HIGH-ENTROPY CARBIDE CERAMIC AND RARE EARTH-CONTAINING HIGH-ENTROPY CARBIDE CERAMIC, FIBERS AND PRECURSORS THEREOF, AND METHODS FOR PREPARING THE SAME

Abstract

Provided are a high-entropy carbide ceramic, a rare earth-containing high-entropy carbide ceramic, fibers thereof, precursors thereof, and preparation methods thereof. The precursor includes at least four elements selected from Ti, Zr, Hf, V, Nb, Ta, Mo, and W, with each metal element accounting for 5-35% of the total molar quantity of metal elements in the precursor. The rare earth-containing high-entropy carbide ceramic precursor includes at least four transition metal elements and at least one rare-earth metal element. The high-entropy ceramic is a single-crystal-phase high-performance ceramic prepared from the precursor, with each element being homogenously distributed at molecular level. The method for preparing the high-entropy ceramic fiber includes uniformly mixing high-entropy carbide ceramic precursor containing target metal elements with spinning aid and solvent to prepare a spinnable precursor solution, followed by spinning, pyrolyzation, and high-temperature solid solution to prepare the high-entropy carbide ceramic fiber.

Claims

1-32. (canceled)

33. A high-entropy carbide ceramic precursor, comprising at least four transition metal elements, wherein each metal element accounts for 5-35% of the total molar quantity of metal elements in the high-entropy carbide ceramic precursor.

34. The high-entropy carbide ceramic precursor according to claim 33, wherein the transition metal elements are selected from Ti, Zr, Hf, V, Nb, Ta, Mo, and W, and the high-entropy carbide ceramic precursor is soluble in at least one selected from methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol methyl ether, and ethylene glycol ethyl ether.

35. The high-entropy carbide ceramic precursor according to claim 34, wherein the high-entropy carbide ceramic precursor has a viscosity change of less than 6% over 12 months, Preferably, wherein molar quantities of each metal element in the high-entropy carbide ceramic precursor are equal.

36. The high-entropy carbide ceramic precursor according to claim 34, further comprising at least one rare-earth metal element.

37. The high-entropy carbide ceramic precursor according to claim 36, wherein the rare-earth metal element is selected from Y and La.

38. The high-entropy carbide ceramic precursor according to claim 37, the high-entropy carbide ceramic precursor has a viscosity change of less than 8% over 12 months, preferably, wherein molar quantities of each metal element in the high-entropy carbide ceramic precursor are equal.

39. A method for preparing the high-entropy carbide ceramic precursor according to claim 33, comprising steps of: (1) obtaining metal alkoxide complexes: adding dropwise a complexing agent into metal alkoxides M(OR).sub.n, followed by stirring for 0.1-5 hours to obtain the metal alkoxide complexes; (2) cohydrolysis: selecting at least four metal alkoxide complexes comprising different metal elements prepared according to step (1), and mixing the same uniformly, followed by dropwise adding of a mixture of water and a monohydric alcohol, refluxing for 1-5 hours, and then atmospheric distillation to obtain a metal alkoxide copolymer; or, selecting at least four transition metal alkoxide complexes comprising different metal elements prepared according to step (1), and mixing the same uniformly with rare earth element-containing compound, followed by dropwise adding of a mixture of water and a monohydric alcohol into the resulted system at a temperature ranging from room temperature to 90° C., refluxing for 1-5 hours, and then atmospheric distillation to obtain a metal alkoxide copolymer; and (3) preparing the precursor: mixing the metal alkoxide copolymer prepared in step (2) uniformly with allyl-functional novolac resin, followed by heating to 50-90° C. for 0.5-4 hours, and then cooling to obtain the high-entropy carbide ceramic precursor or the rare earth-containing high-entropy carbide ceramic precursor.

40. The method for preparing the high-entropy carbide ceramic precursor according to claim 39, wherein in step (1), a molar ratio of each metal alkoxide to the complexing agent is 1:(0.15-0.5)n; when M in the metal alkoxides is selected from Ti, Zr, and Hf, n is 4; when M in the metal alkoxides is selected from V, Nb, Ta, and Mo, n is 5; when M is W, n is 6; and the complexing agent is acetylacetone and/or ethyl acetoacetate.

41. The method for preparing the high-entropy carbide ceramic precursor according to claim 40, wherein in step (2), a molar ratio of water to total metal elements is 0.8-1.3:1; a mass ratio of the monohydric alcohol to water is 3-8:1; and the monohydric alcohol is one or more selected from methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol methyl ether, and ethylene glycol ethyl ether.

42. The method for preparing the high-entropy carbide ceramic precursor according to claim 41, wherein in step (3), a ratio of the total molar quantity of metal elements in the metal alkoxide copolymer to the mass of the allyl-functional novolac resin is 1 mol:13-15 g or 1 mol:18-20 g.

43. The method for preparing the high-entropy carbide ceramic precursor according to claim 39, wherein when M in the metal alkoxides is selected from Hf, V, Nb, Ta, Mo, and W, the metal alkoxides in step (1) are prepared by reacting a metal salt with a monohydric alcohol as follows: dispersing the metal salt MCl.sub.n or M(NO.sub.3).sub.n in a solvent, followed by dropwise adding monohydric alcohol at −10 to 5° C. and then adding dropwise triethylamine to obtain a mixture, which is then refluxed for 1-5 hours and filtered to obtain a metal alkoxide solution, wherein a ratio of the metal salt to the monohydric alcohol to triethylamine is 1:(1-2)n:(1-1.5)n; the solvent is one or more selected from n-hexane, n-heptane, toluene, xylene, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and tert-butyl methyl ether; and the monohydric alcohol is one or more selected from methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol methyl ether, and ethylene glycol ethyl ether.

44. The method for preparing the high-entropy carbide ceramic precursor according to claim 39, wherein in step (1), the complexing agent is added dropwise into the metal alkoxides M(OR).sub.n at a temperature ranging from room temperature to 80° C., and in step (2), the mixture of water and the monohydric alcohol is added dropwise into the system of the various mixed metal alkoxide complexes at a temperature ranging from room temperature to 90° C.

45. The method for preparing the high-entropy carbide ceramic precursor according to claim 39, wherein in step (2), the rare earth element-containing compound is at least one selected from yttrium acetylacetonate and lanthanum acetylacetonate.

46. The method for preparing the high-entropy carbide ceramic precursor according to claim 45, wherein step (2), before mixing the rare earth element-containing compound with the transition metal alkoxide complexes, further comprises adding a monohydric alcohol to the rare earth element-containing compound, followed by refluxing for 0.5-5 hours, wherein a molar ratio of the monohydric alcohol to the rare earth element-containing compound is 5-10:1, and the monohydric alcohol is one or more selected from methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol methyl ether, and ethylene glycol ethyl ether.

47. A high-entropy carbide ceramic product, is (A) or (B) or (C): (A). A high-entropy carbide ceramic, prepared from the high-entropy carbide ceramic precursor according to claim 33, wherein the high-entropy carbide ceramic has a single-phase structure, with all distributed homogenously at molecular level; and the high-entropy carbide ceramic comprises at least four elements selected from Ti, Zr, Hf, V, Nb, Ta, Mo, and W, and each with a molar percentage 5-35% of the total molar quantity of metal elements in the ceramic; preferably, the high-entropy carbide ceramic comprises no less than five of or six to eight of the metal elements, molar quantity of each metal elements in the ceramic are equal. (B). A rare earth-containing high-entropy carbide ceramic, having a single-phase structure, and comprising at least four transition metal elements and at least one rare-earth metal element, and all elements contained therein distributing homogenously at at molecular level; preferably, the transition metal elements are selected from Ti, Zr, Hf, V, Nb, Ta, Mo, and W, and the rare earth element is selected from Y and La; more preferably, the molar quantity of each transition metal element and the rare earth element in the ceramic are equal. (C). A high-entropy carbide ceramic fiber, comprising at least four elements selected from Ti, Zr, Hf, V, Nb, Ta, Mo, and W, and having a single-phase structure, and all elements contained therein distributing homogenously at at molecular level.

48. The high-entropy carbide ceramic product according to claim 47, wherein each metal elements in the high-entropy ceramic fiber accounts for 5-35% of the total molar quantity of metal elements contained therein; preferably, molar quantities of each metal elements are equal.

49. A method for preparing the high-entropy carbide ceramic product, is (I) or (II) or (III): (I). A method for preparing the high-entropy carbide ceramic, wherein the high-entropy carbide ceramic is prepared by curing and pyrolysis the high-entropy carbide ceramic precursor according to claim 33, wherein the pyrolysis is carried out at a temperature of not lower than 1400° C., preferably at a temperature of 1700-2000° C., for 0.5-5 hours, under protection of a vacuum environment or an inert atmosphere. (II). A method for preparing the rare earth-containing high-entropy carbide ceramic, wherein the rare earth-containing high-entropy carbide ceramic is prepared by curing and pyrolysis the rare earth-containing high-entropy carbide ceramic precursor, wherein the pyrolysis is carried out at a temperature of not lower than 1600° C., preferably at a temperature of 1700-2000° C., for 0.5-5 hours, under protection of a vacuum environment or an inert atmosphere. (III). A method for preparing the high-entropy carbide ceramic fiber, comprising: uniformly mixing high-entropy carbide ceramic precursor containing target metal elements with spinning aid and solvent to prepare a spinnable precursor solution, followed by spinning, pyrolyzation, and high-temperature solid solution, to prepare the high-entropy carbide ceramic fiber.

50. The method for preparing the high-entropy carbide ceramic product according to claim 49, wherein in the method for preparing the high-entropy carbide ceramic fiber, the spinning aid is one or more selected from polymethyl methacrylate, polyvinyl acetate, polyvinyl butyral, and polyvinylpyrrolidone; or, wherein the solvent is one or more selected from ethanol, acetone, n-propanol, ethylene glycol methyl ether, and N,N-dimethylformamide.

51. The method for preparing the high-entropy carbide ceramic product according to claim 49, wherein the pyrolyzation comprises heating to 500-600° C. at a heating rate of 0.5-5° C./min under an inert atmosphere and keeping at the temperature for 2-4 hours; or, wherein the high-temperature solid solution comprises: solutionizing at a temperature of not lower than 1400° C. under vacuum or under an inert atmosphere, wherein the inert atmosphere used for the high-temperature solutionizing does not comprise an nitrogen atmosphere; preferably, the solid solution is carried out at a temperature of 1400-1800° C., for 0.5-5 hours.

52. The method for preparing the high-entropy carbide ceramic product according to claim 49, wherein the spinning is one selected from blowing spinning, electrospinning, and centrifugal spinning.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0081] FIG. 1 is an XRD pattern of a ceramic obtained in Example 1;

[0082] FIG. 2 is a SEM-EDX image of the ceramic obtained in Example 1;

[0083] FIG. 3 is an XRD pattern of a ceramic obtained in Example 2;

[0084] FIG. 4 is an XRD pattern of a ceramic obtained in Example 3;

[0085] FIG. 5 is a TEM-EDS image of the ceramic obtained in Example 3;

[0086] FIG. 6 is an XRD pattern of a ceramic obtained in Example 4;

[0087] FIG. 7 is an XRD pattern of a ceramic obtained in Example 5;

[0088] FIG. 8 is an XRD pattern of a ceramic obtained in Example 6;

[0089] FIG. 9 is an XRD pattern of a ceramic obtained in Example 7;

[0090] FIG. 10 is an XRD pattern of a ceramic obtained in Example 8;

[0091] FIG. 11 is an XRD pattern of a high-entropy ceramic obtained in Example 10;

[0092] FIG. 12 is a TEM image and a TEM-EDS image of the high-entropy ceramic obtained in Example 10;

[0093] FIG. 13 is an XRD pattern of a high-entropy ceramic obtained in Example 11;

[0094] FIG. 14 is a TEM image and a TEM-EDS image of the high-entropy ceramic obtained in Example 11;

[0095] FIG. 15 is an XRD pattern of a high-entropy ceramic obtained in Example 12;

[0096] FIG. 16 is a TEM image and a TEM-EDS image of the high-entropy ceramic obtained in Example 12;

[0097] FIG. 17 is an XRD pattern of a fiber obtained in Example 19 of the present invention;

[0098] FIG. 18 is a SEM image of the fiber obtained in Example 19 of the present invention;

[0099] FIG. 19 is an XRD pattern of a fiber obtained in Example 20 of the present invention;

[0100] FIG. 20 is a SEM image of the fiber obtained in Example 20 of the present invention;

[0101] FIG. 21 is a SEM image of a fiber obtained in Comparative Example 10 of the present invention; and

[0102] FIG. 22 is a SEM image of a fiber obtained in Comparative Example 11 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0103] The present invention will be further described below in conjunction with particular embodiments. The present invention, however, is not limited to the following embodiments. Unless otherwise specified, methods used are all conventional ones, and raw materials used can all be obtained from open commercial channels.

Example 1

[0104] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0105] (1) Obtaining metal alkoxides: Metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were selected. Among them, Hf(OPr).sub.4, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were prepared as follows. Metal salts HfCl.sub.4, TaCl.sub.5, MoCl.sub.5, and WCl.sub.6 were separately dispersed in n-heptane to obtain respective mixtures, into which monohydric alcohols n-propanol, n-propanol, ethylene glycol ethyl ether, and ethylene glycol methyl ether were respectively added at −10° C., followed by adding triethylamine dropwise. After that, each mixtures were refluxed for 1 hour and then filtered to obtain respective metal alkoxide solutions. Ratios of the metal salts to the respective monohydric alcohols to triethylamine were 1:4:4, 1:5:6, 1:6:5, and 1:8:7, respectively.

[0106] (2) Preparing metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 at 40° C., followed by stirring for 0.1 hour. Molar ratios of the metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 to acetylacetone were 1:0.8, 1:1, 1:1, 1:1.2, and 1:1.5, respectively.

[0107] (3) Cohydrolysis: The metal alkoxide complexes obtained in step (2) were uniformly mixed in an equal metal molar ratio. A mixture of water and n-propanol was added dropwise into the resulted system at room temperature. A molar ratio of water to total metal elements was 1:1, and a mass ratio of n-propanol to water was 4:1. Then, refluxing was performed for 5 hours, followed by atmospheric distillation to obtain a metal alkoxide copolymer.

[0108] (4) Preparation of a precursor: The metal alkoxide copolymer obtained in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the alkoxide copolymer to a mass of the allyl-functional novolac resin was 1 mol:18 g. The resultant mixture was heated to 80° C. and reacted for 1 hour, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0109] The obtained precursor was heated and cured in an oven, then pyrolyzed at 1700° C. for 2 hours in a high-temperature furnace under vacuum, and cooled to obtain (HfMoTaWZr)C.sub.5 high-entropy ceramic. The XRD pattern of the ceramic is shown in FIG. 1. The XRD pattern presents only one set of diffraction peaks, indicating occurrence of solutionizing which enables metal atoms to be completely solutionized into one crystal lattice, and the system does not contain oxide impurities. FIG. 2 is a scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) image of the obtained high-entropy carbide ceramic. It can be seen from the image that the elements are distributed uniformly.

Example 2

[0110] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0111] (1) Obtaining metal alkoxides: Metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ti(Oi—Pr).sub.4, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were selected. Among them, Hf(OPr).sub.4, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were prepared by the method as used in Example 1.

[0112] (2) Preparing metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ti(Oi—Pr).sub.4, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 at 80° C., followed by stirring for 0.1 hour. Molar ratios of the metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ti(Oi—Pr).sub.4, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 to acetylacetone were 1:1, 1:1, 1:2, 1:1, and 1:2, respectively.

[0113] (3) Cohydrolysis: The metal alkoxide complexes obtained in step (2) were uniformly mixed in an equal metal molar ratio. A mixture of water and n-propanol was added dropwise into the resulted system at room temperature. A molar ratio of water to total metal elements was 1.3:1, and a mass ratio of n-propanol to water was 6:1. Then, refluxing was performed for 5 hours, followed by atmospheric distillation to obtain a metal alkoxide copolymer.

[0114] (4) Preparation of a precursor: The metal alkoxide copolymer obtained in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the alkoxide copolymer to a mass of the allyl-functional novolac resin was 1 mol:18.5 g. The resultant mixture was heated to 50° C. and reacted for 4 hours, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0115] The obtained precursor was heated and cured in an oven, then pyrolyzed at 1700° C. for 2 hours in a high-temperature furnace under vacuum, and cooled to obtain (HfMoTiWZr)C.sub.5 high-entropy ceramic. The XRD pattern of the ceramic is shown in FIG. 3. The XRD pattern presents only one set of diffraction peaks, indicating occurrence of solutionizing which enables metal atoms to be completely solutionized into one crystal lattice, and the system does not contain oxide impurities.

Example 3

[0116] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0117] (1) Obtaining metal alkoxides: Metal alkoxides Zr(Oi—Pr).sub.4, Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, and Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 were selected. Among them, Hf(Oi—Pr).sub.4 and Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 were prepared as follows. Metal salts HfCl.sub.4 and TaCl.sub.5 were dispersed in xylene and tert-butyl methyl ether respectively to obtain respective mixtures, into which monohydric alcohols isopropanol and ethylene glycol methyl ether were respectively added at 0° C., followed by adding triethylamine dropwise. After that, each mixtures were refluxed for 2 hours and then filtered to obtain respective metal alkoxide solutions. Ratios of the metal salts to the respective monohydric alcohols to triethylamine were 1:4:4 and 1:10:6, respectively.

[0118] (2) Preparing metal alkoxide complexes: Ethyl acetoacetate was added dropwise into each of the metal alkoxides Zr(OPr).sub.4, Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, and Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 at room temperature, followed by stirring for 0.5 hour. Molar ratios of the metal alkoxides Zr(OPr).sub.4, Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, and Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 to ethyl acetoacetate were 1:2, 1:0.6, 1:1 and 1:2.5, respectively.

[0119] (3) Cohydrolysis: The metal alkoxide complexes obtained in step (2) were uniformly mixed in an equal metal molar ratio. A mixture of water and ethylene glycol ethyl ether was added dropwise into the resulted system at room temperature. A molar ratio of water to total metal elements was 0.8:1, and a mass ratio of propanol to water was 5:1. Then, refluxing was performed for 5 hours, followed by atmospheric distillation to obtain a metal alkoxide copolymer.

[0120] (4) Preparation of a precursor: The metal alkoxide copolymer obtained in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the alkoxide copolymer to a mass of the allyl-functional novolac resin was 1 mol:20 g. The resultant mixture was heated to 80° C. and reacted for 1 hour, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0121] The obtained precursor was heated and cured in an oven, then pyrolyzed at 1800° C. for 1 hour in a high-temperature furnace under argon, and cooled to obtain (ZrHfTaTi)C.sub.4 high-entropy ceramic. The XRD pattern of the ceramic is shown in FIG. 4. The XRD pattern presents only one set of diffraction peaks, indicating occurrence of solutionizing which enables metal atoms to be completely solutionized into one crystal lattice, and the system does not contain oxide impurities. FIG. 5 is a scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) image of the ceramic. It can be seen from the image that the elements in the system are distributed very uniformly.

Example 4

[0122] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0123] (1) Obtaining metal alkoxides: Metal alkoxides Zr(Oi—Pr).sub.4, Hf(OPr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Mo(OPr).sub.5, and W(Oi—Pr).sub.6 were selected. Among them, Mo(OPr).sub.5 and W(Oi—Pr).sub.6 were prepared as follows. Metal salts MoCl.sub.5 and WCl.sub.6 were dispersed in n-hexane and petroleum ether respectively to obtain respective mixtures, into which monohydric alcohols n-propanol and isopropanol were respectively added at 0° C., followed by adding triethylamine dropwise. After that, each mixtures were refluxed for 2 hours and then filtered to obtain respective metal alkoxide solutions. Ratios of the metal salts to the respective monohydric alcohols to triethylamine were 1:6:6 and 1:8:7, respectively.

[0124] (2) Preparing metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Zr(Oi—Pr).sub.4, Hf(OPr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Mo(OPr).sub.5, and W(Oi—Pr).sub.6 at room temperature, followed by stirring for 1 hour. Molar ratios of the metal alkoxides Zr(Oi—Pr).sub.4, Hf(OPr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Mo(OPr).sub.5, and W(Oi—Pr).sub.6 to acetylacetone were 1:2, 1:0.6, 1:1, 1:1.5, 1:2.5, and 1:0.9, respectively.

[0125] (3) Cohydrolysis: The metal alkoxide complexes obtained in step (2) were uniformly mixed in an equal metal molar ratio. A mixture of water and n-propanol was added dropwise into the resulted system at 80° C. A molar ratio of water to total metal elements was 1.2:1, and a mass ratio of n-propanol to water was 3:1. Then, refluxing was performed for 3 hours, followed by atmospheric distillation to obtain a metal alkoxide copolymer.

[0126] (4) Preparation of a precursor: The metal alkoxide copolymer obtained in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the alkoxide copolymer to a mass of the allyl-functional novolac resin was 1 mol:19 g. The resultant mixture was heated to 80° C. and reacted for 1 hour, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0127] The obtained precursor was heated and cured in an oven, then pyrolyzed at 1700° C. for 5 hours in a high-temperature furnace under vacuum, and cooled to obtain (TiZrHfTaMoW)C.sub.6 high-entropy ceramic. The XRD pattern of the ceramic is shown in FIG. 6. The XRD pattern presents only one set of diffraction peaks, indicating occurrence of solutionizing which enables metal atoms to be completely solutionized into one crystal lattice, and the system does not contain oxide impurities.

Example 5

[0128] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0129] (1) Obtaining metal alkoxides: Metal alkoxides Zr(Oi—Pr).sub.4, Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Nb(OPr).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were selected. Among them, Hf(OPr).sub.4 and Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 were prepared by the method as used in Example 3, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 was prepared by the method as used in Example 1. Nb(OPr).sub.5 was prepared as follows. A metal salt NbCl.sub.5 was dispersed in n-hexane to obtain a mixture, into which a monohydric alcohol n-propanol was added at 5° C., followed by adding triethylamine dropwise. After that, the mixture was refluxed under heating for 2 hours and then filtered to obtain a metal alkoxide solution. A ratio of the metal salt to the monohydric alcohol to triethylamine was 1:6:6.

[0130] (2) Preparing metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Zr(Oi—Pr).sub.4, Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Nb(OPr).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 at room temperature, followed by stirring for 1 hour. Molar ratios of the metal alkoxides Zr(Oi—Pr).sub.4, Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Nb(OPr).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 to acetylacetone were 1:2, 1:0.6, 1:1, 1:1.5, 1:2.5, and 1:0.9, respectively.

[0131] (3) Cohydrolysis: The metal alkoxide complexes obtained in step (2) were uniformly mixed in an equal metal molar ratio. A mixture of water and n-propanol was added dropwise into the resulted system at 70° C. A molar ratio of water to total metal elements was 1.3:1, and a mass ratio of n-propanol to water was 8:1. Then, refluxing was performed for 1 hour, followed by atmospheric distillation to obtain a metal alkoxide copolymer.

[0132] (4) Preparation of a precursor: The metal alkoxide copolymer obtained in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the alkoxide copolymer to a mass of the allyl-functional novolac resin was 1 mol:20 g. The resultant mixture was heated to 80° C. and reacted for 1 hour, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0133] The obtained precursor was heated and cured in an oven, then pyrolyzed at 2000° C. for 0.5 hour in a high-temperature furnace under helium, and cooled to obtain (TiZrHfNbTaW)C.sub.6 high-entropy ceramic. The XRD pattern of the ceramic is shown in FIG. 7. The XRD pattern presents only one set of diffraction peaks, indicating occurrence of solutionizing which enables metal atoms to be completely solutionized into one crystal lattice, and the system does not contain oxide impurities.

Example 6

[0134] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0135] (1) Obtaining metal alkoxides: Metal alkoxides Ti(O—Pr).sub.4, Zr(Oi—Pr).sub.4, Hf(Oi—Pr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, Nb(CH.sub.2CH.sub.2OCH.sub.3).sub.5, W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were obtained. Among them, Hf(Oi—Pr).sub.4 and Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 were prepared by the method as used in Example 3, and Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5 and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were prepared by the method as used in Example 1. Nb(CH.sub.2CH.sub.2OCH.sub.3).sub.5 was prepared as follows. A metal salt NbCl.sub.5 was dispersed in n-heptane to obtain a mixture, into which a monohydric alcohol ethylene glycol methyl ether was added at 0° C., followed by adding triethylamine dropwise. After that, the mixture was refluxed under heating for 2 hours and then filtered to obtain a metal alkoxide solution. A ratio of the metal salt to the monohydric alcohol to triethylamine was 1:5:5.

[0136] (2) Preparing metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Ti(O—Pr).sub.4, Zr(Oi—Pr).sub.4, Hf(Oi—Pr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, Nb(CH.sub.2CH.sub.2OCH.sub.3).sub.5, W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 at 80° C., followed by stirring for 1 hour. Molar ratios of the metal alkoxides Zr(Oi—Pr).sub.4, Hf(Oi—Pr).sub.4, Ti(O—Pr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, Nb(CH.sub.2CH.sub.2OCH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 to acetylacetone were 1:2, 1:0.6, 1:1, 1:1.5, 1:2, 1:1, and 1:1.5, respectively.

[0137] (3) Cohydrolysis: The metal alkoxide complexes obtained in step (2) were uniformly mixed in an equal metal molar ratio. A mixture of water and n-propanol was added dropwise into the resulted system at 80° C. A molar ratio of water to total metal elements was 1.1:1, and a mass ratio of n-propanol to water was 8:1. Then, refluxing was performed for 2 hours, followed by atmospheric distillation to obtain a metal alkoxide copolymer.

[0138] (4) Preparation of a precursor: The metal alkoxide copolymer obtained in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the alkoxide copolymer to a mass of the allyl-functional novolac resin was 1 mol:20 g. The resultant mixture was heated to 80° C. and reacted for 1 hour, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0139] The obtained precursor was heated and cured in an oven, then pyrolyzed at 1800° C. for 1 hour in a high-temperature furnace under helium, and cooled to obtain (TiZrHfNbTaMoW)C.sub.7 high-entropy ceramic. The XRD pattern of the ceramic is shown in FIG. 8. The XRD pattern presents only one set of diffraction peaks, indicating occurrence of solutionizing which enables metal atoms to be completely solutionized into one crystal lattice, and the system does not contain oxide impurities.

Example 7

[0140] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0141] (1) Obtaining metal alkoxides: Metal alkoxides Zr(Oi—Pr).sub.4, Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and Nb(OPr).sub.5 were obtained. Among them, Hf(Oi—Pr).sub.4 and Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 were prepared by the method as used in Example 3, and Nb(OPr).sub.5 was prepared by the method as used in Example 5.

[0142] (2) Preparing metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Zr(Oi—Pr).sub.4, Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and Nb(OPr).sub.5 at 50° C., followed by stirring for 1 hour. Molar ratios of the metal alkoxides Zr(Oi—Pr).sub.4, Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and Nb(OPr).sub.5 to acetylacetone were 1:1.2, 1:0.6, 1:1, 1:2, and 1:1.5, respectively.

[0143] (3) Cohydrolysis: The metal alkoxide complexes obtained in step (2) were uniformly mixed in an equal metal molar ratio. A mixture of water and n-propanol was added dropwise into the resulted system at 60° C. A molar ratio of water to total metal elements was 1.1:1, and a mass ratio of n-propanol to water was 7:1. Then, refluxing was performed for 2 hours, followed by atmospheric distillation to obtain a metal alkoxide copolymer.

[0144] (4) Preparation of a precursor: The metal alkoxide copolymer obtained in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the alkoxide copolymer to a mass of the allyl-functional novolac resin was 1 mol:19.5 g. The resultant mixture was heated to 80° C. and reacted for 1 hour, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0145] The obtained precursor was heated and cured in an oven, then pyrolyzed at 1800° C. for 2 hours in a high-temperature furnace under vacuum, and cooled to obtain (TiZrHfTaNb)C.sub.5 high-entropy ceramic. The XRD pattern of the ceramic is shown in FIG. 9. The XRD pattern presents only one set of diffraction peaks, indicating occurrence of solutionizing which enables metal atoms to be completely solutionized into one crystal lattice, and the system does not contain oxide impurities.

Example 8

[0146] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0147] (1) Obtaining metal alkoxides: Metal alkoxides Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and Nb(OPr).sub.5 were obtained. Among them, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5 was prepared by the method as used in Example 1; Hf(Oi—Pr).sub.4 and Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 were prepared by the method as used in Example 3; and Nb(OPr).sub.5 was prepared by the method as used in Example 5.

[0148] (2) Preparing metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and Nb(OPr).sub.5 at 50° C., followed by stirring for 1 hour. Molar ratios of the metal alkoxides Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and Nb(OPr).sub.5 to acetylacetone were 1:1.1, 1:0.8, 1:1, 1:2, and 1:1.5, respectively.

[0149] (3) Cohydrolysis: The metal alkoxide complexes obtained in step (2) were uniformly mixed in an equal metal molar ratio. A mixture of water and n-propanol was added dropwise into the system at 70° C. A molar ratio of water to total metal elements was 1.2:1, and a mass ratio of n-propanol to water was 8:1. Then, refluxing was performed for 2 hours, followed by atmospheric distillation to obtain a metal alkoxide copolymer.

[0150] (4) Preparation of a precursor: The metal alkoxide copolymer obtained in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the alkoxide copolymer to a mass of the allyl-functional novolac resin was 1 mol:19.5 g. The resultant mixture was heated to 80° C. and reacted for 1 hour, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0151] The obtained precursor was heated and cured in an oven, then pyrolyzed at 1450° C. for 2 hours in a high-temperature furnace under vacuum, and cooled to obtain (TiHfNbTaMo)C.sub.5 high-entropy ceramic. The XRD pattern of the ceramic is shown in FIG. 10. The XRD pattern presents only one set of diffraction peaks, indicating occurrence of solutionizing which enables metal atoms to be completely solutionized into one crystal lattice, and the system does not contain oxide impurities.

Comparative Example 1

[0152] Implementation of this comparative example was the same as that of Example 2 except that the molar ratio of Ti(Oi—Pr).sub.4 to acetylacetone in step (2) was adjusted to 1:2.1.

Comparative Example 2

[0153] Implementation of this comparative example was the same as that of Example 3 except that the molar ratio of Hf(Oi—Pr).sub.4 to ethyl acetoacetate in step (2) was adjusted to 1:0.5.

Comparative Example 3

[0154] Implementation of this comparative example was the same as that of Example 2 except that the molar ratio of water to total metal elements in step (3) was adjusted to 1.4:1.

Comparative Example 4

[0155] Implementation of this comparative example was the same as that of Example 3 except that the molar ratio of water to total metal elements in step (3) was adjusted to 0.7:1.

Experimental Example 9

[0156] This experimental example studied the storage stability of the high-entropy ceramic precursors by the following test method. Initial viscosity of the precursors prepared in the examples and comparative examples of the present invention, as well as viscosity of the precursors after being stored at room temperature for 12 months were measured, and a comparative analysis of viscosity change rates was conducted. This experimental example also recorded the morphology and properties of the precursors prepared in the examples and comparative examples during and at the end of the reaction processes, which are shown in the following table.

TABLE-US-00001 Viscosity Initial after storage Viscosity viscosity for 12 months change Morphology and Precursors (mPa .Math. S) (mPa .Math. S) rate (%) properties Example 1 80.2 83.6 4.2% A homogeneous and soluble copolymer was formed. Example 2 82.1 85.2 3.8% A homogeneous and soluble copolymer was formed. Example 3 90.5 93.8 3.7% A homogeneous and soluble copolymer was formed. Example 4 84.9 87.1 2.6% A homogeneous and soluble copolymer was formed. Example 5 100.3  102.5  2.2% A homogeneous and soluble copolymer was formed. Example 6 96.6 98.9 2.4% A homogeneous and soluble copolymer was formed. Example 7 87.4 91.4 4.6% A homogeneous and soluble copolymer was formed. Example 8 93.7 99.1 5.8% A homogeneous and soluble copolymer was formed. Comparative 88.9 — — The system Example 1 gelled after 6 months, and the viscosity could not be measured. Comparative — — — Partial Example 2 precipitation occurred, and a homogeneous and soluble copolymer could not be formed. Comparative — — — Partial Example 3 precipitation occurred, and a homogeneous and soluble copolymer could not be formed. Comparative 98.7 — — The system Example 4 gelled after 4 months, and the viscosity could not be measured.

[0157] As can be seen from the above table, the precursors provided in Examples 1 to 8 of the present invention are all metal-containing copolymers exhibiting a uniform elements distribution and easily soluble in conventional organic reagents. In each of Comparative Examples 1 and 2, the ratio of the metal alkoxide to the complexing agent is adjusted. When the complexing agent is used in a relatively low content, the rate of the subsequent hydrolysis reaction is relatively fast, and precipitation occurs during the reaction, making it impossible to obtain a soluble precursor with uniform elements distribution. When the complexing agent is used in a relatively high content, the rate of the hydrolysis is so slow that the reaction is incomplete, causing remaining of a large number of alkoxy groups, which leads to instability of the precursor and therefore gelation during storage thereof. Similarly, in each of Comparative Examples 3 and 4, the proportion of water in the hydrolysis process is adjusted compared with that in the examples, making the hydrolysis reaction too fast or incomplete, thus making it impossible to prepare a precursor having uniformly elements distribution and suitable for long-term storage.

Example 10

[0158] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0159] (1) Obtaining metal alkoxides: Metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ta(OPr).sub.5, and Ti(OPr).sub.4 were selected. Among them, Hf(OPr).sub.4 and Ta(OPr).sub.5 were prepared as follows. Metal salts HfCl.sub.4 and TaCl.sub.5 were dispersed in n-heptane and ethylene glycol dimethyl ether, respectively, into each of which a monohydric alcohol n-propanol was added at −10° C., followed by adding triethylamine dropwise. After that, each mixtures were refluxed for 1 hour and then filtered to obtain respective metal alkoxide solutions, and metal alkoxides were obtained after reduced pressure distillation respectively. Ratios of the metal salts to the respective monohydric alcohols to triethylamine were 1:4:4 and 1:5:6, respectively.

[0160] (2) Preparation of metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ta(OPr).sub.5, and Ti(OPr).sub.4 at 40° C., followed by stirring for 0.1 hour. Molar ratios of the metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ta(OPr).sub.5, and Ti(OPr).sub.4 to acetylacetone were 1:0.8, 1:1, 1:1, and 1:1.5, respectively.

[0161] (3) Cohydrolysis: The transition metal alkoxide complexes obtained in step (2) were uniformly mixed in an equal metal molar ratio to obtain a mixture of alkoxides. N-propanol, with a total molar quantity ten times to that of La and Y elements, was added into the mixture of La(acac).sub.3 and Y(acac).sub.3, molar quantities of La and Y being the same with that of single metal element in the mixture of alkoxides, followed by refluxing the resulted mixture for 2 hours, and then cooling to room temperature to obtain a rare earth compound-containing solution. The mixture of alkoxides and the rare earth compound-containing solution were mixed uniformly. A mixture of water and n-propanol was added dropwise into the resulted system at room temperature, with a molar ratio of water to total metal elements being 0.8:1, and a mass ratio of n-propanol to water being 8:1. Then, refluxing was performed for 5 hours, followed by atmospheric distillation to obtain a metal copolymer.

[0162] (4) Preparation of a precursor: The metal copolymer prepared in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the metal copolymer to a mass of the allyl-functional novolac resin was 1 mol:13 g. The resultant mixture was heated to 80° C. and reacted for 1 hour, and then cooled to obtain a rare earth-containing high-entropy carbide ceramic precursor.

[0163] The obtained precursor was heated and cured in an oven, then polysized at 1700° C. for 2 hours in a high-temperature furnace under vacuum, and cooled to obtain (ZrHfTaTiLaY)C.sub.6 high-entropy ceramic. The XRD pattern of the ceramic is shown in FIG. 11. As can be seen from the figure, metal atoms are completely solutionized into one crystal lattice, and the system does not contain oxide impurities. A TEM image and a TEM-EDS image of the ceramic are shown in FIG. 12. It can be seen from the figure that metal atoms are distributed uniformly.

Example 11

[0164] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0165] (1) Obtaining metal alkoxides: Metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ti(Oi—Pr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 were selected. Among them, Hf(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 were prepared as follows. Metal salts HfCl.sub.4, TaCl.sub.5, and NbCl.sub.5 were dispersed in n-heptane, n-hexane, and ethylene glycol dimethyl ether respectively to obtain respective mixtures, into which monohydric alcohols n-propanol, ethylene glycol ethyl ether, and ethylene glycol methyl ether were respectively added at −10° C., followed by adding triethylamine dropwise. After that, each mixtures were refluxed for 1 hour and then filtered to obtain respective metal alkoxide solutions, and metal alkoxides were obtained after reduced pressure distillation respectively. Ratios of the metal salts to the respective monohydric alcohols to triethylamine were 1:4:4, 1:5:6, and 1:6:6, respectively.

[0166] (2) Preparation of metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ti(Oi—Pr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 at 80° C., followed by stirring for 0.1 hour. Molar ratios of the metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ti(Oi—Pr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 to acetylacetone were 1:1, 1:0.6, 1:2, 1:1, and 1:2, respectively.

[0167] (3) Cohydrolysis: The transition metal alkoxide complexes prepared in step (2) were selected and uniformly mixed in an equal metal molar ratio to obtain a mixture of alkoxides. N-propanol, with a total molar quantity five times to that of La and Y elements, was added into the mixture of La(acac).sub.3 and Y(acac).sub.3, molar quantities of La and Y being the same with that of a single metal element in the mixture of alkoxides, followed by refluxing the resulted mixture for 0.5 hour, and then cooling to room temperature to obtain a rare earth compound-containing solution. The mixture of alkoxides and the rare earth compound-containing solution were mixed uniformly. A mixture of water and n-propanol was added dropwise into the resulted system at 90° C., with a molar ratio of water to total metal elements being 1.3:1, and a mass ratio of n-propanol to water being 3:1. Then, refluxing was performed for 2 hours, followed by atmospheric distillation to obtain a metal copolymer.

[0168] (4) Preparation of a precursor: The metal copolymer prepared in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the metal copolymer to a mass of the allyl-functional novolac resin was 1 mol:15 g. The resultant mixture was heated to 50° C. and reacted for 4 hours, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0169] The obtained precursor was heated and cured in an oven, then pyrolyzed at 1800° C. for 2 hours in a high-temperature furnace under argon, and cooled to obtain (ZrHfTaTiNbLaY)C.sub.7 high-entropy ceramic. The XRD pattern of the ceramic is shown in FIG. 13. As can be seen from the figure, metal atoms are completely solutionized into one crystal lattice, and the system does not contain oxide impurities. A TEM image and a TEM-EDS image of the ceramic are shown in FIG. 14. It can be seen from the figure that metal atoms are distributed uniformly.

Example 12

[0170] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0171] (1) Obtaining metal alkoxides: Metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ti(Oi—Pr).sub.4, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were selected. Among them, Hf(OPr).sub.4, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were prepared as follows. Metal salts HfCl.sub.4, TaCl.sub.5, MoCl.sub.5, and WCl.sub.6 each were dispersed in toluene to obtain respective mixtures, into which monohydric alcohols n-propanol, n-propanol, ethylene glycol ethyl ether, and ethylene glycol methyl ether were respectively added at −5° C., followed by adding triethylamine dropwise. After that, each mixtures were refluxed for 1 hour and then filtered to obtain respective metal alkoxide solutions. Ratios of the metal salts to the respective monohydric alcohols to triethylamine were 1:4:4, 1:5:6, 1:6:5, and 1:8:7, respectively.

[0172] (2) Preparation of metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ti(Oi—Pr).sub.4, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 at 80° C., followed by stirring for 2 hours. Molar ratios of the metal alkoxides Zr(OPr).sub.4, Hf(OPr).sub.4, Ti(Oi—Pr).sub.4, Ta(OPr).sub.5,

[0173] Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 to acetylacetone were 1:1, 1:0.8, 1:2, 1:1, 1:2, and 1:2.5, respectively.

[0174] (3) Cohydrolysis: The transition metal alkoxide complexes prepared in step (2) were selected and uniformly mixed in an equal metal molar ratio to obtain a mixture of alkoxides. N-propanol, with a total molar quantity eight times to that of La element, was added into La(acac).sub.3, with a molar quantity of La being the same with that of a single metal element in the mixture of alkoxides, followed by refluxing the resulted mixture for 2 hours, and then cooling to room temperature to obtain a rare earth compound-containing solution. The mixture of alkoxides and the rare earth compound-containing solution were mixed uniformly. A mixture of water and n-propanol was added dropwise into the resulted system at 60° C., with a molar ratio of water to total metal elements being 1.3:1, and a mass ratio of n-propanol to water being 6:1. Then, refluxing was performed for 2 hours, followed by atmospheric distillation to obtain a metal copolymer.

[0175] (4) Preparation of a precursor: The metal copolymer prepared in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the metal copolymer to a mass of the allyl-functional novolac resin was 1 mol:14 g. The resultant mixture was heated to 50° C. and reacted for 4 hours, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0176] The obtained precursor was heated and cured in an oven, then pyrolyzed at 1800° C. for 2 hours in a high-temperature furnace under argon, and cooled to obtain (TiZrHfTaMoWLa)C.sub.7 high-entropy ceramic. The XRD pattern of the ceramic is shown in FIG. 15. As can be seen from the figure, metal atoms are completely solutionized into one crystal lattice, and the system does not contain oxide impurities. A TEM image and a TEM-EDS image of the ceramic are shown in FIG. 16. It can be seen from the figure that metal atoms are distributed uniformly.

Example 13

[0177] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0178] (1) Obtaining metal alkoxides: Metal alkoxides Hf(OPr).sub.4, Ti(Oi—Pr).sub.4, V(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 were selected. Among them, Hf(OPr).sub.4, V(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 were prepared as follows. Metal salts HfCl.sub.4, VCl.sub.5, and NbCl.sub.5 were dispersed in n-heptane, ethylene glycol dimethyl ether, and ethylene glycol dimethyl ether respectively to obtain respective mixtures, into which monohydric alcohols n-propanol, ethylene glycol methyl ether, and ethylene glycol methyl ether were respectively added at 5° C., followed by adding triethylamine dropwise. After that, each mixtures were refluxed for 5 hours and then filtered to obtain respective metal alkoxide solutions, and metal alkoxides were obtained after reduced pressure distillation respectively. Ratios of the metal salts to the respective monohydric alcohols to triethylamine were 1:8:6, 1:10:7.5, and 1:5:7.5, respectively.

[0179] (2) Preparation of metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Hf(OPr).sub.4, Ti(Oi—Pr).sub.4, V(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5at 50° C., followed by stirring for 0.1 hour. Molar ratios of the metal alkoxides Hf(OPr).sub.4, Ti(Oi—Pr).sub.4, V(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5 to acetylacetone were 1:2, 1:0.6, 1:2.5, and 1:0.75, respectively.

[0180] (3) Cohydrolysis: The transition metal alkoxide complexes prepared in step (2) were selected and uniformly mixed in an equal metal molar ratio to obtain a mixture of alkoxides. A mixture of methanol and ethanol, with a total molar quantity seven times to that of La element, was added into La(acac).sub.3, a molar quantity of La being the same with that of single metal element in the mixture of alkoxides, followed by refluxing the resulted mixture for 3 hours, and then cooling to room temperature to obtain a rare earth compound-containing solution. The mixture of alkoxides and the rare earth compound-containing solution were mixed uniformly. A mixture of water, methanol, and ethanol was added dropwise into the resulted system at 60° C., with a molar ratio of water to total metal elements being 1.1:1, and a mass ratio of the alcohols to water being 4:1. Then, refluxing was performed for 5 hours, followed by atmospheric distillation to obtain a metal copolymer.

[0181] (4) Preparation of a precursor: The metal copolymer prepared in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the metal copolymer to a mass of the allyl-functional novolac resin was 1 mol:13 g. The resultant mixture was heated to 90° C. and reacted for 0.5 hour, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0182] The obtained precursor was heated and cured in an oven, then pyrolyzed at 1750° C. for 2.5 hours in a high-temperature furnace under vacuum, and cooled to obtain (HfTiNbVLa)C.sub.5 high-entropy ceramic.

Example 14

[0183] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0184] (1) Obtaining metal alkoxides: Metal alkoxides Zr(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5 were selected. Among them, Ta(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5 were prepared as follows. Metal salts TaCl.sub.5, NbCl.sub.5, and MoCl.sub.5 were dispersed in n-heptane, n-hexane, and tert-butyl methyl ether respectively to obtain respective mixtures, into which ethylene glycol ethyl ether, ethylene glycol methyl ether, and ethylene glycol ethyl ether were respectively added at 1° C., followed by adding triethylamine dropwise. After that, each mixtures were refluxed for 3 hours and then filtered to obtain respective metal alkoxide solutions, and metal alkoxides were obtained after reduced pressure distillation respectively. Ratios of the metal salts to the respective monohydric alcohols to triethylamine were 1:7:6, 1:7.5:7.5, and 1:5:5, respectively.

[0185] (2) Preparation of metal alkoxide complexes: Ethyl acetoacetate was added dropwise into each of the metal alkoxides Zr(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5 at 70° C., followed by stirring for 2 hours. Molar ratios of the metal alkoxides Zr(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5 to acetylacetone were 1:1.2, 1:1.5, 1:2, and 1:1.25, respectively.

[0186] (3) Cohydrolysis: The transition metal alkoxide complexes prepared in step (2) were selected and uniformly mixed in an equal metal molar ratio to obtain a mixture of alkoxides. A mixture of ethylene glycol methyl ether and ethylene glycol ethyl ether, with a total molar quantity nine times the same to that of Y element, was added into Y(acac).sub.3, a molar quantity of Y being the same with that of single metal element in the mixture of alkoxides, followed by refluxing the resulted mixture under heating for 5 hours, and then cooling to room temperature to obtain a rare earth compound-containing solution. The mixture of alkoxides and the rare earth compound-containing solution were mixed uniformly. A mixture of water, ethylene glycol methyl ether, and ethylene glycol ethyl ether was added dropwise into the system at room temperature, with a molar ratio of water to total metal elements being 0.9:1, and a mass ratio of the alcohols to water being 7:1. Then, refluxing was performed for 1 hour, followed by atmospheric distillation to obtain a metal copolymer.

[0187] (4) Preparation of a precursor: The metal copolymer prepared in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the metal copolymer to a mass of the allyl-functional novolac resin was 1 mol:15 g. The resultant mixture was heated to 70° C. and reacted for 2 hours, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0188] The obtained precursor was heated and cured in an oven, then pyrolyzed at 2000° C. for 0.5 hour in a high-temperature furnace under nitrogen, and cooled to obtain (ZrTaNbMoY)C.sub.5 high-entropy ceramic.

Example 15

[0189] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0190] (1) Obtaining metal alkoxides: Metal alkoxides hafnium n-butoxide, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were selected. Among them, hafnium n-butoxide, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were prepared as follows. Metal salts HfCl.sub.4, TaCl.sub.5, MoCl.sub.5, and WCl.sub.6 were dispersed in toluene, n-hexane, n-heptane, and xylene respectively to obtain respective mixtures, into which monohydric alcohols n-butanol, n-propanol, ethylene glycol ethyl ether, and ethylene glycol methyl ether were respectively added at −5° C., followed by adding triethylamine dropwise. After that, each mixtures were refluxed for 2 hours and then filtered to obtain respective metal alkoxide solutions, and metal alkoxides were obtained after reduced pressure distillation respectively. Ratios of the metal salts to the respective monohydric alcohols to triethylamine were 1:6:5, 1:8:6, 1:6:5, 1:12:9, respectively.

[0191] (2) Preparation of metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides hafnium n-butoxide, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 at room temperature, followed by stirring for 5 hours. Molar ratios of the metal alkoxides hafnium n-butoxide, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 to acetylacetone were 1:1, 1:1.5, 1:2, and 1:0.9, respectively.

[0192] (3) Cohydrolysis: The transition metal alkoxide complexes prepared in step (2) were selected and uniformly mixed in an equal metal molar ratio to obtain a mixture of alkoxides. A mixture of n-butanol and n-propanol, with a total molar quantity five times to that of La element, was added into La(acac).sub.3, a molar quantity of La being the same with that of single metal element in the mixture of alkoxides, followed by refluxing the resulted mixture under heating for 4 hours, and then cooling to room temperature to obtain a rare earth compound-containing solution. The mixture of alkoxides and the rare earth compound-containing solution were mixed uniformly. A mixture of water, n-butanol, and n-propanol was added dropwise into the system at room temperature, with a molar ratio of water to total metal elements being 1:1, and a mass ratio of the alcohols to water being 3:1. Then, refluxing was performed for 5 hours, followed by atmospheric distillation to obtain a metal copolymer.

[0193] (4) Preparation of a precursor: The metal copolymer prepared in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the metal copolymer to a mass of the allyl-functional novolac resin was 1 mol:14 g. The resultant mixture was heated to 60° C. and reacted for 1.5 hours, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0194] The obtained precursor was heated and cured in an oven, then pyrolyzed at 1900° C. for 1 hour in a high-temperature furnace under argon, and cooled to obtain (HfTaMoWLa)C.sub.5 high-entropy ceramic.

Example 16

[0195] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0196] (1) Obtaining metal alkoxides: Metal alkoxides Zr(OPr).sub.4, hafnium isobutoxide, Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were selected. Among them, hafnium isobutoxide, Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were prepared as follows. Metal salts HfCl.sub.4, NbCl.sub.5, and WCl.sub.6 were dispersed in n-hexane, n-heptane, and tert-butyl methyl ether respectively to obtain respective mixtures, into which isobutanol, ethylene glycol methyl ether, and ethylene glycol methyl ether were respectively added at 0° C., followed by adding triethylamine dropwise. After that, each mixtures were refluxed for 1 hour and then filtered to obtain respective metal alkoxide solutions, and metal alkoxides were obtained after reduced pressure distillation respectively. Ratios of the metal salts to the respective monohydric alcohols to triethylamine were 1:8:6, 1:5:5, and 1:7.5:7.5, respectively.

[0197] (2) Preparation of metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Zr(OPr).sub.4, hafnium isobutoxide, Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 at 40° C., followed by stirring for 2 hours. Molar ratios of the metal alkoxides Zr(OPr).sub.4, hafnium isobutoxide, Nb(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 to acetylacetone were 1:0.8, 1:2, 1:2, and 1:3, respectively.

[0198] (3) Cohydrolysis: The transition metal alkoxide complexes prepared in step (2) were selected and uniformly mixed in an equal metal molar ratio to obtain a mixture of alkoxides. A mixture of isobutanol and n-propanol, with a total molar quantity seven times to that of Y element, was added into Y(acac).sub.3, a molar quantity of Y being the same with that of single metal element in the mixture of alkoxides, followed by refluxing the resulted mixture for 1.5 hours, and then cooling to room temperature to obtain a rare earth compound-containing solution. The mixture of alkoxides and the rare earth compound-containing solution were mixed uniformly. A mixture of water, n-butanol, and n-propanol was added dropwise into the system at 60° C., with a molar ratio of water to total metal elements being 0.8:1, and a mass ratio of the alcohols to water being 8:1. Then, refluxing was performed for 2 hours, followed by atmospheric distillation to obtain a metal copolymer.

[0199] (4) Preparation of a precursor: The metal copolymer prepared in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the metal copolymer to a mass of the allyl-functional novolac resin was 1 mol:13 g. The resultant mixture was heated to 80° C. and reacted for 1 hour, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0200] The obtained precursor was heated and cured in an oven, then pyrolyzed at 1850° C. for 3.5 hours in a high-temperature furnace under vacuum, and cooled to obtain (ZrHfNbWY)C.sub.5 high-entropy ceramic.

Example 17

[0201] In this example, a precursor and a high-entropy ceramic are prepared using the following methods.

[0202] (1) Obtaining metal alkoxides: Metal alkoxides Ti(Oi—Pr).sub.4, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were selected. Among them, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were prepared as follows. Metal salts TaCl.sub.5, MoCl.sub.5, and WCl.sub.6 were dispersed in n-heptane, toluene, and xylene respectively to obtain respective mixtures, into which monohydric alcohols n-propanol, ethylene glycol ethyl ether, and ethylene glycol methyl ether were respectively added at −8° C., followed by adding triethylamine dropwise. After that, each mixtures were refluxed for 2 hours and then filtered to obtain respective metal alkoxide solutions, and metal alkoxides were obtained after reduced pressure distillation respectively. Ratios of the metal salts to the respective monohydric alcohols to triethylamine were 1:10:7, 1:8:6, and 1:7:6, respectively.

[0203] (2) Preparation of metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Ti(Oi—Pr).sub.4, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 at room temperature, followed by stirring for 5 hours. Molar ratios of the metal alkoxides Ti(Oi—Pr).sub.4, Ta(OPr).sub.5, Mo(OCH.sub.2CH.sub.2OCH.sub.2CH.sub.3).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 to acetylacetone were 1:0.6, 1:2.5, 1:1, and 1:0.9, respectively.

[0204] (3) Cohydrolysis: The transition metal alkoxide complexes prepared in step (2) were selected and uniformly mixed in a molar ratio of Ta:Ti:Mo:W=35:5:20:15 to obtain a mixture of alkoxides. N-propanol, with a total molar quantity five times to that of La and Y elements, was added into a mixture of La(acac).sub.3 and Y(acac).sub.3, a ratio of molar quantities of La and Y to the metal elements in the mixture of alkoxides being Ta:Ti:Mo:W:La:Y=35:5:20:15:15:10, followed by refluxing the resulted mixture under heating for 5 hours, and then cooling to room temperature to obtain a rare earth compound-containing solution. The mixture of alkoxides and the rare earth compound-containing solution were mixed uniformly. A mixture of water, n-butanol, and n-propanol was added dropwise into the system at room temperature, with a molar ratio of water to total metal elements being 1.2:1, and a mass ratio of the alcohols to water being 8:1. Then, refluxing was performed for 5 hours, followed by atmospheric distillation to obtain a metal copolymer.

[0205] (4) Preparation of a precursor: The metal copolymer prepared in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the alkoxide copolymer to a mass of the allyl-functional novolac resin was 1 mol:13 g. The resultant mixture was heated to 50° C. and reacted for 4 hours, and then cooled to obtain a high-entropy carbide ceramic precursor.

[0206] The obtained precursor was heated and cured in an oven, then pyrolyzed at 2000° C. for 1 hour in a high-temperature furnace under vacuum, and cooled to obtain a high-entropy carbide ceramic containing elements Ta, Ti, Mo, W, La, and Y.

Comparative Example 5

[0207] Implementation of this comparative example was the same as that of Example 11 except that the molar ratio of Hf(OPr).sub.4 to acetylacetone in step (2) was adjusted to 1:0.5.

Comparative Example 6

[0208] Implementation of this comparative example was the same as that of Example 16 except that the molar ratio of W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 to acetylacetone in step (2) was adjusted to 1:3.1.

Comparative Example 7

[0209] Implementation of this comparative example was the same as that of Example 12 except that the molar ratio of water to total metal elements in step (3) was adjusted to 1.4:1.

Comparative Example 8

[0210] Implementation of this comparative example was the same as that of Example 16 except that the molar ratio of water to total metal elements in step (3) was adjusted to 0.7:1.

Comparative Example 9

[0211] Implementation of this comparative example was the same as that of Example 14 except that the atmospheric distillation in step (3) used to obtain the metal copolymer was substituted with reduced pressure distillation.

Experimental Example 18

[0212] This experimental example studied the storage stability of the high-entropy ceramic precursors by the following test method. Initial viscosity of the precursors prepared in the examples and comparative examples of the present invention, as well as viscosity of the precursors after being stored at room temperature for 12 months were measured, and a comparative analysis of viscosity change rates was conducted. This experimental example also recorded the morphology and properties of the precursors prepared in the examples and comparative examples during and at the end of the reaction processes, which are shown in the following table.

TABLE-US-00002 Viscosity Initial after storage Viscosity viscosity for 12 months change Morphology and Precursors (Pa .Math. S) (Pa .Math. S) rate (%) properties Example 10 92.5 99.7 7.8% A homogeneous and soluble copolymer was formed. Example 11 92.3 97.9 6.15% A homogeneous and soluble copolymer was formed. Example 12 94.1 100.0 6.3% A homogeneous and soluble copolymer was formed. Example 13 91.7 95.2 3.8% A homogeneous and soluble copolymer was formed. Example 14 90.6 93.9 3.7% A homogeneous and soluble copolymer was formed. Example 15 89.4 91.5 2.4% A homogeneous and soluble copolymer was formed. Example 16 89.9 91.9 2.3% A homogeneous and soluble copolymer was formed. Example 17 96.0 103.1  7.4% A homogeneous and soluble copolymer was formed. Comparative 100.1  — — The system Example 5 gelled after 5 months, and the viscosity could not be measured. Comparative — — — Partial Example 6 precipitation occurred, and a homogeneous and soluble copolymer could not be formed. Comparative — — — Partial Example 7 precipitation occurred, and a homogeneous and soluble copolymer could not be formed. Comparative 98.6 — — The system Example 8 gelled after 4 months, and the viscosity could not be measured. Comparative 90.8 130 43.2%  A homogeneous Example 9 and soluble copolymer was formed.

[0213] As can be seen from the above table, the precursors provided in Examples 10 to 17 of the present invention are all metal-containing copolymers exhibiting uniform element distribution and easily soluble in conventional organic reagents. In each of Comparative Examples 5 and 6, the ratio of the metal alkoxide to the complexing agent is adjusted. When the complexing agent is used in a relatively low content, the rate of the subsequent hydrolysis reaction is relatively fast, and precipitation occurs during the reaction, making it impossible to obtain a soluble precursor with uniform elements distribution. When the complexing agent is used in a relatively high content, the rate of the hydrolysis is so slow that the reaction is incomplete, causing residual of a large number of alkoxy groups, which leads to instability of the precursor and therefore gelation during storage thereof. Similarly, in each of Comparative Examples 7 and 8, the proportion of water in the hydrolysis process is adjusted compared with that in the examples, making the hydrolysis reaction too fast or incomplete, thus making it impossible to prepare a precursor having uniform element distribution and suitable for long-term storage.

[0214] In Comparative Example 9, distillation method used in the hydrolysis process is adjusted by substituting the atmospheric distillation with reduced pressure distillation. In atmospheric distillation process, the polymer precursor may further undergo post-polymerization during the distillation process, which may further reduce excess hydroxyl groups generated by the hydrolysis reaction in the system, thereby improving the storage stability of the precursor. The inventors found that the viscosity change rate of precursor prepared by atmospheric distillation is significantly smaller than that prepared by reduced pressure distillation, and therefore atmospheric distillation is more suitable for producing precursors with good storage properties.

Example 19

[0215] In this example, a high-entropy carbide ceramic fiber is prepared using the following methods.

[0216] (1) Preparation of spinnable precursor solution: The high-entropy carbide ceramic precursor comprising Ti, Hf, Nb, Ta, and Mo was prepared by the method described in Example 8. 30 g high-entropy carbide ceramic precursor, 10 g polyvinylpyrrolidone, and 300 g ethanol were mixed under stirring to obtain a brown homogenous solution.

[0217] (2) Spinning and collection: Compressed air was used as a gas source. The precursor solution obtained in step (1) was stretched into a nanofiber using a blow spinning device at a spinning pressure of 0.09 MPa, with a feeding speed being 50 mL/h, and a collecting distance being 50 cm.

[0218] (3) Pyrolyzation: The nanofiber collected in step (2) was placed in a heat treatment device, and heated to 500° C. at a heating rate of 1° C./min under a nitrogen atmosphere, and kept at the temperature for 2 hours to obtain a pyrolyzed fiber.

[0219] (4) High-temperature solid solution: The pyrolyzed fiber prepared in step (3) was placed in a heat treatment device, and solutionized at 1600° C. under vacuum for 2 hours to obtain a high-entropy carbide fiber.

[0220] The XRD pattern of the high-entropy carbide fiber is shown in FIG. 17, and a SEM image thereof is shown in FIG. 18.

Example 20

[0221] In this example, a high-entropy carbide ceramic fiber is prepared using the following methods.

[0222] A high-entropy carbide ceramic precursor comprising Ti, Hf, Nb, Ta, and W was prepared as follows.

[0223] (1) Obtaining metal alkoxides: Metal alkoxides Ti(OPr).sub.4, Hf(Oi—Pr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Nb(OPr).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were obtained. Among them, Hf(Oi—Pr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Nb(OPr).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 were prepared by the method descried in Example 5.

[0224] (2) Preparation of metal alkoxide complexes: Acetylacetone was added dropwise into each of the metal alkoxides Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Nb(OPr).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 at room temperature, followed by stirring for 1 hour. Molar ratios of the metal alkoxides Hf(Oi—Pr).sub.4, Ti(OPr).sub.4, Ta(OCH.sub.2CH.sub.2OCH.sub.3).sub.5, Nb(OPr).sub.5, and W(OCH.sub.2CH.sub.2OCH.sub.3).sub.6 to acetylacetone were 1:0.6, 1:1, 1:1.5, 1:2.5, and 1:0.9, respectively.

[0225] (3) Cohydrolysis: The metal alkoxide complexes prepared in step (2) were uniformly mixed in an equal metal molar ratio. A mixture of water and n-propanol was added dropwise into the system at 70° C., a molar ratio of water to total metal elements being 1.3:1, and a mass ratio of n-propanol to water being 8:1. Then, refluxing was performed for 1 hour, followed by atmospheric distillation to obtain a metal alkoxide copolymer.

[0226] (4) Preparation of a precursor: The metal alkoxide copolymer prepared in step (3) was uniformly mixed with allyl-functional novolac resin. A ratio of a total molar quantity of metal elements in the metal alkoxide copolymer to a mass of the allyl-functional novolac resin was 1 mol:20 g. The resultant mixture was heated to 80° C. and reacted for 1 hour, and then cooled to obtain a high-entropy carbide ceramic polymer precursor.

[0227] (5) Preparation of a spinnable precursor solution: 30 g of the above high-entropy carbide ceramic precursor, 6 g polyvinyl butyral, and 280 g n-propanol were mixed under stirring to obtain a brown homogenous solution.

[0228] (6) Spinning and collection: Compressed nitrogen was used as a gas source. The precursor solution obtained in step (5) was stretched into a nanofiber using a blow spinning device at a spinning pressure of 0.06 MPa, with a feeding speed being 30 mL/h, and a collecting distance being 40 cm.

[0229] (7) Pyrolyzation: The nanofiber collected in step (6) was placed in a heat treatment device, heated to 600° C. at a heating rate of 1.5° C./min under an argon atmosphere, and kept at the temperature for 2 hours to obtain a pyrolyzed fiber.

[0230] (8) High-temperature solutionizing: The pyrolyzed fiber prepared in step (7) was placed in a heat treatment device, and solutionized at a high temperature of 1600° C. under vacuum for 2 hours to obtain a high-entropy carbide fiber.

[0231] The XRD pattern of the high-entropy carbide fiber is shown in FIG. 19, and a SEM image thereof is shown in FIG. 20.

Example 21

[0232] In this example, a high-entropy carbide ceramic fiber is prepared using the following methods.

[0233] (1) Preparation of a spinnable precursor solution: A high-entropy carbide ceramic precursor comprising Zr, Hf, Ti, and Ta was prepared by the method described in Example 3. 30 g high-entropy carbide ceramic precursor, 10 g polyvinyl acetate, and 290 g ethylene glycol methyl ether were mixed under stirring to obtain a brown homogenous solution.

[0234] (2) Spinning and collection: The precursor solution obtained in step (1) was stretched into a nanofiber using an electrospinning device at a spinning voltage of 10 kV, with a feeding speed being 30 mL/h, and a collecting distance being 45 cm.

[0235] (3) Pyrolyzation: The nanofiber collected in step (2) was placed in a heat treatment device, heated to 600° C. at a heating rate of 1° C./min under a nitrogen atmosphere, and kept at the temperature for 2 hours to obtain a pyrolyzed fiber.

[0236] (4) High-temperature solutionizing: The pyrolyzed fiber prepared in step (3) was placed in a heat treatment device, and solutionized at a high temperature of 1800° C. under vacuum for 1 hour to obtain a high-entropy carbide fiber.

Example 22

[0237] In this example, a high-entropy carbide ceramic fiber is prepared using the following methods.

[0238] (1) Preparation of a spinnable precursor solution: A high-entropy carbide ceramic precursor comprising Zr, Hf, Ti, Ta, Mo, and W was prepared by the method described in Example 4. 30 g high-entropy carbide ceramic precursor, 15 g of polymethyl methacrylate, and 600 g ethanol were mixed under stirring to obtain a brown homogenous solution.

[0239] (2) Spinning and collection: The precursor solution obtained in step (1) was stretched into a nanofiber using an electrospinning device at a spinning voltage of 15 kV, with a feeding speed being 30 mL/h, and a collecting distance being 40 cm.

[0240] (3) Pyrolyzation: The nanofiber collected in step (2) was placed in a heat treatment device, heated to 600° C. at a heating rate of 1.5° C./min under a helium atmosphere, and kept at the temperature for 2 hours to obtain a pyrolyzed fiber.

[0241] (4) High-temperature solutionizing: The pyrolyzed fiber prepared in step (3) was placed in a heat treatment device, and solutionized at a temperature of 1700° C. under an argon atmosphere for 2 hours to obtain a high-entropy carbide fiber.

Example 23

[0242] In this example, a high-entropy carbide ceramic fiber is prepared using the following methods.

[0243] (1) Preparation of a spinnable precursor solution: A high-entropy carbide ceramic precursor comprising Zr, Hf, Ti, Ta, Nb, and W was prepared by the method described in Example 5. 30 g high-entropy carbide ceramic precursor, 12 g polyvinyl butyral, and 180 g n-propanol were mixed under stirring to obtain a brown homogenous solution.

[0244] (2) Spinning and collection: The precursor solution obtained in step (1) was stretched into a fiber using a centrifugal spinning device at a rotation speed of 1000 r/min, with a collecting distance being 40 cm.

[0245] (3) Pyrolyzation: The nanofiber collected in step (2) was placed in a heat treatment device, heated to 600° C. at a heating rate of 1.5° C./min under a nitrogen atmosphere, and kept at the temperature for 2 hours to obtain a pyrolyzed fiber.

[0246] (4) High-temperature solutionizing: The pyrolyzed fiber prepared in step (3) was placed in a heat treatment device, and solutionized at a temperature of 2000° C. under an argon atmosphere for 0.5 hour to obtain a high-entropy carbide fiber.

Example 24

[0247] In this example, a high-entropy carbide ceramic fiber is prepared using the following methods.

[0248] (1) Preparation of a spinnable precursor solution: A high-entropy carbide ceramic precursor comprising Zr, Hf, Ti, Ta, Nb, Mo, and W was prepared by the method described in Example 6. 30 g high-entropy carbide ceramic precursor, 3 g polyvinyl butyral, and 180 g ethylene glycol methyl ether were mixed under stirring to obtain a brown homogenous solution.

[0249] (2) Spinning and collection: The precursor solution obtained in step (1) was stretched into a nanofiber using a centrifugal spinning device at a rotation speed of 1500 r/min, with a collecting distance being 30 cm.

[0250] (3) Pyrolyzation: The nanofiber collected in step (2) was placed in a heat treatment device, heated to 600° C. at a heating rate of 2° C./min under an argon atmosphere, and kept at the temperature for 2 hours to obtain a pyrolyzed fiber.

[0251] (4) High-temperature solutionizing: The pyrolyzed fiber prepared in step (3) was placed in a heat treatment device, and solutionized at a high temperature of 2000° C. under an argon atmosphere for 0.5 hour to obtain a high-entropy carbide fiber.

Example 25

[0252] In this example, a high-entropy carbide ceramic fiber is prepared using the following methods.

[0253] (1) Preparation of a spinnable precursor solution: A high-entropy carbide ceramic precursor comprising Ti, Hf, Nb, Ta, and Mo was prepared by the method described in Example 8. 30 g high-entropy carbide ceramic precursor, 6 g polyvinyl butyral, 4 g polyvinylpyrrolidone, and 300 g N,N-dimethylformamide were mixed under stirring to obtain a brown homogenous solution.

[0254] (2) Spinning and collection: Compressed argon was used as a gas source. The precursor solution obtained in step (1) was stretched into a nanofiber using a blow spinning device at a spinning pressure of 0.02 MPa, with a feeding speed being 10 mL/h, and a collecting distance being 10 cm.

[0255] (3) Pyrolyzation: The nanofiber collected in step (2) was placed in a heat treatment device, heated to 550° C. at a heating rate of 0.5° C./min under a nitrogen atmosphere, and kept at the temperature for 4 hours to obtain a pyrolyzed fiber.

[0256] (4) High-temperature solutionizing: The pyrolyzed fiber prepared in step (3) was placed in a heat treatment device, and solutionized at a high temperature of 1400° C. under vacuum for 5 hours to obtain a high-entropy carbide fiber.

Example 26

[0257] In this example, a high-entropy carbide ceramic fiber is prepared using the following methods.

[0258] (1) Preparation of a spinnable precursor solution: A high-entropy carbide ceramic precursor comprising Ti, Hf, Nb, Ta, and W was prepared by the method described in Example 20. 30 g high-entropy ceramic precursor, 1 g polyvinyl acetatel, 5 g polyvinyl butyral, and 280 g tert-butyl methyl ether were mixed under stirring to obtain a brown homogenous solution.

[0259] (2) Spinning and collection: Compressed nitrogen was used as a gas source. The precursor solution obtained in step (1) was stretched into a nanofiber using a blow spinning device at a spinning pressure of 0.02 MPa, with a feeding speed being 60 mL/h, and a collecting distance being 50 cm.

[0260] (3) Pyrolyzation: The nanofiber collected in step (2) was placed in a heat treatment device, heated to 600° C. at a heating rate of 3.5° C./min under an argon atmosphere, and kept at the temperature for 3 hours to obtain a pyrolyzed fiber.

[0261] (4) High-temperature solutionizing: The pyrolyzed fiber prepared in step (3) was placed in a heat treatment device, and solutionized at a high temperature of 1500° C. under vacuum for 4 hours to obtain a high-entropy carbide fiber.

Example 27

[0262] In this example, a high-entropy carbide ceramic fiber is prepared using the following methods.

[0263] (1) Preparation of a spinnable precursor solution: A high-entropy carbide ceramic precursor comprising Zr, Hf, Ti, and Ta was prepared by the method described in Example 3. 30 g high-entropy ceramic precursor, 7 g polymethyl methacrylate, 3 g polyvinyl acetate, 200 g ethylene glycol methyl ether, and 90 g ethanol were mixed under stirring to obtain a brown homogenous solution.

[0264] (2) Spinning and collection: The precursor solution obtained in step (1) was stretched into a nanofiber using an electrospinning device at a spinning voltage of 5 kV, with a feeding speed being 10 mL/h, and a collecting distance being 10 cm.

[0265] (3) Pyrolyzation: The nanofiber collected in step (2) was placed in a heat treatment device, heated to 500° C. at a heating rate of 2.5° C./min under a nitrogen atmosphere, and kept at the temperature for 2 hours to obtain a pyrolyzed fiber.

[0266] (4) High-temperature solutionizing: The pyrolyzed fiber prepared in step (3) was placed in a heat treatment device, and solutionized at a high temperature of 1600° C. under vacuum for 1.5 hours to obtain a high-entropy carbide fiber.

Example 28

[0267] In this example, a high-entropy carbide ceramic fiber is prepared using the following methods.

[0268] (1) Preparation of a spinnable precursor solution: A high-entropy carbide ceramic precursor comprising Zr, Hf, Ti, Ta, Mo, and W was prepared by the method described in Example 4. 30 g high-entropy carbide ceramic precursor, 15 g polymethyl methacrylate, 100 g ethanol, and 80 g ethylene glycol methyl ether were mixed under stirring to obtain a brown homogenous solution.

[0269] (2) Spinning and collection: The precursor solution obtained in step (1) was stretched into a nanofiber using an electrospinning device at a spinning voltage of 10 kV, with a feeding speed being 60 mL/h, and a collecting distance being 50 cm.

[0270] (3) Pyrolyzation: The nanofiber collected in step (2) was placed in a heat treatment device, heated to 600° C. at a heating rate of 2° C./min under a helium atmosphere, and kept at the temperature for 3 hours to obtain a pyrolyzed fiber.

[0271] (4) High-temperature solutionizing: The pyrolyzed fiber prepared in step (3) was placed in a heat treatment device, and solutionized at a temperature of 1700° C. under a helium atmosphere for 2 hours to obtain a high-entropy carbide fiber.

Example 29

[0272] In this example, a high-entropy carbide ceramic fiber is prepared using the following methods.

[0273] (1) Preparation of a spinnable precursor solution: A high-entropy carbide ceramic precursor comprising Zr, Hf, Ti, Ta, Nb, and W was prepared by the method described in Example 5. 30 g high-entropy ceramic precursor, 12 g polyvinyl butyral, 120 g n-propanol, 60 g acetone were mixed under stirring to obtain a brown homogenous solution.

[0274] (2) Spinning and collection: The precursor solution obtained in step (1) was stretched into a fiber using a centrifugal spinning device at a rotation speed of 500 r/min, with a collecting distance being 20 cm.

[0275] (3) Pyrolyzation: The nanofiber collected in step (2) was placed in a heat treatment device, heated to 600° C. at a heating rate of 1.5° C./min under a nitrogen atmosphere, and kept at the temperature for 2 hours to obtain a pyrolyzed fiber.

[0276] (4) High-temperature solutionizing: The pyrolyzed fiber prepared in step (3) was placed in a heat treatment device, and solutionized at a temperature of 2000° C. under an argon atmosphere for 0.5 hour to obtain a high-entropy carbide fiber.

Example 30

[0277] In this example, a high-entropy carbide ceramic fiber is prepared using the following methods.

[0278] (1) Preparation of a spinnable precursor solution: A high-entropy carbide ceramic precursor comprising Zr, Hf, Ti, Ta, Nb, Mo, W was prepared by the method described in Example 6. 30 g high-entropy ceramic precursor, 30 g polyvinyl butyral, and 300 g ethylene glycol methyl ether were mixed under stirring to obtain a brown homogenous solution.

[0279] (2) Spinning and collection: The precursor solution obtained in step (1) was stretched into a nanofiber using a centrifugal spinning device at a rotation speed of 5000 r/min, with a collecting distance being 100 cm.

[0280] (3) Pyrolyzation: The nanofiber collected in step (2) was placed in a heat treatment device, heated to 600° C. at a heating rate of 2° C./min under a nitrogen atmosphere, and kept at the temperature for 2 hours to obtain a pyrolyzed fiber.

[0281] (4) High-temperature solutionizing: The pyrolyzed fiber prepared in step (3) was placed in a heat treatment device, and solutionized at a high temperature of 2000° C. under an argon atmosphere for 0.5 hour to obtain a high-entropy carbide fiber.

Comparative Example 10

[0282] This comparative example was the same as Example 20 except that the adding amount of the spinning aid polyvinylpyrrolidonein step (1) was adjusted to 32 g. Morphology of the obtained fiber is shown in FIG. 21.

[0283] As can be seen from the morphology of the fibers in FIG. 21, the fibers prepared in Comparative Example 10 exhibit relatively uniform morphology but are short in length, which limits applications thereof. The reason is that when the amount of the spinning aid exceeds a certain level, the amount of the precursor in the green fibers would be relatively lower, and as the spinning aid leaves the system during the pyrolyzation, the lack of precursor leads to breakage of the fibers.

Comparative Example 11

[0284] This comparative example was the same as Example 19 except that the spinning aid in step (1) was removed, and the spinnable precursor solution was prepared only with the high-entropy carbide ceramic precursor and the solvent. Morphology of the obtained fiber is shown in FIG. 22.

[0285] As can be seen from the morphology of the fibers in FIG. 21, the fibers prepared in Comparative Example 11 are not uniform in thickness and have shots in some parts thereof. This is because the spinning aid is removed in Comparative Example 11, leading to insufficient entanglement of the precursor in the spinnable precursor solution. The spinnable solution is further subjected to a drafting force during the spinning process, in which case the entanglement is destroyed, resulting in the generation of shots.

INDUSTRIAL APPLICATION

[0286] The present invention brings the follow beneficial effects.

[0287] 1. The present invention prepares high-entropy carbide ceramics from polymer precursors. The polymer precursors demonstrate molecular-level uniform dispersion of elements. The uniform distribution of elements maintained during the curing and pyrolysis processes is conducive to realizing homogenous elements distribution of the carbide solid solution, as a consequence of which a completely chemically uniform solid solution can be obtained at a relatively low temperature (1700° C.) without any high pressure. This method can be used to prepare not only high-entropy carbide ceramics with low entropy-forming ability, such as HfNbTaTiWC.sub.5, HfTaTiWZrC.sub.5, HfMoTaWZrC.sub.5, etc., but also six-element, seven-element, and eight-element high-entropy carbide ceramics that have not been reported in the literature.

[0288] 2. The present invention prepares rare earth element-containing high-entropy carbide ceramics from polymer precursors. The polymer precursors demonstrate molecular-level uniform dispersion of elements. The uniform distribution of elements and short-range distribution of atoms maintained during the curing and pyrolysis processes are conducive to solid solution process and obtain solid solution with homogenous element distribution, as a consequence of which even an element with a relatively large difference in atomic radii can be utilized to obtain a completely chemically uniform solid solution at a relatively low temperature (1700° C.) without any high pressure.

[0289] 3. The present invention prepares high-entropy carbide ceramic fibers for the first time from high-entropy carbide ceramic polymer precursors, which comprising at least four metal elements selected from Ti, Zr, Hf, V, Nb, Ta, Mo, and W, and the molar quantity of each metal element accounts for 5-35% of the total molar quantity of the metal elements. The spinning method can be blowing spinning, electrospinning, or centrifugal spinning.

[0290] 4. The spinnable high-entropy ceramic precursor solutions provided by the present invention have adjustable rheological properties, which improves spinning property. The spinning solutions can be stored with seal at room temperature for over 3 weeks, which further improves the spinning efficiency.

[0291] 5. The present invention prepares high-entropy ceramic fibers by blowing spinning, electrospinning, or centrifugal spinning, which requires simple equipment, is convenient to operate, and can be realized at low costs. Continuous fiber cotton or non-woven fabric with controllable average diameters can be obtained, and rapid scale-up production can be achieved.