High-entropy carbide ceramic and rare earth-containing high-entropy carbide ceramic, fibers and precursors thereof, and methods for preparing the same
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.
1 . A method for preparing the high-entropy carbide ceramic precursor comprising steps of:
(1) obtaining metal alkoxide complexes: adding dropwise a complexing agent into metal alkoxides M(OR) 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 first 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 a 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 second metal alkoxide copolymer; and
(3) preparing the precursor: mixing the first metal alkoxide copolymer or the second 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.
2 . The method for preparing the high-entropy carbide ceramic precursor according to claim 1 , 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.
3 . The method for preparing the high-entropy carbide ceramic precursor according to claim 2 , 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.
4 . The method for preparing the high-entropy carbide ceramic precursor according to claim 3 , 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.
5 . The method for preparing the high-entropy carbide ceramic precursor according to claim 1 , 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 n or M(NO 3 ) 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.
6 . The method for preparing the high-entropy carbide ceramic precursor according to claim 1 , wherein in step (1), the complexing agent is added dropwise into the metal alkoxides M(OR) 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 a system of the various mixed metal alkoxide complexes at a temperature ranging from room temperature to 90° C.
7 . The method for preparing the high-entropy carbide ceramic precursor according to claim 1 , wherein in step (2), the rare earth element-containing compound is at least one selected from yttrium acetylacetonate and lanthanum acetylacetonate.
8 . The method for preparing the high-entropy carbide ceramic precursor according to claim 7 , 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.