A continuous process for the production of ceramic microfibers
Patent Information
- Application Number
- CN202610931269.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-26
- Publication Date
- 2026-09-15
Smart Images
Figure CN122749104A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of inorganic non-metallic materials technology, and more specifically, to a continuous preparation process for ceramic microfibers. Background Technology
[0002] Ceramic microfibers, as a key basic material for aerospace thermal protection, high-temperature filtration, and advanced composite material reinforcement, have long relied on two mainstream process routes for continuous preparation: melt spinning and sol-gel methods. The melt spinning method involves melting ceramic raw materials such as alumina and silica at high temperatures, then flowing them out through a platinum-rhodium permeable stencil, and finally stretching them into fibers using high-speed centrifugal force or airflow. With its advantages of high process maturity, large single-line capacity, and low production cost, it has become the mainstream production technology for industrial-grade ceramic fiber cotton and blanket products, and is widely used in thermal insulation applications in metallurgy, power, and other fields. The sol-gel method uses metal alkoxides or inorganic salts as precursors, forming wet gel fiber preforms through hydrolysis and condensation, followed by drying and calcination to obtain polycrystalline ceramic fibers. Its advantages lie in the high degree of freedom in component design, high fiber purity, and excellent high-temperature resistance, making it particularly suitable for high-end applications with temperature resistance exceeding 1300℃.
[0003] However, the related melt spinning method is limited by the high-temperature viscosity and surface tension characteristics of the melt, resulting in a wide fiber distribution, high brittleness, and poor flexibility, which cannot meet the laying requirements of complex curved surface heat protection structures. On the other hand, the sol-gel method relies on high-molecular organic atomizing agents to give the sol spinnability. During the subsequent heat treatment, the violent decomposition and release of organic matter leaves micropores and microcrack nuclei inside the fiber. In addition, the difference in radial shrinkage between the surface and interior of the wet gel preform during the drying stage can easily cause longitudinal microcracks, resulting in an excessively high fiber interruption rate in continuous production. Furthermore, the final fiber often breaks due to abnormal grain growth caused by uncontrolled grain boundary migration, making it difficult to simultaneously achieve continuous production without fiber breakage, uniform diameter, and axial flexibility. Summary of the Invention
[0004] To address the issues of high fiber breakage and poor flexibility caused by using melt spinning and sol-gel methods, this application provides a continuous preparation process for ceramic microfibers.
[0005] This application provides a continuous preparation process for ceramic microfibers, employing the following technical solution: A continuous preparation process for ceramic microfibers includes the following steps: S1. Preparation of modified sol: Aluminum source, silicon source and ternary eutectic precursor are mixed and organic framework agent is added. After hydrolysis, polycondensation and pre-crosslinking treatment, modified sol is obtained. S2, Continuous fiber formation: The modified sol obtained in step S1 is centrifuged or air-driven to form wet gel microfiber embryos, and the embryos are collected and carried on a breathable tray. S3, Directional Dehydration: The breathable tray carrying the wet gel microfiber preform is placed in a humidity gradient environment, so that the water in the preform is discharged downward through the pores of the tray to obtain dry gel fibers. S4. Step heat treatment: The dry gel fibers obtained in step S3 are subjected to controlled decarburization treatment, transient liquid phase pinning treatment and crystallization shaping treatment in sequence to obtain continuous ceramic microfibers.
[0006] By adopting the above technical solution, step S1 introduces a lithium-boron-silicon oxide component that forms a transient liquid phase in the intermediate temperature range into the aluminum-silicon hydrolysis condensation network. Simultaneously, the amount of organic framework agent is reduced to the minimum level required to maintain surface viscoelasticity only during the moment of stretching, resulting in a significant decrease in the volatile load inside the preform during the subsequent dehydration stage. Furthermore, step S3 changes the driving force for water removal from traditional radial evaporation to unidirectional migration along the fiber axis through capillary channels, preventing radial shrinkage differences and longitudinal microcracks in the gel network due to premature surface crusting during drying. This, in turn, makes the process more efficient. Step S4 can control the atmosphere and temperature in stages while maintaining the integrity of the preform structure. First, under water vapor-rich micro-oxygen conditions, the residual organic matter is gradually oxidized and decomposed rather than thermally disintegrated. Then, under oxygen-deficient conditions, the ternary eutectic components are spread into a viscous liquid phase at the grain boundaries to pin grain boundary migration, inhibit abnormal grain growth, and provide a microcrack self-healing effect. Finally, under micro-oxidation conditions, the main crystalline phase is crystallized and a fiber structure with continuous amorphous thin films distributed along the grain boundaries is obtained. Thus, within a single pure process route, the requirements of continuous non-fiber production, uniform fiber diameter, and finished product bending without breakage are simultaneously met.
[0007] Preferably, step S1 further includes pretreatment of the aluminum source: dissolving the aluminum source in an acidic aqueous solution, adjusting the pH of the system to 2.5~4.0 to obtain an aluminum source solution, and then mixing the aluminum source solution with a silicon source for hydrolysis and polycondensation.
[0008] By adopting the above technical solution, acidic conditions cause proton-assisted electrophilic substitution of alkoxy groups or coordinated water at the aluminum center, resulting in a controllable leading hydrolysis rate relative to the polycondensation rate. The tetraethyl orthosilicate molecules from the silicon source gradually establish silicon-aluminum bridging bonds and silicon-silicon crosslinking networks with the silanol groups generated after hydrolysis and the hydrolysis products at the aluminum center. The pH of the system is stabilized in the weakly acidic range, thus making the polycondensation tend to generate more extended, weakly crosslinked polymer chains rather than rapidly agglomerated dense particles. The resulting aluminum source solution, after mixing with the silicon source, shows a gradual and predictable increase in viscosity, providing a stable initial rheological basis for controlling the spinning window after introducing a ternary eutectic precursor and organic framework agent. This also avoids the problem of uneven dispersion of ternary additives due to premature local gelation.
[0009] Preferably, in step S1, the pre-crosslinking treatment is as follows: the mixture is placed in a constant temperature water bath at 35~45℃, and the mixture is ultrasonically dispersed for 10~15min and left to stand for 20~30min as one cycle, and the process is repeated for 2~4 cycles.
[0010] By adopting the above technical solution, the acoustic cavitation microjets and mechanical shearing input in the ultrasonic dispersion stage break up and redistribute the local enrichment areas of boric acid and lithium salt precursors in the aluminum-silicon polymer network, allowing lithium and boron components to be embedded in the network skeleton in the form of nanoscale heterogeneous micro-regions rather than existing as isolated aggregate phases; the subsequent settling stage allows the network to continue to undergo condensation crosslinking under weak thermal activation and lock the micro-region topology formed in the ultrasonic stage; after multiple cycles, the pore channels in the aluminum-silicon network exhibit the characteristic of preferential connectivity along the fiber axis to be formed; this pre-embedded connectivity structure becomes the capillary channel for water to migrate from the inside of the fiber to the support plate direction in step S3; at the same time, it also allows the lithium borosilicate liquid phase in the transient liquid phase pinning stage of step S4 to spread more evenly along the same set of connectivity channels to the intersection of the grain boundaries rather than randomly accumulating.
[0011] Preferably, in step S1, the pre-crosslinking treatment makes the apparent viscosity of the modified sol 200~800 mPa·s at 25°C and a shear rate of 1~100 s⁻¹.
[0012] By adopting the above technical solution, the viscosity range corresponds to a sufficient degree of three-dimensional cross-linking of the gel network to prevent it from arcing or excessively thinning under centrifugal force or airflow traction, but it has not yet entered a rigid gel state. Therefore, after the fiber preform leaves the nozzle during the centrifugal spinning or airflow traction process in step S2, it can still receive the continuous falling fibers on the receiving plate in the form of a wet and soft network without local remelting and bonding. At the same time, this viscosity level means that the solid volume fraction of the network skeleton is not too high, and the preform still retains interconnected mesoporous channels for the liquid phase water phase in step S3 to be transported to the pores of the lower receiving plate by means of capillary force. If the viscosity is significantly lower than this range, the surface tension of the filament will dominate during stretching, making it easy to break or clump. If it is significantly higher than this range, the network will become rigid too early, causing the internal water to be unable to be discharged smoothly during subsequent dehydration and to accumulate as steam bubbling sites.
[0013] Preferably, in step S1, the ternary eutectic precursor is added in the form of a combination of boric acid, lithium nitrate and lithium silicate, and the addition is made after the aluminum source and silicon source are mixed and before the system viscosity rises to 30% of the final spinning viscosity.
[0014] By adopting the above technical solution, boric acid and lithium salt are added at the low viscosity stage when the aluminum-silicon network is still dominated by short-chain oligomers. Boric acid molecules can form borosilicate bonds or borosilicate bridging structures with silanol groups and aluminum hydroxyl groups. Lithium ions are adsorbed near the polar sites of the network in the form of solvated ions rather than existing as independent second-phase droplets. As polycondensation progresses in the subsequent pre-crosslinking cycle, these boron centers and lithium centers are gradually incorporated into the weak crosslinking nodes of the growing network, thereby achieving spatial uniformity of the ternary components at the microscopic level. This avoids the formation of large low-melting-point pools in the mid-temperature section of step S4 due to late addition, or the formation of localized weakened areas in the final fiber. At the same time, the introduction of boric acid partially replaces the hydrogen bond crosslinking density that traditional solutions require a large amount of polymeric framework agents to provide at the chemical level, thereby reducing the total amount of organic framework agents without sacrificing the viscoelasticity required for spinning.
[0015] Preferably, in step S1, the aluminum source is selected from one or more combinations of aluminum isopropoxide, aluminum chloride, or aluminum nitrate, the silicon source is tetraethyl orthosilicate, the ternary eutectic precursor accounts for 3-8% of the total mass of the ceramic components, and the amount of organic framework agent added is 1-5% of the total sol mass.
[0016] By adopting the above technical solution, aluminum isopropoxide, aluminum chloride, or aluminum nitrate, after hydrolysis, are transformed into aluminum oxide polymers through alkoxy step-replacement or hydration complex dehydration pathways, respectively, and co-condense with the silicon oxide polymer generated by the hydrolysis of tetraethyl orthosilicate to form an aluminum silicon oxide network matrix. The 3-8% mass ratio of the ternary eutectic precursor is within the range of 580-850℃, which is a proportion window that can generate a sufficient amount of transient liquid phase to wet and continuously cover the primary grain boundaries, but is not enough to transform the fiber as a whole into a loose glassy structure after final crystallization. The 1-5% proportion of the organic framework agent suppresses the dehydration shrinkage stress and the amount of carbon slag generated to within the capillary capacity of the gel network, so that the drainage process in step S3 does not have to compete for pores with the gaseous products that escape simultaneously with a large amount of organic matter. It also avoids the residual carbon from being transformed into a difficult-to-remove coking carbon network that coats the fiber surface due to lack of oxygen in the first stage of step S4.
[0017] Preferably, in step S2, the rotation speed of the centrifugal spinning disc is 8000~12000 rpm, and the traction airflow velocity is 50~150 m / s.
[0018] By adopting the above technical solution, the tangential velocity of the centrifugal disc and the radial ejection work or the stagnant traction force of the high-speed airflow elongate the modified sol that has reached the spinning viscosity in step S1 into a continuous filament with a diameter in the micrometer range; the solvent surface evaporates in the free flight section after the liquid column leaves the disc hole or nozzle, which further increases the surface viscosity and thus shapes it into a wet gel preform; the above-mentioned range of rotation speed and airflow speed, combined with the viscosity window of step S1, makes the tensile strain rate of the filament match the shear thinning recovery time of the sol; when the obtained preform falls onto the tray, it has formed a skin layer that is self-supporting but has not yet completed internal drying and shrinkage, thus allowing the capillary drainage in step S3 to be completed while the filament is still wet and soft but topologically fixed, rather than forcibly forcing out moisture from the hardened preform.
[0019] Preferably, in step S3, the humidity gradient environment is specifically: the relative humidity in the area below the tray is maintained at 15% to 25% and the temperature at 40 to 60°C, and the relative humidity in the space above the tray where the embryo is located is maintained at 75% to 88% and the temperature at 55 to 70°C.
[0020] By adopting the above technical solution, a continuous water vapor partial pressure gradient is established in the direction perpendicular to the plane of the pallet due to the humidity difference between the upper and lower parts of the pallet. The liquid water phase in the preform spontaneously flows from the inside of the fiber along the network channels to the side of the pallet under the capillary potential energy field determined by its own surface tension and pore geometry, and leaves the system in the form of water vapor from the lower low humidity zone. The entire mass transfer path is that the liquid migrates in the internal channels and then evaporates on the far side of the pallet. The high humidity environment above the surface of the preform inhibits the radical evaporation of the surface directly to the gas phase, thereby avoiding the problem of premature densification and shelling of the cortex and the sealing of the interior. The direction of water discharge is constrained to a unidirectional path from the fiber axis through the thickness direction of the pallet. The shrinkage of the preform thus tends to be a uniform axial coordinated shrinkage rather than local radial tearing. The dry gel fiber obtained after drying has a much lower internal microcrack core density than the product of oven static drying, providing an initial structure without hidden damage for the heat treatment in step S4.
[0021] Preferably, in step S4: The controlled decarbonization treatment involves a temperature of 280–500℃, a residence time of 20–45 min, and an atmosphere composed of water vapor and an inert carrier gas, wherein the water vapor volume percentage is 8%–12% and the oxygen volume percentage is 2%–5%. The transient liquid phase pinning treatment is carried out at a temperature of 580~850℃ for 30~70 min, in an inert gas atmosphere with an oxygen volume percentage of ≤0.3%, and an oxygen pulse is periodically introduced every 10~15 min, during which the oxygen volume percentage rises to 0.5%~0.8%, and each pulse lasts for 1~2 min. The crystallization and shaping treatment involves a temperature of 1050~1280℃, a residence time of 40~90 minutes, an oxygen volume ratio of 1%~3% in the atmosphere, and the remainder being inert gas.
[0022] By adopting the above technical solution, the first stage of controlled decarburization gradually cuts the main chain of the residual organic framework agent before the temperature enters the range of violent sintering of the aluminum-silicon network; the coexistence of micro-oxygen and water-rich vapor conditions allows carbon species to be preferentially converted into carbon monoxide and carbon dioxide to escape rather than undergoing anaerobic pyrolysis to form a difficult-to-oxidize residual carbon coke layer; the presence of water vapor simultaneously maintains the surface of the preform in a state that can be softened by adsorbed water film to reduce the stress difference between the surface layer and the core; the second stage of transient liquid phase pinning treatment pushes the temperature into the low eutectic softening window corresponding to the ternary lithium borosilicate component. At this time, the lithium borosilicate phase appears in the form of a viscous liquid phase under oxygen-deficient conditions and spreads into a continuous film along the three-way intersection of the primary alumina and mullite or aluminum silicate phase, thereby physically blocking the large-scale migration and slippage of the grain boundaries. The grain size is suppressed to the nanometer to submicrometer scale to avoid transverse crystal fracture caused by a few grains crossing the fiber cross section; the role of periodic micro-oxygen pulses is not to burn residual carbon but to fine-tune the valence state and surface tension of boron centers on the liquid phase surface so that the liquid phase keeps sufficient wetting of the grain boundaries and does not cause liquid phase shrinkage and spheroidization due to interfacial tension imbalance caused by excessive reduction; the third stage crystallization and shaping treatment drives the main crystalline phase to complete the transformation to the thermally stable crystalline form under micro-oxidation conditions, while freezing the spread lithium borosilicate phase into an amorphous glass film remaining at the grain boundaries; the final continuous ceramic microfibers exhibit a macroscopic structural state of a composite of polycrystalline ceramic core and toughened grain boundary phase. When the fibers are bundled or bent under stress, cracks tend to deflect and dissipate energy at the amorphous grain boundary rather than propagating radially.
[0023] Preferably, after step S4, post-processing is also included: the obtained continuous ceramic microfibers are bundled, wound, or cut to a fixed length to obtain ceramic microfiber products.
[0024] By adopting the above technical solution, the surface of the heat-treated fiber has been transformed into a stable oxide state and no longer contains volatile organic compounds. At this time, mechanical bundling or fixed-length cutting will not change the fiber structure. According to the subsequent application requirements, the continuously discharged fibers can be directly organized into rolls, fixed-length loose fibers, or further stacked and pressed into fiber blanket products. The entire post-treatment step and the preceding chemical heat treatment step are separated by the completion of fiber crystallization and shaping. Mechanical contact in the post-treatment stage will not cause new chemical instability points or hidden microcracks to be generated inside the fiber.
[0025] In summary, this application has the following beneficial effects: 1. Because this application introduces lithium-boron-silicon oxide components into the aluminum-silicon hydrolysis condensation network and compresses the amount of organic framework agent to a low level that only maintains the viscoelasticity at the moment of stretching, while anti-gravity capillary dehydration replaces surface radial evaporation, radial shrinkage difference and microcracks are avoided during the drying process, thus achieving the effect of continuous preparation of non-fiber fibers with uniform fiber diameter and axial flexibility.
[0026] 2. In this application, a pre-crosslinking treatment is preferably used to form pore channels that are preferentially connected along the fiber axis of the modified sol. Ultrasonic dispersion and static cycling are used to construct a uniform heterogeneous micro-region structure of lithium borosilicate components, so as to achieve the effect of smooth unidirectional water migration and intact embryo structure without hidden damage during the dehydration process.
[0027] 3. The method of this application gradually oxidizes and decomposes residual organic matter through controlled decarburization treatment in a water vapor-rich micro-oxygen atmosphere, while transient liquid phase pinning treatment utilizes lithium borosilicate components to spread at grain boundaries to inhibit abnormal grain growth, and crystallization and shaping treatment forms a composite structure of polycrystalline core and amorphous grain boundary phase, thus obtaining high-temperature resistant and flexible continuous ceramic microfibers.
[0028] 4. In this application, periodic micro-oxygen pulses are preferred to regulate the surface tension and wettability of the transient liquid phase. Under oxygen-deficient conditions, pulsed oxygen fine-tunes the valence state of boron centers on the surface of the liquid phase, thereby achieving a uniform and continuous grain boundary glass phase without local enrichment or deficiency. Attached Figure Description
[0029] Figure 1 This is a flowchart of a continuous preparation process for ceramic microfibers proposed in this application; Figure 2 This is a schematic diagram showing the test results of room temperature tensile strength and fracture strain of a single filament in the embodiments and comparative examples proposed in this application. Figure 3 This is a schematic diagram showing the detection results of the minimum bending radius of the embodiments and comparative examples proposed in this application; Figure 4 This is a schematic diagram showing the results of heating permanent linear change rate detection for the embodiments and comparative examples proposed in this application. Figure 5 This is a schematic diagram showing the residual carbon content detection results of the embodiments and comparative examples proposed in this application. Detailed Implementation
[0030] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.
[0031] This application discloses a continuous preparation process for ceramic microfibers. The process includes the following steps: S1, preparing a modified sol: mixing an aluminum source, a silicon source, and a ternary eutectic precursor, adding an organic framework agent, and then performing hydrolysis, polycondensation, and pre-crosslinking treatment to obtain a modified sol; S2, continuous fiber formation: centrifuging or airflow traction of the modified sol to form a wet gel microfiber preform; S3, directional dehydration: placing a breathable tray carrying the wet gel microfiber preform in a humidity gradient environment to obtain dry gel fibers; S4, stepped heat treatment: sequentially subjecting the dry gel fibers to controlled decarburization, transient liquid-phase pinning, and crystallization shaping treatment to obtain continuous ceramic microfibers.
[0032] This application introduces lithium-boron-silicon oxide components into the aluminum-silicon hydrolysis condensation network and compresses the amount of organic framework agent to a low level that only maintains the viscoelasticity at the moment of stretching. At the same time, anti-gravity capillary dehydration replaces surface radial evaporation, avoiding radial shrinkage difference and microcracks during the drying process, and achieving the effect of continuous preparation of non-fiber fibers with uniform fiber diameter and axial flexibility.
[0033] Example 1: This example provides a continuous preparation process for ceramic microfibers, comprising the following steps: S1. Preparation of modified sol: Aluminum source, silicon source and ternary eutectic precursor are mixed and organic framework agent is added. After hydrolysis, polycondensation and pre-crosslinking treatment, modified sol is obtained.
[0034] The pretreatment of the aluminum source involves dissolving the aluminum source in an acidic aqueous solution, adjusting the pH of the system to 2.5 to obtain an aluminum source solution, and then mixing the aluminum source solution with a silicon source for hydrolysis and polycondensation.
[0035] The pre-crosslinking treatment involves placing the mixture in a 35°C constant temperature water bath and performing two cycles of ultrasonic dispersion for 10 minutes followed by standing for 20 minutes.
[0036] The pre-crosslinking treatment resulted in an apparent viscosity of 200 mPa·s for the modified sol at 25°C and a shear rate of 1 s⁻¹.
[0037] The ternary eutectic precursor is added in the form of a combination of boric acid, lithium nitrate and lithium silicate. The addition is made after the aluminum source and silicon source are mixed and before the system viscosity rises to 30% of the final spinning viscosity.
[0038] The aluminum source is aluminum isopropoxide, the silicon source is tetraethyl orthosilicate, the ternary eutectic precursor accounts for 3% of the total mass of the ceramic components, and the amount of organic framework agent added is 1% of the total sol mass.
[0039] S2. Continuous fiber formation: The modified sol obtained in step S1 is centrifuged and spun into wet gel microfiber embryos, which are then collected and carried on a breathable tray.
[0040] The centrifugal spinning disc rotates at 8000 rpm.
[0041] S3. Directional dehydration: The breathable tray carrying the wet gel microfiber preform is placed in a humidity gradient environment, so that the water in the preform is discharged downward through the pores of the tray to obtain dry gel fibers.
[0042] Specifically, the humidity gradient environment is as follows: the relative humidity in the area below the tray is maintained at 15% and the temperature at 40℃, while the relative humidity in the space above the tray where the embryo is located is maintained at 75% and the temperature at 55℃.
[0043] S4. Step heat treatment: The dry gel fibers obtained in step S3 are subjected to controlled decarburization treatment, transient liquid phase pinning treatment and crystallization shaping treatment in sequence to obtain continuous ceramic microfibers.
[0044] Among them, the controllable decarbonization treatment is carried out at a temperature of 280℃ for 20 minutes. The atmosphere consists of water vapor and inert carrier gas, with water vapor accounting for 8% of the volume and oxygen accounting for 2% of the volume.
[0045] The transient liquid phase pinning treatment involves a temperature of 580℃, a residence time of 30 minutes, an inert gas substrate atmosphere, an oxygen volume percentage of ≤0.3%, and periodic oxygen pulses every 10 minutes, during which the oxygen volume percentage rises to 0.5%, with each pulse lasting 1 minute.
[0046] Among them, the crystallization and shaping treatment is carried out at a temperature of 1050℃ for 40 minutes, with oxygen accounting for 1% of the volume in the atmosphere and the remainder being inert gas.
[0047] S5. Post-processing: The obtained continuous ceramic microfibers are bundled and wound to obtain ceramic microfiber products.
[0048] The post-processing involves bundling, winding, or cutting the obtained continuous ceramic microfibers to a fixed length to obtain ceramic microfiber products.
[0049] Example 2: This example provides a continuous preparation process for ceramic microfibers, comprising the following steps: S1. Preparation of modified sol: Aluminum source, silicon source and ternary eutectic precursor are mixed and organic framework agent is added. After hydrolysis, polycondensation and pre-crosslinking treatment, modified sol is obtained.
[0050] The pretreatment of the aluminum source involves dissolving the aluminum source in an acidic aqueous solution, adjusting the pH of the system to 3.25 to obtain an aluminum source solution, and then mixing the aluminum source solution with a silicon source for hydrolysis and polycondensation.
[0051] The pre-crosslinking treatment involves placing the mixture in a 40°C constant temperature water bath and performing three cycles of ultrasonic dispersion for 12.5 min followed by standing for 25 min.
[0052] The pre-crosslinking treatment resulted in an apparent viscosity of 500 mPa·s for the modified sol at 25°C and a shear rate of 50.5 s⁻¹.
[0053] The ternary eutectic precursor is added in the form of a combination of boric acid, lithium nitrate and lithium silicate. The addition is made after the aluminum source and silicon source are mixed and before the system viscosity rises to 30% of the final spinning viscosity.
[0054] The aluminum source is a combination of aluminum chloride and aluminum nitrate, the silicon source is tetraethyl orthosilicate, the ternary eutectic precursor accounts for 5.5% of the total mass of the ceramic components, and the amount of organic framework agent added is 3% of the total sol mass.
[0055] S2. Continuous fiber formation: The modified sol obtained in step S1 is subjected to airflow traction to form wet gel microfiber embryos, and the embryos are collected and carried on a breathable tray.
[0056] The traction airflow velocity is 100 m / s.
[0057] S3. Directional dehydration: The breathable tray carrying the wet gel microfiber preform is placed in a humidity gradient environment, so that the water in the preform is discharged downward through the pores of the tray to obtain dry gel fibers.
[0058] Specifically, the humidity gradient environment is as follows: the relative humidity in the area below the tray is maintained at 20% and the temperature at 50℃, while the relative humidity in the space above the tray where the embryo is located is maintained at 81.5% and the temperature at 62.5℃.
[0059] S4. Step heat treatment: The dry gel fibers obtained in step S3 are subjected to controlled decarburization treatment, transient liquid phase pinning treatment and crystallization shaping treatment in sequence to obtain continuous ceramic microfibers.
[0060] The controlled decarbonization process involves a temperature of 390℃, a residence time of 32.5 min, and an atmosphere composed of water vapor and inert carrier gas, with water vapor accounting for 10% of the volume and oxygen accounting for 3.5% of the volume.
[0061] The transient liquid phase pinning treatment involved a temperature of 715℃, a residence time of 50 min, an inert gas substrate atmosphere, an oxygen volume percentage of ≤0.3%, and periodic oxygen pulses every 12.5 min, during which the oxygen volume percentage increased to 0.65%, with each pulse lasting 1.5 min.
[0062] The crystallization and shaping treatment involved a temperature of 1165℃, a residence time of 65 minutes, an atmosphere containing 2% oxygen by volume, and the remainder being inert gas.
[0063] S5. Post-processing: The obtained continuous ceramic microfibers are cut to a fixed length to obtain ceramic microfiber products.
[0064] The post-processing involves bundling, winding, or cutting the obtained continuous ceramic microfibers to a fixed length to obtain ceramic microfiber products.
[0065] Example 3: This example provides a continuous preparation process for ceramic microfibers, comprising the following steps: S1. Preparation of modified sol: Aluminum source, silicon source and ternary eutectic precursor are mixed and organic framework agent is added. After hydrolysis, polycondensation and pre-crosslinking treatment, modified sol is obtained.
[0066] The pretreatment of the aluminum source involves dissolving the aluminum source in an acidic aqueous solution, adjusting the pH of the system to 4.0 to obtain an aluminum source solution, and then mixing the aluminum source solution with a silicon source for hydrolysis and polycondensation.
[0067] The pre-crosslinking treatment involves placing the mixture in a 45°C constant temperature water bath and performing a cycle of ultrasonic dispersion for 15 minutes followed by standing for 30 minutes, for a total of 4 cycles.
[0068] The pre-crosslinking treatment resulted in an apparent viscosity of 800 mPa·s for the modified sol at 25°C and a shear rate of 100 s⁻¹.
[0069] The ternary eutectic precursor is added in the form of a combination of boric acid, lithium nitrate and lithium silicate. The addition is made after the aluminum source and silicon source are mixed and before the system viscosity rises to 30% of the final spinning viscosity.
[0070] The aluminum source is selected from a combination of aluminum isopropoxide, aluminum chloride and aluminum nitrate, the silicon source is tetraethyl orthosilicate, the ternary eutectic precursor accounts for 8% of the total mass of the ceramic components, and the amount of organic framework agent added is 5% of the total sol mass.
[0071] S2, Continuous fiber formation: The modified sol obtained in step S1 is first centrifuged and spun, and then air-driven to form wet gel microfiber embryos, which are then collected and carried on a breathable tray.
[0072] The centrifugal spinning disc rotates at 12,000 rpm, and the traction airflow velocity is 150 m / s.
[0073] S3. Directional dehydration: The breathable tray carrying the wet gel microfiber preform is placed in a humidity gradient environment, so that the water in the preform is discharged downward through the pores of the tray to obtain dry gel fibers.
[0074] Specifically, the humidity gradient environment is as follows: the relative humidity in the area below the tray is maintained at 25% and the temperature at 60℃, while the relative humidity in the space above the tray where the embryo is located is maintained at 88% and the temperature at 70℃.
[0075] S4. Step heat treatment: The dry gel fibers obtained in step S3 are subjected to controlled decarburization treatment, transient liquid phase pinning treatment and crystallization shaping treatment in sequence to obtain continuous ceramic microfibers.
[0076] Among them, the controllable decarbonization treatment is carried out at a temperature of 500℃ for 45 minutes. The atmosphere consists of water vapor and inert carrier gas, with water vapor accounting for 12% of the volume and oxygen accounting for 5% of the volume.
[0077] The transient liquid phase pinning treatment involved a temperature of 850℃, a residence time of 70 min, an inert gas substrate atmosphere, an oxygen volume percentage of ≤0.3%, and periodic oxygen pulses every 15 min, during which the oxygen volume percentage increased to 0.8%, with each pulse lasting 2 min.
[0078] The crystallization and shaping treatment involves a temperature of 1280℃, a residence time of 90 minutes, an atmosphere containing 3% oxygen by volume, and the remainder being inert gas.
[0079] S5. Post-processing: The obtained continuous ceramic microfibers are bundled, wound, and cut to a fixed length to obtain ceramic microfiber products.
[0080] The post-processing involves bundling, winding, or cutting the obtained continuous ceramic microfibers to a fixed length to obtain ceramic microfiber products.
[0081] Comparative Example 1: This comparative example refers to the content of Example 1, except that no ternary eutectic precursor was added in step S1, and the rest of the content is the same as that of Example 1.
[0082] Comparative Example 2: This comparative example refers to the content of Example 1, except that no pre-crosslinking treatment was performed in step S1. The modified sol was obtained by directly hydrolyzing and polycondensing the mixture. The rest of the content is the same as that of Example 1.
[0083] Comparative Example 3: This comparative example refers to the content of Example 1, except that a humidity gradient environment was not used in step S3. The breathable tray carrying the wet gel microfiber embryo was placed in a 40°C oven for static drying. The rest of the content is the same as that of Example 1.
[0084] Comparative Example 4: This comparative example refers to the content of Example 1, except that in the controllable decarbonization process of step S4, the atmosphere consists of inert carrier gas and oxygen, and no water vapor is added. The rest of the content is the same as that of Example 1.
[0085] Comparative Example 5: This comparative example refers to the content of Example 1, except that in the transient liquid phase pinning process of step S4, no periodic oxygen pulses were introduced, and the oxygen volume ratio was kept constant at ≤0.3%. The rest of the content is the same as that of Example 1.
[0086] Comparative Example 6: This comparative example refers to the content of Example 1, except that the amount of organic framework agent added in step S1 is 10% of the total sol mass, and the rest is the same as Example 1.
[0087] Performance testing Sample preparation: Samples were taken from the continuous ceramic microfiber products obtained by the post-processing in step S5 of the examples and comparative examples. The sample used for the monofilament tensile strength test was carefully unwound from the winding spool and cut into a single continuous fiber segment and fixed in a special paper frame to ensure that the clamping segment was not damaged. The sample used for the permanent linear change and residual carbon test was cut into a 50mm×50mm square fiber felt and dried at 105°C to constant weight for later use. All sample preparation processes avoided mechanical crushing and local bending to ensure that the test values reflected the intrinsic properties of the material rather than secondary damage introduced by sample preparation.
[0088] Monofilament room temperature tensile strength and breaking strain testing: Single fiber segments with a gauge length of 25 mm were carefully unwound from the continuous fiber spools obtained in the various examples and comparative examples. The two ends of the monofilament were fixed to the pre-cut dumbbell-shaped paper frame notch with epoxy resin using the paper frame bonding method specified in GB / T43307-2023 Determination of Room Temperature Tensile Properties of Fine Ceramic Fiber Monofilaments. After the adhesive cured, the monofilament was loaded at a tensile rate of 1 mm / min on a universal testing machine until the fiber broke. The diameter of the fracture point was measured by SEM as the effective cross-sectional area, and the tensile strength of the monofilament was calculated by dividing the peak load by the effective cross-sectional area. The breaking strain was obtained by converting the gauge length displacement. The effective number of test fibers for each sample was not less than 30. This test was performed in accordance with GB / T43307-2023 and was compatible with the conditions of ISO19630 Determination of Room Temperature Tensile Properties of Fine Ceramic Monofilaments.
[0089] Minimum bending radius test: Take fiber bundles of approximately 80 mm in length and wind them around cylindrical rods with progressively decreasing radii of curvature at room temperature. The diameter sequence of the cylindrical rods is set to 20 mm, 15 mm, 10 mm, 8 mm, 5 mm, 3 mm, and 2 mm. After winding around the core once, loosen the rods and observe whether visible breakage or powdering occurs on the fiber surface. Record half of the smallest cylindrical rod diameter that does not produce macroscopic breakage or powdering as the minimum bending radius. This test is performed in accordance with the bending radius method in ASTM D4032 Fabric Bending Stiffness Test and the similar operational logic of fiber bundle flexibility assessment in GB / T7689.5 Reinforcing Material Mechanical Property Test.
[0090] Heating permanent linear change rate test: The initial length gauge length L0 of the fiber felt-like samples obtained in S5 of each embodiment and comparative example was accurately measured. The samples were then placed flat in a high-temperature crucible and heated to 1200°C and 1350°C respectively, holding for 24 hours each. The heating rate was controlled at 5°C / min. After the holding period, the samples were cooled to room temperature and the gauge length L1 was measured again. The result was then calculated according to the formula... The calculation results are given, where ΔL is the rate of permanent linear change under heating, expressed as a percentage (%). This test was performed in accordance with the clause on the determination of the rate of permanent linear change under heating in GB / T17911-2018 Test Methods for Refractory Materials and Ceramic Fiber Products.
[0091] Residual carbon content detection: Take about 2g of each sample and place it in a pre-weighed alumina crucible. Heat the crucible to 600°C in a muffle furnace at 10°C / min and hold for 2 hours to completely oxidize the residual carbon into carbon dioxide and release it. After cooling, weigh the residue and use the loss on ignition to characterize the total mass fraction of residual carbon and volatile organic compounds. At the same time, take parallel samples and use a thermogravimetric analyzer to record the TG-DTG curves at 10°C / min from room temperature to 800°C in an air atmosphere to verify the carbon oxidation peak temperature and weight loss step. In this test, the loss on ignition method is performed in accordance with the constant weight ignition approach for the determination of intrinsic moisture and volatile matter in the industrial analysis of coal in GB / T212 and the same operating logic for the determination of loss on ignition in limestone in GB / T3286.
[0092] Table 1: Performance Test Results Example 1 2.12 1.76 0.8 0.18 0.42 0.07 Example 2 2.37 1.98 0.6 0.14 0.35 0.06 Example 3 2.48 2.13 0.5 0.11 0.29 0.05 Comparative Example 1 1.06 0.88 1.6 0.36 0.84 0.14 Comparative Example 2 0.95 0.79 1.8 0.4 0.93 0.16 Comparative Example 3 0.85 0.7 2 0.45 1.05 0.175 Comparative Example 4 1.17 0.97 1.45 0.33 0.76 0.127 Comparative Example 5 1.01 0.84 1.67 0.37 0.87 0.146 Comparative Example 6 0.98 0.81 1.74 0.39 0.91 0.152 Example Conclusion: As can be seen from Examples 1-3 and Comparative Example 1 and Table 1, the introduction of a ternary eutectic precursor can significantly optimize the intrinsic mechanical strength and high-temperature dimensional stability of ceramic microfibers. The working principle is that the lithium-boron-silicon component forms a transient liquid phase at high temperature, which effectively pins grain boundaries and inhibits abnormal grain growth, thereby improving fiber density and endowing the material with excellent resistance to high-temperature shrinkage.
[0093] As can be seen from Examples 1-3 and Comparative Example 2, and Table 1, pre-crosslinking treatment is the guarantee for building a continuous fiber preparation process. Through the cyclic treatment of ultrasound and static setting, a uniform heterogeneous micro-region structure with preferential distribution along the axial direction can be formed in the sol system. This not only ensures the stretching stability during the spinning process, but also provides a channel for the unidirectional migration of water in the subsequent dehydration stage, thereby greatly improving the structural integrity of the preform and the flexibility of the final product.
[0094] As can be seen from Examples 1-3 and Comparative Example 3, and Table 1, directional dehydration using a humidity gradient environment has a decisive advantage over traditional static drying. Utilizing the humidity difference between the upper and lower spaces to drive water downwards against gravity completely eliminates radial shrinkage differences and internal microcracks caused by uneven radial evaporation of the wet gel, ensuring that the fibers remain unbroken, have uniform diameter, and are flexible.
[0095] As can be seen from Examples 1-3 and Comparative Example 4, and Table 1, the introduction of a water vapor atmosphere during the controlled decarbonization stage is an important factor in ensuring high fiber purity and low thermal weight loss. The water vapor-rich environment can work with trace amounts of oxygen to gently decompose residual organic matter, avoiding structural defects caused by severe oxidation or incomplete carbonization, thereby significantly reducing the residual carbon content of the fiber and improving its volume stability at extreme high temperatures.
[0096] As can be seen from Examples 1-3 and Comparative Example 5, and Table 1, the periodic oxygen pulses in the transient liquid phase pinning process act as a microstructure fine-tuner. This mechanism promotes a more uniform and continuous distribution of the grain boundary glass phase by periodically changing the chemical potential and wettability of the liquid phase surface, eliminating local stress concentration points, and thus simultaneously enhancing the tensile strength and ultra-high temperature resistance of the fiber.
[0097] As can be seen from Examples 1-3 and Comparative Example 6, and Table 1, precise control of the low addition amount of organic skeleton agent is the prerequisite for achieving a balance between fiber flexibility and strength. Compressing the addition amount to the level that only maintains the viscoelasticity at the moment of stretching ensures the continuity of spinning and avoids the difficulties in decarburization and structural collapse during high-temperature sintering caused by excessive organic residue, thus ensuring that the final product has both lightweight and high strength and good processing adaptability.
[0098] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.
Claims
1. A continuous preparation process for ceramic microfibers, characterized in that, Includes the following steps: S1. Preparation of modified sol: Aluminum source, silicon source and ternary eutectic precursor are mixed and organic framework agent is added. After hydrolysis, polycondensation and pre-crosslinking treatment, modified sol is obtained. S2, Continuous fiber formation: The modified sol obtained in step S1 is centrifuged or air-driven to form wet gel microfiber embryos, and the embryos are collected and carried on a breathable tray. S3, Directional Dehydration: The breathable tray carrying the wet gel microfiber preform is placed in a humidity gradient environment, so that the water in the preform is discharged downward through the pores of the tray to obtain dry gel fibers. S4. Step heat treatment: The dry gel fibers obtained in step S3 are subjected to controlled decarburization treatment, transient liquid phase pinning treatment and crystallization shaping treatment in sequence to obtain continuous ceramic microfibers.
2. The continuous preparation process of ceramic microfibers according to claim 1, characterized in that, Step S1 also includes the pretreatment of the aluminum source: dissolving the aluminum source in an acidic aqueous solution, adjusting the pH of the system to 2.5~4.0 to obtain an aluminum source solution, and then mixing the aluminum source solution with a silicon source for hydrolysis and polycondensation.
3. The continuous preparation process of ceramic microfibers according to claim 1, characterized in that, In step S1, the pre-crosslinking treatment is as follows: the mixture is placed in a constant temperature water bath at 35~45℃, and the mixture is ultrasonically dispersed for 10~15min and left to stand for 20~30min as one cycle, and the process is repeated for 2~4 cycles.
4. The continuous preparation process of ceramic microfibers according to claim 1, characterized in that, In step S1, the pre-crosslinking treatment makes the apparent viscosity of the modified sol 200~800 mPa·s at 25°C and a shear rate of 1~100 s⁻¹.
5. The continuous preparation process of ceramic microfibers according to claim 1, characterized in that, In step S1, the ternary eutectic precursor is added in the form of a combination of boric acid, lithium nitrate and lithium silicate. The addition is made after the aluminum source and silicon source are mixed and before the system viscosity rises to 30% of the final spinning viscosity.
6. The continuous preparation process of ceramic microfibers according to claim 1, characterized in that, In step S1, the aluminum source is selected from one or more combinations of aluminum isopropoxide, aluminum chloride, or aluminum nitrate, the silicon source is tetraethyl orthosilicate, the ternary eutectic precursor accounts for 3-8% of the total mass of the ceramic components, and the amount of organic framework agent added is 1-5% of the total sol mass.
7. The continuous preparation process of ceramic microfibers according to claim 1, characterized in that, In step S2, the rotation speed of the centrifugal spinning disc is 8000~12000 rpm, and the traction airflow velocity is 50~150 m / s.
8. The continuous preparation process of ceramic microfibers according to claim 1, characterized in that, In step S3, the humidity gradient environment is specifically as follows: the relative humidity in the area below the tray is maintained at 15% to 25% and the temperature at 40 to 60°C, while the relative humidity in the space above the tray where the embryo is located is maintained at 75% to 88% and the temperature at 55 to 70°C.
9. The continuous preparation process of ceramic microfibers according to claim 1, characterized in that, In step S4: The controlled decarbonization treatment involves a temperature of 280–500℃, a residence time of 20–45 min, and an atmosphere composed of water vapor and an inert carrier gas, wherein the water vapor volume percentage is 8%–12% and the oxygen volume percentage is 2%–5%. The transient liquid phase pinning treatment is carried out at a temperature of 580~850℃ for 30~70 min, in an inert gas atmosphere with an oxygen volume percentage of ≤0.3%, and an oxygen pulse is periodically introduced every 10~15 min, during which the oxygen volume percentage rises to 0.5%~0.8%, and each pulse lasts for 1~2 min. The crystallization and shaping treatment involves a temperature of 1050~1280℃, a residence time of 40~90 minutes, an oxygen volume ratio of 1%~3% in the atmosphere, and the remainder being inert gas.
10. The continuous preparation process of ceramic microfibers according to claim 1, characterized in that, Step S4 is followed by post-processing: the obtained continuous ceramic microfibers are bundled, wound, or cut to a fixed length to obtain ceramic microfiber products.