A porous nanofiber-based elastic ceramic flake, a preparation method and application thereof

Abstract

This invention relates to a porous nanofiber-based elastic ceramic floc and its preparation method and application. The method includes the following steps: S1, preparing the spinning solution: adding a ligand with a multidentate phosphoryl group at one end and a phosphonic acid group at the other end to one or more metal alkoxide monomers for preliminary coordination; preparing a gradient inert ligand solution to obtain the coordination-modified metal alkoxide monomer, obtaining a linear inorganic long-chain solution with high polymerization degree, and obtaining the spinning solution; S2, crimping the fiber: passing the spinning solution into a high-speed jet nozzle to solidify the whipping jet, obtaining the precursor crimped nanofibers; S3, three-dimensional dynamic assembly; S4, pressure stabilization and shaping; S5, pore formation and ceramization: performing deep ultraviolet pretreatment, calcining in an oxygen-deficient atmosphere, and obtaining porous nanofiber-based elastic ceramic flocs. Compared with the prior art, this invention has advantages such as excellent compression resilience, high porosity, excellent heat insulation and sound absorption properties, controllability of structure and performance, and high tensile strength.

Description

Technical Field

[0001] This invention relates to the field of nanofiber materials technology, and in particular to a porous nanofiber-based elastic ceramic flocculent, its preparation method, and its application. Background Technology

[0002] Ceramic nanofibers, with their excellent high-temperature resistance, chemical stability, and low thermal conductivity, have become key materials in cutting-edge fields such as aerospace thermal protection systems, high-temperature gas filtration, and flexible electronic devices. With the rapid development of hypersonic vehicles and thermal management technologies for complex operating conditions, applications have placed extremely stringent dual requirements on ceramic fiber materials: on the one hand, it is necessary to further reduce thermal conductivity and density by constructing micro-nano porous structures within the fibers; on the other hand, it is even more urgent to require that the materials maintain structural integrity and excellent macroscopic resilience under dynamic mechanical environments such as high-frequency vibration, large-strain tension, and repeated compression, thereby completely solving the inherent brittleness bottleneck of traditional porous ceramic materials, which are characterized by "collapse under pressure and break under bending."

[0003] However, existing technologies have consistently struggled to prepare materials that balance "microscopic porous structure" and "macroscopic aggregate mechanics." Firstly, regarding the contradiction between pore-forming processes and matrix brittleness, while patents ZL201010237944.2 and CN201010162738.X successfully prepared porous fibers using precipitation-grading principles and microemulsion methods to introduce pore-forming agents, their precursor designs remain confined to traditional rigid sol-gel network systems. This rigid framework lacks flexibility and cannot buffer the massive volume shrinkage and thermal stress concentration caused by organic phase decomposition during subsequent high-temperature calcination to remove the template / pore-forming agent. This easily leads to the collapse of the originally constructed pores or cracking on the fiber surface, severely weakening the intrinsic strength of individual fibers. Secondly, the fibers constructed in these two patents are all straight fibers, lacking geometric curls and physical connections similar to springs. They are prone to irreversible slippage and densification under compressive loads, preventing the material from returning to its original state and causing a sharp decline in its performance. In addition, Nat. Commun. 2022, 13, 2637 prepared elastic ceramic nanofiber flocs using reactive electrospinning technology. However, the single fiber has a dense structure, and the reactive window of sol spinning in this technology is extremely difficult to control, making it difficult to achieve large-scale, low-cost industrial preparation and failing to meet the needs of engineering applications. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of the prior art by providing a porous nanofiber-based elastic ceramic floc and its preparation method and application, which has excellent compression resilience, high porosity and excellent heat insulation and sound absorption properties, controllability of structure and performance, high tensile strength, wide applicability and functionality.

[0005] The objective of this invention can be achieved through the following technical solutions: This invention provides a method for preparing porous nanofiber-based elastic ceramic flocs, comprising the following steps: S1. Preparation of spinning solution: A ligand with a multidentate phosphoryl group at one end and a phosphonic acid group at the other end is added to one or more metal alkoxide monomers for initial coordination; then, weakly inert, moderately inert, and strongly inert ligands are prepared into a gradient inert ligand solution. Based on the difference in electronegativity or electronegativity, the strongly inert ligand preferentially coordinates with the highly active metal alkoxide, aligning with the hydrolysis rate of the metal alkoxide monomer, to obtain a fully coordinated modified metal alkoxide monomer; then, hydrolysis-condensation, chain extension, and end-capping reactions are carried out to obtain a linear inorganic long-chain solution with a high degree of polymerization; finally, an alcohol solvent and a pore-forming binder are added to obtain the spinning solution; S2, Crimped Fiber Forming: The spinning solution obtained in S1 is passed into a high-speed jet nozzle, and a coupled force field of electrostatic field and airflow field is applied to make the spinning solution form a whipping jet; at the same time, a micro airflow with set parameters is delivered to the whipping zone of the jet using a micro-region air supply device to rapidly solidify the whipping jet and obtain the precursor crimped nanofiber. S3, Three-dimensional dynamic assembly: Controlling the relative movement between the spinneret and the conveyor belt, the precursor crimped nanofibers obtained in S2 are dynamically interwoven in three dimensions in the air and assembled into fluffy precursor crimped nanofiber flakes. S4, Pressure Stabilization and Shaping: The precursor crimped nanofiber flakes obtained in S3 are fed into the pressure stabilization and shaping device, and pressure stabilization and shaping are performed by applying a gradient pressure with a small pressure difference through the gradient pressure roller group inside the pressure stabilization and shaping device. S5. Pore Formation and Ceramization: The flocs after S4 shaping are subjected to deep ultraviolet pretreatment to remove organic components in the fibers to form a porous structure; then, they are calcined in an oxygen-deficient atmosphere to obtain porous nanofiber-based elastic ceramic flocs. The micro-area air supply device includes a mixing chamber, a buffer chamber, a transition chamber, and a grid chamber arranged sequentially from top to bottom. The mixing chamber has at least one mixing compartment at its upper part and at least three tangential air inlets at its top for supplying gases of different temperatures and humidity levels. A first horizontal air outlet is provided on its side wall. A primary air supply plate is provided between the mixing chamber and the buffer chamber, with multiple through-flow primary air supply channels inside. A buffer compartment is provided inside the buffer chamber, with a second horizontal air outlet on its side wall. Secondary and tertiary air supply plates are respectively provided between the buffer chamber and the transition chamber, and between the transition chamber and the grid chamber. Multiple through-flow secondary and tertiary air supply channels are provided inside the secondary and tertiary air supply plates, respectively. The number of primary, secondary, and tertiary air supply channels increases progressively and they are arranged in a fractal pattern, ensuring that the gas is delivered into the whipping area at a slow and uniform speed. An adjustable grid plate is provided at the bottom of the grid chamber.

[0006] Furthermore, the ligand having a multidentate phosphoryl group at one end and a phosphonic acid group at the other end is selected from one or more combinations of 11-phosphono-1,1,1-tris(dimethoxyphosphonomethyl)undecane, 11-(bis(2-(dimethoxyphosphonooxy)ethyl)amino)-undecylphosphonic acid, 1,1-bis(dimethoxyphosphonomethyl)-1-(8-phosphonooctyl)propane, bis(dimethoxyphosphonomethyl)-(8-phosphonooctyl)phosphine oxide, and N,N-bis(2-(dimethoxyphosphono)ethyl)-11-phosphonoundecaneamide.

[0007] Furthermore, the metal alkoxide is selected from one or more of the following: zirconium tetraethanolamine, zirconium tetramethanol, zirconium isopropoxide, zirconium n-propoxide, zirconium isobutoxide, zirconium tert-butoxide, zirconium n-butoxide, zirconium tetrapentoxide, titanium tetraethanolamine, titanium isobutoxide, titanium n-propoxide, titanium n-butoxide, titanium tetraethanolamine, titanium tert-butoxide, titanium isooctanol, titanium tetrapentoxide, titanium isopropoxide, tin n-propoxide, tin n-butoxide, tin tetraethanolamine, tin tert-butoxide, tin tetraethanolamine, tin isobutoxide, tin isopropoxide, aluminum n-butoxide, aluminum trimethoxy, aluminum tri-n-propoxy, aluminum isopropoxide, aluminum sec-butoxide, aluminum triethanolamine, aluminum tert-butoxide, indium isopropoxide, indium triethoxy, indium tert-butoxide, gallium isopropoxide, gallium tert-butoxide, hafnium isopropoxide, hafnium n-butoxide, tantalum isopropoxide, tantalum n-butoxide, niobium isopropoxide, and niobium n-butoxide. The three ligands with different inertness are weakly inert ligands, moderately inert ligands, and strongly inert ligands; the weakly inert ligands are selected from one or more combinations of diethyl ether, acetone, 1,4-dioxane, tetrahydrofuran, and butanone; the moderately inert ligands are selected from one or more combinations of formic acid, acetic acid, propionic acid, isobutyric acid, butyric acid, butyl acetate, ethyl acetate, methyl methacrylate, methylamine, cyclohexanone, ethylamine, isopropylamine, n-propylamine, and methylcyclohexanone; the strongly inert ligands are selected from one or more combinations of acetylacetone, hexafluoroacetylacetone, benzoylacetone, trifluoroacetylacetone, methyl acetoacetate, diethanolamine, tert-butyl acetoacetate, ethyl acetoacetate, and triethanolamine. The alcohol solvent is one or a combination of several of methanol, n-propanol, glycerol, n-pentanol, tert-butanol, isopropanol, sec-butanol, n-butanol, butanediol, hexanediol, ethylene glycol, or ethanol; the pore-forming binder is one or a combination of several of n-octyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, bis(dodecyl)dimethylammonium bromide, decaalkyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, eicosyltrimethylammonium bromide, octadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, (2-hydroxyethyl)hexadecyldimethylammonium bromide, cocamidopropyl betaine, and 1-hexadecyl-3-methylimidazolium bromide.

[0008] Furthermore, the high-speed jet nozzle in S2 is a coaxial nozzle. The inner channel is used to supply the spinning solution, and the outer channel is used to apply a high-speed airflow. The outer wall of the inner channel outlet has an annular guide surface, and the outer diameter increases and then decreases along the nozzle axis from the inside to the outside. The wall diameter of the outer channel outlet gradually decreases and remains parallel to the decreasing outer diameter portion of the annular guide surface. Therefore, the outer channel is an annular channel with gradually decreasing thickness, and the angle of the channel outlet is parallel to the outer surface of the Taylor cone. This not only gradually transforms the supplied gas into a thin airflow but also allows the airflow to tangentially drive the Taylor cone, causing it to be jetted at high speed in the stable region and rapidly dissipated in the whipping region. The inner diameter of the inner channel is 0.25~1.40mm, and the inner diameter of the outer channel is 0.33~1.55mm.

[0009] Furthermore, the spinneret includes two types: one is a single-row spinneret with the nozzle direction vertical, and the other is a double-row spinneret with two rows of nozzles symmetrically and inclined; the spinneret reciprocates at a speed of 0.1~1.5 m / min in a direction perpendicular to the conveyor belt, and the conveyor belt moves forward at a speed of 0.1~20 m / min; the nozzle angle of the single-row spinneret is defined as 0°, and the angle of the double-row spinneret is 10~70°.

[0010] Furthermore, the crimped nanofibers prepared by the single-row spinneret and the crimped nanofibers prepared by the double-row spinneret will interweave in three dimensions in the air; in addition, the spinneret moves cyclically in a direction perpendicular to the conveyor belt, and the conveyor belt moves forward at a specific speed. With the cooperation of the two, the three-dimensionally interwoven crimped nanofibers will dynamically assemble to form precursor crimped nanofiber flakes.

[0011] Furthermore, the ultraviolet light bands for the deep ultraviolet pretreatment described in S5 are 185nm and 254nm, and the power is 40~350W / dm. 2 The calcination process includes pulsed microwave treatment and oxygen-deficient heating treatment. The pulsed microwave power is 10~500 kW, the pulse width is 0.1~5 s, and the pulse interval is 0.1~0.5 Hz. The oxygen concentration in the oxygen-deficient atmosphere is ≤15%, and the heating temperature is 400~1500 ℃. The deep ultraviolet pretreatment device can treat oxygen and water in the air into highly reactive hydroxyl radicals. This substance can efficiently remove organic components from the fiber, not only efficiently removing organic ligands but also forming a porous structure inside the fiber.

[0012] During pulsed microwave treatment, the fibers are rapidly and uniformly heated under high-energy pulsed microwaves, causing the amorphous phase structure to quickly transform into a large number of uniformly sized nucleation sites. Under the subsequent oxygen-deficient atmosphere, the growth of a large number of crystal nuclei is inhibited, ultimately resulting in the preparation of small-grained, multi-grain-bound crystal structures. Moreover, these treatments also prevent excessive crystal growth and avoid burying the fiber's internal pore structure, thus obtaining porous, crimped fiber-composed elastic ceramic nanofiber flocs.

[0013] Furthermore, the micro-airflow delivered by the micro-area air supply device is a normal temperature dry, normal temperature high humidity, high temperature dry, or high temperature high humidity airflow, with a wind speed of 0.1~3 m / s; wherein, the normal temperature is 20~27℃, the high temperature is 30~45℃, the dry humidity is 20~30%, and the high humidity is 60~90%.

[0014] Furthermore, the mixing chamber of the micro-area air supply device has a spherical structure, and three air inlets are provided on the upper part of the inner wall of the mixing chamber, namely, a normal temperature drying air inlet, a normal temperature high humidity air inlet, and a high temperature drying air inlet; when the airflow is delivered to the mixing chamber from the air inlet, the airflow will fly along the spherical wall and collide to form turbulence, thereby accelerating the mixing of different airflows; the mixed airflow will overflow from the horizontally set first air outlet, the overflow direction is perpendicular to the first-stage air supply channel, and the gas will collide perpendicularly with the side baffle of the mixing chamber, thus reducing the airflow velocity for the first time; the number of the mixing chambers is set to 2 to 4, and the first air outlet of a single mixing chamber is set to 2 to 4; After the blended gas fills the blending chamber, it enters the buffer chamber from the primary air supply channel and impacts the bottom partition of the buffer chamber vertically, reducing the airflow velocity for the second time. When the blended gas fills the buffer chamber, it overflows from the horizontally set second air outlet and impacts the side wall of the buffer chamber vertically, reducing the airflow velocity for the third time. The number of buffer chambers is set to 4 to 8, and the number of second air outlets is set to 2 to 4. The air supply ducts of the primary, secondary, and tertiary air supply channels increase progressively, which can subdivide the airflow into densely and evenly distributed micro-airflows. The number of primary air supply channels is set to 4 to 8, the number of secondary air supply channels is set to 16 to 64, and the number of tertiary air supply channels is set to 256 to 1024. The micro-airflow is delivered to the grid cavity from the three-stage air supply channel, and the gas direction can be controlled by adjusting the grid plate; the adjustment angle of the grid plate is -60~60° (the vertical direction is set to 0°).

[0015] Furthermore, the gradient pressure roller group in the pressure stabilizing and shaping device is equipped with a pressure sensing layer inside, which is used to provide real-time feedback on the pressure changes of the flakes, and dynamically adjust the applied pressure of the rollers through the pressure control component; the skin material of the rollers is selected from perfluoroalkoxy resin, polytetrafluoroethylene, silicone rubber, fluorinated ethylene propylene copolymer or fluororubber; the applied pressure is 0.01~1MPa, and the pressure difference is 0.05~0.2MPa.

[0016] This invention also provides a porous nanofiber-based elastic ceramic floc, prepared by the above-described method. The building blocks of the floc are porous, coiled ceramic nanofibers, with a single fiber having a diameter of 50-800 nm, a coiling rate of not less than 28%, a radius of curvature of 1-9 μm, a pore size of 0.5-50 nm, and a pore volume of 0.1-1 cm³. 3 / g, specific surface area of ​​100~1500 m² 2 / g.

[0017] Furthermore, the thickness of the floc is 5~110 mm, the thickness CV value is less than 5%, the porosity is not less than 98.5%, the tensile strength reaches more than 2.8 MPa, the compressive elastic recovery rate is not less than 96%, the thermal conductivity is not higher than 0.029 W / (m·K), and the noise reduction coefficient is greater than 0.7.

[0018] This invention also provides an application of porous nanofiber-based elastic ceramic flocs, in which the elastic ceramic flocs described in claim 8 or 9 are applied to aerospace thermal protection and noise reduction systems, battery thermal runaway barrier components, insulating fireproof and sound-absorbing noise reduction layers, personal protective equipment thermal insulation layers, flame-retardant energy-saving insulation and safety protection layers, industrial adsorption fillers, catalyst carriers, or gas sensor sensing elements.

[0019] The technical principle of this invention is as follows: (1) Mechanism of preparing the coiled structure in this invention: In the process of synthesizing linear inorganic molecular chains, a series of inert ligands are introduced to replace metal alkoxides, transforming these ligands into organic side groups of the molecular chains. The hydrophilic and hydrophobic properties of these side groups directly regulate the physicochemical properties of the spinning solution. Based on this, this invention prepares the target spinning solution by screening inert ligands with specific properties, and uses a micro-area air supply device to apply a micro-airflow with matching characteristics to achieve rapid solidification of the jet coiled structure. For example, when hydrophobic inert ligands are introduced, the spinning solution tends to undergo phase separation with the aqueous phase. At this time, applying a high-humidity micro-airflow can significantly promote the phase separation kinetics of the jet, thereby accelerating the shaping and solidification of the coiled structure.

[0020] (2) Mechanism of the preparation of porous structure in this invention: Active hydroxyl radicals are prepared by using 185nm and 254nm dual-band ultraviolet light, and based on the bond energy difference between metal-oxygen bonds and organic bonds, organic side groups and pore-forming binders on inorganic long chains are precisely removed, while the inorganic main chain skeleton is completely preserved and a porous structure is created inside the fiber; Subsequently, microwave treatment in the oxygen-rich stage enables rapid and uniform nucleation in the precursor fiber; In the subsequent oxygen-deficient calcination stage, the low oxygen partial pressure environment induces a large number of oxygen vacancies in the inorganic lattice, which significantly reduces the grain boundary migration rate and inhibits grain coarsening from a kinetic perspective; At the same time, the restricted lattice diffusion behavior hinders the filling of material into the porous structure region, so that the ultraviolet-induced nanopores can be stably preserved. Finally, an elastic ceramic fiber composed of small grains, multiple grain boundaries and porous structure is successfully constructed.

[0021] Compared with the prior art, the present invention has the following advantages: (1) Excellent compression and rebound performance: The compression and rebound rate of the prepared elastic ceramic nanofiber flocs is not less than 96%, and it can still be repeatedly compressed and rebounded even at a high temperature of 1300℃, which effectively solves the intrinsic brittleness bottleneck of traditional porous ceramic materials.

[0022] (2) High porosity and excellent thermal insulation and sound absorption performance: The building blocks of this floc are porous, coiled nanofibers, resulting in a final floc porosity of no less than 98.5%, a thermal conductivity of no more than 0.029 W / m·K, and a noise reduction coefficient of more than 0.7. This high porosity structure significantly enhances the thermal insulation and sound absorption performance of the material.

[0023] (3) Controllability of structure and performance: The structure and performance of materials can be precisely controlled. For example, the thickness of the floc can be precisely controlled within the range of 5~110mm and the thickness uniformity is high (CV value less than 5%); the morphological parameters of single fibers such as diameter, crimp rate, pore size, and specific surface area can also be controlled within a certain range through process parameters, thereby meeting different application requirements.

[0024] (4) High tensile strength: Compared with traditional brittle porous ceramics, the flocs prepared by this invention have excellent mechanical properties, with a tensile strength of more than 2.8 MPa, which enables them to maintain structural integrity under dynamic mechanical environment.

[0025] (5) Wide applicability and functionality: It is suitable for preparing elastic ceramic nanofibers of various systems such as zirconium, titanium, aluminum, and silicon. In addition, the obtained porous nanofiber materials can be used as "white activated carbon" for adsorption, catalysis, filtration and other fields, and can be regenerated and reused through calcination.

[0026] By introducing ligands with a multidentate phosphoryl group at one end and a phosphonic acid group at the other end, and a gradient inert ligand solution, a highly polymerized linear inorganic long chain was prepared, providing a flexible precursor basis for the formation of nanofibers with a coiled structure.

[0027] By utilizing a micro-area air supply device, a micro-airflow with specific temperature and humidity parameters is uniformly and slowly delivered to the spinning zone through multi-level buffering and fractal distribution channels, thereby precisely controlling the jet curing process and stably obtaining precursor fibers with a crimped structure.

[0028] By using spinnerets arranged in different ways (vertical and symmetrically tilted) and controlling the combined movement of the spinnerets and the conveyor belt, the dynamic three-dimensional interlacing and assembly of crimped fibers in the air was achieved, forming a fluffy floc structure.

[0029] A pressure-stabilizing and shaping device with pressure sensing and feedback control system is used to apply a gradient pressure with a small pressure difference to the fluffy flakes, so as to avoid the collapse or breakage of the structure during the compaction process, thus achieving gentle and stable shaping.

[0030] Deep ultraviolet pretreatment utilizes the generated hydroxyl radicals to efficiently and selectively remove organic components from the fibers, forming a porous structure within the fibers. Subsequent calcination under the synergistic effect of pulsed microwaves and an oxygen-deficient atmosphere rapidly forms a large number of fine, uniform crystal nuclei and inhibits their excessive growth, ultimately yielding elastic ceramic fibers with small grains, multiple grain boundaries, and a retained porous structure, achieving both "porosity" and "elasticity." Attached Figure Description

[0031] Figure 1 A schematic diagram of a micro-area air supply device; Figure 2 This is a schematic diagram of the spinning area; Figure 3 This is a schematic diagram of a voltage stabilizing and shaping device; Figure 4 Image of elastic ceramic coiled nanofiber flocs.

[0032] Figure reference numerals: 1 is a micro-area air supply device; 1-1 is a mixing chamber; 1-1-1 is a mixing bin; 1-1-11 is a normal temperature dry air inlet; 1-1-12 is a normal temperature high humidity air inlet; 1-1-13 is a high temperature dry air inlet; 1-1-14 is a first air outlet; 1-2 is a buffer chamber; 1-2-1 is a buffer bin; 1-2-11 is a second air outlet; 1-3 is a transition chamber; 1-4 is a grid chamber; 1- 4-1 is a grating plate; 1-5 is a primary air supply plate; 1-5-1 is a primary air supply channel; 1-6 is a secondary air supply plate; 1-6-1 is a secondary air supply channel; 1-7 is a tertiary air supply plate; 1-7-1 is a tertiary air supply channel; 2-1 is a single-row spinneret; 2-2 is a double-row spinneret; 3 is a conveyor belt; 4 is a pressure stabilizing and shaping device; 4-1 is a gradient pressure roller group; 4-2 is a pressure sensing layer; 4-3 is a pressure control component. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0034] Example 1 This embodiment provides a method for preparing porous nanofiber-based elastic ceramic flocs, such as... Figure 1-4 As shown, it includes the following steps: S1. Preparation of spinning solution: A ligand with a multidentate phosphoryl group at one end and a phosphonic acid group at the other end is added to one or more metal alkoxide monomers for initial coordination; then, weakly inert, moderately inert, and strongly inert ligands are prepared into a gradient inert ligand solution. Based on the difference in electronegativity or electronegativity, the strongly inert ligand preferentially coordinates with the highly active metal alkoxide, aligning with the hydrolysis rate of the metal alkoxide monomer, to obtain a fully coordinated modified metal alkoxide monomer; then, hydrolysis-condensation, chain extension, and end-capping reactions are carried out to obtain a linear inorganic long-chain solution with a high degree of polymerization; finally, an alcohol solvent and a pore-forming binder are added to obtain the spinning solution; S2, Crimped Fiber Forming: The spinning solution obtained in S1 is passed into a high-speed jet nozzle, and a coupled force field of electrostatic field and airflow field is applied to make the spinning solution form a whipping jet; at the same time, a micro airflow with set parameters is delivered to the whipping jet area by a micro-region air supply device 1 to rapidly solidify the whipping jet and obtain the precursor crimped nanofiber. S3, Three-dimensional dynamic assembly: Controlling the relative movement between the spinneret and the conveyor belt 3, the precursor coiled nanofibers obtained in S2 are dynamically interwoven in three dimensions in the air and assembled into fluffy precursor coiled nanofiber flakes. S4, Pressure Stabilization and Shaping: The precursor crimped nanofiber flakes obtained in S3 are fed into the pressure stabilization and shaping device 4. The gradient pressure with a small pressure difference is applied by the gradient pressure roller group 4-1 inside the pressure stabilization and shaping device 4 to perform pressure stabilization and shaping. S5. Pore Formation and Ceramization: The flocs after S4 shaping are subjected to deep ultraviolet pretreatment to remove organic components in the fibers to form a porous structure; then, they are calcined in an oxygen-deficient atmosphere to obtain porous nanofiber-based elastic ceramic flocs. The micro-area air supply device 1 includes a mixing chamber 1-1, a buffer chamber 1-2, a transition chamber 1-3, and a grid chamber 1-4 arranged sequentially from top to bottom. The mixing chamber 1-1 has at least one mixing compartment 1-1-1 at its upper part, and at least three tangential air inlets at its top for supplying gases of different temperatures and humidity levels. A first horizontal air outlet 1-1-14 is provided on its side wall. A primary air supply plate 1-5 is provided between the mixing chamber 1-1 and the buffer chamber 1-2, and the primary air supply plate 1-5 has multiple through-flow primary air supply channels 1-5-1 inside. The buffer chamber 1-2 has a buffer compartment 1-2-1 inside, and the side wall of the buffer compartment 1-2-1 has a first horizontal air outlet 1-1-14. Two horizontal air outlets 1-2-11; a secondary air supply plate 1-6 and a tertiary air supply plate 1-7 are respectively provided between the buffer cavity 1-2 and the transition cavity 1-3, and between the transition cavity 1-3 and the grid cavity 1-4. The secondary air supply plate 1-6 and the tertiary air supply plate 1-7 are respectively provided with multiple through secondary air supply channels 1-6-1 and tertiary air supply channels 1-7-1; the number of primary air supply channels 1-5-1, secondary air supply channels 1-6-1 and tertiary air supply channels 1-7-1 increases progressively and is arranged in a fractal pattern, which can ensure that the gas is delivered into the whipping area at a slow speed and evenly. The bottom of the grid cavity 1-4 is provided with an angle-adjustable grid plate 1-4-1.

[0035] This embodiment also provides a porous nanofiber-based elastic ceramic floc, prepared by the above-described method. The building blocks of the floc are porous, coiled ceramic nanofibers. The diameter of a single fiber is 50–800 nm, the coiling rate is not less than 28%, the radius of curvature is 1–9 μm, the pore size is 0.5–50 nm, and the pore volume is 0.1–1 cm³. 3 / g, specific surface area of ​​100~1500 m² 2 / g.

[0036] Example 2 This embodiment provides a method for preparing porous nanofiber-based elastic ceramic flocs, such as... Figure 1-4 As shown, it includes the following steps: S1. Preparation of spinning solution: A ligand with a multidentate phosphoryl group at one end and a phosphonic acid group at the other end is added to one or more metal alkoxide monomers for initial coordination; then, weakly inert, moderately inert, and strongly inert ligands are prepared into a gradient inert ligand solution. Based on the difference in electronegativity or electronegativity, the strongly inert ligand preferentially coordinates with the highly active metal alkoxide, aligning with the hydrolysis rate of the metal alkoxide monomer, to obtain a fully coordinated modified metal alkoxide monomer; then, hydrolysis-condensation, chain extension, and end-capping reactions are carried out to obtain a linear inorganic long-chain solution with a high degree of polymerization; finally, an alcohol solvent and a pore-forming binder are added to obtain the spinning solution; S2, Crimped Fiber Forming: The spinning solution obtained in S1 is passed into a high-speed jet nozzle, and a coupled force field of electrostatic field and airflow field is applied to make the spinning solution form a whipping jet; at the same time, a micro airflow with set parameters is delivered to the whipping jet area by a micro-region air supply device 1 to rapidly solidify the whipping jet and obtain the precursor crimped nanofiber. S3, Three-dimensional dynamic assembly: Controlling the relative movement between the spinneret and the conveyor belt 3, the precursor coiled nanofibers obtained in S2 are dynamically interwoven in three dimensions in the air and assembled into fluffy precursor coiled nanofiber flakes. S4, Pressure Stabilization and Shaping: The precursor crimped nanofiber flakes obtained in S3 are fed into the pressure stabilization and shaping device 4. The gradient pressure with a small pressure difference is applied by the gradient pressure roller group 4-1 inside the pressure stabilization and shaping device 4 to perform pressure stabilization and shaping. S5. Pore Formation and Ceramization: The flocs after S4 shaping are subjected to deep ultraviolet pretreatment to remove organic components in the fibers to form a porous structure; then, they are calcined in an oxygen-deficient atmosphere to obtain porous nanofiber-based elastic ceramic flocs. The micro-area air supply device 1 includes a mixing chamber 1-1, a buffer chamber 1-2, a transition chamber 1-3, and a grid chamber 1-4 arranged sequentially from top to bottom. The mixing chamber 1-1 has at least one mixing compartment 1-1-1 at its upper part, and at least three tangential air inlets at its top for supplying gases of different temperatures and humidity levels. A first horizontal air outlet 1-1-14 is provided on its side wall. A primary air supply plate 1-5 is provided between the mixing chamber 1-1 and the buffer chamber 1-2, and the primary air supply plate 1-5 has multiple through-flow primary air supply channels 1-5-1 inside. The buffer chamber 1-2 has a buffer compartment 1-2-1 inside, and the side wall of the buffer compartment 1-2-1 has a first horizontal air outlet 1-1-14. Two horizontal air outlets 1-2-11; a secondary air supply plate 1-6 and a tertiary air supply plate 1-7 are respectively provided between the buffer cavity 1-2 and the transition cavity 1-3, and between the transition cavity 1-3 and the grid cavity 1-4. The secondary air supply plate 1-6 and the tertiary air supply plate 1-7 are respectively provided with multiple through secondary air supply channels 1-6-1 and tertiary air supply channels 1-7-1; the number of primary air supply channels 1-5-1, secondary air supply channels 1-6-1 and tertiary air supply channels 1-7-1 increases progressively and is arranged in a fractal pattern, which can ensure that the gas is delivered into the whipping area at a slow speed and evenly. The bottom of the grid cavity 1-4 is provided with an angle-adjustable grid plate 1-4-1.

[0037] In a specific embodiment, the ligand having a multidentate phosphoryl group at one end and a phosphonic acid group at the other end is selected from one or more combinations of 11-phosphono-1,1,1-tris(dimethoxyphosphonomethyl)undecane, 11-(bis(2-(dimethoxyphosphonooxy)ethyl)amino)undecylphosphonic acid, 1,1-bis(dimethoxyphosphonomethyl)-1-(8-phosphonooctyl)propane, bis(dimethoxyphosphonomethyl)-(8-phosphonooctyl)phosphine oxide, and N,N-bis(2-(dimethoxyphosphono)ethyl)-11-phosphonoundecaneamide.

[0038] In a specific embodiment, the metal alkoxide is selected from one or more of the following: zirconium tetraethanolamine, zirconium tetramethanol, zirconium isopropoxide, zirconium n-propoxide, zirconium isobutoxide, zirconium tert-butoxide, zirconium n-butoxide, zirconium tetrapentoxide, titanium tetraethanolamine, titanium isobutoxide, titanium n-propoxide, titanium n-butoxide, titanium tetraethanolamine, titanium tert-butoxide, titanium isooctanol, titanium tetrapentoxide, titanium isopropoxide, tin n-propoxide, tin n-butoxide, tin tetraethanolamine, tin tert-butoxide, tin tetraethanolamine, tin isobutoxide, tin isopropoxide, aluminum n-butoxide, aluminum trimethoxy, aluminum tri-n-propoxy, aluminum isopropoxide, aluminum sec-butoxide, aluminum triethanolamine, aluminum tert-butoxide, indium isopropoxide, indium triethoxy, indium tert-butoxide, gallium isopropoxide, gallium tert-butoxide, hafnium isopropoxide, hafnium n-butoxide, tantalum isopropoxide, tantalum n-butoxide, niobium isopropoxide, and niobium n-butoxide. The three ligands with different inertness are weakly inert ligands, moderately inert ligands, and strongly inert ligands; the weakly inert ligands are selected from one or more combinations of diethyl ether, acetone, 1,4-dioxane, tetrahydrofuran, and butanone; the moderately inert ligands are selected from one or more combinations of formic acid, acetic acid, propionic acid, isobutyric acid, butyric acid, butyl acetate, ethyl acetate, methyl methacrylate, methylamine, cyclohexanone, ethylamine, isopropylamine, n-propylamine, and methylcyclohexanone; the strongly inert ligands are selected from one or more combinations of acetylacetone, hexafluoroacetylacetone, benzoylacetone, trifluoroacetylacetone, methyl acetoacetate, diethanolamine, tert-butyl acetoacetate, ethyl acetoacetate, and triethanolamine. The alcohol solvent is one or a combination of several of methanol, n-propanol, glycerol, n-pentanol, tert-butanol, isopropanol, sec-butanol, n-butanol, butanediol, hexanediol, ethylene glycol, or ethanol; the pore-forming binder is one or a combination of several of n-octyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, bis(dodecyl)dimethylammonium bromide, decaalkyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, eicosyltrimethylammonium bromide, octadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, (2-hydroxyethyl)hexadecyldimethylammonium bromide, cocamidopropyl betaine, and 1-hexadecyl-3-methylimidazolium bromide.

[0039] In a specific embodiment, the high-speed jet nozzle in S2 is a coaxial nozzle. The inner channel is used to supply the spinning solution, and the outer channel is used to apply a high-speed airflow. The outer wall of the inner channel outlet is provided with an annular guide surface, and the outer diameter increases and then decreases along the nozzle axis from the inside to the outside. The wall diameter of the outer channel outlet gradually decreases and remains parallel to the decreasing outer diameter portion of the annular guide surface. Therefore, the outer channel is an annular channel with gradually decreasing thickness, and the angle of the channel outlet is parallel to the outer surface of the Taylor cone. This not only gradually transforms the supplied gas into a thin airflow, but also allows the airflow to tangentially drive the Taylor cone, causing it to be jetted at high speed in the stable region and rapidly dissipated in the whipping region. The inner diameter of the inner channel is 0.25~1.40mm, and the inner diameter of the outer channel is 0.33~1.55mm.

[0040] In a specific embodiment, the spinneret includes two types: one is a single-row spinneret 2-1 with the nozzle direction vertical, and the other is a double-row spinneret 2-2 with two rows of nozzles symmetrically and obliquely arranged; the spinneret reciprocates in a direction perpendicular to the conveyor belt 3 at a speed of 0.1~1.5 m / min, and the conveyor belt 3 moves forward at a speed of 0.1~20 m / min; the nozzle angle of the single-row spinneret 2-1 is defined as 0°, and the angle of the double-row spinneret 2-2 is 10~70°.

[0041] In a specific embodiment, the crimped nanofibers prepared by the single-row spinneret 2-1 and the crimped nanofibers prepared by the double-row spinneret 2-2 will interweave in three dimensions in the air; in addition, the spinneret moves cyclically in a direction perpendicular to the conveyor belt, and the conveyor belt moves forward at a specific speed. With the cooperation of the two, the three-dimensionally interwoven crimped nanofibers will be dynamically assembled to form precursor crimped nanofiber flakes.

[0042] In a specific implementation, the deep ultraviolet pretreatment in S5 uses ultraviolet light bands of 185nm and 254nm, with a power of 40~350 W / dm. 2 The calcination process includes pulsed microwave treatment and oxygen-deficient heating treatment. The pulsed microwave power is 10~500kW, the pulse width is 0.1~5s, and the pulse interval is 0.1~0.5Hz. The oxygen concentration in the oxygen-deficient atmosphere is ≤15%, and the heating temperature is 400~1500℃. The deep ultraviolet pretreatment device can treat oxygen and water in the air into highly reactive hydroxyl radicals. This substance can efficiently remove organic components from the fiber, not only efficiently removing organic ligands but also forming a porous structure inside the fiber.

[0043] During pulsed microwave treatment, the fibers are rapidly and uniformly heated under high-energy pulsed microwaves, causing the amorphous phase structure to quickly transform into a large number of uniformly sized nucleation sites. Under the subsequent oxygen-deficient atmosphere, the growth of a large number of crystal nuclei is inhibited, ultimately resulting in the preparation of small-grained, multi-grain-bound crystal structures. Moreover, these treatments also prevent excessive crystal growth and avoid burying the fiber's internal pore structure, thus obtaining porous, crimped fiber-composed elastic ceramic nanofiber flocs.

[0044] In a specific embodiment, the micro-airflow delivered by the micro-area air supply device 1 is a normal temperature dry, normal temperature high humidity, high temperature dry, or high temperature high humidity airflow, with a wind speed of 0.1~3 m / s; wherein, the normal temperature is 20~27℃, the high temperature is 30~45℃, the dry humidity is 20~30%, and the high humidity is 60~90%.

[0045] In a specific embodiment, the mixing chamber 1-1-1 of the micro-area air supply device 1 has a spherical structure, and three tangential air inlets are provided on the upper part of the inner wall of the mixing chamber 1-1-1, namely, a normal temperature drying air inlet 1-1-11, a normal temperature high humidity air inlet 1-1-12, and a high temperature drying air inlet 1-1-13; when the airflow is delivered from the air inlet to the mixing chamber 1-1-1, the airflow will fly along the spherical wall and collide to form turbulence, thereby accelerating the mixing of different airflows; the mixed airflow will overflow from the horizontally set first air outlet 1-1-14, the overflow direction is perpendicular to the first-stage air supply channel 1-5-1, and the gas will collide perpendicularly with the side partition of the mixing chamber 1-1, thus reducing the airflow speed for the first time; the number of mixing chambers 1-1-1 is set to 2 to 4, and the first air outlet 1-1-14 of a single mixing chamber is set to 2 to 4; After the mixed airflow fills the mixing chamber 1-1, it enters the buffer chamber from the primary air supply channel 1-5-1 and impacts the bottom partition of the buffer chamber 1-2-1 vertically, reducing the airflow velocity for the second time. When the mixed gas fills the buffer chamber 1-2-1, it overflows from the horizontally set second air outlet 1-2-11 and impacts the side wall of the buffer chamber 1-2 vertically, reducing the airflow velocity for the third time. The number of buffer chambers is set to 4 to 8, and the number of second air outlets 1-2-11 is set to 2 to 4. The air supply ducts of the primary air supply duct 1-5-1, the secondary air supply duct 1-6-1, and the tertiary air supply duct 1-7-1 increase progressively, which can subdivide the airflow into densely and evenly distributed micro-airflows. The number of primary air supply ducts is set to 4 to 8, the number of secondary air supply ducts is set to 16 to 64, and the number of tertiary air supply ducts is set to 256 to 1024. The micro-airflow is delivered from the three-stage air supply channel 1-7-1 to the grille cavity 1-4, and the gas direction can be controlled by adjusting the grille plate 1-4-1; the adjustment angle of the grille plate 1-4-1 is -60~60° and the vertical direction is set to 0°.

[0046] In a specific embodiment, the gradient pressure roller group 4-1 in the pressure stabilizing and shaping device 4 is provided with a pressure sensing layer 4-2, which is used to provide real-time feedback on the pressure changes of the flakes, and dynamically adjust the applied pressure of the rollers through the pressure control component 4-3; the surface material of the rollers is selected from perfluoroalkoxy resin, polytetrafluoroethylene, silicone rubber, fluorinated ethylene propylene copolymer or fluororubber; the applied pressure is 0.01~1MPa, and the pressure difference is 0.05~0.2MPa.

[0047] This embodiment also provides a porous nanofiber-based elastic ceramic floc, prepared by the above-described method. The building blocks of the floc are porous, coiled ceramic nanofibers. The diameter of a single fiber is 50–800 nm, the coiling rate is not less than 28%, the radius of curvature is 1–9 μm, the pore size is 0.5–50 nm, and the pore volume is 0.1–1 cm³. 3 / g, specific surface area of ​​100~1500 m² 2 / g.

[0048] In a specific embodiment, the thickness of the floc is 5~110 mm, the thickness CV value is less than 5%, the porosity is not less than 98.5%, the tensile strength reaches more than 2.8 MPa, the compressive elastic recovery rate is not less than 96%, the thermal conductivity is not higher than 0.029 W / m·K, and the noise reduction coefficient is greater than 0.7.

[0049] Example 3 This embodiment provides a method for preparing porous nanofiber-based elastic ceramic flocs, such as... Figure 1-4 As shown, the specific steps are as follows: (1) Bis(dimethoxyphosphonomethyl)-(8-phosphonooctyl)phosphine oxide was added to zirconium tetraethanolamine and indium isopropoxide (molar ratio of the two was 1:1) for initial coordination, wherein the total molar ratio of bis(dimethoxyphosphonomethyl)-(8-phosphonooctyl)phosphine oxide to the alkoxide was 1:1; subsequently, a gradient inert ligand solution was prepared by combining the weakly inert ligand tetrahydrofuran, the moderately inert ligand ethyl acetate, and the strongly inert ligand diethanolamine (mass ratio of the three was 3:3:4), and the strong ligand was further classified based on the difference in electronegativity or electronegativity. Inert ligands preferentially coordinate with highly reactive metal alkoxides, thereby aligning the hydrolysis rate of the metal alkoxide monomer to obtain a fully coordinated modified metal alkoxide monomer. Then, hydrochloric acid is added to the above alkoxide monomer (controlling the molar ratio of H+ to total metal alkoxide in the system to be 2:1), followed by the addition of 15 wt% water of the total metal alkoxide, to carry out a depolymerization-condensation reaction, yielding a low-polymerization-degree linear inorganic molecular chain. Finally, diisopropoxydiacetylacetonate titanium (at an amount equal to 5% of the low-polymerization-degree linear inorganic molecular chain) is added to the system. The reaction system temperature was adjusted to 80℃ and the pressure to -0.1MPa, and the reaction was continued for 5 hours to complete the chain extension of the low degree of polymerization linear inorganic molecular chain. After the chain extension reaction was completed, an end-capping agent was added to the system. The molar ratio of the added amount to titanium diisopropoxybisacetylacetonate was 1:1 to terminate the growth of the linear inorganic molecular chain and obtain a high degree of polymerization linear inorganic long chain solution with zirconium-oxygen-indium-oxygen as the repeating unit. Finally, ethanol with a mass ratio of 4:6 to the linear inorganic long chain and hexadecyltrimethylammonium bromide with a ratio of 1:0.1 to the alkoxide monomer were added to prepare the spinning solution. (2) The prepared spinning solution is loaded onto the coaxial high-speed jet nozzle and a coupling force field of electrostatics and airflow is applied to it to stretch and deform the solution to obtain an unstable curled whip jet; at this time, the micro-area air supply device 1 delivers a room temperature and high humidity micro airflow (temperature 25℃, humidity 85%) with a speed of 0.5m / s to the whip zone, so that the whip jet can quickly separate and solidify to obtain the curled precursor nanofibers; (3) Then, the spinneret reciprocates at a speed of 0.5 m / min, and the conveyor belt 3 moves forward at a speed of 0.5 m / min. The precursor coiled nanofibers are dynamically assembled in three dimensions in the air to obtain fluffy precursor coiled nanofiber flakes. (4) The precursor coiled nanofiber flakes are fed into the pressure stabilizing and shaping device 4, and the gradient pressure difference of the pressure roller group is set to 0.2MPa to stabilize and shape the precursor coiled nanofiber flakes. (5) The shaped precursor coiled nanofiber flakes are fed into a deep ultraviolet pretreatment device, and the power is set to 150W / dm. 2 The process effectively removes organic components from the fibers, not only efficiently removing organic ligands but also forming a porous structure inside the fibers. Subsequently, the fibers are transported to an oxygen-deficient calcination device, with the calcination temperature set at 800℃ and the oxygen concentration set at 15%, thereby obtaining elastic ceramic nanofiber flocs composed of porous crimped fibers. (6) The obtained porous coiled nanofibers have a diameter of 300 nm, a coiling rate of 30%, a radius of curvature of 5 μm, a pore size of 20 nm, and a pore volume of 0.5 cm³. 3 / g, specific surface area 500m² 2 / g; (7) The obtained elastic ceramic nanofiber flocs have a thickness of 5 cm, a porosity of 99.8%, a bulk density of 10 mg / cm3, a tensile strength of 2.0 MPa, a compressive elastic recovery rate of 97.8%, and a thermal conductivity of 0.023 W / m·K.

[0050] Example 4 This embodiment provides a porous nanofiber-based elastic ceramic floc and its preparation method, such as Figure 1-4 As shown, the specific steps are as follows: (1) 11-(bis(2-(dimethoxyphosphoryloxy)ethyl)amino)-undecylphosphonic acid was added to titanium tetraethanol and titanium tetrabutoxide (molar ratio of the two was 2:1) for preliminary coordination, wherein the total molar ratio of 11-(bis(2-(dimethoxyphosphoryloxy)ethyl)amino)-undecylphosphonic acid was 3:1; subsequently, a gradient inert ligand solution was prepared by preparing a weakly inert ligand acetone, a moderately inert ligand acetic acid, and a strongly inert ligand ethyl acetoacetate (mass ratio of the three was 3:3:4), and based on the difference in electronegativity or electronegativity, the strongly inert ligand preferentially coordinated with the highly active metal alkoxide, thereby aligning the hydrolysis rate of the metal alkoxide monomer to obtain a fully coordinated modified metal alkoxide monomer; then, hydrochloric acid was added to the above alkoxide monomer (to control the H in the system). + A hydrolysis-condensation reaction was carried out using a 2:1 molar ratio of total metal alkoxides to water, followed by the addition of 15 wt% water to the total metal alkoxides, to obtain low-polymerization linear inorganic molecular chains. Then, titanium diisopropoxybisacetylacetonate (5 mol% of the low-polymerization linear inorganic molecular chain material) was added to the system. The reaction temperature was adjusted to 80℃ and the pressure to -0.1 MPa, and the reaction was continued for 5 hours to complete the chain extension of the low-polymerization linear inorganic molecular chains. After the chain extension reaction, a capping agent was added to the system at a molar ratio of 1:1 to titanium diisopropoxybisacetylacetonate to terminate the growth of the linear inorganic molecular chains, resulting in a high-polymerization linear inorganic long-chain solution with titanium-oxygen as the repeating unit. Finally, ethanol (4:6 mass ratio of high-polymerization linear inorganic long chains to ethanol) and eicosyltrimethylammonium bromide (4:1 molar ratio of eicosyltrimethylammonium bromide to alkoxide monomers) were added to prepare the spinning solution. (2) The prepared spinning solution is loaded onto the coaxial high-speed jet nozzle and a coupling force field of electrostatics and airflow is applied to it to stretch and deform the solution to obtain an unstable curled whip jet. At this time, the micro-area air supply device 1 delivers a room temperature dry micro-airflow (temperature 24℃, humidity 25%) with a speed of 1m / s to the whip zone to accelerate the evaporation of the solvent in the whip jet and make it solidify quickly to obtain the curled precursor nanofibers. (3) Then, the spinneret reciprocates at a speed of 0.7 m / min, and the conveyor belt 3 moves forward at a speed of 1 m / min. The precursor coiled nanofibers are dynamically assembled in three dimensions in the air to obtain fluffy precursor coiled nanofiber flakes. (4) The precursor coiled nanofiber flakes are fed into the pressure stabilizing and shaping device 4, and the gradient pressure difference of the pressure roller group is set to 0.1MPa to stabilize and shape the precursor coiled nanofiber flakes. (5) The shaped precursor coiled nanofiber flakes are fed into a deep ultraviolet pretreatment device, and the power is set to 200W / dm. 2The process effectively removes organic components from the fibers, not only efficiently removing organic ligands but also forming a porous structure inside the fibers. Subsequently, the fibers are transported to an oxygen-deficient calcination device, with the calcination temperature set at 600℃ and the oxygen concentration set at 13%, thereby obtaining elastic ceramic nanofiber flocs composed of porous crimped fibers. (6) The obtained porous coiled nanofibers have a diameter of 400 nm, a coiling rate of 40%, a radius of curvature of 9 μm, a pore size of 40 nm, and a pore volume of 0.8 cm³. 3 / g, specific surface area 100m² 2 / g; (7) The obtained elastic ceramic nanofiber flocs have a thickness of 10 cm, a porosity of 99.2%, a tensile strength of 2.8 MPa, a compressive elastic recovery rate of 98.6%, and a thermal conductivity of 0.022 W / m·K.

[0051] Example 5 This embodiment provides a porous nanofiber-based elastic ceramic floc and its preparation method, such as Figure 1-4 As shown, the specific steps are as follows: (1) 1,1-bis(dimethoxyphosphorylmethyl)-1-(8-phosphonooctyl)propane was added to tetrabutyl titanate and zirconium butoxide (molar ratio of the two was 1:1) for preliminary coordination, wherein the total molar ratio of 1,1-bis(dimethoxyphosphorylmethyl)-1-(8-phosphonooctyl)propane was 1:1; subsequently, a gradient inert ligand solution (mass ratio of the three was 4:2:4) was prepared by combining the weakly inert ligand acetone, the moderately inert ligand propionic acid, and the strongly inert ligand trifluoroacetylacetone, and the strongly inert ligand based on the difference in electronegativity or electronegativity to preferentially coordinate the strongly inert ligand with the highly active metal alkoxide, thereby aligning the hydrolysis rate of the metal alkoxide monomer and obtaining a fully coordinated modified metal alkoxide monomer; then, hydrochloric acid was added to the above alkoxide monomer (to control the H in the system) +The molar ratio of the total metal alkoxide to the total metal alkoxide is 2:1. Then, 12 wt% of water (total metal alkoxide) is added to the mixture to carry out a hydrolysis-condensation reaction, yielding a low-polymerization-degree linear inorganic molecular chain. Then, bis(diethylcitrate) dipropoxide zirconium (added in an amount equal to 5% of the low-polymerization-degree linear inorganic molecular chain) is added to the system. The reaction system temperature was adjusted to 90℃ and the pressure to -0.1MPa, and the reaction was continued for 3 hours to complete the chain extension of the low-polymerization degree linear inorganic molecular chain. After the chain extension reaction was completed, an end-capping agent was added to the system. The molar ratio of the added agent to the molar ratio of di(diethylcitrate)dipropoxide zirconium was 1:1 to terminate the growth of the linear inorganic molecular chain and obtain a high-polymerization degree linear inorganic long-chain solution with titanium-oxygen-zirconium-oxygen as the repeating unit. Finally, n-propanol (the mass ratio of the high-polymerization degree linear inorganic long chain to propanol was 6:4) and dodecyltrimethylammonium bromide (the molar ratio of dodecyltrimethylammonium bromide to alkoxide monomer was 0.2:1) were added to prepare the spinning solution. (2) The prepared spinning solution is loaded onto the coaxial high-speed jet nozzle and a coupling force field of electrostatics and airflow is applied to it to stretch and deform the solution to obtain an unstable curled whip jet. At this time, the micro-area air supply device 1 delivers a high-temperature dry micro-airflow (temperature 40℃, humidity 18%) with a speed of 2.0m / s to the whip zone, so that the solvent in the whip jet evaporates rapidly due to the high temperature, and the jet solidifies quickly to obtain the curled precursor nanofibers. (3) Then, the spinneret reciprocates at a speed of 1.0 m / min, and the conveyor belt 3 moves forward at a speed of 1.5 m / min. The precursor coiled nanofibers are dynamically assembled in three dimensions in the air to obtain fluffy precursor coiled nanofiber flakes. (4) The precursor coiled nanofiber flakes are fed into the pressure stabilizing and shaping device 4, and the gradient pressure difference of the pressure roller group is set to 0.15MPa to stabilize and shape the precursor coiled nanofiber flakes. (5) The shaped precursor coiled nanofiber flakes are fed into a deep ultraviolet pretreatment device, and the power is set to 300W / dm. 2 The process effectively removes organic components from the fibers, not only efficiently removing organic ligands but also forming a porous structure inside the fibers. Subsequently, the fibers are transported to an oxygen-deficient calcination device, with the calcination temperature set at 1300℃ and the oxygen concentration set at 10%, thereby obtaining elastic ceramic nanofiber flocs composed of porous crimped fibers. (6) The obtained porous coiled nanofibers have a diameter of 280 nm, a coiling rate of 35%, a radius of curvature of 5 μm, a pore size of 25 nm, and a pore volume of 0.5 cm³. 3 / g, specific surface area 650m² 2 / g; (7) The obtained elastic ceramic nanofiber flocs have a thickness of 8 cm, a porosity of 99.0%, a tensile strength of 3.8 MPa, a compressive elastic recovery rate of 99.0%, and a thermal conductivity of 0.025 W / m·K.

[0052] Example 6 This embodiment provides a porous nanofiber-based elastic ceramic floc and its preparation method, such as Figure 1-4 As shown, the specific steps are as follows: (1) 1,1-bis(dimethoxyphosphorylmethyl)-1-(8-phosphonooctyl)propane was added to tetrabutyl titanate and tetraethyl orthosilicate (molar ratio of the two was 1:1) for preliminary coordination, wherein the total molar ratio of 1,1-bis(dimethoxyphosphorylmethyl)-1-(8-phosphonooctyl)propane was 1:1; subsequently, a gradient inert ligand solution (mass ratio of the three was 3:3:4) was prepared by the weakly inert ligand tetrahydrofuran, the moderately inert ligand ethyl acetate and the strongly inert ligand diethanolamine, and the strongly inert ligand was preferentially coordinated with the highly active metal alkoxide based on the difference in electronegativity or electronegativity, thereby aligning the hydrolysis rate of the metal alkoxide monomer to obtain a fully coordinated modified metal alkoxide monomer; then, hydrochloric acid was added to the above alkoxide monomer (to control the H in the system) + The molar ratio of the total metal alkoxide to the total metal alkoxide is 2:1. Then, 15 wt% water of the total metal alkoxide is added to carry out a hydrolysis-condensation reaction to obtain a low-polymerization degree linear inorganic molecular chain. Then, diisopropoxydiacetylacetonate titanium (added in an amount equal to 5% of the low-polymerization degree linear inorganic molecular chain) is added to the system. The reaction system temperature was adjusted to 80℃ and the pressure to -0.1MPa, and the reaction was continued for 4 hours to complete the chain extension of the low-polymerization degree linear inorganic molecular chain. After the chain extension reaction was completed, an end-capping agent was added to the system, with the addition amount in a molar ratio of 1:1 to titanium diisopropoxybisacetylacetone, to terminate the growth of the linear inorganic molecular chain and obtain a high-polymerization degree linear inorganic long-chain solution with titanium-oxygen-silicon-oxygen as the repeating unit. Finally, n-propanol (the mass ratio of the high-polymerization degree linear inorganic long chain to propanol was 1:1) and hexadecyltrimethylammonium bromide (the molar ratio of hexadecyltrimethylammonium bromide to alkoxide monomer was 0.5:1) were added to prepare the spinning solution. (2) The prepared spinning solution is loaded onto the coaxial high-speed jet nozzle and a coupling force field of electrostatics and airflow is applied to it to stretch and deform the solution to obtain an unstable curled whip jet. At this time, the micro-area air supply device 1 delivers a room temperature and high humidity micro airflow (temperature 25℃, humidity 65%) with a speed of 0.8m / s to the whip zone, so that the whip jet can quickly separate and solidify to obtain the curled precursor nanofiber. (3) Then, the spinneret reciprocates at a speed of 0.5 m / min, and the conveyor belt 3 moves forward at a speed of 0.8 m / min. The precursor coiled nanofibers are dynamically assembled in three dimensions in the air to obtain fluffy precursor coiled nanofiber flakes. (4) The precursor coiled nanofiber flakes are fed into the pressure stabilizing and shaping device 4, and the gradient pressure difference of the pressure roller group is set to 0.05MPa to stabilize and shape the precursor coiled nanofiber flakes. (5) The shaped precursor coiled nanofiber flakes are fed into a deep ultraviolet pretreatment device, and the power is set to 150W / dm. 2 The process effectively removes organic components from the fibers, not only efficiently removing organic ligands but also forming a porous structure inside the fibers. Subsequently, the fibers are transported to an oxygen-deficient calcination device, with the calcination temperature set at 1050℃ and the oxygen concentration set at 15%, thereby obtaining elastic ceramic nanofiber flocs composed of porous crimped fibers. (6) The obtained porous coiled nanofibers have a diameter of 450 nm, a coiling rate of 45%, a radius of curvature of 12 μm, a pore size of 55 nm, and a pore volume of 0.9 cm³. 3 / g, specific surface area 450m² 2 / g; (7) The obtained elastic ceramic nanofiber flocs have a thickness of 12 cm, a porosity of 99.5%, a tensile strength of 2.2 MPa, a compressive elastic recovery rate of 98.0%, and a thermal conductivity of 0.021 W / m·K.

Claims

1. A method for preparing porous nanofiber-based elastic ceramic flocs, characterized in that, Includes the following steps: S1. Preparation of spinning solution: A ligand with a multidentate phosphoryl group at one end and a phosphonic acid group at the other end is added to one or more metal alkoxide monomers for initial coordination; then, weakly inert, moderately inert, and strongly inert ligands are prepared into a gradient inert ligand solution. Based on the difference in electronegativity or electronegativity, the strongly inert ligand preferentially coordinates with the highly active metal alkoxide, aligning with the hydrolysis rate of the metal alkoxide monomer, to obtain a coordination-modified metal alkoxide monomer; then, hydrolysis-condensation, chain extension, and end-capping reactions are carried out to obtain a linear inorganic long-chain solution with a high degree of polymerization; finally, an alcohol solvent and a pore-forming binder are added to obtain the spinning solution; S2, Crimped Fiber Forming: The spinning solution obtained in S1 is passed into a high-speed jet nozzle, and a coupling force field of electrostatic field and airflow field is applied to make the spinning solution form a whipping jet; at the same time, a micro airflow with set parameters is delivered to the whipping jet area by a micro-region air supply device (1) to solidify the whipping jet and obtain the precursor crimped nanofiber. S3, Three-dimensional dynamic assembly: Control the relative movement between the spinneret and the conveyor belt (3) to dynamically interweave the precursor coiled nanofibers obtained in S2 in the air to assemble them into precursor coiled nanofiber flakes. S4, Pressure Stabilization and Shaping: The precursor crimped nanofiber flakes obtained in S3 are fed into the pressure stabilization and shaping device (4), and gradient pressure is applied through the gradient pressure roller group (4-1) inside the pressure stabilization and shaping device (4) for pressure stabilization and shaping. S5. Pore Formation and Ceramization: The flocs after S4 shaping are subjected to deep ultraviolet pretreatment to remove organic components in the fibers to form a porous structure; then, they are transported to a calcination device under an oxygen-deficient atmosphere for calcination to obtain porous nanofiber-based elastic ceramic flocs. The micro-area air supply device (1) includes a mixing chamber (1-1), a buffer chamber (1-2), a transition chamber (1-3), and a grid chamber (1-4) arranged sequentially from top to bottom. The mixing chamber (1-1) has at least one mixing compartment (1-1-1) at its upper part, at least three tangential air inlets at its top for supplying gases of different temperatures and humidity, and a first horizontal air outlet (1-1-14) on its side wall. A primary air supply plate (1-5) is provided between the mixing chamber (1-1) and the buffer chamber (1-2), and the primary air supply plate (1-5) has multiple through-flow primary air supply channels (1-5-1) inside. The buffer chamber (1-2) has a buffer compartment (1-2-1) inside, and the buffer compartment (1-2-1) has multiple through-flow primary air supply channels (1-5-1) inside. The side wall of the -2-1) is provided with a second horizontal air outlet (1-2-11); the buffer cavity (1-2) and the transition cavity (1-3), and the transition cavity (1-3) and the grille cavity (1-4) are respectively provided with a secondary air supply plate (1-6) and a tertiary air supply plate (1-7), and the secondary air supply plate (1-6) and the tertiary air supply plate (1-7) are respectively provided with multiple through secondary air supply channels (1-6-1) and tertiary air supply channels (1-7-1); the number of primary air supply channels (1-5-1), secondary air supply channels (1-6-1) and tertiary air supply channels (1-7-1) increases step by step and is arranged in a fractal pattern; the bottom of the grille cavity (1-4) is provided with an angle-adjustable grille plate (1-4-1).

2. The method for preparing porous nanofiber-based elastic ceramic flocs according to claim 1, characterized in that, The ligand having a multidentate phosphoryl group at one end and a phosphonic acid group at the other end is selected from one or more combinations of 11-phosphono-1,1,1-tris(dimethoxyphosphonomethyl)undecane, 11-(bis(2-(dimethoxyphosphonooxy)ethyl)amino)undecylphosphonic acid, 1,1-bis(dimethoxyphosphonomethyl)-1-(8-phosphonooctyl)propane, bis(dimethoxyphosphonomethyl)-(8-phosphonooctyl)phosphine oxide, and N,N-bis(2-(dimethoxyphosphono)ethyl)-11-phosphonoundecaneamide.

3. The method for preparing porous nanofiber-based elastic ceramic flocs according to claim 1, characterized in that, The high-speed jet nozzle described in S2 is a coaxial nozzle. The inner channel is used to supply the spinning solution, and the outer channel is used to apply a high-speed airflow. The outer wall of the inner channel outlet is provided with an annular guide surface, and the outer diameter increases and then decreases along the nozzle axis from the inside to the outside. The wall diameter of the outer channel outlet gradually decreases and remains parallel to the decreasing outer diameter portion of the annular guide surface.

4. The method for preparing porous nanofiber-based elastic ceramic flocs according to claim 1, characterized in that, The spinnerets include two types: one is a single-row spinneret (2-1) with the nozzle direction vertical, and the other is a double-row spinneret (2-2) with two rows of nozzles symmetrically and inclined; the spinnerets reciprocate at a speed of 0.1~1.5 m / min in a direction perpendicular to the conveyor belt (3), and the conveyor belt (3) moves forward at a speed of 0.1~20 m / min; the nozzle angle of the single-row spinneret (2-1) is defined as 0°, and the angle of the double-row spinneret (2-2) is 10~70°.

5. The method for preparing porous nanofiber-based elastic ceramic flocs according to claim 1, characterized in that, The deep ultraviolet pretreatment described in S5 uses ultraviolet light bands of 185nm and 254nm, with a power of 40~350 W / dm². 2 The calcination process includes pulsed microwave treatment and oxygen-deficient heating treatment. The pulsed microwave power is 10~500 kW, the pulse width is 0.1~5 s, and the pulse interval is 0.1~0.5 Hz. The oxygen concentration in the oxygen-deficient atmosphere is ≤15%, and the heating temperature is 400~1500 ℃.

6. The method for preparing porous nanofiber-based elastic ceramic flocs according to claim 1, characterized in that, The micro-area air supply device (1) delivers micro-airflow that is room temperature dry, room temperature high humidity, high temperature dry or high temperature high humidity airflow, with a wind speed of 0.1~3 m / s; wherein, the room temperature is 20~27℃, the high temperature is 30~45℃, the dry humidity is 20~30%, and the high humidity is 60~90%.

7. The method for preparing porous nanofiber-based elastic ceramic flocs according to claim 1, characterized in that, The gradient pressure roller group (4-1) in the pressure stabilizing and shaping device (4) is equipped with a pressure sensing layer (4-2) inside, which is used to provide real-time feedback on the pressure change of the flakes, and dynamically adjust the applied pressure of the rollers through the pressure control component (4-3); the surface material of the rollers is selected from perfluoroalkoxy resin, polytetrafluoroethylene, silicone rubber, fluorinated ethylene propylene copolymer or fluororubber; the applied pressure is 0.01~1MPa, and the pressure difference is 0.05~0.2MPa.

8. A porous nanofiber-based elastic ceramic flocculent, prepared by the method according to any one of claims 1-7, characterized in that, The building blocks of the flocs are porous, coiled ceramic nanofibers. Each fiber has a diameter of 50–800 nm, a coiling rate of at least 28%, a radius of curvature of 1–9 μm, a pore size of 0.5–50 nm, and a pore volume of 0.1–1 cm³. 3 / g, specific surface area of ​​100~1500 m² 2 / g.

9. The porous nanofiber-based elastic ceramic flocculent according to claim 8, characterized in that, The thickness of the floc is 5~110 mm, the thickness CV value is less than 5%, the porosity is not less than 98.5%, the tensile strength reaches more than 2.8 MPa, the compressive elastic recovery rate is not less than 96%, the thermal conductivity is not higher than 0.029 W / (m·K), and the noise reduction coefficient is greater than 0.

7.

10. An application of a porous nanofiber-based elastic ceramic flocculant, characterized in that, The elastic ceramic flocs described in claim 8 or 9 can be applied to aerospace thermal protection and noise reduction systems, battery thermal runaway barrier components, insulating fireproof and sound-absorbing noise reduction layers, personal protective equipment insulation layers, flame-retardant energy-saving insulation and safety protection layers, industrial adsorption fillers, catalyst carriers, or gas sensor sensing elements.

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