A method for preparing a silicon-based ceramic material

Abstract

This invention relates to the field of ceramic material preparation technology and discloses a method for preparing silicon-based ceramic materials, comprising: dispersing ceramic fibers and inorganic fillers to prepare a primary slurry; adding a silane coupling agent to form a silanol modification layer on the fiber surface; adding an aluminum-based inorganic flocculant to generate a polynuclear aluminum hydroxyl complex and adsorbing it onto the modification layer to obtain a composite slurry; filtration and dehydration to obtain a wet blank; inducing dehydration condensation of silanol and polynuclear aluminum hydroxyl complex in a thermal field of 90°C to 150°C, generating covalent silicon-oxygen-aluminum bonds in situ at fiber cross-nodes to construct a three-dimensional cross-linked framework; and impregnating and drying with silica sol under reduced pressure. This invention utilizes interfacial chemical bonding to replace organic adhesives, eliminating the smoking and blackening phenomena of materials under high-temperature environments, and enhancing the integrity and flexural strength of the framework structure through the microscopic condensation of polynuclear components.

Description

Technical Field

[0001] This invention belongs to the field of ceramic material preparation technology, and particularly relates to a method for preparing silicon-based ceramic materials. Background Technology

[0002] Currently, ceramic fiber insulation boards are core components of industrial thermal equipment, special kilns, and refractory components. In wet forming processes, ceramic fibers and inorganic fillers are typically used as the skeleton material, combined with an inorganic binder primarily composed of silica sol and an organic binder primarily composed of starch to construct a slurry system. The organic binder, in the slurry preparation stage, not only enhances the flexural strength of the primary green body but also acts as a flocculant to promote the sedimentation of ceramic fibers and fillers. However, when the ambient temperature exceeds 200℃ to 250℃, the organic components in ceramic fiber boards undergo thermal degradation. The decomposition and generation of smoke and carbonization blackening phenomena pose significant limitations in precision thermal working conditions where high environmental cleanliness is required. Although the industry often removes organic matter through pre-calcination processes, this method increases production energy consumption and process steps. If organic adhesives are directly removed, the boards rely solely on the rigid -Si-O-Si-glass network formed by inorganic sols for connection after drying and curing. This rigid structure located at the fiber interlacing nodes is prone to stress concentration when subjected to mechanical loads or thermal shock stress, leading to brittle fracture of the nodes and inducing the failure of the overall strength of the board.

[0003] Although the industry has attempted to improve the wettability of inorganic particle surfaces using silanes, these methods have failed to fundamentally change the rigid connection at the nodes. This results in pure inorganic ceramic fiber boards, while maintaining high-temperature stability, struggling to achieve sufficient flexural strength to support processing and handling. Chinese invention patent application CN118704276A discloses a ceramic fiber board and its preparation method, which adds polyethylene glycol and iron sol, combined with a pulping process to improve product density and strength. However, this approach still relies on organic components such as polyethylene glycol and starch to provide bonding properties, resulting in smoke and discoloration at high temperatures. After high-temperature sintering, the introduced iron sol and silica sol form a stack of hard phases with single physicochemical properties at the fiber interface, lacking a heterogeneous chemical bonding structure with steric buffering effect. Under severe thermal shock or complex stress conditions, the fiber nodes of the board suffer fatigue damage or brittle failure. Constructing a heterogeneous bonding network with tough bridging effect at the fiber nodes is key to improving the performance of all-inorganic ceramic materials.

[0004] Therefore, how to construct a ceramic material with a tough bridging network and no organic components, and solve the problems of brittle connection and plate strength deterioration at fiber nodes in pure inorganic ceramic fiber materials, has become the technical problem to be solved by this invention. Summary of the Invention

[0005] This invention provides a method for preparing silicon-based ceramic materials, comprising the following steps:

[0006] Step 101: Add ceramic fibers and inorganic fillers to deionized water. By weight, the ceramic fibers are 75 to 85 parts, and the inorganic fillers are 15 to 25 parts, with the sum of the weight parts of the ceramic fibers and inorganic fillers being 100 parts. Prepare a primary slurry by shearing and stirring at 300 r / min to 500 r / min. The total weight of the ceramic fibers and inorganic fillers accounts for 3% to 5% of the total weight of the primary slurry.

[0007] Step 102: Add silane coupling agent to the primary slurry to hydrolyze the silane coupling agent on the surface of ceramic fibers to generate silanol groups, and form a silanol modified layer on the surface of ceramic fibers.

[0008] Step 103: Add aluminum-based inorganic flocculant to the primary slurry. The aluminum-based inorganic flocculant generates a positively charged polynuclear hydroxy aluminum complex in the aqueous phase of the primary slurry. The polynuclear hydroxy aluminum complex is adsorbed onto the silanol modification layer on the surface of the ceramic fiber through electrostatic interaction to obtain a composite slurry.

[0009] Step 104: The composite slurry is introduced into a vacuum forming mold and dehydrated under a vacuum pressure of -0.05MPa to -0.08MPa to obtain a wet blank.

[0010] Step 105: Place the wet blank in a thermal environment and control the temperature within the range of 90℃ to 150℃ to allow the silanol groups in the silanol modified layer to undergo a dehydration condensation reaction with the hydroxyl groups on the surface of the polynuclear aluminum hydroxy complex, thereby generating covalent bonds of aluminum oxysilane at the cross nodes of the ceramic fibers and constructing a three-dimensional cross-linked framework.

[0011] Step 106: The preform formed by the three-dimensional cross-linked skeleton is subjected to secondary vacuum impregnation using silica sol with a solid content of 15% to 20%. The preform after impregnation is dried at 105°C to 120°C until the moisture content is less than 0.5%, thereby obtaining silicon-based ceramic material.

[0012] Preferably, in step 102, the silane coupling agent is added to the primary slurry at a weight of 0.5% to 1.5% of the total weight of the primary slurry. The silane coupling agent is hydrolyzed in an aqueous environment at a stirring rate of 500 r / min to 800 r / min, and the generated silanol groups are dehydrated and condensed with the hydroxyl groups on the surface of the ceramic fiber to form a silanol modified layer. The silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, or 3-methacryloyloxypropyltrimethoxysilane.

[0013] Preferably, in step 103, the aluminum-based inorganic flocculant is selected from at least one of aluminum sulfate, polyaluminum chloride, or polyaluminum sulfate, and its addition amount is 1% to 3% of the total weight of the primary slurry; the polynuclear hydroxyaluminum complex exhibits the following characteristics in the aqueous phase: The polynuclear complex ions of the configuration guide the ceramic fibers and inorganic fillers to aggregate at the cross nodes of the ceramic fibers through charge neutralization.

[0014] Preferably, in step 101, the ceramic fiber is selected from at least one of aluminosilicate fiber, high-alumina fiber or zirconium-containing fiber, and the aspect ratio of the ceramic fiber is 50 to 200; the inorganic filler is selected from at least one of expanded perlite, alumina powder or silica powder, and the particle size range of the inorganic filler is 1 μm to 10 μm.

[0015] Preferably, step 105 specifically includes: step 1051: raising the temperature of the thermal field environment to 95°C at a heating rate of 2°C / min to 5°C / min, and holding for 60min to 90min to remove free water from the wet blank; step 1052: continuing to raise the temperature to 135°C and holding for 120min to 180min to allow the silanol group and the polynuclear aluminum hydroxyl complex to complete the dehydration condensation reaction.

[0016] Preferably, the drying process after step 106 is carried out in a constant temperature forced-air drying oven, and the drying temperature is maintained until the moisture content of the silicon-based ceramic material is lower than 0.5%, so that the silica sol introduced by the secondary depressurization impregnation is cured and forms an interpenetrating network with the three-dimensional cross-linked skeleton.

[0017] Preferably, a ceramic fiber pretreatment step is included before step 101: Step 1011: Immerse the ceramic fiber in a dilute hydrochloric acid solution with a mass fraction of 3% to 5% to remove metal oxide impurities on the surface of the ceramic fiber; Step 1012: Rinse the ceramic fiber with deionized water until neutral and then dehydrate it to increase the grafting density of silanol groups on the surface of the ceramic fiber in step 102.

[0018] Preferably, in step 103, while adding the aluminum-based inorganic flocculant, the pH value of the composite slurry is controlled within the range of 6.5 to 7.5 by adjusting the addition of a sodium hydroxide solution with a mass fraction of 1% to 2%, so as to adjust the degree of polymerization of the polynuclear aluminum hydroxy complex.

[0019] Preferably, in step 106, the secondary decompression impregnation is carried out by controlling the vacuum level to be maintained at -0.08MPa to -0.09MPa for 5 to 10 minutes, which drives the silica sol into the pores of the three-dimensional cross-linked framework and improves the flexural strength of the silicon-based ceramic material.

[0020] Compared with existing technologies, the method for preparing silicon-based ceramic materials of the present invention has the following advantages:

[0021] 1. In the preparation of silicon-based ceramic materials, the rigid network at the intersection of ceramic fibers evolves from a single -Si-O-Si- to a heterogeneous chemical bond structure containing -Si-O-Al-. This heterogeneous covalent bond has a high bond angle tolerance and constructs a flexible bridging network with steric hindrance buffering effect at the microscopic level. This alleviates the stress concentration phenomenon of the pure inorganic system under stress, thereby avoiding the intrinsic brittle fracture of the plate during macroscopic deformation. Since the formation of this hybrid network does not depend on carbon-based organic matter, the plate does not produce smoke or blackening in the early stage of high-temperature service, thus resolving the conflict between the intrinsic brittleness and high-temperature stability of inorganic materials.

[0022] 2. The polynuclear hydroxy aluminum complex precursor generated by the hydrolysis of aluminum-based inorganic flocculant in an aqueous environment is pre-anchored to the active sites of ceramic fiber nodes through electrostatic attraction. Under a thermal field of 90 to 150 degrees Celsius, this precursor undergoes directional dehydration and polycondensation with active silanols generated by silane pretreatment. This process transforms the flocculant from a single physical sedimentation component into a chemical cross-linking hub at the micro-interface. Without introducing organic binders such as starch, it improves the bonding strength between fibers. This chemical bonding-based connection method has stronger interfacial adhesion than the traditional van der Waals force physical stacking, ensuring the structural integrity of the board during handling and processing.

[0023] 3. The secondary impregnation process and the pre-treated silica sol form a gradient reinforcement distribution. The silica sol with a solid content of 15% to 20% penetrates and solidifies in the pores of the already formed primary hybrid network, filling the micro-capillary channels and repairing interface defects that may exist during the molding process. This multi-level, multi-component synergistic coupling logic, combined with a specific reaction window of 90 to 150 degrees Celsius, enables siloxanes and polynuclear aluminum ions to undergo deep cross-linking at fiber nodes. This mechanism not only enhances the flexural strength of the board, but also effectively blocks the heat conduction path in the solid skeleton by constructing a dense silica-alumina hybrid network, thereby improving the thermal insulation performance and thermal shock stability of the material. Attached Figure Description

[0024] Figure 1 This is a diagram illustrating the six-step standardized preparation process of the silicon-based ceramic material of this invention;

[0025] Figure 2 This is a diagram illustrating the entire process deployment scheme of this invention, from slurry modification to skeleton construction. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0027] It should be noted that all directional and positional terms used in this invention, such as: up, down, left, right, front, back, vertical, horizontal, inner, outer, top, bottom, transverse, longitudinal, center, etc., are only used to explain the relative positional relationship and connection between components in a specific state (as shown in the accompanying drawings). They are only for the convenience of describing this invention and do not require that this invention be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention. In addition, the descriptions of "first," "second," etc., in this invention are 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.

[0028] In the description of this invention, unless otherwise explicitly specified and limited, the terms installation, connection, and linking should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0029] In the description of this specification, references to the terms "an embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example, and the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0030] A method for preparing a silicon-based ceramic material includes the following steps:

[0031] Step 101: Add ceramic fibers and inorganic fillers to deionized water. By weight, the ceramic fibers are 75 to 85 parts and the inorganic fillers are 15 to 25 parts, with the sum of the weight parts of the ceramic fibers and inorganic fillers being 100 parts, and make up the difference to 100 parts. Prepare a primary slurry with a solid content of 3% to 5% by shearing and stirring at 300 r / min to 500 r / min; wherein the total weight of the ceramic fibers and inorganic fillers accounts for 3% to 5% of the total weight of the primary slurry.

[0032] Step 102: Add silane coupling agent to the primary slurry to hydrolyze the silane coupling agent on the surface of ceramic fibers to generate silanol groups, and form a silanol modified layer on the surface of ceramic fibers.

[0033] Step 103: Add aluminum-based inorganic flocculant to the primary slurry. The aluminum-based inorganic flocculant generates a positively charged polynuclear hydroxy aluminum complex in the aqueous phase of the primary slurry. The polynuclear hydroxy aluminum complex is adsorbed onto the silanol modification layer on the surface of the ceramic fiber through electrostatic interaction to obtain a composite slurry.

[0034] Step 104: The composite slurry is introduced into a vacuum forming mold and dehydrated under a vacuum pressure of -0.05MPa to -0.08MPa to obtain a wet blank.

[0035] Step 105: Place the wet blank in a thermal environment and control the temperature within the range of 90℃ to 150℃ to allow the silanol groups in the silanol modified layer to undergo a dehydration condensation reaction with the hydroxyl groups on the surface of the polynuclear aluminum hydroxy complex, thereby generating covalent bonds of aluminum oxysilane at the cross nodes of the ceramic fibers and constructing a three-dimensional cross-linked framework.

[0036] Step 106: The preform formed by the three-dimensional cross-linked skeleton is subjected to secondary vacuum impregnation using silica sol with a solid content of 15% to 20%. The preform after impregnation is dried at 105°C to 120°C until the moisture content is less than 0.5%, thereby obtaining silicon-based ceramic material.

[0037] Preferably, in step 102, the silane coupling agent is added to the primary slurry at a weight of 0.5% to 1.5% of the total weight of the primary slurry. The silane coupling agent is hydrolyzed in an aqueous environment at a stirring rate of 500 r / min to 800 r / min, and the generated silanol groups are dehydrated and condensed with the hydroxyl groups on the surface of the ceramic fiber to form a silanol modified layer. The silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, or 3-methacryloyloxypropyltrimethoxysilane.

[0038] Preferably, in step 103, the aluminum-based inorganic flocculant is selected from at least one of aluminum sulfate, polyaluminum chloride, or polyaluminum sulfate, and its addition amount is 1% to 3% of the total weight of the primary slurry; the polynuclear hydroxyaluminum complex exhibits the following characteristics in the aqueous phase: The polynuclear complex ions of the configuration guide the ceramic fibers and inorganic fillers to aggregate at the cross nodes of the ceramic fibers through charge neutralization.

[0039] Preferably, in step 101, the ceramic fiber is selected from at least one of aluminosilicate fiber, high-alumina fiber or zirconium-containing fiber, and the aspect ratio of the ceramic fiber is 50 to 200; the inorganic filler is selected from at least one of expanded perlite, alumina powder or silica powder, and the particle size range of the inorganic filler is 1 μm to 10 μm.

[0040] Preferably, in step 106, by controlling the time of the secondary vacuum impregnation and the solid content of the silica sol, the loading amount of silica sol in the three-dimensional cross-linked framework is made to meet the following formula requirement: ,in, This represents the mass loading, with a value ranging from 0.12 to 0.18. The mass of silica sol consumed during the secondary vacuum impregnation process is ω, where ω is the solid content of the silica sol. This refers to the weight of the ceramic fibers. This represents the weight of the inorganic filler.

[0041] Preferably, step 105 specifically includes: step 1051: raising the temperature of the thermal field environment to 95°C at a heating rate of 2°C / min to 5°C / min, and holding for 60min to 90min to remove free water from the wet blank; step 1052: continuing to raise the temperature to 135°C and holding for 120min to 180min to allow the silanol group and the polynuclear aluminum hydroxyl complex to complete the dehydration condensation reaction.

[0042] Preferably, the drying process after step 106 is carried out in a constant temperature forced-air drying oven, and the drying temperature is maintained until the moisture content of the silicon-based ceramic material is lower than 0.5%, so that the silica sol introduced by the secondary depressurization impregnation is cured and forms an interpenetrating network with the three-dimensional cross-linked skeleton.

[0043] Preferably, a ceramic fiber pretreatment step is included before step 101: Step 1011: Immerse the ceramic fiber in a dilute hydrochloric acid solution with a mass fraction of 3% to 5% to remove metal oxide impurities on the surface of the ceramic fiber; Step 1012: Rinse the ceramic fiber with deionized water until neutral and then dehydrate it to increase the grafting density of silanol groups on the surface of the ceramic fiber in step 102.

[0044] Preferably, in step 103, while adding the aluminum-based inorganic flocculant, the pH value of the composite slurry is controlled within the range of 6.5 to 7.5 by adjusting the addition of a sodium hydroxide solution with a mass fraction of 1% to 2%, so as to adjust the degree of polymerization of the polynuclear aluminum hydroxy complex.

[0045] Preferably, in step 106, the secondary decompression impregnation is carried out by controlling the vacuum level to be maintained at -0.08MPa to -0.09MPa for 5 to 10 minutes, which drives the silica sol into the pores of the three-dimensional cross-linked framework and improves the flexural strength of the silicon-based ceramic material.

[0046] Example 1: In the application scenario of ultra-high vacuum precision heat treatment furnace lining, in response to the smoke and carbonization pollution generated by the decomposition of organic components under high temperature conditions of 1000℃, and the fracture failure caused by node brittleness of pure inorganic plates under handling or high-frequency vibration conditions, the implementation process of the preparation method of the present invention is as follows: 80 parts by weight of short-cut aluminosilicate ceramic fibers with a specific gravity of 400 and 20 parts by weight of alumina powder are added to deionized water to prepare a primary slurry in which the total weight of ceramic fibers and alumina powder accounts for 4% of the total weight of the primary slurry; 1.0% by weight of 3-glycidyl etheroxypropyltrimethoxysilane is added to the primary slurry, and stirring is maintained in an aqueous environment at 35℃ to allow the silane coupling agent to hydrolyze and generate a silanol-modified layer on the surface of the ceramic fibers; 2% polyaluminum chloride is added, and the pH value of the slurry is adjusted to 7.0 by adding a 1.5% sodium hydroxide solution by mass, so that the positively charged polynuclear hydroxyaluminum complex generated by the polyaluminum chloride in the aqueous phase presents as... The polynuclear complex ions of the configuration are pre-anchored to the silanol-modified layer at the cross nodes of ceramic fibers through electrostatic attraction.

[0047] After the slurry is prepared, the resulting material is introduced into a vacuum forming mold and dehydrated under a vacuum pressure of -0.07 MPa to obtain a wet blank. The wet blank is placed in a thermal environment and heated to 95°C at a rate of 3°C / min and held for 80 min to remove free water. The temperature is then increased to 135°C and held for 150 min. Within this temperature range, thermal energy drives the active hydroxyl groups on the surface of the polynuclear aluminum hydroxyl complex to undergo a directional dehydration and condensation reaction with the silanol groups at the fiber nodes, generating -Si-O-Al- heterogeneous chemical covalent bonds in situ at the cross-linking sites of the ceramic fibers, constructing a three-dimensional cross-linked framework. Due to the high bond angle tolerance of the -Si-O-Al- covalent bonds, steric hindrance buffering is generated when the plate is subjected to macroscopic deformation or mechanical stress, effectively alleviating stress concentration at the fiber contact interface. This invention addresses the intrinsic brittleness of a single silicon-oxygen network by employing a secondary vacuum impregnation process with a silica sol containing 18% solids. The vacuum level is maintained at -0.085 MPa, and the material is dried at 110°C until the moisture content is below 0.5%. This process allows the secondary silica sol to solidify within the pores of the framework, forming an interpenetrating network structure. The resulting silicon-based ceramic material exhibits no smoke or blackening under actual heat treatment at 1000°C, and the overall structure remains intact. No chipping or cracking is observed during vibration testing in simulated long-distance transportation. Experimental results demonstrate that, through the chemical functional transformation of an aluminum-based inorganic flocculant under a specific thermal field, this invention enhances the microscopic toughness and macroscopic flexural strength of the ceramic framework by utilizing interfacial heterogeneous bonding, while eliminating the need for carbon-based organic binders.

[0048] Example 2: In a test environment consisting of a bending tester with a load accuracy of 0.05N and a drying oven with a temperature control accuracy of ±1℃, the data came from the real-time acquisition of the kinematic viscosity of the slurry by physical sensors. The sampling period parameter t was determined based on the trade-off between the thermal shrinkage rate of ceramic fibers and the water migration rate. t was set to be less than 0.1 times the characteristic period of water evaporation. For slurries where the total weight of ceramic fibers and inorganic fillers accounted for 4% of the total weight of the primary slurry, t was determined to be 0.5h. Before entering the 90℃ to 150℃ hot zone, the initial kinematic viscosity of the sample group of this invention, the control group using 2% cationic starch, the partially deficient control group lacking aluminum-based inorganic flocculant, and the out-of-range control group with 4.5% aluminum-based inorganic flocculant were all within the range of 152.4 mPa·s to 158.2 mPa·s.

[0049] Monitoring charge transfer impedance at ceramic fiber nodes using micro-impedance analysis At 115°C, the sample group of the present invention The value is 2.48M Reduced to 0.82M This numerical change corresponds to Polynuclear complex ions induce dehydration and condensation reactions at ceramic fiber nodes, generating -Si-O-Al- heterogeneous chemical covalent bonds, while the partially missing control group... The value remained at 2.31 MΩ without showing a downward trend, corresponding to the constant charge conduction state in the physical stacked structure; when the content of aluminum-based inorganic flocculant exceeded the upper limit of 4.5%, The value rebounded to 1.45 MΩ, and this nonlinear numerical rebound corresponds to the self-aggregation distribution of excess aluminum-based components on the surface of ceramic fibers.

[0050] After calcination at 1000℃ for 2 hours, the measured flexural strength of the sample group of this invention was 1.15 MPa, while the flexural strength of the cationic starch control group was 0.36 MPa. The data reflects the evolution of the skeleton structure after the decomposition of organic components. Under the condition of simulated 25 dB environmental mechanical vibration noise, the standard deviation of the flexural strength fluctuation of the sample group of this invention was 0.023 MPa, while the standard deviation of the fluctuation of the control group was 0.158 MPa. The data confirms the inhibitory effect of the -Si-O-Al- three-dimensional cross-linked skeleton on mechanical disturbance, and the structural stability of silicon-based ceramic materials under high-temperature service environment.

[0051] Example 3: In the process of producing ceramic sintering trays with controlled thermal stress deformation index below 0.1%, to address the tray warping caused by fiber node stress mismatch during the rapid heating stage at 1000℃, and the problem of inconsistent microhardness of the plate cross-section exceeding 10HV, the impregnation resistance was eliminated by calibrating the pore structure of the wet blank. 85 parts by weight of 400 chopped aluminosilicate ceramic fibers and 15 parts by weight of silica powder were added to deionized water. Under a stirring speed of 400 r / min, a primary slurry was prepared with the total weight of ceramic fibers and silica powder accounting for 3% of the total weight of the primary slurry. The average pore diameter d of the blank was adjusted using vacuum pressure P. The average pore diameter d and vacuum pressure P follow the following linear mapping relationship: Where d is the average pore size of the ceramic fiber preform, P is the vacuum pressure, and k is the structural proportionality coefficient, with a value of -120. The baseline value for the packing pore size under normal pressure is taken as 15.5 μm. Based on the effective stress compression principle of porous media, the shrinkage deformation of the fiber skeleton pores exhibits an approximately linear response to the applied absolute pressure. The structural proportionality coefficient k and the baseline value for the packing pore size under normal pressure are then obtained. Numerical analysis was performed on the primary slurry from the same batch. Five pressure gradients were set within the range of -0.02 MPa to -0.08 MPa for filtration molding. The average pore size of the wet preforms obtained under the corresponding pressures was measured using a mercury porosimeter. A linear regression equation was fitted between the pressure input value and the measured pore size response using the least squares method. The slope output of the equation is k, and the intercept output is... When the vacuum pressure is set to -0.07MPa, the average pore size generated inside the wet blank is located at 7.1μm. The physical size of this passage provides a definite interfacial resistance benchmark for the subsequent diffusion of silica sol particles.

[0052] The wet blank was placed in a controlled thermal field and held at 95°C for 80 minutes to remove free water. It was then heated to 135°C at a rate of 2°C / min. During this process, pre-adsorbed ions at the fiber junction sites were utilized. The electrostatic field generated by the polynuclear complex ions induces the deflection of the silanol electron cloud, enabling the dehydration condensation reaction between -Si-OH and -Al-OH to overcome the chemical energy barrier at 135℃, generating in situ -Si-O-Al- heterogeneous chemical covalent bonds. By monitoring the evolution of the volume shrinkage rate of the system with the temperature gradient, the volume shrinkage rate change gradient is less than 0.01% / min after maintaining 135℃ for 120 min, indicating that the chemical cross-linking framework of the ceramic fiber cross nodes has been completed. In this microscopic reaction process, the macroscopic thermal field of 135℃ serves as the energy input, driving the excited desorption of coordinated water molecules on the surface of the polynuclear complex ions. This dehydration process causes the spatial shielding layer of the complex ions to collapse, instantaneously exposing the unshielded high-density local electrostatic field. This transient micro-electric field directly and strongly polarizes the adjacent silanol covalent bonds within an angstrom-level distance, thus completing the physical bridging of macroscopic thermal energy to microscopic catalytic electric field, enabling the condensation reaction to be successfully triggered under conventional low-temperature thermal fields.

[0053] Finally, a silica sol with a solid content of 20% was selected for secondary vacuum impregnation of the primary skeleton, with the vacuum degree maintained at -0.08MPa. Since the flow rate of the silica sol in the 7.1μm pore size is increased by 45% with a solid content of 20% compared to that with a solid content of 30%, the silica sol particles achieve uniform penetration in the cross-sectional direction of the plate. The resulting silicon-based ceramic material has a macroscopic deformation rate of 0.08% when in service at 1000℃, and the microhardness range at various points on the cross-section of the plate is 4.2HV. This confirms that by accurately calibrating the matching relationship between physical forming pressure and chemical bonding environment, the structural internal stress caused by uneven impregnation in traditional processes can be eliminated, the structural instability problem of ceramic fiberboard under extreme thermal stress conditions can be solved, and the comprehensive performance of silicon-based ceramic materials can be improved.

[0054] Example 4: In a production scenario where the specific gravity of ceramic fiber raw materials fluctuates within a range of ±50, to determine the uniformity of 3-glycidyl etheroxypropyltrimethoxysilane coverage on the ceramic fiber surface, a calibration method based on the physicochemical properties of methylene blue adsorption was adopted. Specifically, 10g of the fiber sample to be tested was weighed and dispersed in deionized water, and the adsorption amount at the adsorption saturation point was measured using a spectrophotometer. and according to Determine the mass addition ratio of 3-glycidyl etheroxypropyltrimethoxysilane The linear mapping relationship between the two is given by the formula Given, among which, The mass ratio of 3-glycidyl etheroxypropyltrimethoxysilane added. Let η be the adsorption capacity of ceramic fibers for methylene blue, and η be the interface coverage coefficient, which is 0.042 in this preparation method system. Based on the positive correlation between the number of active sites on the solid surface and the saturated adsorption capacity of the characteristic substance in the Langmuir monolayer adsorption model, the interface coverage coefficient η is calibrated. Three sets of standard aluminosilicate fiber samples with known different specific surface areas are prepared. Silane coupling agent is titrated to the monolayer coverage limit, and the mass of coupling agent consumed is recorded and divided by the measured value of the saturated adsorption capacity of methylene blue in the corresponding sample. The arithmetic mean of the three quotients is output as the value of η for this batch of slurry system. When a certain batch of fibers... When the measured value was 25.4 mg / g, the calculated value was... The concentration was 1.07%. Based on this, the feeding parameters in the primary slurry were adjusted to maintain the distribution density of the generated silanol groups on the surface of the ceramic fibers in the range of 4.5 to 4.8 per square nanometer.

[0055] When the system faces operating conditions where the conductivity of production water fluctuates between 200 μS / cm and 800 μS / cm, in order to maintain the formation of polyaluminum chloride in the aqueous phase... The proportion of polynuclear complex ions was adjusted using a coupling method of conductivity and pH, specifically by using an inductive sensor to collect the initial conductivity of the slurry. and according to The formula for determining the dropping frequency f of sodium hydroxide solution is as follows: Where f is the opening frequency of the solenoid valve for adding sodium hydroxide solution, and λ is the basic dropping frequency constant, with a value of 2.5 Hz. The measured value of the initial conductivity of the primary slurry. The baseline conductivity was set at 500 μS / cm. At the obtained frequency f, a 1.5% sodium hydroxide solution was added dropwise to the composite slurry using a peristaltic pump until the pH of the slurry stabilized at 7.2. At this point, the aluminum species... The molar percentage of the complex ions was maintained above 82%, and the dehydration rate deviation of the wet plate during the filtration process was kept within 5%.

[0056] Example 5: In the production of silicon-based ceramic plates with thicknesses ranging from 20mm to 100mm, the secondary decompression impregnation time was determined. To address the physical constraint of plate thickness on penetration depth, the measured value of plate thickness H was obtained using a length comparator, and then combined with the effective porosity ε of the primary skeleton to determine... The set value, its linear mapping relationship follows the formula ,in, The immersion holding time under vacuum pressure of -0.085 MPa is given by γ, the permeation resistance compensation factor, which is set to 0.12 min / mm. H represents the measured thickness of the plate, and ε represents the measured effective porosity. Based on the fundamental law of capillary permeation kinetics, which states that the penetration time of a fluid in a homogeneous porous medium is positively correlated with the medium thickness and negatively correlated with the effective porosity, the permeation resistance compensation factor γ is established. Standard raw test plates with thicknesses ranging from 20 mm to 100 mm are selected. Under a constant vacuum of -0.085 MPa, the actual permeation time of silica sol with a specified solid content through the cross-section of the test plate is measured. The measured time is multiplied by the effective porosity of the standard test plate and divided by the measured thickness to output a series of dispersion coefficients. After removing extreme values, the arithmetic mean is taken and set as γ. For a sample with H of 50.0 mm and ε of 0.65, the following calculations are performed: The pressure holding time for the second impregnation process was adjusted to 9.23 min, and the measured solidification density difference of the silicon-based ceramic material in the thickness direction was found to be 0.008 g / cm³. Within.

[0057] When the production system faces challenges due to fluctuations in slurry temperature... When polynuclear complex ions undergo uncontrolled agglomeration before molding, the stability of the slurry is maintained by establishing an adaptive adjustment method based on the conductivity deviation. The real-time conductivity of the slurry is collected using an inductive sensor. And calculate its conductivity compared to the reference conductivity. The absolute deviation ratio is used to determine the mass addition ratio of the stabilizer. Its calculation formula is ,in, The stabilizer addition ratio is relative to the total weight of the primary slurry, and κ is the sensitivity coefficient with a value of 0.08. To set the reference conductivity, a value of 500 was chosen. S / cm, The measured value of conductivity in real time is used to determine the proportion. By adjusting the feeding parameters, the gelation time of the slurry before filtration and molding was maintained at 45.5 min, and the cross-sectional structure of the resulting silicon-based ceramic material remained consistent under the service environment of 1000℃.

[0058] In the fabrication of precision ceramic gaskets requiring a linear shrinkage rate of less than 1%, a filler blending method based on the thermal expansion coefficient deviation is adopted to address the matching requirements of different types of inorganic fillers for their thermal expansion coefficients. The thermal expansion coefficient of the ceramic fibers is then measured using a thermal expansion meter. And select a coefficient of thermal expansion of Alumina powder with a coefficient of thermal expansion of The silica powder is compounded, and the mass percentage of silica powder is as follows: Follow the formula ,in, This represents the mass fraction of silica powder in the inorganic filler. This is the preset target value for the overall thermal expansion coefficient of the ceramic material. This is the measured value of the thermal expansion coefficient of ceramic fibers. and The values ​​are the measured coefficients of thermal expansion of alumina powder and silica powder, respectively; by adjusting... By distributing the filler particles within the pores of the ceramic fiber cross nodes and forming a steric hindrance synergy with the -Si-O-Al- hybrid network, the resulting silicon-based ceramic material exhibits a dimensional deviation within 0.05% during a 1000℃ thermal cycling test.

[0059] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A method for preparing a silicon-based ceramic material, characterized in that, Includes the following steps: Step 101: Add ceramic fibers and inorganic fillers to deionized water. By weight, the ceramic fibers are 75 to 85 parts, and the inorganic fillers are 15 to 25 parts, with the sum of the weight parts of the ceramic fibers and inorganic fillers being 100 parts. Prepare a primary slurry by shearing and stirring at 300 r / min to 500 r / min. The total weight of the ceramic fibers and inorganic fillers accounts for 3% to 5% of the total weight of the primary slurry. Step 102: Add silane coupling agent to the primary slurry to hydrolyze the silane coupling agent on the surface of ceramic fibers to generate silanol groups, and form a silanol modified layer on the surface of ceramic fibers. Step 103: Add aluminum-based inorganic flocculant to the primary slurry. The aluminum-based inorganic flocculant generates a positively charged polynuclear hydroxy aluminum complex in the aqueous phase of the primary slurry. The polynuclear hydroxy aluminum complex is adsorbed onto the silanol modification layer on the surface of the ceramic fiber through electrostatic interaction to obtain a composite slurry. Step 104: The composite slurry is introduced into a vacuum forming mold and dehydrated under a vacuum pressure of -0.05MPa to -0.08MPa to obtain a wet blank. Step 105: Place the wet blank in a thermal environment and control the temperature within the range of 90℃ to 150℃ to allow the silanol groups in the silanol modified layer to undergo a dehydration condensation reaction with the hydroxyl groups on the surface of the polynuclear aluminum hydroxy complex, thereby generating covalent bonds of aluminum oxysilane at the cross nodes of the ceramic fibers and constructing a three-dimensional cross-linked framework. Step 106: The preform formed by the three-dimensional cross-linked skeleton is subjected to secondary vacuum impregnation using silica sol with a solid content of 15% to 20%. The preform after impregnation is dried at 105°C to 120°C until the moisture content is less than 0.5%, thereby obtaining silicon-based ceramic material.

2. The method for preparing a silicon-based ceramic material according to claim 1, characterized in that, In step 102, a silane coupling agent is added to the primary slurry at a weight of 0.5% to 1.5% of the total weight of the primary slurry. The silane coupling agent is hydrolyzed in an aqueous environment at a stirring rate of 500 r / min to 800 r / min, and the generated silanol groups are dehydrated and condensed with the hydroxyl groups on the surface of the ceramic fiber to form a silanol modified layer. The silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, or 3-methacryloyloxypropyltrimethoxysilane.

3. The method for preparing a silicon-based ceramic material according to claim 1, characterized in that, In step 103, the aluminum-based inorganic flocculant is selected from at least one of aluminum sulfate, polyaluminum chloride, or polyaluminum sulfate, and its addition amount is 1% to 3% of the total weight of the primary slurry; the polynuclear hydroxyaluminum complex exhibits the following characteristics in the aqueous phase: The polynuclear complex ions of the configuration guide the ceramic fibers and inorganic fillers to aggregate at the cross nodes of the ceramic fibers through charge neutralization.

4. The method for preparing a silicon-based ceramic material according to claim 1, characterized in that, In step 101, the ceramic fiber is selected from at least one of aluminosilicate fiber, high alumina fiber or zirconium-containing fiber, and the aspect ratio of the ceramic fiber is 50 to 200; the inorganic filler is selected from at least one of expanded perlite, alumina powder or silica powder, and the particle size range of the inorganic filler is 1 μm to 10 μm.

5. The method for preparing a silicon-based ceramic material according to claim 1, characterized in that, Step 105 specifically includes: Step 1051: Raise the temperature of the thermal field environment to 95°C at a heating rate of 2°C / min to 5°C / min, and hold for 60min to 90min to remove free water from the wet blank; Step 1052: Continue to raise the temperature to 135°C and hold for 120min to 180min to allow the silanol group and the polynuclear aluminum hydroxyl complex to complete the dehydration condensation reaction.

6. The method for preparing a silicon-based ceramic material according to claim 1, characterized in that, The drying process after step 106 is carried out in a constant temperature forced-air drying oven, maintaining the drying temperature until the moisture content of the silicon-based ceramic material is below 0.5%, so that the silica sol introduced by the secondary depressurization impregnation can be cured and form an interpenetrating network with the three-dimensional cross-linked skeleton.

7. The method for preparing a silicon-based ceramic material according to claim 1, characterized in that, Before step 101, a ceramic fiber pretreatment step is also included: Step 1011: Immerse the ceramic fiber in a dilute hydrochloric acid solution with a mass fraction of 3% to 5% to remove metal oxide impurities on the surface of the ceramic fiber; Step 1012: Rinse the ceramic fiber with deionized water until neutral and then dehydrate it to increase the grafting density of silanol groups on the surface of the ceramic fiber in step 102.

8. The method for preparing a silicon-based ceramic material according to claim 1, characterized in that, In step 103, while adding aluminum-based inorganic flocculant, the pH value of the composite slurry is controlled within the range of 6.5 to 7.5 by adjusting the addition of sodium hydroxide solution with a mass fraction of 1% to 2% to adjust the degree of polymerization of polynuclear aluminum hydroxy complex.

9. The method for preparing a silicon-based ceramic material according to claim 1, characterized in that, In step 106, the secondary decompression impregnation is carried out by controlling the vacuum level to be maintained at -0.08MPa to -0.09MPa for 5 to 10 minutes, which drives the silica sol into the pores of the three-dimensional cross-linked framework and improves the flexural strength of the silicon-based ceramic material.

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