Liquid zirconium carbide precursor with high ceramic yield and method of making same

Abstract

This application relates to the field of ceramic precursor materials technology, and discloses a high-ceramic-yield liquid zirconium carbide precursor and its preparation method. The high-ceramic-yield liquid zirconium carbide precursor is made from raw materials comprising the following parts by weight: zirconium n-butoxide: 100 parts; allyl acetoacetate: 74-82 parts; deionized water: 2.3-3.8 parts; furfuryl alcohol-maleic anhydride adduct modifier: 48-60 parts; wherein the furfuryl alcohol-maleic anhydride adduct modifier is the Diels-Alder reaction product of furfuryl alcohol and maleic anhydride. This invention introduces a Diels-Alder adduct of furfuryl alcohol and maleic anhydride to construct a thermally latent system. At room temperature, the adduct maintains a cyclic inert structure, giving the precursor low viscosity and long-term storage stability. At high temperatures, crosslinking is achieved by releasing active monomers through a reverse Diels-Alder reaction.

Description

Technical Field

[0001] This invention relates to the field of ceramic precursor materials technology, specifically to a liquid zirconium carbide precursor with high ceramic yield and its preparation method. Background Technology

[0002] Zirconium carbide ceramics possess extremely high melting points and excellent ablation resistance, making them key candidate materials for hypersonic vehicle thermal protection systems and rocket propulsion components. To prepare complex, high-temperature resistant composite materials, the industry widely employs precursor impregnation pyrolysis processes. This process requires the starting material to be liquid with good fluidity to penetrate deeply into the dense fibrous preform and, after high-temperature treatment, to transform into a structurally complete ceramic matrix.

[0003] Current preparation techniques mostly use zirconium alkoxides as the basic raw material. Since the residual carbon content after the cracking of pure zirconium alkoxides is insufficient to form zirconium carbide, existing techniques typically introduce additional carbon sources. Common methods include physical blending of zirconium alkoxides with phenolic resins, pitch, or high molecular weight polymers. Some studies have also used coordination chemistry principles to chemically modify zirconium alkoxides by adding acetylacetone or specific organic acids. These methods can adjust the rheological properties of the precursors under laboratory conditions and have verified the feasibility of converting organic precursors into inorganic ceramics.

[0004] However, the above-mentioned approaches have significant drawbacks in practical applications. Physically blended systems often suffer from poor microscopic compatibility, leading to stratification during storage. During high-temperature pyrolysis, the thermal decomposition temperatures of the organic carbon source and the inorganic zirconium source are mismatched, causing a large amount of carbon source to volatilize prematurely in small molecule form, resulting in a low final ceramic yield and numerous internal defects. Attempts to use highly reactive carbon-rich monomers for chemical modification are limited by the control of reaction rates. For example, monomers such as furfuryl alcohol readily undergo vigorous self-polymerization reactions at room temperature under acidic environments or catalysis by metal ions. This uncontrollable reaction causes the viscosity of the precursor to spike rapidly during storage, even gelling before the impregnation process, severely shortening the material's service life. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a liquid zirconium carbide precursor with high ceramic yield and its preparation method, which solves the technical problems of uncontrollable polymerization and poor storage stability caused by the introduction of highly active carbon sources in existing liquid zirconium carbide precursors, as well as low ceramic yield caused by the volatilization and loss of carbon sources during high-temperature pyrolysis.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a liquid zirconium carbide precursor with high ceramic yield, employing the following technical solution: A high-ceramic-yield liquid zirconium carbide precursor is made from raw materials comprising the following parts by weight: 100 parts of zirconium n-butoxide, 74 to 82 parts of allyl acetoacetate, 2.3 to 3.8 parts of deionized water, and 48 to 60 parts of furfuryl alcohol and maleic anhydride adduct modifier; wherein the furfuryl alcohol and maleic anhydride adduct modifier is a Diels-Alder reaction product of furfuryl alcohol and maleic anhydride.

[0007] By adopting the above technical solution, the present invention utilizes the chemical reaction characteristics between raw materials to construct a stable precursor system: First, zirconium n-butoxide is used as the zirconium source, and allyl acetoacetate is used as the chelating agent. Through a ligand exchange reaction, the reactive alkoxy group in zirconium n-butoxide is replaced, forming a chemically stable chelated zirconium precursor, which inhibits the hydrolytic activity of the zirconium source in subsequent processing. The introduced deionized water initiates controlled micro-hydrolysis, promoting intermolecular dehydration condensation of zirconium alkoxide molecules to form an inorganic oligomer core containing Zr-O-Zr bonds. This inorganic core provides the skeletal basis for the final ceramicized product.

[0008] Secondly, the furfuryl alcohol and maleic anhydride adduct modifier plays a dual role in the system. During room temperature storage and low-temperature processing, the adduct maintains a stable cyclic chemical structure, existing as a non-reactive component, effectively diluting the system viscosity and imparting good flowability and storage stability to the precursor. During high-temperature curing or pyrolysis, the adduct undergoes a reverse Diels-Alder reaction, dissociating in situ to release polymerizable furfuryl alcohol monomers and grafting-active maleic anhydride monomers. The released maleic anhydride monomers undergo esterification reactions with the hydroxyl groups on the surface of the zirconium oxide clusters through the anhydride groups, grafting organic segments onto the inorganic framework; the released furfuryl alcohol monomers simultaneously undergo self-polymerization or copolymerization. This in-situ generated organic network interpenetrates and chemically bonds with the inorganic framework, effectively suppressing the volatilization of small carbon molecules during pyrolysis, thereby significantly improving the yield of the final zirconium carbide ceramic.

[0009] Preferably, the raw materials are in the following weight proportions: 100 parts zirconium n-butoxide, 74.1 to 81.5 parts allyl acetoacetate, 2.34 to 3.76 parts deionized water, and 48.5 to 58.8 parts furfuryl alcohol and maleic anhydride adduct modifier.

[0010] By adopting the above technical solution, the stoichiometric ratio of each component was optimized. This ratio ensures that zirconium atoms have a suitable degree of chelation, preventing excessive chelation from hindering network formation or insufficient chelation from leading to uncontrolled hydrolysis; at the same time, it ensures that the number of active groups released by the modifier at high temperature matches the number of reaction sites on the inorganic framework, thereby improving the crosslinking density.

[0011] Preferably, the furfuryl alcohol and maleic anhydride adduct modifier is prepared by reacting furfuryl alcohol and maleic anhydride, wherein the molar ratio of furfuryl alcohol to maleic anhydride is 1.0 to 1.3 to 0.9 to 1.0.

[0012] By employing the above technical solution, controlling the molar ratio of furfuryl alcohol to maleic anhydride to be close to the theoretical amount or with a slight excess of furfuryl alcohol ensures that the two monomers generated after the reverse Diels-Alder reaction can fully participate in the curing process. A trace excess of furfuryl alcohol helps improve the wettability of the system and preferentially forms a high-carbon-residue furan resin phase at high temperatures.

[0013] Preferably, the deionized water is added in the form of a diluent, which is a mixture of deionized water and anhydrous ethanol, wherein the mass ratio of deionized water to anhydrous ethanol is 1 to 5.0 to 6.0.

[0014] By employing the above technical solution, deionized water is highly dispersed using anhydrous ethanol. This dilution effect increases the dispersion distance of water molecules in the reaction system, avoids localized high concentrations of water contacting zirconium alkoxides to form precipitation, and ensures that the micro-hydrolysis reaction proceeds stably in a homogeneous system, thereby obtaining a clear and transparent precursor solution.

[0015] Secondly, the present invention provides a method for preparing a liquid zirconium carbide precursor with high ceramic yield, employing the following technical solution: A method for preparing a liquid zirconium carbide precursor with high ceramic yield includes the following steps: Step S1: Under low temperature stirring conditions, allyl acetoacetate is slowly added dropwise to a solution containing zirconium n-butoxide. After the addition is complete, the reaction is carried out at room temperature. Step S2: Mix deionized water with solvent to prepare a diluent, and slowly add it dropwise to the system in step S1. After the addition is complete, heat the system and keep it warm for curing. Step S3: The system from step S2 is subjected to vacuum distillation under heating conditions to remove the solvent and byproducts, resulting in a viscous liquid. Step S4: Lower the temperature of the system in step S3, add furfuryl alcohol and maleic anhydride adduct modifier, mix evenly, and then raise the temperature to above 95°C for isothermal reaction. Step S5: Monitor the viscosity of the reaction solution. When the viscosity reaches 800 mPa·s to 1200 mPa·s, immediately perform rapid cooling and filter to obtain liquid zirconium carbide precursor.

[0016] By adopting the above technical solution, the present invention achieves the directional construction of precursor microstructure through stepwise control: Step S1 involves low-temperature ligand exchange, where allyl acetoacetate replaces n-butanol. The low-temperature environment inhibits the accumulation of reaction heat, preventing uncontrolled self-condensation of zirconium alkoxide. Step S2 induces controlled hydrolysis and condensation of zirconium alkoxide through dilution hydrolysis and temperature ripening, growing uniformly sized zirconium-oxygen inorganic clusters. Structural defects are eliminated through ripening.

[0017] In step S3, before introducing the modifier, the solvent and reaction byproducts in the system are removed by vacuum distillation. This eliminates the steric hindrance and chain transfer effects of the solvent molecules, increasing the concentration of the effective components in the system and creating an environment conducive to the subsequent high-density cross-linking reaction.

[0018] Step S4 is crucial for constructing the organic-inorganic hybrid network. The modifier is first mixed at a lower temperature to prevent premature decomposition, followed by heating to above 95°C to induce a reverse Diels-Alder reaction. This step utilizes a temperature switch to control the in-situ release of the active monomers maleic anhydride and furfuryl alcohol. The newly generated active monomers rapidly react with or self-polymerize with zirconium oxide clusters. This "in-situ release-instant reaction" mechanism avoids the localized burst polymerization or phase separation that might result from directly adding highly active monomers.

[0019] Step S5 controls the reaction endpoint by controlling viscosity and temperature. When the viscosity reaches the preset range, it indicates that the system has formed a precursor with a suitable molecular weight. At this point, the heat of reaction is rapidly removed by quenching, and the system temperature is lowered below the activation energy of the reaction to terminate the chemical reaction, prevent excessive cross-linking that could lead to gelation, and finally obtain a liquid product with both fluidity and high carbon residue.

[0020] Preferably, in step S1, the temperature inside the reactor is controlled at 10°C to 15°C, and the reactor temperature is controlled not to exceed 30°C during the dropwise addition of allyl acetoacetate; after the dropwise addition is completed, the reactor is stirred at room temperature for 20 to 40 minutes.

[0021] By adopting the above technical solution, the reaction initiation temperature and process temperature rise are limited, side reactions during ligand exchange are reduced, and allyl acetoacetate is ensured to bind with zirconium atoms in the expected coordination mode.

[0022] Preferably, in step S2, the temperature for heat preservation and ripening is 60°C, and the ripening time is 1.0 hour to 2.0 hours; in step S3, the temperature for vacuum distillation is 60°C to 65°C, and the vacuum degree is controlled at -0.08 MPa to -0.09 MPa.

[0023] By adopting the above technical solution, the aging temperature of 60℃ provides a suitable activation energy, allowing the hydrolysis-condensation reaction to proceed gently. High-vacuum distillation within a similar temperature range can efficiently remove high-boiling-point byproducts while avoiding excessively high temperatures that could damage the already formed zirconium-oxygen coordination structure.

[0024] Preferably, in step S4, the temperature of the isothermal reaction is 95°C to 105°C; the rate of heating to the isothermal reaction temperature is 1.0°C to 5.0°C per minute.

[0025] By employing the above technical solution, the reverse Diels-Alder reaction temperature of furfuryl alcohol and maleic anhydride adduct was matched between 95℃ and 105℃. Controlling the heating rate can balance the dissociation rate and polymerization rate of the adduct, preventing excessively high local monomer concentrations due to rapid dissociation, and ensuring that the organic network grows uniformly around the inorganic framework.

[0026] Preferably, in step S5, the viscosity test temperature is 25°C; the rapid cooling is achieved by introducing a refrigerant at -10°C to -15°C to lower the material temperature to below 40°C.

[0027] By adopting the above technical solution and using a large temperature difference refrigerant for cryogenic treatment, the residual heat of the reaction in the system can be quickly removed, the reaction can be terminated in a very short time, and the degree of polymerization of the final product can be precisely controlled.

[0028] Preferably, the furfuryl alcohol and maleic anhydride adduct modifier described in step S4 is prepared in advance by the following method: furfuryl alcohol is placed in a reaction vessel and the temperature is controlled at 35°C to 45°C; maleic anhydride solid is added in batches under stirring, and the system temperature is controlled not to exceed 50°C during the addition process; after the addition is completed, the reaction is kept at 35°C to 45°C for 1.0 hour to 3.0 hours.

[0029] By adopting the above technical solution and employing a phased feeding and low-temperature long-time reaction strategy, the exothermic effect of the Diels-Alder addition reaction was controlled, preventing furfuryl alcohol from undergoing self-polymerization under acidic conditions, and ensuring the acquisition of high-purity adduct modifiers.

[0030] This invention provides a liquid zirconium carbide precursor with high ceramic yield and its preparation method. It has the following beneficial effects: 1. This invention introduces a Diels-Alder adduct of furfuryl alcohol and maleic anhydride to construct a thermally latent system. At room temperature, the adduct maintains a cyclic inert structure, giving the precursor low viscosity and long-term storage stability. At high temperature, it releases active monomers through reverse Diels-Alder reaction to achieve crosslinking, which solves the problem that the existing technology of directly adding highly active carbon sources such as furfuryl alcohol leads to room temperature self-polymerization, a sharp increase in viscosity, or even gelation, which cannot meet the requirements of liquid phase molding process. 2. This invention utilizes in-situ released active groups to construct an organic-inorganic double interpenetrating network. During high-temperature pyrolysis, the dissociated maleic anhydride anchors the zirconium oxygen skeleton, and furfuryl alcohol monomers simultaneously polymerize to fill the space, forming a dense hybrid structure. This effectively suppresses the volatilization of small carbon molecules during pyrolysis, converting the theoretical carbon source into the actual carbon retention. Compared with the traditional physical mixing method, which suffers from severe carbon source loss and low ceramic yield due to poor component compatibility, this invention significantly improves the ceramicization efficiency of the final material. 3. This invention employs a synthesis strategy combining ligand modification and stepwise solvent removal. By controlling the hydrolysis rate of zirconium butoxide through allyl acetoacetate and combining it with a pre-removal solvent process, the interference of solvent effects on subsequent polymerization reactions is eliminated. The precursor obtained in this way has a uniform molecular structure and no precipitation. In view of the shortcomings of existing zirconium alkoxide hydrolysis processes, which are prone to local over-hydrolysis and the generation of particulate matter, as well as the decrease in curing density caused by residual solvent, this scheme achieves precise control of the precursor microstructure. Attached Figure Description

[0031] Figure 1 This is a graph showing the temperature change over time in the reaction system of the test example of this invention. Figure 2 This is a bar chart showing the dynamic viscosity of the precursor of the test example of the present invention before and after storage at 25°C. Figure 3 This is a DSC heat flow analysis curve of the precursor of the test example of the present invention; Figure 4 This is a thermogravimetric analysis curve of a test example of the present invention heated to 1000°C under a nitrogen atmosphere. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0034] Zirconium n-butoxide was prepared using a n-butanol solution with a zirconium n-butoxide content of 80 wt% (CAS No.: 1071-76-7). Allyl acetoacetate purity ≥98% (CAS No.: 1118-84-9). Maleic anhydride purity ≥99.5% (CAS No.: 108-31-6). Furfuryl alcohol purity ≥98% (CAS No.: 98-00-0). Anhydrous ethanol, deionized water, etc., were all commercially available standard products.

[0035] Preparation Example 1: This preparation example provides a method for preparing a furfuryl alcohol-maleic anhydride Diels-Alder adduct modifier, comprising the following steps: 107.9 g (1.1 mol) of furfuryl alcohol was added to a reactor equipped with a mechanical stirrer, thermometer, and condenser. The stirring was started (250 rpm) and the temperature inside the reactor was controlled at 40°C. Under constant temperature conditions, a total of 98.1 g (1.0 mol) of maleic anhydride solid was added in four portions, with each addition 10 minutes apart. The temperature was closely monitored during the addition process, and the system temperature was controlled not to exceed 45°C by cooling with a jacket. After the addition was completed, the reaction was continued at 40°C for 1.5 hours until the solid in the reaction system completely disappeared and the solid-liquid mixture changed into a homogeneous, transparent, reddish-brown viscous liquid. The mixture was then cooled to room temperature and discharged, sealed, and stored to obtain modifier A1.

[0036] Preparation Example 2: This preparation example provides a method for preparing a furfuryl alcohol-maleic anhydride Diels-Alder adduct modifier, comprising the following steps: Add 127.5 g (1.3 mol) of furfuryl alcohol to a reactor equipped with a mechanical stirrer, thermometer, and condenser. Start stirring (300 rpm) and control the temperature inside the reactor at 35°C. Under constant temperature conditions, add a total of 98.1 g (1.0 mol) of maleic anhydride solid in three portions, with an interval of 15 minutes between each addition. During the addition process, control the system temperature to not exceed 40°C by cooling with a jacket. After the addition is complete, continue to keep the reaction at 35°C for 3.0 hours until the solid in the reaction system completely disappears and changes from a solid-liquid mixture to a uniform, transparent, slightly yellow, viscous liquid. Cool to room temperature and discharge the product, seal and store it to obtain modifier A2.

[0037] Preparation Example 3: This preparation example provides a method for preparing a furfuryl alcohol-maleic anhydride Diels-Alder adduct modifier, comprising the following steps: Add 98.1 g (1.0 mol) of furfuryl alcohol to a reactor equipped with a mechanical stirrer, thermometer, and condenser. Start stirring (250 rpm) and control the temperature inside the reactor at 45°C. Under constant temperature conditions, add a total of 88.3 g (0.9 mol) of maleic anhydride solid in five portions, with an interval of 8 minutes between each addition. During the addition process, control the system temperature to not exceed 50°C by cooling with a jacket. After the addition is complete, continue to keep the reaction at 45°C for 1.0 hour until the solid in the reaction system completely disappears and the solid-liquid mixture changes into a homogeneous, transparent, dark reddish-brown viscous liquid. Cool to room temperature and discharge the product. Seal and store to obtain modifier A3.

[0038] Example 1: This example provides a liquid zirconium carbide precursor with high ceramic yield and its preparation method, including the following steps: (1) Add 479.6g of 80wt% zirconium butoxide solution (containing 1.0mol zirconium butoxide) to a reactor equipped with a reflux condenser, a high-shear stirring paddle and a constant-pressure dropping funnel, start stirring and lower the temperature inside the reactor to 15℃; slowly add 284.3g (2.0mol) allyl acetoacetate, control the dropping rate so that the temperature inside the reactor does not exceed 30℃, and stir at room temperature for 30 minutes after the dropping is completed; (2) Mix 10.8g (0.6mol) of deionized water with 60g of anhydrous ethanol to prepare a diluent. Add the solution very slowly to the above system under vigorous stirring to prevent local precipitation. After the addition is complete, heat to 60℃ and keep warm for 1.5 hours. (3) Maintain the kettle temperature at 60℃, connect the vacuum system, adjust the vacuum degree to -0.08MPa to -0.09MPa for reduced pressure distillation until no obvious fraction flows out of the condenser, and obtain a high viscosity clear liquid; (4) Cool the reactor to 50°C, add 206.0g of the modifier A1 obtained in Preparation Example 1 at once, stir for 20 minutes until it is mixed evenly; then raise the temperature to 100°C at a rate of 1.5°C / min and carry out a constant temperature reaction. (5) When the viscosity of the reaction liquid reaches 1000 mPa·s (25℃), -10℃ frozen brine is introduced into the jacket for rapid cooling. When the material temperature drops below 40℃, the material is discharged and filtered through a microporous membrane to obtain a dark reddish-brown clear and transparent liquid zirconium carbide precursor.

[0039] Example 2: This example provides a liquid zirconium carbide precursor with high ceramic yield and its preparation method, including the following steps: (1) Add 479.6g of 80wt% zirconium butoxide solution (containing 1.0mol zirconium butoxide) to a reactor equipped with a reflux condenser, a high-shear stirring paddle and a constant-pressure dropping funnel, start stirring and lower the temperature inside the reactor to 10℃; slowly add 312.7g (2.2mol) allyl acetoacetate, control the dropping rate so that the temperature inside the reactor does not exceed 25℃, and stir at room temperature for 30 minutes after the dropping is completed; (2) Mix 9.0g (0.5mol) of deionized water with 50g of anhydrous ethanol to prepare a diluent. Add the solution dropwise to the above system very slowly under vigorous stirring. After the addition is complete, heat the solution to 60℃ and keep it warm for 1.0 hour. (3) Heat to 65°C, connect to the vacuum system, adjust the vacuum to -0.09MPa for vacuum distillation, remove solvent and by-products until no distillate flows out; (4) Cool the reactor to 50°C, add 225.6g of the modifier A2 obtained in Preparation Example 2 at once, stir for 15 minutes until it is mixed evenly; then raise the temperature to 95°C at a rate of 1.0°C / min for constant temperature reaction; (5) When the viscosity of the reaction liquid reaches 800 mPa·s (25℃), -15℃ frozen brine is introduced into the jacket for rapid cooling. When the material temperature drops below 40℃, the material is discharged and filtered to obtain liquid zirconium carbide precursor.

[0040] Example 3: This example provides a liquid zirconium carbide precursor with high ceramic yield and its preparation method, including the following steps: (1) Add 479.6g of 80wt% zirconium butoxide solution (containing 1.0mol zirconium butoxide) to a reactor equipped with a reflux condenser, a high-shear stirring paddle and a constant-pressure dropping funnel, start stirring and lower the temperature inside the reactor to 15℃; slowly add 284.3g (2.0mol) allyl acetoacetate, control the dropping rate so that the temperature inside the reactor does not exceed 30℃, and stir at room temperature for 30 minutes after the dropping is completed; (2) Mix 14.4g (0.8mol) of deionized water with 80g of anhydrous ethanol to prepare a diluent. Add the solution dropwise to the above system very slowly under vigorous stirring. After the addition is complete, heat the solution to 60℃ and keep it warm for 2.0 hours. (3) Maintain the kettle temperature at 60°C and perform full vacuum distillation at -0.085MPa to ensure the removal of free water and solvent; (4) Cool the reactor to 55°C, add 186.4g of the modifier A3 obtained in Preparation Example 3 at once, stir for 20 minutes until it is mixed evenly; then heat to 105°C for constant temperature reaction; (5) When the viscosity of the reaction solution reaches 1200 mPa·s (25℃), immediately start the freezing brine circulation for rapid cooling. After the material cools down to room temperature, discharge and filter to obtain liquid zirconium carbide precursor.

[0041] Example 4: This example provides a liquid zirconium carbide precursor with high ceramic yield and its preparation method, including the following steps: (1) Add 239.8g of 80wt% zirconium butoxide solution (containing 0.5mol zirconium butoxide) to the reaction vessel and cool it to 15℃; add 149.3g (1.05mol) allyl acetoacetate dropwise and control the temperature for reaction; (2) Dilute 5.4 g (0.3 mol) of deionized water in 30 g of anhydrous ethanol, slowly add it dropwise into the system, and then ripen at 60 °C for 1.5 hours; (3) Distill under reduced pressure at 65℃ and -0.09MPa until no liquid droplets flow out; (4) Cool down to 50°C, add 103.0g of the modifier A1 obtained in Preparation Example 1, mix well, and then heat up to 98°C to react; (5) After reacting for about 4 hours, when the viscosity reaches 950 mPa·s (25℃), the material is cooled and discharged, and filtered to obtain the precursor.

[0042] Example 5: This example provides a liquid zirconium carbide precursor with high ceramic yield and its preparation method. The formulation is the same as in Example 1, except for the polymerization process parameters in steps (4) and (5), including the following steps: Steps (1) to (3) are exactly the same as in Example 1; Step (4): Cool the reactor to 50°C, add 206.0g of the modifier A1 obtained in Preparation Example 1 and mix evenly. Then, rapidly heat the reactor to 105°C at a rate of 4.0°C / min-5.0°C / min for a constant-temperature reaction. Step (5): Closely monitor the viscosity change. After about 3 hours of reaction, the viscosity reaches 1100 mPa·s (25℃). Immediately perform a deep cryogenic cooling operation, and filter the discharged material to obtain the precursor.

[0043] Comparative Example 1: Compared to Example 1, the difference lies in that the pre-reaction step of furfuryl alcohol and maleic anhydride in Example 1 is not performed. Specifically, in step 4, modifier A1 is not added; instead, equimolar amounts of liquid furfuryl alcohol and solid maleic anhydride are directly added to the reactor after it has been cooled to 50 degrees Celsius. All other steps and parameters remain the same.

[0044] Comparative Example 2: Compared to Example 1, the difference lies in the omission of the micro-hydrolysis passivation operation in step 2. Specifically, after obtaining the zirconium chelate in step 1, the addition of deionized water dilution and subsequent aging are omitted, and vacuum desolvation and thermal cascade polymerization are carried out directly, while the remaining steps and parameters remain the same.

[0045] Comparative Example 3: Compared to Example 1, the difference is that maleic anhydride was not added when preparing the modifier. Specifically, in step 4, pure furfuryl alcohol (107.9 g, 1.1 mol) with the same molar content as furfuryl alcohol in modifier A1 was added to the system instead of modifier A1, while the remaining steps and parameters remained the same.

[0046] Comparative Example 4: Compared with Example 1, the difference is that an equimolar amount of acetylacetone is used instead of allyl acetoacetate as the chelating agent, while the other steps and parameters remain the same.

[0047] Comparative Example 5: Compared to Example 1, the difference is that modifier A1 is not added. Specifically, after vacuum desolvation in step 3, the final product, which is a partially hydrolyzed zirconium chelate precursor, is obtained directly, while the remaining steps and parameters remain the same.

[0048] Test Example 1: Test objective: To verify the effects of micro-hydrolysis passivation technology and furfuryl alcohol-maleic anhydride adduct on the exothermic behavior and phase stability of the reaction system, and to evaluate the process safety and engineering feasibility.

[0049] Experimental steps: 1. Set up a test device, using an adiabatic reaction calorimeter equipped with a precision temperature sensor with an accuracy of 0.1℃, mechanical stirring, and a data acquisition system.

[0050] 2. Take the zirconium-containing intermediates from Examples 1 to 5 and Comparative Examples 1 and 2 after the vacuum desolvation step, place them in a reactor, adjust the stirring speed to 300 rpm, and keep the initial temperature of the material constant at 50.0℃.

[0051] 3. At the initial moment, according to the formulation amount of each embodiment or comparative example, the corresponding organic component is added quickly at once; wherein in Examples 1 to 5, the prepared furfuryl alcohol-maleic anhydride adduct is added, in Comparative Example 1, a physical mixture of furfuryl alcohol liquid and maleic anhydride solid is added, and in Comparative Example 2, the furfuryl alcohol-maleic anhydride adduct is added but its zirconium matrix has not been hydrolyzed and passivated.

[0052] 4. Starting from the moment of feeding, continuously record the internal temperature changes of the system at a frequency of once every 5 seconds for 60 minutes; record the highest temperature value of the reaction system and the time to reach the highest temperature.

[0053] 5. After the reaction is complete, visually observe the fluidity, color, and homogeneity of the material in the reactor, and record whether there is precipitation, stratification, or gelation.

[0054] The experimental results are shown in Table 1: Table 1: Temperature rise characteristics and physical state records of different reaction systems

[0055] Results Analysis and Conclusions: Based on Table 1 and... Figure 1 The test data and phenomena showed that Comparative Example 2 exhibited a violent exothermic reaction upon contact, with a temperature rise exceeding 130°C and rapid gelation. This result indicates that the untreated zirconium alkoxide possesses extremely strong Lewis acid catalytic activity, and the furfuryl alcohol monomer underwent uncontrolled cationic chain polymerization under the catalysis of the strong acid center, leading to instantaneous cross-linking and solidification of the system. This confirms that the purely organic-inorganic mixed pathway carries extremely high process safety risks and cannot achieve stable preparation of liquid precursors.

[0056] In Examples 1 to 5, the temperature rise was controlled within 6°C, and the products remained in a homogeneous, transparent liquid state. This indicates that the micro-hydrolysis passivation strategy employed in this invention effectively altered the coordination environment of the zirconium center. By introducing appropriate amounts of water and chelating agents, the highly active zirconium-alkoxy group was converted into a less active zirconium-oxy-zirconium inorganic cluster. The catalytic activity of zirconium was suppressed using steric hindrance and electronic effects, thus preventing the instantaneous polymerization of furfuryl alcohol.

[0057] Although Comparative Example 1 did not experience explosive polymerization, its temperature rise was significantly higher than that of the Example, reaching 21.3°C, and the product exhibited phase separation and precipitation. This was because the furfuryl alcohol-maleic anhydride adduct was not prepared in advance, and solid maleic anhydride was difficult to dissolve in the zirconium system at low temperatures, leading to a heterogeneous reaction; at the same time, the free furfuryl alcohol came into contact with locally high concentrations of active centers, triggering some exothermic reactions, resulting in poor system homogeneity.

[0058] In summary, this invention achieves chemical inertness and physical compatibility of highly active components at low temperatures by constructing a dual mechanism of furfuryl alcohol-maleic anhydride adduct and zirconium-based micro-hydrolysis passivation, thus ensuring the thermodynamic stability of the system during mixing and storage.

[0059] Test Example 2: Test objective: To investigate the processing applicability and long-term storage stability of the synthesized product as a liquid precursor, with a focus on verifying the chemical inertness of the furfuryl alcohol-maleic anhydride adduct at room temperature and its inhibitory effect on the viscosity increase of the system.

[0060] Experimental steps: 1. Fresh liquid samples prepared in Examples 1 to 5 and Comparative Examples 3, 4 and 5 were selected as test subjects.

[0061] 2. Using a rotational viscometer equipped with a constant temperature water bath jacket, the sample temperature is precisely controlled at 25℃. A rotor with an appropriate range is selected, and the initial dynamic viscosity of the sample is measured under the condition of a shear rate of 50 seconds reciprocal.

[0062] 3. Dispense each of the above samples into brown glass bottles, fill them with nitrogen for protection, seal them, and store them in a constant temperature and humidity chamber at 25°C and 45% relative humidity.

[0063] 4. After 30 days of storage, take out the sample and observe its appearance and fluidity. Then, measure its dynamic viscosity again according to the test conditions in step 2. Calculate the viscosity growth rate according to the formula "(30-day viscosity - initial viscosity) / initial viscosity × 100%".

[0064] The experimental results are shown in Table 2: Table 2: Initial viscosity and 30-day storage stability test data of precursors

[0065] Results Analysis and Conclusions: Based on Table 2 and... Figure 2 According to the data, the initial viscosity of the precursors prepared in Examples 1 to 5 ranged from 800 to 1210 mPa·s, a viscosity range suitable for subsequent processing such as fiber impregnation and coating. After 30 days of storage, the viscosity growth rate of the example groups was controlled within 8%, demonstrating excellent storage stability. This indicates that furfuryl alcohol and maleic anhydride in the system exist in the form of a Diels-Alder adduct. This structure locks the double bond active sites at room temperature, effectively shielding furfuryl alcohol from contact with residual active groups in the system and preventing slow crosslinking or self-polymerization at room temperature.

[0066] Comparative Example 3 showed a viscosity increase of up to 193.02%, with a low initial viscosity (645 mPa·s). This is because the system did not introduce maleic anhydride, resulting in a lack of rigid structural support and a low initial molecular weight. At the same time, the free furfuryl alcohol lacked the protection of a "chemical valve" and underwent spontaneous condensation reaction under the influence of the microenvironment during storage, leading to a sharp increase in viscosity and rendering it unusable.

[0067] The initial viscosity of Comparative Example 4 was only 120 mPa·s, significantly lower than that of the Example. This is because acetylacetone was used instead of allyl acetoacetate, and the ligand lacked polymerizable double bonds, making it impossible to form a high molecular weight alternating copolymer backbone through the charge transfer complex mechanism. As a result, the product was only a low molecular weight zirconium chelate solution, which could not meet the requirements of ceramic precursors for film formation and solid content.

[0068] In summary, this invention, through molecular structure design, not only achieves controllable growth of the precursor molecular weight, giving it a suitable processing viscosity, but also utilizes reversible chemical bonds to achieve room temperature passivation of active groups, solving the technical problem of short shelf life of traditional high-activity precursors.

[0069] Test Example 3: Test objective: To use differential scanning calorimetry (DSC) to monitor the heat flow changes of the precursor in situ, and to verify the occurrence of the reverse Diels-Alder dissociation reaction and the polymerization reaction of charge-transfer complex (CTC) by analyzing the peak characteristics of the thermal effect, and to confirm the temperature-controlled chemical release mechanism.

[0070] Experimental steps: 1. Instrument calibration: Use high-purity indium and zinc standard samples to perform temperature and heat flux correction on the differential scanning calorimeter to ensure a flat baseline.

[0071] 2. Sample preparation: Take about 5 to 8 mg of fresh liquid samples from Example 1, Comparative Example 1 and Comparative Example 5 respectively, drop them into the bottom of the liquid aluminum crucible, immediately cover and use a tablet press for cold sealing to prevent volatiles from overflowing.

[0072] 3. Atmosphere control: Place the sealed sample into the DSC furnace and purge with high-purity nitrogen at a flow rate of 50 ml per minute. Equilibrate the baseline for 5 minutes.

[0073] 4. Temperature scan: Set the temperature program to linearly increase the sample temperature from 30℃ to 250℃ at a temperature increase rate of 10℃ per minute, with a data acquisition frequency of 10 Hz.

[0074] 5. Data Analysis: Use thermal analysis software to integrate the heat flow curve, identify and record the onset and peak temperatures of endothermic or exothermic peaks, and distinguish between physical phase transition and chemical reaction regions.

[0075] The experimental results are shown in Table 3: Table 3: Characteristic Parameters of Precursor DSC Thermal Analysis

[0076] Results Analysis and Conclusions: Based on Table 3 and... Figure 3 The data from Example 1 showed two distinct thermal event regions during the heating process. First, a significant endothermic peak was observed near 102.4°C, corresponding to the energy absorption process of the reverse Diels-Alder reaction in the furfuryl alcohol-maleic anhydride adduct. The presence of this characteristic peak confirmed the presence of a large number of pre-constructed adduct structures in the precursor system. Subsequently, an exothermic solidification signal was detected only at 128.5°C, with the exothermic peak delayed to 165.2°C. This time and temperature lag between endothermic and exothermic reactions indicates that the release of the active monomer is strictly thermodynamically controlled; only when the temperature exceeds the dissociation threshold are the dienes and dienophiles released and participate in subsequent reactions, confirming the slow-release mechanism of a "chemical valve."

[0077] In contrast, no endothermic dissociation peak was detected in Comparative Example 1, and the curing initiation temperature was as low as 85.3℃. This is because there is a large amount of free furfuryl alcohol in the physical mixture system, which can undergo disordered free radical or ionic polymerization with zirconium centers or acid anhydrides at low temperatures. The lack of a temperature threshold restricts the reaction, resulting in uncontrollable reaction kinetics.

[0078] The peak curing temperature of Comparative Example 5 was 145.8℃, significantly lower than the 165.2℃ of Example 1. The higher polymerization temperature of Example 1 indicates that it followed a different reaction pathway, namely, the released donor and acceptor monomers formed a charge-transfer complex (CTC) at high temperatures, which then underwent alternating copolymerization. CTC polymerization typically requires higher activation energies, resulting in a more ordered polymer backbone with higher heat resistance. In summary, this invention, through thermal analysis, confirms the stepwise reaction mechanism in molecular design, achieving precise control from low-temperature lock-in to high-temperature ordered polymerization.

[0079] Test Example 4: Test objective: To quantitatively characterize the mass retention of precursors during high-temperature pyrolysis using thermogravimetric analysis (TGA), and to verify the contribution of alternating copolymer structures of charge-transfer complexes and interpenetrating polymer networks to carbon solidification and inorganic framework stability by comparing the final ceramic yield.

[0080] Experimental steps: 1. The liquid precursors prepared in Examples 1 to 5 and Comparative Examples 3, 4 and 5 were placed in a polytetrafluoroethylene mold and cured in a 150°C forced-air drying oven for 4 hours to obtain a fully cross-linked thermosetting resin solid, which was then ground into powder as a test sample.

[0081] 2. Turn on the thermogravimetric analyzer, introduce high-purity nitrogen as a protective atmosphere, set the gas flow rate to 60 ml per minute, and perform baseline calibration.

[0082] 3. Weigh 10 to 15 milligrams of the above powder sample and place it in an alumina crucible, accurately recording the initial mass.

[0083] 4. Run the heating program to raise the temperature from room temperature to 1000℃ at a rate of 10℃ per minute, and record the sample mass change curve with temperature in real time.

[0084] 5. After the experiment, extract the residual mass at 1000℃ and calculate the residual mass percentage (ceramic yield).

[0085] The experimental results are shown in Table 4: Table 4: Yield data of ceramicization of precursor at high temperature pyrolysis

[0086] Results Analysis and Conclusions: Based on Table 4 and... Figure 4 The data shows that the ceramic yields of Examples 1 to 5 remained consistently high, ranging from 69.88% to 73.41%. This result indicates that the molecular structure constructed in this invention effectively suppresses the pyrolysis and volatilization of organic components at high temperatures. The zirconium-ligand-maleic anhydride alternating copolymer structure formed in the precursor backbone exhibits high orderliness and thermal stability, reducing random chain breakage in the initial stage of pyrolysis. Simultaneously, the in-situ formed interpenetrating polymer network physically restricts the thermal movement of molecular chain segments and locks the carbon-rich furan ring structure around the inorganic zirconium framework, achieving efficient solidification of carbon elements. This facilitates subsequent in-situ conversion to the zirconium carbide ceramic phase via carbothermic reduction reaction at higher temperatures (e.g., >1400℃).

[0087] The ceramic yield of Comparative Example 3 was 48.33%, significantly lower than that of the Example. Because maleic anhydride was not introduced into this system, a charge-transfer complex could not be formed; the system relied solely on the self-condensation of furfuryl alcohol to form the random furan resin. This random structure has poor thermal stability and lacks the support of a rigid alternating backbone, making it prone to depolymerization during pyrolysis and escaping in small molecule form, resulting in a significant decrease in char yield.

[0088] Comparative Example 4 yielded only 41.73%. This comparative example used acetylacetone, which does not contain double bonds, as a ligand. Although the zirconium atoms were chelated, they could not participate in the polymerization reaction of the organic network. At high temperatures, the organic network separated from the zirconium center, and the unbound organic matter rapidly volatilized, resulting in a low final yield and a loose structure.

[0089] Comparative Example 5, representing a traditional zirconium precursor, exhibited the lowest yield, at only 35.85%. This confirms that in traditional sol-gel systems, due to the lack of effective molecular-level hybridization design, a large amount of organic solvent and unreacted alkoxy groups directly volatilize during heating, failing to be effectively converted into a ceramic framework. The comparative results fully demonstrate the significant technical advantages of this invention in improving the ceramicization efficiency of liquid precursors.

[0090] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A liquid zirconium carbide precursor with high ceramic yield, characterized in that, Made from the following ingredients in parts by weight: Zirconium n-butoxide: 100 parts; Allyl acetoacetate: 74-82 parts; Deionized water: 2.3-3.8 parts; Furfuryl alcohol-maleic anhydride adduct modifier: 48-60 parts; The furfuryl alcohol-maleic anhydride adduct modifier is the Diels-Alder reaction product of furfuryl alcohol and maleic anhydride.

2. The high ceramic yield liquid zirconium carbide precursor according to claim 1, characterized in that, The weight parts of the raw materials are: Zirconium n-butoxide: 100 parts; Allyl acetoacetate: 74.1-81.5 parts; Deionized water: 2.34-3.76 parts; Furfuryl alcohol-maleic anhydride adduct modifier: 48.5-58.8 parts.

3. The high ceramic yield liquid zirconium carbide precursor according to claim 1, characterized in that, The furfuryl alcohol-maleic anhydride adduct modifier is prepared by reacting furfuryl alcohol with maleic anhydride, wherein the molar ratio of furfuryl alcohol to maleic anhydride is 1.0-1.3:0.9-1.

0.

4. The high ceramic yield liquid zirconium carbide precursor according to claim 1, characterized in that, The deionized water is added in the form of a diluent, which is a mixture of deionized water and anhydrous ethanol, wherein the mass ratio of deionized water to anhydrous ethanol is 1:5.0-6.

0.

5. A method for preparing a high-ceramic-yield liquid zirconium carbide precursor according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Under low temperature stirring conditions, allyl acetoacetate was slowly added dropwise to a solution containing zirconium n-butoxide, and the reaction was carried out at room temperature after the addition was completed. S2. Mix deionized water with solvent to prepare a dilution solution, and slowly add it dropwise to the system of S1. After the addition is complete, heat the system and keep it warm for curing. S3. The S2 system is subjected to vacuum distillation under heating conditions to remove the solvent and byproducts, resulting in a viscous liquid. S4. Lower the temperature of the S3 system, add furfuryl alcohol-maleic anhydride adduct modifier, mix evenly, and then raise the temperature to above 95℃ for constant temperature reaction. S5. Monitor the viscosity of the reaction solution. When the viscosity reaches 800-1200 mPa·s, immediately perform rapid cooling and filter to obtain the liquid zirconium carbide precursor.

6. The method for preparing liquid zirconium carbide precursor with high ceramic yield according to claim 5, characterized in that, In step S1, the temperature inside the reactor is controlled at 10-15℃, and the temperature inside the reactor is controlled not to exceed 30℃ during the dropwise addition of allyl acetoacetate; after the dropwise addition is completed, the mixture is stirred at room temperature for 20-40 minutes.

7. The method for preparing liquid zirconium carbide precursor with high ceramic yield according to claim 5, characterized in that, In step S2, the temperature for heat preservation and curing is 60°C, and the curing time is 1.0-2.0 hours; In step S3, the temperature of vacuum distillation is 60-65℃, and the vacuum degree is controlled between -0.08MPa and -0.09MPa.

8. The method for preparing liquid zirconium carbide precursor with high ceramic yield according to claim 5, characterized in that, In step S4, the temperature of the isothermal reaction is 95-105℃; the rate of heating to the isothermal reaction temperature is 1.0-5.0℃ / min.

9. The method for preparing liquid zirconium carbide precursor with high ceramic yield according to claim 5, characterized in that, In step S5, the viscosity test temperature is 25°C; the rapid cooling is achieved by introducing a refrigerant at -10°C to -15°C to lower the material temperature to below 40°C.

10. The method for preparing liquid zirconium carbide precursor with high ceramic yield according to claim 5, characterized in that, The furfuryl alcohol-maleic anhydride adduct modifier described in step S4 is prepared in advance by the following method: Place furfuryl alcohol in a reaction vessel and control the temperature at 35-45℃; add maleic anhydride solid in batches while stirring, and control the system temperature to not exceed 50℃ during the addition process; after the addition is complete, keep the reaction at 35-45℃ for 1.0-3.0 hours.

Images