A method for preparing a flexible SiC nanofiber membrane

Abstract

The application discloses a preparation method of flexible SiC fiber membrane, which comprises the following steps: preparing monodisperse SiO2 small balls, preparing a spinning solution, electrospinning, pre-oxidation treatment, heat treatment and the like. The application mainly replaces commercial products as a silicon source by using self-prepared monodisperse SiO2 small balls, and successfully prepares the flexible SiC fiber membrane by means of a nano toughening mechanism and controlling the particle size. The method overcomes the problems of large brittleness, relatively thick fiber diameter and fiber fracture of pure SiC fiber prepared by using commercial silicon sources. The obtained flexible SiC fiber membrane has controllable morphology, and the crystal grains are uniformly distributed in the fiber. The fiber membrane shows the characteristics of bendable, elastic, high-temperature resistant and strong electromagnetic wave absorption, and has strong applicability. Moreover, the preparation method is simple in process, strong in controllability, easy to realize large-scale production and practical.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a flexible silicon carbide fiber film for electromagnetic wave absorption and high-temperature insulation, and belongs to the technical field of material synthesis and preparation. BACKGROUND

[0002] With the progress of science and technology, electromagnetic pollution poses an increasingly serious threat to human health and electronic equipment, and therefore electromagnetic wave protection research has attracted much attention. Wave-absorbing materials can convert electromagnetic waves into other forms of energy, fundamentally solving the problem of electromagnetic pollution, and therefore have attracted widespread attention. However, with the diversified needs of application fields, wave-absorbing materials are no longer only focused on strong attenuation, but also have higher requirements in terms of light weight, wide frequency, etc., which makes it particularly important to develop new wave-absorbing materials with excellent performance. At present, there have been a large number of research reports on electromagnetic wave-absorbing materials, and flexibility and hydrophobicity are two important factors affecting the practical application performance of wave-absorbing materials. In particular, in order to meet the complex extreme application environment, the electromagnetic wave-absorbing materials used must have excellent properties such as flexibility, hydrophobicity, acid and alkali corrosion resistance, high temperature stability, etc.

[0003] Silicon carbide (SiC) is a wide band gap semiconductor material, which has many excellent physical and chemical properties such as adjustable electrical conductivity, high temperature resistance, oxidation resistance, high modulus, high thermal conductivity and good chemical stability, making it have great application in the field of electromagnetic wave absorption. Compared with metal materials, polymer materials or carbon materials, SiC has many advantages, but its brittleness greatly limits its application. In the past few decades, silicon carbide has been prepared into different forms of materials, including thin films, rods, fibers, etc. Among them, flexible SiC fibers have attracted widespread attention due to their combination of flexibility, adjustable electrical resistance, electromagnetic wave absorption and high temperature resistance. However, traditional SiC fiber preparation methods include: (1) chemical vapor deposition (CVD), (2) activated carbon fiber conversion method, (3) ultra-fine powder high temperature sintering method, (4) polymer precursor conversion method. These methods have the defects of high equipment and production cost, large fiber brittleness, thick fiber diameter and poor oxidation resistance, etc. Therefore, it is urgent to develop an economical and practical new flexible high-quality SiC fiber preparation method.

[0004] In recent years, electrospinning technology has attracted much attention due to its relatively low cost and simple operation device, and has been widely used in the preparation of various flexible oxide ceramic nanofibers with controllable diameter and size, such as TiO2, SiO2, Al2O3 and the like. However, there are still many challenges in the preparation of flexible carbide ceramic nanofibers by electrospinning technology. This is because the carbide ceramic nanofibers usually require a high sintering temperature, generally above 1400℃, and the ultra-high temperature preparation process is easy to cause the grain growth of electrospun fibers, increase the brittleness, and difficult to control the stoichiometric ratio. Therefore, obtaining flexible carbide ceramic fibers by electrospinning technology puts higher requirements on the chemical composition and structure of the spinning solution precursor material, the electrospinning process parameters, the fiber material heat treatment technology and the process flow. Taking SiC fibers as an example, the pure SiC fibers prepared by electrospinning technology currently exist problems such as uneven radial size and grain distribution, coarse fiber diameter, low aspect ratio, high brittleness and easy to break.

[0005] The existing literature and patents report that the flexible silicon carbide fibers prepared by electrospinning technology are mainly composed of carbon fiber composite silicon carbide particles, and it is difficult to maintain the continuity and flexibility of pure SiC fibers. SUMMARY

[0006] The technical problem to be solved by the present application is that the traditional pure SiC fiber preparation process has the defects of uneven radial size and grain distribution of the fiber, difficulty in obtaining continuous fiber filaments, and easy breaking of the fiber.

[0007] To solve the above technical problems, the technical solutions of the present application are as follows:

[0008] A preparation method of a flexible SiC fiber film, characterized in that it comprises the following steps:

[0009] Step 1), preparation of monodisperse SiO2 beads: tetraethyl orthosilicate and ammonia are dissolved in anhydrous ethanol respectively, mixed, and constant temperature stirring to obtain a white suspension; centrifugation, water washing and freeze drying;

[0010] Step 2), preparation of spinning solution: dissolving the spinning aid, monodisperse SiO2 beads and surfactant in the spinning solvent, stirring until mixed uniformly to obtain the spinning solution;

[0011] Step 3), electrospinning: using the spinning solution for spinning to prepare SiC precursor nanofibers, and then drying in an oven at 50-100℃ for 3-12h;

[0012] Step 4), pre-oxidation treatment: heat treatment of the SiC precursor nanofibers in air atmosphere to complete the solidification and crosslinking;

[0013] Step 5), heat treatment: the SiC precursor nanofiber after pre-oxidation treatment is placed in a tube furnace, and first low-temperature carbonization is performed under inert atmosphere, and then carbon thermal reduction is performed by heating, so that the flexible SiC fiber film prepared by using monodisperse SiO2 small balls is obtained.

[0014] Preferably, in the step 1), the concentration of the ethyl orthosilicate in the white suspension is 0.1-1 mol / L, and the concentration of the ammonia solution is 0.1-1.1 mol / L; the volume fraction of the ammonia solution in the white suspension is 10-30%, and the obtained monodisperse SiO2 particle size is 1-2000 nm.

[0015] Preferably, in the step 1), the constant temperature is 30-90℃; the stirring time is 3-24 h, and the freeze-drying time is 12-48 h.

[0016] Preferably, in the step 2), the spinning aid is any one or more of polyvinyl alcohol, polyacrylonitrile, polystyrene, polyester, and polyamide; the surfactant is any one or more of sodium dodecyl sulfate (SDS), polysorbate, alkylphenol polyoxyethylene ether (APEO), and polyoxyethylene fatty acid ester; and the spinning solvent is one or more of N,N-dimethylformamide, sodium thiocyanate, formic acid, tetrahydrofuran, dimethyl sulfoxide, and acetone.

[0017] Preferably, in the step 2), the mass ratio of the spinning aid, the monodisperse SiO2 small balls, and the surfactant is 1-20:1-40:1-10; the stirring temperature is 30-90℃, and the stirring time is 5-24 h.

[0018] Preferably, in the step 3), the process parameters of the spinning are as follows: the spinning voltage is 10-30 kV, the spinning solution advancing speed is 0.005-0.5 mL / min, the rotating speed is 100-500 r / min, and the distance between the collection drum and the spinneret is 15-25 cm.

[0019] Preferably, in the step 4), the temperature for heat treatment, solidification, and crosslinking is 150-300℃, the heating rate is 1-5℃ / min, and the constant temperature time is 1-5 h.

[0020] Preferably, in the step 5), the temperature for low-temperature carbonization is 300-1000℃, the heating rate is 1-10℃ / min, and the constant temperature time is 1-5 h; the heating rate for carbon thermal reduction is 1-10℃ / min, the heating target is 1200-1600℃, and the constant temperature time is 1-10 h.

[0021] The application is easy to implement and simple to operate, mainly adopts electrospinning and carbon thermal reduction process to obtain flexible SiC nanofiber film material with good nanofiber morphology, excellent electromagnetic wave absorption and heat insulation performance. The application prepares pure SiC flexible nanofiber film by preparing uniform monodisperse nano SiO2 microspheres as a silicon source and combining electrospinning and carbon thermal reduction technology. The prepared pure SiC flexible nanofiber film not only inherits the excellent electromagnetic wave absorption and heat insulation performance of SiC material, but also endows the SiC fiber film material with good flexibility and elasticity. The SiC nanofiber film with flexibility and electromagnetic wave absorption and heat insulation performance shows great application potential in electromagnetic shielding, stealth technology, flexible electronic devices and high-temperature insulation.

[0022] Compared with the prior art, the application has the following beneficial effects:

[0023] The application provides a preparation method of flexible SiC nanofiber film. The method is prepared by combining electrospinning and carbon thermal reduction, uses a spinning aid as a carbon source, uses self-prepared monodisperse SiO2 microspheres as a silicon source, dissolves an auxiliary surfactant in a spinning solvent, prepares a polymer nanofiber film precursor containing SiO2 through electrospinning technology, and then is converted into pure SiC nanofiber film through pre-oxidation and high-temperature heat treatment. The pure SiC nanofiber film prepared by the method has good continuity and flexibility due to the excellent mechanical properties of single nanofiber and the uniform nanoscale diameter distribution. Compared with SiC fibers prepared by a commercial silicon source, the method overcomes the problems of large brittleness, coarse diameter and fiber fracture of pure SiC nanofiber, and the obtained flexible SiC nanofiber film has bendability, elasticity, heat resistance and strong electromagnetic wave absorption capacity. These characteristics endow it with wide application potential. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a process schematic diagram for preparing the flexible SiC nanofiber film of the application;

[0025] Figure 2 It is an SEM diagram of the flexible SiC nanofiber prepared in Example 1;

[0026] Figure 3 It is an XRD diagram of the flexible SiC nanofiber prepared in Example 1;

[0027] Figure 4Appearance pictures of SiC samples obtained in Examples and Comparative Examples: a represents appearance picture of flexible SiC nanofiber membrane synthesized using self-made silicon source (Example 1), b represents appearance picture of flexible SiC nanofiber membrane aerogel synthesized using self-made silicon source (Example 1), c represents brittle SiC sample synthesized using commercial hydrophobic silicon source (Example 2), d represents SiC powder sample synthesized using commercial hydrophobic silicon source (Example 2), e represents brittle SiC sample synthesized using commercial hydrophilic silicon source (Example 3), f represents collapsed SiC sample synthesized according to CN113097469A (Comparative Example 1);

[0028] Figure 5 Schematic diagram of compression mechanical experiment of flexible SiC nanofiber membrane prepared in Example 1;

[0029] Figure 6 Infrared thermal imaging picture of heat insulation performance of flexible SiC nanofiber membrane aerogel sample prepared in Example 1;

[0030] Figure 7 Three-dimensional electromagnetic wave absorption picture of SiC fiber membrane obtained in Examples and Comparative Examples: (a) flexible SiC nanofiber in Example 1; (b) brittle SiC sample in Example 2; (c) brittle SiC sample in Example 3; (d) SiC powder sample in Comparative Example 1. DETAILED DESCRIPTION

[0031] In order to make the present application more obvious and easy to understand, the preferred embodiments are described in detail below with the help of the accompanying drawings.

[0032] In the present application, the materials and reagents used are commercially available unless otherwise specified. In the present application, unless otherwise specified, the numerical range "a~b" represents a shorthand representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "5~12" represents that all real numbers between "5~12" have been listed herein, and "5~12" is only a shorthand representation of these numerical combinations.

[0033] Example 1

[0034] (1) 0.5 mol / L TEOS and 0.5 mol / L ammonia water were dissolved in an appropriate amount of anhydrous ethanol respectively, mixed, then stirred at 60°C for 10 h, finally centrifuged, washed with water for 2~3 times and freeze-dried for 24 h to obtain monodisperse SiO2 beads with a particle size of 1~2000 nm.

[0035] (2) PAN, monodisperse SiO2 beads obtained in step (1) and alkylphenol polyoxyethylene ether surfactant were sampled and dissolved in an appropriate amount of tetrahydrofuran at a mass ratio of 6:14:3, and stirred at 55°C for 12 h to obtain a uniform spinning solution.

[0036] (3) The solution of step (2) is moved into a spinning machine to spin at a pushing rate of 0.1 mL / min, the distance between the collection drum and the spinneret is 20 cm, the spinning voltage is 26 kV, the rotation speed of the collection drum is 400 r / min, the spun fiber film is taken off from the receiver and placed in a drying box for vacuum drying at 90℃ for 10 h.

[0037] (4) The dried fiber film is heated to 200℃ at a rate of 5℃ / min in an air atmosphere, and kept for 4 h to complete pre-oxidation.

[0038] (5) The pre-oxidized fiber film is placed in a tube furnace for carbonization treatment, heated to 900℃ at a rate of 5℃ / min for 4 h, and then heated to 1500℃ at a rate of 3℃ / min for 7 h to obtain a flexible SiC fiber film sample by carbothermal reduction, and the whole pyrolysis process is protected by argon.

[0039] (6) The pre-oxidized fiber cloth is stacked and placed in a tube furnace for carbonization treatment, heated to 900℃ at a rate of 5℃ / min for 4 h, and then heated to 1500℃ at a rate of 3℃ / min for 7 h to obtain a SiC fiber film aerogel sample by carbothermal reduction, and the whole pyrolysis process is protected by argon.

[0040] The micro-morphology of the flexible SiC nanofiber prepared in this example is shown in Figure 2 , and the XRD crystal structure is shown in Figure 3 . The appearance of the SiC flexible nanofiber film and aerogel is shown in Figure 4 a and 4b. It can be seen that the SiC fiber film prepared by the present application has good flexibility, the SEM image shows that the nanofiber maintains uniform size and continuity, and the nanofiber film aerogel prepared by multi-layer stacking has good elasticity and excellent heat insulation performance as shown in Figure 5 and 6 . The wave absorption performance of the flexible SiC fiber film prepared by the present application is shown in Figure 7 a. When the thickness is 9.6 mm, it has the smallest reflection loss of -48.1 dB, and the effective absorption bandwidth EAB is 5.0 GHz. It can be seen that the continuous and flexible fiber prepared by the present application has good wave absorption performance.

[0041] Example 2

[0042] The difference between this example and example 1 is only that the hydrophobic nano-SiO2 used is a commercial product purchased, with a diameter of 20-2000 nm.

[0043] The rest is exactly the same as described in example 1.

[0044] The appearance of the SiC fiber film prepared in this embodiment is shown in Figure 4 c. It can be seen that the SiC fiber film synthesized by using a series of sizes of commercial hydrophobic nano-SiO2 is brittle and not flexible, and part of the product presents a crumb particle shape as shown in Figure 4 d.

[0045] In addition, the wave absorption performance of the brittle SiC is shown in Figure 7 b. It can be seen that when the thickness is 7.2 mm, the minimum reflection loss is -11.8 dB, and the effective absorption bandwidth EAB is 0.9 GHz, so the wave absorption performance is poor. Example 3

[0046] The difference between this embodiment and Example 1 is only that the hydrophilic nano-SiO2 used is a commercial product with a diameter of 20-2000 nm.

[0047] The rest is exactly the same as described in Example 1.

[0048] The appearance of the SiC fiber film prepared in this embodiment is shown in Figure 4 e. It can be seen that the SiC fiber film synthesized by using a series of sizes of commercial hydrophilic nano-SiO2 is brittle and not flexible. In addition, the wave absorption performance of the brittle SiC is shown in Figure 7 c. It can be seen that when the thickness is 6.2 mm, the minimum reflection loss is -27.3 dB, and the effective absorption bandwidth EAB is 3.0 GHz, so the wave absorption performance is poor. Comparative Example 1

[0049] The technical solution of this embodiment refers to CN113097469A.

[0050] (1) At 70℃, polyacrylonitrile, nano commercial silicon dioxide and N,N-dimethylformamide (DMF) were weighed according to the mass ratio of 1:3:5, and uniformly stirred for 12h to obtain a spinning solution.

[0051] (4) Under argon conditions, the SiO2 / C nanomembrane material was heated to 1500℃ at a rate of 5℃ / min and kept for 2h to obtain a Si / SiC / C nanofiber membrane.

[0052] (5) The obtained Si / SiC / C nanofiber membrane was decarburized at 800℃ for 2h to obtain a pure Si / SiC nanofiber membrane.

[0053] In the preparation process of the embodiment, it can be obviously seen that the SiC fiber synthesized by this way has no flexibility after high-temperature decarburization and collapses due to fiber fracture Figure 4 f). In addition, the wave absorption performance of the broken fiber is known from Figure 7 d that when the thickness is 7.1 mm, the minimum reflection loss is -31.5 dB, the effective absorption bandwidth EAB is 4.2 GHz, and the wave absorption performance is poorer than that of the flexible SiC nanofiber film prepared in the embodiment 1 of the application.

Claims

1. A method for producing a flexible SiC fiber film, characterized by, The method comprises the following steps: Step 1), preparing monodisperse SiO2 beads: ethyl orthosilicate and ammonia are dissolved in anhydrous ethanol respectively, mixed, and constant temperature stirring is performed to obtain a white suspension; centrifugation, water washing and freeze drying are performed; Step 2), preparing a spinning solution: a spinning aid, monodisperse SiO2 beads and a surfactant are dissolved in a spinning solvent to obtain a spinning liquid by stirring until mixed uniformly; Step 3), electrospinning: spinning is performed by using the spinning liquid to prepare SiC precursor nanofibers, and then the SiC precursor nanofibers are dried in an oven at 50-100 DEG C for 3-12 h; Step 4), pre-oxidation treatment: the SiC precursor nanofibers are heat treated in an air atmosphere to complete solidification and crosslinking; The temperature for heat treatment and solidification and crosslinking is 150-300 DEG C, the temperature rising speed is 1-5 DEG C / min, and the constant temperature time is 1-5 h; Step 5), heat treatment: the SiC precursor nanofibers after pre-oxidation treatment are placed in a tube furnace, and first low-temperature carbonization is performed under inert atmosphere, and then carbon thermal reduction is performed by temperature rising, so that flexible SiC fiber membranes prepared by using monodisperse SiO2 beads are obtained; the temperature for low-temperature carbonization is 300-1000 DEG C, the temperature rising speed is 1-10 DEG C / min, and the constant temperature time is 1-5 h; the temperature rising speed for carbon thermal reduction is 1-10 DEG C / min, the temperature rising target is 1200-1600 DEG C, and the constant temperature time is 1-10 h.

2. The production method according to claim 1, wherein In the step 1), the concentration of ethyl orthosilicate in the white suspension is 0.1-1 mol / L, and the concentration of the ammonia solution is 0.1-1.1 mol / L; the volume fraction of the ammonia solution in the white suspension is 10-30%, and the obtained monodisperse SiO2 particle size is 1-2000 nm.

3. The production method according to claim 1, wherein In the step 1), the constant temperature is 30-90 DEG C; the stirring time is 3-24 h, and the freeze drying time is 12-48 h.

4. The production method according to claim 1, wherein In the step 2), the spinning aid is any one or more of polyvinyl alcohol, polyacrylonitrile, polystyrene, polyester and polyamide; the surfactant is any one or more of sodium dodecyl sulfate, polysorbate, alkylphenol polyoxyethylene ether and polyoxyethylene fatty acid ester; and the spinning solvent is one or more of N,N-dimethylformamide, sodium thiocyanate, formic acid, tetrahydrofuran, dimethyl sulfoxide and acetone.

5. The production method according to claim 1, wherein In the step 2), the mass ratio of the spinning aid, monodisperse SiO2 beads and surfactant is 1-20:1-40:1-10; the stirring temperature is 30-90 DEG C, and the stirring time is 5-24 h.

6. The production method according to claim 1, wherein In the step 3), the process parameters for spinning are as follows: the spinning voltage is 10-30 kV, the spinning solution advancing speed is 0.005-0.5 mL / min, the rotating speed is 100-500 r / min, and the distance between the collection drum and the spinneret is 15-25 cm.

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