SiON micro-nano fiber membrane with electromagnetic wave-transparent and high-temperature insulation functions, and preparation method and application thereof

Abstract

The application discloses a SiON micro-nano fiber membrane with electromagnetic wave transmission and high-temperature heat insulation, and a preparation method and application thereof, and relates to the technical field of ceramic fibers.The fiber membrane is formed by overlapping SiON micro-nano fibers; the arrangement mode of the SiON micro-nano fibers in the fiber membrane is disordered or directional; the diameter of the SiON micro-nano fibers is 100 nm to 1.3 mu m; the content of Si element in the SiON micro-nano fibers is greater than 35 at.%, the content of O element is greater than 30 at.%, the content of N element is greater than 12 at.%, and the content of C element is less than 7 at.%. The SiON fiber membrane prepared by the application has the component / structure characteristics of micro-nano fiber diameter (100-1200 nm), low carbon and amorphous, and exhibits the characteristics of light weight, porosity, wave transmission, heat insulation, high-temperature stability and the like, and is a novel wave transmission and heat insulation integrated fiber material with wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic fibers, and particularly relates to SiON micro-nano fiber membranes with electromagnetic wave transmission and high-temperature heat insulation and a preparation method and application thereof. BACKGROUND

[0002] Hypersonic vehicles usually undertake practical tasks such as electromagnetic communication, precise guidance and attack and defense confrontation, and are in a complex electromagnetic wave environment. At the same time, when the hypersonic vehicle flies at high speed in the near space, it also needs to cope with the long-term high-temperature service test under the action of aerodynamic heating. For example, the radar antenna cover part of the vehicle not only undertakes the important communication task of transmitting and receiving electromagnetic waves, but also is in a harsh aerodynamic heating environment (the temperature can be as high as 1000 DEG C), and it is urgent to apply wave-transparent and heat-insulating integrated materials to ensure that the internal electronic equipment of the radar antenna cover works at a suitable temperature and transmits and receives undamaged electromagnetic wave communication signals.

[0003] High-temperature wave-transparent materials can be generally divided into oxides, phosphates and nitrides, etc., among which Si3N4 ceramics exhibit high strength, high temperature resistance, thermal shock resistance and adjustable dielectric properties, and are the research focus in the field of wave-transparent materials. However, Si3N4 ceramics have high intrinsic thermal conductivity, and need to be doped with components and designed in structure to meet the requirements of wave-transparent and heat-insulating integration. High-temperature heat-insulating materials are usually oxide fiber materials, among which SiO2-based fiber materials have excellent wave-transparent performance and low intrinsic thermal conductivity, and the high-porosity structure formed by the lapping of large-aspect-ratio fibers can further improve the heat-insulating performance. However, SiO2 has significantly poorer temperature resistance than nitride ceramics, and it is difficult to be used at high temperature for a long time or repeatedly. In summary, it can be inferred that SiON fiber materials of ternary system are expected to integrate the advantages of Si3N4 and SiO2, and have excellent thermal stability (temperature resistance at 1000 DEG C), low dielectric loss (dielectric loss factor lower than 0.01) and low thermal conductivity (lower than 0.1 W / (m·K)), and become a potential new generation of high-temperature wave-transparent and heat-insulating integrated materials.

[0004] The use of wave-transparent and heat-insulating materials requires higher requirements for the structure and composition of SiON fiber materials. In terms of structure, reducing the fiber filament diameter from microns (greater than 5 µm) to micro-nanometers (100~1000 nm) can greatly improve the porosity, which is beneficial to the transmission of electromagnetic waves and the prevention of heat transfer; in terms of composition, element regulation and amorphous state control are the key points for simultaneous optimization of the wave-transparent and heat-insulating properties of SiON fibers. At present, the research on wave-transparent / heat-insulating micro-nano materials is still in its infancy, and the only examples are porous materials such as Si3N4 nanowire foam (Composites Part B: Engineering, 2021, 224: 109129), Si3N4 nanobelt aerogel (ACS Applied Material Interfaces, 2019, 11: 15795-15803), and Si3N4 / SiO2 nanofiber aerogel (Journal of Hazardous Materials, 2021, 419: 126385) and their preparation methods. The common feature of these one-dimensional nanomaterials is the nanoscale diameter (50~150 nm) and the single-crystal composition characteristics, which form a high-porosity structure and a low intrinsic dielectric constant, giving the material good heat-insulating and wave-transparent properties. However, the above work mainly uses chemical vapor deposition technology, which has the problems of low product yield, small aspect ratio (which is not conducive to the construction of thin-layer heat-blocking pore structure), and single-crystal structure of the product (which has a higher intrinsic thermal conductivity than amorphous state). Moreover, the porous materials obtained by this method have a large thickness (10~100 mm), which limits their application scenarios. Polymer-derived ceramics is a common process for mass production of amorphous ceramics. Melt spinning combined with polymer-derived ceramics can be used to mass-produce continuous fibers with large aspect ratios (such as commercial SiC and Si3N4 fibers), but the fiber diameter is mostly 5~20 µm, which is difficult to achieve micro-nano fiber diameter. In contrast, electrospinning as a high-efficiency and stable micro-nano fiber synthesis process is expected to be combined with polymer-derived ceramics and has the potential to be used for the preparation of two-dimensional thin-layer micro-nano ceramic fiber membranes. At present, the use of electrospinning combined with polymer-derived ceramics to prepare ternary system SiON ceramic fibers is a blank in the field, and the synthesis mechanism is unknown, and the process is difficult. The main technical difficulties include:

[0005] (1) It is difficult to obtain polymer precursors that can be directly converted into SiON phase. Polymer precursors that can be directly converted into SiON phase ceramics at high temperature pyrolysis have great technical difficulties in synthesis, regulation, mass production and stable storage, and have not been commercially available. Polycarbosilane and polysilazane, the precursors of SiC and SiCN ceramics, are commercially available precursors that are easy to synthesize, but it is difficult to directly convert SiON phase. It is necessary to design the process based on the components of the two precursors during the ceramic transformation stage to obtain the indirect conversion of SiON phase.

[0006] (2) The precursor has poor spinnability. Polycarbosilane and polysilazane are both oligomers (relative molecular mass of about 500-2000), especially polysilazane is a low molecular weight and low conductivity liquid polymer, which is difficult to form a high degree of molecular chain entanglement, stretch and set into continuous fibers under high voltage electric field, and maintain the fiber morphology during solidification and heat treatment. It is necessary to reasonably design the formula of the spinning solution, such as introducing spinning aids and fiber morphology stabilizers, to synthesize a spinning solution with good spinnability.

[0007] (3) It is difficult to control the elements and amorphous state. First, the core of element regulation is to reduce the content of C element and increase the content of N and O elements to reduce the dielectric constant of SiON fiber and weaken the loss of electromagnetic wave. Second, compared with single crystal and polycrystalline structure, amorphous structure not only has lower intrinsic thermal conductivity, but also has less grain boundary content, which can reduce the loss of electromagnetic wave. However, element regulation and amorphous state control face significant process difficulties: ① It is difficult to control the doping of carbon and nitrogen. The structure of polycarbosilane is mainly Si-C long chain, which contains a large amount of C element and does not contain N and O elements. Polysilazane mainly contains Si, C and N elements, but the content of C element is high, and the content of N and O elements is limited. Therefore, the process requirements for doping oxygen, doping nitrogen and removing carbon are high during the conversion of the two precursors; ② It is difficult to obtain high-temperature amorphous structure. The above two precursors complete the ceramic transformation above 1300°C, and a large amount of SiC and Si3N4 grains will be generated with the increase of temperature, gradually forming a polycrystalline structure and being difficult to maintain in an amorphous state. It is necessary to design the key process parameters (such as temperature and atmosphere) in the solidification and heat treatment process to realize the regulation of element composition and the maintenance of amorphous state.

[0008] In summary, the wave-transparent and heat-insulating integrated material has important research value and application demand in the field of aerospace, and has gradually attracted the attention of researchers. In view of the communication requirements and heat insulation difficulties in high temperature environment, it is urgent to develop a SiON micro-nano fiber film material with high temperature resistance, good wave transparency and low thermal conductivity and its preparation technology. SUMMARY

[0009] In view of the problems in the prior art, the present application mainly solves the problems of poor spinnability of the precursor, difficulty in micronization of the SiON fiber diameter, difficulty in regulating the microstructure components, and difficulty in simultaneously achieving wave-transparent and heat-insulating properties. The present application provides a SiON micro-nano fiber membrane with electromagnetic wave-transparent and high-temperature heat-insulating properties, a preparation method and application thereof. The method uses polycarbosilane or polysilazane as the precursor and is assisted by heat treatment to solve the problem of difficulty in obtaining the SiON ceramic precursor; the spinnability of the mixed precursor is effectively improved by using a spinning additive; based on the characteristics of high activity and easy oxidation of the mixed precursor, the precursor is cured in a mixed atmosphere of nitrogen and oxygen to introduce an appropriate amount of O element; the precursor fiber is assisted by a mixed atmosphere of nitrogen and ammonia with higher reactivity to complete the ceramic transformation, and the C and N elements are regulated by the ammoniation reaction. The O element combines with the C element to form small gas molecules during the ceramic transformation process, achieving the purpose of carbon removal and nitrogen doping; the complex components increase the system disorder, effectively inhibit crystallization, and achieve amorphous control. The SiON micro-nano fiber membrane disclosed by the present application can maintain good stability at a temperature above 1000℃, has significant advantages in electromagnetic wave-transparent function, high-temperature heat-insulating performance, and light and thin layer, and is expected to develop into a multifunctional integrated aerospace material and serve in high-temperature harsh environments.

[0010] The first object of the present application is to provide a SiON micro-nano fiber membrane with electromagnetic wave-transparent and high-temperature heat-insulating properties, wherein the fiber membrane is formed by overlapping SiON micro-nano fibers;

[0011] The arrangement mode of the SiON micro-nano fibers in the fiber membrane is disordered or directional;

[0012] The diameter of the SiON micro-nano fibers is 100 nm to 1.3 μm;

[0013] The content of Si element in the SiON micro-nano fibers is > 35 at.%, the content of O element is > 30 at.%, the content of N element is > 12 at.%, and the content of C element is < 7 at.%.

[0014] Preferably, the thickness of the fiber membrane is 0.1 to 1.0 mm, the porosity is 85% to 95%, and the density is 50 to 120 mg / cm 3 .

[0015] Preferably, the fiber membrane is a precursor fiber membrane with disordered or directional distribution prepared by electrospinning of a SiON phase ceramic precursor; then, amorphous state is synthesized and maintained at a temperature above 1300℃.

[0016] Preferably, the SiON phase ceramic precursor is prepared by dissolving polycarbosilane and / or polysilazane in an organic solvent.

[0017] The second object of the present application is to provide a preparation method of SiON micro-nano fiber membrane with electromagnetic wave-transparent and high-temperature insulation, comprising the following steps:

[0018] chloroform and N, N-dimethylformamide are mixed in a certain proportion as a solvent; a certain amount of polycarbosilane and / or polysilazane is added to the solvent as a SiON phase ceramic precursor; a certain amount of polyvinylpyrrolidone is added to the solvent as a spinning aid; a certain amount of 1-vinylimidazole is added to the solvent as a fiber morphology stabilizer; the mixture is uniformly mixed to prepare a spinning solution;

[0019] Based on electrospinning technology, the spinning solution is pushed out of a spinning needle with a certain inner diameter at a certain liquid discharge rate, a certain direct current voltage is applied to the needle and the receiver respectively, and spinning is carried out under the action of the electric field, and a precursor micro-nano fiber membrane is prepared on the receiver;

[0020] The precursor micro-nano fiber membrane is dried at 65~75℃ for 1~3h, and then the precursor micro-nano fiber membrane is placed in an oven, a mixed gas of a certain proportion of nitrogen and oxygen is introduced, heated to a temperature T1 at a heating rate v1 and kept for a time t1, then heated to a temperature T2 at a heating rate v2 and kept for a time t2, to obtain a cured precursor micro-nano fiber membrane;

[0021] The volume ratio of nitrogen and oxygen in the mixed gas is 2~7:3; the heating rate v1 is 5~8℃ / min, and v2 is 1~2℃ / min; the heating temperature T1 is 140~160℃, and T2 is 200~220℃; the holding time t1 is 0.5~2 h, and t2 is 1~3 h;

[0022] The cured precursor micro-nano fiber membrane is placed in a tube furnace, a mixed gas of nitrogen and ammonia is introduced at the ammoniation temperature section, nitrogen or argon is introduced at the remaining temperature sections, the temperature is raised to T3 and kept for t3, and then the temperature is raised to T4 at a certain rate v3 and kept for t4, to complete the ceramicization of the fiber, i.e. to obtain the SiON micro-nano fiber membrane with electromagnetic wave-transparent and high-temperature insulation;

[0023] The temperature at the ammoniation temperature section is raised from 200 to 900℃; the heating rate v3 is 1~2℃ / min; the heating temperature T3 is 800~900℃, and T4 is 1300~1500℃; the holding time t3 is 0.5~2 h, and t4 is 1~3 h.

[0024] Preferably, in the process of preparing the spinning solution, the mass ratio of chloroform to N,N-dimethylformamide in the solvent is 3-6:1; the amount of the ceramic precursor added is 10-50 wt.% of the mass of the solvent; the amount of the polyvinylpyrrolidone added is 2-8 wt.% of the mass of the solvent; and the amount of the 1-vinylimidazole added is 1-5 wt.% of the mass of the solvent.

[0025] Preferably, in the process of preparing the precursor micro-nano fiber membrane, the inner diameter of the spinning needle is 0.3-0.6 mm; the liquid discharge rate is 20-50 µL / min; the collection distance between the needle and the receiver is 14-22 cm; and the direct current voltage includes a direct current positive voltage of 16-24 kV and a negative voltage of -2-4 kV.

[0026] Preferably, when the receiver is a flat plate, the prepared precursor micro-nano fiber membrane is a fiber membrane with disordered distribution; and when the receiver is a roller, the prepared precursor micro-nano fiber membrane is a fiber membrane with directional distribution.

[0027] Preferably, the volume ratio of nitrogen to ammonia in the ammonia temperature section is 0-1:1.

[0028] A third object of the present application is to provide an application of the SiON micro-nano fiber membrane in wave-transparent heat insulation.

[0029] The present application provides a SiON micro-nano fiber membrane and a preparation method thereof, which adopts electrospinning combined with a polymer-to-ceramic process, uses PCS or PSN as a precursor, and designs and controls the microstructure and components of the fiber by adjusting important process parameters such as the ratio of the spinning solution, the spinning voltage, the heat treatment atmosphere, and the temperature, so as to obtain a SiON micro-nano fiber membrane with good wave-transparent performance, heat insulation performance, and high-temperature stability.

[0030] In terms of the microstructure, the SiON micro-nano fiber has a diameter of 100-1300 nm and a length of several hundred to several thousand microns; in the SiON micro-nano fiber membrane, the fibers are mutually overlapped to form a loose porous structure (porosity: 70-90%); and the SiON micro-nano fiber membrane has the characteristics of light and thin layer and exhibits good high-temperature heat insulation performance under an ultra-thin thickness. In terms of the components, the SiON micro-nano fiber is composed of a SiON phase that remains amorphous at high temperatures and exhibits good electromagnetic wave transmission performance. Under the synergistic action of the microstructure and the components, the SiON micro-nano fiber membrane has good heat insulation and wave-transparent performance.

[0031] Compared with the prior art, the present application has the following beneficial effects:

[0032] (1) The SiON micro-nano fiber membrane involved in the present application adopts PCS or PSN as a precursor, and combines with the ammonia gas ammoniation heat treatment process to realize the ceramic conversion of the fiber SiON phase in the membrane, and solves the problem of difficult acquisition of the SiON precursor.

[0033] (2) The SiON micro-nano fiber membrane involved in the present application is obtained by mixing the precursor with a corresponding solvent, a spinning aid and a fiber morphology stabilizer to perform the electrostatic spinning process, overcomes the spinning difficulty of the two precursors PCS and PSN due to the low intrinsic molecular weight and low conductivity, realizes the fiber diameter refinement to the micro-nano level, and is beneficial to form a structure with high porosity, low density and large specific surface area, which significantly contributes to the heat insulation performance of the fiber membrane.

[0034] (3) The SiON micro-nano fiber membrane involved in the present application effectively controls the C and N element content in the fiber under the ammonia gas ammoniation heat treatment process, realizes the nitrogen doping and carbon removal, and simultaneously inhibits the crystallization behavior, obtains the component characteristics of rich nitrogen and less carbon and amorphous state, and is beneficial to improve the wave transmission and heat insulation performance of the fiber membrane.

[0035] (4) The preparation process of the SiON micro-nano fiber membrane involved in the present application utilizes the electrostatic spinning method combined with the polymer conversion ceramic method to respectively complete the forming (fiber spinning) and the property forming (ceramic conversion) of the micro-nano fiber membrane. The morphology and distribution are controlled during the forming, and the element composition and amorphous state are controlled during the forming, and the synergistic optimization of the microstructure and components of the fiber membrane makes it have good wave transmission performance and heat insulation performance.

[0036] (5) The SiON micro-nano fiber membrane involved in the present application has the characteristics of low density and small thickness, and the advantages of such light and thin layer make it more suitable for application as a wave transmission and heat insulation integrated material for covering electronic equipment or device components in a narrow space compared with three-dimensional foam materials.

[0037] (6) The preparation method of the SiON micro-nano fiber membrane involved in the present application is simple and stable, has a short synthesis period and low cost, and can synthesize a large amount of SiON micro-nano fiber membranes, thereby developing into an industrialized preparation technology of wave transmission and heat insulation integrated fiber membranes. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is the (a) macroscopic photo and (b-c) microscopic morphology of the SiON nano fiber membrane in Example 1 of the present application;

[0039] Figure 2 is the (a) X-ray diffraction spectrum and (b) transmission electron microscope photo of the SiON nano fiber membrane in Example 1 of the present application;

[0040] Figure 3are the (a) real part of dielectric constant, (b) imaginary part of dielectric constant and (c) dielectric loss of the SiON nanofiber membrane in Example 1 of the present application;

[0041] Figure 4 are the thermal imaging characterization results of the SiON nanofiber membrane in Example 1 of the present application: (a) infrared photo of the front side of the sample; (b) infrared photo of the back side of the sample after heating for 10 min; (c) infrared photo of the back side of the sample after heating for 20 min; (d) infrared photo of the back side of the sample after heating for 30 min;

[0042] Figure 5 are (a) macroscopic photo and (b-c) microscopic morphology of the SiON nanofiber membrane in Example 2 of the present application;

[0043] Figure 6 are (a) X-ray diffraction pattern and (b) transmission electron microscope photo of the SiON nanofiber membrane in Example 2 of the present application;

[0044] Figure 7 are the (a) real part of dielectric constant, (b) imaginary part of dielectric constant and (c) dielectric loss of the SiON nanofiber membrane in Example 2 of the present application;

[0045] Figure 8 are the thermal imaging characterization results of the SiON nanofiber membrane in Example 2 of the present application: (a) infrared photo of the front side of the sample; (b) infrared photo of the back side of the sample after heating for 10 min; (c) infrared photo of the back side of the sample after heating for 20 min; (d) infrared photo of the back side of the sample after heating for 30 min;

[0046] Figure 9 is the thermogravimetric curve of the SiON nanofiber membrane in Example 2 of the present application under air atmosphere;

[0047] Figure 10 are (a) macroscopic photo and (b-c) microscopic morphology of the SiON micro-nanofiber membrane in Example 3 of the present application;

[0048] Figure 11 are (a) X-ray diffraction pattern and (b) transmission electron microscope photo of the SiON micro-nanofiber membrane in Example 3 of the present application;

[0049] Figure 12 are the (a) real part of dielectric constant, (b) imaginary part of dielectric constant and (c) dielectric loss of the SiON micro-nanofiber membrane in Example 3 of the present application

[0050] Figure 13is the thermal imaging characterization result of the SiON micro-nano fiber membrane in Example 3 of the present application: (a) infrared photo of the front side of the sample; (b) infrared photo of the back side of the sample after heating for 10 min; (c) infrared photo of the back side of the sample after heating for 20 min; (d) infrared photo of the back side of the sample after heating for 30 min;

[0051] Figure 14 is the thermogravimetric curve of the SiON micro-nano fiber membrane in Example 3 of the present application under air atmosphere.

[0052] Figure 15 is (a) macroscopic photo and (b-c) microscopic morphology of the SiON micro-nano fiber membrane in Example 4 of the present application;

[0053] Figure 16 is (a) X-ray diffraction pattern and (b) transmission electron microscope photo of the SiON micro-nano fiber membrane in Example 4 of the present application;

[0054] Figure 17 is (a) real part of dielectric constant, (b) imaginary part of dielectric constant and (c) dielectric loss of the SiON micro-nano fiber membrane in Example 4 of the present application

[0055] Figure 18 is the thermal imaging characterization result of the SiON micro-nano fiber membrane in Example 4 of the present application: (a) infrared photo of the front side of the sample; (b) infrared photo of the back side of the sample after heating for 10 min; (c) infrared photo of the back side of the sample after heating for 20 min; (d) infrared photo of the back side of the sample after heating for 30 min;

[0056] Figure 19 is the microscopic morphology of the SiON micro-nano fiber membrane in Counterexample 1 of the present application;

[0057] Figure 20 is the microscopic morphology of the SiON micro-nano fiber membrane in Counterexample 2 of the present application;

[0058] Figure 21 is (a) real part of dielectric constant, (b) imaginary part of dielectric constant and (c) dielectric loss of the SiON micro-nano fiber membrane in Counterexample 4 of the present application;

[0059] Figure 22 is (a) real part of dielectric constant, (b) imaginary part of dielectric constant and (c) dielectric loss of the SiON micro-nano fiber membrane in Counterexample 5 of the present application;

[0060] Figure 23 is (a) real part of dielectric constant, (b) imaginary part of dielectric constant and (c) dielectric loss of the SiON micro-nano fiber membrane in Counterexample 6 of the present application. DETAILED DESCRIPTION

[0061] In order to make the technical scheme of the present application better understood by the skilled in the art and to enable the same to be carried into practice, the following will provide further description of the present application with reference to the specific embodiments and the accompanying drawings, but the embodiments are not intended to limit the present application.

[0062] In order to provide a wave-transparent and heat-insulating integrated material for harsh service environment, the present application combines the polymer-to-ceramic method with the electrospinning method, uses polycarbosilane (SiC ceramic precursor) or polysilazane (SiCN ceramic precursor) as the SiON phase ceramic precursor to prepare a spinning solution, prepares a precursor micro-nano fiber membrane through the electrospinning process, performs carbon removal and nitrogen doping treatment in a mixed atmosphere of nitrogen and ammonia, and completes the ceramic transformation to obtain a SiON micro-nano fiber membrane. The preparation process has the advantages of short cycle, simple process, strong designability, high repeatability, and suitability for mass production. The SiON fiber membrane prepared under the technical scheme provided by the present application has a micro-nano level fiber diameter (100-1200 nm), low carbon, and amorphous component / structure characteristics, and exhibits the characteristics of light weight, porosity, wave transparency, heat insulation, high temperature stability, etc., and is a new type of wave-transparent and heat-insulating integrated fiber material with wide application prospects.

[0063] In order to achieve the above-mentioned purpose, the present application provides a SiON micro-nano fiber membrane with electromagnetic wave-transparent and high-temperature heat-insulating functions in a first aspect.

[0064] The arrangement mode of the SiON micro-nano fibers in the fiber membrane is disordered or directional.

[0065] The diameter of the SiON micro-nano fibers is 100 nm-1.3 μm.

[0066] The Si element content in the SiON micro-nano fibers is > 35 at.%, the O element content is > 30 at.%, the N element content is > 12 at.%, the C element content is < 7 at.%, and the total is 100 at.%.

[0067] The thickness of the fiber membrane is 0.1-1.0 mm, the porosity is 85%-95%, and the density is 50-120 mg / cm 3 .

[0068] The fiber membrane is a precursor fiber membrane with disordered or directional distribution prepared by electrospinning of the SiON phase ceramic precursor, and then synthesized at 1300℃ or above and kept in an amorphous state.

[0069] The SiON phase ceramic precursor is prepared by dissolving polycarbosilane and / or polysilazane in an organic solvent.

[0070] Specifically, the SiON micro-nano fiber membrane is synthesized at 1300 DEG C or above and remains amorphous, and is mainly composed of SiON phase inside.

[0071] The SiON micro-nano fiber membrane has low density and small thickness, and the advantages of the light and thin layer make it more suitable for application as a wave-transparent and heat-insulating integrated material for covering electronic devices or device components in narrow spaces compared to three-dimensional foam materials.

[0072] The second aspect of the present application provides a preparation method of a SiON micro-nano fiber membrane with electromagnetic wave-transparent and high-temperature heat-insulating functions, comprising the following steps:

[0073] chloroform and N, N-dimethylformamide are mixed in a certain proportion as a solvent; a certain amount of polycarbosilane and / or polysilazane is added to the solvent as a SiON phase ceramic precursor; a certain amount of polyvinylpyrrolidone is added to the solvent as a spinning aid; a certain amount of 1-vinylimidazole is added to the solvent as a fiber morphology stabilizer; the mixture is uniformly mixed to prepare a spinning solution;

[0074] During the preparation of the spinning solution, the mass ratio of chloroform to N, N-dimethylformamide in the solvent is 3-6:1; the addition amount of the ceramic precursor is 10-50 wt.% of the mass of the solvent; the addition amount of the polyvinylpyrrolidone is 2-8 wt.% of the mass of the solvent; and the addition amount of the 1-vinylimidazole is 1-5 wt.% of the mass of the solvent.

[0075] Based on the electrospinning technology, the spinning solution is pushed out of a spinning needle with a certain inner diameter at a certain liquid discharge rate, a certain direct current voltage is applied to the needle and the receiver respectively, and the spinning is carried out under the action of the electric field, and the precursor micro-nano fiber membrane is prepared on the receiver.

[0076] During the preparation of the precursor micro-nano fiber membrane, the inner diameter of the spinning needle is 0.3-0.6 mm; the liquid discharge rate is 20-50 µL / min; the collection distance between the needle and the receiver is 14-22 cm; and the direct current voltage includes a direct current positive voltage of 16-24 kV and a negative voltage of -2-4 kV.

[0077] When the receiver is a flat plate, the precursor micro-nano fiber membrane prepared is a disordered distributed fiber membrane, and when the receiver is a roller, the precursor micro-nano fiber membrane prepared is a directional distributed fiber membrane.

[0078] The precursor micro-nano fiber membrane is dried at 65-75 DEG C for 1-3 h, and then the precursor micro-nano fiber membrane is placed in an oven, a mixed gas of nitrogen and oxygen in a certain proportion is introduced, heated to a temperature T1 at a certain heating rate v1 and kept for a time t1, then heated to a temperature T2 at a heating rate v2 and kept for a time t2, to obtain the cured precursor micro-nano fiber membrane.

[0079] The volume ratio of nitrogen and oxygen in the mixed gas is 2-7:3; the heating rate v1 is 5-8℃ / min, and v2 is 1-2℃ / min; the heating temperature T1 is 140-160℃, and T2 is 200-220℃; the holding time t1 is 0.5-2 h, and t2 is 1-3 h;

[0080] The precursor micro-nano fiber membrane after solidification is placed in a tube furnace, a mixed gas of nitrogen and ammonia is introduced in the ammoniation temperature section, nitrogen or argon is introduced in the remaining temperature section, the temperature is raised to T3 and the holding time is t3, the temperature is continuously raised to T4 at a certain rate v3 and the holding time is t4, the ceramic conversion of the fiber is completed, and the SiON micro-nano fiber membrane with electromagnetic wave-transparent and high-temperature heat-insulating properties is obtained.

[0081] The temperature in the ammoniation temperature section is raised from 200 to 900℃; the heating rate v3 is 1-2℃ / min; the heating temperature T3 is 800-900℃, and T4 is 1300-1500℃; the holding time t3 is 0.5-2 h, and t4 is 1-3 h. The volume ratio of nitrogen and ammonia introduced in the ammoniation temperature section is 0-1:1.

[0082] The SiON micro-nano fiber membrane relates to the technical field of electrospinning process combined with polymer-to-ceramic method, and the precursor, spinning aid and fiber morphology stabilizer used in the method need to be fully dissolved in the solvent to prepare the spinning solution. The addition of the spinning aid is conducive to improving the viscosity and conductivity of the spinning solution, and the fiber morphology stabilizer can be crosslinked with the long chain of the polymer and self-crosslinked, so that the micro-nano fiber remains stable in the morphology during the solidification and heat treatment stages. The spinning solution droplet is split into fibers by the positive high-voltage direct current power, and the precursor micro-nano fiber formed can be enriched on the receiver connected to the negative high-voltage direct current power. The solution propulsion speed and the positive and negative high voltage significantly affect the droplet splitting degree, the fiber morphology and the diameter, and the type of the receiver determines the arrangement mode of the fibers in the membrane, which is disordered or directional. The precursor micro-nano fiber membrane peeled off from the collector is dried to remove the volatile solvent, and then the long chain reaction crosslinking between the polymers is promoted through the solidification step to form a network structure. In the solidification step, the mixed gas of nitrogen and oxygen is introduced to facilitate the oxygen element doping of the micro-nano fiber membrane and improve the oxygen content. A lower heating rate (v2) is adopted between T1 and T2, so that the micro-nano fiber membrane can fully perform the crosslinking and solidification reaction in the rapid weight loss zone, and form a network structure to prepare for the ceramic transformation. Through the heat treatment step, the precursor micro-nano fiber membrane can complete the ceramic transformation to obtain the SiON micro-nano fiber membrane with electromagnetic wave transmission and high-temperature thermal insulation. In this step, the mixed atmosphere of nitrogen and ammonia is introduced to remove carbon and dope nitrogen by using the ammoniation reaction to realize the component regulation of the fiber; meanwhile, the heating section of 200-900 DEG C is the continuous endothermic decomposition stage of the solidified precursor, and a lower heating rate (v3) is adopted, which is conducive to fully performing the side chain group rupture and the reaction of ammonia carbon removal and nitrogen doping.

[0083] In an embodiment, a preparation method of a SiON micro-nano fiber membrane with electromagnetic wave transmission and high-temperature thermal insulation is provided, which specifically comprises the following steps:

[0084] Step 1. Preparing the spinning solution: mixing chloroform and N, N-dimethylformamide (DMF) according to a certain proportion as the solvent; adding a certain amount of polycarbosilane (PCS) or polysilazane (PSN) into the solvent as the SiON phase ceramic precursor; adding a certain amount of polyvinylpyrrolidone (PVP) into the solvent as the spinning aid; adding a certain amount of 1-vinylimidazole into the solvent as the fiber morphology stabilizer; and ensuring that the solution is fully mixed through magnetic stirring;

[0085] The mass ratio of chloroform to DMF in the solvent ranges from 3:1 to 6:1;

[0086] The addition amount of the ceramic precursor is 10-50 wt.% of the solvent;

[0087] The addition amount of the PVP is 2-8 wt.% of the solvent.

[0088] The 1-vinylimidazole is added in an amount of 1-5 wt.% of the solvent mass;

[0089] The magnetic stirring process is continuous stirring at a speed of 200-400 r / min for 8-48 hours.

[0090] Step 2. Preparation of precursor micro-nano fiber membrane by electrospinning: the spinning solution is pushed out of a spinning needle with a certain inner diameter at a certain liquid discharge rate, a certain direct current high voltage and low voltage are applied to the needle and the receiver respectively, and the preparation of the precursor micro-nano fiber and the collection of the fiber membrane are completed under the action of the electric field.

[0091] The inner diameter of the metal spinning needle is 0.3-0.6 mm;

[0092] The spinning liquid discharge rate is 20-50 µL / min;

[0093] The spinning direct current positive voltage is 16-24 kV, and the negative voltage is -2-4 kV;

[0094] The collection distance between the needle and the receiver is 14-22 cm;

[0095] When the receiver is a flat plate, a fiber membrane with disordered fiber distribution can be obtained, and when the receiver is a roller, a fiber membrane with oriented fiber distribution can be obtained.

[0096] Step 3. Curing of the precursor micro-nano fiber membrane: the precursor micro-nano fiber membrane obtained by electrospinning is placed in a hot air drying oven at 70℃ for 1-3 hours to fully evaporate the solvent; then the precursor micro-nano fiber membrane is placed in an oven, a mixed gas of nitrogen and oxygen in a certain proportion is introduced to promote the oxidation of the precursor and increase the oxygen content of the fiber, heated to temperature T1 at a certain heating rate v1 and kept for time t1, then heated to temperature T2 at rate v2 and kept for time t2, using the easy oxidation characteristics of the precursor to dope O element, and promoting the cross-linking and curing of the long chain of the polymer to form a network structure;

[0097] The volume ratio of nitrogen to oxygen in the mixed gas is 2-7:3;

[0098] The heating rate v1 of the curing is 5-8℃ / min, and v2 is 1-2℃ / min;

[0099] The heating temperature T1 of the curing is 140-160℃, and T2 is 200-220℃;

[0100] The holding time t1 of the curing is 0.5-2 h, and t2 is 1-3 h.

[0101] Step 4. Heat treatment of precursor micro-nano fiber membrane: then the solidified precursor micro-nano fiber membrane is placed in a tube furnace, a mixed gas of nitrogen and ammonia is introduced at the ammoniation temperature section for carbon removal and nitrogen doping, nitrogen or argon is introduced as inert protective gas at the remaining temperature sections, the temperature is increased to T3 and kept for a time t3, then the temperature is increased to the highest heat treatment temperature T4 at a rate v3 and kept for a time t4, the ceramic conversion of the fiber is completed, and a SiON micro-nano fiber membrane is obtained.

[0102] The volume ratio of nitrogen and ammonia in the mixed gas is 0-1:1;

[0103] The temperature of the ammoniation temperature section is increased from 200 to 900℃;

[0104] The heating rate v3 of the heat treatment is 1-2℃ / min;

[0105] The heating temperature T3 of the heat treatment is 800-900℃, and T4 is 1300-1500℃;

[0106] The holding time t3 of the heat treatment is 0.5-2 h, and t4 is 1-3 h.

[0107] The polymer precursor includes but is not limited to PCS, PSN and a mixture thereof.

[0108] The spinning aid includes but is not limited to PVP, polycaprolactone, polystyrene and other common electrospinning polymers.

[0109] During the solidification process, for the PCS precursor micro-nano fiber membrane, the ratio of nitrogen and oxygen in the introduced mixed gas should be greater than 2:3; for the PSN precursor micro-nano fiber membrane, the ratio of nitrogen and oxygen in the introduced mixed gas should be less than 7:3.

[0110] During the heat treatment process, for the PCS precursor micro-nano fiber membrane, the ammoniation temperature section should include but is not limited to 600-800℃; for the PSN precursor micro-nano fiber membrane, the ammoniation temperature section should include but is not limited to 400-800℃.

[0111] During the heat treatment process, for the PCS precursor micro-nano fiber membrane, the ratio of nitrogen and ammonia in the introduced mixed gas should be greater than 1:3; for the PSN precursor micro-nano fiber membrane, the ratio of nitrogen and ammonia in the introduced mixed gas should be less than 1:1.

[0112] During the heat treatment process, the flow rates of the atmospheres introduced at the ammoniation temperature section and the other temperature sections should be kept consistent, and the flow rate range is 80-120 mL / min.

[0113] The third aspect of the present application provides an application of the SiON micro-nano fiber membrane in wave-transparent heat insulation.

[0114] It should be noted that the experimental methods used in the present application are conventional methods unless otherwise specified; the reagents and materials used are commercially available unless otherwise specified.

[0115] Example 1

[0116] Step 1. Preparation of spinning solution: chloroform and DMF are mixed in a mass ratio of 4:1 as solvents; 10 wt.% of PCS is added to the solvents as a SiON phase ceramic precursor; 4 wt.% of PVP is added to the solvents as a spinning aid; 1 wt.% of 1-vinylimidazole is added to the solvents as a fiber morphology stabilizer; the solution is stirred at a speed of 400 r / min for 48 hours to ensure sufficient mixing.

[0117] Step 2. Preparation of PCS nanofibers by electrospinning: the stirred spinning solution is filled into a syringe, a metal needle with an inner diameter of 0.33 mm is connected to the syringe, and the syringe is placed on a pusher, the pusher speed is set to adjust the liquid discharge rate of the needle to 50 µL / min; a direct current positive high voltage of 18 kV is applied to the spinning needle, so that the liquid droplets split to form nanofibers, which are collected on a receiver connected to a direct current negative voltage of -2 kV after moving in the electric field, the collection distance between the needle and the receiver is 16 cm.

[0118] Step 3. Solidification of PCS nanofibers: the PCS nanofibers obtained by electrospinning are placed in a drying oven at 70℃ for 1 hour to volatilize most of the solvent; then the dried PCS nanofibers are placed in an oven, a mixed gas of nitrogen and oxygen with a volume ratio of 2:3 is introduced, the temperature is raised to 140℃ at a rate of 5℃ / min and kept for 0.5 h, then heated to 210℃ and kept for 2 hours, to promote polymer chain crosslinking and oxygen element doping, forming a network structure.

[0119] Step 4. Heat treatment of PCS nanofibers: the solidified PCS nanofibers are placed in a tube furnace, heated to 900℃ and kept for 0.5 h, then heated to 1300℃ at a rate of 2℃ / min and kept for 2 hours. A mixed gas of nitrogen and ammonia with a volume ratio of 1:3 is introduced at an ammonia temperature of 250℃ to 850℃ at a flow rate of 80 mL / h, and nitrogen gas is introduced at the same flow rate at the remaining temperature. Finally, the ceramic transformation of the fiber is completed, and SiON nanofibers are obtained.

[0120] The SiON nanofiber prepared in this embodiment is an oriented fiber with a diameter distribution of 100-300 nm, and the fiber is an amorphous SiON phase with a chemical formula of SiO 0.998 C 0.051 N 0.441 In terms of wave transmission, the real part of the dielectric constant, the imaginary part of the dielectric constant and the dielectric loss factor of the SiON nanofiber film in the frequency band of 8.2-12.4 GHz are 2.41-2.54, 0.00055-0.019 and 0.00022-0.0074, respectively, and the electromagnetic wave transmission performance is better; in terms of heat insulation, the thermal conductivity of the SiON nanofiber film is 0.021 W / (m·K), and the average temperature of the back surface of the fiber film with a thickness of 1 mm is 275.74℃, 288.55℃ and 305.89℃, respectively, when the front surface is heated by a spray gun with a temperature of about 1300℃ for 10 min, 20 min and 30 min.

[0121] Example 2

[0122] Step 1. Preparation of spinning solution: chloroform and DMF are mixed in a mass ratio of 6:1 as the solvent; 10 wt.% of PCS is added to the solvent as a SiON phase ceramic precursor; 2 wt.% of PVP is added to the solvent as a spinning aid; 2.5 wt.% of 1-vinylimidazole is added to the solvent as a fiber morphology stabilizer; the solution is continuously stirred at a stirring speed of 300 r / min for 48 hours to ensure sufficient mixing.

[0123] Step 2. Preparation of PCS nanofiber by electrospinning: the stirred spinning solution is filled into a syringe, a metal needle with an inner diameter of 0.33 mm is connected to the syringe, and the syringe is placed on a pusher, the liquid discharge rate of the needle is adjusted to 40 µL / min by setting the pusher speed; a direct current positive high voltage of 20 kV is applied to the spinning needle, so that the liquid droplets split to form nanofibers, which are collected on a receiver connected to a direct current negative voltage of-2 kV after moving in the electric field, and the collection distance between the needle and the receiver is 18 cm.

[0124] Step 3. Solidification of PCS nanofiber: the PCS nanofiber obtained by electrospinning is placed in a drying oven at 70℃ for 1 hour to volatilize most of the solvent; then the dried PCS nanofiber is placed in an oven, a mixed gas of nitrogen and oxygen with a volume ratio of 2:3 is introduced, and the temperature is raised to 160℃ at a rate of 5℃ / min and kept for 0.5 h, then heated to 210℃ and kept for 1.5 hours, to promote polymer chain crosslinking and oxygen element doping, forming a network structure.

[0125] Step 4. The cured PCS nanofibers were placed in a tube furnace and heated to 850°C for 0.5 h. The temperature was then increased to 1300°C at a rate of 1°C / min and held for 3 hours. A nitrogen-ammonia mixture was introduced at a volume ratio of 0:1 at a flow rate of 100 mL / h during the ammonia treatment period (550°C to 850°C). Nitrogen was introduced at a constant flow rate during the remaining temperature periods. This completed the ceramicization of the fibers, yielding SiON nanofibers.

[0126] Compared with Example 1, this example mainly changes the concentration, temperature range and gas flow rate of the ammonia gas introduced during the heat treatment process. The SiON nanofibers prepared in this example are oriented fibers with a diameter distribution of 100-300 nm. The fibers contain an amorphous SiON phase, and its chemical formula is SiO 0.897 C 0.152 N 0.293 In terms of wave transmission, the real part of the dielectric constant, the imaginary part of the dielectric constant, and the dielectric loss factor of the SiON nanofiber membrane in the frequency band of 8.2-12.4 GHz are 2.69-2.72, 0.007-0.026, and 0.0026-0.0095, respectively, indicating good electromagnetic wave transmittance. In terms of thermal insulation, the thermal conductivity of the SiON nanofiber membrane is 0.016 W / (m·K). When a 1 mm thick fiber membrane is heated with a spray gun at a temperature of approximately 1300°C for 10 min, 20 min, and 30 min, the average back surface temperature is 258.32°C, 272.28°C, and 283.18°C, respectively.

[0127] Example 3

[0128] Step 1. Prepare the spinning solution: Mix chloroform and DMF in a mass ratio of 3:1 as the solvent; add 16 wt.% PSN as a SiON phase ceramic precursor to the solvent; add 4.7 wt.% PVP as a spinning aid to the solvent; add 6 wt.% 1-vinylimidazole to the solvent as a fiber morphology stabilizer; and ensure that the solution is fully mixed by continuous stirring at 500 r / min for 12 hours.

[0129] Step 2. Preparation of PSN micro-nanofibers by electrospinning: The stirred spinning solution was filled into a syringe, connected to the syringe with a metal needle with an inner diameter of 0.6 mm, and placed on a propeller. The liquid discharge rate of the needle was adjusted to 25 µL / min by setting the propeller's propulsion speed. A 24 kV DC positive high voltage was applied to the spinning needle to split the liquid droplets from the needle into micro-nanofibers. After moving in the electric field, the droplets could be collected on a receiver connected to a DC negative voltage of -3 kV. The collection distance between the needle and the receiver was 15 cm.

[0130] Step 3. Solidification of the PSN micro-nanofiber: The electrostatically obtained PSN micro-nanofiber was placed in a drying oven at 70℃ for 3 hours to allow most of the solvent to evaporate; then the dried PSN nanofiber was placed in an oven, a mixed gas of nitrogen and oxygen was passed in at a volume ratio of 7:3, and the temperature was raised to 160℃ at a rate of 10℃ / min and kept for 2 hours, and then heated to 200℃ and kept for 1 hour to promote crosslinking and solidification of the polymer chain, forming a network structure.

[0131] Step 4. Heat treatment of the PSN micro-nanofiber: The solidified PSN micro-nanofiber was placed in a tube furnace, and a mixed gas of nitrogen and ammonia was passed in, and the temperature was raised to 1300℃ at a rate of 5℃ / min and kept for 2 hours. A mixed gas of nitrogen and ammonia was passed in at a volume ratio of 1:1 at a flow rate of 120 mL / h during the temperature rise from 400℃ to 900℃, which is the ammoniation temperature, and nitrogen was passed in at the same flow rate during the rest of the temperature rise. Finally, the ceramic conversion of the fiber was completed, and SiON micro-nanofiber was obtained.

[0132] Compared with Example 1, the type of precursor used in this example was changed. The SiON micro-nanofiber prepared in this example is a directional fiber with a diameter distribution of 300-1200 nm, and the fiber is amorphous SiON phase, with a chemical formula of SiO 0.905 C 0.085 N 0.361 In terms of wave transmission, the real part of the dielectric constant, the imaginary part of the dielectric constant and the dielectric loss factor of the SiON micro-nanofiber film in the frequency band of 8.2-12.4 GHz are 1.08-1.15, 0.0012-0.0078 and 0.0001-0.0068, respectively, and the electromagnetic wave transmission is good; in terms of heat insulation, the thermal conductivity of the SiON nanofiber film is 0.055 W / (m·K), and the average temperature of the back surface of the fiber film with a thickness of 1 mm is 305.28℃, 319.46℃ and 323.40℃ respectively after 10 min, 20 min and 30 min of heating by a spray gun with a temperature of about 1300℃; in terms of high temperature stability, the weight gain rate of the SiON nanofiber film in an air environment at 1500℃ is 6.92%, and the weight gain rate in a nitrogen environment at 1500℃ is 0.94%, and the stability is good.

[0133] Example 4

[0134] Step 1. Preparation of the spinning solution: chloroform and DMF were mixed in a mass ratio of 3:1 as the solvent; 16 wt.% PSN was added to the solvent as the SiON phase ceramic precursor; 4.7 wt.% PVP was added to the solvent as the spinning aid; 6 wt.% 1-vinylimidazole was added to the solvent as the fiber morphology stabilizer; the solution was stirred at a speed of 500 r / min for 12 hours to ensure sufficient mixing.

[0135] Step 2. Preparation of PSN micro-nano fibers by electrospinning: the stirred spinning solution was filled into a syringe, a metal needle with an inner diameter of 0.6 mm was connected to the syringe, and the syringe was placed on a pusher. The pusher was set to adjust the liquid discharge rate of the needle to 25 µL / min; a direct current positive high voltage of 24 kV was applied to the spinning needle, so that the liquid droplets split to form micro-nano fibers, which were collected on a receiver connected to a direct current negative voltage of -3 kV after moving in the electric field. The collection distance between the needle and the receiver was 15 cm.

[0136] Step 3. Solidification of PSN micro-nano fibers: the PSN micro-nano fibers obtained by electrospinning were placed in a drying oven at 70℃ for 3 hours to volatilize most of the solvent; then the dried PSN nano fibers were placed in an oven, a mixed gas of nitrogen and oxygen was introduced at a volume ratio of 7:3, and the temperature was raised to 160℃ at a rate of 10℃ / min and kept for 2 hours, then heated to 200℃ and kept for 1 hour to promote crosslinking and solidification of the polymer chains, forming a network structure.

[0137] Step 4. Heat treatment of PSN micro-nano fibers: the solidified PSN micro-nano fibers were placed in a tube furnace, and a mixed gas of nitrogen and ammonia was introduced, with a temperature rising rate of 5℃ / min to 1500℃ and then kept for 2 hours. During the temperature rising from 400℃ to 900℃, a mixed gas of nitrogen and ammonia was introduced at a volume ratio of 1:1, with a gas flow rate of 120 mL / h. During the rest of the temperature rising, nitrogen gas was introduced at the same flow rate. Finally, the ceramicization of the fibers was completed, and SiON micro-nano fibers were obtained.

[0138] Compared with Example 1, the highest temperature of the heat treatment was changed in this example. The SiON micro-nano fibers prepared in this example were oriented fibers with a diameter distribution of 300-1200 nm, and the fiber was amorphous SiON phase, with a chemical formula of SiO 0.783 C 0.119 N 0.451In terms of wave transmission, the real part of dielectric constant, the imaginary part of dielectric constant and the dielectric loss factor of the SiON micro-nano fiber membrane in the frequency band of 8.2-12.4 GHz are 1.27-1.31, 0.0026-0.013 and 0.0020-0.0099 respectively, and the electromagnetic wave transmission is better; in terms of heat insulation, the thermal conductivity of the SiON nano fiber membrane is 0.075 W / (m·K), and the average temperature of the back surface of the fiber membrane with a thickness of 1 mm is 332.53℃, 344.84℃ and 353.62℃ respectively after being heated by a spray gun with a temperature of about 1300℃ for 10 min, 20 min and 30 min.

[0139] Counterexample 1

[0140] Compared with Example 1, this example cancels the addition of 1-vinylimidazole, a fiber morphology stabilizer in the solvent. In this counterexample, the PCS micro-nano fibers reach the melting point of PCS in the curing stage, and a small amount of PCS melting occurs in the crosslinking process as a solid precursor, resulting in some adhesion between the micro-nano fibers, providing more solid-phase heat transfer sites, which is not conducive to reducing the thermal conductivity of the SiON micro-nano fiber membrane.

[0141] Counterexample 2

[0142] Compared with Example 3, this example cancels the addition of 1-vinylimidazole, a fiber morphology stabilizer in the solvent. In this counterexample, the PSN micro-nano fibers reach the melting point of PSN in the curing stage, and a large amount of PSN melting occurs in the crosslinking process as a high-viscosity liquid precursor, resulting in complete adhesion between the micro-nano fibers to form a sheet, and more solid-phase heat transfer sites are provided after heat treatment, making it difficult to maintain the morphology of the SiON micro-nano fibers.

[0143] Counterexample 3

[0144] Compared with Example 1, this example changes the mixed gas atmosphere of nitrogen and oxygen in the curing step to air atmosphere. The content of nitrogen and oxygen in the air atmosphere is about 4:1, which is higher than the ratio of the mixed gas atmosphere in the example. This results in a weaker oxidation degree of the fiber membrane in the air atmosphere than in the mixed gas atmosphere, and a weaker oxygen doping effect. The O element content in the SiON micro-nano fiber membrane obtained after heat treatment after air curing is less than 20 at.%, which is significantly lower than that of Example 1 (40.08 at.%). Similar phenomena are observed for the PSN precursor micro-nano fiber membrane.

[0145] Counterexample 4

[0146] Compared with Example 2, this example changes the ammoniation temperature section to a temperature section of 250℃ to 550℃ during heat treatment. The micro-nano fibers in this example are Si℃N phase, and the chemical formula is SiO 0.518 C 1.129 N0.466 , which is characterized by high content of both C and N elements. This is because the temperature range does not reach the temperature at which ammonia and the precursor generate a vigorous reaction, and is insufficient to provide sufficient driving force for the ammoniation reaction. Since the bond energy of Si-C bond (318 kJ / mol) is slightly higher than that of Si-H bond (315 kJ / mol), the Si-H bond in the precursor is more likely to break, and reacts with ammonia to form Si-NH2 bond, completing the doping of N element while retaining the C element in the system. In terms of wave transmission, the real part of the dielectric constant, the imaginary part of the dielectric constant and the dielectric loss factor of the SiON nanofiber membrane in the frequency range of 8.2-12.4 GHz are 3.34-3.39, 0.76-0.98 and 0.22-0.29, respectively, and the loss of electromagnetic waves is strong, but the wave transmission performance is not effective.

[0147] Counterexample 5

[0148] Compared with Example 2, the ammoniation temperature range is changed to a holding period at 1300℃ in the heat treatment process in this example. The micro-nanofiber of this example is characterized by low content of both C and N elements, and its chemical formula is SiO 1.222 C 0.136 N 0.007 This is because the decomposition reaction of ammonia is more violent at this temperature range, and a large amount of ammonia is decomposed into nitrogen and hydrogen before contacting the fiber, so the concentration of ammonia actually participating in the ammoniation reaction is low, which weakens the carbon removal and nitrogen doping effect of ammonia. In terms of wave transmission, the real part of the dielectric constant, the imaginary part of the dielectric constant and the dielectric loss factor of the SiON nanofiber membrane in the frequency range of 8.2-12.4 GHz are 3.12-3.30, 1.10-1.61 and 0.34-0.51, respectively, and the loss of electromagnetic waves is strong, but the wave transmission performance is not effective.

[0149] Counterexample 6

[0150] Compared with Example 3, the precursor fiber is not treated with ammonia in the heat treatment process in this example. The micro-nanofiber prepared in this example is amorphous Si@N phase, and its chemical formula is SiO 0.777 C 0.926 N 0.364 In terms of wave transmission, the real part of the dielectric constant, the imaginary part of the dielectric constant and the dielectric loss factor of the SiON nanofiber membrane in the frequency range of 8.2-12.4 GHz are 1.32-1.39, 0.0063-0.073 and 0.0046-0.054, respectively. Since no ammoniation treatment is performed, the fiber has a high carbon content (more than 20%), and thus the loss of electromagnetic waves is large and the wave transmission performance is poor.

[0151] In order to illustrate the related performance of the SiON micro-nanofiber membrane provided by the present application, the following describes the same with reference to the accompanying drawings.

[0152] Figure 1 are (a) macroscopic photo and (b-c) microscopic morphology of SiON nanofiber membrane in Example 1 of the present application;

[0153] From the macroscopic photo of Example 1, the SiON nanofiber membrane appears to be grayish white and has a smooth surface. From the scanning photo, it can be seen that the fibers in the membrane have a certain orientation arrangement and nanoscale diameter distribution (about 100-300 nm), and the fibers have good continuity, and the fibers overlap to form a porous structure.

[0154] Figure 2 are (a) X-ray diffraction pattern and (b) transmission electron microscope photo of SiON nanofiber membrane in Example 1 of the present application;

[0155] The XRD spectrum of Example 1 shows that the SiON nanofiber membrane is in an amorphous state, and no obvious crystal diffraction peak is observed. The low and broad peak between 20° and 30° represents the existence of Si-O-Si amorphous structure. The high-resolution transmission photo of Example 1 does not exhibit nanocrystalline crystal diffraction stripes, and its selected area electron diffraction also shows a diffuse central spot, further confirming that the SiON nanofiber membrane in Example 1 is in an amorphous state, which is consistent with the analysis result of XRD.

[0156] Table 1 is the element content and chemical formula of the SiON nanofiber membrane in Example 1 of the present application;

[0157] Table 1

[0158]

[0159] Figure 3 are (a) real part of dielectric constant, (b) imaginary part of dielectric constant and (c) dielectric loss factor of SiON nanofiber membrane in Example 1 of the present application; from Figure 3 It can be seen that the real part of the dielectric constant of the material represents its ability to polarize and store energy under the action of electromagnetic waves, and the imaginary part of the dielectric constant represents its ability to attenuate electromagnetic waves. From Figure 3 It can be seen that the real and imaginary part curves of the dielectric constant of the SiON nanofiber membrane in Example 1 are relatively smooth in the X-band (8.2-12.4 GHz frequency band), and the numerical values are at a relatively low level, which are 2.41-2.54 and 0.00055-0.019, respectively. The dielectric loss factor tan delta e is the ratio of the real and imaginary parts of the dielectric constant, which indicates the ability of the material to lose electromagnetic waves. The tan delta eThe values are 0.00022-0.0074, all lower than 0.01, showing that the electromagnetic wave transmission performance is better. The amorphous SiON component and the high porosity structure are both beneficial to the low dielectric loss characteristics.

[0160] Figure 4 is the thermal imaging characterization result of the SiON nanofiber membrane in Example 1 of the present application: (a) infrared photo of the front side of the sample; (b) infrared photo of the back side of the sample after heating for 10 min; (c) infrared photo of the back side of the sample after heating for 20 min; (d) infrared photo of the back side of the sample after heating for 30 min; from Figure 4 It can be seen that, facing the butane flame spray gun with a flame temperature of about 1300℃, the SiON nanofiber membrane with a thickness of about 1mm can effectively block the flame and play a role in temperature reduction and heat insulation. The average temperature of the SiON nanofiber membrane facing the flame in Example 1 is 1015.81℃. After heating for 10 minutes, the average temperature of the back side of the fiber membrane is 275.74℃; after heating for 20 minutes, the average temperature of the back side of the fiber membrane slightly rises to 288.55℃; after heating for 30 minutes, the average temperature of the back side of the fiber membrane reaches 305.89℃. It can be seen that the heat insulation effect of this SiON nanofiber membrane is good and relatively stable. The amorphous SiON phase has a relatively low intrinsic thermal conductivity, and the porous structure formed by the lapping of nanofibers can effectively block the heat transfer, which is beneficial to enhancing the heat insulation effect.

[0161] Figure 5 is (a) macroscopic photo and (b-c) microscopic morphology of the SiON nanofiber membrane in Example 2 of the present application; from Figure 5 It can be seen from the macroscopic photo of Example 2 that the SiON nanofiber membrane presents white color and has flexible wrinkles on the surface. It can be seen from the scanning photo that the fibers in the membrane have a certain orientation arrangement and a nanoscale diameter distribution (about 100-300nm), the fiber continuity is good, and the porous structure is formed by the lapping of fibers.

[0162] Figure 6 is (a) X-ray diffraction pattern and (b) transmission electron microscope photo of the SiON nanofiber membrane in Example 2 of the present application; from Figure 6 It can be seen that the XRD spectrum of Example 2 shows that the SiON nanofiber membrane is in an amorphous state, and no obvious crystal diffraction peak is observed. The large drum-shaped wide peak between 20° and 30° represents the existence of a large amount of Si-O-Si amorphous structure. The high-resolution transmission photo of Example 2 does not exhibit nanocrystal diffraction stripes, and the selected area electron diffraction also shows a diffuse central spot, further confirming that the SiON nanofiber membrane in Example 2 is in an amorphous state, which is consistent with the analysis result of XRD.

[0163] Table 2 is the element content and chemical formula of the SiON nanofiber membrane in Example 2 of the present application;

[0164] Table 2

[0165]

[0166] Figure 7 are the (a) real part of dielectric constant, (b) imaginary part of dielectric constant and (c) dielectric loss of the SiON nanofiber membrane in Example 2 of the present application; from Figure 7 It can be seen that the real part of the dielectric constant of the material represents its ability to polarize and store energy under the action of electromagnetic waves, while the imaginary part of the dielectric constant represents its ability to attenuate electromagnetic waves. From Figure 7 It can be seen that the real part and imaginary part of the dielectric constant of the SiON nanofiber membrane in Example 2 are relatively smooth in the X-band (8.2-12.4 GHz frequency band), and the values are at a relatively low level, which are 2.69-2.72 and 0.007-0.026, respectively. The dielectric loss factor tan delta e is the ratio of the real part and the imaginary part of the dielectric constant, which indicates the ability of the material to lose electromagnetic waves. The tan delta e of the SiON nanofiber membrane in Example 2 is 0.0026-0.0095, which is lower than 0.01, indicating that it has good electromagnetic wave transmission performance. The amorphous SiON component and the high porosity structure are beneficial to make it exhibit low dielectric and low loss characteristics.

[0167] Figure 8 are the thermal imaging characterization results of the SiON nanofiber membrane in Example 2 of the present application: (a) infrared photo of the front surface of the sample; (b) infrared photo of the back surface of the sample after heating for 10 min; (c) infrared photo of the back surface of the sample after heating for 20 min; (d) infrared photo of the back surface of the sample after heating for 30 min; from Figure 8 It can be seen that the SiON nanofiber membrane with a thickness of about 1 mm can effectively block the flame and play a role in reducing temperature and heat insulation when facing the butane flame spray gun with a flame temperature of about 1300℃. The average temperature of the SiON nanofiber membrane facing the flame in Example 2 is 953.86℃. After heating for 10 minutes, the average temperature of the back surface of the fiber membrane is 258.32℃; after heating for 20 minutes, the average temperature of the back surface of the fiber membrane slightly rises to 272.28℃; after heating for 30 minutes, the average temperature of the back surface of the fiber membrane reaches 283.18℃. It can be seen that the heat insulation effect of this SiON nanofiber membrane is good and stable. The amorphous SiON phase has a relatively low intrinsic thermal conductivity, and the porous structure formed by the lapping of nanofibers can effectively block the heat transfer, which is beneficial to enhance the heat insulation effect.

[0168] Figure 9is the thermal stability result of SiON nanofiber membrane in Example 2 of the present application: (a) thermogravimetric curve in air atmosphere; (b) XRD spectrum of the fiber membrane after butane flame heating for 30 min. From Figure 9 It can be seen that the curve of SiON nanofiber membrane in air atmosphere can characterize the thermal stability of the fiber membrane in high-temperature oxidation environment. As shown in Figure 9 The fiber membrane first undergoes endothermic reaction when the temperature is raised from room temperature to 1300℃, and the mass slightly decreases, and then starts to release heat, and the mass increases. The sample mass is minimum at 664.4℃, and the weight loss rate is 1.89%, which may be caused by evaporation of water adsorbed by the fiber membrane and oxidation loss of a small amount of C element remaining therein; when the temperature is above 664.4℃, the mass of the fiber membrane gradually increases, and the mass is maximum at 1300℃, and the weight gain rate is 5.54%, which may be caused by slight oxidation of the fiber membrane at high temperature. From the XRD results, it can be seen that after butane torch high-temperature heating for 30 min, the fiber membrane is still in amorphous state, and no crystallization phenomenon is found, which proves that the composition stability of the fiber membrane is good under high-temperature short-time condition. In summary, the SiON nanofiber membrane in Example 2 has good thermal stability.

[0169] Figure 10 is (a) macroscopic photo and (b-c) microscopic morphology of SiON micro-nanofiber membrane in Example 3 of the present application; from Figure 10 It can be seen from the macroscopic photo of Example 3 that the SiON micro-nanofiber membrane is white and has smooth surface. From the scanning photo, it can be seen that the fibers in the membrane have certain orientation arrangement and micro-nano level diameter distribution (about 300-1200 nm), the fibers have good continuity, and the fibers form a porous structure by lapping.

[0170] Figure 11 is (a) X-ray diffraction pattern and (b) transmission electron microscope photo of SiON micro-nanofiber membrane in Example 3 of the present application; from Figure 11 It can be seen that the XRD spectrum of Example 3 shows that the SiON micro-nanofiber membrane is in amorphous state, and no obvious crystal diffraction peak is found. The high-resolution transmission photo of Example 3 does not exhibit nanocrystal crystal diffraction stripes, and the selected area electron diffraction also shows diffuse central spots, which further confirms that the SiON micro-nanofiber membrane in Example 3 is in amorphous state, which is consistent with the analysis result of XRD.

[0171] Table 3 is the element content and chemical formula of SiON micro-nanofiber membrane in Example 3 of the present application;

[0172] Table 3

[0173]

[0174] Figure 12are the (a) real part of dielectric constant, (b) imaginary part of dielectric constant and (c) dielectric loss of the SiON micro-nano fiber membrane in Example 3 of the present application, from Figure 12 It can be seen that the real part of the dielectric constant of the material represents its ability to polarize and store energy under the action of electromagnetic waves, while the imaginary part of the dielectric constant represents its ability to attenuate electromagnetic waves. From Figure 12 It can be seen that the real part and imaginary part of the dielectric constant of the SiON micro-nano fiber membrane in Example 3 are relatively smooth in the X-band (8.2-12.4 GHz frequency band), and the values are relatively low, which are 1.08-1.15 and 0.0012-0.0078 respectively. The dielectric loss factor tan delta e is the ratio of the real part and the imaginary part of the dielectric constant, which indicates the ability of the material to lose electromagnetic waves. The tan delta e of the SiON micro-nano fiber membrane in Example 3 is 0.0001-0.0068, which is lower than 0.01, indicating that it has good electromagnetic wave transmission performance. The amorphous SiON component and the high porosity structure are beneficial to make it exhibit low dielectric and low loss characteristics.

[0175] Figure 13 are the thermal imaging characterization results of the SiON micro-nano fiber membrane in Example 3 of the present application: (a) infrared photo of the front surface of the sample; (b) infrared photo of the back surface of the sample after heating for 10 min; (c) infrared photo of the back surface of the sample after heating for 20 min; (d) infrared photo of the back surface of the sample after heating for 30 min, from Figure 13 It can be seen that the SiON micro-nano fiber membrane with a thickness of about 1 mm can effectively block the flame and play a role in reducing temperature and heat insulation when facing the butane flame spray gun with a flame temperature of about 1300℃. The average temperature of the SiON micro-nano fiber membrane facing the flame in Example 3 is 903.53℃. After heating for 10 minutes, the average temperature of the back surface of the fiber membrane is 305.28℃; after heating for 20 minutes, the average temperature of the back surface of the fiber membrane slightly rises to 319.46℃; after heating for 30 minutes, the average temperature of the back surface of the fiber membrane reaches 323.40℃. It can be seen that the heat insulation effect of this SiON micro-nano fiber membrane is good and stable. The amorphous SiON phase has a relatively low intrinsic thermal conductivity, and the porous structure formed by the lapping of micro-nano fibers can effectively block the heat transfer, which is beneficial to enhance the heat insulation effect.

[0176] Figure 14 are the thermal stability of the SiON micro-nano fiber membrane in Example 3 of the present application: (a) thermogravimetric curve in air atmosphere and nitrogen atmosphere; (b) XRD spectrum of the fiber membrane after heating by butane flame for 30 min. From Figure 14 It can be seen that the TG curves of the SiON micro-nano fiber membrane in air atmosphere and nitrogen atmosphere can exhibit its thermal stability in high temperature oxidation environment. For example,Figure 14 As shown in the table, the weight gain rate of the SiON micro-nano fiber membrane in Example 3 in the air environment at 1500℃ is 6.92%, and the weight gain rate in the nitrogen environment at 1500℃ is 0.94%, both of which show good thermal stability. For the fiber membrane heated for 30 min under the 1300℃ butane spray gun, its XRD pattern shows that it is still amorphous, further verifying the high-temperature stability of the components.

[0177] Figure 15 Fig. 4 is a macroscopic photo and micro-morphology of the SiON micro-nano fiber membrane in Example 4 of the present application; from Figure 15 As can be seen from the macroscopic photo of Example 4, the SiON micro-nano fiber membrane is white and has a smooth surface. As can be seen from the scanning photo, the fibers in the membrane have a certain orientation arrangement and a micro-nano level diameter distribution (about 300-1200 nm), the fibers have good continuity, and the fibers form a porous structure by lapping.

[0178] Figure 16 Fig. 5 is an X-ray diffraction pattern and a transmission electron microscope photo of the SiON micro-nano fiber membrane in Example 4 of the present application; from Figure 16 As can be seen from the XRD spectrum of Example 4, the SiON nano fiber membrane is basically in an amorphous state, but there are a small number of small peaks. The large drum-shaped peak between 20° and 30° represents the existence of a large amount of Si-O-Si amorphous structure. The high-resolution transmission photo of Example 4 does not find the crystal diffraction stripes of nanocrystals, and the selected area electron diffraction is also a diffuse central spot, which further confirms that the SiON nano fiber membrane in Example 4 is basically in an amorphous state, which is consistent with the analysis result of the XRD.

[0179] Table 4 is the element content and chemical formula of the SiON micro-nano fiber membrane in Example 4 of the present application;

[0180] Table 4

[0181]

[0182] Figure 17 Fig. 6 is the real part of the dielectric constant, the imaginary part of the dielectric constant and the dielectric loss of the SiON micro-nano fiber membrane in Example 4 of the present application; from Figure 17 As can be seen, the real part of the dielectric constant of the material represents its ability to polarize and store energy under the action of electromagnetic waves, and the imaginary part of the dielectric constant represents its attenuation ability to electromagnetic waves. From Figure 17 As can be seen, the real part and the imaginary part of the dielectric constant of the SiON micro-nano fiber membrane in Example 4 in the X wave band (8.2-12.4 GHz frequency band) are relatively smooth, and the values are both at a low level, which are 1.27-1.31 and 0.0026-0.013, respectively. The dielectric loss factor tandelta e The tan is the ratio of the real part and the imaginary part of the dielectric constant, which indicates the material's ability to lose electromagnetic waves. The tan of the SiON micro-nano fiber membrane in Example 4 is delta e The value is 0.0020~0.0099, which is lower than 0.01, indicating that its electromagnetic wave transmission performance is better. The amorphous SiON component and the high porosity structure are beneficial to make it exhibit low dielectric and low loss characteristics.

[0183] Figure 18 is the thermal imaging characterization result of the SiON micro-nano fiber membrane in Example 4 of the present application: (a) infrared photo of the front surface of the sample; (b) infrared photo of the back surface of the sample after heating for 10 min; (c) infrared photo of the back surface of the sample after heating for 20 min; (d) infrared photo of the back surface of the sample after heating for 30 min; from Figure 18 It can be seen that the SiON micro-nano fiber membrane with a thickness of about 1 mm can effectively block the flame and play a role in temperature reduction and heat insulation when facing the butane flame spray gun with a flame temperature of about 1300℃. The average temperature of the SiON micro-nano fiber membrane facing the flame in Example 4 is 947.47℃. After heating for 10 minutes, the average temperature of the back surface of the fiber membrane is 332.53℃; after heating for 20 minutes, the average temperature of the back surface of the fiber membrane slightly rises to 344.84℃; after heating for 30 minutes, the average temperature of the back surface of the fiber membrane reaches 353.62℃. It can be seen that the heat insulation effect of this SiON micro-nano fiber membrane is good and relatively stable. The amorphous SiON phase has a relatively low intrinsic thermal conductivity, and the porous structure formed by the lapping of micro-nano fibers can effectively block the heat transfer, which is beneficial to enhance the heat insulation effect.

[0184] Figure 19 is the micro-morphology of the SiON micro-nano fiber membrane in the counterexample 1 of the present application; from Figure 19 It can be seen from the scanning photo of the counterexample 1 that the SiON nanofiber membrane converted from the PCS spinning solution without adding 1-vinylimidazole has fiber adhesion, which is manifested in the adhesion and adhesion at the fiber cross-lapping place, and the fiber separation is weak. This is because the highest temperature in the solidification stage is close to the melting point of PCS (about 210~230℃), and a small amount of PCS melting occurs at the fiber intersection, resulting in fiber adhesion, forming more solid heat transfer sites and being not conducive to the heat insulation performance of the fiber membrane. In Example 1, 1-vinylimidazole is added as a fiber morphology stabilizer in the spinning solution, which can complete self-crosslinking and crosslinking with PCS at a lower solidification temperature, thereby forming a network-like bonding structure to a certain extent, inhibiting the melting and adhesion of PCS, and realizing the preparation of nanofibers with strong separation.

[0185] Figure 20 is the micro-morphology of the SiON micro-nano fiber membrane in the counterexample 2 of the present application; fromFigure 20 It can be seen from the scanning electron micrograph of Example 2 that the SiON micro-nano fiber film prepared from the PSN spinning solution without 1-vinylimidazole has a serious fiber adhesion problem, and the fibers are completely adhered to each other to form a film and cannot be separated, and no fiber-based porous structure is formed. This is because the PSN precursor has a high intrinsic viscosity in a liquid state, and after the electrospinning process, a separated fiber morphology is achieved. However, during the curing stage, the highest curing temperature is higher than the melting point of the PSN precursor (about 130-160°C), and the PSN has melted before reaching the curing temperature, resulting in the loss of fiber morphology and the occurrence of film formation. In Example 3, 1-vinylimidazole is added to the spinning solution as a fiber morphology stabilizer, which can complete self-crosslinking at a temperature lower than the melting point of PSN, form a network structure on the surface and inside the fiber to maintain the fiber morphology, and crosslink with PSN to stabilize the structure and state of PSN, inhibit the melting and adhesion of PSN, and achieve the preparation of strong separated nanofibers.

[0186] Table 5 is the element content and chemical formula of the SiON micro-nano fiber film in Example 3 of the present application;

[0187] Table 5

[0188]

[0189] Table 6 is the element content and chemical formula of the SiON micro-nano fiber film in Example 4 of the present application;

[0190] Table 6

[0191]

[0192] Figure 21 is the (a) real part of the dielectric constant, (b) imaginary part of the dielectric constant and (c) dielectric loss of the SiON micro-nano fiber film in Example 4 of the present application; from Figure 21 It can be seen that the real part of the dielectric constant of the material represents its ability to polarize and store energy under the action of electromagnetic waves, and the imaginary part of the dielectric constant represents its ability to attenuate electromagnetic waves. From Figure 21 It can be seen that the real part and imaginary part curves of the dielectric constant of the SiON nanofiber film in Example 4 are relatively high in the X band (8.2-12.4 GHz frequency band), which are 3.34-3.39 and 0.76-0.98, respectively. The dielectric loss factor tan delta e is the ratio of the real and imaginary parts of the dielectric constant, which indicates the ability of the material to lose electromagnetic waves. The tan delta eThe value ranges from 0.22 to 0.29, far exceeding 0.01, indicating excessive loss and inadequate wave transmission. This is due to the low-temperature ammonia treatment, which results in lower reactivity, better nitrogen doping, and weaker carbon removal. The large amount of carbon in the fiber easily leads to conductivity and polarization losses, preventing the fiber from achieving a low dielectric constant and dielectric loss.

[0193] Table 7 shows the element content and chemical formula of the Si℃ micro-nanofiber membrane in Counterexample 5 of the present invention;

[0194] Table 7

[0195]

[0196] Figure 22 are (a) the real part of the dielectric constant, (b) the imaginary part of the dielectric constant and (c) the dielectric loss of the Si℃ micro-nanofiber membrane in Counterexample 5 of the present invention; Figure 22 It can be seen that the real part of the dielectric constant of a material represents its ability to generate polarization and store energy under the action of electromagnetic waves, while the imaginary part of the dielectric constant represents its ability to attenuate electromagnetic waves. Figure 23 It can be seen that the dielectric constant real and imaginary parts of the SiON nanofiber membrane in Counterexample 5 in the X-band (8.2-12.4 GHz) are both at a high level, ranging from 3.12 to 3.30 and 1.10 to 1.61, respectively. delta e is the ratio of the real part to the imaginary part of the dielectric constant, which describes the material's ability to lose electromagnetic waves. delta e The value ranges from 0.34 to 0.51, significantly higher than the standard of 0.01 for wave transmission, indicating a lack of electromagnetic wave transmission. This is because ammonia decomposes easily at high temperatures, resulting in a low concentration of ammonia in the reaction, but high reactivity. This results in significant carbon removal but low nitrogen doping efficiency, making it prone to forming numerous defects and voids within the fiber. This, in turn, generates polarization losses under the influence of electromagnetic waves, hindering the achievement of low-dielectric, low-loss wave transmission characteristics.

[0197] Table 8 shows the element content and chemical formula of the Si℃N micro-nanofiber membrane in Counterexample 6 of the present invention;

[0198] Table 8

[0199]

[0200] Figure 23 are (a) the real part of the dielectric constant, (b) the imaginary part of the dielectric constant and (c) the dielectric loss of the Si℃N micro-nanofiber membrane in Counterexample 6 of the present invention; Figure 23It can be seen that the real part of the dielectric constant of the material represents its ability to polarize and store energy under the action of electromagnetic waves, while the imaginary part of the dielectric constant represents its ability to attenuate electromagnetic waves. Figure 23 It can be seen that the real part and imaginary part of the dielectric constant of the SiON micro-nano fiber membrane in Counterexample 6 in the X-band (8.2~12.4 GHz frequency band) are at a low level, respectively 1.32~1.39 and 0.0063~0.073. The dielectric loss factor tan delta e The ratio of the real part and the imaginary part of the dielectric constant, which indicates the ability of the material to lose electromagnetic waves. The tan delta e of the SiON micro-nano fiber membrane in Counterexample 6 is 0.0046~0.054, which fails to achieve a value less than 0.01, showing that its electromagnetic wave transmission performance is weak. This is because the carbon elements carried inside the fiber are difficult to be fully removed without ammonia treatment, which is easy to form polarization loss, causing the dielectric constant and dielectric loss factor of the fiber membrane to be difficult to be further reduced, limiting its wave transmission performance.

[0201] The preparation method of the SiON micro-nano fiber membrane according to the present application can realize the synthesis of the target morphology and composition of the fiber: by utilizing the chemical properties of 1-vinylimidazole, the composition of the spinning solution of the SiON micro-nano fiber membrane is designed, the problem of fiber morphology instability caused by precursor melting during solidification is solved, and continuous fibers with good separation are obtained; by utilizing the easy oxidation characteristics of the precursor, the fiber membrane is subjected to oxygen doping treatment by optimizing the oxygen concentration in the solidification stage, a high oxygen content of about 100% is achieved, which is beneficial to inhibit crystallization and reduce dielectric loss and thermal conductivity; by utilizing the ammonia gas reactivity, efficient carbon removal and nitrogen doping treatment are implemented by comprehensively adjusting the ammonia atmosphere and temperature of the heat treatment, an ideal amorphous SiON composition is formed, which is beneficial to the reduction of dielectric loss and thermal conductivity. Through the above three aspects of process design, the present application effectively coordinates the target of the morphology and composition of the fiber facing the demand for wave transmission and heat insulation, and creatively obtains the SiON micro-nano fiber membrane and its preparation method which have both wave transmission performance and heat insulation performance, thereby providing a basis and idea for the development of wave transmission and heat insulation functional integrated film materials.

[0202] The present application describes preferred embodiments and their effects. However, once the basic inventive concept is known to those skilled in the art, additional changes and modifications can be made to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0203] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. A method for preparing a SiON micro-nano fiber membrane with both electromagnetic wave transmission and high-temperature thermal insulation, characterized in that: The following steps are involved: Chloroform and N,N-dimethylformamide are mixed in a certain proportion as a solvent; a certain amount of polycarbosilane and / or polysilazane is added to the solvent as a SiON phase ceramic precursor; a certain amount of polyvinyl pyrrolidone is added to the solvent as a spinning aid; a certain amount of 1-vinylimidazole is added to the solvent as a fiber morphology stabilizer; and the mixture is uniformly mixed to prepare a spinning solution. Based on the electrospinning technology, the spinning solution is pushed out of a spinning needle with a certain inner diameter at a certain liquid discharge rate. A certain DC voltage is applied to the needle and the receiver respectively. Under the action of the electric field, spinning is carried out, and a precursor micro-nano fiber membrane is produced in the receiver. The precursor micro-nano fiber membrane is dried at 65-75°C for 1-3 hours, and then placed in an oven, a mixture of nitrogen and oxygen in a certain proportion is introduced, and heated to temperature T1 at a certain heating rate v1 and kept at this temperature for a time t1, and then heated to temperature T2 at a heating rate v2 and kept at this temperature for a time t2, to obtain a solidified precursor micro-nano fiber membrane; The volume ratio of nitrogen to oxygen in the mixed gas is 2-7:3; the heating rate v1 is 5-8°C / min, and v2 is 1-2°C / min; the heating temperature T1 is 140-160°C, and T2 is 200-220°C; the holding time t1 is 0.5-2 h, and t2 is 1-3 h; The solidified precursor micro-nano fiber membrane is placed in a tubular furnace, and a mixed gas of nitrogen and ammonia is introduced into the ammoniating temperature section, and nitrogen or argon is introduced into the remaining temperature sections. After the temperature reaches T3 and the temperature is kept at this temperature for a time t3, the temperature is further increased at a certain rate v3 to T4 and the temperature is kept at this temperature for a time t4, completing the ceramic transformation of the fiber, thereby obtaining a SiON micro-nano fiber membrane with both electromagnetic wave transmission and high-temperature thermal insulation. The temperature of the amination temperature section is increased from 200 to 900°C; the heating rate v3 is 1-2°C / min; the heating temperature T3 is 800-900°C, and T4 is 1300-1500°C; the holding time t3 is 0.5-2 h, and t4 is 1-3 h.

2. The method for preparing the SiON micro-nano fiber membrane with both electromagnetic wave transmission and high temperature thermal insulation according to claim 1, characterized in that: During the spinning solution preparation process, the mass ratio of chloroform to N,N-dimethylformamide in the solvent is 3-6:1; the amount of the ceramic precursor added is 10-50 wt.% of the solvent mass; the amount of the polyvinyl pyrrolidone added is 2-8 wt.% of the solvent mass; and the amount of 1-vinylimidazole added is 1-5 wt.% of the solvent mass.

3. The method for preparing the SiON micro-nano fiber membrane with both electromagnetic wave transmission and high temperature thermal insulation according to claim 1, characterized in that: During the preparation of the precursor micro-nanofiber membrane, the inner diameter of the spinning needle was 0.3-0.6 mm; the liquid output rate was 20-50 µL / min; the collection distance between the needle and the receiver was 14-22 cm; and the DC voltage included: a positive DC voltage of 16-24 kV and a negative DC voltage of -2-4 kV.

4. The method for preparing the SiON micro-nano fiber membrane with both electromagnetic wave transmission and high temperature thermal insulation according to claim 1, characterized in that: When the receiver is a flat plate, the precursor micro-nano fiber membrane obtained is a fiber membrane with disordered distribution; when the receiver is a roller, the precursor micro-nano fiber membrane obtained is a fiber membrane with directional distribution.

5. The method for preparing the SiON micro-nano fiber membrane with both electromagnetic wave transmission and high temperature thermal insulation properties according to claim 1, characterized in that: The volume ratio of nitrogen and ammonia introduced into the ammonia temperature section is 0-1:

1.

6. A SiON micro-nano fiber membrane having both electromagnetic wave transmission and high temperature thermal insulation properties, prepared by the method according to any one of claims 1 to 5, characterized in that: The fiber membrane is formed by overlapping SiON micro-nano fibers; The arrangement of the SiON micro-nano fibers in the fiber membrane is disordered or directional; The diameter of the SiON micro-nano fiber is 100 nm to 1.3 μm; The SiON micro-nano fibers contain Si elements with a content of more than 35 at.%, O elements with a content of more than 30 at.%, N elements with a content of more than 12 at.%, and C elements with a content of less than 7 at.%.

7. The SiON micro-nano fiber membrane with both electromagnetic wave transmission and high temperature thermal insulation properties according to claim 6, characterized in that: The thickness of the fiber membrane is 0.1-1.0 mm, the porosity is 85%-95%, and the density is 50-120 mg / cm 3 .

8. The SiON micro-nano fiber membrane with both electromagnetic wave transmission and high temperature thermal insulation properties according to claim 6, characterized in that: The fiber membrane is prepared by electrostatically spinning a SiON phase ceramic precursor to obtain a disordered or directional distributed precursor fiber membrane; subsequently, the precursor is synthesized at above 1300° C. and maintained in an amorphous state.

9. The SiON micro-nano fiber membrane with both electromagnetic wave transmission and high temperature thermal insulation properties according to claim 6, characterized in that: The SiON phase ceramic precursor is prepared by dissolving polycarbosilane and / or polysilazane in an organic solvent.

10. Use of the SiON micro-nano fiber membrane according to any one of claims 6 to 9 in wave transmission and heat insulation.

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