SiON micro-nano fiber membrane with both electromagnetic wave transmission and high-temperature heat insulation as well as preparation method and application of SiON micro-nano fiber membrane

Abstract

The invention discloses a SiON micro-nanofiber membrane with both electromagnetic wave transmission and high-temperature heat insulation as well as 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 oriented; the diameter of the SiON micro-nano fiber is 100 nm to 1.3 [mu] m; in the SiON micro-nano fiber, the content of Si element is more than 35 at.%, the content of O element is more than 30 at.%, the content of N element is more than 12 at.%, and the content of C element is less than 7 at.%. The prepared SiON fiber membrane has the micro-nano fiber diameter (100-1200 nm), low carbon and amorphous component / structure characteristics, shows 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 prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic fibers, and specifically relates to a SiON micro-nano fiber membrane that combines electromagnetic wave-transmissiveness and high temperature heat insulation, and a preparation method and application thereof. Background Art

[0002] Hypersonic aircraft usually undertake practical tasks such as electromagnetic communication, precision guidance, and offensive and defensive confrontation, and are in a complex electromagnetic wave environment. At the same time, when hypersonic aircraft fly at high speed in near-space, they also need to cope with the test of long-term high-temperature service under the action of aerodynamic heating. For example, the radar antenna cover of the aircraft not only undertakes the important communication task of sending and receiving electromagnetic waves, but also is in a harsh aerodynamic heating environment (the temperature can be as high as 1000℃). It is urgent to apply wave-transmitting and heat-insulating integrated materials to ensure that the electronic equipment inside the radar antenna cover works at a suitable temperature and sends and receives lossless electromagnetic wave communication signals.

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

[0004] The demand for wave transmission and thermal insulation has put forward higher requirements on the structure and component regulation of SiON fiber materials. In terms of structure, reducing the diameter of the fiber monofilament from the micron level (greater than 5 µm) to the micro-nano level (100~1000 nm) can greatly increase the porosity, which is conducive to the transmission of electromagnetic waves and prevents heat transmission; in terms of composition, element regulation and amorphous control are the key points for simultaneously optimizing the wave transmission and thermal insulation performance of SiON fibers. At present, the research on wave transmission / thermal insulation micro-nano materials is still in its infancy. The only typical 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 features of this type of one-dimensional nanomaterials are the nanoscale diameter (50~150 nm) and the component characteristics of single crystals. The high porosity structure and low intrinsic dielectric constant formed give the material good thermal insulation and wave transmission properties. However, the above work mainly uses chemical vapor deposition technology, which has problems such as low product yield, small aspect ratio (not conducive to the construction of thin-layer heat-resistant pore structure), and single crystal product structure (higher intrinsic thermal conductivity compared to amorphous state). In addition, the porous material obtained has a large thickness (10~100 mm), which limits its application scenarios. The polymer conversion ceramic method is a common process for mass production of amorphous ceramics. Melt spinning combined with polymer conversion ceramic method can be used to batch prepare continuous fibers with large aspect ratio (such as commercial SiC, Si3N4 fibers), but the diameter of the prepared fibers is mostly 5~20 µm, which is difficult to achieve micro-nano fiber diameter. In contrast, electrospinning, as an efficient and stable micro-nano fiber synthesis process, is expected to be combined with the polymer conversion ceramic method and has the potential to be used to prepare two-dimensional thin-layer micro-nano ceramic fiber membranes. At present, the research on the preparation of ternary SiON ceramic fibers by electrospinning combined with polymer conversion ceramic method is a blank field, the synthesis mechanism is unclear, and the process is difficult. The main technical difficulties include: (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 under high temperature pyrolysis have great technical difficulties in synthesis, regulation, mass production and stable storage, and have not yet been commercialized. Polycarbosilane and polysilazane, the precursors of SiC and SiCN ceramics, are commercial precursors that are easy to synthesize, but it is difficult to directly convert them into SiON phase. It is necessary to design a process based on the components of these two precursors during the ceramic transformation stage to obtain indirect conversion of SiON phase; (2) The precursor has poor spinnability. Both polycarbosilane and polysilazane are oligomers (relative molecular weight is about 500~2000), especially polysilazane, which is a liquid polymer with low molecular weight and low conductivity. It is difficult to form a high degree of molecular chain entanglement and fully stretch and shape it into continuous fibers under a high voltage electric field, and maintain the fiber morphology during curing and heat treatment. It is necessary to rationally design the formula of the spinning solution, such as introducing spinning aids and fiber morphology stabilizers, to synthesize a spinning solution with good spinnability; (3) Element regulation and amorphous control are difficult. First, the core of element regulation is to reduce the C content and increase the N and O content to reduce the dielectric constant of SiON fiber and weaken the loss of electromagnetic waves; second, compared with single crystal and polycrystalline structures, amorphous structures not only have lower intrinsic thermal conductivity, but also have less grain boundary content, which can reduce the interface loss of electromagnetic waves. However, element regulation and amorphous control face significant process difficulties: ① It is difficult to regulate carbon removal and nitrogen doping. The structure of polycarbosilane is mainly Si-C long chain, which contains a large amount of C elements but no N and O elements; polysilazane mainly contains Si, C and N elements, but the C content is relatively high and the N and O content is limited. Therefore, in the process of transformation of the two precursors, the process requirements for oxygen doping, nitrogen doping and carbon removal are relatively high; ② It is difficult to obtain high-temperature amorphous structure. The above two precursors complete the ceramic transformation above 1300°C. As the temperature rises, a large number of SiC and Si3N4 grains will be generated respectively, gradually forming a polycrystalline structure that is difficult to maintain in an amorphous state. Key process parameters such as temperature and atmosphere in curing and heat treatment processes need to be designed to regulate element composition and maintain amorphous state.

[0005] In summary, wave-transmitting and heat-insulating integrated materials have important research value and application needs in the aerospace field, and are gradually attracting the attention of researchers. Facing the communication requirements and heat insulation dilemma in high-temperature environments, it is urgent to develop a SiON micro-nano fiber membrane material with high temperature resistance, good wave transmission, and low thermal conductivity and its preparation technology. Summary of the invention

[0006] In view of the deficiencies in the above-mentioned background technology, the present invention mainly solves the problems in the prior art such as poor spinnability of precursors, difficulty in micronizing the diameter of SiON fibers, difficulty in regulating microstructure components, and difficulty in taking into account both wave transmission and heat insulation. The present invention provides a SiON micro-nano fiber membrane having both electromagnetic wave transmission and high-temperature heat insulation, and a preparation method and application thereof. The method selects polycarbosilane or polysilazane as a precursor and assists with heat treatment regulation to solve the problem that SiON ceramic precursors are difficult to obtain; uses spinning additives to effectively improve the spinnability of the mixed precursor; based on the characteristics of the mixed precursor being highly active and easy to oxidize, solidifies in a mixed atmosphere of nitrogen and oxygen, and introduces an appropriate amount of O element; uses a mixed atmosphere of nitrogen and ammonia with better reaction activity to assist the precursor fiber in completing the ceramic transformation, and uses ammonia reaction to regulate C and N elements. During the ceramic transformation process, the O element combines with the C element to form a small gas molecule, thereby achieving the purpose of carbon removal and nitrogen doping; the complex components increase the disorder of the system, effectively inhibit crystallization, and realize amorphous control. The SiON micro-nano fiber membrane involved in the present invention can maintain good stability above 1000°C, and has significant advantages in electromagnetic wave transmission function, high-temperature thermal insulation performance, light weight and thin layer, etc. It is expected to develop into a multifunctional integrated aerospace material and serve in high-temperature and harsh environments.

[0007] A first object of the present invention is to provide a SiON micro-nano fiber membrane that combines electromagnetic wave-permeability and high temperature heat insulation, and the fiber membrane is made of SiON micro-nano fibers through overlapping; The SiON micro-nanofibers in the fiber membrane are arranged in disorder or orientation; The diameter of the SiON micro-nanofiber is 100 nm~1.3 μm; The Si element content in the SiON micro-nanofiber is >35 at.%, the O element content is >30 at.%, the N element content is >12 at.%, and the C element content is <7 at.%.

[0008] Preferably, the fiber membrane has a thickness of 0.1 to 1.0 mm, a porosity of 85% to 95%, and a density of 50 to 120 mg / cm 3 .

[0009] Preferably, the fiber membrane is a precursor fiber membrane with disordered or directionally distributed SiON phase ceramic precursor by electrospinning; then, it is synthesized at 1300°C or above and maintained in an amorphous state.

[0010] Preferably, the SiON phase ceramic pioneer is prepared by dissolving polycarbosilane and / or polysilazane in an organic solvent.

[0011] A second object of the present invention is to provide a preparation method for SiON micro-nanofiber membrane that combines electromagnetic wave-transmissiveness and high temperature heat insulation, including the following steps: 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-vinyl imidazole is added to the solvent as a fiber morphology stabilizer; and the mixture is mixed uniformly to obtain 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 outlet rate, a certain DC voltage is applied to the needle and the receiver respectively, spinning is carried out under the action of the electric field, and a precursor micro-nano fiber membrane is obtained 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 mixed gas of nitrogen and oxygen in a certain proportion is introduced, and heated to a temperature T1 at a certain heating rate v1 and kept at a temperature for a time of t1, and then heated to a temperature T2 at a heating rate v2 and kept at a temperature for a time of 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 insulation 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, a mixed gas of nitrogen and ammonia is introduced into the ammoniating temperature section, and nitrogen or argon is introduced into the other temperature sections. After the temperature reaches T3, the temperature is kept at T3 for a time period of t3, and the temperature is continued to be raised to T4 at a certain rate v3 and kept at T4 for a time period of t4 to complete the ceramic transformation of the fiber, thus obtaining a SiON micro-nano fiber membrane having both electromagnetic wave transmission and high temperature heat insulation. Among them, the temperature of the ammonization temperature section is 200~900°C; the temperature increase rate v3 is 1~2°C / min; the heating temperature T3 is 800~900°C, and T4 is 1300~1500°C; the insulation time t3 is 0.5~2 h, and t4 is 1~3 h.

[0012] Preferably, during 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 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.

[0013] 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 output rate is 20~50 µL / min; the collection distance between the needle and the receiver is 14~22 cm; the DC voltage includes: the DC positive voltage is 16~24 kV, and the negative voltage is -2~4 kV.

[0014] Preferably, the precursor micro-nanofiber membrane produced when the receiver is a flat plate is a fiber membrane with disorderly distribution, and the precursor micro-nanofiber membrane produced when the drum is a fiber membrane with directionally distribution.

[0015] Preferably, the volume ratio of nitrogen and ammonia gas introduced into the ammonia temperature section is 0 to 1:1.

[0016] A third object of the present invention is to provide a use of SiON micro-nanofiber membrane in wave-transmissive heat insulation.

[0017] The present invention proposes a SiON micro-nano fiber membrane and a preparation method thereof, which adopts electrospinning combined with polymer-to-ceramic technology, 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 spinning solution ratio, spinning voltage, heat treatment atmosphere and temperature, so as to obtain a SiON micro-nano fiber membrane with good wave transmission performance, thermal insulation performance and high-temperature stability.

[0018] In terms of microstructure, the diameter of SiON micro-nano fibers is 100-1300 nm, and the length can reach several hundred to thousands of microns; in the SiON micro-nano fiber membrane, the fibers overlap each other to form a loose porous structure (porosity is 70-90%); the SiON micro-nano fiber membrane presents the characteristics of a light and thin layer, and exhibits good high-temperature thermal insulation performance at ultra-thin thickness. In terms of components, SiON micro-nano fibers are composed of SiON phases that remain amorphous at high temperatures, showing good electromagnetic wave transmission performance. Under the synergistic effect of microstructure and components, the SiON micro-nano fiber membrane has both good thermal insulation and wave transmission performance.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The SiON micro-nano fiber membrane of the present invention adopts PCS or PSN as a precursor and combines it with a heat treatment process of ammonia amination to achieve the ceramic transformation of the SiON phase of the fiber in the membrane, thus solving the problem of the difficulty in obtaining SiON precursors.

[0020] (2) The SiON micro-nano fiber membrane of the present invention overcomes the spinning difficulties caused by the low intrinsic molecular weight and low electrical conductivity of the two precursors PCS and PSN by mixing the precursor with the corresponding solvent, spinning aid and fiber morphology stabilizer, and achieves the goal of refining the fiber diameter to the micro-nano level, which is conducive to forming a structure with high porosity, low density and large specific surface area, and contributes significantly to the thermal insulation performance of the fiber membrane.

[0021] (3) The SiON micro-nano fiber membrane involved in the present invention effectively regulates the C and N element contents in the fiber under the ammonia ammonia heat treatment process, achieves nitrogen doping and carbon removal while suppressing crystallization behavior, and obtains components with nitrogen-rich, carbon-less and amorphous characteristics, which is beneficial to improving the wave transmission and thermal insulation properties of the fiber membrane.

[0022] (4) The preparation process of SiON micro-nano fiber membranes involved in the present invention utilizes electrostatic spinning combined with polymer-to-ceramic conversion to complete the forming (fiber spinning) and properties (ceramic transformation) of the micro-nano fiber membranes. During the forming process, the morphology and distribution are regulated, and the element composition and amorphous state are controlled. This coordinated optimization of the microstructure and components of the fiber membrane enables it to have both good wave transmission and thermal insulation properties.

[0023] (5) The SiON micro-nano fiber membrane of the present invention has the characteristics of low density and small thickness. The advantages of this lightweight thin layer make it more suitable for use as a wave-transmitting and heat-insulating integrated material for covering electronic equipment or device components in a narrow space compared to three-dimensional foam materials.

[0024] (6) The method for preparing SiON micro-nano fiber membranes involved in the present invention has a simple and stable process, a short synthesis cycle and low cost, and is capable of synthesizing large quantities of SiON micro-nano fiber membranes, thereby developing into an industrial preparation technology for wave-transmitting and heat-insulating integrated fiber membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the (a) macroscopic photo and (b~c) microscopic morphology of SiON nanofiber membrane in Example 1 of the present invention; Figure 2 It is (a) X-ray diffraction pattern and (b) transmission electron microscope photo of SiON nanofiber membrane in Example 1 of the present invention; Figure 3 It is the (a) real part of the dielectric constant, (b) imaginary part of the dielectric constant and (c) dielectric loss of the SiON nanofiber membrane in Example 1 of the present invention; Figure 4The thermal imaging characterization results of the SiON nanofiber membrane in Example 1 of the present invention are as follows: (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; Figure 5 It is the (a) macroscopic photo and (b~c) microscopic morphology of SiON nanofiber membrane in Example 2 of the present invention; Figure 6 It is (a) X-ray diffraction pattern and (b) transmission electron microscope photo of SiON nanofiber membrane in Example 2 of the present invention; Figure 7 It is the (a) real part of the dielectric constant, (b) imaginary part of the dielectric constant and (c) dielectric loss of the SiON nanofiber membrane in Example 2 of the present invention; Figure 8 The thermal imaging characterization results of the SiON nanofiber membrane in Example 2 of the present invention are as follows: (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; Fig. 9 It is the thermogravimetric curve of SiON nanofiber membrane in air atmosphere in Example 2 of the present invention; Fig.10 It is the (a) macroscopic photo and (b~c) microscopic morphology of SiON micro-nanofiber membrane in Example 3 of the present invention; Fig.11 It is (a) X-ray diffraction pattern and (b) transmission electron microscope photo of SiON micro-nanofiber membrane in Example 3 of the present invention; Fig.12 It is the (a) real part of the dielectric constant, (b) imaginary part of the dielectric constant and (c) dielectric loss of the SiON micro-nanofiber membrane in Example 3 of the present invention. Fig.13 The thermal imaging characterization results of the SiON micro-nano fiber membrane in Example 3 of the present invention are as follows: (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; Fig.14 It is the thermogravimetric curve of SiON micro-nanofiber membrane in air atmosphere in Example 3 of the present invention.

[0026] Fig.15 It is the (a) macroscopic photo and (b~c) microscopic morphology of SiON micro-nanofiber membrane in Example 4 of the present invention; Fig.16It is (a) X-ray diffraction pattern and (b) transmission electron microscope photo of SiON micro-nanofiber membrane in Example 4 of the present invention; Fig.17 It is the (a) real part of the dielectric constant, (b) imaginary part of the dielectric constant and (c) dielectric loss of the SiON micro-nanofiber membrane in Example 4 of the present invention. Fig.18 The thermal imaging characterization results of the SiON micro-nano fiber membrane in Example 4 of the present invention are as follows: (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; Fig.19 It is the micromorphology of the SiON micro-nanofiber membrane in counterexample 1 of the present invention; Fig. 20 It is the micromorphology of the SiON micro-nanofiber membrane in counterexample 2 of the present invention; Fig.21 It is the (a) real part of the dielectric constant, (b) imaginary part of the dielectric constant and (c) dielectric loss of the Si℃N micro-nano fiber membrane in the counterexample 4 of the present invention; Fig. 22 It is the (a) real part of the dielectric constant, (b) imaginary part of the dielectric constant and (c) dielectric loss of the Si℃ micro-nanofiber membrane in the counterexample 5 of the present invention; Fig.23 It is the (a) real dielectric constant part, (b) imaginary dielectric constant part and (c) dielectric loss of the Si℃N micro-nanofiber film in the counterexample 6 of the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0028] In order to provide a wave-transmitting and heat-insulating integrated material for use in harsh service environments, the present invention adopts polycarbosilane (SiC ceramic precursor) or polysilazane (SiCN ceramic precursor) as SiON phase ceramic precursor to prepare spinning solution based on polymer conversion ceramic method combined with electrospinning method, prepares micro-nano fiber membrane of the precursor by electrospinning process, performs carbon removal and nitrogen doping treatment in a mixed atmosphere of nitrogen and ammonia and completes ceramic transformation to obtain SiON micro-nano fiber membrane. The preparation process involved in the present invention 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 invention has micro-nano fiber diameter (100-1200 nm), low carbon and amorphous component / structural characteristics, and exhibits characteristics such as light weight, porosity, wave transmission, heat insulation, high temperature stability, etc. It is a new type of wave-transmitting and heat-insulating integrated fiber material with broad application prospects.

[0029] In order to achieve the above object, the first aspect of the present invention provides a SiON micro-nano fiber membrane that combines electromagnetic wave-permeability and high temperature heat insulation. The fiber membrane is made of SiON micro-nano fibers through overlapping; The SiON micro-nanofibers in the fiber membrane are arranged in disorder or orientation; The diameter of the SiON micro-nanofiber is 100 nm~1.3 μm; The Si element content in the SiON micro-nanofiber is >35 at.%, the O element content is >30 at.%, the N element content is >12 at.%, and the C element content is <7 at.%, totaling 100 at.%.

[0030] Among them, 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 .

[0031] The fiber membrane is a precursor of SiON phase ceramics by electrospinning to obtain a disordered or directionally distributed precursor fiber membrane; then, it is synthesized at 1300°C or above and maintained in an amorphous state.

[0032] The SiON phase ceramic pioneer is made by dissolving polycarbosilane and / or polysilazane in an organic solvent.

[0033] Specifically, SiON micro-nanofiber membranes are synthesized at above 1300°C and remain amorphous, and the interior is mainly composed of SiON phase.

[0034] The SiON micro-nano fiber membrane provided by the present invention has the characteristics of low density and small thickness. The advantages of this light and thin layer make it more suitable for use as a wave-transmitting and heat-insulating integrated material for covering electronic equipment or device components in a narrow space compared to three-dimensional foam materials.

[0035] The second aspect of the present invention provides a preparation method for a SiON micro-nano fiber membrane that combines electromagnetic wave-transmissiveness and high temperature heat insulation, including the following steps: 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-vinyl imidazole is added to the solvent as a fiber morphology stabilizer; and the mixture is mixed uniformly to obtain a spinning solution; When 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 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.

[0036] Based on the electrospinning technology, the spinning solution is pushed out of a spinning needle with a certain inner diameter at a certain liquid outlet rate, a certain DC voltage is applied to the needle and the receiver respectively, spinning is carried out under the action of the electric field, and a precursor micro-nano fiber membrane is obtained in the receiver; In the process of preparing precursor micro-nano fiber membrane, the inner diameter of the spinning needle is 0.3~0.6 mm; the liquid output rate is 20~50 µL / min; the collection distance between the needle and the receiver is 14~22 cm; the DC voltage includes: DC positive voltage is 16~24kV, and negative voltage is -2~4 kV.

[0037] The precursor micro-nanofiber membrane produced in a flat plate is a fiber membrane with disorderly distribution, and the precursor micro-nanofiber membrane produced in a drum is a fiber membrane with directionally distributed.

[0038] The precursor micro-nano fiber membrane is dried at 65-75°C for 1-3 hours, and then placed in an oven, a mixed gas of nitrogen and oxygen in a certain proportion is introduced, and heated to a temperature T1 at a certain heating rate v1 and kept at a temperature for a time of t1, and then heated to a temperature T2 at a heating rate v2 and kept at a temperature for a time of 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 insulation 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, a mixed gas of nitrogen and ammonia is introduced into the ammoniating temperature section, and nitrogen or argon is introduced into the other temperature sections. After the temperature reaches T3, the temperature is kept at T3 for a time period of t3, and the temperature is continued to be raised to T4 at a certain rate v3 and kept at T4 for a time period of t4 to complete the ceramic transformation of the fiber, thus obtaining a SiON micro-nano fiber membrane having both electromagnetic wave transmission and high temperature heat insulation. The temperature of the ammoniation temperature section is 200-900°C; the heating rate v3 is 1-2°C / min; the heating temperature T3 is 800-900°C, T4 is 1300-1500°C; the insulation time t3 is 0.5-2 h, t4 is 1-3 h. The volume ratio of nitrogen and ammonia introduced into the ammoniation temperature section is 0-1:1.

[0039] The SiON micro-nano fiber membrane of the present invention is synthesized by an electrostatic spinning process combined with a polymer conversion ceramic method. The precursor, spinning aid and fiber morphology stabilizer used need to be fully dissolved in a solvent and prepared to obtain a spinning solution, wherein 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 cross-linked and self-cross-linked with the polymer long chain, so that the micro-nano fiber maintains a stable morphology during the curing and heat treatment stages. The spinning solution droplets are split into filaments by a positive high-voltage DC power supply, and the formed precursor micro-nano fibers can be enriched on a receiver connected to a negative high-voltage DC power supply, wherein the solution propulsion speed and the positive and negative high voltages significantly affect the degree of droplet splitting and the morphology and diameter of the formed fibers, and the type of receiver determines whether the arrangement of the fibers in the membrane is disordered or directional. The precursor micro-nano fiber membrane obtained by stripping from the collector is fully removed of the volatile solvent through a drying step, and then the reaction cross-linking between the polymer long chains is promoted through a curing step to form a network-like bonding structure. In the curing step, the introduction of a mixed gas of nitrogen and oxygen is conducive to the oxygen doping of the micro-nano fiber membrane and increasing its oxygen content; a lower heating rate (v2) is used between T1 and T2 so that the micro-nano fiber membrane can fully undergo cross-linking and curing reactions in this rapid weight loss zone, forming a networked bonding structure to prepare for the ceramic transformation. The precursor micro-nano fiber membrane can complete the ceramic transformation through the heat treatment step, and a SiON micro-nano fiber membrane with both electromagnetic wave transmission and high-temperature thermal insulation is obtained. In this step, a mixed atmosphere of nitrogen and ammonia is introduced to utilize the amination reaction to remove carbon and nitrogen, thereby achieving fiber component regulation; at the same time, the heating section of 200~900℃ is the stage of continuous endothermic decomposition of the curing precursor, and a lower heating rate (v3) is used, which is conducive to the full side chain group cleavage and ammonia decarbonization and nitrogen doping reactions.

[0040] In one embodiment, a preparation method for SiON micro-nanofiber membrane that combines electromagnetic wave-transmissiveness and high temperature heat insulation is provided, specifically including the following steps: Step 1. Prepare spinning solution: mix chloroform and N, N-dimethylformamide (DMF) in a certain proportion as solvent; add a certain amount of polycarbosilane (PCS) or polysilazane (PSN) as SiON phase ceramic precursor to the solvent; add a certain amount of polyvinyl pyrrolidone (PVP) as spinning aid to the solvent; add a certain amount of 1-vinyl imidazole as fiber morphology stabilizer to the solvent; ensure that the solution is fully mixed by magnetic stirring; The mass ratio of chloroform and DMF in the solvent ranges from 3:1 to 6:1; The amount of the ceramic precursor added is 10 to 50 wt.% of the solvent mass The amount of PVP added is 2-8 wt.% of the solvent mass; The amount of 1-vinyl imidazole is 1 to 5 wt.% of the solvent mass; The magnetic stirring process is to continuously stir at a speed of 200 to 400 r / min for 8 to 48 hours.

[0041] 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 outlet rate, and a certain DC high voltage and low voltage are applied to the needle and the receiver respectively. The preparation of the precursor micro-nano fibers and the collection of the fiber membrane are completed under the action of the electric field.

[0042] The inner diameter of the metal spinning needle is 0.3~0.6 mm; The spinning liquid outlet rate is 20-50 μL / min; The positive voltage of the spinning DC is 16~24 kV and the negative voltage is -2~4 kV; The collection distance between the needle and the receiver is 14~22 cm; When the receiver is a flat plate, a fiber membrane with irregular fiber distribution can be obtained, and when it is a roller, a fiber membrane with directional fiber distribution can be obtained.

[0043] 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 and dried at 70°C for 1-3 hours to fully volatilize the solvent; then the precursor micro-nano fiber membrane is placed in an oven, and a mixed gas of nitrogen and oxygen in a certain proportion is introduced to promote oxidation of the precursor and increase the oxygen content of the fiber, and heated to temperature T1 at a certain heating rate v1 and kept warm (time t1), and then heated to temperature T2 at a rate v2 and kept warm (time t2), and the easy oxidation property of the precursor is used to dope the O element, and the long-chain cross-linking and curing of the polymer is promoted to form a network bonding structure; The volume ratio of nitrogen and oxygen in the mixed gas is 2~7:3; The temperature increase rate of the curing v1 is 5~8℃ / min, and v2 is 1~2℃ / min; The heating temperature T1 of the curing is from 140 to 160°C and from 200 to 220°C; The insulation time t1 of the curing is 0.5~2 h, and t2 is 1~3 h.

[0044] Step 4. Heat treatment of the precursor micro-nano fiber membrane: The solidified precursor micro-nano fiber membrane is then placed in a tubular furnace, and a mixed gas of nitrogen and ammonia is introduced into the ammoniating temperature section for carbon removal and nitrogen doping treatment, and nitrogen or argon is introduced into the remaining temperature sections as an inert protective gas. After the temperature is raised to T3, it is kept warm (time is t3), and the temperature is continued to be raised to the maximum heat treatment temperature T4 at a certain rate v3 and kept warm (time is t4), completing the ceramic transformation of the fiber to obtain a SiON micro-nano fiber membrane.

[0045] The volume ratio of nitrogen and ammonia in the mixed gas is 0~1:1; The ammoniation temperature range is 200-900°C; The heating rate v3 of the heat treatment is 1-2°C / min; The heating temperature T3 of the heat treatment is 800~900℃, and T4 is 1300~1500℃; The heat treatment insulation time t3 is 0.5~2 h, and t4 is 1~3 h.

[0046] Among them, the polymer precursor includes but is not limited to PCS, PSN and a mixture of both.

[0047] The spinning additives include but are not limited to common electrospinning polymers such as PVP, polycaprolactone, and polystyrene.

[0048] During the curing process, for PCS precursor micro-nano fiber membrane, the ratio of nitrogen to oxygen in the introduced mixed gas should be less than 2:3; for PSN precursor micro-nano fiber membrane, the ratio of nitrogen to oxygen in the introduced mixed gas should be less than 7:3.

[0049] During the heat treatment process, for PCS precursor micro-nano fiber membrane, the ammoniation temperature section should include but not be limited to 600-800°C; for PSN precursor micro-nano fiber membrane, the ammoniation temperature section should include but not be limited to 400-800°C.

[0050] During the heat treatment process, for PCS precursor micro-nano fiber membrane, the ratio of nitrogen and ammonia in the introduced mixed gas should be less than 1:3; for PSN precursor micro-nano fiber membrane, the ratio of nitrogen and ammonia in the introduced mixed gas should be less than 1:1.

[0051] During the heat treatment process, the atmosphere entering the ammonization temperature section and other temperature sections should maintain the flow rate consistent, with the flow rate range of 80~120 mL / min.

[0052] The third aspect of the present invention provides an application of SiON micro-nanofiber membrane in wave-transmissive heat insulation.

[0053] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0054] Example 1 Step 1. Prepare the spinning solution: mix chloroform and DMF in a mass ratio of 4:1 as the solvent; add 10 wt.% PCS as the SiON phase ceramic precursor to the solvent; add 4 wt.% PVP as the spinning aid to the solvent; add 1 wt.% 1-vinyl imidazole to the solvent as the fiber morphology stabilizer; stir continuously at a speed of 400 r / min for 48 hours by magnetic stirring to ensure that the solution is fully mixed.

[0055] Step 2. Preparation of PCS nanofibers by electrospinning: Fill the stirred spinning solution into a syringe, connect the syringe to a metal needle with an inner diameter of 0.33 mm, and place the syringe on a propeller. Adjust the liquid discharge rate of the needle to 50 µL / min by setting the propulsion speed of the propeller. Apply a DC positive high voltage of 18 kV to the spinning needle to split the liquid droplets from the needle to form nanofibers, which can be collected on a receiver connected to a DC negative pressure of -2 kV after moving in the electric field. The collection distance between the needle and the receiver is 16 cm.

[0056] Step 3. Curing of PCS nanofibers: The PCS nanofibers obtained by electrospinning were placed in a drying oven and dried at 70°C for 1 hour to allow most of the solvent to evaporate; the dried PCS nanofibers were then placed in an oven and a mixed gas of nitrogen and oxygen was introduced at a volume ratio of 2:3. The temperature was raised to 140°C at a rate of 5°C / min and kept warm for 0.5 h, then heated to 210°C and kept warm for 2 hours to promote cross-linking and curing of the polymer chains and the doping of oxygen elements to form a network bonding structure.

[0057] Step 4. Heat treatment of PCS nanofibers: Place the cured PCS nanofibers in a tubular furnace, heat to 900°C and keep warm for 0.5 h, then heat to 1300°C at a heating rate of 2°C / min and keep warm for 2 hours. In the ammoniating temperature section from 250°C to 850°C, a mixed gas of nitrogen and ammonia is introduced at a volume ratio of 1:3, with a gas flow rate of 80 mL / h, and nitrogen is introduced at the remaining temperature sections at an equal flow rate. Finally, the ceramic transformation of the fiber is completed to obtain SiON nanofibers.

[0058] The SiON nanofiber prepared in this example is a directional fiber with a diameter distribution of 100~300 nm. The fiber is an amorphous SiON phase, and its chemical formula is SiO 0.998 C 0.051 N 0.441In 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 2.41~2.54, 0.00055~0.019 and 0.00022~0.0074, respectively, and its electromagnetic wave transmission performance is good; in terms of heat insulation, the thermal conductivity of the SiON nanofiber membrane is 0.021 W / (m·K), and the average back temperature of the 1 mm thick fiber membrane when heated by a spray gun at a temperature of about 1300°C for 10 min, 20 min and 30 min is 275.74°C, 288.55°C and 305.89°C, respectively.

[0059] Example 2 Step 1. Prepare the spinning solution: mix chloroform and DMF in a mass ratio of 6:1 as the solvent; add 10 wt.% PCS as a SiON phase ceramic precursor to the solvent; add 2 wt.% PVP as a spinning aid to the solvent; add 2.5 wt.% 1-vinyl imidazole to the solvent as a fiber morphology stabilizer; stir continuously at a speed of 300 r / min for 48 hours by magnetic stirring to ensure that the solution is fully mixed.

[0060] Step 2. Preparation of PCS nanofibers by electrospinning: Fill the stirred spinning solution into a syringe, connect the syringe with a metal needle with an inner diameter of 0.33 mm, and place the syringe on a propeller. Adjust the liquid discharge rate of the needle to 40 µL / min by setting the propulsion speed of the propeller. Apply a 20 kV DC positive high voltage to the spinning needle to split the liquid droplets from the needle to form nanofibers, which can be collected on a receiver connected to a DC negative pressure of -2 kV after moving in the electric field. The collection distance between the needle and the receiver is 18 cm.

[0061] Step 3. Curing of PCS nanofibers: The PCS nanofibers obtained by electrospinning were placed in a drying oven and dried at 70°C for 1 hour to allow most of the solvent to evaporate; the dried PCS nanofibers were then placed in an oven and a mixed gas of nitrogen and oxygen was introduced at a volume ratio of 2:3. The temperature was raised to 160°C at a rate of 5°C / min and kept warm for 0.5 h, then heated to 210°C and kept warm for 1.5 hours to promote cross-linking and curing of the polymer chains and the doping of oxygen elements to form a network bonding structure.

[0062] Step 4. Place the cured PCS nanofibers in a tubular furnace, heat to 850°C and keep warm for 0.5 h, then heat to 1300°C at a heating rate of 1°C / min and keep warm for 3 hours. In the ammoniating temperature section from 550°C to 850°C, a mixed gas of nitrogen and ammonia is introduced at a volume ratio of 0:1, with a gas flow rate of 100 mL / h, and nitrogen is introduced at the same flow rate in the remaining temperature sections. Finally, the ceramic transformation of the fiber is completed to obtain SiON nanofibers.

[0063] Compared with Example 1, this example mainly changes the concentration, temperature range and gas flow rate of the ammonia gas introduced in the heat treatment process. The SiON nanofibers prepared in this example are oriented fibers with a diameter distribution of 100-300 nm, and the fibers contain an amorphous SiON phase, whose 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 8.2~12.4GHz are 2.69~2.72, 0.007~0.026 and 0.0026~0.0095, respectively, and its electromagnetic wave transmittance is good; in terms of heat insulation, the thermal conductivity of the SiON nanofiber membrane is 0.016 W / (m·K), and the average back temperature of the 1 mm thick fiber membrane when heated by a spray gun at a temperature of about 1300℃ for 10 min, 20 min and 30 min is 258.32℃, 272.28℃ and 283.18℃ respectively.

[0064] Example 3 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-vinyl imidazole to the solvent as a fiber morphology stabilizer; and stir the solution at a speed of 500 r / min for 12 hours by magnetic stirring to ensure that the solution is fully mixed.

[0065] Step 2. Preparation of PSN micro-nanofibers by electrospinning: Fill the stirred spinning solution into a syringe, connect the syringe with a metal needle with an inner diameter of 0.6 mm, and place the syringe on a propeller. Adjust the liquid discharge rate of the needle to 25 µL / min by setting the propulsion speed of the propeller; apply a 24 kV DC positive high voltage to the spinning needle to split the liquid droplets from the needle to form micro-nanofibers, which can be collected on a receiver connected to a DC negative pressure of -3 kV after moving in the electric field. The collection distance between the needle and the receiver is 15 cm.

[0066] Step 3. Curing of PSN micro-nanofibers: The PSN micro-nanofibers obtained by electrostatics were placed in a drying oven and dried at 70°C for 3 hours to allow most of the solvent to evaporate; the dried PSN nanofibers were then placed in an oven, and a mixed gas of nitrogen and oxygen was introduced at a volume ratio of 7:3. The temperature was raised to 160°C at a rate of 10°C / min and kept at this temperature for 2 hours, and then heated to 200°C and kept at this temperature for 1 hour to promote cross-linking and curing of the polymer chains to form a network bonding structure.

[0067] Step 4. Heat treatment of PSN micro-nano fibers: Place the cured PSN micro-nano fibers in a tubular furnace, introduce a mixture of nitrogen and ammonia, heat the temperature to 1300°C at a heating rate of 5°C / min, and keep the temperature for 2 hours. In the ammoniating temperature section from 400°C to 900°C, introduce a mixture of nitrogen and ammonia at a volume ratio of 1:1, with a gas flow rate of 120 mL / h, and introduce nitrogen at the same flow rate in the remaining temperature sections. Finally, the ceramic transformation of the fiber is completed to obtain SiON micro-nano fibers.

[0068] Compared with Example 1, this example mainly changes the type of the selected precursor. The SiON micro-nano fibers prepared in this example are oriented fibers with a diameter distribution of 300-1200 nm. The fibers contain an amorphous SiON phase, and its chemical formula is 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-nano fiber membrane 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 its electromagnetic wave transmittance is good; in terms of heat insulation, the thermal conductivity of the SiON nanofiber membrane is 0.055 W / (m·K), and the average back temperature of the 1mm thick fiber membrane when heated by a spray gun at a temperature of about 1300℃ for 10 min, 20 min and 30 min is 305.28℃, 319.46℃ and 323.40℃ respectively; in terms of high temperature stability, the weight gain rate of the SiON nanofiber membrane 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.

[0069] Example 4 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-vinyl imidazole to the solvent as a fiber morphology stabilizer; and stir the solution at a speed of 500 r / min for 12 hours by magnetic stirring to ensure that the solution is fully mixed.

[0070] Step 2. Preparation of PSN micro-nanofibers by electrospinning: Fill the stirred spinning solution into a syringe, connect the syringe with a metal needle with an inner diameter of 0.6 mm, and place the syringe on a propeller. Adjust the liquid discharge rate of the needle to 25 µL / min by setting the propulsion speed of the propeller; apply a 24 kV DC positive high voltage to the spinning needle to split the liquid droplets from the needle to form micro-nanofibers, which can be collected on a receiver connected to a DC negative pressure of -3 kV after moving in the electric field. The collection distance between the needle and the receiver is 15 cm.

[0071] Step 3. Curing of PSN micro-nanofibers: The PSN micro-nanofibers obtained by electrostatics were placed in a drying oven and dried at 70°C for 3 hours to allow most of the solvent to evaporate; the dried PSN nanofibers were then placed in an oven, and a mixed gas of nitrogen and oxygen was introduced at a volume ratio of 7:3. The temperature was raised to 160°C at a rate of 10°C / min and kept at this temperature for 2 hours, and then heated to 200°C and kept at this temperature for 1 hour to promote cross-linking and curing of the polymer chains to form a network bonding structure.

[0072] Step 4. Heat treatment of PSN micro-nano fibers: Place the cured PSN micro-nano fibers in a tubular furnace, introduce a mixture of nitrogen and ammonia, heat the temperature to 1500°C at a heating rate of 5°C / min, and keep the temperature for 2 hours. In the ammoniating temperature section from 400°C to 900°C, a mixture of nitrogen and ammonia is introduced at a volume ratio of 1:1, with a gas flow rate of 120 mL / h, and nitrogen is introduced at the same flow rate in the remaining temperature sections. Finally, the ceramic transformation of the fiber is completed to obtain SiON micro-nano fibers.

[0073] Compared with Example 1, this example mainly changes the maximum temperature of the heat treatment. The SiON micro-nano fibers prepared in this example are oriented fibers with a diameter distribution of 300-1200 nm. The fibers contain an amorphous SiON phase, and its chemical formula is SiO 0.783 C 0.119 N 0.451 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-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 its electromagnetic wave transmittance is good; in terms of heat insulation, the thermal conductivity of the SiON nanofiber membrane is 0.075 W / (m·K), and the average back temperature of the fiber membrane with a thickness of 1 mm when heated by a spray gun at a temperature of about 1300℃ for 10 min, 20 min and 30 min is 332.53℃, 344.84℃ and 353.62℃ respectively.

[0074] Counterexample 1 Compared with Example 1, this example cancels the addition of 1-vinyl imidazole, a fiber morphology stabilizer, in the solvent. In this counterexample, the PCS micro-nano fibers reach the melting point of PCS during the curing stage. PCS, as a solid precursor, melts a small amount of PCS during the cross-linking process, resulting in a certain adhesion between the micro-nano fibers, providing more sites for solid-phase heat transfer, which is not conducive to reducing the thermal conductivity of the SiON micro-nano fiber membrane.

[0075] Counterexample 2 Compared with Example 3, this example cancels the addition of 1-vinyl imidazole, a fiber morphology stabilizer, in the solvent. In this counterexample, the PSN micro-nano fibers reach the melting point of PSN during the curing stage. As a high-viscosity liquid precursor, a large amount of PSN melts during the cross-linking process, resulting in complete adhesion between the micro-nano fibers. After heat treatment, more solid-phase heat transfer sites are provided, making it difficult to maintain the morphology of the SiON micro-nano fibers.

[0076] Counterexample 3 Compared with Example 1, this example changes the mixed atmosphere of nitrogen and oxygen in the curing step to an 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 atmosphere in the example. This results in the oxidation degree of the fiber membrane in the air atmosphere being weaker than that in the mixed atmosphere, and the oxygen doping effect is weaker. The O element content in the SiON micro-nano fiber membrane obtained by heat treatment after air curing is less than 20 at.%, which is significantly lower than Example 1 (40.08 at.%). For the PSN precursor micro-nano fiber membrane, there is a similar phenomenon.

[0077] Counterexample 4 Compared with Example 2, in this example, the amination temperature section is changed to a temperature section of 250°C to 550°C during the heat treatment process. The micro-nano fiber of this example is SiC N phase, and its chemical formula is SiO 0.518 C 1.129 N 0.466 , with high C and N content. This is because this temperature range does not reach the temperature at which ammonia and the precursor react actively, and is insufficient to provide sufficient driving force for the amination reaction. Since the bond energy of the Si-C bond (318 kJ / mol) is slightly higher than that of the Si-H bond (315 kJ / mol), the Si-H bond in the precursor is easier to break, reacting with ammonia to form a Si-NH2 bond, completing the doping of the 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 band of 8.2~12.4 GHz are 3.34~3.39, 0.76~0.98 and 0.22~0.29, respectively. It has a strong loss capacity for electromagnetic waves, but does not have effective wave transmission performance.

[0078] Counterexample 5 Compared with Example 2, in this example, the amination temperature section is changed to a 1300°C holding section during the heat treatment process. The micro-nano fibers of this example have the characteristics of low C and N content, and their chemical formula is SiO 1.222 C 0.136 N 0.007 . This is because the decomposition reaction of ammonia is more intense in this temperature range. A large amount of ammonia has been decomposed into nitrogen and hydrogen before contacting the fiber. The actual concentration of ammonia participating in the amination reaction is low, which weakens the carbon removal and nitrogen doping effects 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 band of 8.2~12.4GHz are 3.12~3.30, 1.10~1.61 and 0.34~0.51 respectively. It has a strong loss capacity for electromagnetic waves, but does not have effective wave transmission performance.

[0079] Counterexample 6 Compared with Example 3, this example does not use ammonia to treat the precursor fiber during the heat treatment process. The micro-nano fiber prepared in this example is an 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 band of 8.2~12.4 GHz are 1.32~1.39, 0.0063~0.073 and 0.0046~0.054 respectively. Since the fiber has not been treated with ammonium, it has a high carbon content (higher than 20%), so the loss of electromagnetic waves is relatively large and the wave transmission performance is poor.

[0080] In order to illustrate the relevant performance of the SiON micro-nano fiber membrane provided by the present invention, it is described below with reference to the accompanying drawings.

[0081] Figure 1 (a) macroscopic photograph and (b-c) microscopic morphology of SiON nanofiber membrane in Example 1 of the present invention; From the macroscopic photo of Example 1, it can be seen that the SiON nanofiber membrane is off-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 nanometer-scale diameter distribution (about 100-300nm), the fiber continuity is good, and the fibers overlap to form a porous structure.

[0082] Figure 2 are (a) an X-ray diffraction pattern and (b) a transmission electron microscope photograph of the SiON nanofiber membrane in Example 1 of the present invention; 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 bulge-shaped broad peak between 20° and 30° represents the presence of Si-O-Si amorphous structure. The high-resolution transmission photograph of Example 1 does not show the crystal diffraction stripes of nanocrystals, and its selected area electron diffraction shows diffuse central spots, which further confirms that the SiON nanofiber membrane in Example 1 is in an amorphous state, which is consistent with the XRD analysis results.

[0083] Table 1 shows the element content and chemical formula of the SiON nanofiber membrane in Example 1 of the present invention; Table 1

[0084] Figure 3 are (a) the real part of the dielectric constant, (b) the imaginary part of the dielectric constant and (c) the dielectric loss factor of the SiON nanofiber membrane in Example 1 of the present invention; Figure 3 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 3 It can be seen that the real and imaginary curves of the dielectric constant of the SiON nanofiber membrane in Example 1 in the X-band (frequency band of 8.2-12.4 GHz) are relatively stable, and the values ​​are at a relatively low level, which are 2.41-2.54 and 0.00055-0.019 respectively. δ e is the ratio of the real part to the imaginary part of the dielectric constant, which illustrates the material's ability to lose electromagnetic waves. δ e The values ​​range from 0.00022 to 0.0074, all lower than 0.01, indicating that it has good electromagnetic wave transmission performance. The amorphous SiON component and high porosity structure are conducive to its low dielectric and low loss characteristics.

[0085] Figure 4 The thermal imaging characterization results of the SiON nanofiber membrane in Example 1 of the present invention are as follows: (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. Figure 4It can be seen that facing a butane flame spray gun with a flame temperature of about 1300°C, a SiON nanofiber membrane with a thickness of about 1mm can effectively block the flame and have a cooling and heat-insulating effect. The average temperature of the fire-facing surface of the SiON nanofiber membrane in Example 1 is 1015.81°C. After heating for 10 minutes, the average temperature of the back-fire surface of the fiber membrane was 275.74°C; after heating for 20 minutes, the average temperature of the back-fire surface of the fiber membrane rose slightly to 288.55°C; after heating for 30 minutes, the average temperature of the back-fire surface of the fiber membrane reached 305.89°C. It can be seen that the thermal insulation effect of this SiON nanofiber membrane is good and relatively stable. The amorphous SiON phase has a low intrinsic thermal conductivity, and the porous structure formed by the overlapping of nanofibers can effectively block heat transfer, which is beneficial to enhance its thermal insulation effect.

[0086] Figure 5 (a) is a macroscopic photograph and (b-c) is a microscopic morphology of the SiON nanofiber membrane in Example 2 of the present invention; Figure 5 It can be seen from the macroscopic photo of Example 2 that the SiON nanofiber membrane is white and has flexible wrinkles on the surface. From the scanning photo, it can be seen that the fibers in the membrane have a certain orientation arrangement and nanometer-scale diameter distribution (about 100-300nm), the fiber continuity is good, and the fibers overlap to form a porous structure.

[0087] Figure 6 are (a) X-ray diffraction pattern and (b) transmission electron microscope photo of SiON nanofiber membrane in Example 2 of the present invention; 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 bulge-shaped broad peak between 20° and 30° represents the presence of a large number of Si-O-Si amorphous structures. The high-resolution transmission photograph of Example 2 does not show the crystal diffraction fringes of nanocrystals, and its selected area electron diffraction shows diffuse central spots, which further confirms that the SiON nanofiber membrane in Example 2 is in an amorphous state, which is consistent with the analysis results of XRD.

[0088] Table 2 shows the element content and chemical formula of the SiON nanofiber membrane in Example 2 of the present invention; Table 2

[0089] Figure 7 are (a) the real part of the dielectric constant, (b) the imaginary part of the dielectric constant and (c) the dielectric loss of the SiON nanofiber membrane in Example 2 of the present invention; Figure 7 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 7It can be seen that the real and imaginary curves of the dielectric constant of the SiON nanofiber membrane in Example 2 in the X-band (frequency band of 8.2-12.4 GHz) are relatively stable, and the values ​​are at a relatively low level, which are 2.69-2.72 and 0.007-0.026 respectively. δ e is the ratio of the real part to the imaginary part of the dielectric constant, which illustrates the material's ability to lose electromagnetic waves. δ e The values ​​range from 0.0026 to 0.0095, all lower than 0.01, indicating that it has good electromagnetic wave transmission performance. The amorphous SiON component and high porosity structure are conducive to its low dielectric and low loss characteristics.

[0090] Figure 8 The thermal imaging characterization results of the SiON nanofiber membrane in Example 2 of the present invention are as follows: (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. Figure 8 It can be seen that facing a butane flame spray gun with a flame temperature of about 1300°C, a SiON nanofiber membrane with a thickness of about 1mm can effectively block the flame and have a cooling and heat-insulating effect. The average temperature of the fire-facing surface of the SiON nanofiber membrane in Example 2 is 953.86°C. After heating for 10 minutes, the average temperature of the back-fire surface of the fiber membrane is 258.32°C; after heating for 20 minutes, the average temperature of the back-fire surface of the fiber membrane rises slightly to 272.28°C; after heating for 30 minutes, the average temperature of the back-fire surface of the fiber membrane reaches 283.18°C. It can be seen that the thermal insulation effect of this SiON nanofiber membrane is good and relatively stable. The amorphous SiON phase has a low intrinsic thermal conductivity, and the porous structure formed by the overlapping of nanofibers can effectively block heat transfer, which is beneficial to enhance its thermal insulation effect.

[0091] Fig. 9 The thermal stability results of SiON nanofiber membrane in Example 2 of the present invention are as follows: (a) thermogravimetric curve under air atmosphere; (b) XRD spectrum of the fiber membrane after heating with butane flame for 30 min. Fig. 9 It can be seen that the curve of SiON nanofiber membrane in air atmosphere can characterize its thermal stability in high temperature oxidative environment. Fig. 9As shown, when the temperature was raised from room temperature to 1300°C, the fiber membrane first had an endothermic reaction, and the mass decreased slightly, then began to release heat, and the mass increased. At 664.4°C, the sample mass was the smallest, and the weight loss rate was 1.89%, which may be due to the evaporation of water adsorbed by the fiber membrane and the oxidation loss of a small amount of residual C element; when the temperature was above 664.4°C, the mass of the fiber membrane gradually increased, and at 1300°C, its mass was the largest, and the weight gain rate was 5.54%, which may be due to slight oxidation of the fiber membrane at high temperature. It can be seen from the XRD results that after being heated at high temperature for 30 min by a butane spray gun, the fiber membrane was still in an amorphous state, and no crystallization phenomenon was found, proving that its component stability was good under high temperature and short-term conditions. In summary, the SiON nanofiber membrane in Example 2 has good thermal stability.

[0092] Fig.10 (a) is a macroscopic photograph and (b-c) is a microscopic morphology of the SiON micro-nano fiber membrane in Example 3 of the present invention; Fig.10 It can be seen from the macroscopic photo of Example 3 that the SiON micro-nano fiber membrane is 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 micro-nano-scale diameter distribution (about 300-1200nm), the fiber continuity is good, and the fiber overlap forms a porous structure.

[0093] Fig.11 are (a) X-ray diffraction pattern and (b) transmission electron microscope photo of SiON micro-nano fiber membrane in Example 3 of the present invention; Fig.11 It can be seen that the XRD spectrum of Example 3 shows that the SiON micro-nano fiber membrane is in an amorphous state, and no obvious crystal diffraction peak is observed. The high-resolution transmission photograph of Example 3 does not show the crystal diffraction fringes of nanocrystals, and its selected area electron diffraction shows diffuse central spots, which further confirms that the SiON micro-nano fiber membrane in Example 3 is in an amorphous state, which is consistent with the analysis results of XRD.

[0094] Table 3 shows the element content and chemical formula of the SiON micro-nano fiber membrane in Example 3 of the present invention; Table 3

[0095] Fig.12 are (a) the real part of the dielectric constant, (b) the imaginary part of the dielectric constant and (c) the dielectric loss of the SiON micro-nano fiber membrane in Example 3 of the present invention, from Fig.12 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. Fig.12It can be seen that the real and imaginary curves of the dielectric constant of the SiON micro-nano fiber membrane in Example 3 in the X-band (frequency band of 8.2-12.4 GHz) are relatively stable, and the values ​​are at a relatively low level, which are 1.08-1.15 and 0.0012-0.0078 respectively. δ e is the ratio of the real part to the imaginary part of the dielectric constant, which illustrates the material's ability to lose electromagnetic waves. δ e The values ​​range from 0.0001 to 0.0068, all lower than 0.01, indicating that it has good electromagnetic wave transmission performance. The amorphous SiON component and high porosity structure are conducive to its low dielectric and low loss characteristics.

[0096] Fig.13 The thermal imaging characterization results of the SiON micro-nano fiber membrane in Example 3 of the present invention are as follows: (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. Fig.13 It can be seen that in the face of a butane flame spray gun with a flame temperature of about 1300°C, a SiON micro-nano fiber membrane with a thickness of about 1 mm can effectively block the flame and have a cooling and heat insulation effect. The average temperature of the fire-facing surface of the SiON micro-nano fiber membrane in Example 3 is 903.53°C. After heating for 10 minutes, the average temperature of the back-fire surface of the fiber membrane is 305.28°C; after heating for 20 minutes, the average temperature of the back-fire surface of the fiber membrane rises slightly to 319.46°C; after heating for 30 minutes, the average temperature of the back-fire surface of the fiber membrane reaches 323.40°C. It can be seen that the thermal insulation effect of this SiON micro-nano fiber membrane is good and relatively stable. The amorphous SiON phase has a low intrinsic thermal conductivity, and the porous structure formed by the overlap of micro-nano fibers can effectively block heat transfer, which is conducive to enhancing its thermal insulation effect.

[0097] Fig.14 The thermal stability of the SiON micro-nano fiber membrane in Example 3 of the present invention is shown in Figure 2: (a) Thermogravimetric curves in air atmosphere and nitrogen atmosphere; (b) XRD spectrum of the fiber membrane after heating with butane flame for 30 min. Fig.14 It can be seen that the TG curves of SiON micro-nano fiber membranes in air and nitrogen atmospheres can show their thermal stability in high temperature oxidative environments. Fig.14As shown in Figure 3, the weight gain of the SiON micro-nano fiber membrane in Example 3 is 6.92% in an air environment at 1500°C, and the weight gain in a nitrogen environment at 1500°C is 0.94%, both showing good thermal stability. For the fiber membrane heated at 1300°C under a butane torch for 30 min, its XRD spectrum shows that it is still amorphous, further verifying the high-temperature stability of its components.

[0098] Fig.15 (a) is a macroscopic photograph and (b-c) is a microscopic morphology of the SiON micro-nano fiber membrane in Example 4 of the present invention; Fig.15 It can be seen from the macroscopic photo of Example 4 that the SiON micro-nano fiber membrane is 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 micro-nano-scale diameter distribution (about 300-1200nm), the fiber continuity is good, and the fiber overlap forms a porous structure.

[0099] Fig.16 are (a) X-ray diffraction pattern and (b) transmission electron microscope photo of SiON micro-nano fiber membrane in Example 4 of the present invention; Fig.16 It can be seen that the XRD spectrum of Example 4 shows that the SiON nanofiber membrane is basically in an amorphous state, but there are a small number of tiny peaks, and the large bulge-type broad peak located between 20° and 30° represents the presence of a large number of Si-O-Si amorphous structures. The high-resolution transmission photograph of Example 4 did not find the crystal diffraction fringes of nanocrystals, and its selected area electron diffraction showed diffuse central spots, further confirming that the SiON nanofiber membrane in Example 4 is basically in an amorphous state, which is consistent with the analysis results of XRD.

[0100] Table 4 shows the element content and chemical formula of the SiON micro-nano fiber membrane in Example 4 of the present invention; Table 4

[0101] Fig.17 are (a) the real part of the dielectric constant, (b) the imaginary part of the dielectric constant and (c) the dielectric loss of the SiON micro-nano fiber membrane in Example 4 of the present invention, from Fig.17 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. Fig.17 It can be seen that the real and imaginary curves of the dielectric constant of the SiON micro-nano fiber membrane in Example 4 in the X-band (frequency band of 8.2-12.4 GHz) are relatively stable, and the values ​​are at a relatively low level, which are 1.27-1.31 and 0.0026-0.013 respectively. Dielectric loss factor tan δ eis the ratio of the real part to the imaginary part of the dielectric constant, which illustrates the material's ability to lose electromagnetic waves. δ e The values ​​range from 0.0020 to 0.0099, all lower than 0.01, indicating good electromagnetic wave transmission performance. The amorphous SiON component and high porosity structure are conducive to its low dielectric and low loss characteristics.

[0102] Fig.18 The thermal imaging characterization results of the SiON micro-nano fiber membrane in Example 4 of the present invention are as follows: (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. Fig.18 It can be seen that in the face of a butane flame spray gun with a flame temperature of about 1300°C, a SiON micro-nano fiber membrane with a thickness of about 1 mm can effectively block the flame and have a cooling and heat insulation effect. The average temperature of the fire-facing surface of the SiON micro-nano fiber membrane in Example 4 is 947.47°C. After heating for 10 minutes, the average temperature of the back-fire surface of the fiber membrane is 332.53°C; after heating for 20 minutes, the average temperature of the back-fire surface of the fiber membrane rises slightly to 344.84°C; after heating for 30 minutes, the average temperature of the back-fire surface of the fiber membrane reaches 353.62°C. It can be seen that the thermal insulation effect of this SiON micro-nano fiber membrane is good and relatively stable. The amorphous SiON phase has a low intrinsic thermal conductivity, and the porous structure formed by the overlap of micro-nano fibers can effectively block heat transfer, which is conducive to enhancing its thermal insulation effect.

[0103] Fig.19 is the microscopic morphology of the SiON micro-nano fiber membrane in Counter Example 1 of the present invention; Fig.19 It can be seen from the scanned photos of Counter-Example 1 that when 1-vinylimidazole is not added, fiber adhesion occurs in the SiON nanofiber membrane obtained by converting the PCS spinning solution, which is manifested in adhesion and adhesion at the cross-over of the fibers, and the fiber separation is weak. This is because the highest temperature in the curing stage is close to the melting point of PCS (about 210~230℃), and a small amount of PCS melts at the intersection of the fibers, resulting in fiber adhesion, forming more solid-phase heat transfer sites and being detrimental to the thermal insulation performance of the fiber membrane. In Example 1, 1-vinylimidazole is added to the spinning solution as a fiber morphology stabilizer, which can complete self-crosslinking and crosslinking with PCS at a temperature lower than the highest curing 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.

[0104] Fig. 20 is the microscopic morphology of the SiON micro-nano fiber membrane in Counter Example 2 of the present invention; Fig. 20It can be seen from the scanning photos of counterexample 2 that when 1-vinylimidazole is not added, there is a serious fiber adhesion problem in the SiON micro-nano fiber membrane obtained by converting the PSN spinning solution. The fibers are completely adhered to each other to form a film and cannot be separated, and no fiber-like porous structure is formed. This is because the PSN precursor is inherently a high-viscosity liquid morphology, and the separable fiber morphology is achieved after the electrospinning process. However, in the curing stage, the maximum curing temperature is higher than the melting point of the PSN precursor (about 130~160℃), and the PSN has melted before reaching the curing temperature, resulting in the loss of fiber morphology and the appearance 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, forming a network structure on the surface and inside of the fiber to maintain the fiber morphology, and crosslinking with PSN to stabilize the structure and state of PSN, inhibit the melting and adhesion of PSN, and realize the preparation of nanofibers with strong separability.

[0105] Table 5 shows the element contents and chemical formula of the SiON micro-nano fiber membrane in Counter Example 3 of the present invention; Table 5

[0106] Table 6 shows the element content and chemical formula of the Si℃N micro-nano fiber membrane in Counter Example 4 of the present invention; Table 6

[0107] Fig.21 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-nano fiber membrane in Counter Example 4 of the present invention; Fig.21 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. Fig.21 It can be seen that the real and imaginary curves of the dielectric constant of the SiON nanofiber membrane in Counterexample 4 in the X-band (frequency band of 8.2~12.4 GHz) are both relatively high, ranging from 3.34 to 3.39 and 0.76 to 0.98 respectively. δ 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. δ e The value is 0.22~0.29, which is much higher than 0.01, indicating that its loss capacity is too strong and does not have the wave transmission effect. This is because the ammonia treatment is carried out in the low temperature section, the reaction activity is low, the nitrogen doping effect is good but the carbon removal effect is weak, and the large amount of carbon phase in the fiber is easy to form conductivity loss and polarization loss, and it is impossible to obtain a low dielectric constant and dielectric loss.

[0108] Table 7 shows the element content and chemical formula of the Si℃ micro-nano fiber membrane in Counter Example 5 of the present invention; Table 7

[0109] Fig. 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-nano fiber membrane in Counter Example 5 of the present invention; Fig. 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. Fig.23 It can be seen that the real and imaginary values ​​of the dielectric constant of the SiON nanofiber membrane in Counterexample 5 in the X-band (frequency band of 8.2~12.4 GHz) are both at a high level, 3.12~3.30 and 1.10~1.61 respectively. δ 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. δ e The value is 0.34~0.51, which is significantly higher than the wave transmission standard of 0.01, indicating that it does not have the electromagnetic wave transmission performance. This is because ammonia is easy to decompose in the high temperature section, and the actual ammonia concentration involved in the reaction is low, but the reaction activity is very high, so its carbon removal effect is significant and the nitrogen doping efficiency is low, which is easy to form a large number of defects and gaps inside the fiber, thereby generating polarization loss under the action of electromagnetic waves, which is not conducive to forming low-dielectric and low-loss wave transmission characteristics.

[0110] Table 8 shows the element contents and chemical formula of the Si℃N micro-nano fiber membrane in Counter Example 6 of the present invention; Table 8

[0111] Fig.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-nano fiber membrane in Counter Example 6 of the present invention; Fig.23 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. Fig.23 It can be seen that the real and imaginary values ​​of the dielectric constant of the SiON micro-nano fiber membrane in Counterexample 6 in the X-band (frequency band of 8.2~12.4 GHz) are both at a low level, 1.32~1.39 and 0.0063~0.073 respectively. δ eis the ratio of the real part to the imaginary part of the dielectric constant, which describes the material's ability to lose electromagnetic waves. δ e The values ​​range from 0.0046 to 0.054, and none of them are lower than 0.01, indicating that its electromagnetic wave transmission performance is weak. This is because without ammonia treatment, the carbon elements carried inside the fiber are difficult to be fully removed, which easily forms polarization loss, making it difficult to further reduce the dielectric constant and dielectric loss factor of the fiber membrane, limiting its wave transmission performance.

[0112] The preparation method of SiON micro-nano fiber membrane involved in the present invention can realize the synthesis of fiber target morphology and components: utilizing the chemical properties of 1-vinyl imidazole, by designing the spinning solution composition of SiON micro-nano fiber membrane, the problem of fiber morphology instability caused by precursor melting during solidification is solved, and continuous fibers with good separation are obtained; utilizing the easy oxidation characteristics of the precursor, by optimizing the oxygen concentration in the solidification stage, the fiber membrane is oxygenated, and a high oxygen content with an increase of about 100% is achieved, which is beneficial to inhibit crystallization and reduce dielectric loss and thermal conductivity; utilizing the reaction activity of ammonia, by comprehensively regulating the ammonia atmosphere and temperature of the heat treatment, efficient carbon removal and nitrogen doping treatment are implemented, forming an ideal amorphous SiON component, and simultaneously gaining the reduction of dielectric loss and thermal conductivity. Combining the above three aspects of process design, the present invention effectively coordinates the goals proposed by the fiber morphology and components for wave transmission and heat insulation requirements, and creatively obtains SiON micro-nano fiber membranes with both wave transmission and heat insulation performance and preparation methods thereof, providing a basis and ideas for the development of integrated film materials with wave transmission and heat insulation functions.

[0113] The present invention describes preferred embodiments and their effects. However, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0114] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A SiON micro-nano fiber membrane with both electromagnetic wave transmission and high temperature insulation, It is 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 oriented; The diameter of the SiON micro-nano fiber is 100 nm to 1.3 μm; The SiON micro-nano fibers contain Si elements >35 at.%, O elements >30 at.%, N elements >12 at.%, and C elements <7 at.%.

2. The SiON micro-nano fiber membrane having both electromagnetic wave transmission and high temperature heat insulation according to claim 1, It is characterized in that The fiber membrane has a thickness of 0.1-1.0 mm, a porosity of 85%-95%, and a density of 50-120 mg / cm 3 .

3. The SiON micro-nano fiber membrane having both electromagnetic wave transmission and high temperature heat insulation properties according to claim 1, It is 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 fiber membrane is synthesized at above 1300° C. and maintained in an amorphous state.

4. The SiON micro-nano fiber membrane having both electromagnetic wave transmission and high temperature heat insulation properties according to claim 1, It is characterized in that The SiON phase ceramic precursor is prepared by dissolving polycarbosilane and / or polysilazane in an organic solvent.

5. A method for preparing the SiON micro-nano fiber membrane having both electromagnetic wave transmission and high temperature heat insulation properties as claimed in any one of claims 1 to 4, It is 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-vinyl imidazole is added to the solvent as a fiber morphology stabilizer; and the mixture is mixed uniformly to obtain 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 outlet rate, a certain DC voltage is applied to the needle and the receiver respectively, spinning is carried out under the action of the electric field, and a precursor micro-nano fiber membrane is obtained 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, and a mixture of nitrogen and oxygen in a certain proportion is introduced at a certain heating rate v 1 Heating to temperature T 1 The holding time is t 1 , then the heating rate v 2 Heating to temperature T 2 The holding time is t 2 , obtaining 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 v 1 5~8℃ / min, v 2 is 1~2℃ / min; the heating temperature T 1 140~160℃, T 2 is 200~220℃; the insulation time t 1 0.5~2 h, t 2 1~3 hours; 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 other temperature sections, and the temperature is raised to T 3 The last holding time is t 3 , at a certain rate v 3 Continue to heat up to temperature T 4 The holding time is t 4 , completing the ceramic transformation of the fiber, and obtaining a SiON micro-nano fiber membrane that has both electromagnetic wave transmission and high-temperature heat insulation; The temperature of the ammoniation temperature section is 200-900°C; the heating rate v 3 is 1~2℃ / min; the heating temperature T 3 800~900℃, T 4 is 1300~1500℃; the holding time t 3 0.5~2 h, t 4 1~3 hours.

6. The method for preparing the SiON micro-nano fiber membrane having both electromagnetic wave transmission and high temperature heat insulation properties according to claim 5, It is characterized in that When 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 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.

7. The method for preparing the SiON micro-nano fiber membrane having both electromagnetic wave transmission and high temperature heat insulation properties according to claim 5, It is characterized in that In the process of preparing precursor micro-nano fiber membrane, the inner diameter of the spinning needle is 0.3~0.6 mm; the liquid output rate is 20~50 µL / min; the collection distance between the needle and the receiver is 14~22 cm; the DC voltage includes: DC positive voltage is 16~24 kV, and negative voltage is -2~4 kV.

8. The method for preparing the SiON micro-nano fiber membrane having both electromagnetic wave transmission and high temperature heat insulation properties according to claim 5, It is characterized in that When the receiver is a flat plate, the precursor micro-nano fiber membrane obtained is a fiber membrane with disordered distribution, and when the receiver is a roller, the precursor micro-nano fiber membrane obtained is a fiber membrane with directional distribution.

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

1.

10. Use of the SiON micro-nano fiber membrane according to any one of claims 1 to 4 in wave transmission and heat insulation.

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