A method for preparing carbon-ceramic composite material

Abstract

The present invention relates to the technical field of ceramic-based composite material preparation, and discloses a method for preparing a carbon-ceramic composite material. The method comprises placing a colloidal suspension containing chopped carbon fibers and ceramic precursor nanoparticles in an ultrasonic standing wave field to orient the fiber network, synchronously triggering a sol-gel transition to achieve in-situ solidification of the fiber network, and then drying and sintering the composite material. This method achieves zero-stress bonding at the fiber-matrix interface in a liquid environment through the spatiotemporal synergy of dynamic acoustic field alignment and static gel solidification, fundamentally avoiding the microcracks caused by thermal mismatch in traditional processes. Combined with an endogenous triggering mechanism of a direct current electric field, this method ensures global consistency in the gelation of large-scale components, resulting in a material that combines both microstructural programmability and macroscopic performance stability.

Description

Technical Field

[0001] The invention relates to a method for preparing a carbon-ceramic composite material, and belongs to the technical field of preparing ceramic-based composite materials. Background Art

[0002] In the field of ceramic-based composites, especially in the preparation of carbon-ceramic composites, chemical vapor infiltration (CVI) and polymer impregnation pyrolysis (PIP) have long been mainstream processes. Such technologies usually require the pre-construction of a carbon fiber preform, and then force the ceramic precursor to be filled into the fiber gaps through multiple rounds of high-temperature cycles. When applied to scenarios such as aviation brake discs that need to withstand complex alternating stresses, this paradigm of first skeleton and then filling gradually exposes deep-seated contradictions: each round of high-temperature infiltration or pyrolysis process, while increasing the density, exerts thermal shock on the fiber-matrix interface. The cumulative damage leads to the initiation of microcracks and even delamination failure during the service of the material.

[0003] Although the industry has tried to alleviate the problem by optimizing preform weaving or reducing the temperature of a single process, it has been unable to circumvent two fundamental limitations: first, the physical weaving process makes it difficult to achieve complex gradient orientation design of fibers, which limits the performance optimization space of components under non-uniform loads; second, in order to compensate for the lack of densification of the low-temperature process, the number of cycles needs to be increased, further amplifying the risk of interface damage and the energy consumption burden.

[0004] Specifically, the existing technology has three major bottlenecks: 1. There is an essential conflict between the high-temperature densification process and the protection of structural integrity, and multiple thermal cycles induce irreversible interface damage; 2. The static physical structure of the fiber preform is difficult to adapt to the dynamic stress field requirements, and the designability of the microstructure is limited; 3. Multiple rounds of high-temperature treatment lead to high energy consumption, and the process complexity and material performance are in an inverted relationship; the above contradictions are particularly prominent in high-end application scenarios such as aerospace and nuclear energy equipment, becoming a key obstacle to the expansion of carbon-ceramic composite materials to more stringent working conditions. Therefore, how to simultaneously achieve precise and controllable arrangement of the fiber network and uniform densification of the matrix under mild conditions, fundamentally avoid thermal stress damage and obtain carbon-ceramic composite materials with designable performance, has become the technical problem to be solved by the present invention. Summary of the Invention

[0005] The present invention provides a method for preparing a carbon-ceramic composite material, the main purpose of which is to solve the technical problems of difficulty in balancing high-temperature densification and structural integrity, limited microstructure designability and excessive energy consumption during the preparation of carbon-ceramic materials.

[0006] To achieve the above object, the present invention provides a method for preparing a carbon-ceramic composite material, the method comprising the following steps:

[0007] Step a, providing a colloidal suspension, wherein the colloidal suspension comprises chopped carbon fibers and ceramic matrix precursor nanoparticles;

[0008] Step b, placing the colloidal suspension in an ultrasonic standing wave field, wherein the ultrasonic standing wave field drives the chopped carbon fibers to be oriented in the colloidal suspension through acoustic radiation force to form an ordered fiber network;

[0009] Step c, triggering a sol-gel transition in the colloidal suspension while the ordered fiber network maintains its directional arrangement to form a gel solidified body that solidifies the ordered fiber network in situ, wherein the sol-gel transition is completed within a temperature range of 0°C to 60°C;

[0010] Step d: drying and sintering the gel solidified body to obtain a carbon-ceramic composite material, wherein the sintering temperature is controlled within a temperature control range of 1000 degrees Celsius to 1400 degrees Celsius.

[0011] Preferably, in step b, the arrangement direction of the chopped carbon fibers is controlled by regulating the frequency, phase or layout of the ultrasonic standing wave field to achieve at least one fiber orientation of zero degree orthogonal, ninety degree orthogonal or quasi-isotropic, or a gradient orientation distributed along a specific function curve.

[0012] Preferably, in step c, the method of triggering the sol-gel transition of the colloidal suspension is to introduce a chemical reagent capable of changing the pH value of the colloidal suspension into the colloidal suspension.

[0013] Preferably, the chemical reagent is aqueous ammonia.

[0014] Preferably, in step a, the ceramic matrix precursor nanoparticles are silica sol or alumina sol.

[0015] Preferably, in step a, the chopped carbon fibers and the ceramic matrix precursor nanoparticles are co-dispersed in a low-viscosity liquid medium, and the low-viscosity liquid medium is water or ethanol.

[0016] Preferably, the method further comprises: during step b, monitoring in real time the acoustic transmission characteristics of the sound wave when it passes through the colloidal suspension; and when the rate of change of the acoustic transmission characteristics ( ) is lower than a preset threshold ( ), stop applying the ultrasonic standing wave field and execute step c, wherein the acoustic transmission characteristics include acoustic impedance or sound velocity.

[0017] Preferably, the acoustic transmission characteristics of the sound wave when passing through the colloidal suspension are obtained by the electrical response parameters of the ultrasonic transducer or by receiving the sound wave detection signal by a pickup on the opposite side of the mold.

[0018] Preferably, in step c, the sol-gel transition of the colloidal suspension is triggered by applying a DC electric field to the colloidal suspension, generating ions that change the pH value of the colloidal suspension in situ through electrolysis, and the ions realize synchronous gelation of the colloidal suspension.

[0019] Preferably, the DC electric field is applied by designing the mold carrying the colloidal suspension as an electrode. Under the action of electrolysis, the electrodes generate hydroxide ions at the cathode and hydrogen ions at the anode. The hydroxide ions adjust the pH value of the colloidal suspension to trigger the sol-gel transition.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. While the ultrasonic standing wave field drives the directional arrangement of chopped carbon fibers to form an ordered network, the sol-gel transition is simultaneously triggered in the liquid phase environment. This dynamic arrangement process and the instant coordination of the static curing mechanism avoid the structural disturbance caused by the transfer of fiber preforms in traditional processes, allowing the fiber-matrix interface to form a complete bond under a zero-stress state, essentially avoiding the microcrack initiation path caused by thermal expansion mismatch.

[0022] 2. The bearing mold is used as an electrolytic electrode to apply a DC electric field, generating hydroxide / hydrogen ions in situ inside the colloidal suspension to adjust the pH value. This endogenous triggering mechanism enables the gelation reaction to start synchronously within the component volume, avoiding the concentration gradient effect of external catalyst diffusion, and ensuring that the spatial orientation fidelity of the fiber network and the matrix curing uniformity in thick-section components reach a self-consistent balance at the molecular scale. At the same time, the ultrasonic transducer has the dual functions of transmission and reception. By analyzing the characteristic inflection points of the impedance spectrum of sound waves propagating in the suspension, the phase change process of the fiber orientation state from disorder to order is perceived in real time. This criterion based on the evolution of the intrinsic physical quantities of the medium replaces the empirical time control mode, so that the timing of acoustic field removal is adaptively matched with the gel triggering node, avoiding cavitation damage caused by energy overload or structural defects of insufficient arrangement.

[0023] 3. The suspended dispersion system of chopped carbon fibers in nano-ceramic sol, combined with acoustic radiation force manipulation and room-temperature sol-gel transition, decouples the traditional high-temperature pyrolysis densification process into a mild physical-chemical sequential reaction. This path reconstruction, which replaces gas phase infiltration with a liquid environment and mechanical weaving with field-controlled arrangement, enables the preparation of ceramic-based composites while maintaining the programmability of the microstructure, while achieving a synergistic transition between the sintering temperature window and the single-shot molding efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a functional flow chart of the preparation process of the carbon-ceramic composite material of the present invention;

[0025] Figure 2This is a temperature control curve diagram of the drying stage and the sintering stage of the present invention;

[0026] Figure 3 This is a timing diagram of real-time monitoring and control of fiber arrangement under ultrasonic field driving of the present invention;

[0027] Figure 4 It is the temperature-time curve diagram of different process stages of the present invention;

[0028] Figure 5 This is a comparison chart of sintering temperatures.

[0029] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0030] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] The present invention provides a method for preparing a carbon-ceramic composite material, comprising the following steps:

[0032] Step a, providing a colloidal suspension, wherein the colloidal suspension comprises chopped carbon fibers and ceramic matrix precursor nanoparticles;

[0033] Step b, placing the colloidal suspension in an ultrasonic standing wave field, wherein the ultrasonic standing wave field drives the chopped carbon fibers to be oriented in the colloidal suspension through acoustic radiation force to form an ordered fiber network;

[0034] Step c, triggering a sol-gel transition in the colloidal suspension while the ordered fiber network maintains its directional arrangement to form a gel solidified body that solidifies the ordered fiber network in situ, wherein the sol-gel transition is completed within a temperature range of 0°C to 60°C;

[0035] Step d: drying and sintering the gel solidified body to obtain a carbon-ceramic composite material, wherein the sintering temperature is controlled within a temperature control range of 1000 degrees Celsius to 1400 degrees Celsius.

[0036] Preferably, in step b, the arrangement direction of the chopped carbon fibers is controlled by regulating the frequency, phase or layout of the ultrasonic standing wave field to achieve at least one fiber orientation of zero degree orthogonal, ninety degree orthogonal or quasi-isotropic, or a gradient orientation distributed along a specific function curve.

[0037] Preferably, in step c, the method of triggering the sol-gel transition of the colloidal suspension is to introduce a chemical reagent capable of changing the pH value of the colloidal suspension into the colloidal suspension.

[0038] Preferably, the chemical reagent is aqueous ammonia.

[0039] Preferably, in step a, the ceramic matrix precursor nanoparticles are silica sol or alumina sol.

[0040] Preferably, in step a, the chopped carbon fibers and the ceramic matrix precursor nanoparticles are co-dispersed in a low-viscosity liquid medium, and the low-viscosity liquid medium is water or ethanol.

[0041] Preferably, the method further comprises: during step b, monitoring in real time the acoustic transmission characteristics of the sound wave when it passes through the colloidal suspension; and when the rate of change of the acoustic transmission characteristics ( ) is lower than a preset threshold ( ), stop applying the ultrasonic standing wave field and execute step c, wherein the acoustic transmission characteristics include acoustic impedance or sound velocity.

[0042] Preferably, the acoustic transmission characteristics of the sound wave when passing through the colloidal suspension are obtained by the electrical response parameters of the ultrasonic transducer or by receiving the sound wave detection signal by a pickup on the opposite side of the mold.

[0043] Preferably, in step c, the sol-gel transition of the colloidal suspension is triggered by applying a DC electric field to the colloidal suspension, generating ions that change the pH value of the colloidal suspension in situ through electrolysis, and the ions realize synchronous gelation of the colloidal suspension.

[0044] Preferably, the DC electric field is applied by designing the mold carrying the colloidal suspension as an electrode. Under the action of electrolysis, the electrodes generate hydroxide ions at the cathode and hydrogen ions at the anode. The hydroxide ions adjust the pH value of the colloidal suspension to trigger the sol-gel transition.

[0045] Example 1: In this example, an ultrasonic standing wave field is introduced into a liquid environment to achieve directional arrangement of the fibers through a colloidal suspension composed of chopped carbon fibers and ceramic matrix precursor nanoparticles, and then a sol-gel transition process is immediately triggered after the ordered structure is formed to solidify the fiber network in situ, thereby constructing a fiber-matrix bonding structure without interfacial residual stress. In the specific implementation process, a colloidal suspension is first prepared, which contains chopped carbon fibers and ceramic matrix precursor nanoparticles, and is dispersed in a low-viscosity liquid medium, which can be water or ethanol. The setting of the dispersion system is beneficial to enhancing the response sensitivity of the chopped carbon fibers under the action of the acoustic field, thereby achieving rapid directional arrangement. On the other hand, the nanoparticle-type ceramic precursor (such as two Silica sol or alumina sol) has good dispersibility and reactivity, and can quickly complete the transition from sol state to gel state under triggering conditions to achieve in-situ locking of the arranged fiber structure; the above-mentioned colloidal suspension is placed in an ultrasonic standing wave field. Under the action of acoustic radiation force, the short-cut carbon fibers are directionally aggregated along the node or anti-node direction of the standing wave field to form an ordered fiber network structure. By regulating the standing wave frequency, phase and spatial layout of the ultrasonic transducer, the fiber arrangement can be controlled, including zero-degree orthogonal arrangement, ninety-degree orthogonal arrangement, quasi-isotropic arrangement, or gradient orientation arrangement that meets a specific function distribution. For non-uniformly loaded components, a fiber orientation distribution along the function curve can be preferably selected to improve the stress adaptability of the local structure.

[0046] In order to accurately judge the dynamic state during the fiber arrangement stage, the present invention introduces a monitoring mechanism based on acoustic transmission characteristics as a judgment standard. Specifically, the electrical response parameters of the ultrasonic transducer or the acoustic detection signal after passing through the colloidal suspension is received by a pickup arranged on the opposite side of the mold to monitor its acoustic transmission characteristics in real time, including acoustic impedance or sound velocity. When the rate of change of the acoustic transmission characteristics is lower than a preset threshold, that is, the absolute value of the rate of change does not exceed a certain threshold, the acoustic transmission characteristics are monitored in real time. When the fiber arrangement is determined to be stable, the ultrasonic standing wave field is stopped and the process proceeds to the next gelation step. The setting of this real-time judgment avoids the errors caused by the traditional control mode based on empirical time and improves the consistency and controllability of the fiber arrangement stage. When the ordered fiber network is still in a stable arrangement state, the sol-gel transition process is immediately triggered to complete the in-situ solidification of the fiber network. The specific triggering method can be achieved by two means: one is to introduce a chemical reagent (such as ammonia water) that can adjust its pH value into the colloidal suspension, thereby increasing the pH value of the system to induce polymerization reaction of the sol system and form a three-dimensional cross-linked structure; the other is to trigger by electrolysis, that is, by designing the mold carrying the colloidal suspension as an electrolysis electrode and applying a DC electric field, so that hydroxide ions are generated in situ inside the liquid to adjust the pH value, thereby initiating the sol-gel transition reaction. This electrolysis method can ensure synchronous gelation reaction throughout the entire component, effectively avoid the structural gradient phenomenon caused by uneven diffusion of the added catalyst, and improve the structural consistency of thick-section components.

[0047] After the gelation process is completed, the formed gel solid body needs to be dried and sintered to obtain the target carbon-ceramic composite material. The temperature of the sintering process is controlled to be significantly lower than the maximum temperature required for densification treatment in traditional chemical vapor infiltration or polymer impregnation cracking processes, at least one hundred degrees Celsius lower. The realization of this temperature lowering is due to the interface construction and structural solidification completed in the previous operation, thereby avoiding thermal shock to the fiber, reducing process energy consumption and simplifying the process complexity. In actual operation, it is recommended to adopt a staged heating method in the drying process to avoid cracking of the gel structure due to rapid dehydration; the sintering process can be based on the thermal decomposition and crystallization behavior of the selected precursor, and a constant temperature treatment can be selected in the temperature control range of 1000 to 1400 degrees Celsius to achieve the closure of the microporous structure and further improve the material density.

[0048] Example 2: In practical applications, for example, for manufacturing a thermal shock-bearing carbon ceramic component with a thick cross-section and complex geometric structure, such as a thermal protection module for a hypersonic aircraft, chopped carbon fibers and ceramic matrix precursor nanoparticles (silica sol) can be used to form an initial colloidal suspension system. The system uses deionized water as the liquid medium. After being fully stirred and mixed at room temperature, it is further treated by a multi-stage ultrasonic dispersion process to ensure that the chopped carbon fibers remain dispersed in a monomeric state and avoid agglomeration. The apparent viscosity of the resulting suspension is controlled to be no higher than 10 mPa·s to ensure good fiber responsiveness under subsequent acoustic radiation. The colloidal suspension is injected into a prefabricated reaction mold, which is a non-metallic inert The composite structure consists of a flexible material and an embedded metal electrode, with a mold cavity of limited morphology inside, corresponding to the molding shape of the target component. A group of ultrasonic transducer arrays facing the liquid area are arranged at the bottom and top of the mold. The array has an adjustable spacing structure to achieve flexible control of the spatial distribution parameters of the standing wave field. After the colloidal suspension is injected into the mold cavity, the ultrasonic transducer system is started with an initial frequency of 1.5 MHz, and a stable standing wave field is formed after phase adjustment. In this sound field, the chopped carbon fibers migrate and aggregate along the direction of the standing wave nodes under the action of the acoustic radiation force, gradually forming a regular and ordered network structure. The fiber migration speed is affected by factors such as its length, the viscosity of the suspension medium and the sound intensity amplitude. Higher arrangement efficiency can be achieved by optimizing the above conditions.

[0049] To achieve dynamic monitoring of the fiber orientation process, this solution embeds a piezoelectric acoustic wave sensor unit in the mold sidewall to receive the response signal after the standing wave signal passes through the suspension. Simultaneously, combined with the electrical impedance spectroscopy response parameters of the ultrasonic transducer, a monitoring mechanism is established to determine the evolution of the structural state in real time. By analyzing the rate of change of the acoustic velocity, if the absolute value of this value remains below a preset threshold (e.g., 0.2 meters per second per second) for a specified period of time, the system determines that the fiber alignment state has stabilized and shuts down the ultrasonic system. The sol-gel transition trigger mechanism is then activated, preferably electrolytically. Metal electrodes are embedded in the mold and a DC voltage is applied (recommended initial value of 6 volts, with a 15 mm inter-electrode spacing). This generates hydroxide ions in situ within the liquid phase to adjust the pH. To ensure that the established fiber network structure is not disturbed, the resulting pH change rate is controlled to no more than 0.5 units per minute. Ultimately, the pH is stabilized between 8.5 and 9.5, causing the silica sol system to enter the gel transition range and undergo three-dimensional crosslinking, achieving spatial locking of the fiber network structure.

[0050] After the gel is formed, it is allowed to stand at room temperature for 48 hours for preliminary stabilization treatment, and then enters a staged drying process. First, it is naturally dried at 35 degrees Celsius for 12 hours, then transferred to a constant temperature box and dried at 55 degrees Celsius for 12 hours, then raised to 80 degrees Celsius and maintained for 6 hours, and finally placed in a vacuum drying oven at 100 degrees Celsius for 4 hours to ensure that the residual liquid inside is fully volatilized to prevent structural cracks caused by rapid dehydration; after the drying is completed, the resulting gel is moved into a high-temperature sintering furnace for sintering treatment. In the heating stage, the initial heating rate is 3 degrees Celsius per minute. After rising to 300 degrees Celsius, the temperature is kept constant for 2 hours to remove organic residues, and then it is raised to 1200 degrees Celsius at a rate of 5 degrees Celsius per minute and kept constant for 3 hours. This temperature control strategy is set according to the crystallization characteristics of the silica precursor, aiming to achieve microstructure densification and avoid the adhesion of fibers and substrates. Structural cracks are caused at the bulk interface due to high-temperature thermal stress. After sintering, a programmed cooling method is adopted with a cooling rate of no more than 2 degrees Celsius per minute until it returns to room temperature to control the uniform shrinkage of the overall structure. The fiber arrangement orientation of the carbon-ceramic composite material obtained by the above process steps is determined by the standing wave node spacing. In this embodiment, the node spacing is controlled between 1.2 and 1.5 mm, forming a spatial structural layout dominated by layered orderly superposition. This arrangement ensures good consistency between the principal stress direction and the load path during the service of the component, which helps to improve the material's fracture delay performance and toughness retention ability under thermal shock environments. At the same time, relying on the spatial synchronization of the gel reaction brought about by electrolytic triggering, the pH distribution is uniform in thick sections and complex components and maintained within a reasonable fluctuation range, which helps to improve the matrix curing consistency. The overall structural density control can meet the service strength requirements in practical applications.

[0051] Example 3: In the verification of this example, a colloidal suspension containing chopped carbon fibers and ceramic matrix precursor nanoparticles was first prepared. The average length of the chopped carbon fibers was controlled at 200 microns and the diameter was 7 microns. The selection was based on the engineering trade-off of ensuring that the fibers had good response sensitivity under the action of the acoustic field while avoiding entanglement due to excessive length or affecting the enhancement effect due to excessive shortness. The ceramic matrix precursor nanoparticles were silica sols with an average particle size of 30 nanometers. Their dispersibility and reactivity were pre-evaluated to ensure that they could quickly complete the transition from the sol state to the gel state under triggering conditions. Deionized water was selected as the low-viscosity liquid medium with a viscosity of 0.89 mPas (25 degrees Celsius). This selection was based on the universality, environmental friendliness and effectiveness of water as a universal solvent for sound wave transmission. Good adaptability, the mass ratio of chopped carbon fibers to ceramic matrix precursor nanoparticles was initially determined to be 1:15; the entire preparation process was carried out under strict control of temperature (25 degrees Celsius) and stirring rate (300 rpm, for 30 minutes) to ensure that the fibers and nanoparticles were highly uniformly suspended and dispersed in the liquid medium, and the apparent viscosity of the resulting colloidal suspension was controlled at no more than 10 mPas to ensure good fiber responsiveness under subsequent acoustic radiation; the prepared colloidal suspension was injected into a transparent rectangular quartz mold with a mold size of 100×50×10 mm. A group of piezoelectric ceramic ultrasonic transducer arrays were arranged at the bottom and top of the mold. The array had an adjustable spacing structure to achieve flexible control of the spatial distribution parameters of the standing wave field.

[0052] During the fiber orientation stage, the frequency of the ultrasonic standing wave field is set to 1.5 MHz. The selection of this frequency is mainly based on the consideration of minimizing the cavitation effect that may occur in the water medium while ensuring that the acoustic radiation force effectively drives the migration of the chopped carbon fibers, thereby avoiding damage to the fibers. The sound field intensity is finely controlled by adjusting the ultrasonic transducer input voltage and is set to 20 volts peak-to-peak to ensure that sufficient driving force is provided to achieve rapid orientation. By adjusting the phase difference of the ultrasonic transducer array, two typical fiber orientation modes are verified: the first is a zero-degree orthogonal arrangement. By adjusting the phase of the ultrasonic transducer array, the sound pressure is adjusted to 0. The nodes are regularly distributed along the length of the mold, guiding the chopped carbon fibers to gather and arrange in this direction; the second is a ninety-degree orthogonal arrangement. By adjusting the phase, the sound pressure nodes are regularly distributed along the width of the mold, realizing the directional arrangement of the chopped carbon fibers along the width direction. In order to realize the dynamic monitoring of the fiber orientation process, a piezoelectric acoustic wave sensor unit is embedded in the side wall of the mold to receive the response signal after the standing wave signal passes through the colloidal suspension. At the same time, combined with the electrical impedance spectrum response parameters of the ultrasonic transducer itself, a monitoring mechanism for real-time judgment of the evolution of the system structure state is established. Through real-time monitoring of the change rate of the acoustic wave transmission characteristics, when its absolute value is continuously lower than the preset threshold After 60 seconds, the system automatically determines that the fiber arrangement state has stabilized, and the application of the ultrasonic standing wave field is stopped at this time. The fundamental technical consideration for setting this criterion is to achieve a technical optimization balance between the speed and stability of fiber network formation. If the threshold of the change rate is set too high, the acoustic field may be stopped before the fibers are fully arranged in order, resulting in insufficient arrangement; conversely, if it is set too low, the acoustic field may act for too long, increase energy consumption and may cause unnecessary medium disturbance; therefore, the determination of this threshold needs to be based on the inherent characteristics of the chopped carbon fiber, the viscosity of the suspension medium, and the intensity of the ultrasonic field, and combined with the fiber arrangement accuracy that must be achieved in specific application scenarios, to set it within a reasonable engineering range that can optimize the overall technical effect.

[0053] Under the condition that the ordered fiber network maintains a directional arrangement, the colloidal suspension is immediately induced to undergo a sol-gel transition to form a gel solidified body that solidifies the ordered fiber network in situ. This embodiment mainly adopts a DC electric field-induced gelation method to verify its ability to achieve global consistency solidification in large-scale components. By embedding high-purity graphite electrodes inside the quartz mold that carries the colloidal suspension and applying a DC voltage, the recommended initial value is 6 volts, and the electrode spacing is 15 mm. Under the action of electrolysis, hydroxide ions are generated at the cathode and hydrogen ions are generated at the anode. The hydroxide ions are generated in situ inside the colloidal suspension and diffuse, and the voltage is gradually adjusted. To ensure that the formed fiber network structure is not disturbed, the pH change rate of the colloidal suspension is strictly controlled to no more than 0.5 units per minute. The fundamental technical consideration in controlling this rate is to strike an optimal balance between ensuring uniform gel curing and avoiding structural stress accumulation. If the pH change rate is too fast, it may cause a sudden increase in the pH value in a local area, leading to rapid gelation, internal stress, and even microcracks. Conversely, if the rate is too slow, the gelation time will be prolonged, reducing production efficiency and possibly introducing unnecessary perturbations under the action of the electric field for a long time. Therefore, the rate needs to be determined within a reasonable engineering range that optimizes the overall gelation effect, based on the reaction kinetics of the ceramic matrix precursor, the dimensions of the component, and the internal stress requirements of the final product. Ultimately, the pH value is stabilized between 8.5 and 9.5, allowing the silica sol system to enter the gel transition region and undergo three-dimensional crosslinking, achieving spatial locking of the fiber network structure. The sol-gel transition is completed at room temperature (25 degrees Celsius) in approximately 2 hours. After the gel solidification is formed, it is first placed at room temperature (25 degrees Celsius) for 48 hours for preliminary stabilization treatment to allow the gel network to fully shrink and strengthen, and then it is dried in stages to avoid cracking of the gel structure due to rapid dehydration. The drying process includes: the first stage is natural drying at 35 degrees Celsius for 12 hours to promote the evaporation of free water and reduce the stress caused by capillary action; the second stage is transferred to a constant temperature box and dried at 55 degrees Celsius for 12 hours to further remove the physically adsorbed water in the gel pores; the third stage is raised to 80 degrees Celsius and maintained for 6 hours to treat the bound water and prepare for subsequent vacuum drying; the fourth stage is finally placed in a vacuum drying oven at 100 degrees Celsius for 4 hours, and the vacuum degree is maintained below 10 Pa to completely remove the residual adsorbed water and some chemically bound water to prevent structural cracks caused by rapid dehydration.

[0054] After drying, the obtained gel solidified body is moved into a high-temperature sintering furnace for sintering. The sintering process strictly follows the programmed heating and cooling curve to achieve microstructure densification and avoid structural cracks caused by high-temperature thermal stress at the interface between the fiber and the matrix. The heating stage of sintering: the initial heating rate is 3 degrees Celsius per minute, and after rising to 300 degrees Celsius, it is kept constant for 2 hours to remove organic residues, and then continues to heat to 1200 degrees Celsius at a rate of 5 degrees Celsius per minute and kept constant for 3 hours. The temperature control strategy is set according to the crystallization characteristics of the silica precursor. Its fundamental purpose is to achieve a technical optimization balance between material densification and avoiding interface thermal stress. If the sintering temperature is too high or the heating rate is too fast, it may cause carbon fiber Oxidation or excessive reaction with the matrix will cause severe interfacial thermal stress and cause microcracks; on the contrary, if the sintering temperature is too low or the constant temperature time is insufficient, it may lead to incomplete densification and excessive porosity of the material, affecting the final mechanical properties; therefore, the determination of the sintering parameters needs to be based on the thermal decomposition and crystallization behavior of the ceramic matrix precursor, the thermal stability of the chopped carbon fiber and the mechanical properties required by the final composite material, to be set within a reasonable engineering range that can optimize the overall material performance. The cooling stage of sintering: after sintering, a programmed cooling method is adopted, with a cooling rate of no more than 2 degrees Celsius per minute until it returns to room temperature, so as to control the uniform shrinkage of the overall structure and further reduce the thermal stress generated during the cooling process.

[0055] Under the action of the ultrasonic standing wave field, the chopped carbon fibers exhibited significant directional migration and aggregation behavior in the colloidal suspension. The rate of change of the sound velocity of the colloidal suspension was monitored in real time through the acoustic wave sensing unit on the side wall of the mold and the electrical impedance spectrum response of the ultrasonic transducer itself to evaluate the dynamic process of fiber arrangement. The typical curve of the rate of change of the sound velocity of the colloidal suspension showed that in the initial stage of the curve, the rate of change of the sound velocity was large, indicating that the chopped carbon fibers were rapidly responding to the acoustic radiation force for directional arrangement. As time went on, the chopped carbon fibers gradually formed an ordered network, and the rate of change of the sound velocity tended to be flat. Until its absolute value continued to be lower than the preset threshold for a specific time, the system automatically determined that the arrangement was stable and stopped the sound field. This verified the effectiveness of the acoustic transmission characteristics as a real-time criterion, avoided the errors that may be caused by the traditional experience-based time control mode, and significantly improved the consistency and controllability of the fiber arrangement stage. By slicing the gel solidified body and observing it through a scanning electron microscope, it was clearly confirmed that the chopped carbon fibers were oriented in the acoustic field. A highly ordered fiber network structure was formed under the action of the electrolytically triggered gelation reaction. In the sample with zero-degree orthogonal arrangement, the chopped carbon fibers were distributed in parallel along a specific direction, with dense arrangement and clear directionality. In the sample with ninety-degree orthogonal arrangement, the chopped carbon fibers showed an ordered structure in the vertical direction. These results strongly support the ability of the present invention to achieve controllable directional arrangement of fibers through the acoustic field. At the same time, in order to verify the uniformity of DC electric field-induced gelation in large-scale components, micro pH sensors were set at different positions (center and edge) inside the gel reaction mold to monitor the changes in pH value in real time. During the electrolysis-triggered gelation process, the pH values ​​at the center and edge positions rose almost synchronously, and the pH value difference was always controlled within a small range. This fully demonstrates that the endogenous triggering mechanism of the DC electric field can effectively avoid the concentration gradient effect caused by uneven diffusion of external catalysts in the gelation reaction, and ensure the spatial orientation fidelity of the fiber network and the uniformity of matrix curing in thick-section components, which is crucial for maintaining the structural consistency of complex components.

[0056] After staged drying and sintering, the resulting carbon-ceramic composite material was subjected to density measurement and micropore structure analysis, and compared with similar materials prepared by traditional processes. The results showed that the process of the present invention can still achieve a final density and average porosity similar to those of the traditional process while significantly reducing the maximum sintering temperature (at least 100 degrees Celsius lower than the traditional process). This confirms that the present invention has successfully achieved a downward shift in the sintering temperature window through the interface construction and structural solidification completed in the early operations, fundamentally avoiding the thermal shock caused to the fibers during the traditional high-temperature cracking process, significantly reducing process energy consumption, and simplifying the process complexity. Microstructural analysis shows that the composite material prepared by the present invention has a tight fiber-matrix interface and no microcrack initiation due to thermal stress was observed.

[0057] Example 4: This example combines Figures 1 to 3 , a method for preparing a carbon ceramic composite material is described. Figure 1 As shown, starting from raw material preparation, it includes the configuration of chopped carbon fibers, ceramic precursor sol and low-viscosity medium in sequence to form a colloidal suspension system suitable for the action of the acoustic field; in the ultrasonic treatment step, the suspension is placed in a 1.5MHz standing wave field, and the acoustic radiation force drives the chopped carbon fibers to align in a directional manner, and real-time acoustic monitoring is used to track the orderly aggregation state of the fibers to ensure the formation of a stable ordered network structure; then enters the electrolysis-triggered gelation link, by applying a 6V DC electric field combined with an in-situ pH adjustment mechanism to achieve room temperature curing, that is, triggering the sol-gel transition while the fibers remain arranged, and curing the obtained gel solid. After 48h of curing, the composite structure enters the heat treatment stage, including a program-controlled process of staged drying and sintering at 1200°C to further improve the density and avoid crack formation. The final carbon-ceramic composite material has comprehensive performance advantages such as zero stress interface, no heat treatment cracks and structural programmability.

[0058] like Figure 2 As shown in the figure, the horizontal axis is the process time (hours) and the vertical axis is the temperature (℃), covering the two process stages of drying and sintering. The solid line in the figure represents the drying stage, and the corresponding temperature control curve shows a slow heating and temperature maintenance in stages to ensure that the structure of the gel solidified body is stable and no cracks occur; after the drying is completed, it enters the sintering stage, which is represented by the dotted line. In this stage, the temperature is first rapidly raised to about 300℃ and a constant temperature treatment is performed to remove organic residues, and then the temperature is continued to be raised to about 1200℃ for constant temperature to achieve microstructure densification, so as to complete the sintering and densification process of the ceramic matrix and improve the material strength and stability.

[0059] like Figure 3 As shown in the figure, at the beginning of the process, the ultrasonic control system starts the standing wave field (1.5MHz), applies the acoustic radiation force to the colloidal suspension through the transducer array, drives the directional migration of the chopped carbon fibers, and the monitoring module collects the real-time acoustic signal. The system executes the loop at a sampling frequency of every 100ms and calculates the , that is, the acoustic characteristic change rate, when When the conditions are met, the alt branch judgment process is triggered, the system sends a compliance signal and turns off the sound field, while continuously optimizing the parameters to ultimately form a stable fiber network. The entire process is controlled by key timing parameters, including sampling frequency: 10Hz, stability criterion: meeting the standard for 5 consecutive times, and response delay: <50ms, to ensure that the control logic responds and stops the sound field in time when the fiber structure tends to be stable, avoiding cavitation damage caused by excessive energy input, thereby achieving precise and orderly arrangement control.

[0060] Example 5: Dissolve polyvinyl alcohol in deionized water, and obtain a polyvinyl alcohol aqueous solution with a mass fraction of 5% by continuous stirring and heating until completely dissolved. At room temperature, slowly add a silica sol with a volume fraction of 30% as a precursor to the solution, and simultaneously add ammonia water with a volume fraction of 2% to preliminarily adjust the pH of the system so that the whole is in a weakly alkaline environment to control the gelation rate of the precursor sol and avoid premature reaction. Subsequently, add dried and pretreated chopped carbon fibers to the obtained mixture, and the carbon fiber length is controlled within the range of one to three millimeters. Ultrasonic treatment is used to uniformly disperse them in the system to form a fiber colloidal suspension. The setting of the fiber length range is intended to achieve stable spatial interlacing to construct a three-dimensional network structure, while reducing the risk of sedimentation caused by long fibers or interface discontinuity caused by short fibers; The fiber colloidal suspension is introduced into a rectangular mold cavity with parallel ultrasonic transducers so that it fills the mold cavity and excludes bubbles. The operating frequency of the transducer is set between 40kHz and 60kHz. The specific frequency is determined according to the geometric dimensions of the mold and the speed of sound wave propagation in the medium, so as to establish a one-dimensional standing wave field along the axis of the transducer. The initial working phase of the transducer remains consistent, and the spatial position of the standing wave node line in the cavity is controlled by phase difference adjustment. Under the action of radiation force, the short-cut carbon fibers tend to and are stably distributed near the node line, thereby achieving an orderly arrangement perpendicular to the node line. The frequency setting forms a balance between maintaining the spatial resolution of the sound field and the response ability of the fiber. Although a low frequency can enhance the radiation driving force, it reduces the spatial control accuracy. A high frequency improves the distribution accuracy but may cause fiber response delay. Therefore, the selected range is a reasonable range for achieving overall arrangement stability.

[0061] After maintaining the ultrasonic standing wave field stable for twenty minutes, titanium electrodes are set on the side walls at both ends of the mold and a DC voltage is applied. The voltage value is controlled between 100 volts and 150 volts. The electrode spacing is set within the range of 5 cm to 15 cm according to the mold length. The electric field guides the directional migration of charged ions in the solution, causing the pH value in the local area to change, thereby inducing a sol-gel transition in the colloidal system. The voltage setting must ensure that the electrolysis induction rate is effective while avoiding the interference of bubble generation on the fiber network structure. Insufficient voltage may cause the gel reaction to lag, and too high a voltage may cause gas evolution to interfere with the uniformity of the gel. The electrolysis duration is controlled within ten minutes to ensure that the arrangement structure of the fibers under the action of the standing wave field is solidified before the gel is completed.

[0062] After gelation is completed, the mold is transferred to a constant temperature drying environment, and the drying temperature is maintained at 60 degrees Celsius for 24 hours. The drying process should avoid gel structure rupture or volume deformation due to rapid water loss. After drying, the molded component is pre-carbonized in a nitrogen atmosphere. The heating process adopts a staged heating method with a heating rate not exceeding 5 degrees Celsius per minute. The pre-carbonization temperature is controlled between 800 and 1,000 degrees Celsius to ensure the stability of the interface structure between the carbon fiber and the matrix formed by the precursor. Subsequently, the temperature is further raised to 2,000 degrees Celsius in a vacuum or argon atmosphere for final heat treatment to fully carbonize the polymer carbon source and achieve dense transformation of the ceramic phase, thereby obtaining a carbon-ceramic composite material with stable structure, orderly fiber arrangement, and good interface bonding. The above process flow realizes the directional distribution of chopped carbon fibers in the sol system and quickly locks the formed network structure by constructing a linkage mechanism of acoustic field induction and electric field curing. The gel curing induced by local pH changes is simultaneously completed during the continuous standing wave guidance state, forming a coordinated consistency between the three-dimensional spatial structure and fiber arrangement.

[0063] Example 6: To prepare an asymmetric aircraft leading edge component, the preset structure of the component requires that its internal fiber reinforcement network have an orientation distributed along a specific function gradient to cope with the non-uniform heat flow and stress field it will be subjected to under predetermined service conditions. The preparation method begins with the calibration of the raw material system. Short-cut carbon fibers with an average length of 200 microns and an aspect ratio of approximately 30 are selected, and silica sol with an average particle size of 30 nanometers are dispersed in deionized water at a mass ratio of 1:15 to form a colloidal suspension. To ensure that the setting of subsequent process parameters has a reproducible physical basis, the actual size distribution of the batch of carbon fibers must first be obtained by laser diffraction, and the apparent viscosity of the colloidal suspension at standard room temperature must be measured using a falling ball viscometer. The measurement results of the two are consistent with the initial disordered suspension reference sound velocity obtained by ultrasonic velocity measuring instrument. , are used as input parameters for subsequent calculations.

[0064] The colloidal suspension is then injected into a non-metallic mold customized for the leading edge component, with an arrayed high-purity graphite electrode embedded in the inner wall. The ultrasonic transducer array outside the mold is activated to generate a standing wave field with a frequency of 1.5 MHz. By independently programming and controlling the phase of each unit in the transducer array, an acoustic potential well with node lines arranged along the aforementioned specific function curve is constructed inside the mold. Under the action of the acoustic radiation force, the chopped carbon fibers migrate to the sound pressure node area and complete the directional arrangement. The key to this process is to determine whether the fiber network has reached a stable and ordered state. An adaptive control algorithm deployed in the system continuously samples and detects the acoustic wave signal at a frequency of ten Hz through the acoustic wave sensor built into the mold wall, and calculates the sound velocity in real time. The criterion used by the algorithm is a dynamic convergence condition, which is related to the physical relaxation time of the system. , rather than a fixed empirical threshold, the relaxation time Viscosity of the medium and sound field energy density Together, we determine that, based on the pre-established physical model, when the rate of change of the speed of sound When the rate of change of the ultrasonic standing wave field drops below 5% of its peak value and this state remains stable for more than five sampling cycles, the control algorithm determines that the fiber network has reached macroscopic stability and immediately terminates the application of the ultrasonic standing wave field.

[0065] At the moment the fiber network structure is locked, the electrolysis-triggered gelation process starts immediately. By applying a DC electric field to the graphite electrodes embedded in the mold, water is electrolyzed in situ to generate hydroxide ions, thereby evenly improving the entire colloidal system. The applied DC voltage value is dynamically adjusted through a feedback control logic whose only goal is to The rate of increase of the value The speed is strictly maintained within the range of 0.4 to 0.5 units per minute. This speed range is established based on experimental data on the kinetics of the silica sol gel. It is intended to ensure that the three-dimensional cross-linking reaction of the gel network occurs uniformly on a sufficient time scale to avoid internal stress concentration. The control system is based on real-time monitoring of value, refer to a preset voltage and The output voltage is dynamically adjusted to ensure the synchronization of the gelation reaction throughout the entire volume of the component.

[0066] After the gel solidification body has been standing in the mold for forty-eight hours, it enters the heat treatment stage. The setting of its temperature control curve is entirely based on the physicochemical transformation data obtained by thermogravimetric analysis and differential scanning calorimetry of the gel body. The first constant temperature platform of the temperature rise curve is set at 300 degrees Celsius, which corresponds to the end point of the first significant weight loss step caused by the volatilization of organic matter and physically adsorbed water in the thermogravimetric analysis curve. The second constant temperature platform, that is, the sintering temperature, is set at 1,200 degrees Celsius. This selection is based on the exothermic peak corresponding to the transformation of silica amorphous to crystalline in the differential scanning calorimetry curve, and combined with the density and strength test results of the samples after sintering at different temperatures, it is determined that this temperature is the balance point for achieving full densification of the material and avoiding carbon fiber reaction. In the final programmed cooling stage, the rate is controlled below two degrees Celsius per minute. The determination of this rate is based on the thermal expansion coefficient of the sintered material. and fracture toughness Measurements based on thermal stress models Calculations show that this cooling rate ensures that the maximum thermal stress caused by the temperature difference between the inside and outside of the material is always below the safety threshold of its fracture toughness. This, in principle, ensures that the interface between the fiber and the matrix does not produce microcracks caused by thermal mismatch after cooling, thereby ensuring the structural integrity of the carbon-ceramic composite material.

[0067] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a carbon-ceramic composite material, characterized in that: The method comprises the following steps: Step a, providing a colloidal suspension, wherein the colloidal suspension comprises chopped carbon fibers and ceramic matrix precursor nanoparticles; Step b, placing the colloidal suspension in an ultrasonic standing wave field, wherein the ultrasonic standing wave field drives the chopped carbon fibers to be oriented in the colloidal suspension through acoustic radiation force to form an ordered fiber network; Step c, triggering the colloidal suspension to undergo a sol-gel transition while the ordered fiber network maintains its directional arrangement, thereby forming a gel solidified body that solidifies the ordered fiber network in situ, wherein the sol-gel transition is completed within a temperature range of 0°C to 60°C; Step d, drying and sintering the gel solidified body to obtain a carbon-ceramic composite material, wherein the sintering temperature is controlled within a temperature control range of 1000 degrees Celsius to 1400 degrees Celsius; The method further comprises: during step b, monitoring in real time the acoustic transmission characteristics of the sound wave when it passes through the colloidal suspension; and when the rate of change of the acoustic transmission characteristics is lower than a preset threshold When , stop applying the ultrasonic standing wave field and perform step c, wherein the acoustic transmission characteristic includes acoustic impedance or sound velocity; And in step c, the method of triggering the sol-gel transition of the colloidal suspension is: applying a DC electric field to the colloidal suspension, generating ions that change its pH value in situ inside the colloidal suspension through electrolysis, and the ions realize synchronous gelation of the colloidal suspension.

2. The method for preparing a carbon-ceramic composite material according to claim 1, wherein: In step b, the arrangement direction of the chopped carbon fibers is controlled by regulating the frequency, phase or layout of the ultrasonic standing wave field to achieve at least one fiber orientation of zero degree orthogonal, ninety degree orthogonal or quasi-isotropic, or a gradient orientation distributed along a specific function curve.

3. The method for preparing a carbon-ceramic composite material according to claim 1, wherein: In step a, the ceramic matrix precursor nanoparticles are silica sol or alumina sol.

4. The method for preparing a carbon-ceramic composite material according to claim 1, wherein: In step a, the chopped carbon fibers and the ceramic matrix precursor nanoparticles are dispersed together in a low-viscosity liquid medium, which is water or ethanol.

5. The method for preparing a carbon-ceramic composite material according to claim 1, wherein: The acoustic transmission characteristics of the sound wave when passing through the colloidal suspension are obtained through the electrical response parameters of the ultrasonic transducer or by receiving the acoustic wave detection signal through the pickup on the opposite side of the mold.

6. The method for preparing a carbon-ceramic composite material according to claim 1, wherein: A DC electric field is applied by designing the mold that carries the colloidal suspension as an electrode. Under the action of electrolysis, the electrodes generate hydroxide ions at the cathode and hydrogen ions at the anode. The hydroxide ions adjust the pH value of the colloidal suspension to trigger the sol-gel transition.

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