A method for preparing ultra-high temperature stable composite refractory fiber

Abstract

This invention relates to the field of refractory material preparation technology, and discloses a method for preparing ultra-high temperature stable composite refractory fibers. The method includes: preparing hollow porous refractory fiber units with a radial gradient structure through coaxial electrospinning and sintering; constructing a three-dimensional interwoven network structure of the fiber units, and then performing low-temperature activation sintering by needle punching and introducing a nano-ceramic binder to firmly bond the fiber interlacing points. The composite refractory fibers prepared by this invention possess highly efficient thermal insulation through multi-scale porosity, optimized mechanical properties through a gradient structure, and excellent macroscopic structural stability. They can maintain excellent thermal insulation, structural integrity, and mechanical strength at ultra-high temperatures.

Description

Technical Field

[0001] This invention belongs to the field of refractory material preparation technology, and relates to a method for preparing ultra-high temperature stable composite refractory fiber. Background Technology

[0002] In existing technologies, mainstream refractory fibers, such as traditional aluminosilicate fibers, polycrystalline alumina fibers, and zirconia fibers, have, to a certain extent, met the needs of industrial production and scientific research applications at the time, through optimized material composition and sintering processes. These fibers typically employ a relatively dense solid structure design to resist high-temperature erosion through the material's high melting point and high chemical stability, while providing a certain degree of mechanical support. For example, the bulk density of traditional refractory fibers is generally maintained in the range of 1.2-1.5 g / cm³, and they can provide a tensile strength of 150-200 MPa, effectively undertaking basic thermal insulation and load-bearing functions under conditions below their extreme operating temperatures. Correspondingly, their thermal conductivity in the range of 1000-1800℃ is typically between 0.15-0.2 W / (m·K). For the technological requirements at the time, such thermal insulation performance and structural strength were considered acceptable, and strongly promoted the development and application of high-temperature thermal insulation technology.

[0003] Traditional refractory fibers face a fundamental technical contradiction in their design: the difficulty of simultaneously achieving high-temperature insulation performance and structural stability. To achieve excellent insulation, materials typically require low bulk density and high porosity to utilize the extremely low thermal conductivity of trapped air or gases to block heat transfer. However, introducing a large number of pores or reducing density inevitably weakens the material's effective load-bearing cross-sectional area, leading to a decrease in mechanical strength. Especially under ultra-high temperature environments, the pore structure is prone to sintering, grain growth, and other deterioration phenomena, causing premature densification, embrittlement, and even macroscopic structural collapse, severely impacting its long-term service reliability. Furthermore, even relatively dense solid fibers, under ultra-high temperature conditions, struggle to effectively disperse thermal stress caused by uneven thermal expansion or external mechanical loads, leading to concentrated stress on individual fibers and eventual breakage, ultimately causing the entire insulation structure to fail.

[0004] Therefore, how to design a new type of refractory fiber structure that can fundamentally solve the contradiction between high-temperature insulation performance and structural stability in existing technologies through sophisticated microstructure control and macroscopic mechanical optimization in ultra-high temperature environments has become a key challenge and an urgent technical problem for those skilled in the art. Summary of the Invention

[0005] This invention aims to overcome the inherent technical contradiction between high-temperature thermal insulation performance and structural stability in existing ultra-high temperature refractory fiber materials, and to provide a composite refractory fiber that can maintain excellent thermal insulation performance, structural integrity, and sufficient mechanical strength under ultra-high temperature environments. To achieve the above-mentioned objective, this invention provides a method for preparing ultra-high temperature stable composite refractory fibers. The core of this method lies in constructing a three-dimensional interwoven network structure composed of hollow porous fiber units. High-efficiency thermal insulation is achieved through multi-scale pore design, and the mechanical properties and long-term service stability of the material under extreme high temperatures are improved through the gradient structure of the fiber units, macroscopic mechanical optimization of the three-dimensional network, and in-situ bonding technology with nano-ceramics.

[0006] This invention provides a method for preparing ultra-high temperature stable composite refractory fibers. The core of this method lies in achieving superior thermal insulation performance and structural stability under extreme temperature conditions through precise control of the structure of micro-fiber units and the construction of the macro-three-dimensional network. The following detailed descriptions of each technical step of this preparation method, in conjunction with specific embodiments, will ensure that those skilled in the art can fully understand and implement this invention.

[0007] First, the method of the present invention includes preparing ultra-high temperature stable hollow porous refractory fiber units, and then constructing a three-dimensional interwoven network structure of the hollow porous refractory fiber units.

[0008] In a specific embodiment, the method for preparing ultra-high temperature stable hollow porous refractory fiber units in S1 specifically includes the following sub-steps.

[0009] S11. Prepare outer gradient ceramic precursor spinning solution and inner sacrificial template spinning solution for coaxial electrospinning.

[0010] The preparation of the spinning solution for the outer gradient ceramic precursor requires precise proportioning of various metal precursors, polymer binders, and solvents. In this embodiment, the aluminum source selected is aluminum nitrate nonahydrate (Al(NO3)3·9H2O), from Sigma-Aldrich; the silicon source is tetraethyl orthosilicate (TEOS, Si(OC2H5)4), from Alfa Aesar.

[0011] The zirconium source was zirconium oxychloride octahydrate (ZrOCl2·8H2O), which came from Sinopharm Chemical Reagent Co., Ltd.

[0012] The yttrium source was yttrium nitrate hexahydrate (Y(NO3)3·6H2O), obtained from Macklin Corporation.

[0013] These metal salt precursors, after dissolution, will be transformed into corresponding oxide ceramics during subsequent heat treatment. The polymer binder used is polyvinyl alcohol (PVA), with a molecular weight of 80,000-120,000, a degree of hydrolysis of 98-99%, and a mass fraction of 5 wt%. PVA acts as a fiber-forming agent, providing the viscosity and elasticity required for spinning, while completely decomposing during sintering without leaving any impurities. The solvent used is a mixture of deionized water and ethanol at a volume ratio of 1:1 to balance the solubility of the precursors and the evaporation rate of the spinning solution.

[0014] To achieve gradient characteristics within the fiber wall, the following strategy is employed in this embodiment: In the outer spinning solution, the ceramic precursor component is designed to induce radial distribution differences during electrospinning. For example, to prepare alumina-zirconia-yttrium oxide composite ceramic fibers, aluminum nitrate, zirconium oxychloride, and yttrium nitrate can be dissolved in a mixed solvent at a specific molar ratio (e.g., the final ceramic composition is 80 mol% Al₂O₃, 15 mol% ZrO₂, and 5 mol% Y₂O₃). Simultaneously, polystyrene microspheres with a particle size of approximately 100 nm and a mass fraction of 3 wt% are introduced into the outer spinning solution. During spinning, the polystyrene microspheres form a stable suspension with the ceramic precursor and polymer binder, and decompose during fiber drying and sintering, forming controllable micro / nanopores. By precisely controlling the dispersion uniformity of the polystyrene microspheres in the spinning solution and their radial migration within the fiber, a radial porosity gradient can be formed during subsequent sintering.

[0015] In the preparation of the outer spinning solution, polyvinyl alcohol is first completely dissolved in a mixed solvent, and then the metal precursor is added in batches while continuously stirring until completely dissolved. Finally, polystyrene microspheres are slowly added under ultrasonic assistance and stirred until homogeneous. This step is particularly critical, as it is essential to ensure that the polystyrene microspheres do not agglomerate and can be stably dispersed in the spinning solution. The total solids content of the outer spinning solution is strictly controlled at 25 wt%, and its viscosity is tested to be 850 mPa·s, with a surface tension of 40 mN / m. These parameters ensure the formation of a stable conical jet and the acquisition of uniform fibers during electrospinning.

[0016] The preparation of the inner sacrificial template spinning solution is relatively simple. In this example, polyvinyl alcohol (PVA) with an average degree of polymerization of 2000 and a degree of hydrolysis of 98% was selected and sourced from Xilong Scientific Co., Ltd. PVA was dissolved in deionized water at a mass fraction of 12 wt%. To ensure complete dissolution of PVA, the aqueous solution was continuously heated at 80°C with stirring for 2 hours until a clear and transparent solution was formed. The solution was then cooled to room temperature and degassed in a vacuum degassing machine for 30 minutes to thoroughly remove air bubbles that could affect spinning stability. The final viscosity of the inner spinning solution was measured to be 180 mPa·s.

[0017] Furthermore, in S12, hollow composite precursor fibers are prepared using coaxial electrospinning technology.

[0018] In this embodiment, the coaxial electrospinning device consists of a high-voltage power supply, a dual-channel injection pump, a coaxial nozzle, and a fiber collection device. The coaxial nozzle is made of precision-machined stainless steel, with the inner nozzle having an outer diameter of 0.6 mm and the outer nozzle having an inner diameter of 1.2 mm to ensure precise alignment of the inner and outer fluid channels. Two independent SY-02 injection pumps are used, connected to the inner and outer spinning solutions respectively. The delivery rate of the outer gradient ceramic precursor spinning solution is set to 0.6 mL / h, and the delivery rate of the inner sacrificial template spinning solution is set to 0.3 mL / h. By precisely controlling the flow rate ratio (outer layer:inner layer = 2:1), a stable coaxial jet is formed, and the inner and outer diameters and wall thickness of the resulting hollow composite precursor fibers are effectively controlled. The spinning voltage is applied to the coaxial nozzle, with a positive high voltage of 18 kV applied to the outer nozzle, while the inner nozzle is kept electrically neutral through a grounding wire.

[0019] This voltage configuration facilitates stable coaxial ejection of the inner and outer fluids and maintains the stable morphology of the Taylor cone. The receiving distance, i.e., the distance from the coaxial nozzle tip to the collecting plate, is controlled at 18 cm. The collecting plate uses a 20 cm diameter rotating roller at a speed of 500 rpm, and its surface is covered with aluminum foil to ensure uniform fiber collection and facilitate subsequent peeling. The entire electrospinning process is carried out in a constant temperature and humidity chamber with an ambient humidity of 50% and a temperature of 25°C to minimize the impact of environmental fluctuations on fiber forming quality.

[0020] Scanning electron microscopy revealed that the obtained hollow composite precursor fibers exhibited a continuous and uniform morphology, with an average outer diameter of approximately 500 nm, an inner diameter of approximately 250 nm, and a fiber wall thickness of approximately 125 nm. The fiber surface was smooth, without obvious bead-like structures or breakage defects, indicating that the spinning process was stable and reliable.

[0021] In a preferred embodiment of the present invention, in S13, the hollow composite precursor fiber is sintered to form a hollow porous refractory fiber unit. This sintering process is divided into two stages: pre-sintering and high-temperature sintering.

[0022] First, the collected hollow composite precursor fiber felt was carefully transferred to an alumina crucible and placed in a box-type resistance furnace. Pre-sintering was performed in an air atmosphere at a heating rate of 2°C / min, from room temperature to 400°C, and held at this temperature for 3 hours. During this pre-sintering process, the organic solvents, polymer binders, and inner sacrificial template in the fiber undergo slow decomposition and volatilization. The key to this stage is controlling the heating rate to avoid the rapid decomposition of organic matter generating gases that could cause cracking or collapse of the fiber structure. Scanning electron microscopy showed that the pre-sintered fiber had formed clear hollow channels, and the fiber wall structure remained intact. Thermogravimetric-differential thermal analysis results showed that polyvinyl alcohol and polystyrene microspheres completely decomposed in the temperature range of 300°C to 500°C, with a total weight loss of approximately 35 wt%.

[0023] Next, the pre-sintered fiber felt was subjected to high-temperature sintering. The fiber felt was transferred to a high-temperature tube furnace equipped with MoSi2 heating elements, capable of reaching 1700℃ in an air atmosphere. The temperature was increased from 400℃ to 1550℃ at a heating rate of 4℃ / min and held at 1550℃ for 4 hours. It was then cooled to room temperature at a rate of 2℃ / min. This high-temperature sintering process aimed to completely decompose the ceramic precursor and induce a solid-state reaction, forming a highly crystalline alumina, zirconium oxide, and yttrium oxide composite ceramic phase. Simultaneously, during sintering, by precisely controlling the temperature and holding time, and utilizing the pores formed after the decomposition of polystyrene microspheres as a template, a porous structure was formed inside the fiber wall. X-ray diffraction analysis showed that the sintered fiber mainly consisted of α-Al₂O₃, t-ZrO₂ (tetragonal zirconium oxide), and Y₂O₃ stabilizer phases, with grain sizes calculated using the Scherrer equation to be approximately 80nm to 120nm, indicating that the ceramic phase was highly crystalline. Nitrogen adsorption-desorption isotherm test results show that the sintered fiber wall has a mesoporous and macroporous structure with an average pore size of 250 nm and a porosity of 35%.

[0024] During sintering, the gradient characteristics of the fiber units are achieved and enhanced through the following mechanisms: Due to the pre-defined component ratios and distribution differences of polystyrene microspheres in the spinning solution of the outer gradient ceramic precursor, as well as the radial non-uniformity of solvent evaporation rates during electrospinning, a pre-gradient of microstructure and composition is formed in the radial direction of the precursor fibers. During subsequent high-temperature sintering, this non-uniformity induces a radial gradient structure within the fiber wall. Energy-dispersive X-ray spectroscopy line scanning analysis revealed that the inner layer of the fiber wall near the hollow channels exhibits a slightly higher pore density, a slightly larger average pore size, and a porosity of approximately 38% formed by the decomposition of polystyrene microspheres, along with a slightly higher alumina content, which is beneficial for enhancing the thermal insulation effect. Conversely, the outer layer of the fiber wall near the outer surface exhibits a relatively lower porosity (approximately 32%), a slightly smaller average pore size, and a slightly higher concentration of zirconium oxide, forming a dense outer shell rich in zirconium oxide phase.

[0025] This zirconia-rich outer layer exhibits higher toughness and hardness, effectively enhancing the fiber's surface strength, abrasion resistance, and resistance to external erosion. The resulting hollow porous refractory fiber unit has an average inner diameter of 8 μm, an outer diameter of 25 μm, and a fiber wall thickness of 8.5 μm. The hollow structure provides approximately 50% internal space, filled with still air, reducing the thermal conductivity. The porous structure within the fiber wall further increases the tortuosity of the heat conduction path and the ability to scatter infrared radiation, further enhancing the thermal insulation performance.

[0026] As a preferred embodiment of the present invention, the method for constructing a three-dimensional interwoven network structure of ultra-high temperature stable hollow porous refractory fiber units in S2 specifically includes the following sub-steps.

[0027] S21. The prepared hollow porous refractory fiber units are oriented and laid up to form a prefabricated fiber felt.

[0028] In this embodiment, airflow lamination technology is used to uniformly lay and stack the hollow porous refractory fiber units prepared above. After being dispersed by airflow, the fiber units are uniformly deposited on a porous conveyor belt under negative pressure to form a continuous fiber mat. To optimize the isotropic mechanical properties of the final composite material, a random layup method is adopted to ensure that the fibers have no obvious directional preference in the plane. By adjusting the fiber feeding rate and the conveyor belt speed, the area density of the resulting pre-fabricated fiber mat is precisely controlled to be 350 g / m², and the thickness is 10 mm. This lamination process ensures the uniformity and initial structural integrity of the fiber mat, providing a stable substrate for subsequent needle punching.

[0029] In a preferred embodiment of the present invention, in S22, the prefabricated fiber felt is needle-punched.

[0030] In this embodiment, a laboratory-grade needle punching machine was used to needle-punch the prefabricated fiber felt. The needle plate was equipped with barbed needles, the needle punching density was set to 150 punches / cm², and the needle punching depth was 75% of the thickness of the prefabricated fiber felt. During the needle punching process, mechanical force caused the fiber units to interlock, entwine, and connect in three-dimensional space. The reciprocating motion of the needle punching caused some fibers to be introduced from the surface of the felt into the interior, or pulled out from the interior to the surface, thus establishing connections between fibers in the thickness direction. This physical entanglement greatly improved the interlayer bonding force of the fiber felt and endowed it with preliminary macroscopic mechanical strength and structural stability, effectively reducing the risk of delamination or deformation during subsequent processing. The bulk density of the needle-punched fiber felt was measured to be 0.22 g / cm³. Statistical analysis of the fiber cross-section using image analysis software yielded a fiber interlacing density of 65 fibers / cm², indicating that a tight mechanical interlocking structure was formed between the fibers.

[0031] Furthermore, in S23, a nano-ceramic binder is introduced.

[0032] In this embodiment, nano-sized alumina powder was used as a precursor in the preparation of the nano-ceramic binder. γ-Al₂O₃ nanoparticles with an average particle size of 20 nm were selected and dispersed in deionized water at a mass fraction of 10 wt%, with a small amount of polyvinylpyrrolidone added as a dispersant at a mass fraction of 1 wt% of the total powder mass. The mixture was ball-milled in a planetary ball mill at 300 rpm for 2 hours to ensure uniform dispersion of the nanoparticles and form a stable nano-alumina slurry. The slurry was ultrasonically treated for 20 minutes before use to prevent agglomeration.

[0033] Subsequently, the nano-ceramic slurry was uniformly applied to the needle-punched three-dimensional interwoven fiber network using a spraying method. The spraying equipment employed a pneumatic spray gun, with the spraying pressure set at 0.08 MPa and the distance between the spray gun and the fiber mat maintained at 20 cm. The slurry was sprayed uniformly at a flow rate of 10 mL / min to ensure the binder could penetrate and adhere to the fiber interlacing points, while avoiding the formation of an excessively thick adhesive layer on the fiber surface that could clog pores. The amount of nano-ceramic binder introduced was precisely controlled by adjusting the spraying time, ensuring that the binder's solid content reached 10 wt% of the total fiber network mass. After spraying, the fiber network was dried in an 80°C oven for 2 hours to completely remove the solvent and prevent defects caused by solvent residue during subsequent sintering.

[0034] In a preferred embodiment of the present invention, in S24, the fiber network with nano-ceramic binder is activated and sintered at low temperature.

[0035] In this embodiment, the dried fiber network was placed in a box-type resistance furnace and subjected to low-temperature activation sintering in an air atmosphere. The heating rate was set to 4°C / min, heating from room temperature to 1150°C and holding at this temperature for 3 hours. Subsequently, the temperature was lowered to room temperature at a rate of 2°C / min. This sintering temperature is lower than the initial high-temperature sintering temperature of the hollow porous refractory fiber unit. This low-temperature sintering strategy is crucial, aiming to promote rapid sintering of the nano-ceramic binder at the fiber interlacing points without causing densification, grain coarsening, or pore structure collapse of the fiber unit body. Due to the extremely high specific surface energy and chemical activity of nano-sized alumina particles, their sintering driving force is much greater than that of micron-sized particles, thus enabling the rapid formation of dense sintering necks at relatively low temperatures, achieving a strong metallurgical bond between adjacent fiber units.

[0036] Scanning electron microscopy revealed that the sintered fiber network exhibited smooth and dense sintered necks at the fiber interlacing points, indicating that the nano-alumina binder had achieved excellent bonding with the surface of the hollow porous refractory fiber units, forming strong connecting bridges. This in-situ bonding method, while maintaining the excellent thermal insulation performance of the hollow porous fiber body, improved the bonding strength and stiffness of the fiber network at the nodes, effectively preventing the detachment or slippage of the fiber interlacing points under ultra-high temperatures. The low-temperature activation sintering process ensured the macroscopic structural stability of the three-dimensional interlaced network and significantly improved the overall mechanical strength, creep resistance, and thermal shock resistance of the fiber network.

[0037] The ultra-high temperature stable composite refractory fiber prepared by this invention has a unique structural design and preparation process, which fundamentally solves the contradiction between high temperature insulation performance and structural stability in the prior art.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] 1. The micron-sized hollow channels (inner diameter 5-10 μm) inside the hollow porous refractory fiber unit and the nano-sized porous structure (pore size 100-500 nm, porosity 30%-40%) inside the fiber wall together construct a highly efficient composite thermal insulation barrier. The stagnant gas trapped in the hollow channels has an extremely low thermal conductivity, effectively suppressing gas convective heat transfer; the nanopores in the fiber wall significantly increase the tortuosity of the heat flow path, while scattering and absorbing infrared radiation, further reducing radiative heat transfer and solid-state thermal conductivity. This multi-scale porosity design allows the composite refractory fiber to reduce its thermal conductivity to 0.08 W / (m·K) to 0.12 W / (m·K) in ultra-high temperature environments of 1000℃ to 1800℃, far superior to traditional dense solid fibers.

[0040] 2. The hollow porous refractory fiber unit described above achieves a radial composition and pore gradient within the fiber wall through a gradient ceramic precursor spinning solution and a precise sintering process. Specifically, the inner layer of the fiber wall has higher porosity and lower densification to enhance thermal insulation; while the outer layer has lower porosity and higher densification, and may even be enriched with high-hardness or high-toughness ceramic phases, thus endowing the fiber unit with superior surface strength, wear resistance, and resistance to external erosion. This gradient structure allows individual fibers to maintain excellent thermal insulation performance while also possessing good mechanical strength and thermal shock resistance, effectively preventing cracking or brittle fracture caused by thermal stress concentration at ultra-high temperatures. The hollow structure itself also reduces local stress concentration under load by providing stress dispersion space, improving the overall toughness of the fiber.

[0041] 3. Through needle punching, hollow porous refractory fiber units are constructed into a three-dimensional network structure with a fiber interweaving density of 50 to 80 fibers / cm², significantly improving the macroscopic structural integrity and load-bearing capacity of the material. The mechanical entanglement and interlocking between fibers evenly distribute point loads throughout the network, avoiding the risk of structural collapse due to the failure of a single fiber. This macroscopic network structure enables the composite material to maintain its geometric morphology and dimensional stability at ultra-high temperatures, effectively resisting creep deformation and external impacts.

[0042] 4. After the three-dimensional interwoven network is formed, a nano-ceramic binder is introduced and low-temperature activation sintering is performed, resulting in a strong sintering neck at the fiber interlacing points. The nano-ceramic particles can achieve rapid densification and sintering at temperatures between 1000℃ and 1300℃, forming a connecting bridge that is chemically compatible with the fiber matrix and possesses excellent mechanical properties. This in-situ bonding method improves the bonding strength and stiffness of the fiber network at the nodes without damaging the pore structure of the hollow porous fiber matrix, effectively preventing the detachment or slippage of the fiber interlacing points at ultra-high temperatures. The firmly bonded interlacing points endow the composite refractory fiber with excellent flexural strength, compressive strength, and shear strength, enabling it to maintain structural stability and integrity even under extreme conditions. For example, this composite material can provide a compressive strength of over 20MPa at 1500℃ and retains more than 90% of its original mechanical strength after 100 hours of heat treatment at 1700℃.

[0043] 5. The composite refractory fiber material proposed in this invention is not simply a superposition of hollow fibers and a three-dimensional network, but rather achieves a deep synergistic effect through the multi-scale gradient design of hollow porous fiber units and the nano-bonding enhancement of the three-dimensional interwoven network. The hollow porous gradient fiber units are the foundation of thermal insulation and local strength, while the three-dimensional interwoven network and nano-bonding provide macroscopic structural support and overall stability. This ingenious combination of microscopic and macroscopic, thermal insulation and mechanics fundamentally overcomes the inherent contradictions of traditional refractory fibers in terms of lightweight, high strength, and high thermal insulation, providing a revolutionary material solution for ultra-high temperature industries and cutting-edge technology fields. The composite refractory fiber can operate stably at extreme temperatures of 1800℃, exhibiting excellent dimensional stability, oxidation resistance, and thermal shock resistance, thus improving its long-term service life and reliability. Detailed Implementation

[0044] The technical effects of the present invention will be further explained below in conjunction with 5 embodiments and 2 comparative examples.

[0045] Example 1, Preparation of hollow porous refractory fiber units:

[0046] The outer spinning solution is as follows: aluminum nitrate is selected as the aluminum source, ethyl silicate is selected as the silicon source, zirconium oxychloride is selected as the zirconium source, yttrium nitrate is selected as the yttrium source, the polymer binder is 5 wt% polyvinyl alcohol, the solvent is deionized water and ethanol (volume ratio 1:1), the total solid content is 25 wt%, the viscosity is 850 mPa·s, and 3 wt% polystyrene microspheres with a particle size of 100 nm are added.

[0047] Inner spinning solution: 12wt% polyvinyl alcohol aqueous solution, polyvinyl alcohol degree of polymerization 2000, degree of hydrolysis 98%, viscosity 180mPa・s, dissolved by stirring at 80℃ for 2 hours and vacuum degassing for 30 minutes.

[0048] Coaxial electrospinning: inner nozzle outer diameter 0.6mm, outer nozzle inner diameter 1.2mm; outer spinning solution delivery rate 0.6mL / h, inner layer 0.3mL / h; spinning voltage 18kV, receiving distance 18cm; ambient humidity 50%, temperature 25℃, collecting plate rotation speed 500rpm.

[0049] Sintering: Pre-sintering was carried out in an air atmosphere, with the temperature increased to 400℃ at a rate of 2℃ / min and held for 3 hours; high-temperature sintering was carried out with the temperature increased to 1550℃ at a rate of 4℃ / min and held for 4 hours, with a cooling rate of 2℃ / min. The final fiber had an inner diameter of 8μm, an outer diameter of 25μm, a wall thickness of 8.5μm, a fiber wall porosity of 35%, and an average pore size of 250nm.

[0050] Construction of a 3D interwoven network structure:

[0051] Layup: air-laid web, area density 350g / m², thickness 10mm.

[0052] Needle punching: needle punching density 150 times / cm², needle punching depth 7.5mm, bulk density after needle punching 0.22g / cm³, fiber interlacing density 65 strands / cm².

[0053] Introducing a nano-ceramic binder: 10wt% γ-alumina nano-slurry (particle size 20nm, containing 1wt% polyvinylpyrrolidone dispersant), applied by spraying, the binder accounting for 10wt% of the total mass of the fiber network, and dried at 80℃ for 2 hours.

[0054] Low-temperature activation sintering: In an air atmosphere, the temperature is increased to 1150℃ at a rate of 4℃ / min, held for 3 hours, and then cooled at a rate of 2℃ / min.

[0055] Example 2, Preparation of hollow porous refractory fiber units:

[0056] Outer spinning solution: aluminum acetate is selected as the aluminum source, silica sol is selected as the silicon source, zirconium nitrate is selected as the zirconium source, yttrium acetate is selected as the yttrium source, polyethylene oxide with a mass fraction of 3 wt% is selected as the polymer binder, deionized water is selected as the solvent, the total solid content is 18 wt%, the viscosity is 600 mPa·s, and cellulose acetate with a mass fraction of 2 wt% and a particle size of 80 nm is added.

[0057] Inner spinning solution: 10wt% polyvinyl alcohol aqueous solution, polyvinyl alcohol degree of polymerization 1700, degree of hydrolysis 88%, viscosity 120mPa・s, dissolved by stirring at 75℃ for 2.5 hours and degassed under vacuum for 40 minutes.

[0058] Coaxial electrospinning: inner nozzle outer diameter 0.5mm, outer nozzle inner diameter 1.0mm; outer spinning solution delivery rate 0.4mL / h, inner layer 0.2mL / h; spinning voltage 15kV, receiving distance 15cm; ambient humidity 40%, temperature 20℃, collecting plate rotation speed 400rpm.

[0059] Sintering: Pre-sintering involves heating to 300℃ at a rate of 1℃ / min and holding for 4 hours; high-temperature sintering involves heating to 1400℃ at a rate of 2℃ / min and holding for 6 hours, with a cooling rate of 1℃ / min. The final fiber has an inner diameter of 5μm, an outer diameter of 20μm, a wall thickness of 7.5μm, a fiber wall porosity of 30%, and an average pore size of 150nm.

[0060] Construction of a 3D interwoven network structure:

[0061] Layup: Mechanically combed layup, with an area density of 200 g / m² and a thickness of 8 mm.

[0062] Needle punching: needle punching density 100 times / cm², needle punching depth 4.8mm, bulk density after needle punching 0.15g / cm³, fiber interlacing density 50 strands / cm².

[0063] Introducing a nano-ceramic binder: 5 wt% zirconia nano-slurry (particle size 10 nm, containing 0.8 wt% polyvinylpyrrolidone dispersant), applied by impregnation, the binder accounting for 5 wt% of the total mass of the fiber network, and dried at 70°C for 3 hours.

[0064] Low-temperature activation sintering: Heat to 1000℃ at 3℃ / min, hold for 5 hours, and cool down at 2℃ / min.

[0065] Example 3, Preparation of hollow porous refractory fiber units:

[0066] The outer spinning solution is composed of aluminum isopropoxide as the aluminum source, sodium silicate as the silicon source, zirconium acetate as the zirconium source, yttrium oxide nanopowder as the yttrium source, 8 wt% polyacrylonitrile as the polymer binder, N,N-dimethylformamide as the solvent, 30 wt% total solids content, 1500 mPa·s viscosity, and 5 wt% polystyrene microspheres with a particle size of 200 nm.

[0067] Inner spinning solution: 15wt% polyvinyl alcohol aqueous solution, polyvinyl alcohol degree of polymerization 2400, degree of hydrolysis 99%, viscosity 300mPa・s, dissolved by stirring at 85℃ for 1.5 hours and then degassed under vacuum for 20 minutes.

[0068] Coaxial electrospinning: inner nozzle outer diameter 0.8mm, outer nozzle inner diameter 1.5mm; outer spinning solution delivery rate 0.8mL / h, inner layer 0.5mL / h; spinning voltage 20kV, receiving distance 20cm; ambient humidity 60%, temperature 30℃, collecting plate rotation speed 600rpm.

[0069] Sintering: Pre-sintering involves heating to 500℃ at a rate of 3℃ / min and holding for 2 hours; high-temperature sintering involves heating to 1700℃ at a rate of 5℃ / min and holding for 3 hours, with a cooling rate of 3℃ / min. The final fiber has an inner diameter of 10μm, an outer diameter of 30μm, a wall thickness of 10μm, a fiber wall porosity of 40%, and an average pore size of 450nm.

[0070] Construction of a 3D interwoven network structure:

[0071] Layup: air-laid web, area density 500g / m², thickness 12mm.

[0072] Needle punching: needle punching density 200 times / cm², needle punching depth 10.8mm, bulk density after needle punching 0.3g / cm³, fiber interlacing density 80 strands / cm².

[0073] Introducing a nano-ceramic binder: 20wt% yttrium oxide nano-slurry (particle size 50nm, containing 1.2wt% polyvinylpyrrolidone dispersant), applied by brushing, the binder accounting for 15wt% of the total mass of the fiber network, and dried at 90℃ for 1.5 hours.

[0074] Low-temperature activation sintering: Heat to 1300℃ at a rate of 5℃ / min, hold for 2 hours, and then cool down at a rate of 3℃ / min.

[0075] Example 4, Preparation of hollow porous refractory fiber units:

[0076] The outer spinning solution consists of aluminum nitrate and aluminum acetate (mass ratio 1:1), silicon ester and silica sol (mass ratio 1:1), zirconium oxychloride and zirconium nitrate (mass ratio 1:1), yttrium nitrate and yttrium acetate (mass ratio 1:1), a polymer binder of 4 wt% polyvinyl alcohol and polyethylene oxide (mass ratio 1:1), a solvent of deionized water and ethanol (volume ratio 2:1), a total solids content of 22 wt%, a viscosity of 900 mPa·s, and 3.5 wt% polystyrene microspheres and cellulose acetate (mass ratio 1:1) with a particle size of 120 nm.

[0077] Inner spinning solution: 13wt% polyvinyl alcohol aqueous solution, polyvinyl alcohol degree of polymerization 1900, degree of hydrolysis 92%, viscosity 220mPa・s, dissolved by stirring at 82℃ for 2 hours and then degassed under vacuum for 25 minutes.

[0078] Coaxial electrospinning: inner nozzle outer diameter 0.7mm, outer nozzle inner diameter 1.3mm; outer spinning solution delivery rate 0.5mL / h, inner layer 0.3mL / h; spinning voltage 17kV, receiving distance 17cm; ambient humidity 45%, temperature 24℃, collecting plate rotation speed 450rpm.

[0079] Sintering: Pre-sintering was carried out by heating to 420℃ at a rate of 2.5℃ / min and holding for 2.5 hours; high-temperature sintering was carried out by heating to 1500℃ at a rate of 3.5℃ / min and holding for 4.5 hours, with a cooling rate of 2.5℃ / min. The final fiber had an inner diameter of 7μm, an outer diameter of 23μm, a wall thickness of 8μm, a fiber wall porosity of 34%, and an average pore size of 280nm.

[0080] Construction of a 3D interwoven network structure:

[0081] Layup: Mechanically combed layup, with an area density of 300 g / m² and a thickness of 9 mm.

[0082] Needle punching: needle punching density 140 times / cm², needle punching depth 6.3mm, bulk density after needle punching 0.19g / cm³, fiber interlacing density 60 strands / cm².

[0083] A nano-ceramic binder was introduced: 12 wt% of a γ-alumina and zirconium oxide nano-mixed slurry (particle size 25 nm, mass ratio 1:1, containing 1 wt% polyvinylpyrrolidone dispersant) was sprayed on, with the binder accounting for 11 wt% of the total mass of the fiber network, and dried at 85°C for 1.8 hours.

[0084] Low-temperature activation sintering: heating to 1100℃ at 4℃ / min, holding at that temperature for 3.5 hours, and cooling at a rate of 2.5℃ / min.

[0085] Example 5, Preparation of hollow porous refractory fiber units:

[0086] The outer spinning solution consists of aluminum isopropoxide and aluminum nitrate (mass ratio 2:1), silicon is sodium silicate and ethyl silicate (mass ratio 2:1), zirconium is zirconium acetate and zirconium oxychloride (mass ratio 2:1), yttrium is yttrium oxide nanopowder and yttrium nitrate (mass ratio 2:1), polymer binder is 6 wt% polyacrylonitrile and polyvinyl alcohol (mass ratio 2:1), solvent is N,N-dimethylformamide and ethanol (volume ratio 1:1), total solids content is 27 wt%, viscosity is 1200 mPa·s, and 4 wt% polystyrene microspheres with a particle size of 160 nm are added.

[0087] Inner spinning solution: 14wt% polyvinyl alcohol aqueous solution, polyvinyl alcohol degree of polymerization 2200, degree of hydrolysis 95%, viscosity 260mPa・s, dissolved by stirring at 84℃ for 1.8 hours and then degassed under vacuum for 30 minutes.

[0088] Coaxial electrospinning: inner nozzle outer diameter 0.7mm, outer nozzle inner diameter 1.4mm; outer spinning solution delivery rate 0.7mL / h, inner layer 0.4mL / h; spinning voltage 19kV, receiving distance 19cm; ambient humidity 55%, temperature 28℃, collecting plate rotation speed 550rpm.

[0089] Sintering: Pre-sintering was carried out by heating to 460℃ at a rate of 2.8℃ / min and holding for 2.2 hours; high-temperature sintering was carried out by heating to 1600℃ at a rate of 4.5℃ / min and holding for 3.5 hours, with a cooling rate of 2.8℃ / min. The final fiber had an inner diameter of 9μm, an outer diameter of 27μm, a wall thickness of 9μm, a fiber wall porosity of 38%, and an average pore size of 350nm.

[0090] Construction of a 3D interwoven network structure:

[0091] Layup: air-laid web, area density 400g / m², thickness 11mm.

[0092] Needle punching: needle punching density 180 times / cm², needle punching depth 9.9mm, bulk density after needle punching 0.26g / cm³, fiber interlacing density 75 strands / cm².

[0093] A nano-ceramic binder was introduced: 18wt% of a yttrium oxide and zirconium oxide nano-mixed slurry (particle size 40nm, mass ratio 2:1, containing 1.1wt% polyvinylpyrrolidone dispersant) was applied by brushing, with the binder accounting for 13wt% of the total mass of the fiber network, and dried at 88℃ for 1.6 hours.

[0094] Low-temperature activation sintering: the temperature is increased to 1250℃ at a rate of 4.5℃ / min, held for 2.5 hours, and then cooled at a rate of 2.8℃ / min.

[0095] Comparative Example 1 (Traditional Solid Refractory Fiber): Solid Refractory Fiber Preparation: Alumina, silicon dioxide, and zirconium oxide were mixed in a mass ratio of 70:20:10 using a melt drawing method, melted at a high temperature of 1800℃, and then drawn into solid fibers with a fiber diameter of 20μm.

[0096] Fiber felt forming: Solid fibers are mechanically combed and laid up with an area density of 350 g / m², a thickness of 10 mm, a needle punching density of 150 times / cm², a needle punching depth of 7.5 mm, without nano-ceramic binders or low-temperature activation sintering steps.

[0097] Comparative Example 2 (Hollow Refractory Fibers without Gradient Structure): Preparation of Hollow Refractory Fiber Units:

[0098] Outer spinning solution: aluminum nitrate is selected as the aluminum source, ethyl silicate is selected as the silicon source, zirconium oxychloride is selected as the zirconium source, yttrium nitrate is selected as the yttrium source, the polymer binder is 5 wt% polyvinyl alcohol, the solvent is deionized water and ethanol (volume ratio 1:1), the total solid content is 25 wt%, the viscosity is 850 mPa·s, no sacrificial template is added, and the components are uniformly mixed without gradient design.

[0099] Inner spinning solution: Same as in Example 1.

[0100] Coaxial electrospinning: Same as Example 1.

[0101] Sintering: Same as in Example 1, the final fiber inner diameter is 8μm, outer diameter is 25μm, wall thickness is 8.5μm, fiber wall porosity is 35%, average pore size is uniform at 250nm, and there is no radial gradient.

[0102] Construction of the three-dimensional interwoven network structure: Same as in Example 1.

[0103] Performance testing and data comparison:

[0104] project Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Thermal conductivity at 1000℃ (W / (m・K)) 0.09 0.11 0.08 0.10 0.085 0.18 0.12 Thermal conductivity at 1500℃ (W / (m・K)) 0.11 0.13 0.10 0.12 0.105 0.21 0.14 Thermal conductivity at 1800℃ (W / (m・K)) 0.12 0.14 0.11 0.13 0.115 0.23 0.15 Compressive strength at 1500℃ (MPa) 22 18 25 20 24 10 16 Compressive strength retention rate (%) after heat treatment at 1700℃ for 100 hours 92 88 95 90 93 55 75 Volume shrinkage rate at 1800℃ (%) 2.1 2.5 1.8 2.3 2.0 5.8 3.5 Thermal shock resistance (cycles from 1800℃ to room temperature, no cracks). 35 30 40 33 38 15 25

[0105] The thermal conductivity of Examples 1-5 was lower than that of Comparative Examples 1 and 2 in the range of 1000℃-1800℃. Example 3 had the lowest thermal conductivity of only 0.11 W / (m·K) at 1800℃ due to the highest fiber wall porosity and larger average pore size. Comparative Example 1, which is a traditional solid fiber without multi-scale pore structure, had a thermal conductivity of 0.23 W / (m·K) at 1800℃. Although Comparative Example 2 has a hollow structure, it lacks a gradient design and its thermal insulation performance is better than that of traditional solid fibers but not as good as that of Examples 1-5. This indicates that the synergistic effect of multi-scale pores and gradient structures can significantly improve thermal insulation performance.

[0106] Examples 1 and 3-5 all exhibited compressive strengths exceeding 20 MPa at 1500℃ (Example 3 reached 25 MPa). Example 2 had a compressive strength of 18 MPa, and after 100 hours of heat treatment at 1700℃, the compressive strength retention rate exceeded 88% (Example 3 reached 95%). Comparative Example 1 showed a compressive strength of only 10 MPa at 11500℃, and its strength decayed rapidly at high temperatures, with a retention rate of only 55% after 100 hours of heat treatment at 1700℃. Comparative Example 2, lacking a gradient structure, exhibited weak fiber surface strength and erosion resistance, resulting in lower compressive strength and retention rate compared to the examples. This demonstrates that the three-dimensional network bonded to the gradient structure and nano-ceramics can enhance high-temperature mechanical strength and stability.

[0107] Examples 1-5 all exhibited a volume shrinkage rate of less than 2.5% at 1800℃ (Example 3 only 1.8%), and over 30 thermal shock cycles (Example 3 reached 40 cycles). Comparative Example 1 showed a volume shrinkage rate of 5.8% at 1800℃ and only 15 thermal shock cycles. Comparative Example 2 demonstrated better volume shrinkage rate and thermal shock resistance than Comparative Example 1 but not as good as the examples, proving that the structural design of the present invention can effectively suppress high-temperature volume shrinkage and improve thermal shock resistance.

[0108] The ultra-high temperature stable composite refractory fiber prepared by this invention overcomes the bottleneck of traditional refractory fibers in achieving both thermal insulation and structural stability through the synergistic effect of multi-scale pores, gradient structure, three-dimensional interwoven network and nano-ceramic bonding. It exhibits excellent comprehensive performance in ultra-high temperature environments and can meet the needs of high-performance refractory materials in aerospace, advanced industrial kilns and other fields.

[0109] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of making an ultra-high temperature stable, composite refractory fiber, characterized by, The method comprises the following steps: S1, preparing an ultra-high temperature stable hollow porous refractory fiber unit, wherein the fiber wall has a radial gradient structure, the inner layer region of the fiber wall close to the hollow channel has high porosity, large average pore size, and high alumina content, and the outer layer region of the fiber wall close to the outer surface of the fiber has low porosity, small average pore size, and high zirconium component concentration; S11, preparing an outer layer gradient ceramic precursor spinning solution and an inner layer sacrificial template spinning solution for coaxial electrospinning, wherein the outer layer gradient ceramic precursor spinning solution is an aluminum source, a silicon source, a zirconium source, a yttrium source, a polymer binder with a mass fraction of 2wt%-8wt%, and a carbon-based or organic sacrificial template with a mass fraction of 1wt%-5wt%, which are dissolved or dispersed in a solvent to form a uniform and stable solution; S12, preparing a hollow composite precursor fiber by using a coaxial electrospinning technology; S13, performing sintering treatment on the hollow composite precursor fiber to form a hollow porous refractory fiber unit; S2, constructing a three-dimensional interwoven network structure of the ultra-high temperature stable hollow porous refractory fiber unit.

2. A method of making an ultra-high temperature stable, composite refractory fiber according to claim 1, wherein, The aluminum source is one or more of aluminum nitrate, aluminum acetate, or aluminum isopropyl alcohol; The silicon source is one or more of ethyl silicate, silica sol, or sodium silicate; The zirconium source is one or more of zirconium oxychloride, zirconium nitrate, or zirconium acetate; The polymer binder is one or more of polyvinyl alcohol, polyethylene oxide, or polyacrylonitrile; The solvent is one or more of deionized water, ethanol, or N,N-dimethylformamide; The total solid content of the outer layer spinning solution is between 15wt% and 30wt%, and the viscosity range is 500mPa·s-1500mPa·s.

3. The method for preparing ultra-high temperature stable composite refractory fiber according to claim 1, characterized in that, The outer layer gradient ceramic precursor spinning solution contains a carbon-based or organic sacrificial template, and the particle size range of the sacrificial template is 50nm-200nm, which is used to decompose and form controllable micro-nano pores in the subsequent sintering process; The sacrificial template is one or more of polystyrene microspheres or cellulose acetate.

4. The method for preparing ultra-high temperature stable composite refractory fiber according to claim 1, characterized in that, In S11, the preparation of the inner layer sacrificial template spinning solution comprises: Polyvinyl alcohol is dissolved in deionized water to form a polyvinyl alcohol aqueous solution with a mass fraction of 8wt%-15wt%; The average polymerization degree of the polyvinyl alcohol is 1700-2400, and the hydrolysis degree is 88%-99%; The viscosity of the inner layer spinning solution is between 100mPa·s and 300mPa·s; The polyvinyl alcohol aqueous solution needs to be completely dissolved under stirring and heating conditions, and degassing treatment is required before use.

5. The method for preparing ultra-high temperature stable composite refractory fiber according to claim 1, characterized in that, In S12, the parameter settings for preparing a hollow composite precursor fiber by using a coaxial electrospinning technology comprise: A coaxial nozzle is used, wherein the outer diameter of the inner layer nozzle is 0.5mm-0.8mm, and the inner diameter of the outer layer nozzle is 1.0mm-1.5mm; The delivery rate of the outer layer gradient ceramic precursor spinning solution is 0.4mL / h-0.8mL / h; The delivery rate of the inner layer sacrificial template spinning solution is 0.2mL / h-0.5mL / h; The spinning voltage is applied to the coaxial nozzle, and the voltage range is 15kV-20kV; The receiving distance, i.e. the distance from the tip of the coaxial nozzle to the collection plate, is 15-20 cm; The electrospinning process is carried out under the conditions of ambient humidity of 40-60% relative humidity and temperature of 20-30℃.

6. The method for preparing ultra-high temperature stable composite refractory fiber according to claim 1, characterized in that, The method of sintering the hollow composite precursor fibers in S13 to form the hollow porous refractory fiber unit comprises: The collected hollow composite precursor fibers are pre-sintered in an air atmosphere, the heating rate is set to 1-3℃ / min, heated from room temperature to 300-500℃, and kept at this temperature for 2-4 hours; High-temperature sintering is carried out in an air atmosphere, the temperature is raised to 1400-1700℃ at a heating rate of 2-5℃ / min, and kept at the highest temperature for 3-6 hours.