Liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor and composite ceramic and preparation method thereof

Abstract

The application discloses a liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor, a composite ceramic and a preparation method. The precursor comprises at least four of Ti, Zr, Hf, V, Nb, Ta, Mo and W elements, carbon element and silicon element, and the mole number of each metal element accounts for 5-35% of the total metal mole number of the precursor. The liquid-phase precursor contains a solvent selected from one or more of toluene, xylene, tetrahydrofuran, ethylene glycol dimethyl ether and ethylene glycol diethyl ether, and the change rate of the viscosity of the precursor is not greater than 10% after being stored at 25 DEG C for 3 months. The precursor can form the high-entropy carbide-silicon carbide composite ceramic with the metal element, the silicon element and the carbon element uniformly distributed in the nanometer size after being cracked.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-entropy materials, and relates to a liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor and a composite ceramic and a preparation method. BACKGROUND

[0002] High-entropy ceramics are a new type of ceramics that have appeared in recent years. Due to the novel "high-entropy effect" brought by the synergy of multiple components, high-entropy ceramics often have higher hardness and modulus, better oxidation resistance, lower thermal conductivity and thermal diffusion coefficient than single-component ceramics. Based on its excellent performance, high-entropy ceramics have a wide application prospect in the field of ultra-high temperature materials.

[0003] Although the oxidation resistance of high-entropy carbide ceramics is greatly improved compared with single-component ceramics, the oxidation resistance of single-component high-entropy carbide ceramics under high-temperature environment still cannot meet the use requirements. Wang et al. (Ceramics International, 2020, 46, 11160-11168) found that the parabolic oxidation rate of (Hf 0.2 Ta 0.2 Zr 0.2 Ti 0.2 Nb 0.2 )C and (Hf 0.25 Zr 0.25 Ta 0.25 Nb 0.25 )C ceramics was significantly reduced when SiC powder was introduced. However, this preparation method by mixing metal carbide powder and silicon carbide powder at high temperature and high pressure can only prepare ceramic bulk materials, and the brittleness of ceramic bulk materials limits the practical application of ceramics. Zhang et al. (Journal of the European Ceramic Society, 2022, 42, 3099-3106) first prepared (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C high-entropy ceramic powder, then brushed the high-entropy ceramic and silicon carbide ceramic powder on the carbon fiber cloth by the slurry brushing method, and then introduced silicon carbide by the precursor impregnation and pyrolysis (PIP) after hot pressing, and repeated 7 cycles to prepare C f / BN i / (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C-SiC mCeramic matrix composites. Cai et al. (Journal of the European Ceramic Society, 2021, 41, 5863-5871) first prepared C f (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C-SiC composites. Since two kinds of powder slurries or alternating impregnation method are used for composite impregnation, the metal elements and silicon elements in the prepared composite are not easy to disperse uniformly, so the effect of mutual inhibition of crystal grains cannot be achieved, and the uneven distribution of elements makes the synergistic effect between high-entropy carbides and silicon carbides not optimal, which is not conducive to further improving the material performance.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] To improve the above technical problems, the present application provides a liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor and a composite ceramic and a preparation method. The liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor of the present application has processability and can be applied in the fields of ceramic matrix composites, nano-ceramic powders, ceramic fibers and ceramic coatings, etc.

[0006] To achieve the above-mentioned application purposes, the present application adopts the following technical solutions:

[0007] The present application provides a liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor, which contains at least 4 kinds of metal elements, carbon elements and silicon elements.

[0008] According to the embodiments of the present application, the precursor further contains a solvent. For example, the solvent can be selected from one or more of toluene, xylene, tetrahydrofuran, ethylene glycol dimethyl ether and ethylene glycol diethyl ether.

[0009] According to the embodiments of the present application, the viscosity change rate of the precursor is not greater than 10% after being stored at 25°C for 3 months.

[0010] According to the embodiments of the present application, the metal elements are selected from at least 4 kinds of elements such as Ti, Zr, Hf, V, Nb, Ta, Mo and W.

[0011] According to the embodiments of the present application, the number of moles of each metal element in the precursor is the same or different, and independently accounts for 5-35% of the total number of moles of metal in the precursor; exemplary values are 5%, 10%, 15%, 20%, 30% and 35%.

[0012] Preferably, the number of moles of each metal element in the precursor is the same.

[0013] According to an embodiment of the present application, the precursor can form a high-entropy carbide-silicon carbide composite ceramic with uniform distribution of metal elements, silicon elements and carbon elements in nanometer size after cracking.

[0014] According to an embodiment of the present application, the liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor is prepared by mixing a metal alkoxide copolymer as a metal source, polycarbosilane as a silicon source and allyl phenolic as a carbon source.

[0015] Preferably, the ratio of the total number of moles of metal in the metal alkoxide copolymer to the weight of allyl phenolic and the weight of polycarbosilane is 1 mol:(17-25) g:(30-7100) g.

[0016] The present application also provides a preparation method of the above-mentioned liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor, which comprises the following steps:

[0017] (1) Preparation of metal alkoxide complex: adding a complexing agent to a metal alkoxide M(OR) n and continuing to stir for 0.1-5 h to obtain a metal alkoxide complex;

[0018] (2) Co-hydrolysis: selecting at least four metal alkoxide complexes containing different metal elements prepared according to step (1), mixing, adding a mixture of water and monohydric alcohol dropwise, refluxing for 1-5 h after dropping, distilling out 1 / 3-1 / 2 of the mass of the system under reduced pressure, adding the same mass of weakly polar solvent, repeating the process of distilling under reduced pressure and adding weakly polar solvent for 2-5 times, and distilling under normal pressure until the metal content of the system is 20-30 wt% to obtain a metal alkoxide copolymer solution;

[0019] (3) Preparation of precursor: adding allyl phenolic to the metal alkoxide copolymer solution prepared in step (2), mixing, then adding polycarbosilane, and mixing to obtain the liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor.

[0020] In the preparation process of the high-entropy carbide-silicon carbide composite ceramic, the metal source is prepared by co-hydrolysis of metal alkoxide to ensure the uniform distribution of each metal at the molecular level; the metal source is mixed with the carbon source to ensure the uniform distribution of the metal source and the carbon source at the molecular level, which is beneficial to the carbothermic reduction reaction and the formation of the solid solution of the metal carbide in the cracking process. Generally, the metal alkoxide copolymer has strong polarity and can only be dissolved in strong polar solvents such as alcohol solvents; and the alcohol solvent will react with the silicon source polycarbosilane to cause gelation, so that the liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor with uniform dispersion of metal and silicon cannot be obtained. In the present application, the by-products and solvents are removed by multiple vacuum distillation to reduce the residual alcohol oxygen group in the product, and weak polar solvents are gradually added to prevent the displacement reaction between the alcohol oxygen group of the metal alkoxide and the monohydric alcohol solvent from affecting the complete hydrolysis of the alkoxide, and finally the hydroxyl groups in the system are further condensed by atmospheric distillation to improve the storage stability of the product. The metal alkoxide copolymer prepared in the present application can be stably stored in a weak polar solvent, and can also be stably coexisted with the silicon source and the carbon source in a weak polar solvent, so that the silicon source and the metal source are uniformly distributed at the molecular level, and the high-entropy carbide and the silicon carbide grain size are mutually inhibited in the cracking process of the precursor, and the high-entropy carbide-silicon carbide composite ceramic with uniform distribution of metal elements and silicon elements at the nanometer scale is generated.

[0021] The precursor obtained by the above preparation method is in liquid phase, and the viscosity change rate of the precursor is not greater than 10% after being stored at 25℃ for 3 months, so that the precursor has processability and can be applied in the fields of ceramic matrix composites, nano ceramic powders, ceramic fibers and ceramic coatings.

[0022] According to the embodiment of the present application, in step (1), the molar ratio of the metal alkoxide and the complexing agent is 1:(0.15-0.5)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.

[0023] According to the embodiment of the present application, the complexing agent is acetylacetone and / or ethyl acetoacetate.

[0024] According to the embodiment of the present application, in step (1), the dropping temperature of the complexing agent is room temperature-80℃.

[0025] According to the embodiment of the present application, in step (2), the total molar ratio of water to metal elements is (0.8-1.3):1, and exemplary values are 0.8:1, 1.0:1, 1.2:1 and 1.3:1.

[0026] According to the embodiment of the present application, in step (2), the mass ratio of monohydric alcohol to water is 3-8:1, and exemplary values are 3:1, 5:1 and 8:1.

[0027] According to the embodiment of the present application, in step (2), 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.

[0028] According to the embodiment of the present application, in step (2), the dropping temperature of the mixture of water and monohydric alcohol is room temperature to 90°C.

[0029] According to the embodiment of the present application, in step (2), the temperature of the reduced pressure distillation is 80-120°C, and exemplary temperatures are 80°C, 90°C, 100°C, and 120°C.

[0030] According to the embodiment of the present application, in step (2), the weakly polar solvent can be selected from one or more of toluene, xylene, tetrahydrofuran, ethylene glycol dimethyl ether, and ethylene glycol diethyl ether.

[0031] According to the embodiment of the present application, in step (3), the ratio of the total moles of metal in the metal alkoxide copolymer, the weight of the allyl phenolic resin, and the weight of the polycarbosilane is 1 mol:(17-25) g:(30-7100) g, and exemplary ratios are 1 mol:17 g:30 g, 1 mol:20 g:30 g, 1 mol:25 g:30 g, 1 mol:17 g:45 g, 1 mol:20 g:500 g, 1 mol:23 g:95 g, 1 mol:17 g:1000 g, 1 mol:17 g:5000 g, 1 mol:17 g:7100 g, 1 mol:25 g:3000 g, and 1 mol:25 g:7100 g.

[0032] In the above preparation method, the molar mass of different metals is different, and it is inconvenient to unify the mass to the same range. In the present application, the total moles of metal in the metal alkoxide copolymer are used for calculation. Allyl phenolic resin and polycarbosilane are non-homopolymer polymers, and it is not suitable to use moles to express. Therefore, the ratio of moles to mass is used for expression. The above ratio of the amount of metal alkoxide copolymer to allyl phenolic resin and polycarbosilane is derived by considering the amount of carbon required for carbonthermal reduction in the pyrolysis process and the target ratio of high-entropy carbide to silicon carbide in the ceramic. If the ratio is not appropriate, metal oxide impurities will be contained in the prepared high-entropy carbide-silicon carbide composite ceramic, or the target ratio of high-entropy carbide-silicon carbide composite ceramic cannot be obtained.

[0033] According to the embodiment of the present application, when M in the metal alkoxide is selected from Hf, V, Nb, Ta, Mo, or W, the metal alkoxide is prepared by reacting a metal salt with a monohydric alcohol, and the specific method is as follows: a metal salt MCl n or M(NO3) nThe metal salt, the monohydric alcohol and the triethylamine are in a ratio of 1:(1-2)n:(1-1.5)n; the organic solvent is one or more of n-hexane, n-heptane, toluene, xylene, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and t-butyl methyl ether; and the monohydric alcohol is one or more of methanol, ethanol, isopropyl alcohol, n-propanol, n-butanol, isobutyl alcohol, ethylene glycol methyl ether, and ethylene glycol ethyl ether.

[0034] According to an embodiment of the present application, the preparation method of the liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor comprises the following steps:

[0035] (1) obtaining a metal alkoxide: selecting transition metal alkoxides containing different types of elements, when M in the metal alkoxide is selected from Hf, V, Nb, Ta, Mo or W, the metal alkoxide is prepared by the following method: dissolving a metal salt MCl n or M(NO3) n in an organic solvent, and then adding a monohydric alcohol dropwise at -10-5°C, followed by adding triethylamine dropwise, heating to reflux for 1-5 h, and filtering to obtain a metal alkoxide solution;

[0036] (2) preparing a metal alkoxide complex: under the condition of room temperature-80°C, a complexing agent is added dropwise to the metal alkoxide M(OR) n selected in step (1), and stirring for 0.1-5 h after the dropping is completed to obtain a metal alkoxide complex;

[0037] (3) co-hydrolysis: selecting at least four metal alkoxide complexes containing different metal elements prepared in step (2), mixing uniformly, and then slowly adding a mixed solution of water and a monohydric alcohol under the condition of room temperature-90°C, wherein the molar ratio of water to total metal is 0.9-1.3:1, and the mass ratio of the monohydric alcohol to water is 3-8:1, refluxing for 1-5 h after the dropping is completed, distilling off 1 / 3-1 / 2 of the mass of the system at 80-120°C under reduced pressure, adding the same mass of a weak polar solvent, repeating the process of distilling under reduced pressure and adding the weak polar solvent for 2-5 times, and distilling under normal pressure until the metal content in the system is 20-30 wt% to obtain a metal alkoxide copolymer solution;

[0038] (4) preparing a precursor: adding an allyl phenolic aldehyde to the metal alkoxide copolymer solution prepared in step (3), mixing, then adding a polycarbosilane, and mixing to obtain a high-entropy carbide-silicon carbide composite ceramic precursor.

[0039] In the above scheme, in order to achieve a molecular level uniform distribution of the metal source (metal alkoxide copolymer), the carbon source (allyl phenol formaldehyde) and the silicon source (polycarbosilane) in the precursor, and to maintain a uniform distribution of each element in the solidification and pyrolysis process, the present application controls the reaction conditions in the preparation of the metal source, such as the amount of ligand and water, the control of the post-reaction treatment method, so that the residual alkoxy and hydroxy groups in the metal source are as few as possible to reduce their polarity, so that they can be dissolved in a weak polar solvent together with the carbon source and the silicon source and can be stored stably. The method of the present application makes the metal, carbon, silicon and the like in the precursor to be uniformly distributed at a molecular level, and then makes each element to be distributed in a short distance in the pyrolysis process, which is beneficial to the carbothermic reduction reaction between each metal element and the carbon source and the solid solution reaction between the metal elements to obtain a carbide solid solution with uniform distribution of elements, and the high-entropy carbide and silicon carbide grain sizes are mutually inhibited in the pyrolysis process to generate a high-entropy carbide-silicon carbide composite ceramic with uniform distribution of metal elements and silicon elements at a nanometer scale.

[0040] The present application also provides a high-entropy carbide-silicon carbide composite ceramic, which comprises at least four of Ti, Zr, Hf, V, Nb, Ta, Mo and W metal elements, and further comprises Si and C elements.

[0041] According to an embodiment of the present application, in the high-entropy carbide-silicon carbide composite ceramic, the number of moles of each metal element is the same or different, and independently accounts for 5-35% of the total number of moles of metal in the ceramic nano-powder; exemplary values are 5%, 10%, 15%, 20%, 30% and 35%. Preferably, the number of moles of each metal element is equal.

[0042] According to an embodiment of the present application, in the high-entropy carbide-silicon carbide composite ceramic, the ratio of the total number of moles of metal elements to the number of moles of silicon elements is 1:20-20:1; exemplary values are 1:20, 1:10, 1:1, 10:1, 15:1 and 20:1.

[0043] According to an embodiment of the present application, the high-entropy carbide-silicon carbide composite ceramic contains two crystal phases of high-entropy carbide and silicon carbide, and each metal element and the silicon element are uniformly distributed at a nanometer level.

[0044] According to an embodiment of the present application, the high-entropy carbide-silicon carbide composite ceramic is prepared by pyrolysis of the above-mentioned high-entropy carbide-silicon carbide composite ceramic precursor under vacuum or in an inert atmosphere at normal pressure.

[0045] According to an embodiment of the present application, the inert atmosphere can be argon, helium or a mixed atmosphere thereof.

[0046] The application further provides a preparation method of the high-entropy carbide-silicon carbide composite ceramic.

[0047] According to the embodiment of the application, the cracking temperature is not lower than 1600 DEG C, preferably the cracking temperature is 1700-2000 DEG C, and exemplarily is 1700 DEG C, 1800 DEG C, 1900 DEG C or 2000 DEG C; and the cracking time is 0.5-5 h, and exemplarily is 0.5 h, 1 h, 2 h, 3 h, 4 h or 5 h.

[0048] According to the embodiment of the application, the cracking is carried out under vacuum environment or inert atmosphere protection.

[0049] Preferably, the solidification atmosphere is air, the solidification temperature is 100-250 DEG C, and exemplarily is 100 DEG C, 150 DEG C, 200 DEG C or 250 DEG C; and the solidification time is 2-24 h, and exemplarily is 2 h, 5 h, 8 h, 12 h or 24 h.

[0050] In the prior art, the high-entropy carbide-silicon carbide composite ceramic is usually prepared by an inorganic powder method, and the metal elements and silicon elements are not easy to be uniformly dispersed, and the effect of mutual inhibition of the grains cannot be achieved. When the high-entropy carbide-silicon carbide composite material is prepared, the high-entropy carbide and silicon carbide precursors are respectively immersed, and the metal elements and silicon elements cannot be uniformly dispersed, the grains of the two elements cannot be inhibited in the cracking process, and the period of immersing the two precursors is long, and the process is complex. The high-entropy carbide-silicon carbide composite ceramic precursor of the application can solve the above problems, and a material with better mechanical and ablation properties can be obtained.

[0051] The application has the following beneficial effects:

[0052] The application prepares a liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor. Since the elements in the precursor are uniformly dispersed at the molecular level, the uniform distribution of the elements can be maintained in the solidification and cracking processes, and the uniform distribution of the elements in the high-entropy carbide-silicon carbide composite ceramic can be achieved. Since the metal elements and silicon elements exist in the precursor at the same time, the grains of the high-entropy carbide and silicon carbide can be inhibited in the cracking process, and the interface problem caused by the large-size phase separation can be effectively prevented.

[0053] The liquid-phase high-entropy carbide-silicon carbide composite ceramic precursor of the application has a viscosity change rate of not more than 10% after being stored for 3 months at 25 DEG C, so that the precursor has a good processing window and can be applied in the fields of ceramic matrix composites, nano ceramic powders, ceramic fibers and ceramic coatings. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 is an XRD pattern of the ceramic obtained in Example 2;

[0055] Figure 2 is an XRD pattern of the ceramic obtained in Example 3;

[0056] Figure 3 is an SEM-EDX pattern of the ceramic obtained in Example 3;

[0057] Figure 4 is an XRD pattern of the ceramic obtained in Example 4. DETAILED DESCRIPTION

[0058] The technical solutions of the present application will be further described in detail below in combination with specific examples. It should be understood that the following examples are only illustratively used to explain and describe the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is covered within the scope of protection intended by the present application.

[0059] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0060] Example 1

[0061] In this embodiment, the precursor and high-entropy ceramic are prepared by the following method:

[0062] (1) Obtain metal alkoxides: select metal alkoxides Ti(OPr)4, Zr(OPr)4, Hf(OPr)4, Nb(OCH2CH2OCH2CH3)5, and Ta(OCH2CH2OCH2CH3)5, wherein Hf(OPr)4, Nb(OCH2CH2OCH2CH3)5, and Ta(OCH2CH2OCH2CH3)5 are obtained by dispersing metal salts HfCl4, NbCl5, and TaCl5 in n-hexane, respectively, and then adding monohydric alcohol n-propanol, ethylene glycol ethyl ether, and ethylene glycol ethyl ether to the n-hexane solution of the metal salt HfCl4, NbCl5, and TaCl5 at -10°C, respectively, followed by the dropwise addition of triethylamine, and heating to reflux for 1 h, and then filtering to obtain a metal alkoxide solution; wherein the molar ratio of the metal salts HfCl4, NbCl5, and TaCl5 to the monohydric alcohol and triethylamine is 1:4:4, 1:5:6, and 1:5:6, respectively;

[0063] (2) Preparation of metal alkoxide complex: acetylacetone was added dropwise into metal alkoxide Ti(OPr)4, Zr(OPr)4, Hf(OPr)4, Nb(OCH2CH2OCH2CH3)5 and Ta(OCH2CH2OCH2CH3)5 respectively at 40℃, and stirring was continued for 0.1h after the dropwise addition was completed; the molar ratios of metal alkoxide Ti(OPr)4, Zr(OPr)4, Hf(OPr)4, Nb(OCH2CH2OCH2CH3)5, Ta(OCH2CH2OCH2CH3)5 and acetylacetone were 1:0.6, 1:0.7, 1:0.8, 1:1 and 1:2 respectively;

[0064] (3) Co-hydrolysis: the metal alkoxide complexes obtained in step (2) were mixed uniformly at an equal metal molar ratio, and a mixed solution of water and n-propanol was slowly added to the system at room temperature, wherein the molar ratio of water to total metal was 1:1, and the mass ratio of n-propanol to water was 4:1; after the dropwise addition was completed, reflux was continued for 5h, 1 / 2 of the mass of the system was distilled under reduced pressure at 90℃, the same mass of ethylene glycol dimethyl ether was added, and the process of distillation under reduced pressure and addition of ethylene glycol dimethyl ether weak polar solvent was repeated for 3 times, and then atmospheric distillation was carried out until the metal content of the system was 25wt%, to obtain a metal alkoxide copolymer solution;

[0065] (4) Preparation of precursor: allyl phenolic aldehyde was added to the metal alkoxide copolymer solution prepared in step (3), and after mixing uniformly, polycarbosilane PCS was added, and after mixing uniformly, a high-entropy carbide-silicon carbide composite ceramic precursor was obtained; the ratio of the total number of moles of metal in the metal alkoxide copolymer to the weight of allyl phenolic aldehyde to the weight of polycarbosilane was 1mol:25g:30g.

[0066] The obtained precursor was heated and cured in an oven at 250℃ for 3h, and then pyrolyzed at 1700℃ under argon in a high-temperature furnace for 2h, and then cooled to obtain a (Ti-Zr-Hf-Nb-Ta)C-SiC composite ceramic.

[0067] Elemental analysis showed that the element weight percentages of Ti, Zr, Hf, Nb, Ta, Si and C in the composite ceramic prepared in this embodiment were 7.3%, 14%, 28.1%, 14.2%, 28.3%, 1.2% and 8.8% respectively.

[0068] Example 2

[0069] In this embodiment, the precursor and high-entropy ceramic were prepared by the following method:

[0070] (1) Preparation of metal alkoxide: metal alkoxides Ti(Oi-Pr)4, Zr(OPr)4, Hf(OPr)4, Nb(OPr)5 and Ta(OCH2CH3)5 were selected, wherein Hf(OPr)4 was prepared according to the method of Example 1; Nb(OPr)5 and Ta(OCH2CH3)5 were prepared by dispersing metal salts NbCl5 and TaCl5 in ethylene glycol dimethyl ether, respectively, at -5℃, dropping monohydric alcohol n-propanol and ethanol, respectively, then dropping triethylamine, heating to reflux for 1h, and filtering to obtain metal alkoxide solutions, respectively; wherein the molar ratios of metal salts NbCl5 and TaCl5 to monohydric alcohol and triethylamine were 1:8:6 and 1:5:5, respectively;

[0071] (2) Preparation of metal alkoxide complex: acetylacetone was dropped into metal alkoxides Ti(Oi-Pr)4, Zr(OPr)4, Hf(OPr)4, Nb(OPr)5 and Ta(OCH2CH3)5 at 80℃, respectively, and stirring was continued for 1h after dropping; the molar ratios of metal alkoxides Ti(Oi-Pr)4, Zr(OPr)4, Hf(OPr)4, Nb(OPr)5, Ta(OCH2CH3)5 to acetylacetone were 1:0.6, 1:0.9, 1:1.6, 1:0.75 and 1:2, respectively;

[0072] (3) Co-hydrolysis: the metal alkoxide complexes obtained in step (2) were mixed uniformly at equal metal molar ratios, a mixed solution of water and n-propanol was slowly dropped into the system at room temperature, wherein the molar ratio of water to total metal was 1.3:1, and the mass ratio of n-propanol to water was 6:1; after dropping, the system was refluxed for 2h, 1 / 3 of the mass of the system was distilled off under reduced pressure at 80℃, the same mass of dimethylbenzene was added, and the process of distillation under reduced pressure and addition of dimethylbenzene weak polar solvent was repeated 4 times, and then atmospheric distillation was carried out until the metal content of the system was 20wt%, to obtain a metal alkoxide copolymer solution;

[0073] (4) Preparation of precursor: allyl phenolic aldehyde was added to the metal alkoxide copolymer solution prepared in step (3), and then polycarbosilane PCS was added, to obtain a high-entropy carbide-silicon carbide composite ceramic precursor; the ratio of the total number of moles of metal in the metal alkoxide copolymer to the weight of allyl phenolic aldehyde to the weight of polycarbosilane was 1 mol:17g:45g.

[0074] The obtained precursor was heated and cured in an oven at 150℃ for 10h, and then pyrolyzed at 1800℃ for 2h under argon in a high-temperature furnace, to obtain a (Ti-Zr-Hf-Nb-Ta)C-SiC composite ceramic.

[0075] The XRD pattern of the composite ceramic prepared in this example is shown in Figure 1As shown, there are only two groups of diffraction peaks in the XRD diagram, one group is the diffraction peaks of high-entropy carbide (Ti-Zr-Hf-Nb-Ta)C, and the other group is the diffraction peaks of SiC ceramic, which indicates that each metal atom is completely solid-solved into a crystal lattice.

[0076] Elemental analysis shows that the weight percentages of Ti, Zr, Hf, Nb, Ta, Si and C in the prepared composite ceramic in this embodiment are 7.1%, 13.3%, 27%, 13.7%, 27.2%, 2% and 10%, respectively.

[0077] Example 3

[0078] In this embodiment, the precursor and high-entropy ceramic are prepared by the following method:

[0079] (1) Obtain metal alkoxide: select metal alkoxide Ti(OPr)4, Hf(Oi-Pr)4, Nb(OPr)5, Ta(OCH2CH2OCH2CH3)5 and Mo(OCH2CH2OCH3)5, wherein Nb(OPr)5 is prepared according to the method of Example 2; Ta(OCH2CH2OCH2CH3)5 is prepared according to the method of Example 1; Hf(Oi-Pr)4 and Mo(OCH2CH2OCH3)5 are obtained by dispersing metal salts HfCl4 and MoCl5 in dimethylbenzene and n-hexane respectively, and then dropping monohydric alcohol isopropyl alcohol and ethylene glycol methyl ether at 0°C, followed by dropping triethylamine, and then heating to reflux for 2h, and then filtering to obtain metal alkoxide solution; wherein the molar ratio of metal salts HfCl4 and MoCl5 to monohydric alcohol and triethylamine is 1:4:4 and 1:10:6 respectively;

[0080] (2) Prepare metal alkoxide complex: at room temperature, drop ethyl acetoacetate into metal alkoxide Ti(OPr)4, Hf(Oi-Pr)4, Nb(OPr)5, Ta(OCH2CH2OCH2CH3)5 and Mo(OCH2CH2OCH3)5 respectively, and continue stirring for 0.5h after dropping; the molar ratio of metal alkoxide Ti(OPr)4, Hf(Oi-Pr)4, Nb(OPr)5, Ta(OCH2CH2OCH2CH3)5 and Mo(OCH2CH2OCH3)5 to ethyl acetoacetate is 1:1.6, 1:0.6, 1:1, 1:0.8 and 1:2 respectively;

[0081] (3) Co-hydrolysis: the metal alkoxide complex obtained in step (2) is mixed uniformly at an equal metal molar ratio, a mixed solution of water and ethylene glycol dimethyl ether is slowly added to the system at room temperature, the molar ratio of water to total metal is 0.9:1, and the mass ratio of ethylene glycol dimethyl ether to water is 5:1, after dropping, reflux for 5h, distill 2 / 5 of the mass of the system at 100℃ under reduced pressure, add the same mass of ethylene glycol dimethyl ether, repeat the process of distillation under reduced pressure and addition of ethylene glycol dimethyl ether weak polar solvent for 5 times, and then distill under normal pressure until the metal content in the system is 30wt%, to obtain a metal alkoxide copolymer solution;

[0082] (4) Preparation of precursor: allyl phenolic aldehyde is added to the metal alkoxide copolymer solution prepared in step (3), mixed uniformly, then polycarbosilane PCS is added, mixed uniformly, to obtain a high-entropy carbide-silicon carbide composite ceramic precursor; the total number of moles of metal in the metal alkoxide copolymer, the weight of allyl phenolic aldehyde, and the weight of polycarbosilane are in a ratio of 1mol:20g:500g.

[0083] The obtained precursor is heated and cured in an oven at 200℃ for 8h, then pyrolyzed at 1800℃ under vacuum in a high-temperature furnace for 2h, and cooled to obtain a (Ti-Hf-Nb-Ta-Mo)C-SiC composite ceramic.

[0084] The XRD pattern of the composite ceramic prepared in this example is shown in Figure 2 The XRD pattern has only two sets of diffraction peaks, one set of diffraction peaks of high-entropy carbide (Ti-Hf-Nb-Ta-Mo)C, and one set of diffraction peaks of SiC ceramic, indicating that each metal atom is completely solid-soluted into a crystal lattice.

[0085] Figure 3 The SEM-EDX pattern of (Ti-Hf-Nb-Ta-Mo)C-SiC composite ceramic is shown in the figure, from which it can be seen that Ti, Hf, Nb, Ta, Mo, Si, C and other elements are uniformly distributed in the obtained ceramic, especially the metal elements and Si elements are uniformly distributed at a nanoscale.

[0086] Example 4

[0087] In this example, the precursor and high-entropy ceramic are prepared by the following method:

[0088] (1) Obtain metal alkoxide: obtain metal alkoxide 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;

[0089] (2) Preparation of metal alkoxide complex: 80℃, acetylacetone was added dropwise into metal alkoxide 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 1h after the dropwise addition was completed; the molar ratio of metal alkoxide Ti(Oi-Pr)4, Zr(Oi-Pr)4, Hf(Oi-Pr)4, Nb(OCH2CH2OCH2CH3)5 and Ta(OCH2CH3)5 to acetylacetone was 1:0.6, 1:0.6, 1:1, 1:1.5 and 1:2 respectively;

[0090] (3) Co-hydrolysis: the metal alkoxide complexes obtained in step (2) were mixed uniformly at an equal metal molar ratio, and a mixed solution of water and n-propanol was slowly added into the system at 80℃, wherein the molar ratio of water to total metal was 1.1:1, and the mass ratio of n-propanol to water was 8:1; after the dropwise addition was completed, reflux was continued for 2h; 1 / 2 of the mass of the system was distilled under reduced pressure at 80℃, and the same mass of toluene was added; the process of distillation under reduced pressure and addition of toluene was repeated 5 times; then, normal pressure distillation was performed until the metal content of the system was 28wt%, thereby obtaining a metal alkoxide copolymer solution;

[0091] (4) Preparation of precursor: allyl phenolic aldehyde was added into the metal alkoxide copolymer solution prepared in step (3), and then polycarbosilane PCS was added after mixing; after mixing, a high-entropy carbide-silicon carbide composite ceramic precursor was obtained; the total number of moles of metal in the metal alkoxide copolymer, the weight of allyl phenolic aldehyde and the weight of polycarbosilane were in the ratio of 1mol:23g:95g.

[0092] The obtained precursor was heated and cured in an oven at 150℃ for 10h, and then pyrolyzed at 1800℃ for 2h under argon in a high-temperature furnace, thereby obtaining a (Ti-Zr-Hf-Nb-Ta)C-SiC composite ceramic.

[0093] Elemental analysis showed that the weight percentages of Ti, Zr, Hf, Nb, Ta, Si and C in the composite ceramic prepared in this example were 5.1%, 9.6%, 19.4%, 9.8%, 19.6%, 20.2% and 15.2% respectively.

[0094] The XRD pattern of the composite ceramic prepared in this example is shown in Figure 4 The XRD pattern showed only two sets of diffraction peaks, one set of diffraction peaks of high-entropy carbide (Ti-Zr-Hf-Nb-Ta)C and one set of diffraction peaks of SiC ceramic, which indicated that each metal atom was completely solid-solved in one crystal lattice.

[0095] The above describes the embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, and the like made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a liquid phase high-entropy carbide-silicon carbide composite ceramic precursor, characterized in that, The preparation method comprises the following steps: (1) Preparation of metal alkoxide complex: drop the complexing agent into the metal alkoxide M(OR) n element selected from at least 4 kinds of Ti, Zr, Hf, V, Nb, Ta, Mo, W elements; (2) co-hydrolysis: selecting at least four metal alkoxide complexes containing different metal elements prepared in step (1), mixing, then adding a mixed solution of water and monohydric alcohol dropwise, refluxing for 1-5 hours after dropping, distilling out 1 / 3-1 / 2 of the mass of the system under reduced pressure, supplementing the same mass of weak polar solvent, repeating the process of distilling under reduced pressure-supplementing weak polar solvent for 2-5 times, and distilling under normal pressure until the metal content of the system is 20-30 wt%, to prepare a metal alkoxide copolymer solution; The weak polar solvent is selected from one or more of toluene, xylene, tetrahydrofuran, ethylene glycol dimethyl ether, and ethylene glycol diethyl ether; The temperature of the distillation under reduced pressure is 80-120°C; (3) Preparation of precursor: adding allyl phenolic aldehyde into the metal alkoxide copolymer solution prepared in step (2), mixing, then adding polycarbosilane, mixing to obtain the liquid phase high-entropy carbide-silicon carbide composite ceramic precursor; the precursor can form high-entropy carbide with uniform distribution of metal elements, silicon elements and carbon elements in nanometer size after cracking silicon carbide composite ceramic The total number of moles of metal in the metal alkoxide copolymer, the weight of allyl phenol formaldehyde, and the weight of polycarbosilane are in the ratio of 1 mol:(17-25) g:(30-7100) g; the molar ratio of the metal alkoxide and the complexing agent is 1:(0.15-0.5) 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, The complexing agent is acetylacetone and / or ethyl acetoacetate.

3. The preparation method according to claim 1, characterized in that, The dropping temperature of the complexing agent is room temperature-80°C.

4. The production method according to any one of claims 1 to 3, characterized by, In step (2), the molar ratio of water to total metal is 0.8-1.3:

1.

5. The method of any one of claims 1-3, wherein, In step (2), the mass ratio of monohydric alcohol to water is 3-8:

1.

6. The method of any one of claims 1-3, wherein, In step (2), the monohydric alcohol is selected from one or more of methanol, ethanol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, isobutyl alcohol, ethylene glycol dimethyl ether, and ethylene glycol diethyl ether.

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

8. A method of producing a high-entropy carbide-silicon carbide composite ceramic, characterized by, The preparation method comprises solidifying and pyrolyzing the high-entropy carbide-silicon carbide composite ceramic precursor prepared by the preparation method of any one of claims 1-7 to prepare the high-entropy carbide-silicon carbide composite ceramic. The pyrolysis temperature is 1700-2000°C, and the pyrolysis time is 0.5-5 hours; The pyrolysis is performed in a vacuum environment or under the protection of an inert atmosphere; The solidification atmosphere is air, the solidification temperature is 100-250°C, and the solidification time is 2-24 hours.

Images