CN111303581B

CN111303581B - High-entropy carbide ceramic precursor containing rare earth, high-entropy ceramic and preparation method

Info

Publication number: CN111303581B
Application number: CN202010171717.8A
Authority: CN
Inventors: 叶丽; 孙娅楠; 韩伟健; 陈凤华; 赵彤
Original assignee: Institute of Chemistry CAS
Current assignee: Institute of Chemistry CAS
Priority date: 2020-03-12
Filing date: 2020-03-12
Publication date: 2021-03-16
Anticipated expiration: 2040-03-12
Also published as: CN111303581A

Abstract

The invention discloses a high-entropy carbide ceramic precursor containing rare earth, which comprises at least 4 transition metal elements and at least 1 rare earth metal element, and is dissolved in one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol monomethyl ether or ethylene glycol ethyl ether. The precursor is prepared by respectively complexing multiple transition metal alkoxides, mixing the transition metal alkoxides with a compound containing rare earth elements for cohydrolysis, and reacting the mixture with a carbon source. The preparation method of the precursor finely adjusts the proportion of the raw materials in the step, so that elements in the precursor are uniformly distributed at a molecular level, and metal elements are diffused in a short distance in the cracking process, so that the elements can be subjected to solid solution at a lower temperature. The preparation of the high-entropy ceramic is different from laser sintering and oxidation reduction in the traditional method, and the high-performance ceramic which has a single crystal phase and is provided with elements in a molecular-level uniform distribution state is prepared on the basis of the precursor.

Description

High-entropy carbide ceramic precursor containing rare earth, high-entropy ceramic and preparation method

Technical Field

The invention belongs to the technical field of high-entropy materials, and particularly relates to a rare earth-containing carbide high-entropy ceramic precursor, high-entropy ceramic and a preparation method of the high-entropy ceramic precursor.

Background

The high-entropy ceramic is a new ceramic which is newly appeared in recent years, the concept of the ceramic is derived from high-entropy alloy, and generally refers to a single solid solution formed by five or more metal compounds which are dissolved together in a (nearly) equal molar ratio. The high-entropy ceramic not only enriches the variety of the ceramic, but also endows the material with rich performance regulation space due to a novel high-entropy effect brought by the multi-component cooperation.

The research on the carbide high-entropy ceramics is mainly focused on the solid of transition metal IVB and VB carbide, and the carbide has a rock salt structure, strong covalent bond characteristics and high melting pointThe point, and therefore the sintering temperature required, is high, often greater than 2000 ℃. In 2018, Castle et al (Scientific Reports 2018,8,8609-8620) firstly reported that carbide powder is subjected to plasma sintering at 2300 ℃ and 16MPa to prepare (Hf-Ta-Zr-Ti) C and (Hf-Ta-Zr-Nb) C quaternary carbide ceramic blocks, wherein only the (Hf-Ta-Zr-Nb) C system forms a single solid solution ceramic, and characterization of the (Hf-Ta-Zr-Nb) C system shows that the hardness (36.1 +/-1.6 GPa) of the ceramic block is far greater than that of any single carbide (the hardness of the single carbide HfC with the highest hardness is 31.5 +/-1.3 GPa). Then, Sarker et al (Nature Communications 2018,9,4980-4988) calculate the capability of 56 five-element high-entropy ceramics, namely the entropy forming capability (EFA), which can be formed by carbides of 8 metals such as Ti, Zr, Hf, V, Nb, Ta, Mo, W and the like by adopting a first principle, and select and prepare 9 of the above, which proves the consistency of the experimental result and theoretical prediction, namely that the larger the EFA is, the easier the solid solution ceramics is formed, and provides an important theoretical basis for the design and preparation of the carbide high-entropy ceramics. The study of (Hf of the American Ceramic Society 2019,103,500-_0.2Zr_0.2Ta_0.2Nb_0.2Ti_0.2) The oxidation behavior of the C high-entropy ceramic at 1300-1500 ℃ shows that the high-entropy ceramic has good high-temperature oxidation resistance, and solid solutions of various oxides are mainly generated after the high-entropy ceramic is oxidized.

In view of the harsh preparation conditions and the novelty in the field, few reports on the carbide high-entropy ceramics are provided at present. The existing preparation methods of high-entropy carbide ceramics mainly comprise a carbide powder reaction sintering method, an element reaction sintering method and an oxide reduction sintering method. Sarker et al (Nature Communications 2018,9,4980-₅、HfNbTaTiZrC₅、HfNbTaTiVC₅、HfMoVWZrC₅、HfMoTiWZrC₅、NbTaTiVWC₅、HfNbTaTiWC₅、HfTaTiWZrC₅And HfMoTaWZrC₅Nine kinds of five-element carbide high-entropy ceramics. As a result, it was found that under these conditions, only the first six forms of entropy were presentA system with relatively high forming capacity can form a single solid solution, and three of the six solid solutions (HfNbTaTiZrC)₅、HfNbTaTiVC₅And HfTaTiWZrC₅) There is a small amount of oxide present and the latter three systems with relatively low entropy forming ability are unable to form a single solid solution of carbide. Lun Feng et al (script materials, 2019,162, 90-93) use metal oxide powder and carbon powder as raw materials, ball mill and mix, sieve, then press into pieces, carry out carbothermic reduction reaction at 1600 ℃, then continue to heat up and carry out solutionizing reaction to prepare HfZrTiTaNbC₅A ceramic. The research shows that the system can basically complete the solutionizing after the system is kept at 2000 ℃ for 1.5 h. The Zhang national army of the university of east China (Journal of the European Ceramic Society,2019,39, 2989) performed three methods (Ti powder reaction sintering method, element reaction sintering method and oxide reduction sintering method)_0.2Zr_0.2Nb_0.2Ta_0.2W_0.2) Preparation of C high entropy ceramics (preparation conditions: 2000 ℃,50 MPa, 5 min). Although single-phase five-element carbide ceramic solid solution can be obtained by the three methods, the relative density of a sample obtained by mutual solid solution of carbides is low (95.7%) due to the high oxygen content in the powder, and a small impurity peak can be seen on an XRD (X-ray diffraction) diagram; because the metal powder is thick, the element distribution in the sample obtained by element reaction sintering is not uniform, and although the problem can be possibly solved by adopting the thin metal powder, new problems can be brought, such as spontaneous combustion and higher oxygen content of the metal powder; oxide reduction method due to ZrO₂The reaction temperature with C is higher, and the obtained product is a single phase, but the segregation of Zr element is obviously seen on an EDS diagram.

As mentioned above, several conventional inorganic powder methods for preparing carbide high-entropy ceramics often require high temperature and high pressure conditions of more than 2000 ℃, the prepared ceramics often have incomplete solid solution reaction and uneven element distribution, and the conventional methods can only be used for preparing ceramic blocks or ceramic powder, which limits the application of high-entropy ceramics in the fields of ceramic matrix composites and fibers.

The application number 201911080643.0 discloses a preparation method of a carbon-supported high-entropy monatomic catalyst, which comprises the steps of mixing soluble metal salt (5-15 of metal elements Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Y, Zr, lu and Ru), a soluble carbon source (glucose), water and ethanol to obtain a mixed aqueous solution, performing ultrasonic dispersion, drying and separating out the mixed solution at 25-80 ℃ to obtain a catalyst precursor, calcining the catalyst precursor at 600-800 ℃ under inert atmosphere and vacuum conditions, cooling and grinding to obtain the carbon-supported high-entropy monatomic catalyst. The rare earth element in the catalyst exists in the form of high-entropy metal alloy, but the property of the rare earth element is completely different from that of high-entropy ceramic, and the rare earth element cannot be directly applied to the field of high-entropy ceramic.

The Chinese patent with application number 201910858887.0 discloses a high-entropy rare earth hafnate ceramic material and a preparation method thereof, wherein the chemical formula of the high-entropy rare earth hafnate is (RE '0.2 Ho0.2Er0.2Tm0.2)4Hf3O12, wherein RE ' is La or Yb, and RE ' is Gd or Lu. The preparation process specifically comprises the following steps: lanthanum oxide powder, gadolinium oxide powder, holmium oxide powder, erbium oxide powder, thulium oxide powder, ytterbium oxide powder, lutetium oxide powder and hafnium oxide powder are used as raw materials, mixed by a wet method and sintered under no pressure in an air atmosphere; and sintering in a hot pressing furnace with protective atmosphere to obtain the high-entropy rare earth hafnate material. The rare earth elements in the high-entropy ceramic prepared by the method exist in the form of oxides.

At present, no research report of carbide high-entropy ceramics containing rare earth metals exists, and the introduction of the rare earth metals can enrich the types of the high-entropy ceramics and possibly enable the ceramics to have certain functionality.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a high-entropy ceramic precursor containing rare earth carbide, high-entropy ceramic and a preparation method thereof, wherein the high-entropy ceramic precursor containing rare earth carbide is prepared by using a mode of cohydrolysis by using transition metal alkoxide and a rare earth-containing compound as raw materials, can realize uniform dispersion of element molecules, and forms a solid solution which can be dissolved in a plurality of conventional reagents, so that the precursor has processability and is suitable for popularization and use.

In order to achieve the technical purpose, the invention adopts the following basic concept:

the invention provides a high-entropy carbide ceramic precursor containing rare earth, which comprises at least 4 transition metal elements and at least 1 rare earth metal element, and is dissolved in one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol monomethyl ether or ethylene glycol ethyl ether.

The further scheme of the invention is as follows: the precursor comprises at least 4 of Ti, Zr, Hf, V, Nb, Ta, Mo and W elements and at least 1 of Y and La elements, and the amount of each metal element in the precursor accounts for 5-35% of the total metal substance.

The further scheme of the invention is as follows: the amount of each metal element in the precursor is the same; the viscosity of the precursor changes by less than 8% within 12 months.

In the scheme, the precursor provided by the invention is a soluble polymer, and due to special treatment in the preparation process, the precursor not only has the processing performance of the polymer, but also can be applied to preparation of ceramic matrix composites, coatings, fibers and the like, and has good storage performance, and the viscosity change of long-term storage at normal temperature is small.

The invention also provides a preparation method of the high-entropy ceramic precursor containing the rare earth carbide, which comprises the following steps:

(1) preparation of transition metal alkoxide complexes: transition metal alkoxide M (OR) at room temperature to 80 DEG C_nDripping a complexing agent into the solution, and continuously stirring the solution for 0.1 to 5 hours after dripping to obtain a complex;

(2) co-hydrolysis: selecting at least 4 transition metal alkoxide complexes containing different metal elements prepared according to the step (1), uniformly mixing the transition metal alkoxide complexes with a compound containing a rare earth element, then slowly dropwise adding a mixed solution of water and monohydric alcohol into the system at room temperature to 90 ℃, refluxing for 1-5 h after dropwise adding, and distilling at normal pressure to obtain a metal copolymer;

(3) preparing a precursor: and (3) uniformly mixing the metal copolymer obtained in the step (2) with allyl phenolic, heating to 50-90 ℃, reacting for 0.5-4 h, and cooling to obtain the carbide high-entropy ceramic polymer precursor.

In the above scheme, the precursor provided by the present invention is a multi-element system containing multiple metal elements, and although the selected transition metal elements are concentrated in groups VB, IVB and VIB, due to the difference in reactivity of the transition metal elements, if the complexing agents are added in similar proportions, a complex can be formed, but in the subsequent mixed hydrolysis process of multiple metal element alkoxide complexes, the reaction equilibrium is tilted due to the difference in the addition amount of the complexing agents, so that a precursor with uniformly distributed molecules cannot be formed. By adopting the ratio of the metal alkoxide to the complexing agent, the competitive reaction between different metal alkoxides can be balanced, so that the subsequent hydrolysis forms a stable system.

According to the above production method, the rare earth element-containing compound in step (2) is at least one selected from yttrium acetylacetonate and lanthanum acetylacetonate.

According to the preparation method, the molar ratio of the transition metal alkoxide to the complexing agent in the step (1) is 1 (0.15-0.5) n; when M in the transition metal alkoxide is selected from Ti, Zr, or Hf, n is 4; when M in the transition metal alkoxide is V, Nb, Ta or Mo, n is 5; when M in the transition metal alkoxide is W, n is 6; the complexing agent is acetylacetone and/or ethyl acetoacetate.

According to the preparation method, before the rare earth element-containing compound and the transition metal alkoxide complex are mixed in the step (2), monohydric alcohol is added into the rare earth element-containing compound for heating and refluxing for 0.5-5 h, the molar ratio of the monohydric alcohol to the rare earth element-containing compound is 5-10: 1, and the monohydric alcohol is selected from one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol monomethyl ether and ethylene glycol ethyl ether.

According to the above preparation method, when M in the metal alkoxide is selected from Hf, V, Nb, Ta, Mo or W, the metal alkoxide in step (1) is prepared by reacting a metal salt with a monohydric alcohol, specifically as follows: adding metal salt MCl_nOr M (NO)₃)_nDispersing in a solvent, dripping monohydric alcohol at the temperature of-10-5 ℃, then dripping triethylamine, heating and refluxing for 1-5 h after dripping is finished, and filtering to obtain a metal alkoxide solution; wherein the ratio of the metal salt, the monohydric alcohol and the triethylamine is 1: (1-2) n: (1-1.5) n; the solvent is one or more of n-hexane, n-heptane, toluene, xylene, ethylene glycol dimethyl ether, ethylene glycol diethyl ether and tert-butyl methyl ether; the monohydric alcohol is selected from one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol monomethyl ether and ethylene glycol ethyl ether.

According to the preparation method, the molar ratio of water to total metals in the step (2) is 0.8-1.3: 1, and the mass ratio of monohydric alcohol to water is 3-8: 1; the monohydric alcohol is selected from one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol monomethyl ether and ethylene glycol ethyl ether.

In the scheme, the proportion of the alcohol to the water provided by the invention is obtained on the basis of considering the mixing of metal alkoxides with different reaction activities, so that the reaction activities of various metal alkoxides in cohydrolysis tend to be similar, and a precursor with uniformly distributed element molecule levels is obtained.

According to the preparation method, the ratio of the total metal content in the metal copolymer in the step (3) to the mass of the allyl phenolic aldehyde is 1mol: 13-15 g.

In the above-mentioned production method, the molar masses of different metals are different and it is not easy to unify the same range by mass, and the present invention is herein calculated based on the total amount of the metal in the metal alkoxide copolymer, while the allyl phenol is a non-homopolymerized polymer and is not suitably expressed in terms of the amount of the substance, and is thus expressed in terms of the ratio of the amount of the substance to the mass.

According to the preparation method, the preparation method specifically comprises the following steps:

(1) obtaining a metal alkoxide: selecting transition metal alkoxide containing different elements, and adding metal salt MCl when M in the metal alkoxide is selected from Hf, V, Nb, Ta, Mo or W_nOr M (NO)₃)_nDispersing in solvent, dripping monohydric alcohol at-10-5 deg.C, and drippingTriethylamine is heated and refluxed for 1-5 hours after the dropwise addition is finished, and a metal alkoxide solution is obtained through filtration; wherein the ratio of the metal salt, the monohydric alcohol and the triethylamine is 1: (1-2) n: (1-1.5) n, wherein when M in the metal salt is selected from Ti, Zr or Hf, n is 4; when M in the metal salt is selected from V, Nb, Ta or Mo, n is 5; when M in the metal salt is W, n is 6; the solvent is one or more of n-hexane, n-heptane, toluene, xylene, ethylene glycol dimethyl ether, ethylene glycol diethyl ether and tert-butyl methyl ether; the monohydric alcohol is selected from one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol monomethyl ether and ethylene glycol ethyl ether;

(2) preparation of metal alkoxide complexes: adding the metal alkoxide M (OR) selected in the step (1) at the temperature of between room temperature and 80 DEG C_nDripping a complexing agent into the solution, and continuously stirring for 0.1-5 hours after dripping to obtain a metal alkoxide complex, wherein the molar ratio of the metal alkoxide to the complexing agent is 1 (0.15-0.5) n; when M in the metal alkoxide is selected from Ti, Zr or Hf, n is 4; when M in the metal alkoxide is selected from V, Nb, Ta or Mo, n is 5; when M in the metal alkoxide is W, n is 6; the complexing agent is acetylacetone and/or ethyl acetoacetate;

(3) co-hydrolysis: selecting at least 4 transition metal alkoxide complexes containing different metal elements prepared in the step (2), uniformly mixing the transition metal alkoxide complexes with a compound containing a rare earth element, slowly dropwise adding a mixed solution of water and monohydric alcohol into the system at room temperature to 90 ℃, wherein the molar ratio of the water to the total metal is 0.8-1.3: 1, the mass ratio of the monohydric alcohol to the water is 3-8: 1, carrying out dropwise reflux for 1-5 h, and distilling at normal pressure to obtain a metal copolymer;

(4) preparing a precursor: mixing the metal copolymer prepared in the step (3) and allyl phenolic aldehyde according to the total amount of metal in the copolymer: and (3) uniformly mixing 13-15 g of allyl phenolic aldehyde with the mass of 1mol, heating to 50-90 ℃, reacting for 0.5-4 h, and then cooling to obtain the carbide high-entropy ceramic precursor.

Preferably, before the rare earth element-containing compound and the transition metal alkoxide complex are mixed in the step (2), adding monohydric alcohol into the rare earth element-containing compound for heating and refluxing for 0.5-5 h, wherein the molar ratio of the monohydric alcohol to the rare earth element-containing compound is 5-10: 1; the compound containing the rare earth element is preferably at least one of yttrium acetylacetonate and lanthanum acetylacetonate; the monohydric alcohol is one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol monomethyl ether and ethylene glycol ethyl ether.

The invention also provides the carbide high-entropy ceramic, which is in a single crystal phase and comprises at least 4 transition metal elements and at least 1 rare earth metal element, wherein all the elements are uniformly distributed in a molecular level; the transition metal elements are selected from Ti, Zr, Hf, V, Nb, Ta, Mo and W elements, the rare earth metal elements are selected from Y and La elements, and the amount of the metal elements accounts for 5-35% of the total metal substances of the precursor; preferably, the amounts of the respective substances of the transition metal element and the rare earth element are the same.

In the scheme, the precursor provided by the invention is prepared by adopting a mode of cohydrolysis of transition metal alkoxide and a rare earth element-containing compound, and the transition metal elements and the rare earth elements in the precursor are uniformly distributed in a molecular level, so that the elements are distributed in a short distance in a cracking process, and solid solution reaction among the metal elements is facilitated to obtain the solid solution.

The invention further provides a preparation method of the carbide high-entropy ceramic, which is prepared by solidifying and cracking the carbide high-entropy ceramic precursor containing rare earth, wherein the cracking temperature is not lower than 1600 ℃, preferably the cracking temperature is 1700-2000 ℃, and the cracking time is 0.5-5 h; the cracking is carried out in a vacuum environment or under the protection of an inert atmosphere, wherein the inert atmosphere is argon, helium or a mixed gas thereof.

In the prior art, most of carbide high-entropy ceramics are prepared by a carbide powder reaction sintering method, the preparation conditions are harsh, high-temperature and high-pressure conditions are required, and the requirements on equipment are high. Furthermore, the obtained solid solution is not high in purity (oxide impurity peaks exist on XRD), and the element distribution is not uniform. Because atom diffusion is difficult, the traditional powder reaction sintering method can not prepare solid solutions with large atom size difference, so the research of the carbide high-entropy ceramics in the prior art is only limited to partial elements of IVB, VB and VIB groups, and no carbide high-entropy ceramics containing rare earth metals are reported.

The invention adopts the polymer precursor method to prepare the carbide high-entropy ceramic containing the rare earth element, and because the elements in the polymer precursor achieve molecular level uniform dispersion, the elements are kept to be uniformly distributed in the curing and cracking processes, atoms are in short-range distribution, and the method is beneficial to solid solution among atoms and uniform distribution of the elements of the solid solution, even the elements with relatively large atomic radius difference can obtain the completely chemically uniform solid solution at relatively low temperature (1700 ℃), and high pressure is not required.

The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention, are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention without limiting the invention to the right. It is obvious that the drawings in the following description are only some embodiments, and that for a person skilled in the art, other drawings can be derived from them without inventive effort. In the drawings:

FIG. 1 is an XRD pattern of the high entropy ceramic obtained in example 1;

FIG. 2 is a TEM image and a TEM-EDS distribution chart of the high-entropy ceramic obtained in example 1;

FIG. 3 is an XRD pattern of the high-entropy ceramic obtained in example 2;

FIG. 4 is a TEM image and a TEM-EDS distribution chart of the high-entropy ceramic obtained in example 2;

FIG. 5 is an XRD pattern of the high entropy ceramic obtained in example 3;

FIG. 6 is a TEM image and a TEM-EDS distribution chart of the high-entropy ceramic obtained from the image in example 3.

It should be noted that the drawings and the description are not intended to limit the scope of the inventive concept in any way, but to illustrate it by a person skilled in the art with reference to specific embodiments.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and the following embodiments are used for illustrating the present invention and are not intended to limit the scope of the present invention.

Example 1

In this example, the precursor and the high-entropy ceramic were prepared by the following method:

(1) obtaining a metal alkoxide: selecting metal alkoxide Zr (OPr)₄、Hf(OPr)₄、Ta(OPr)₅And Ti (OPr)₄Wherein Hf (OPr)₄、Ta(OPr)₅Is prepared from metal salt HfCl₄、TaCl₅Respectively dispersing in n-heptane and ethylene glycol dimethyl ether, respectively dripping monohydric alcohol n-propanol at-10 ℃, then dripping triethylamine, heating and refluxing for 1h after dripping is finished, respectively filtering to obtain metal alkoxide solution, and finally carrying out reduced pressure distillation to obtain metal alkoxide; wherein the ratio of the metal salt to the monohydric alcohol to the triethylamine is 1:4:4 and 1:5:6 respectively;

(2) preparation of metal alkoxide complexes: at 40 ℃ to a metal alkoxide Zr (OPr)₄、Hf(OPr)₄、Ta(OPr)₅And Ti (OPr)₄Dripping acetylacetone into the mixture, and continuing stirring for 0.1h after dripping; metal alkoxide Zr (OPr)₄、Hf(OPr)₄、Ta(OPr)₄、Ti(OPr)₄And acetylacetone at a molar ratio of 1:0.8, 1:1, and 1:1.5, respectively;

(3) co-hydrolysis: selecting the transition metal alkoxide complex prepared in the step (2), uniformly mixing the transition metal alkoxide complex and the metal in an equal molar ratio to obtain an alkoxide mixed solution, and adding La (acac)₃And Y (acac)₃Adding n-propanol of which the total amount of La and Y metal is 10 times that of the alkoxide mixed solution, heating and refluxing for 2h, and cooling to room temperature to obtain a rare earth compound-containing solution; uniformly mixing the alkoxide mixed solution and the rare earth compound-containing solution, slowly dropwise adding the mixed solution of water and n-propanol into the system at room temperature, wherein the molar ratio of water to total metals is 0.8:1, and the mass ratio of the n-propanol to the waterThe ratio is 8:1, the mixture is dripped and refluxed for 5 hours, and the metal copolymer is obtained by normal pressure distillation;

(4) preparing a precursor: and (3) uniformly mixing the metal copolymer prepared in the step (3) with allyl phenolic aldehyde, wherein the mass ratio of the total amount of metal elements in the metal copolymer to the allyl phenolic aldehyde is 1mol:13g, heating to 80 ℃, reacting for 1h, and then cooling to obtain the carbide high-entropy ceramic precursor.

Heating and curing the obtained precursor in an oven, then cracking for 2h at 1700 ℃ in a high-temperature furnace under vacuum, and cooling to obtain (ZrHfTaTiLaY) C₆High entropy ceramics. The XRD pattern of the ceramic is shown in FIG. 1, from which it can be seen that the metal atoms are completely dissolved into one crystal lattice and the system contains no oxide impurities. The TEM image and TEM-EDS elemental distribution of the ceramic are shown in FIG. 2, and it can be seen that the metal atoms are uniformly distributed.

Example 2

(1) obtaining a metal alkoxide: selecting metal alkoxide Zr (OPr)₄、Hf(OPr)₄、Ti(Oi-Pr)₄、Ta(OCH₂CH₂OCH₂CH₃)₅And Nb (OCH)₂CH₂OCH₃)₅Wherein Hf (OPr)₄、Ta(OCH₂CH₂OCH₂CH₃)₅And Nb (OCH)₂CH₂OCH₃)₅Is prepared from metal salt HfCl₄、TaCl₅And NbCl₅Respectively dispersing in n-heptane, n-hexane and ethylene glycol dimethyl ether, respectively dripping monohydric alcohol n-propanol, ethylene glycol ethyl ether and ethylene glycol methyl ether at-10 ℃, then respectively dripping triethylamine, heating and refluxing for 1h after dripping is finished, respectively filtering to obtain metal alkoxide solution, and finally carrying out reduced pressure distillation to obtain metal alkoxide; wherein the metal salt, the monohydric alcohol and the triethylamine are respectively in a ratio of 1:4:4, 1:5:6 and 1:6: 6;

(2) preparation of metal alkoxide complexes: at 80 ℃ to obtain metal alkoxide Zr (OPr)₄、Hf(OPr)₄、Ti(Oi-Pr)₄、Ta(OCH₂CH₂OCH₂CH₃)₅、Nb(OCH₂CH₂OCH₃)₅Dripping acetylacetone into the mixture, and continuing stirring for 0.1h after dripping; metal alkoxide Zr (OPr)₄、Hf(OPr)₄、Ti(Oi-Pr)₄、Ta(OCH₂CH₂OCH₂CH₃)₅、Nb(OCH₂CH₂OCH₃)₅And acetylacetone in a molar ratio of 1:1, 1:0.6, 1:2, 1:1, and 1:2, respectively;

(3) co-hydrolysis: selecting the transition metal alkoxide complex prepared in the step (2), uniformly mixing the transition metal alkoxide complex and the metal in an equal molar ratio to obtain an alkoxide mixed solution, and adding La (acac)₃And Y (acac)₃Adding n-propanol of which the total amount of La and Y metal is 5 times of that of the alkoxide mixed solution, heating and refluxing for 0.5h, and cooling to room temperature to obtain a rare earth compound-containing solution; uniformly mixing the alkoxide mixed solution and the rare earth compound-containing solution, slowly dropwise adding the mixed solution of water and n-propanol into the system at 90 ℃, wherein the molar ratio of water to total metal is 1.3:1, the mass ratio of the n-propanol to the water is 3:1, refluxing for 2h after dropwise adding is finished, and distilling at normal pressure to obtain a metal copolymer;

(4) preparing a precursor: and (3) uniformly mixing the metal copolymer prepared in the step (3) with allyl phenolic aldehyde, wherein the mass ratio of the total amount of metal elements in the metal copolymer to the allyl phenolic aldehyde is 1mol:15g, heating to 50 ℃, reacting for 4h, and then cooling to obtain the carbide high-entropy ceramic precursor.

Heating and curing the obtained precursor in a drying oven, then cracking for 2h at 1800 ℃ in a high-temperature furnace under argon, and cooling to obtain (ZrHfTaTiNbLaY) C₇High entropy ceramics. The XRD pattern of the ceramic is shown in fig. 3. As can be seen from the figure, the metal atoms are completely dissolved into one crystal lattice, and the system does not contain oxide impurities. The TEM image and TEM-EDS elemental distribution of the ceramic are shown in FIG. 4, and it can be seen that the metal atoms are uniformly distributed.

Example 3

(1) obtaining metal alkoxides: metal alkoxide Zr (OPr)₄、Hf(OPr)₄、Ti(Oi-Pr)₄、Ta(OPr)₅、Mo(OCH₂CH₂OCH₂CH₃)₅And W (OCH)₂CH₂OCH₃)₆Wherein Hf (OPr)₄、Ta(OPr)₅、Mo(OCH₂CH₂OCH₂CH₃)₅And W (OCH)₂CH₂OCH₃)₆Is prepared from metal salt HfCl₄、TaCl₅、MoCl₅And WCl₆Respectively dispersing in toluene, respectively dripping monohydric alcohol n-propanol, ethylene glycol ethyl ether and ethylene glycol methyl ether at-5 ℃, then dripping triethylamine, heating and refluxing for 1h after dripping is finished, and respectively filtering to obtain metal alkoxide solution; wherein the metal salt, the monohydric alcohol and the triethylamine are respectively in a ratio of 1:4:4, 1:5:6, 1:6:5 and 1:8: 7;

(2) preparation of metal alkoxide complexes: at 80 ℃ to obtain metal alkoxide Zr (OPr)₄、Hf(OPr)₄、Ti(Oi-Pr)₄、Ta(OPr)₅、Mo(OCH₂CH₂OCH₂CH₃)₅And W (OCH)₂CH₂OCH₃)₆Dripping acetylacetone into the solution, and continuing stirring for 2h after dripping; metal alkoxide Zr (OPr)₄、Hf(OPr)₄、Ti(Oi-Pr)₄、Ta(OPr)₅、Mo(OCH₂CH₂OCH₂CH₃)₅、W(OCH₂CH₂OCH₃)₆And acetylacetone in a molar ratio of 1:1, 1:0.8, 1:2, 1:1, 1:2, and 1:2.5, respectively;

(3) co-hydrolysis: selecting the transition metal alkoxide complex prepared in the step (2), uniformly mixing the transition metal alkoxide complex and the metal in an equal molar ratio to obtain an alkoxide mixed solution, and adding La (acac)₃Adding n-propanol of which the amount is 8 times that of La metal substances, wherein the amount of the La metal substances is the same as that of single metal element substances in the alkoxide mixed solution, heating and refluxing for 2 hours, and cooling to room temperature to obtain a rare earth compound-containing solution; uniformly mixing the alkoxide mixed solution and the rare earth compound-containing solution, and slowly dropwise adding the mixed solution of water and n-propanol into the system at 60 DEG CThe molar ratio of water to total metal is 1.3:1, the mass ratio of n-propanol to water is 6:1, the metal copolymer is obtained after dripping and refluxing for 2 hours and normal pressure distillation;

(4) preparing a precursor: and (3) uniformly mixing the metal copolymer prepared in the step (3) with allyl phenolic aldehyde, wherein the mass ratio of the total amount of metal elements in the metal copolymer to the allyl phenolic aldehyde is 1mol:14g, heating to 50 ℃, reacting for 4h, and then cooling to obtain the carbide high-entropy ceramic precursor.

Heating and curing the obtained precursor in a drying oven, then cracking for 2h at 1800 ℃ in a high-temperature furnace under argon, and cooling to obtain (TiZrHfTaMoWLa) C₇High entropy ceramics. The XRD pattern of the ceramic is shown in fig. 5. As can be seen from the figure, the metal atoms are completely dissolved into one crystal lattice, and the system does not contain oxide impurities. The TEM image and TEM-EDS elemental distribution of the ceramic are shown in FIG. 6, and it can be seen that the metal atoms are uniformly distributed.

Example 4

(1) obtaining a metal alkoxide: selecting metal alkoxide Hf (OPr)₄、Ti(Oi-Pr)₄、V(OCH₂CH₂OCH₃)₅And Nb (OCH)₂CH₂OCH₃)₅Wherein Hf (OPr)₄、V(OCH₂CH₂OCH₃)₅And Nb (OCH)₂CH₂OCH₃)₅Is prepared from metal salt HfCl₄、VCl₅And NbCl₅Respectively dispersing in n-heptane, ethylene glycol dimethyl ether and ethylene glycol dimethyl ether, respectively dripping monohydric alcohol n-propanol, ethylene glycol methyl ether and ethylene glycol methyl ether at 5 ℃, then respectively dripping triethylamine, heating and refluxing for 5h after dripping is finished, respectively filtering to obtain metal alkoxide solution, and finally carrying out reduced pressure distillation to obtain metal alkoxide; wherein the ratio of the metal salt to the monohydric alcohol to the triethylamine is 1:8:6, 1:10:7.5 and 1:5:7.5 respectively;

(2) preparation of metal alkoxide complexes: at 50 deg.C, adding into metal alkoxide Hf (OPr)₄、Ti(Oi-Pr)₄、V(OCH₂CH₂OCH₃)₅And Nb (OCH)₂CH₂OCH₃)₅Dripping acetylacetone into the mixture, and continuing stirring for 0.1h after dripping; metal alkoxides Hf (OPr)₄、Ti(Oi-Pr)₄、V(OCH₂CH₂OCH₃)₅、Nb(OCH₂CH₂OCH₃)₅And acetylacetone at a molar ratio of 1:2, 1:0.6, 1:2.5, and 1:0.75, respectively;

(3) co-hydrolysis: selecting the transition metal alkoxide complex prepared in the step (2), uniformly mixing the transition metal alkoxide complex and the metal in an equal molar ratio to obtain an alkoxide mixed solution, and adding La (acac)₃Adding a methanol and ethanol mixed solution with the amount of La metal substances being 7 times that of the alcohol salt mixed solution, wherein the amount of the La metal substances is the same as that of a single metal element in the alcohol salt mixed solution, heating and refluxing for 3 hours, and cooling to room temperature to obtain a rare earth compound-containing solution; uniformly mixing the alkoxide mixed solution and the rare earth compound-containing solution, slowly dripping the mixed solution of water, methanol and ethanol into the system at the temperature of 60 ℃, wherein the molar ratio of the water to the total metal is 1.1:1, the mass ratio of the alcohol to the water is 4:1, refluxing for 5 hours after dripping is finished, and distilling at normal pressure to obtain a metal copolymer;

(4) preparing a precursor: and (3) uniformly mixing the metal copolymer prepared in the step (3) with allyl phenolic aldehyde, wherein the mass ratio of the total amount of metal elements in the metal copolymer to the allyl phenolic aldehyde is 1mol:13g, heating to 90 ℃, reacting for 0.5h, and then cooling to obtain the carbide high-entropy ceramic precursor.

Heating and curing the obtained precursor in a drying oven, then cracking the precursor for 2.5h at 1750 ℃ in a high-temperature furnace under the vacuum condition, and cooling to obtain (HfTiNbVLa) C₅High entropy ceramics.

Example 5

(1) obtaining a metal alkoxide: selecting metal alkoxide Zr (OPr)₄、Ta(OCH₂CH₂OCH₂CH₃)₅、Nb(OCH₂CH₂OCH₃)₅And Mo (OCH)₂CH₂OCH₂CH₃)₅Wherein Ta (OCH)₂CH₂OCH₂CH₃)₅、Nb(OCH₂CH₂OCH₃)₅And Mo (OCH)₂CH₂OCH₂CH₃)₅Is prepared from metal salt TaCl₅、NbCl₅And MoCl₅Respectively dispersing the mixture in n-heptane, n-hexane and tert-butyl methyl ether, respectively dripping ethylene glycol ethyl ether, ethylene glycol methyl ether and ethylene glycol ethyl ether at the temperature of 1 ℃, then respectively dripping triethylamine, heating and refluxing for 3 hours after dripping is finished, respectively filtering to obtain metal alkoxide solution, and finally carrying out reduced pressure distillation to obtain metal alkoxide; wherein the ratio of the metal salt to the monohydric alcohol to the triethylamine is 1:7:6, 1:7.5:7.5 and 1:5:5 respectively;

(2) preparation of metal alkoxide complexes: respectively adding Zr (OPr) at 70 deg.C₄、Ta(OCH₂CH₂OCH₂CH₃)₅、Nb(OCH₂CH₂OCH₃)₅And Mo (OCH)₂CH₂OCH₂CH₃)₅Dripping ethyl acetoacetate, and continuing stirring for 2h after dripping; metal alkoxide Zr (OPr)₄、Ta(OCH₂CH₂OCH₂CH₃)₅、Nb(OCH₂CH₂OCH₃)₅、Mo(OCH₂CH₂OCH₂CH₃)₅And acetylacetone at a molar ratio of 1:1.2, 1:1.5, 1:2, and 1:1.25, respectively;

(3) co-hydrolysis: selecting the transition metal alkoxide complex prepared in the step (2), uniformly mixing the transition metal alkoxide complex and the metal in an equal molar ratio to obtain an alkoxide mixed solution, and adding Y (acac)₃Adding a mixed solution of ethylene glycol monomethyl ether and ethylene glycol ethyl ether with the amount of Y metal substances being 9 times that of the alkoxide mixed solution, heating and refluxing for 5 hours, and cooling to room temperature to obtain a rare earth compound-containing solution; uniformly mixing the alkoxide mixed solution and the rare earth compound-containing solution, slowly dripping the mixed solution of water, ethylene glycol monomethyl ether and ethylene glycol ethyl ether into the system at room temperature, wherein the molar ratio of water to total metal is 0.9:1, the mass ratio of alcohol to water is 7:1, refluxing for 1h after dripping, and distilling at normal pressure to obtain a metal copolymer;

(4) preparing a precursor: and (3) uniformly mixing the metal copolymer prepared in the step (3) with allyl phenolic aldehyde, wherein the mass ratio of the total amount of metal elements in the metal copolymer to the allyl phenolic aldehyde is 1mol:15g, heating to 70 ℃, reacting for 2h, and then cooling to obtain the carbide high-entropy ceramic precursor.

Heating and curing the obtained precursor in an oven, then cracking for 0.5h at 2000 ℃ in a high-temperature furnace under nitrogen, and cooling to obtain (ZrTaNbMoY) C₅High entropy ceramics.

Example 6

(1) obtaining a metal alkoxide: selecting metal alkoxide such as n-butyl hafnium, Ta (OPr)₅、Mo(OCH₂CH₂OCH₂CH₃)₅And W (OCH)₂CH₂OCH₃)₆Wherein n-butanol hafnium, Ta (OPr)₅、Mo(OCH₂CH₂OCH₂CH₃)₅And W (OCH)₂CH₂OCH₃)₆Is prepared from metal salt HfCl₄、TaCl₅、MoCl₅And WCl₆Respectively dispersing in toluene, n-hexane, n-heptane and xylene, respectively dripping monohydric alcohol n-butanol, n-propanol, ethylene glycol ethyl ether and ethylene glycol methyl ether at-5 ℃, then respectively dripping triethylamine, heating and refluxing for 2h after dripping is finished, respectively filtering to obtain metal alkoxide solution, and finally carrying out reduced pressure distillation to obtain metal alkoxide; wherein the metal salt, the monohydric alcohol and the triethylamine are respectively in a ratio of 1:6:5, 1:8:6, 1:6:5 and 1:12: 9;

(2) preparation of metal alkoxide complexes: respectively adding metal alkoxides of n-butyl alcohol hafnium, Ta (OPr) at room temperature₅、Mo(OCH₂CH₂OCH₂CH₃)₅And W (OCH)₂CH₂OCH₃)₆Dripping acetylacetone into the mixture, and continuing stirring for 5 hours after dripping; metal alkoxides of hafnium n-butoxide, Ta (OPr)₅、Mo(OCH₂CH₂OCH₂CH₃)₅、W(OCH₂CH₂OCH₃)₆And acetylacetone at a molar ratio of 1:1, 1:1.5, 1:2, and 1:0.9, respectively;

(3) co-hydrolysis: selecting the transition metal alkoxide complex prepared in the step (2), uniformly mixing the transition metal alkoxide complex and the metal in an equal molar ratio to obtain an alkoxide mixed solution, and adding La (acac)₃Adding a mixed solution of n-butanol and n-propanol in an amount which is 5 times that of a La metal substance, wherein the amount of the La metal substance is the same as that of a single metal element in the alkoxide mixed solution, heating and refluxing for 4 hours, and cooling to room temperature to obtain a rare earth compound-containing solution; uniformly mixing the alkoxide mixed solution and the rare earth compound-containing solution, slowly dripping the mixed solution of water, n-butyl alcohol and n-propyl alcohol into the system at room temperature, wherein the molar ratio of water to total metal is 1:1, the mass ratio of alcohol to water is 3:1, refluxing for 5 hours after dripping, and distilling at normal pressure to obtain a metal copolymer;

(4) preparing a precursor: and (3) uniformly mixing the metal copolymer prepared in the step (3) with allyl phenolic aldehyde, wherein the mass ratio of the total amount of metal elements in the metal copolymer to the allyl phenolic aldehyde is 1mol:14g, heating to 60 ℃, reacting for 1.5h, and then cooling to obtain the carbide high-entropy ceramic precursor.

Heating and curing the obtained precursor in an oven, then cracking for 1h at 1900 ℃ in a high-temperature furnace under argon, and cooling to obtain (HfTaMoWLa) C₅High entropy ceramics.

Example 7

(1) obtaining a metal alkoxide: selecting metal alkoxide Zr (OPr)₄Isobutyl alcohol hafnium, Nb (OCH)₂CH₂OCH₃)₅And W (OCH)₂CH₂OCH₃)₆Wherein isobutyl alcohol hafnium, Nb (OCH)₂CH₂OCH₃)₅And W (OCH)₂CH₂OCH₃)₆Is prepared from metal salt HfCl₄、NbCl₅And WCl₆Respectively dispersing in n-hexane, n-heptane and tert-butyl methyl ether, respectively dripping isobutanol, ethylene glycol methyl ether and ethylene glycol methyl ether at 0 ℃, then respectively dripping triethylamine, heating and refluxing for 1h after dripping is finished, respectively filtering to obtain goldPreparing metal alkoxide solution, and finally carrying out reduced pressure distillation to obtain metal alkoxide; wherein the ratio of the metal salt to the monohydric alcohol to the triethylamine is 1:8:6, 1:5:5 and 1:7.5:7.5 respectively;

(2) preparation of metal alkoxide complexes: respectively adding Zr (OPr) at 40 deg.C₄Isobutyl alcohol hafnium, Nb (OCH)₂CH₂OCH₃)₅And W (OCH)₂CH₂OCH₃)₆Dripping acetylacetone into the solution, and continuing stirring for 2h after dripping; metal alkoxide Zr (OPr)₄Isobutyl alcohol hafnium, Nb (OCH)₂CH₂OCH₃)₅、W(OCH₂CH₂OCH₃)₆And acetylacetone at a molar ratio of 1:0.8, 1:2, and 1:3, respectively;

(3) co-hydrolysis: selecting the transition metal alkoxide complex prepared in the step (2), uniformly mixing the transition metal alkoxide complex and the metal in an equal molar ratio to obtain an alkoxide mixed solution, and adding Y (acac)₃Adding a mixed solution of isobutanol and n-propanol with the amount of 7 times that of a Y metal substance, wherein the amount of the Y metal substance is the same as that of a single metal element in the alkoxide mixed solution, heating and refluxing for 1.5h, and cooling to room temperature to obtain a rare earth compound-containing solution; uniformly mixing the alkoxide mixed solution and the rare earth compound-containing solution, slowly dripping the mixed solution of water, isobutanol and n-propanol into the system at the temperature of 60 ℃, wherein the molar ratio of the water to the total metal is 0.8:1, the mass ratio of the alcohol to the water is 8:1, refluxing for 2 hours after dripping, and distilling at normal pressure to obtain a metal copolymer;

Heating the obtained precursor in an oven for curing, then cracking at 1850 ℃ for 3.5h under the vacuum condition in a high-temperature furnace, and cooling to obtain (ZrHfNbWY) C₅High entropy ceramics.

Example 8

(1) obtaining a metal alkoxide: selecting metal alkoxide Ti (Oi-Pr)₄、Ta(OPr)₅、Mo(OCH₂CH₂OCH₂CH₃)₅And W (OCH)₂CH₂OCH₃)₆Wherein Ta (OPr)₅、Mo(OCH₂CH₂OCH₂CH₃)₅And W (OCH)₂CH₂OCH₃)₆Is prepared from metal salt TaCl₅、MoCl₅And WCl₆Respectively dispersing in n-heptane, toluene and xylene, respectively dripping monohydric alcohol n-propanol, ethylene glycol ethyl ether and ethylene glycol methyl ether at-8 ℃, then dripping triethylamine, heating and refluxing for 2h after dripping is finished, respectively filtering to obtain metal alkoxide solution, and finally carrying out reduced pressure distillation to obtain metal alkoxide; wherein the ratio of the metal salt to the monohydric alcohol to the triethylamine is 1:10:7, 1:8:6 and 1:7:6 respectively;

(2) preparation of metal alkoxide complexes: respectively adding metal alkoxide Ti (Oi-Pr) at room temperature₄、Ta(OPr)₅、Mo(OCH₂CH₂OCH₂CH₃)₅And W (OCH)₂CH₂OCH₃)₆Dripping acetylacetone into the mixture, and continuing stirring for 5 hours after dripping; metal alkoxide Ti (Oi-Pr)₄、Ta(OPr)₅、Mo(OCH₂CH₂OCH₂CH₃)₅、W(OCH₂CH₂OCH₃)₆And acetylacetone at a molar ratio of 1:0.6, 1:2.5, 1:1, and 1:0.9, respectively;

(3) co-hydrolysis: selecting the transition metal alkoxide complex prepared in the step (2), uniformly mixing according to the molar ratio of Ta to Ti to Mo to W of 35:5:20:15 to obtain an alkoxide mixed solution, adding La (acac)₃And Y (acac)₃Adding n-propanol of which the amount is 5 times that of La and Y metal substances into the mixture, wherein the ratio of the amount of the La and Y metal substances to the amount of each metal element substance in the alkoxide mixed solution is Ta: Ti: Mo: W: La: Y: 35:5:20:15:15:10, heating and refluxing for 5 hours, and cooling to room temperature to obtain a rare earth-containing compound solution; uniformly mixing the alkoxide mixed solution and the rare earth compound-containing solution, and slowly dripping the mixed solution of water, n-butyl alcohol and n-propyl alcohol into the system at room temperature, whereinThe molar ratio of water to total metal is 1.2:1, the mass ratio of alcohol to water is 8:1, the mixture is dripped and refluxed for 5 hours, and the metal copolymer is obtained by normal pressure distillation;

(4) preparing a precursor: and (3) uniformly mixing the metal copolymer prepared in the step (3) with allyl phenolic aldehyde, wherein the mass ratio of the total amount of metal elements in the metal copolymer to the allyl phenolic aldehyde is 1mol:13g, heating to 50 ℃, reacting for 4h, and then cooling to obtain the carbide high-entropy ceramic precursor.

And heating and curing the obtained precursor in an oven, then cracking for 1h at 2000 ℃ in a high-temperature furnace under a vacuum condition, and cooling to obtain the carbide high-entropy ceramic containing Ta, Ti, Mo, W, La and Y elements.

Comparative example 1

This comparative example Hf (OPr) in step (2) was added based on example 2₄The molar ratio of acetylacetone to acetylacetone was adjusted to 1:0.5, and the other embodiment of this comparative example was the same as example 2.

Comparative example 2

This comparative example is based on example 7, and W (OCH) in step (2)₂CH₂OCH₃)₆The molar ratio of acetylacetone to acetylacetone was adjusted to 1:3.1, and the other embodiment of this comparative example was the same as example 7.

Comparative example 3

This comparative example was conducted in the same manner as in example 3 except that the molar ratio of water to the total metal in step (3) was adjusted to 1.4:1 based on example 3.

Comparative example 4

This comparative example was conducted in the same manner as in example 7 except that the molar ratio of water to the total metal in step (3) was adjusted to 0.7:1 based on example 7.

Comparative example 5

In this comparative example, the metal copolymer obtained by atmospheric distillation in the step (3) was adjusted to a metal copolymer obtained by vacuum distillation based on example 5, and other embodiments of this comparative example were the same as example 5.

Experimental example 1

The experimental examples examined the storage stability of the high-entropy ceramic precursor by measuring the initial viscosity of the precursors prepared in the examples and comparative examples of the present invention and the viscosity after 12 months storage at room temperature, respectively, and performing comparative analysis of the rate of change. Meanwhile, the experimental example also describes the shape and property of the precursors prepared in the examples and the comparative examples in the reaction process and at the end, and the detailed expression is shown in the following table.

As can be seen from the above table, the precursors provided in embodiments 1 to 8 of the present application are all metal copolymers with uniformly distributed elements and easily soluble in conventional organic reagents. The comparative examples 1 and 2 adjust the adding proportion of the metal alkoxide and the complexing agent, when the content of the complexing agent is low, the speed of the subsequent hydrolysis reaction is high, precipitation occurs in the reaction process, a soluble precursor with uniformly distributed elements cannot be obtained, and when the content of the complexing agent is high, the speed of the hydrolysis process is low, so that sufficient reaction cannot be achieved, a large amount of alcoholic oxygen residue causes instability of the precursor, and gelation occurs in the storage process. Similarly, in comparative examples 3 to 4, the proportion of water added in the hydrolysis process was adjusted on the basis of the examples, so that the hydrolysis reaction was too fast or insufficient, and a precursor with uniformly distributed molecules and suitable for long-term storage could not be prepared.

Comparative example 5 is a distillation mode in which the hydrolysis process was adjusted, atmospheric distillation was used instead of vacuum distillation, and the polymer precursor further underwent post-polymerization reaction during distillation, further reducing the excess hydroxyl groups generated by the hydrolysis reaction in the system, and thus improving the storage stability of the precursor. The inventor researches and finds that the viscosity change rate of atmospheric distillation is obviously smaller than that of vacuum distillation, and the method is more suitable for producing precursors with good storage property.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. The high-entropy carbide ceramic precursor containing rare earth is characterized by comprising at least 4 transition metal elements and at least 1 rare earth metal element, wherein the amount of each metal element in the precursor accounts for 5-35% of the total amount of metal substances, and each element is uniformly dispersed in a molecular level; dissolving the precursor in one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol monomethyl ether or ethylene glycol ethyl ether; the viscosity change of the precursor is less than 8% within 12 months; the transition metal element is selected from Ti, Zr, Hf, V, Nb, Ta, Mo or W element, and the rare earth metal element is selected from Y or La element.

2. A rare-earth-containing carbide high-entropy ceramic precursor according to claim 1, wherein the amount of each metal element substance in the precursor is the same.

3. A method for producing a high-entropy ceramic precursor containing rare-earth carbide according to claim 1 or 2, characterized by comprising:

(3) preparing a precursor: uniformly mixing the metal copolymer obtained in the step (2) with allyl phenolic aldehyde, heating to 50-90 ℃, reacting for 0.5-4 h, and cooling to obtain a carbide high-entropy ceramic polymer precursor;

the molar ratio of the transition metal alkoxide to the complexing agent in the step (1) is 1 (0.15-0.5) n; when M in the transition metal alkoxide is selected from Ti, Zr, or Hf, n is 4; when M in the transition metal alkoxide is V, Nb, Ta or Mo, n is 5; when M in the transition metal alkoxide is W, n is 6, and the complexing agent is acetylacetone and/or ethyl acetoacetate;

the molar ratio of water to total metal in the step (2) is 0.8-1.3: 1.

4. A method for preparing a high-entropy ceramic precursor containing rare-earth carbide according to claim 3, wherein the rare-earth element-containing compound in the step (2) is at least one selected from yttrium acetylacetonate and lanthanum acetylacetonate.

5. The preparation method of the high-entropy ceramic precursor containing the rare earth carbide according to claim 4, wherein before the mixing of the rare earth element-containing compound and the transition metal alkoxide complex, a monohydric alcohol is added into the rare earth element-containing compound in the step (2) for heating and refluxing for 0.5-5 h, the molar ratio of the monohydric alcohol to the rare earth element-containing compound is 5-10: 1, and the monohydric alcohol is selected from one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol monomethyl ether and ethylene glycol ethyl ether.

6. The preparation method of the high-entropy ceramic precursor containing the rare earth carbide according to claim 5, wherein the mass ratio of monohydric alcohol to water in the step (2) is 3-8: 1; the monohydric alcohol is selected from one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol monomethyl ether and ethylene glycol ethyl ether.

7. The method for preparing the high-entropy ceramic precursor containing the rare earth carbide according to claim 3, wherein the mass ratio of the total metal content in the metal copolymer to the allyl phenol formaldehyde content in the step (3) is 1mol: 13-15 g.

8. The carbide high-entropy ceramic is characterized in that the carbide high-entropy ceramic is in a single crystal phase and comprises at least 4 transition metal elements and at least 1 rare earth metal element, and all the elements are uniformly distributed in a molecular level; the carbide high-entropy ceramic is prepared from the rare earth-containing carbide high-entropy ceramic precursor of claim 1 or 2.

9. The preparation method of the carbide high-entropy ceramic as claimed in claim 8, which is characterized in that the carbide high-entropy ceramic precursor containing rare earth as claimed in claim 1 or 2 is prepared by solidifying and cracking, wherein the cracking temperature is not lower than 1600 ℃, and the cracking time is 0.5-5 h; the cracking is carried out under the protection of a vacuum environment or an inert atmosphere.

10. The method for preparing the carbide high-entropy ceramic according to claim 9, wherein the cracking temperature is 1700 to 2000 ℃.