A high-entropy carbide-high-entropy boride composite ceramic precursor and a composite nanoceramic powder and a preparation method thereof

Abstract

The application discloses a high-entropy carbide-high-entropy boride composite ceramic precursor and a preparation method of a composite nanometer ceramic powder, the precursor comprises B elements and C elements and at least four of Ti, Zr, Hf, V, Nb, Ta, Mo and W elements, and the mole number of each metal element accounts for 5-35% of the total mole number of the metal of the precursor; the precursor can generate the high-entropy carbide-high-entropy boride composite ceramic nanometer powder after cracking under vacuum or under normal pressure in inert atmosphere protection. The high-entropy carbide-high-entropy boride nanometer ceramic powder of the application has the following characteristics: each element is uniformly distributed at a molecular level, the average particle size of the nanometer powder is not more than 500 nm, the content of O impurities is not more than 1 wt%, the mole ratio of the B element and the C element in the nanometer powder is 1:19-38:1, and the nanometer powder further contains at least four of Ti, Zr, Hf, V, Nb, Ta, Mo and W metal elements.

Description

Technical Field

[0001] This invention belongs to the field of high-entropy materials technology, and relates to a high-entropy carbide-high-entropy boride multiphase ceramic precursor, multiphase nano-ceramic powder, and preparation method thereof. Background Technology

[0002] High-entropy ceramics are a new type of ceramic that has emerged in recent years. The concept of this ceramic originates from high-entropy alloys, and generally refers to a single solid solution formed by dissolving five or more metallic compounds together in a (near) equimolar ratio. High-entropy ceramics not only enrich the types of ceramics, but also endow the materials with a rich space for performance adjustment due to the novel "high-entropy effect" brought about by the synergy of multiple components.

[0003] In 2016, Joshua Gild et al. (Scientific Reports 2016, 6, 1-10) first reported the preparation of pentagonal high-entropy boride bulk ceramics with hexagonal AlB2 metal diborides, namely (Hf-Zr-Ta-Nb-Ti)B2, (Hf-Zr-Ta-Mo-Ti)B2, (Hf-Zr-Mo-Nb-Ti)B2, (Hf-Mo-Ta-Nb-Ti)B2, (Mo-Zr-Ta-Nb-Ti)B2, (Hf-Zr-W-Mo-Ti)B2, and (Hf-Zr-Ta-Cr-Ti)B2, using commercially available boride powders as raw materials. These ceramics were prepared by plasma sintering at 2000℃ and 30 MPa. In 2018, Castle et al. (Scientific Reports)... The first report (2018, 8, 8609-8620) described the preparation of quaternary carbide ceramic blocks with rock-salt structures (Hf-Ta-Zr-Ti)C and (Hf-Ta-Zr-Nb)C by plasma sintering of carbide powders at 2300℃ and 16MPa. Subsequently, there have been increasing reports on the preparation and performance studies of high-entropy boride ceramics and high-entropy carbide ceramics. Currently, the main preparation methods for high-entropy boride and high-entropy carbide ceramics employ inorganic powder methods. For example, the main methods for preparing high-entropy boride ceramics are boride powder reaction sintering, boronothermal / boronothermal reduction, and self-propagating synthesis; while the main methods for preparing high-entropy carbide ceramics are carbide powder reaction sintering, elemental reaction sintering, and oxide reduction sintering. However, the inorganic powder method for preparing high-entropy ceramics often results in the presence of oxide impurities in the prepared ceramics, and may also lead to incomplete solid solution reactions or uneven elemental distribution, thus affecting the ceramic's performance.

[0004] In recent years, researchers have found that single boride or carbide ceramics often fail to meet the comprehensive performance requirements of materials in extreme environments. Two-phase or multiphase ceramics often exhibit better mechanical properties and oxidation resistance, especially boride-carbide multiphase ceramics, such as TiB2-TiC, ZrB2-ZrC, and NbB2-NbC, which possess high melting point / eutectic temperature and good electronic conductivity. Sijia Huo et al. (Journal of the American Ceramic Society, 2020, 103, 6101-6105; Journal of the European Ceramic Society, 2020, 40, 4373-4380) prepared (Ti-Zr)B2-(Zr-Ti)C multiphase ceramics using ZrB2 and TiC as raw materials via hot pressing. The mechanical properties of the multiphase ceramics were significantly improved compared to the pure phase ceramics. Mingde Qin et al. (Journal of the European Ceramic Society, 2020, 40, 5037–5050) prepared high-entropy carbide-high-entropy boride multiphase ceramics using N types of boride powder and (5-N) types of carbide powder as raw materials by spark plasma sintering (sintering conditions: 2200 ℃, 80 MPa). By adjusting the ratio of carbide raw materials to boride raw materials, the ratio of high-entropy carbide and high-entropy boride in the product could be adjusted. The study found that the hardness, Young's modulus, and shear modulus of the multiphase high-entropy ceramics were all higher than the average values ​​calculated based on RoM. Because WC balls were used during the ball milling and mixing of raw materials, W heteroatom contamination was present in the final ceramic. Si-Chun Luo et al. (Journal of the European Ceramic Society, 2021, 41, 3189–3195) synthesized (Ti-Zr-Hf-Nb-Ta)B2-(Ti-Zr-Hf-Nb-Ta)C multiphase high-entropy ceramics using metal oxide powder as raw material and employing boronothermal / carbothermal reduction combined with discharge plasma sintering technology (sintering conditions: 2000℃, 30MPa). The ratio of the two high-entropy phases could be adjusted by changing the ratio of B4C and C.

[0005] Due to the novelty of the research field, there are very few research reports on high-entropy carbide-high-entropy boride multiphase ceramics. Existing reports all use inorganic powder methods for preparation, and the preparation must be carried out under high temperature and high pressure. As a result, the ceramics prepared by this method can only exist in bulk form, which limits the application of multiphase high-entropy ceramics in the fields of ceramic matrix composites and ceramic coatings.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a high-entropy carbide-high-entropy boride multiphase ceramic precursor, multiphase nano-ceramic powder, and a preparation method thereof. In the high-entropy carbide-high-entropy boride multiphase ceramic precursor, the precursor backbone is a metal-oxygen bridge bond, and the precursor side chain contains boron and a carbon-forming oligomer (the carbon-forming oligomer refers to a carbon-containing substance formed by high-temperature pyrolysis of an oligomer under inert atmosphere or vacuum conditions). The carbon-forming oligomer can be a phenolic resin, but is not limited to phenolic resin (e.g., allyl phenolic resin). In this invention, the metal source, boron source, and carbon source in the high-entropy carbide-high-entropy boride multiphase ceramic precursor are connected by chemical bonds, which effectively ensures the uniform molecular-level distribution of each element, thus facilitating the preparation of elementally uniform high-entropy carbide-high-entropy boride multiphase ceramics through precursor pyrolysis. The high-entropy carbide-high-entropy boride multiphase ceramic precursor of this invention first obtains a metal source through co-hydrolysis of metal alkoxides to ensure a uniform molecular-level distribution of each metal. The metal source then reacts and bonds with boron and carbon sources to ensure a uniform molecular-level distribution of the metal, boron, and carbon sources, thereby facilitating their reaction and solid solution formation during the pyrolysis process to form high-entropy carbide-high-entropy boride multiphase ceramic nanopowders. Furthermore, by adjusting the ratio of metal, boron, and carbon sources during precursor synthesis, the content of high-entropy carbides and high-entropy borides in the ceramic can also be adjusted.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0009] This invention provides a high-entropy carbide-high-entropy boride multiphase ceramic precursor, wherein the precursor is an organic compound including elements B and C, and also includes at least four of the following metallic elements: Ti, Zr, Hf, V, Nb, Ta, Mo, and W.

[0010] According to an embodiment of the present invention, in the precursor, the number of moles of each metal element is the same or different, and each independently accounts for 5% to 35% of the total number of moles of the precursor metal; exemplary values ​​are 5%, 10%, 15%, 20%, 30%, and 35%.

[0011] Preferably, in the precursor, the number of moles of each metal element is the same.

[0012] This invention also provides a method for preparing the above-mentioned high-entropy carbide-high-entropy boride multiphase ceramic precursor, the preparation method comprising the following steps:

[0013] (1) Preparation of metal alkoxide complexes: To metal alkoxide M(OR) n Add the complexing agent dropwise, and continue stirring for 0.1–5 hours after the addition is complete to obtain the metal alkoxide complex;

[0014] (2) Co-hydrolysis: Select at least four metal alkoxide complexes containing different metal elements obtained in step (1), mix them, add a mixture of water and monohydric alcohol dropwise, reflux for 1-5 hours after the addition is complete, cool to room temperature, remove solvent by low-temperature rotary evaporation until the metal content of the system is 25-35%, and obtain a metal alkoxide copolymer solution.

[0015] (3) Preparation of precursor: Allylphenol is added to the metal alkoxide copolymer solution obtained in step (2), stirred, and then boron-containing compound is added. The temperature is raised to 70-95℃ and reacted for 30 min-3 h to obtain a uniform and transparent gel. Then the temperature is raised for gel aging and drying, and the temperature is lowered to obtain a high-entropy carbide-high-entropy boride multiphase ceramic precursor.

[0016] According to an embodiment of the present invention, in step (1), the metal alkoxide M(OR) n The molar ratio of the complexing agent is 1:(0.1~0.25)n; when M in the metal alkoxide is selected from Ti, Zr or Hf, n is 4; when M in the metal alkoxide is selected from V, Nb, Ta or Mo, n is 5; when M is W, n is 6.

[0017] According to an embodiment of the present invention, the complexing agent is acetylacetone and / or ethyl acetoacetate.

[0018] According to an embodiment of the present invention, in step (1), the dripping temperature of the complexing agent is room temperature to 80 °C.

[0019] In the above scheme, the researchers of this invention discovered that different types of metal elements have different reactivity in the process of forming complexes, when the metal alkoxide M(OR) n When the molar ratio of metal alkoxide to complexing agent is not in the range of 1:(0.1~0.25)n, although complexes can be formed, the reaction equilibrium will be tilted due to the difference in the amount of complexing agent added during the subsequent mixed hydrolysis of multiple metal alkoxide complexes, resulting in the inability to form a precursor with uniform molecular distribution. In addition, the amount of complexing agent added will also affect the amount of residual active groups in the resulting metal alkoxide copolymer, thereby affecting the reactivity of the metal alkoxide copolymer with boron and carbon sources. However, when the molar ratio of metal alkoxide to complexing agent is in the range of 1:(0.1~0.25)n, the difference in reactivity of each metal during subsequent hydrolysis can be relatively small, while the reactivity of metal alkoxide with boron and carbon sources is preserved.

[0020] According to an embodiment of the present invention, in step (2), the total molar ratio of water to metal element is 0.9 to 1.5:1, with examples being 0.9:1, 1.0:1, 1.2:1, and 1.5:1.

[0021] According to an embodiment of the present invention, in step (2), the mass ratio of monohydric alcohol to water is 3 to 8:1, for example 3:1, 5:1, or 8:1.

[0022] According to an embodiment of the present invention, in step (2), the monohydric alcohol is selected from one or more of isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol methyl ether, and ethylene glycol ethyl ether.

[0023] According to an embodiment of the present invention, in step (2), a mixture of water and monohydric alcohol is added dropwise at room temperature to 90°C, and the temperature of the rotary evaporation is not higher than 40°C.

[0024] The above scheme is based on the mass ratio of alcohol to water, which is derived from the mixing of metal alkoxides with different reactivity. This makes the reactivity of various metal alkoxides similar during co-hydrolysis, thereby obtaining alkoxide copolymers with uniform distribution of metal elements at the molecular level, while retaining the reactivity of the metal alkoxide copolymers with boron and carbon sources.

[0025] To further enhance the reactivity of the metal alkoxide copolymer with boron and carbon sources, this invention also increases the metal content of the metal alkoxide copolymer by low-temperature rotary evaporation, while controlling the amount of complexing agent and water. At the same time, low-temperature rotary evaporation can also prevent the active groups from decreasing due to continued reaction.

[0026] According to an embodiment of the present invention, in step (3), the boron-containing compound is selected from one or a mixture of several of boric acid, trimethyl borate, triethyl borate, tripropyl borate, tributyl borate, glyceryl borate, and triethanolamine borate.

[0027] According to an embodiment of the present invention, in step (3), the ratio of the total number of moles of metal elements in the metal alkoxide copolymer, the number of moles of boron elements in the boron-containing compound, to the mass of allylphenol aldehyde is 1 mol: (1-7) mol: (5-30) g, for example 1 mol: 1 mol: 5 g, 1 mol: 3 mol: 5 g, 1 mol: 7 mol: 5 g, 1 mol: 7 mol: 5 g, 1 mol: 7 mol: 15 g, 1 mol: 1 mol: 30 g.

[0028] In the above preparation methods, the molar masses of different metals are different, making it inconvenient to unify them into a uniform range based on mass. Therefore, this invention calculates the mass based on the total molar number of metal elements in the metal alkoxide copolymer, and the molar number of boron-containing compounds. Allylphenolic resin is a non-homogeneous polymer, unsuitable for molar representation; therefore, it is expressed as a ratio of molar number to mass. The ratio of the metal copolymer to the boron-containing compound and allylphenolic resin is derived considering the amount of boron and carbon required for the borothermic / carbothermic reduction of the precursor during pyrolysis. An inappropriate ratio will result in the preparation of high-entropy carbide-high-entropy boride nanoceramic powder containing impurities such as metal oxides, metal carbides, or boron carbide, or will prevent the formation of high-entropy carbide-high-entropy boride multiphase ceramics.

[0029] According to an embodiment of the present invention, in step (3), the aging temperature is 90 to 120°C, for example 90°C, 100°C, or 120°C; and the aging time is 1 to 5 hours, for example 1 hour, 3 hours, or 5 hours.

[0030] According to an embodiment of the present invention, in step (3), the drying method can be a conventional method in the art, such as vacuum drying at 50-150°C or forced air drying at 50-150°C.

[0031] According to an embodiment of the present invention, when M in the metal alkoxide is selected from Hf, V, Nb, Ta, Mo, or W, the metal alkoxide in step (1) is prepared by reacting a metal salt with a monohydric alcohol, specifically as follows: The metal salt MCl... n Or M(NO3) n The mixture is dispersed in an organic solvent, and a monohydric alcohol is added dropwise at -10 to 5°C, followed by triethylamine. After the addition is complete, the mixture is heated under reflux for 1 to 5 hours and then filtered to obtain a metal alkoxide solution. The ratio of the metal salt, monohydric alcohol, and triethylamine is 1:(1 to 2)n:(1 to 1.5)n. The organic solvent is one or more of n-hexane, n-heptane, toluene, xylene, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and tert-butyl methyl ether. The monohydric alcohol is selected from one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol methyl ether, and ethylene glycol ethyl ether.

[0032] According to an embodiment of the present invention, the preparation method of the high-entropy carbide-high-entropy boride multiphase ceramic precursor includes the following steps:

[0033] (1) Preparation of metal alkoxides: Select transition metal alkoxides containing different types of metal elements. When M in the metal alkoxide is selected from Hf, V, Nb, Ta, Mo, or W, the preparation method of the metal alkoxide is as follows: MCl is prepared by... n Or M(NO3) nDispersed in an organic solvent, a monohydric alcohol was added dropwise at -10 to 5°C, followed by triethylamine. After the addition was complete, the mixture was heated under reflux for 1 to 5 hours and then filtered to obtain a metal alkoxide solution.

[0034] (2) Preparation of metal alkoxide complex: Under the conditions of room temperature to 80°C, the metal alkoxide M(OR) selected in step (1) is subjected to the following reaction: n Add the complexing agent dropwise, and continue stirring for 0.1–5 hours after the addition is complete to obtain the metal alkoxide complex;

[0035] (3) Co-hydrolysis: Select at least four metal alkoxide complexes containing different metal elements obtained in step (2), mix them evenly, and slowly add a mixture of water and monohydric alcohol at room temperature to 90°C. After the addition is complete, reflux for 1 to 5 hours, cool to room temperature, and remove the solvent by low-temperature rotary evaporation until the metal content of the system is 25 to 35%, and obtain a metal alkoxide copolymer solution.

[0036] (4) Preparation of precursor: Allylphenol is added to the metal alkoxide copolymer solution obtained in step (3), and after stirring evenly, boron-containing compound is added. The temperature is raised to 70-95℃ and reacted for 30 min-3 h to obtain a uniform and transparent gel. Then the temperature is raised to 90-120℃ and aged for 1-5 h, dried at 50-150℃, and cooled to obtain a high-entropy carbide-high-entropy boride multiphase ceramic precursor.

[0037] In the above preparation method, to achieve a molecular-level uniform distribution of the metal source (metal alkoxide copolymer), boron source (boron-containing compound), and carbon source (allylphenolic resin) in the precursor, and to maintain a uniform distribution of each element during curing and pyrolysis, this invention controls the reaction conditions during the metal source preparation process, such as controlling the amount of complexing agent and water, and controlling the post-reaction treatment method. This ensures that a large number of active groups are retained in the metal source, facilitating the reaction with the carbon and boron sources to generate a uniform gel. This design allows the metal, boron, and carbon to bond to the same molecular chain, maintaining a uniform distribution of elements during curing. Furthermore, it results in a short-range distribution of elements during pyrolysis, which is beneficial for the borothermic / carbathemic reduction reactions between the metal elements and the boron and source, as well as for solid solution reactions between the metal elements, resulting in a uniformly distributed multiphase solid solution ceramic nanopowder.

[0038] The present invention also provides a high-entropy carbide-high-entropy boride multiphase ceramic nanopowder, wherein the nanopowder includes elements B and C, and the nanopowder also contains at least four of the following metallic elements: Ti, Zr, Hf, V, Nb, Ta, Mo, and W.

[0039] According to an embodiment of the present invention, the molar ratio of element B to element C in the nanopowder is 1:19 to 38:1; exemplary ratios are 1:19, 1:10, 1:1, 10:1, 20:19, 30:1, and 38:1.

[0040] According to an embodiment of the present invention, in the nanopowder, the molar number of each metal element may be the same or different, and each independently accounts for 5% to 35% of the total molar number of metals in the ceramic nanopowder; exemplary values ​​are 5%, 10%, 15%, 20%, 30%, and 35%. Preferably, the molar number of each metal element is equal.

[0041] According to an embodiment of the present invention, the high-entropy carbide in the nanopowder is a single cubic crystal phase, the high-entropy boride is a single hexagonal crystal phase, and the elements therein are uniformly distributed at the molecular level.

[0042] According to an embodiment of the present invention, the average particle size of the nanopowder is not greater than 500 nm.

[0043] According to an embodiment of the present invention, the content of O impurities in the nanopowder is not greater than 1 wt%.

[0044] According to an embodiment of the present invention, the nanopowder is prepared by pyrolyzing the above-mentioned high-entropy carbide-high-entropy boride multiphase ceramic precursor under vacuum or inert atmosphere protection at normal pressure.

[0045] According to an embodiment of the present invention, the inert atmosphere may be argon, helium, or a mixture thereof.

[0046] The present invention also provides a method for preparing high-entropy carbide-high-entropy boride multiphase ceramic nanopowder, comprising curing and pyrolyzing the above-mentioned high-entropy carbide-high-entropy boride multiphase ceramic precursor to obtain the high-entropy carbide-high-entropy boride multiphase ceramic nanopowder.

[0047] According to an embodiment of the present invention, the pyrolysis temperature is not lower than 1700°C, preferably 1800-2000°C, with examples being 1800°C, 1900°C, and 2000°C; the pyrolysis time is 0.5-5h, with examples being 0.5h, 1h, 2h, 3h, 4h, and 5h.

[0048] According to an embodiment of the invention, the pyrolysis is carried out in a vacuum environment or under an inert atmosphere. Preferably, the inert atmosphere is selected from argon, helium, or a mixture of both.

[0049] In the existing technology, high-entropy carbide-high-entropy boride multiphase ceramics are mainly prepared by inorganic powder reaction sintering, which can only produce bulk materials, thus limiting the application fields of ceramics.

[0050] The present invention also provides the application of the above-mentioned high-entropy carbide-high-entropy boride multiphase ceramics in the fields of ceramic matrix composites and ceramic coatings.

[0051] The beneficial effects of this invention are:

[0052] This invention employs a precursor method to prepare high-entropy carbide-high-entropy boride multiphase ceramic nanopowders. Since the elements in the precursor are uniformly dispersed at the molecular level, they can maintain a uniform distribution during solidification and pyrolysis, which is beneficial for achieving a uniform distribution of elements in the solid solution. Therefore, high-purity, completely chemically homogeneous multiphase ceramic nanopowders can be obtained at a relatively low temperature (1700℃). Attached Figure Description

[0053] Figure 1 This is the XRD pattern of the ceramic obtained in Example 1.

[0054] Figure 2 This is a SEM image of the ceramic obtained in Example 1.

[0055] Figure 3 This is a SEM-EDX image of the ceramic obtained in Example 1.

[0056] Figure 4 This is the XRD pattern of the ceramic obtained in Example 2.

[0057] Figure 5 This is a SEM-EDX image of the ceramic obtained in Example 2.

[0058] Figure 6 This is the XRD pattern of the ceramic obtained in Example 3.

[0059] Figure 7 This is the XRD pattern of the ceramic obtained in Example 4. Detailed Implementation

[0060] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0061] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0062] Example 1

[0063] In this embodiment, the precursor and high-entropy ceramic are prepared using the following method:

[0064] (1) Obtaining metal alkoxides: Select metal alkoxides Ti(OPr)4, Zr(OPr)4, Hf(OPr)4, Nb(OCH2CH2OCH2CH3)5 and Ta(OCH2CH2OCH2CH3)5, among which Hf(OPr)4, Nb(OCH2CH2OCH2CH3)5 and Ta(OCH2CH2OCH2CH3)5 were prepared by dispersing metal salts HfCl4, NbCl5, and TaCl5 in n-heptane, respectively. At -10°C, monohydric alcohols n-propanol, ethylene glycol ethyl ether, and ethylene glycol ethyl ether were added dropwise to the n-heptane solutions of HfCl4, NbCl5, and TaCl5, respectively, followed by the addition of triethylamine. After the addition was complete, the mixture was heated under reflux for 1 hour, and the solutions were filtered to obtain metal alkoxide solutions. The ratios of the metal salts HfCl4, NbCl5, and TaCl5 to the monohydric alcohol and triethylamine were 1:4:4, 1:5:6, and 1:5:6, respectively.

[0065] (2) Preparation of metal alkoxide complexes: Acetylacetone was added dropwise to metal alkoxides Ti(OPr)4, Zr(OPr)4, Hf(OPr)4, Nb(OCH2CH2OCH2CH3)5 and Ta(OCH2CH2OCH2CH3)5 at 40℃, and stirring was continued for 0.1 h after the addition was completed; the molar ratios of metal alkoxides Ti(OPr)4, Zr(OPr)4, Hf(OPr)4, Nb(OCH2CH2OCH2CH3)5, Ta(OCH2CH2OCH2CH3)5 and acetylacetone were 1:0.4, 1:0.8, 1:1, 1:1.25 and 1:0.6, respectively;

[0066] (3) Co-hydrolysis: The metal alkoxide complex obtained in step (2) is mixed evenly according to the same metal molar ratio. At room temperature, a mixed solution of water and n-propanol is slowly added dropwise to the system, wherein the molar ratio of water to total metal is 1.5:1 and the mass ratio of n-propanol to water is 4:1. After the addition is complete, the mixture is refluxed for 5 hours, cooled to room temperature, and rotary evaporated at 30°C until the metal content of the system is 25 wt%, thus obtaining a metal alkoxide copolymer solution.

[0067] (4) Preparation of precursor: Allylphenol aldehyde was added to the metal alkoxide copolymer solution obtained in step (3), and after stirring evenly, a mixture of borate glycerol ester and boric acid was added. The mixture was heated to 70℃ and reacted for 2 hours to obtain a uniform and transparent gel. Then, the mixture was heated to 100℃ and aged for 3 hours. It was dried by blowing air at 150℃ and cooled to obtain a high-entropy carbide-high-entropy boride multiphase ceramic precursor. The ratio of the total number of moles of metal in the metal alkoxide copolymer to the number of moles of borate glycerol ester and boric acid and the mass of allylphenol aldehyde was 1 mol: 1.5 mol: 1.5 mol: 10 g.

[0068] The obtained precursor was placed in an oven and heated to 250℃ for 2 hours to cure. Then it was pyrolyzed in a high-temperature furnace under vacuum at 1700℃ for 3 hours. After cooling, high-entropy ceramic nanopowder (Ti-Zr-Hf-Nb-Ta)C-(Ti-Zr-Hf-Nb-Ta)B2 was obtained.

[0069] The XRD pattern of the ceramic powder prepared in this embodiment is as follows: Figure 1 As shown, the XRD pattern shows two sets of diffraction peaks: one set is the diffraction peak of cubic high-entropy carbide ceramics, and the other set is the diffraction peak of high-entropy boride ceramics. This indicates that the metal elements have undergone solid solution and that the system does not contain impurity peaks of metal oxides, metal carbides, or boron carbide.

[0070] The SEM image of the ceramic powder prepared in this embodiment is as follows: Figure 2 As shown in the figure, the average particle size of the ceramic is 300 nm.

[0071] Figure 3 The image shows the SEM-EDX image of the ceramic powder prepared in this embodiment. As can be seen from the image, the elements in the nano-ceramic powder are evenly distributed.

[0072] Example 2

[0073] In this embodiment, the precursor and high-entropy ceramic are prepared using the following method:

[0074] (1) Obtaining metal alkoxides: Select metal alkoxides Ti(Oi-Pr)4, Zr(OPr)4, Hf(OPr)4, Nb(OPr)5 and Ta(OCH2CH3)5, wherein Hf(OPr)4 is prepared according to the method in Example 1; Nb(OPr)5 and Ta(OCH2CH3)5 are prepared by dispersing metal salts NbCl5 and TaCl5 in ethylene glycol dimethyl ether, respectively, adding monohydric alcohol n-propanol and ethanol dropwise at -5℃, followed by adding triethylamine dropwise, and heating under reflux for 1 h after the addition is complete, and filtering to obtain metal alkoxide solutions; wherein the ratios of metal salts NbCl5 and TaCl5 to monohydric alcohol and triethylamine are 1:8:6 and 1:5:5, respectively;

[0075] (2) Preparation of metal alkoxide complexes: Acetylacetone was added dropwise to metal alkoxides Ti(Oi-Pr)4, Zr(OPr)4, Hf(OPr)4, Nb(OPr)5 and Ta(OCH2CH3)5 at 80℃, and stirring was continued for 1 h after the addition was completed; the molar ratios of metal alkoxides Ti(Oi-Pr)4, Zr(OPr)4, Hf(OPr)4, Nb(OPr)5, Ta(OCH2CH3)5 and acetylacetone were 1:0.5, 1:1, 1:0.6, 1:0.5 and 1:1.25, respectively;

[0076] (3) Co-hydrolysis: The metal alkoxide complex obtained in step (2) is mixed evenly according to the same metal molar ratio. At room temperature, a mixed solution of water and ethylene glycol ethyl ether is slowly added dropwise to the system, wherein the molar ratio of water to total metal is 1.3:1 and the mass ratio of ethylene glycol ethyl ether to water is 6:1. After the addition is complete, the mixture is refluxed for 2 hours, cooled to room temperature, and rotary evaporated at 35°C until the metal content of the system is 30wt%, thus obtaining a metal alkoxide copolymer solution.

[0077] (4) Preparation of precursor: Allylphenol aldehyde was added to the metal alkoxide copolymer solution obtained in step (3), stirred evenly, borate glycerol was added, and the temperature was raised to 95℃ and reacted for 30 min to obtain a uniform and transparent gel. Then the temperature was raised to 110℃ and aged for 1 h, dried at 100℃, and cooled to obtain a high-entropy carbide-high-entropy boride multiphase ceramic precursor. The ratio of the total number of moles of metal in the metal alkoxide copolymer to the total number of moles of boron in the boron-containing compound to the mass of allylphenol aldehyde was 1 mol: 3 mol: 30 g.

[0078] The obtained precursor was placed in an oven and heated to 250℃ for 2 hours to cure. Then it was pyrolyzed in a high-temperature furnace under vacuum at 1800℃ for 2 hours. After cooling, (Ti-Zr-Hf-Nb-Ta)C-(Ti-Zr-Hf-Nb-Ta)B2 high-entropy ceramic nanopowder was obtained.

[0079] The XRD pattern of the ceramic prepared in this embodiment is as follows. Figure 4 As shown, the XRD pattern shows two sets of diffraction peaks: one set is the diffraction peak of cubic high-entropy carbide ceramics, and the other set is the diffraction peak of high-entropy boride ceramics. This indicates that the metal elements have undergone solid solution and that the system does not contain impurity peaks of metal oxides, metal carbides, or boron carbide.

[0080] Figure 5 The image shows the SEM-EDX image of the ceramic sample prepared in this embodiment. As can be seen from the image, the elements in the ceramic are evenly distributed.

[0081] Example 3

[0082] In this embodiment, the precursor and high-entropy ceramic are prepared using the following method:

[0083] (1) Obtaining metal alkoxides: Selected metal alkoxides Ti(OPr)4, Zr(Oi-Pr)4, Hf(Oi-Pr)4, Nb(OPr)5 and Ta(OCH2CH2OCH3)5, wherein Nb(OPr)5 is prepared according to the method in Example 2; Hf(Oi-Pr)4 and Ta(OCH2CH2OCH3)5 are prepared by dispersing metal salts HfCl4 and TaCl5 in xylene and n-hexane respectively, and adding monohydric alcohol isopropanol and ethylene glycol methyl ether dropwise at 0°C, followed by adding triethylamine dropwise. After the addition is complete, the mixture is heated under reflux for 2 hours and filtered to obtain metal alkoxide solutions; wherein the ratio of metal salt, monohydric alcohol and triethylamine is 1:4:4 and 1:10:6, respectively.

[0084] (2) Preparation of metal alkoxide complexes: At room temperature, ethyl acetoacetate was added dropwise to metal alkoxides Ti(OPr)4, Zr(Oi-Pr)4, Hf(Oi-Pr)4, Nb(OPr)5 and Ta(OCH2CH2OCH3)5 respectively, and stirring was continued for 0.5 h after the addition was completed; the molar ratios of metal alkoxides Ti(OPr)4, Zr(Oi-Pr)4, Hf(Oi-Pr)4, Nb(OPr)5 and Ta(OCH2CH2OCH3)5 to ethyl acetoacetate were 1:0.8, 1:0.6, 1:1, 1:0.8 and 1:1 respectively;

[0085] (3) Co-hydrolysis: The metal alkoxide complex obtained in step (2) is mixed evenly according to the same metal molar ratio. At room temperature, a mixed solution of water and ethylene glycol ethyl ether is slowly added dropwise to the system, wherein the molar ratio of water to total metal is 0.9:1 and the mass ratio of ethylene glycol ethyl ether to water is 5:1. After the addition is complete, the mixture is refluxed for 5 hours, cooled to room temperature, and rotary evaporated at 40°C until the metal content of the system is 35wt%, thus obtaining a metal alkoxide copolymer solution.

[0086] (4) Preparation of precursor: Allylphenol aldehyde was added to the metal alkoxide copolymer solution obtained in step (3), stirred evenly, and then trimethyl borate was added. The mixture was heated to 85°C and reacted for 1 h to obtain a uniform and transparent gel. Then, the mixture was heated to 120°C and aged for 1 h, dried under vacuum at 50°C, and cooled to obtain a high-entropy carbide-high-entropy boride multiphase ceramic precursor. The ratio of the total number of moles of metal in the metal alkoxide copolymer to the total number of moles of boron in the boron-containing compound to the mass of allylphenol aldehyde was 1 mol: 1 mol: 5 g.

[0087] The obtained precursor was placed in an oven and heated to solidify, and then pyrolyzed in a high-temperature furnace at 2000℃ for 1 h under argon atmosphere. After cooling, high-entropy ceramic nanopowder (Ti-Zr-Hf-Nb-Ta)C-(Ti-Zr-Hf-Nb-Ta)B2 was obtained.

[0088] The XRD pattern of the ceramic prepared in this embodiment is as follows. Figure 6 As shown, the XRD pattern shows two sets of diffraction peaks: one set is the diffraction peak of cubic high-entropy carbide ceramics, and the other set is the diffraction peak of high-entropy boride ceramics. This indicates that the metal elements have undergone solid solution and that the system does not contain impurity peaks of metal oxides, metal carbides, or boron carbide.

[0089] Example 4

[0090] In this embodiment, the precursor and high-entropy ceramic are prepared using the following method:

[0091] (1) Obtaining metal alkoxides: Obtaining metal alkoxides Ti(Oi-Pr)4, Zr(Oi-Pr)4, Hf(Oi-Pr)4, Nb(OCH2CH2OCH2CH3)5 and Ta(OCH2CH3)5, wherein Nb(OCH2CH2OCH2CH3)5 is prepared according to the method of Example 1, Ta(OCH2CH3)5 is prepared according to the method of Example 2, and Hf(Oi-Pr)4 is prepared according to the method of Example 3;

[0092] (2) Preparation of metal alkoxide complexes: At 80 °C, acetylacetone was added dropwise to metal alkoxides Ti(Oi-Pr)4, Zr(Oi-Pr)4, Hf(Oi-Pr)4, Nb(OCH2CH2OCH2CH3)5 and Ta(OCH2CH3)5, respectively, and stirring was continued for 1 h after the addition was completed; the molar ratios of metal alkoxides Ti(Oi-Pr)4, Zr(Oi-Pr)4, Hf(Oi-Pr)4, Nb(OCH2CH2OCH2CH3)5 and Ta(OCH2CH3)5 to acetylacetone were 1:0.6, 1:0.6, 1:0.4, 1:1 and 1:1.2, respectively;

[0093] (3) Co-hydrolysis: The metal alkoxide complex obtained in step (2) is mixed evenly according to the same metal molar ratio. At 80°C, a mixed solution of water and n-propanol is slowly added dropwise to the system, wherein the molar ratio of water to total metal is 1.1:1 and the mass ratio of n-propanol to water is 8:1. After the addition is complete, the mixture is refluxed for 2 hours, cooled to room temperature, and rotary evaporated at 35°C until the metal content of the system is 28wt% to obtain a metal alkoxide copolymer solution.

[0094] (4) Preparation of precursor: Allylphenol aldehyde was added to the metal alkoxide copolymer solution obtained in step (3), stirred evenly, and then tripropyl borate was added. The mixture was heated to 90°C and reacted for 3 hours to obtain a uniform and transparent gel. Then, the mixture was heated to 100°C and aged for 5 hours. It was then dried under vacuum at 150°C and cooled to obtain a high-entropy carbide-high-entropy boride multiphase ceramic precursor. The ratio of the total number of moles of metal in the metal alkoxide copolymer to the number of moles of boron in the boron-containing compound to the mass of allylphenol aldehyde was 1 mol: 5 mol: 20 g.

[0095] The obtained precursor was placed in an oven and heated to solidify, and then pyrolyzed in a high-temperature furnace at 2000℃ for 1 h under argon atmosphere. After cooling, high-entropy ceramic nanopowder (Ti-Zr-Hf-Nb-Ta)C-(Ti-Zr-Hf-Nb-Ta)B2 was obtained.

[0096] The XRD pattern of the ceramic prepared in this embodiment is as follows. Figure 7 As shown, the XRD pattern shows two sets of diffraction peaks: one set is the diffraction peak of cubic high-entropy carbide ceramics, and the other set is the diffraction peak of high-entropy boride ceramics. This indicates that the metal elements have undergone solid solution and that the system does not contain impurity peaks of metal oxides, metal carbides, or boron carbide.

[0097] Elemental analysis was performed on the nanoceramics prepared in this embodiment. The molar ratio of each element in the ceramics was Ti:Zr:Hf:Nb:Ta:B:C = 1:1.01:1.05:1.01:1.03:9.70:0.82, and the content of O in the ceramics was 0.7 wt%.

[0098] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-entropy carbide-high-entropy boride multiphase ceramic precursor, characterized in that, The preparation method comprises the following steps: (1) Preparation of metal alkoxide complex: a complexing agent, which is acetylacetone and / or ethyl acetoacetate, is dropped into a metal alkoxide M(OR) n solution in a solvent, and stirring is continued for 0.1-5 h after the dropping is completed to prepare a metal alkoxide complex; (2) Co-hydrolysis: at least four metal alkoxide complexes containing different metal elements prepared in step (1) are selected, mixed, and then a mixed solution of water and monohydric alcohol is added dropwise, after the dropwise addition is completed, reflux is carried out for 1-5 hours, the temperature is lowered to room temperature, and the solvent is removed by rotary evaporation at low temperature until the metal content of the system is 25-35%, to obtain a metal alkoxide copolymer solution; in step (2), the temperature of the rotary evaporation is not higher than 40°C; (3) Preparation of a precursor: an allyl phenolic aldehyde is added to the metal alkoxide copolymer solution prepared in step (2), stirred, and then a boron-containing compound is added, and the temperature is raised to 70-95°C for reaction for 30 minutes-3 hours to obtain a uniform transparent gel, and then the temperature is raised for gel aging and drying, and the temperature is lowered to obtain a high-entropy carbide-high-entropy boride composite ceramic precursor; The boron-containing compound is selected from one or a mixture of several of boric acid, trimethyl borate, tripropyl borate, and boric acid glycerol ester; The ratio of the total number of moles of metal elements in the metal alkoxide copolymer, the number of moles of boron elements in the boron-containing compound, and the mass of the allyl phenolic aldehyde is 1 mol:(1-7) mol:(5-30) g; The temperature of the aging is 90-120°C, and the time of the aging is 1-5 hours; The precursor is an organic substance, includes B and C elements, and further includes at least four of Ti, Zr, Hf, V, Nb, Ta, Mo, and W metal elements; In the precursor, the number of moles of each metal element is the same and independently accounts for 5-35% of the total number of moles of metals in the precursor. In step (1), the molar ratio of the metal alkoxide to the complexing agent is 1:(0.1-0.25)n; when M in the metal alkoxide is selected from Ti, Zr, or Hf, n is 4; when M in the metal alkoxide is selected from V, Nb, Ta, or Mo, n is 5; and when M is W, n is 6.

2. The production method according to claim 1, characterized by, In step (1), the dropwise addition temperature of the complexing agent is room temperature-80°C.

3. The preparation method according to claim 1, characterized in that, In step (2), the total molar ratio of water to metal elements is 0.9-1.5:

1.

4. The production method according to any one of claims 1 to 3, characterized by, In step (2), the mass ratio of monohydric alcohol to water is 3-8:

1.

5. The method of any one of claims 1-3, wherein, In step (2), the monohydric alcohol is selected from one or several of isopropyl alcohol, n-propanol, n-butanol, isobutyl alcohol, ethylene glycol methyl ether, and ethylene glycol ethyl ether.

6. The method of any one of claims 1-3, wherein, In step (2), the mixed solution of water and monohydric alcohol is added dropwise at room temperature-90°C.

7. A high-entropy carbide-high-entropy boride multiphasic ceramic nanopowder, characterized in that, The nano-powder is prepared by solidifying and cracking the precursor prepared by the preparation method of any one of claims 1-6 under vacuum or in an inert atmosphere at normal pressure; the nano-powder includes B and C elements, and further includes at least four of Ti, Zr, Hf, V, Nb, Ta, Mo, and W metal elements.

8. The high entropy carbide-high entropy boride multiphasic ceramic nanpowder of claim 7, wherein, In the nano-powder, the molar ratio of B elements to C elements is 1:19-38:

1.

9. The high entropy carbide-high entropy boride multiphasic ceramic nanpowder of claim 7, wherein, In the nano-powder, the amount of substance of each metal element is the same and independently accounts for 5-35% of the total amount of substance of metals in the ceramic nano-powder.

10. The high entropy carbide-high entropy boride multiphasic ceramic nanpowder of claim 7, wherein, In the nano-powder, the high-entropy carbide is a single cubic crystal phase, the high-entropy boride is a single hexagonal crystal phase, and each element is uniformly distributed at a molecular level.

11. The high entropy carbide-high entropy boride multiphasic ceramic nanpowder of claim 7, wherein, The average particle size of the nanopowder is not more than 500 nm.

12. The high entropy carbide-high entropy boride multiphasic ceramic nanopowder of claim 7, wherein, The O impurity content in the nanopowder is not more than 1 wt%.

13. The method of making high entropy carbide-high entropy boride multiphasic ceramic nanpowder of any one of claims 7-12, characterized in that, The preparation method comprises the following steps: solidifying and cracking the high-entropy carbide-high-entropy boride composite ceramic precursor prepared by the preparation method in any of claims 1-6 under vacuum or in an inert atmosphere at normal pressure to obtain the high-entropy carbide-high-entropy boride composite ceramic nanopowder.

14. The production method according to claim 13, wherein The cracking temperature is 1800-2000 ℃, and the cracking time is 0.5-5 h.

15. Application of the high-entropy carbide-high-entropy boride composite ceramic nanopowder in any of claims 7-12 in the field of ceramic matrix composites and ceramic coatings.

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