carbonization of the kapok hollow fibers during the preparation process is attached. Figure 2 As shown, the hollow structure is clearly visible. Testing revealed that the material in this embodiment, with a thickness of 3.3 mm, achieves a minimum reflection loss of -45.9 dB at 9.7 GHz and an effective absorption bandwidth of 5.79 GHz.

[0041] Example 2

[0042] The preparation method in this embodiment includes the following steps:

[0043] (1) Dissolve sodium chlorite in deionized water and adjust the pH of the sodium chlorite solution to 4.5 with hydrochloric acid. Then add the original hollow kapok fibers to the solution and keep it in a 90℃ oven for 6 hours. Then cool naturally and wash the fiber mixture repeatedly with deionized water 5 times. Finally, dry it in a 75℃ forced-air drying oven for 10 hours to obtain cleaned and degreased hollow kapok fibers.

[0044] (2) The cleaned and degreased kapok hollow fibers are placed in a tube furnace and heated to 850°C at a rate of 2°C / min under nitrogen atmosphere protection. The temperature is held for 3 hours to obtain carbon micron tube fibers.

[0045] (3) Disperse carbon microtube fibers in distilled water at a concentration of 30 mg / mL and stir vigorously with a magnetic force at 30°C for 3 h to ensure uniform dispersion of the fibers. Pour the above fiber dispersion into a polytetrafluoroethylene mold and then freeze it in liquid nitrogen for 0.5 h. Subsequently, place the sample in a freeze dryer and evacuate it for 48 h to obtain a carbon microtube fiber aerogel preform.

[0046] (4) Silicon powder and silica powder were ball-milled at a mass ratio of 7:15 for 5 hours to mix evenly. Then, the mass of the carbon microtube fiber aerogel preform was weighed, and the mass of the mixed powder was determined according to a silicon to carbon molar ratio of 4:1. The mixed powder was transferred to a silica crucible, with the carbon microtube fiber aerogel preform placed on top of the mixed powder. Finally, the aerogel preform and the mixed powder were placed in a tube furnace, and under argon atmosphere protection, the temperature was raised to 1500℃ at a heating rate of 2℃ / min and held for 2 hours to carry out a high-temperature carbothermic reduction reaction, thereby obtaining silicon carbide fiber aerogel microwave absorbing material.

[0047] The SEM image of the silicon carbide fiber aerogel absorbing material prepared in this embodiment is attached. Figure 3 As shown, silicon carbide nanowires are grown around silicon carbide microtubes, with the fibers intertwined and crisscrossing each other; the XRD pattern of this material is attached. Figure 4 As shown, its compressive strength is 0.59 MPa at 10% deformation; with a thickness of 3.5 mm, its minimum reflection loss at 11.0 GHz reaches -51.2 dB, and its effective absorption bandwidth is 4.29 GHz.

[0048] Example 3

[0049] The preparation method in this embodiment includes the following steps:

[0050] (1) Dissolve sodium chlorite in deionized water and adjust the pH of the sodium chlorite solution to 4.0 with phosphoric acid. Then add the original hollow kapok fibers to the solution and place it in an oven at 85°C for 6 hours. Then cool naturally and wash the fiber mixture with deionized water four times. Finally, dry it in an oven at 85°C for 6 hours to obtain cleaned and degreased hollow kapok fibers.

[0051] (2) The cleaned and degreased kapok hollow fibers are placed in a tube furnace and heated to 900°C at a rate of 2°C / min under nitrogen atmosphere protection. The temperature is held for 2 hours to obtain carbon micron tube fibers.

[0052] (3) Disperse carbon microtube fibers in distilled water at a concentration of 40 mg / mL and stir vigorously with a magnetic force at 30°C for 3 h to ensure uniform dispersion of the fibers. Pour the above fiber dispersion into a polytetrafluoroethylene mold and freeze it in a freeze dryer for 7 h. Then place the sample in a freeze dryer and evacuate it for 24 h to obtain a carbon microtube fiber aerogel preform.

[0053] (4) Silicon powder and silica powder were ball-milled at a mass ratio of 7:15 for 5 hours to mix them evenly. Then, the mass of the carbon microtube fiber aerogel preform was weighed, and the mass of the mixed powder was determined according to a silicon to carbon molar ratio of 4:1. The mixed powder was transferred to a silica crucible, with the carbon microtube fiber aerogel preform placed on top of the mixed powder. Finally, the aerogel preform and the mixed powder were placed in a tube furnace, and under nitrogen atmosphere protection, the temperature was raised to 1400℃ at a heating rate of 2℃ / min and held for 5 hours to carry out a high-temperature carbothermic reduction reaction, thereby obtaining silicon carbide fiber aerogel microwave absorbing material.

[0054] The compressive stress-strain curve of the silicon carbide fiber aerogel microwave absorbing material prepared in this embodiment is attached. Figure 5 As shown, the compressive strength is 0.56 MPa at 10% deformation; at a thickness of 4.1 mm, the minimum reflection loss reaches -47.2 dB at 9.5 GHz, and the effective absorption bandwidth is 6.23 GHz.

[0055] Example 4

[0056] The preparation method in this embodiment includes the following steps:

[0057] (1) Dissolve sodium chlorite in deionized water and adjust the pH of the sodium chlorite solution to 4.5 with phosphoric acid. Then add the original hollow kapok fibers to the solution and keep it in a 90℃ oven for 6 hours. Then cool naturally and wash the fiber mixture three times with deionized water. Finally, dry it in an 85℃ forced-air drying oven for 5 hours to obtain cleaned and degreased kapok hollow fibers.

[0058] (2) The cleaned and degreased kapok hollow fibers were placed in a tube furnace and heated to 800°C at a rate of 2°C / min under helium atmosphere protection. The temperature was held for 4 hours to obtain carbon micron tube fibers.

[0059] (3) Disperse carbon microtube fibers in distilled water at a concentration of 45 mg / mL and stir vigorously with a magnet at 25°C for 4 h to ensure uniform dispersion. Pour the fiber dispersion into a polytetrafluoroethylene mold and freeze for 6 h. Then place the sample in a freeze dryer and vacuum for 48 h to obtain a carbon microtube fiber aerogel preform.

[0060] (4) Silicon powder and silica powder were ball-milled at a mass ratio of 7:15 for 5 hours to mix evenly. Then, the mass of the carbon microtube fiber aerogel preform was weighed, and the mass of the mixed powder was determined according to a silicon to carbon molar ratio of 4:1. The mixed powder was transferred to a silica crucible, with the carbon microtube fiber aerogel preform placed on top of the mixed powder. Finally, the aerogel preform and the mixed powder were placed in a tube furnace, and under nitrogen atmosphere protection, the temperature was raised to 1450℃ at a heating rate of 2℃ / min and held for 3 hours to carry out a high-temperature carbothermic reduction reaction to obtain silicon carbide fiber aerogel microwave absorbing material.

[0061] The silicon carbide fiber aerogel absorbing material prepared in this embodiment has a compressive strength of 0.63 MPa at 10% deformation; at a thickness of 2.8 mm, it achieves a minimum reflection loss of -53.3 dB at 10.7 GHz, an effective absorption bandwidth of 4.68 GHz, and electromagnetic wave reflection loss as... Figure 6 As shown.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing biomass-derived silicon carbide fiber aerogel, characterized in that: Includes the following steps: (1) The kapok raw fibers were degreased, washed and dried to obtain kapok hollow fibers; (2) Carbon microtube fibers are obtained by high-temperature carbonization of cleaned and degreased kapok hollow fibers; (3) At 25℃~60℃, carbon microtube fibers are uniformly dispersed in distilled water at a concentration of 5~55mg / mL, and frozen at -18℃~-196℃ for 2~8h. Then, the carbon microtube fiber aerogel preform is obtained by placing it in a freeze dryer and vacuuming for 24~48h. (4) Mix silicon powder and silica powder at a mass ratio of 7:15 and ball mill for 3-8 hours to obtain mixed powder; place the carbon microtube fiber aerogel blank above the mixed powder and place it in a tube furnace according to a silicon to carbon molar ratio of 4:1, and carry out a high-temperature carbothermic reduction reaction under a protective atmosphere to obtain silicon carbide fiber aerogel material; wherein, the heating rate of the high-temperature carbothermic reduction reaction is 1-5℃ / min, and the temperature is maintained at 1400℃-1500℃ for 2-6 hours.

2. The method for preparing a biomass-derived silicon carbide fiber aerogel according to claim 1, characterized in that: In step (1), sodium chlorite is dissolved in deionized water and the pH of the solution is adjusted to 3.5-5.0 with acid. Then, the kapok fiber is added to the sodium chlorite aqueous solution and placed in an oven at 80℃-90℃ for 4-8 hours. Then, it is cooled naturally and the fiber mixture is washed repeatedly with deionized water 3-5 times. Finally, it is placed in a forced-air drying oven at 60℃-90℃ for 3-24 hours to obtain the kapok hollow fiber.

3. The method for preparing a biomass-derived silicon carbide fiber aerogel according to claim 2, characterized in that: The sodium chlorite aqueous solution contains 0.5-5 wt% sodium chlorite.

4. The method for preparing a biomass-derived silicon carbide fiber aerogel according to claim 2, characterized in that: The acids include acetic acid, phosphoric acid, and hydrochloric acid.

5. The method for preparing a biomass-derived silicon carbide fiber aerogel according to claim 1, characterized in that: In step (2), the cleaned and degreased kapok fibers are placed in a tube furnace, and the heating rate is 1~5℃ / min under a protective atmosphere. The carbonization temperature is 650℃~900℃, and the holding time is 2~6h to obtain carbon micron tube fibers.

6. The method for preparing a biomass-derived silicon carbide fiber aerogel according to claim 1, characterized in that: In step (3), the carbon microtube fibers are uniformly dispersed in distilled water by vigorous magnetic stirring at 25℃~60℃ for 1~3h.

7. The method for preparing a biomass-derived silicon carbide fiber aerogel according to claim 1, characterized in that: In step (3), the vacuum degree of the freeze dryer is always below 25 Pa during the freeze drying process.

8. A biomass-derived silicon carbide fiber aerogel, characterized in that: The aerogel is prepared by any one of the methods described in claims 1-7. The aerogel contains silicon carbide microtube fibers and silicon carbide nanowires distributed inside. The silicon carbide microtube fibers have a hollow structure. The silicon carbide nanowires grow around the silicon carbide microtubes. The silicon carbide microtubes and silicon carbide nanowires are interspersed inside the aerogel.

9. The application of a biomass-derived silicon carbide fiber aerogel as described in claim 8, characterized in that: Used in electromagnetic wave absorbing materials.

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