Method for preparing a fiber ceramic composite material with controllable porosity and material thereof

Abstract

The application relates to a preparation method and material of a fiber ceramic composite material with controllable porosity, and the method comprises the following steps: S1, configuring a fiber suspension; S2, based on electrostatic adsorption, making a high-temperature binder and a high-temperature cosolvent pre-attached to the surface of the fiber; S3, filtering the modified fiber suspension through a screen to prepare multiple fiber paper embryo bodies; S4, stacking the fiber paper embryo bodies to form a layered structure of the fiber ceramic embryo body; S5, performing first heat preservation on the dried fiber ceramic embryo body under high-temperature environmental conditions, so that the high-temperature binder and the high-temperature cosolvent pre-attached to the surface of the fiber form a flowable active liquid phase; S6, applying quasi-static compression to the fiber ceramic embryo body until the fiber ceramic embryo body is compressed to a target thickness; and S7, performing second heat preservation on the fiber ceramic embryo body after the quasi-static compression to obtain a final material. The application realizes active design and precise control of the fiber ceramic composite material body porosity, and simultaneously has excellent mechanical properties and heat insulation performance.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, specifically to a method for preparing a fiber-ceramic composite material with controllable porosity and the material itself, which possesses both excellent mechanical and thermal insulation properties, and whose porosity is controllable. This invention is particularly suitable for extreme environments where materials require lightweight, high strength, and thermal insulation performance, such as aerospace thermal control systems, special protective equipment, and building insulation. Background Technology

[0002] Fiber-coated porous ceramic composites, as an emerging three-dimensional porous material, possess excellent properties such as lightweight, high porosity, low density, and low thermal conductivity, demonstrating great application potential in high-temperature extreme thermal insulation fields, particularly in spacecraft thermal protection systems, industrial kiln insulation, and building energy conservation. Among numerous fiber materials, oxide ceramic fibers such as silica fibers, mullite fibers, and alumina fibers are considered ideal matrix materials for preparing high-performance thermal insulation fiber-coated ceramic composites due to their excellent high and low temperature resistance, intrinsically low thermal conductivity, and certain mechanical load-bearing capacity.

[0003] However, existing fiber-porous ceramic composite materials still face two major interconnected core technological bottlenecks in practical applications.

[0004] First, the inherent high porosity of fibrous porous ceramic materials and the low strength of the micron-sized fibers themselves result in severely insufficient mechanical strength and significant brittleness. This is a significant gap between the mechanical properties and the complex load conditions such as compression, vibration, and thermal shock faced by fibrous porous ceramics in actual working conditions. Traditionally, researchers have attempted to improve mechanical properties by increasing the binder content, reducing the fiber aspect ratio, or increasing the sintering temperature. However, these methods all have limitations: while excessively high binder content can fill some pores, its contribution to improving mechanical properties is not significant; reducing the fiber aspect ratio can promote denser bonding between fibers, but excessively short fibers will significantly weaken the load-bearing skeleton of the material, leading to a decrease in overall strength; while increasing the sintering temperature can promote material diffusion and bonding at fiber nodes, excessively high temperatures can lead to fiber decomposition, necking, and abnormal grain growth, which in turn degrades mechanical properties.

[0005] Secondly, the porosity of fiber-reinforced porous ceramics is difficult to control precisely. This is especially true for medium-porosity materials with a porosity range of approximately 50% to 60%, which require sufficient mechanical strength to withstand structural loads while maintaining adequate closed pores to preserve low thermal conductivity. Due to the random distribution of fibers during natural settling or traditional wet molding processes, random pores determined by the packing pattern always exist between the fibers. This randomness in porosity results in poor batch-to-batch consistency of the mechanical and thermal properties of the final product, failing to meet the stringent requirements of high-end applications for designable, predictable, and repeatable material properties.

[0006] Therefore, developing a preparation method that can achieve quantitative control of the porosity of fibrous porous ceramics while simultaneously ensuring high mechanical strength and low thermal conductivity has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The present invention aims to overcome the above-mentioned shortcomings of the prior art and provide a fiber-ceramic composite material with controllable porosity and its preparation method. Specifically, the technical problem to be solved by the present invention is: how to prepare a fiber-ceramic composite material whose porosity can be precisely controlled within a predetermined range (especially in the medium porosity range of 50% to 60%), and simultaneously possess a compressive strength of not less than 5 MPa and a thermal conductivity of less than 0.15 W / (m·K), thereby achieving the integration of mechanical load-bearing and efficient thermal insulation functions.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution.

[0009] Firstly, the present invention discloses a method for preparing a fiber-ceramic composite material with controllable porosity, specifically comprising the following steps:

[0010] S1, Prepare a fiber suspension comprising fibers, a high-temperature binder, and a high-temperature co-solvent; S2, Based on electrostatic adsorption, pre-attach the high-temperature binder and the high-temperature co-solvent to the surface of the fibers to form fiber-functional phase units, thereby obtaining a modified fiber suspension; S3, Filter the modified fiber suspension through a sieve to sequentially prepare multiple fiber paper blanks formed by deposition based on the fiber-functional phase composite units; S4, Stack the multiple fiber paper blanks to form a layered fiber ceramic blank with a predetermined thickness, and dry the fiber ceramic blank; S5, Place the dried fiber ceramic blank in a high-temperature environment. The process involves: S6, initial heat treatment under ambient conditions to allow at least partial melting of the high-temperature binder and high-temperature flux pre-attached to the fiber surface, forming a flowable active liquid phase; S7, applying quasi-static compression at a strain rate of 0.001 / s to 0.01 / s to the fiber ceramic preform while maintaining the high-temperature environment, causing new overlapping nodes to form between the fibers due to rearrangement, and enriching the active liquid phase at the overlapping nodes, until the target thickness is achieved; S8, further heat treatment of the compressed fiber ceramic preform to solidify the active liquid phase enriched at the overlapping nodes, forming a sintering neck, resulting in a layered fiber ceramic composite material with controllable porosity.

[0011] The preparation method provided by the invention organically integrates three levels of technological innovation: "preconstruction of fiber-functional phase composite units", "macro-assembly to layered ordered structures" and "precise control of microstructure under force-thermal multi-field coupling". This systematically solves the problems of low strength and uncontrollable porosity of fiber porous ceramics in the prior art.

[0012] Specifically, in step S1, an initial fiber suspension containing fibers, a high-temperature binder, and a high-temperature flux is first prepared. The purpose of this step is to initially mix the three basic solid components that constitute the final composite material in a liquid medium.

[0013] However, simple mechanical mixing cannot solve the problem of the large loss of micro- and nano-scale functional phases (high-temperature binders and fluxes) and their uneven distribution on the fiber surface during the subsequent filtration and molding process.

[0014] To address this, step S2 introduces a crucial "electrostatic adsorption" process. Through electrostatic adsorption, high-temperature binder and flux particles are firmly "pre-attached" to the fiber surface in a liquid environment at room temperature, forming a fiber-functional phase composite unit with the fiber as the framework and the functional phase particles as the "attachment." The benefits of this pretreatment are twofold: First, it ensures that the functional phase particles are retained along with the fiber in the subsequent sieve filtration step S3, achieving a near 100% retention rate of the functional phase and avoiding raw material waste and uncontrollable composition. Second, it achieves nanoscale uniform dispersion of the functional phase on the surface of each fiber, laying a solid structural foundation for the functional phase to exert its precise "node welding" effect in the subsequent high-temperature treatment stage.

[0015] Step S3 involves solid-liquid separation of the modified fiber suspension obtained in step S2 using a sieve filtration technique. During filtration, the liquid passes through the sieve, while the pre-constructed fiber-functional phase composite units are retained and deposited layer by layer on the sieve surface, forming a fiber paper blank with a very thin thickness and relatively uniform fiber distribution. Multiple fiber paper blanks can be prepared sequentially by repeating this step or through continuous operation.

[0016] Step S4 involves stacking these two-dimensional fiber paper blanks to construct a three-dimensional block fiber ceramic blank with a predetermined thickness and a layered structure. This "layered structure" is not merely a simple stacking, but rather a structural prerequisite for the precise implementation of the subsequent "controllable compression" step in this invention.

[0017] Step S5 is the activation of the active liquid phase. Specifically, the dried fiber ceramic preform is placed in a high-temperature environment for initial heat preservation. This stage has a dual function: firstly, the organic adsorbents on the fiber surface (derived from the components that realize the electrostatic adsorption process) and any room-temperature plasticizers present are completely thermally decomposed and vaporized at high temperatures, leaving a clean and unobstructed interface on the fiber and functional phase surfaces; secondly, and more importantly, the high-temperature environment (preferably 900°C to 1100°C) is sufficient to allow the high-temperature binder (such as nano-silicon carbide) pre-attached to the fiber surface to undergo surface pre-melting or eutectic melting, or at least partial melting, with the assistance of a high-temperature flux (such as nano-boron carbide), thereby transforming from solid particles into a flowable active liquid phase. At this time, the active liquid phase is distributed on the fiber surface in the form of a film or droplets, in a state of "activated but not yet fully functional" standby.

[0018] Step S6 involves network reconstruction and directional enrichment of the liquid phase under force-thermal coupling. Specifically, while maintaining the high-temperature environment of step S5, quasi-static compression is applied to the activated fiber ceramic preform. The key aspect is the extremely low compression rate, with the strain rate strictly controlled within the range of 0.001 / s to 0.01 / s. This low-speed compression process triggers two crucial microstructural evolutions:

[0019] Firstly, there is the orderly reconstruction of the fiber network. Under the slow action of quasi-static compression, each fiber in the fiber network has sufficient time to slide, rotate, and rearrange to adapt to the reduction in macroscopic volume. This rearrangement effectively avoids stress concentration and fiber breakage damage common under high-speed compression. At the same time, the layered structure that originally had a certain spacing is compacted, and the interlayer fibers interpenetrate with each other, forming a large number of new, uniformly distributed fiber-fiber overlap nodes.

[0020] Secondly, the active liquid phase is driven by capillary force to achieve directional enrichment. The active liquid phase, already capable of flow at high temperatures, is driven by the strong capillary negative pressure generated by the wedge-shaped gaps at fiber overlap points, spontaneously migrating and enriching from the free surface region of the fiber towards the tip region of the overlap point. This "on-demand distribution" liquid phase migration mechanism ensures that the limited functional phase material is precisely delivered to the location most in need of bonding and reinforcement (i.e., the node), greatly improving the utilization efficiency of the functional phase and avoiding ineffective accumulation of the liquid phase in non-critical areas (such as within large pores).

[0021] By precisely controlling the displacement of quasi-static compression (compressed to the target thickness), the overall porosity can be accurately controlled.

[0022] In step S7, the preform compressed to the target thickness is held at a high temperature again. During this stage, the active liquid phase enriched at the overlap joints fully wets and encapsulates the fiber contact area under continuous high temperature through liquid phase sintering mechanisms such as dissolution-precipitation and viscous flow. As the subsequent cooling process proceeds, the active liquid phase solidifies, forming a robust sintered neck with finite dimensions at each overlap joint. These sintered necks permanently "weld" and lock the densified fiber network structure reconstructed in step S6, thereby endowing the final composite material with excellent macroscopic mechanical strength (compressive strength not less than 5 MPa).

[0023] In summary, through the combination and synergy of steps S1 to S7, the present invention achieves simultaneous optimization of the porosity, mechanical strength and thermal insulation performance of fiber ceramic composite materials, especially achieving precise and controllable preparation of medium porosity (e.g., 50% to 60%).

[0024] According to the preparation method disclosed in the first aspect of the present invention, in step S6, the compression displacement of the quasi-static compression is determined based on the target porosity, and the relationship between the target porosity and the compression displacement satisfies the following formula:

[0025]

[0026] in, For the target porosity, For compression displacement, denoted as ρ, where ρ is the fiber density; l is the length of the fiber ceramic preform after drying; w is the width of the fiber ceramic preform after drying; h is the height of the fiber ceramic preform after drying; and W0 is the mass of the fiber ceramic preform after drying.

[0027] This provides a specific physical model for quantitatively controlling and predicting the porosity of the final product. Based on the principles of mass conservation and volume superposition, the model directly links the "quasi-static compression" process to the target product performance of "porosity." Using this formula, the operator only needs to measure the initial dimensions and mass of the dried preform to accurately calculate the required compression displacement Δh based on the preset target porosity P. Conversely, the final porosity under a given compression displacement can also be predicted. Establishing this quantitative relationship elevates the method of this invention from "empirical trial and error" to "theoretically guided predictable manufacturing," greatly improving the accuracy, reliability, and repeatability of the process. This is a key technological support for achieving the core inventive objective of "controllable porosity."

[0028] According to the preparation method disclosed in the first aspect of the present invention, the high-temperature binder includes nano-silicon carbide, and in the fiber suspension of step S1, the mass ratio of the high-temperature binder to the fiber is 5% to 12%; the high-temperature co-solvent includes nano-boron carbide, and in the fiber suspension of step S1, the mass ratio of the high-temperature co-solvent to the fiber is 5% to 12%.

[0029] Nano-silicon carbide can form an active liquid phase above 900℃, which is the main phase source for forming sintering necks between fiber nodes. Nano-boron carbide, as a highly efficient sintering flux, can lower the melting temperature of silicon carbide and promote the flow and spreading of the liquid phase. The mass ratio of both to the fiber is limited to 5% to 12%. If the content is less than 5%, the amount of active liquid phase is insufficient, failing to form a sufficiently strong sintering neck at the fiber node, resulting in substandard compressive strength in the final product. If the content is greater than 12%, the excessive liquid phase not only leads to an unnecessary increase in material density and thermal conductivity but may also cause excessive fiber dissolution or abnormal coarsening of the sintering neck, negatively impacting mechanical and thermal insulation properties. Therefore, this ratio range ensures sufficient bonding and strengthening of the nodes while maximizing the preservation of beneficial closed pores within the material, achieving the optimal balance between mechanical and thermal insulation properties.

[0030] According to the preparation method disclosed in the first aspect of the present invention, step S2 includes the following steps performed in sequence: adding a positively charged adsorbent to the fiber suspension and stirring to make the surfaces of the fiber, high-temperature binder, and high-temperature co-solvent positively charged; subsequently adding a negatively charged adsorbent, and using electrostatic attraction between the positive and negative charges to pre-attach the high-temperature binder and the high-temperature co-solvent to the surface of the fiber, forming a fiber-functional phase unit, thereby obtaining a modified fiber suspension. In a preferred embodiment, the positively charged adsorbent includes polyethyleneimine, and the negatively charged adsorbent includes polyacrylamide.

[0031] This adsorption scheme cleverly utilizes the multilayer adsorption and bridging flocculation principle of polyelectrolytes at the solid-liquid interface. First, a positively charged adsorbent (such as polyethyleneimine) is added to the suspension, allowing it to be uniformly adsorbed onto the surfaces of fibers, nano-silicon carbide, and nano-boron carbide particles, uniformly modifying the interfacial properties of all solid particles to be positively charged. At this point, the particles remain dispersed and stable due to electrostatic repulsion. Subsequently, a negatively charged adsorbent (such as polyacrylamide) is slowly added. The negatively charged groups on its long-chain molecules electrostatically attract multiple positively charged particle surfaces, thus acting as a "molecular bridge" to firmly "bind" and anchor the nanoscale functional phase particles to the surface of the micron-sized fibers. This sequential addition of positively and negatively charged adsorbents is key to achieving uniform, efficient, and robust pre-attachment of the functional phase, effectively preventing loss and segregation of the functional phase during subsequent filtration.

[0032] According to the preparation method disclosed in the first aspect of the present invention, the fiber suspension further includes a room temperature shaping agent, wherein the mass ratio of the room temperature shaping agent to the fiber is 5% to 12%, and the room temperature shaping agent includes water-soluble starch; the room temperature shaping agent is completely thermally decomposed and vaporized during the first heat preservation process in step S5, so as to avoid hindering the wetting and node enrichment of the active liquid phase.

[0033] By introducing a room-temperature plasticizer, the problems of low strength and difficulty in handling of fiber paper preforms in both wet and dry states are solved. In step S3, during the preparation of the fiber paper preform, and the subsequent stacking process in S4, the fiber paper preform is extremely prone to breakage. Adding water-soluble starch at a mass ratio of 5% to 12% as a room-temperature plasticizer significantly improves the plasticity of the wet preform and the temporary bonding strength of the dry preform, making the smooth stacking of multi-layered fiber paper possible, thus ensuring the successful construction of the layered structure preform. More importantly, it is explicitly defined that this room-temperature plasticizer will completely thermally decompose and vaporize during the initial high-temperature holding process in step S5. This characteristic is crucial because it ensures that the fiber surface is clean and residue-free during the subsequent high-temperature densification and sintering stages in S6 and S7, preventing carbonized residues of the plasticizer from hindering the wetting, spreading, and capillary migration of the active liquid phase to the overlapping nodes on the fiber surface. The mass ratio range of 5% to 12% is an optimized result that avoids excessive additives interfering with the electrostatic adsorption process in step S2 and prevents excessive gas generation during pyrolysis from affecting the integrity of the green body, while ensuring sufficient plasticity.

[0034] According to the preparation method disclosed in the first aspect of the present invention, the diameter of the fiber is 5 μm to 10 μm, and the fiber is selected from at least one of silica fiber, mullite fiber, and alumina fiber. Fibers of the aforementioned size have sufficient flexibility and aspect ratio, enabling them to form a stable three-dimensional network skeleton through winding and overlapping, and also possessing a certain load-bearing capacity under stress. Fibers that are too thin have low strength and are easily broken, while fibers that are too thick have high rigidity, are difficult to form a uniform network, and will affect the overall thermal insulation performance of the material due to their significant contribution to thermal conductivity. The selected silica fiber, mullite fiber, or alumina fiber are all ceramic fibers with excellent high-temperature resistance, low thermal conductivity, and good chemical stability. As the skeleton of the composite material, they ensure the long-term reliability of the final product under extreme environments.

[0035] According to the preparation method disclosed in the first aspect of the present invention, the high-temperature environment in step S5 is 900°C to 1100°C. This temperature range ensures the melting of the nano-silicon carbide-boron carbide system. Below 900°C, the active liquid phase is difficult to form effectively; above 1100°C, the fibers (especially silica fibers) may crystallize, decompose, or neck, impairing the material strength.

[0036] According to the preparation method disclosed in the first aspect of the present invention, the initial holding time in step S5 is 30 to 120 minutes; this time window is sufficient to allow the interior of the preform to reach a uniform temperature and ensure that the active liquid phase is fully formed and has good fluidity, while avoiding fiber thermal damage that may be caused by excessively long holding times. The second holding time in step S7 is 5 to 30 minutes. This time window is sufficient to allow the active liquid phase enriched at the nodes to complete the growth and solidification of the sintering neck, stabilizing the structure, while avoiding unnecessary prolonged high-temperature holding times.

[0037] According to the preparation method disclosed in the first aspect of the present invention, the drying temperature in step S4 is 70°C to 90°C, and the drying time is 6 hours to 10 hours. These mild drying conditions effectively remove moisture from the embryo while avoiding cracking or deformation of the embryo due to internal stress caused by excessively rapid drying.

[0038] According to the preparation method disclosed in the first aspect of the present invention, in step S1, the fiber suspension is stirred for 10 to 30 minutes to ensure that the fibers are evenly dispersed. This ensures that the fibers are fully dispersed in the suspension, prevents agglomeration, and lays the foundation for the subsequent formation of a uniform fiber paper blank.

[0039] The second aspect of the present invention discloses a fiber-ceramic composite material with controllable porosity, which is prepared by the preparation method disclosed in the first aspect of the present invention.

[0040] According to the second aspect of the present invention, the fiber-ceramic composite material has a layered structure. That is, the product has a unique microstructure of "layered structure" and "node sintering neck reinforcement", which is imparted by the preparation method specific to the present invention (especially the stacking of S4 and the quasi-static compression of S6).

[0041] According to the second aspect of the present invention, the fiber-ceramic composite material has a thermal conductivity of less than 0.15 W / (m·K) and a compressive strength of not less than 5 MPa; the porosity of the fiber-ceramic composite material is 50% to 60%. The thermal conductivity of less than 0.15 W / (m·K) ensures its excellent thermal insulation capability; the compressive strength of not less than 5 MPa guarantees its load-bearing capacity as a structural or protective component; and the porosity of 50% to 60% directly reflects the core advantage of the present invention: "controllable porosity." This product successfully achieves a synergistic unity of lightweight, high strength, and efficient thermal insulation properties, making it an ideal material for applications in aerospace thermal protection, special protective clothing, and building insulation.

[0042] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects:

[0043] 1. Precise and controllable preparation of porosity: Through the quasi-static compression process in step S6, this invention achieves for the first time the active design and precise control of the bulk porosity of fiber ceramic composite materials. In particular, it solves the problem that existing technologies cannot obtain medium porosity materials with a porosity range of 50% to 60%, which greatly improves the predictability of product performance and batch consistency.

[0044] 2. Significantly Enhanced Mechanical Properties: This invention ensures the in-situ and uniform generation of the active liquid phase in the fiber network through the pre-construction of fiber-functional phase composite units in step S2; the quasi-static compression in step S6 induces capillary-driven enrichment of the liquid phase at the overlapping nodes, and the reheating in step S7 forms a robust sintering neck. This "on-demand distribution" node strengthening mechanism achieves efficient "welding" of the fiber network skeleton with a very small amount of functional phase added (5% to 12%), resulting in a final composite material with a compressive strength of no less than 5 MPa, completely changing the traditional impression that "high porosity equals low strength" of fiber porous ceramics.

[0045] 3. Maintaining Excellent Thermal Insulation Performance: Although this invention increases the material's density through compression, it also preserves a large number of tiny closed pores within the fiber network through quasi-static compression. Furthermore, the layered structure artificially introduced via the stacking process (S4) increases the interfacial thermal resistance perpendicular to the layer direction. These two factors work together to ensure that while the material's strength is significantly improved, its thermal conductivity remains at an excellent level of less than 0.15 W / (m·K), achieving synergistic optimization of mechanical and thermal insulation properties.

[0046] 4. Simple process, good continuity, and strong applicability: The overall process flow of this invention is clear and can be achieved using existing mature wet papermaking equipment and general-purpose equipment such as universal testing machines and muffle furnaces, without the need for complex or expensive specialized equipment. All raw materials used are commercially available conventional products, making costs controllable. This method is not only applicable to silica fibers but can also be extended to various ceramic fiber systems such as mullite fibers and alumina fibers, demonstrating good industrial application prospects and broad market adaptability.

[0047] The preparation method and materials of the fiber ceramic composite material with controllable porosity of the present invention are disclosed in detail below with reference to the embodiments shown in the accompanying drawings and the reference numerals. Attached Figure Description

[0048] Figure 1 A step-fluid diagram illustrating the preparation method of the porosity-controllable fiber-ceramic composite material of the present invention is shown.

[0049] Figure 2 A process flow diagram for preparing the fiber-ceramic composite material with controllable porosity in this invention is shown.

[0050] Figure Labels

[0051] Beaker 1, sieve frame 2, fiber paper blank 3, fiber ceramic blank 4 Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0053] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0054] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. If the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0055] Figure 1 A step-fluid diagram illustrating the preparation method of the porosity-controllable fiber-ceramic composite material of the present invention is shown. Figure 2 A process flow diagram for preparing the fiber-ceramic composite material with controllable porosity in this invention is shown.

[0056] Combination Figure 1 and Figure 2 As shown, the preparation method of the present invention includes the following steps:

[0057] S1, prepare a fiber suspension, wherein the fiber suspension includes fibers, a high-temperature binder and a high-temperature co-solvent;

[0058] S2, based on electrostatic adsorption, the high-temperature binder and the high-temperature co-solvent are pre-attached to the surface of the fiber to form a fiber-functional phase unit, resulting in a modified fiber suspension;

[0059] S3, the modified fiber suspension is filtered through a sieve to sequentially prepare multiple fiber paper blanks formed by deposition based on the fiber-functional phase composite unit;

[0060] S4, stack multiple sheets of the fiber paper blanks to form a fiber ceramic blank with a layered structure of a preset thickness, and dry the fiber ceramic blank;

[0061] S5, the dried fiber ceramic preform is subjected to a first heat treatment under high temperature conditions so that the high temperature binder and the high temperature flux pre-attached to the fiber surface are at least partially melted to form a flowable active liquid phase;

[0062] S6, while maintaining the high temperature environment, apply quasi-static compression with a strain rate of 0.001 / s to 0.01 / s to the fiber ceramic preform, so that new overlapping nodes are formed between the fibers due to rearrangement, and the active liquid phase is enriched at the overlapping nodes, until the target thickness is reached.

[0063] S7, the compressed fiber ceramic preform is heated again to solidify the active liquid phase enriched at the overlapping nodes to form a sintering neck, thus obtaining a layered fiber ceramic composite material with controllable porosity.

[0064] In step S1, the shredded fibers are placed in a blender and crushed at 1100 rpm for 2 minutes. The crushing time is closely related to the aspect ratio of the fibers; a higher rotation speed and a longer crushing time will result in fibers that are too short, while a lower rotation speed and a shorter crushing time will result in fibers that are too long.

[0065] Additionally, in step S1, the diameter of the fiber is 5 μm to 10 μm, and the fiber is selected from at least one of silica fiber, mullite fiber, and alumina fiber.

[0066] The high-temperature binder comprises nano-silicon carbide, and the mass ratio of the high-temperature binder to the fiber is 5% to 12%. This content is directly related to the bonding strength between the fiber nodes. A low content of high-temperature binder will result in weak bonding between the fiber nodes, thereby reducing the strength of the fiber-ceramic composite material; an excessive content of high-temperature binder will lead to a significant increase in the density and thermal conductivity of the material without significantly improving the mechanical strength.

[0067] The high-temperature flux includes nano-boron carbide, and the mass ratio of the high-temperature flux to the fiber is 5% to 12%. This content is also directly related to the bonding strength between the fiber nodes. A low content of high-temperature flux will lead to weak bonding between the fiber nodes, thereby reducing the strength of the fiber-ceramic composite material. An excessively high content of high-temperature flux will lead to a significant increase in the density and thermal conductivity of the material without significantly improving the mechanical strength, and may even cause the fiber to decompose and neck due to over-sintering.

[0068] In a preferred embodiment, the fiber suspension further includes a room-temperature shaping agent, wherein the mass ratio of the room-temperature shaping agent to the fiber is 5% to 12%, and the room-temperature shaping agent includes water-soluble starch. The content of the room-temperature shaping agent directly affects the plasticity of the fiber ceramic preform, and excessively high content of room-temperature shaping agent will affect the adsorption effect of high-temperature binders and fluxes.

[0069] In step S1, the fiber suspension is stirred for 10 to 30 minutes to ensure uniform fiber dispersion. In a preferred embodiment, the fiber suspension is stirred in a mixer for 20 minutes to ensure uniform fiber dispersion and prevent fiber agglomeration.

[0070] In step S2, a positively charged adsorbent is first added to the fiber suspension and stirred to give the surfaces of the fiber, high-temperature binder, and high-temperature flux a positive charge. Then, a negatively charged adsorbent is added, and the high-temperature binder and flux are pre-attached to the surface of the fiber through electrostatic attraction between the positive and negative charges, forming a fiber-functional phase unit, thus obtaining a modified fiber suspension. That is, the positively charged adsorbent (e.g., polyethyleneimine) and the subsequently added negatively charged adsorbent synergistically adsorb high-temperature binder particles (e.g., nano-silicon carbide) and high-temperature flux particles (e.g., nano-boron carbide) onto the fiber.

[0071] Specifically, in step S2, a negatively charged adsorbent solution (such as polyacrylamide solution) is added to the fiber suspension until obvious precipitation occurs in the fibers and the upper part of the solution in the beaker becomes clearly clear. Its function is to work synergistically with the previously added positively charged adsorbent to adsorb high-temperature binder particles (such as nano-silicon carbide) and high-temperature flux particles (such as nano-boron carbide) onto the fibers. The previously added positively charged adsorbent is uniformly distributed on the fibers, high-temperature binder particles, and high-temperature flux particles. With the addition of the negatively charged adsorbent, this adsorbent also becomes uniformly distributed on the fibers, high-temperature binder particles, and high-temperature flux particles; therefore, the high-temperature binder and flux are adsorbed onto the fibers under the influence of positive and negative charges.

[0072] In a preferred embodiment, the positively charged adsorbent comprises polyethyleneimine, and the negatively charged adsorbent comprises polyacrylamide.

[0073] In step S3, the fiber suspension is filtered using a sieve to form a fiber paper blank. The sieve frame is placed at the bottom of a square water tank, and the fiber suspension is poured into the tank. After stirring evenly, the suspension is allowed to settle. Once the sedimentation is complete, the sieve frame is lifted, and the filter paper frame is left to stand horizontally for about 10 minutes to form a silica fiber paper blank.

[0074] Between steps S3 and S4, a step of cutting the obtained fiber paper blank to a preset size is included. In step S4, the cut fiber paper blanks are stacked. The drying temperature in step S4 is 70°C to 90°C, and the drying time is 6 to 10 hours. In a preferred embodiment, the drying temperature and time of the fiber ceramic blank are 80°C and 8 hours, respectively, to remove water from the inside of the fibers and prevent it from affecting the sintering effect.

[0075] In subsequent step S5, the method of the present invention generates a quasi-layered fibrous porous ceramic preform through sieve filtration technology, and combines it with subsequent drying and quasi-static high-temperature compression technology to achieve controllable porosity and self-enhanced mechanical properties of fibrous porous ceramics.

[0076] It should be noted that in step S5, the quasi-static compression rate is 0.001 / s-0.01 / s. This low compression rate allows sufficient time for the fibers to release stress, preventing excessive internal damage that could affect the mechanical load-bearing capacity of the porous fiber ceramic. If the compression rate is too fast, the nodal stress between the fibers cannot be released in time, leading to fiber damage and failure. If the compression rate is too slow, the sample will be exposed to high temperatures for an extended period, resulting in over-sintering, particularly causing necking and decomposition of the fibers. Furthermore, prolonged heat treatment leads to excessive energy consumption.

[0077] The high-temperature environment in step S5 is 900℃ to 1100℃. This temperature allows the nano-binder to begin melting at 900℃. If the temperature is too low, the nano-binder cannot melt, thus failing to bind the nodes between fibers. If the temperature is too high, it will cause the fibers to decompose and neck, which will seriously affect the mechanical properties of the fiber-ceramic composite material. On the other hand, it is also a waste of equipment and energy.

[0078] The initial heat treatment time in step S5 is 30 to 120 minutes. In a preferred embodiment, the heat treatment time is 60 minutes. Too short a heat treatment time will not allow the nano-binder to melt sufficiently, thus failing to bind the nodes between fibers; too long a heat treatment time will cause the fibers to decompose and neck, thereby severely affecting the mechanical properties of the fiber-ceramic composite material.

[0079] The reheating time in step S7 is 5 to 30 minutes. In a preferred embodiment, the reheating time is 10 minutes, allowing sufficient time for the reconstituted fiber internal structure to sinter and form a stable structure.

[0080] In step S6, the compression displacement of the quasi-static compression is determined based on the target porosity, and the relationship between the target porosity and the compression displacement satisfies the following formula:

[0081]

[0082] in, For the target porosity, For compression displacement, denoted as ρ, where ρ is the fiber density; l is the length of the fiber ceramic preform after drying; w is the width of the fiber ceramic preform after drying; h is the height of the fiber ceramic preform after drying; and W0 is the mass of the fiber ceramic preform after drying.

[0083] The fiber-ceramic composite material obtained by the present invention has at least one of the following beneficial effects:

[0084] This invention employs a multi-layer fiber paper stacking technique to stack materials in... Figure 2 The XYZ coordinate system shown is artificially divided into multiple interface layers along the Z-axis (thickness direction), which realizes the quasi-layered structure design of the fiber porous ceramic. The quasi-layered structure design makes the material have lower thermal conductivity and stronger mechanical properties along the direction perpendicular to the layer.

[0085] This invention uses fiber. Firstly, the raw material is widely available, and its mechanical and thermal properties are relatively stable. Secondly, the fiber screen filtration technology employed is already widely used in the papermaking industry and is a mature technology.

[0086] The present invention employs a high-temperature quasi-static compression technique in the reconstruction process of fiber porous ceramics, which allows for precise control of the compression rate and compression size, thereby achieving precise control of the porosity of fiber porous ceramic composite materials.

[0087] Quasi-static compression at high temperatures not only reduces porosity, but more importantly, at low rates, the fibers have sufficient time for stress release and rearrangement, avoiding internal damage. Simultaneously, the high temperature melts the binder (such as nano-silicon carbide), firmly bonding the fiber nodes at their new compressed locations, forming a dense and tough interlayer interface and network structure. This "deformation first, then shaping" mechanism achieves self-reinforcement of mechanical properties.

[0088] Furthermore, the quasi-layered structure and quasi-static compression synergistically solve the thermal insulation performance problem. Specifically, the quasi-layered structure itself increases thermal resistance (interfacial thermal resistance) in the direction perpendicular to the layers. Although the compression process reduces the total porosity, it retains closed, tiny pores, and combined with the layered structure, achieves an organic combination of mechanical strength and thermal insulation performance.

[0089] Furthermore, the fiber-reinforced porous ceramic composite materials prepared using sieve filtration and high-temperature compression techniques possess excellent properties such as high strength, low thermal conductivity, and controllable porosity. These superior overall properties make them promising for applications in spacecraft thermal control systems, high-end outdoor equipment, and building energy-saving insulation.

[0090] The difference between the high-temperature quasi-static compression of this invention and the traditional hot-pressing sintering in the ceramic field is as follows: the traditional hot-pressing sintering technology in the ceramic field is a process for dense ceramics, the purpose of which is to completely remove pores from the ceramic material; while the high-temperature quasi-static compression technology in this invention is for fibrous porous ceramic materials, the purpose of which is to obtain fiber ceramic composite materials with precise porosity, especially medium-porosity fiber ceramic composite materials with porosity between 50-60%.

[0091] The present invention also provides a fiber-ceramic composite material with controllable porosity, which is prepared according to the aforementioned preparation method. The prepared fiber-ceramic composite material has a layered structure, a thermal conductivity of less than 0.15 W / (m·K), and a compressive strength of not less than 5 MPa; the porosity of the fiber-ceramic composite material is 50% to 60%.

[0092] The preparation process of the fiber ceramic composite material in this invention will be described below with reference to specific equipment.

[0093] The fiber-ceramic composite material device used, such as Figure 2 As shown, the high-temperature quasi-static compression apparatus includes a universal testing machine, a muffle furnace, and a coaxial compression chamber. During the high-temperature compression process, the silica fiber ceramic preform is placed in the coaxial compression chamber and then positioned between the indenters. The muffle furnace enables precise temperature control, while the universal testing machine enables precise control of the compression rate and compression dimensions, thereby achieving accurate acquisition of the sample porosity.

[0094] Example 1

[0095] 1) Preparation of the silica fiber suspension. First, the cut silica fibers are placed in a high-speed blender and crushed at 11000 r / min for 2 minutes. The crushing time is directly related to the length of the crushed silica fibers. Then, the crushed fiber suspension is placed in beaker 1, and nano-silicon carbide, nano-boron carbide, polyethyleneimine, and potato starch are added. The mixture is stirred for 20 minutes to ensure even distribution. Simultaneously, polyacrylamide is added to water and stirred thoroughly to obtain a polyacrylamide solution. Then, an appropriate amount of polyacrylamide solution is poured into the silica fiber suspension to allow the nano-silicon carbide, nano-boron carbide, and potato starch to be adsorbed onto the fibers. The mixture is then stirred for another 20 minutes to prevent fiber agglomeration.

[0096] 2) Filter the silica fiber suspension using a sieve to form a silica fiber paper blank. Place the sieve frame 2 at the bottom of a square water tank, pour the fiber suspension into the water tank, stir it evenly and allow it to settle. After the sedimentation is complete, lift the sieve frame 2 and let the filter paper frame stand horizontally for 10 minutes to form a silica fiber paper blank 3.

[0097] 3) Cutting of the fiber preform. The silica fiber paper preform 3 is cut to form a silica fiber paper preform 3 with a fixed size of 50 mm × 50 mm.

[0098] 4). Stacking of fixed-size silica fiber ceramic preforms. Sixty fixed-size silica fiber paper preforms 3 are stacked to form a silica fiber ceramic preform 4 with a thickness of 30 mm.

[0099] 5) High-temperature compression of silica fiber ceramics. The silica fiber ceramic preform 4 was placed in a coaxial pressure box and then placed between indenters. The ambient temperature was controlled at 1000℃ in a muffle furnace and held for 60 min. Then, a universal testing machine was used to compress it at a rate of 0.48 mm / min, with a compression dimension of 18 mm (to achieve a compressive strain of 60%). Finally, it was held at this temperature for 10 min.

[0100] Implementation effect

[0101] Through the above process, the resulting fiber-ceramic composite material not only possesses excellent thermal insulation properties with a thermal conductivity as low as 0.15 W / (m·K), but also significantly improves its mechanical properties, achieving a compressive strength of ~6 MPa and a density of 0.75 g / cm³. This provides greater possibilities for its application in thermal insulation in extreme environments. Compared with traditional fiber-ceramic composite materials, this composite material exhibits superior mechanical properties.

[0102] Example 2

[0103] The only difference between this embodiment and Embodiment 1 is that the compression dimension of the universal testing machine in step 5) is 12 mm, and the corresponding compressive strain is 40%. The remaining steps and parameters are exactly the same as in Embodiment 1.

[0104] The properties of the obtained fiber-ceramic composite material are: compressive strength of 5 MPa, thermal conductivity of 0.12 W / (m·K), and density of 0.5 g / cm³.

[0105] In some embodiments, different types of fibers may be used instead, such as silica fibers, mullite fibers, and alumina fibers.

[0106] In some embodiments, different types of high-temperature adhesives may be used instead, such as nano-silicon carbide.

[0107] The properties of the fiber ceramic preform 4 can be optimized by adjusting the ratio of boron carbide, silicon carbide, water-soluble starch and polyacrylamide. Increasing the content of water-soluble starch to a certain extent can improve the shaping effect of the ceramic preform.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for producing a fiber ceramic composite material with controllable porosity, characterized by, Includes the following steps: S1, prepare a fiber suspension, wherein the fiber suspension includes fibers, a high-temperature binder and a high-temperature co-solvent; S2, based on electrostatic adsorption, the high-temperature binder and the high-temperature co-solvent are pre-attached to the surface of the fiber to form a fiber-functional phase unit, resulting in a modified fiber suspension; S3, the modified fiber suspension is filtered through a sieve to sequentially prepare multiple fiber paper blanks formed by deposition based on the fiber-functional phase composite unit; S4, stack multiple sheets of the fiber paper blanks to form a fiber ceramic blank with a layered structure of a preset thickness, and dry the fiber ceramic blank; S5, the dried fiber ceramic preform is subjected to a first heat treatment under high temperature conditions so that the high temperature binder and the high temperature flux pre-attached to the fiber surface are at least partially melted to form a flowable active liquid phase; S6, while maintaining the high temperature environment, apply quasi-static compression with a strain rate of 0.001 / s to 0.01 / s to the fiber ceramic preform, so that new overlapping nodes are formed between the fibers due to rearrangement, and the active liquid phase is enriched at the overlapping nodes, until the target thickness is reached. S7, the compressed fiber ceramic preform is heated again to solidify the active liquid phase enriched at the overlapping nodes to form a sintering neck, thus obtaining a layered fiber ceramic composite material with controllable porosity.

2. The production method according to claim 1, characterized by, In step S6, the compression displacement of the quasi-static compression is determined based on the target porosity, and the relationship between the target porosity and the compression displacement satisfies the following formula: wherein, is the target porosity, is the amount of compression displacement, is the density of the fiber; I is the length of the fiber ceramic body after drying; w is the width of the fiber ceramic body after drying; h is the height of the fiber ceramic body after drying; W0 is the mass of the fiber ceramic body after drying.

3. The preparation method according to claim 1, characterized in that, The high-temperature binder comprises nano-silicon carbide, and in the fiber suspension of step S1, the mass ratio of the high-temperature binder to the fiber is 5% to 12%. The high-temperature co-solvent includes nano-boron carbide, and in the fiber suspension of step S1, the mass ratio of the high-temperature co-solvent to the fiber is 5% to 12%.

4. The method of claim 1, wherein, Step S2 includes the following steps performed in sequence: A positively charged adsorbent is added to the fiber suspension and stirred to make the surfaces of the fiber, high-temperature binder and high-temperature co-solvent positively charged. Subsequently, a negatively charged adsorbent is added, and the high-temperature binder and the high-temperature co-solvent are pre-attached to the surface of the fiber through electrostatic attraction between the positive and negative charges, forming a fiber-functional phase unit to obtain a modified fiber suspension.

5. The preparation method according to claim 4, characterized in that, The positively charged adsorbent includes polyethyleneimine, and the negatively charged adsorbent includes polyacrylamide.

6. The preparation method according to claim 1, characterized in that, The fiber suspension also includes a room-temperature shaping agent, wherein the mass ratio of the room-temperature shaping agent to the fiber is 5% to 12%, and the room-temperature shaping agent includes water-soluble starch.

7. The preparation method according to claim 1, characterized in that, The fiber has a diameter of 5 μm to 10 μm and is selected from at least one of silica fiber, mullite fiber and alumina fiber.

8. The preparation method according to claim 1, characterized in that, The high-temperature environment in step S5 is 900°C to 1100°C; The initial heat preservation time in step S5 is 30 to 120 minutes; the subsequent heat preservation time in step S7 is 5 to 30 minutes. In step S4, the drying temperature is 70°C to 90°C, and the drying time is 6 to 10 hours. In step S1, the fiber suspension is stirred for 10 to 30 minutes to ensure that the fibers are evenly dispersed.

9. A fiber-ceramic composite material with controllable porosity, characterized in that, It is prepared by any one of the preparation methods according to claims 1-8.

10. The fiber-ceramic composite material according to claim 9, characterized in that, The fiber-ceramic composite material has a layered structure, a thermal conductivity of less than 0.15 W / (m·K), and a compressive strength of not less than 5 MPa; The porosity of the fiber-ceramic composite material is 50% to 60%.

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