MXene-based ceramic reinforced material and preparation method thereof

Abstract

The invention discloses a ceramic reinforced material based on MXene and a preparation method thereof, and belongs to the technical field of ceramic composites.The surface of MXene is sequentially coated with SiO2 and ZnO through a hydrothermal method, then a yttrium-magnesium-aluminum composite sintering aid is prepared in combination with a chemical coprecipitation method, composite nanosheets are evenly dispersed in ceramic matrix slurry through an electrostatic self-assembly technology, and the ceramic reinforced material is obtained. And finally, sintering and molding through a spark plasma sintering technology to obtain the ceramic reinforced material. MXene is protected from high-temperature oxidation through multi-stage coating, low-temperature efficient sintering is realized by utilizing a composite sintering aid, uniform dispersion of a reinforcing phase is ensured by virtue of self-assembly, the problems that MXene is easy to oxidize, the function is difficult to maintain and the dispersity is poor in the ceramic are synergistically solved, and the obtained ceramic material has the advantages of low cost and high efficiency on the basis of maintaining high strength. The thermal shock resistance and the functional durability in a high-temperature environment are improved, and the material is suitable for green special refractory components with strict requirements on mechanical properties and thermal shock resistance.

Description

Technical Field

[0001] This invention belongs to the field of ceramic composite materials technology, specifically a ceramic reinforcing material based on MXene and its preparation method. Background Technology

[0002] Ceramic materials, due to their high melting point, high hardness, and excellent chemical stability, have become indispensable key materials in aerospace, defense, and other fields. For example, thermal protection structures such as the nose cone of aerospace vehicles and high-temperature components of engines rely on their high-temperature resistance. However, traditional ceramic materials face the problem of insufficient thermal shock stability during high-temperature service. Under conditions of rapid heating or thermal cycling, thermal stress concentration occurs within the material due to the mismatch in thermal expansion coefficients, which easily leads to the initiation and propagation of microcracks, ultimately causing structural failure and severely limiting their service life under extreme thermal environments.

[0003] To improve the thermal shock performance of ceramic materials, the industry generally adopts a composite modification strategy that introduces functional phases. Among them, two-dimensional nanomaterials have become a research focus due to their unique layered structure and potential for thermophysical property regulation. MXene, as a novel two-dimensional transition metal carbide, has both high thermal conductivity and tunable thermophysical properties. It can improve the thermal shock stability of ceramic matrices by adjusting the thermal conductivity of the material and alleviating thermal mismatch stress, and is regarded as a highly promising functional phase.

[0004] Chinese patent application CN112142449A discloses a method for preparing MXene-reinforced ceramic composites. This method aims to improve the performance of ceramic composites by utilizing MXene. However, during the high-temperature sintering process at 1400-1600℃, MXene will undergo oxidation, decomposition, or phase transformation due to thermodynamic instability. The two-dimensional layered MXene, which should be the core functional phase, will be transformed into conventional oxide / carbide particles such as TiO2 and TiC.

[0005] This phase transition process causes MXene to lose its intrinsic two-dimensional layered structure, which in turn leads to the failure of its thermophysical functions such as high thermal conductivity and thermal expansion regulation. Therefore, the composite material cannot achieve an active thermal conductivity-thermal expansion synergistic regulation mechanism through MXene, and it is difficult to effectively resist thermal stress concentration and damage propagation caused by thermal shock. Ultimately, this severely restricts the application potential of this type of material in high-end thermal shock sensitive environments with stringent requirements for active thermal management and thermal shock reliability, such as engine hot-end components and aerospace vehicle nose cones. Summary of the Invention

[0006] The purpose of this invention is to provide a ceramic reinforcement material based on MXene and its preparation method. By multi-level coating of MXene nanosheets, the two-dimensional structure and thermophysical functions of MXene are effectively protected during high-temperature sintering and service. The introduction of yttrium-magnesium-aluminum composite sintering aids achieves low-temperature and high-efficiency sintering, and the self-assembly ensures uniform dispersion of the reinforcing phase. This invention synergistically solves the problems of easy oxidation failure, difficulty in maintaining function, and poor dispersion uniformity of MXene in ceramics. The prepared ceramic material maintains high strength while improving its thermal shock stability and functional durability under high-temperature conditions. It is suitable for green special refractory structures such as thermal protection components of aerospace vehicles and high-temperature components of engines with stringent requirements for thermal management capabilities and thermal shock resistance.

[0007] The objective of this invention can be achieved through the following technical solutions: A method for preparing MXene-based ceramic reinforcement materials includes the following steps: Step 1: Using MXene nanosheets, tetraethyl orthosilicate and urea as raw materials, MXene@SiO2 nanosheets are prepared by hydrothermal in-situ coating.

[0008] Step 2: A zinc oxide nanoshell is constructed on the surface of MXene@SiO2 using a hydrothermal in-situ growth method to obtain zinc oxide / MXene@SiO2 composite nanosheets.

[0009] Step 3: Using yttrium nitrate, magnesium nitrate and aluminum nitrate as raw materials, a sintering aid for yttrium-magnesium-aluminum composite oxide is prepared by chemical co-precipitation and calcination.

[0010] Step 4: Combine zinc oxide / MXene@SiO2 composite nanosheets, alumina ceramic powder, and yttrium-magnesium-aluminum composite oxide sintering aid to obtain ceramic composite powder, sinter it to form a ceramic reinforced material based on MXene.

[0011] Furthermore, the sintering conditions are as follows: heating to 1400-1500℃ at a heating rate of 100-150℃ / min, while applying a pressure of 30-50MPa and holding for 5-10 minutes.

[0012] Furthermore, the specific preparation steps of the ceramic composite powder are as follows: Zinc oxide / MXene@SiO2 composite nanosheets were dispersed in anhydrous ethanol and ultrasonically dispersed for 20-40 min. The pH was then adjusted to 8-10 with ammonia to obtain a nanosheet dispersion. Alumina ceramic powder and yttrium-magnesium-aluminum composite sintering aid were ball-milled at 300-350 r / min for 3-5 h. The pH was adjusted to 4-6 with dilute hydrochloric acid to obtain a basic slurry. Under continuous stirring, the nanosheet dispersion was slowly added dropwise to the basic slurry over 1-2 h using a constant pressure dropping funnel. After the addition was complete, the mixture was stirred for another 1 h to ensure complete assembly. A 5% (w / w) polyvinyl butyral ethanol solution was added, and the mixture was stirred for 0.5-1.5 h. The mixture was then freeze-dried, ground, and sieved to obtain the ceramic composite powder.

[0013] Furthermore, the ratio of zinc oxide / MXene@SiO2 composite nanosheets, anhydrous ethanol, alumina ceramic powder, yttrium-magnesium-aluminum composite sintering aid, and polyvinyl butyral (PVB) ethanol solution is 2-3g: 23-28mL: 25-30g: 0.75-1.3g: 0.5-0.75g.

[0014] Furthermore, the specific steps for producing zinc oxide / MXene@SiO2 composite nanosheets are as follows: Under nitrogen protection, MXene@SiO2 nanosheets and deionized water were added to a reaction vessel and ultrasonically dispersed for 20-40 min. Sodium citrate and poloxamer 407 were added, and the mixture was stirred at 35-45℃ and 400-500 r / min for 10-20 min. Zinc acetate was then added and stirred for 35-55 min. Subsequently, hexamethylenetetramine was added and stirring was continued for 20-40 min. The mixture was reacted at a constant temperature of 90-95℃ for 6-8 h. After cooling, centrifugation, washing, and drying, zinc oxide modified MXene@SiO2 nanosheets were obtained.

[0015] Furthermore, the ratio of MXene@SiO2 nanosheets, deionized water, sodium citrate, poloxamer 407, zinc acetate, and hexamethylenetetramine is 2-3g: 320-480mL: 3.2-4.8g: 1.2-1.8g: 3.6-5.4g: 8-12g.

[0016] Furthermore, the specific steps for producing MXene@SiO2 nanosheets are as follows: Under nitrogen protection, MXene nanosheets and isopropanol were added to a reaction vessel and sonicated for 20-40 min to form a stable suspension. A mixture of tetraethyl orthosilicate, urea and deionized water was then added to the vessel and the reaction was carried out at 140-150℃ and 250-350 r / min for 8-10 h. After the reaction was completed, the mixture was cooled, centrifuged, washed and dried to obtain MXene@SiO2 nanosheets.

[0017] Furthermore, the ratio of MXene nanosheets, isopropanol, tetraethyl orthosilicate, urea, and deionized water is 2-3g: 500-750mL: 29-44g: 14.5-22g: 200-300mL.

[0018] Furthermore, the specific preparation steps of the yttrium-magnesium-aluminum composite sintering aid are as follows: Yttrium nitrate hexahydrate, magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and deionized water were added to a reaction vessel and stirred until dissolved. The mixed alkaline solution was slowly added dropwise to the reaction vessel over 2 hours at 50-60℃ and 300-500 r / min, with the pH value controlled at 8.5-9. After the addition was completed, the mixture was aged at 75-85℃ for 7-9 hours, filtered, washed, vacuum dried, and preliminarily ground. It was then placed in a muffle furnace and calcined at 3℃ / min to 800-900℃ for 2-4 hours. After cooling to room temperature, it was ground and sieved to obtain the yttrium-magnesium-aluminum composite sintering aid.

[0019] Furthermore, the ratio of yttrium nitrate hexahydrate, magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, deionized water, and mixed alkaline solution is 1.1-1.2g: 1.25-1.3g: 1.85-1.9g: 90-110mL: 90-120mL.

[0020] Furthermore, the mixed alkaline solution is prepared by mixing ammonium carbonate, concentrated ammonia, and deionized water in a ratio of 4.5-5g:4-6mL:90-110mL.

[0021] The beneficial effects of this invention are: 1. This invention constructs a synergistic process system of "enhanced phase coating protection - low-temperature sintering of composite additives - electrostatic self-assembly and uniform dispersion - rapid densification by discharge plasma". While achieving structural protection and uniform dispersion of MXene, it effectively reduces the overall sintering temperature of ceramics and shortens the high-temperature holding time. It synergistically solves the problems of easy oxidation failure, difficulty in maintaining function and poor dispersion uniformity of MXene in ceramics. The prepared ceramic material maintains high strength while improving its thermal shock stability and functional durability under high temperature environment. It can meet the specific requirements of special refractory components in aerospace, energy and chemical industries for basic mechanical properties and thermal shock resistance under high temperature environment.

[0022] 2. The zinc oxide / MXene@SiO2 composite nanosheets of this invention serve as the core reinforcement. Their "core-shell-shell" multi-level structure enhances the composite material's performance through a triple synergistic mechanism. First, the inner amorphous SiO2 and the outer ZnO form a physicochemical synergistic barrier to inhibit oxygen diffusion, effectively protecting the structural stability and thermophysical functions of the internal MXene under high-temperature processing and service environments. Second, during subsequent sintering, the outer ZnO may undergo a solid-state reaction with the Al2O3 matrix at the interface, tending to generate zinc-aluminum spinel (ZnAl2O3) in situ. 4) The transition phase is expected to form a good bond with the ceramic matrix, thereby helping to optimize the interfacial bonding force and stress transfer efficiency between the zinc oxide / MXene@SiO2 composite nanosheets and the ceramic matrix, which has a positive impact on the mechanical properties of the material. Finally, the buffering effect of the SiO2 interlayer and the thermal expansion characteristics of the ZnAl2O4 interfacial phase, which are similar to those of the Al2O3 matrix, aim to construct a thermal expansion gradient transition from the reinforcement to the matrix, which helps to alleviate the interfacial stress concentration caused by thermal mismatch under thermal shock, thereby improving the thermal shock resistance of the material.

[0023] 3. The yttrium-magnesium-aluminum composite sintering aid of the present invention can form a eutectic liquid phase at relatively low temperatures, effectively promoting the rearrangement and mass transfer process of ceramic particles, thereby reducing the densification sintering temperature of the material and providing a mild process window for the thermosensitive MXene reinforcement. Furthermore, its uniformly dispersed nanoparticles can generate multiple pinning effects at grain boundaries, effectively suppressing abnormal coarsening of ceramic matrix grains at high temperatures, which helps to achieve fine grain strengthening and improve the strength and hardness of the material. In addition, the aid can undergo interfacial reactions with the alumina ceramic matrix and the reinforcement coating layer to generate a high-melting-point stable transition layer, which not only optimizes the interfacial bonding and stress transfer, but also forms a double oxygen barrier with the protective layer SiO2 / ZnO of the reinforcement, synergistically improving the high-temperature stability and mechanical properties of the composite material.

[0024] 4. The electrostatic self-assembly composite and discharge plasma sintering processes of this invention constitute a key preparation path for high-performance composite materials. The electrostatic self-assembly process controls the surface charge of the reinforcement and the ceramic matrix, enabling them to achieve spontaneous and uniform composite by means of electrostatic attraction. This overcomes the problem of nano-reinforcement aggregation at the microscale and provides a structural basis for obtaining macroscopically uniform composite materials. At the same time, the discharge plasma sintering process utilizes the synergistic effect of its rapid heating and axial pressure to achieve complete densification of the material in a short time. Its ultra-short holding time significantly reduces the risk of high-temperature exposure of the heat-sensitive reinforcement and, in conjunction with composite sintering aids, achieves the goal of "low-temperature and short-time" green sintering. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1: A method for preparing MXene-based ceramic reinforcement materials, comprising the following steps: S1: Under nitrogen protection, 2.5g of MXene (Ti3C2T) was added. X MXene@SiO2 nanosheets and 650 mL of isopropanol were added to a reaction vessel and sonicated at 150 W for 30 min to form a stable suspension. A mixture of 36.5 g of tetraethyl orthosilicate (TEOS), 18 g of urea and 250 mL of deionized water was added to the vessel and the mixture was kept at 145 °C and 300 r / min for 9 h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged at 8000 r / min for 10 min, the precipitate was collected, washed alternately with anhydrous ethanol and deionized water, and dried to obtain MXene@SiO2 nanosheets.

[0027] A hydrothermal in-situ coating method was adopted, using MXene nanosheets as structural units and isopropanol to form a stable suspension. Tetraethyl orthosilicate (TEOS) was used as the silicon source. Under the catalysis of the alkaline environment generated by the hydrothermal decomposition of urea, TEOS molecules first undergo a hydrolysis reaction to generate active silanol groups. Subsequently, these silanol groups and the abundant functional groups on the surface of MXene nanosheets further undergo intermolecular dehydration condensation reactions, gradually crosslinking on the MXene surface to form an amorphous three-dimensional SiO2 network structure.

[0028] S2: Under nitrogen protection, 2.5g of MXene@SiO2 nanosheets and 400mL of deionized water (deoxygenated by nitrogen) were added to the reactor and ultrasonically dispersed for 30min. 4g of sodium citrate and 1.5g of poloxamer 407 were added to the reactor and stirred for 15min at 40℃ and 450r / min. Then, 4.5g of zinc acetate was added and stirred for 45min under the same conditions. Subsequently, 10g of hexamethylenetetramine (HMT) was added and stirring was continued for 30min. The mixture was kept at 90℃ for 7h and allowed to cool naturally to room temperature. It was then centrifuged at 7500r / min for 10min, washed alternately with deionized water and anhydrous ethanol, and vacuum dried at 65℃ for 10h to obtain zinc oxide / MXene@SiO2 composite nanosheets.

[0029] A hydrothermal in-situ growth method was employed under nitrogen protection, using MXene@SiO2 core-shell nanosheets as the substrate, zinc acetate as the zinc source, hexamethylenetetramine (HMT) as the precipitant, and sodium citrate as the complexing agent to control Zn. 2+ Poloxamer 407 acts as a dispersant to prevent aggregation, and HMT hydrolyzes to release OH-. - Inducing Zn 2+ Heterogeneous nucleation and crystallization occur on the surface of the nanosheets, ultimately forming zinc oxide / MXene@SiO2 composite nanosheets with a "core-shell-shell" structure.

[0030] S3: Dissolve 4.8g of ammonium carbonate and 5mL of concentrated ammonia in 100mL of deionized water to prepare a mixed alkaline solution; add 1.157g of yttrium nitrate hexahydrate, 1.282g of magnesium nitrate hexahydrate, 1.875g of aluminum nitrate nonahydrate, and 100mL of deionized water to the reaction vessel and stir until dissolved. Under conditions of 55℃ and 400r / min, slowly add 105mL of the mixed alkaline solution dropwise to the reaction vessel over 2 hours using a constant pressure dropping funnel, controlling the pH value during the addition process. The concentration was 9. After the addition was completed, the mixture was aged at 80℃ for 8 hours. After the reaction was completed, the mixture was filtered and the filter cake was washed alternately with water and anhydrous ethanol until the last washing liquid was neutral. The solid was collected and vacuum dried at 80℃ for 12 hours. After preliminary grinding, it was placed in a muffle furnace and heated to 850℃ at a heating rate of 3℃ / min in air atmosphere. It was then calcined at this temperature for 3 hours. Finally, it was cooled to room temperature with the furnace, ground, and passed through a 300-mesh sieve to obtain the yttrium-magnesium-aluminum composite sintering aid.

[0031] A chemical coprecipitation method was used, with yttrium nitrate, magnesium nitrate, and aluminum nitrate as raw materials, to release Y upon dissolution. 3+ Mg 2+ Al 3+ A hydrated cation is formed in the aqueous solution, and CO3 is slowly added dropwise with the ammonium carbonate-ammonia water mixture. 2- With OH - The reaction produces a homogeneous basic carbonate / hydroxide composite precursor, which undergoes particle growth and crystal form refinement through aging treatment at 80℃. After high-temperature calcination, this precursor decomposes, dehydrates, and undergoes a crystal phase transformation, releasing CO3. 2- OH - and NO3 - Escapes in gaseous form, Y 3+ Mg 2+ Al 3+ It is then reconstructed into a composite oxide crystal with "yttrium-magnesium-aluminum synergy" characteristics, thus obtaining a yttrium-magnesium-aluminum composite sintering aid.

[0032] S4: 2.5g of zinc oxide / MXene@SiO2 composite nanosheets were dispersed in 25mL of anhydrous ethanol and ultrasonically dispersed for 30min. Then, the pH was adjusted to 9 with ammonia to make the surface negatively charged, resulting in a nanosheet dispersion. 28g of alumina ceramic powder and 1g of yttrium-magnesium-aluminum composite sintering aid were added to a ball mill jar. Anhydrous ethanol was used as the dispersion medium, and the ball-to-powder ratio was 4:1. The mixture was ball-milled at 300r / min for 4h. The pH was adjusted to 5 with dilute hydrochloric acid to make the surface positively charged, resulting in a basic slurry. Under continuous magnetic stirring, the nanosheet dispersion was slowly added dropwise to the basic slurry over 2h using a constant pressure dropping funnel. After the addition was complete, the mixture was stirred for another 1h to ensure complete assembly. 0.6g of 5% polyvinyl butyral (PVB) ethanol solution was added as a binder. The mixture was magnetically stirred for 1h, vacuum freeze-dried for 12-16h, ground, and passed through a 300-mesh sieve to obtain the ceramic composite powder.

[0033] S5: 25g of ceramic composite powder was loaded into a graphite mold and placed in a spark plasma sintering furnace. After evacuation, argon gas was introduced and heated to 1450℃ at a heating rate of 120℃ / min. At the same time, a pressure of 40MPa was applied and the temperature was held for 8min. The furnace was then cooled to obtain MXene-based ceramic reinforced material.

[0034] Example 2: A method for preparing MXene-based ceramic reinforcement materials, comprising the following steps: S1: Under nitrogen protection, 2g of MXene (Ti3C2T) was added. X MXene@SiO2 nanosheets and 500 mL of isopropanol were added to a reaction vessel and sonicated at 150 W for 20 min to form a stable suspension. A mixture of 29 g of tetraethyl orthosilicate (TEOS), 14.5 g of urea and 200 mL of deionized water was added to the vessel and the mixture was kept at 140 °C and 250 r / min for 8 h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 7000 r / min for 8 min. The precipitate was collected, washed alternately with anhydrous ethanol and deionized water, and dried to obtain MXene@SiO2 nanosheets.

[0035] S2: Under nitrogen protection, 2g of MXene@SiO2 nanosheets and 320mL of deionized water (after nitrogen deoxygenation) were added to the reactor and ultrasonically dispersed for 20min. 3.2g of sodium citrate and 1.2g of poloxamer 407 were added to the reactor and stirred for 10min at 35℃ and 400r / min. Then, 3.6g of zinc acetate was added and stirred for 35min under the same conditions. Subsequently, 8g of hexamethylenetetramine (HMT) was added and stirred for another 20min. The mixture was kept at 90℃ for 6h and allowed to cool naturally to room temperature. It was then centrifuged at 7000r / min for 8min, washed alternately with deionized water and anhydrous ethanol, and vacuum dried at 60℃ for 8h to obtain zinc oxide modified MXene@SiO2 nanosheets.

[0036] S3: Dissolve 4.5g of ammonium carbonate and 4mL of concentrated ammonia in 90mL of deionized water to prepare a mixed alkaline solution. Add 1.1g of yttrium nitrate hexahydrate, 1.25g of magnesium nitrate hexahydrate, 1.85g of aluminum nitrate nonahydrate, and 90mL of deionized water to the reaction vessel and stir until dissolved. Under conditions of 50℃ and 300r / min, slowly add 90mL of the mixed alkaline solution dropwise to the reaction vessel over 2 hours using a constant pressure dropping funnel, controlling the pH value to 8.5 during the addition process. After the addition was completed, the mixture was aged at 75℃ for 7 hours. After the reaction was completed, the mixture was filtered and the filter cake was washed alternately with water and anhydrous ethanol until the last washing liquid was neutral. The solid was collected and vacuum dried at 75℃ for 10 hours. After preliminary grinding, it was placed in a muffle furnace and heated to 800℃ at a heating rate of 3℃ / min in an air atmosphere. It was then calcined at this temperature for 2 hours and finally cooled to room temperature with the furnace. The mixture was then ground and passed through a 300-mesh sieve to obtain the yttrium-magnesium-aluminum composite sintering aid.

[0037] S4: 2g of zinc oxide / MXene@SiO2 composite nanosheets were dispersed in 23mL of anhydrous ethanol and ultrasonically dispersed for 20min. Then, the pH was adjusted to 8 with ammonia to make the surface negatively charged, resulting in a nanosheet dispersion. 25g of alumina ceramic powder and 0.75g of yttrium-magnesium-aluminum composite sintering aid were added to a ball mill jar. Anhydrous ethanol was used as the dispersion medium, and the ball-to-powder ratio was 4:1. The mixture was ball-milled at 300r / min for 3h. The pH was adjusted to 4 with dilute hydrochloric acid to make the surface positively charged, resulting in a basic slurry. Under continuous magnetic stirring, the nanosheet dispersion was slowly added dropwise to the basic slurry over 1h using a constant pressure dropping funnel. After the addition was complete, the mixture was stirred for another 1h to ensure complete assembly. 0.5g of 5% polyvinyl butyral (PVB) ethanol solution was added as a binder. The mixture was magnetically stirred for 0.5h, vacuum freeze-dried for 12h, ground, and passed through a 300-mesh sieve to obtain the ceramic composite powder.

[0038] S5: 20g of ceramic composite powder was loaded into a graphite mold and placed in a spark plasma sintering furnace. After evacuation, argon gas was introduced and heated to 1400℃ at a heating rate of 100℃ / min. At the same time, a pressure of 30MPa was applied and the temperature was held for 5min. The furnace was then cooled to obtain MXene-based ceramic reinforced material.

[0039] Example 3: A method for preparing MXene-based ceramic reinforcement materials, comprising the following steps: S1: Under nitrogen protection, 3g of MXene (Ti3C2T) was added. X MXene@SiO2 nanosheets and 750 mL of isopropanol were added to a reaction vessel and sonicated at 150 W for 40 min to form a stable suspension. A mixture of 44 g of tetraethyl orthosilicate (TEOS), 22 g of urea and 300 mL of deionized water was added to the vessel and the mixture was kept at 150 °C and 350 r / min for 10 h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 9000 r / min for 12 min. The precipitate was collected, washed alternately with anhydrous ethanol and deionized water, and dried to obtain MXene@SiO2 nanosheets.

[0040] S2: Under nitrogen protection, 3g of MXene@SiO2 nanosheets and 480mL of deionized water (after nitrogen deoxygenation) were added to the reactor and ultrasonically dispersed for 40min. 4.8g of sodium citrate and 1.8g of poloxamer 407 were added to the reactor and stirred for 20min at 45℃ and 500r / min. Then, 5.4g of zinc acetate was added and stirred for 55min under the same conditions. Subsequently, 12g of hexamethylenetetramine (HMT) was added and stirring was continued for 40min. The mixture was kept at 95℃ for 8h and allowed to cool naturally to room temperature. It was then centrifuged at 8000r / min for 12min, washed alternately with deionized water and anhydrous ethanol, and vacuum dried at 70℃ for 12h to obtain zinc oxide modified MXene@SiO2 nanosheets.

[0041] S3: Dissolve 5g of ammonium carbonate and 6mL of concentrated ammonia in 110mL of deionized water to prepare a mixed alkaline solution; add 1.2g of yttrium nitrate hexahydrate, 1.3g of magnesium nitrate hexahydrate, 1.9g of aluminum nitrate nonahydrate, and 110mL of deionized water to the reaction vessel and stir until dissolved. Under conditions of 60℃ and 500r / min, slowly add 120mL of the mixed alkaline solution dropwise to the reaction vessel over 2 hours using a constant pressure dropping funnel. Maintain the pH at 9 during the dropping process. After the addition was completed, the mixture was aged at 85℃ for 9 hours. After the reaction was completed, the mixture was filtered and the filter cake was washed alternately with water and anhydrous ethanol until the last washing liquid was neutral. The solid was collected and vacuum dried at 85℃ for 14 hours. After preliminary grinding, it was placed in a muffle furnace and heated to 900℃ at a heating rate of 3℃ / min in an air atmosphere. It was then calcined at this temperature for 4 hours and finally cooled to room temperature with the furnace. The mixture was then ground and passed through a 300-mesh sieve to obtain the yttrium-magnesium-aluminum composite sintering aid.

[0042] S4: 3g of zinc oxide / MXene@SiO2 composite nanosheets were dispersed in 28mL of anhydrous ethanol and ultrasonically dispersed for 40min. Then, the pH was adjusted to 10 with ammonia to make the surface negatively charged, resulting in a nanosheet dispersion. 30g of alumina ceramic powder and 1.3g of yttrium-magnesium-aluminum composite sintering aid were added to a ball mill jar. Anhydrous ethanol was used as the dispersion medium, and the ball-to-material ratio was 4:1. The mixture was ball-milled at 350r / min for 5h. The pH was adjusted to 6 with dilute hydrochloric acid to make the surface positively charged, resulting in a basic slurry. Under continuous magnetic stirring, the nanosheet dispersion was slowly added dropwise to the basic slurry over 2h using a constant pressure dropping funnel. After the addition was complete, the mixture was stirred for another 1h to ensure complete assembly. 0.75g of 5% polyvinyl butyral (PVB) ethanol solution was added as a binder. The mixture was magnetically stirred for 1.5h, vacuum freeze-dried for 16h, ground, and passed through a 300-mesh sieve to obtain the ceramic composite powder.

[0043] S5: 30g of ceramic composite powder was loaded into a graphite mold, placed in a spark plasma sintering furnace, evacuated, and argon gas was introduced. The temperature was increased to 1500℃ at a heating rate of 150℃ / min, while a pressure of 50MPa was applied. The temperature was held for 10min and then cooled with the furnace to obtain MXene-based ceramic reinforced material.

[0044] The raw materials used in Examples 1-3 of this application are all commercially available. Specifically, tetraethyl orthosilicate (purity ≥99.5%) was purchased from Zhangjiagang Xinya Chemical Co., Ltd.; urea (99%), ammonium carbonate (reagent grade), concentrated ammonia (concentration 25-28%), alumina ceramic powder (α phase, purity 99.9%, particle size 500nm), and MXene (Ti3C2T) were also used. XThe nanosheets (single-layer titanium carbide (Ti3C2Tx)MXene nanosheets, purity approximately 98 at%) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; sodium citrate (purity ≥98%), poloxamer 407 (purified), hexamethylenetetramine, yttrium nitrate hexahydrate (AR, purity ≥99.5%) and aluminum nitrate nonahydrate (purity ≥98%) were purchased from Shanghai Aladdin Biochemical Co., Ltd.

[0045] Comparative Example 1: Based on Example 1, steps S1 and S2 of the preparation of MXene@SiO2 nanosheets and zinc oxide / MXene@SiO2 composite nanosheets were omitted. In step S4, 2.5g of unmodified original MXene nanosheets were directly used to replace the zinc oxide / MXene@SiO2 composite nanosheets. All other steps and parameters remained unchanged to obtain ceramic materials.

[0046] Comparative Example 2: Based on Example 1, step S2, the preparation of zinc oxide / MXene@SiO2 composite nanosheets, was omitted. In step S4, the product of step S1, MXene@SiO2 nanosheets, was directly used to replace the zinc oxide / MXene@SiO2 composite nanosheets. All other steps and parameters remained unchanged, and a ceramic material was obtained.

[0047] Comparative Example 3: Based on Example 1, step S3, the preparation of the yttrium-magnesium-aluminum composite sintering aid, was omitted. In step S4, the composite sintering aid was not added, and only alumina ceramic powder was ball-milled. All other parameters remained unchanged to obtain the ceramic material.

[0048] The ceramic materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests. The flexural strength was tested in accordance with the GB / T 6569-2006 standard using the three-point bending method. The material was loaded at a constant displacement rate of 0.5 mm / min on a universal testing machine, and the maximum load at which the specimen broke was recorded. The flexural strength was then calculated. A higher flexural strength indicates a stronger load-bearing capacity, fewer internal defects, a stronger interfacial bond between the reinforcing phase and the matrix, and superior macroscopic mechanical properties and structural reliability of the material.

[0049] Fracture toughness was determined according to GB / T 23806-2025 standard. The single-sided notched beam method was used to record the load-displacement curve. The plane strain fracture toughness (KIC) value of the material was calculated by combining the sample geometry and the pre-crack depth. The higher the fracture toughness (KIC) value, the stronger the material's ability to resist crack propagation. The more significant the effect of reinforcing phases such as MXene in consuming fracture energy through crack deflection, bridging, and lamellar pull-out, the better the brittleness of the material is, and the higher its safety under high stress or impact loads.

[0050] Thermal shock resistance was tested according to GB / T 30873-2014 standard. The air-cooling method was used, in which the sample was placed in a high-temperature furnace at 1400℃ and held for 20 minutes. After being quickly removed, it was cooled in still air at room temperature. This process was recorded as one thermal shock cycle, and a total of 20 cycles were performed. After the cycle, the sample surface was visually inspected under natural light to check for cracks, chipping, or breakage. The higher the surface integrity rate after 20 cycles, the stronger the material's ability to resist thermal stress, the better the stability of the internal structure under thermal shock, and the longer the service reliability and service life of the refractory material under high temperature and rapid change conditions.

[0051] The results are shown in Table 1: Table 1 Performance test results of various ceramic materials As shown in Table 1, the ceramic reinforced materials prepared in Examples 1-3 of this invention exhibit good comprehensive performance. In terms of mechanical properties, the examples demonstrate good flexural strength and fracture toughness, indicating that the materials have the potential for superior load-bearing capacity and crack propagation resistance. In terms of thermal stability, after undergoing multiple thermal shock cycles, the surface condition of the sample remains relatively intact, indicating that the materials have certain thermal shock resistance. In summary, this invention, by constructing a synergistic technology system of "core-shell protection-low-temperature sintering," prepares ceramic materials that meet the requirements of special refractory applications.

[0052] Comparative Example 1 uses uncoated MXene nanosheets as the reinforcing phase. Performance test results show that its mechanical properties and thermal shock resistance are poor. This may be because unprotected MXene is prone to oxidation phase transformation during high-temperature sintering. This indicates that constructing a SiO2 / ZnO composite coating layer is indispensable for isolating the high-temperature oxidation environment and maintaining the stability of the two-dimensional structure of MXene. It is a prerequisite for the reinforcing phase to function effectively.

[0053] Comparative Example 2 used only a single layer of SiO2-coated MXene nanosheets without the growth of a ZnO outer layer. Its performance test results showed that although its bending strength and fracture toughness were better than those of Comparative Example 1, they were still significantly lower than all other examples. Moreover, its thermal shock resistance was characterized by the appearance of microcracks at the edges. This indicates that the protective effect of a single SiO2 coating layer under extreme conditions is still limited. In contrast, the present invention, by introducing a ZnO outer shell to form a "core-shell-shell" structure, constructs a denser and more stable physicochemical barrier, which can optimize the interfacial bonding between the reinforcing phase and the ceramic matrix. The comparative results show that the introduction of the ZnO outer layer not only jointly constructs a denser physicochemical synergistic barrier with the SiO2 layer, but its strong interfacial bonding with the matrix is ​​also the key to achieving high material strength.

[0054] Comparative Example 3 omitted the yttrium-magnesium-aluminum composite sintering aid and kept all other process parameters the same as in Example 1. The resulting comparative material showed a significant deterioration in flexural strength and fracture toughness, and completely fractured after thermal shock resistance testing. This result indicates that at the same temperature and time, the absence of the composite sintering aid leads to insufficient mass transfer kinetics of the ceramic matrix and a significant reduction in densification, thereby causing a comprehensive deterioration of the material properties. This result demonstrates the crucial role of the composite sintering aid in achieving rapid densification of materials at low temperatures.

[0055] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0056] 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.

Claims

1. A method for preparing MXene-based ceramic reinforcing materials, characterized in that, Includes the following steps: Step 1: Using MXene nanosheets, tetraethyl orthosilicate and urea as raw materials, MXene@SiO2 nanosheets are prepared by hydrothermal in-situ coating. Step 2: A zinc oxide nanoshell was constructed on the surface of MXene@SiO2 using a hydrothermal in-situ growth method to prepare zinc oxide / MXene@SiO2 composite nanosheets; Step 3: Using yttrium nitrate, magnesium nitrate and aluminum nitrate as raw materials, a sintering aid for yttrium-magnesium-aluminum composite oxide is prepared by chemical co-precipitation and calcination; Step 4: Combine zinc oxide / MXene@SiO2 composite nanosheets, alumina ceramic powder, and yttrium-magnesium-aluminum composite oxide sintering aid to obtain ceramic composite powder, sinter it to form a ceramic reinforced material based on MXene.

2. The method for preparing an MXene-based ceramic reinforcement material according to claim 1, characterized in that, The sintering conditions are as follows: heating to 1400-1500℃ at a heating rate of 100-150℃ / min, while applying a pressure of 30-50MPa and holding for 5-10min.

3. The method for preparing an MXene-based ceramic reinforcement material according to claim 1, characterized in that, The specific preparation steps of the ceramic composite powder are as follows: Zinc oxide / MXene@SiO2 composite nanosheets were dispersed in anhydrous ethanol and ultrasonically dispersed for 20-40 min. The pH was then adjusted to 8-10 with ammonia to obtain a nanosheet dispersion. Alumina ceramic powder and yttrium-magnesium-aluminum composite sintering aid were ball-milled at 300-350 r / min for 3-5 h. The pH was adjusted to 4-6 with dilute hydrochloric acid to obtain a basic slurry. Under continuous stirring, the nanosheet dispersion was slowly added dropwise to the basic slurry over 1-2 h using a constant pressure dropping funnel. After the addition was complete, the mixture was stirred for another 1 h to ensure complete assembly. A 5% (w / w) polyvinyl butyral ethanol solution was added, and the mixture was stirred for 0.5-1.5 h. The mixture was then freeze-dried, ground, and sieved to obtain the ceramic composite powder.

4. The method for preparing an MXene-based ceramic reinforcement material according to claim 3, characterized in that, The ratio of zinc oxide / MXene@SiO2 composite nanosheets, anhydrous ethanol, alumina ceramic powder, yttrium-magnesium-aluminum composite sintering aid, and polyvinyl butyral (PVB) ethanol solution is 2-3g: 23-28mL: 25-30g: 0.75-1.3g: 0.5-0.75g.

5. The method for preparing an MXene-based ceramic reinforcement material according to claim 3, characterized in that, The specific steps for producing the zinc oxide / MXene@SiO2 composite nanosheets are as follows: Under nitrogen protection, MXene@SiO2 nanosheets and deionized water were added to a reaction vessel and ultrasonically dispersed for 20-40 min. Sodium citrate and poloxamer 407 were added, and the mixture was stirred at 35-45℃ and 400-500 r / min for 10-20 min. Zinc acetate was then added and stirred for 35-55 min. Subsequently, hexamethylenetetramine was added and stirring was continued for 20-40 min. The mixture was reacted at a constant temperature of 90-95℃ for 6-8 h. After cooling, centrifugation, washing, and drying, zinc oxide modified MXene@SiO2 nanosheets were obtained.

6. The method for preparing an MXene-based ceramic reinforcement material according to claim 5, characterized in that, The ratio of MXene@SiO2 nanosheets, deionized water, sodium citrate, poloxamer 407, zinc acetate, and hexamethylenetetramine is 2-3g: 320-480mL: 3.2-4.8g: 1.2-1.8g: 3.6-5.4g: 8-12g.

7. The method for preparing an MXene-based ceramic reinforcement material according to claim 5, characterized in that, The specific steps for producing the MXene@SiO2 nanosheets are as follows: Under nitrogen protection, MXene nanosheets and isopropanol were added to a reaction vessel and sonicated for 20-40 min to form a stable suspension. A mixture of tetraethyl orthosilicate, urea and deionized water was added to the vessel and the reaction was carried out at 140-150℃ and 250-350 r / min for 8-10 h. After the reaction was completed, the mixture was cooled, centrifuged, washed and dried to obtain MXene@SiO2 nanosheets. The ratio of MXene nanosheets, isopropanol, tetraethyl orthosilicate, urea, and deionized water is 2-3g: 500-750mL: 29-44g: 14.5-22g: 200-300mL.

8. The method for preparing an MXene-based ceramic reinforcement material according to claim 3, characterized in that, The specific preparation steps of the yttrium-magnesium-aluminum composite sintering aid are as follows: Yttrium nitrate hexahydrate, magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and deionized water were added to a reaction vessel and stirred until dissolved. The mixed alkaline solution was slowly added dropwise to the reaction vessel over 2 hours at 50-60℃ and 300-500 r / min, with the pH value controlled at 8.5-9. After the addition was completed, the mixture was aged at 75-85℃ for 7-9 hours, filtered, washed, vacuum dried, and preliminarily ground. It was then placed in a muffle furnace and heated to 800-900℃ at 3℃ / min for 2-4 hours. After cooling to room temperature, it was ground and sieved to obtain the yttrium-magnesium-aluminum composite sintering aid. The ratio of the amounts of yttrium nitrate hexahydrate, magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, deionized water, and the mixed alkaline solution is 1.1-1.2g: 1.25-1.3g: 1.85-1.9g: 90-110mL: 90-120mL.

9. The method for preparing an MXene-based ceramic reinforcement material according to claim 8, characterized in that, The mixed alkaline solution is prepared by mixing ammonium carbonate, concentrated ammonia, and deionized water in a ratio of 4.5-5g:4-6mL:90-110mL.

10. An MXene-based ceramic reinforcement material, prepared according to any one of claims 1-9.

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