CN116284804A - High-entropy boride ceramic precursor, ceramic powder, and preparation methods and applications thereof - Google Patents

High-entropy boride ceramic precursor, ceramic powder, and preparation methods and applications thereof Download PDF

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CN116284804A
CN116284804A CN202111566900.9A CN202111566900A CN116284804A CN 116284804 A CN116284804 A CN 116284804A CN 202111566900 A CN202111566900 A CN 202111566900A CN 116284804 A CN116284804 A CN 116284804A
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boride ceramic
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弓伟露
叶丽
赵彤
韩伟健
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Abstract

The invention belongs to the technical field of high-entropy materials, and particularly relates to a high-entropy boride ceramic precursor, ceramic powder, a preparation method and application thereof, wherein the high-entropy boride ceramic precursor is a polymer formed by connecting a metal source and a boron carbon source through a bridge oxygen bond, and comprises a metal element M and a boron element, and the metal element M is at least 4 kinds selected from Ti, zr, hf, V, nb, ta, mo, W. The ceramic powder is a solid solution with high purity and complete chemical uniformity, and each element in the solid solution is uniformly distributed in molecular level.

Description

High-entropy boride ceramic precursor, ceramic powder, and preparation methods and applications thereof
Technical Field
The invention belongs to the technical field of high-entropy materials, and particularly relates to a high-entropy boride ceramic precursor, ceramic powder, and a preparation method and application thereof.
Background
The superhigh temperature ceramic is a compound with melting point higher than 3000 ℃, has excellent heat protection characteristics such as high modulus, high hardness, high strength and the like, can adapt to extreme environments such as superhigh speed long-time flight, atmospheric reentry, straddling flight, rocket propulsion system and the like, and can be applied to various key components such as nose cones, wing front edges, engine hot ends and the like of aircrafts. The transition metal boride ceramic has high melting point, high hardness, high electrical conductivity, high thermal conductivity, low thermal expansion coefficient, good oxidation resistance and thermal shock resistance, is a candidate material of ultra-high temperature ceramic, and has wide application prospect in the aerospace field.
The high-entropy alloy is an alloy obtained by alloying 5 or more than 5 element components according to the equal atomic ratio or near equal atomic ratio, has superior properties which are incomparable with the traditional alloy, such as high strength, high hardness, high wear resistance and corrosion resistance, and the like, and the high-entropy ceramic has the advantages of high melting point, high hardness and the like, and becomes a great research hotspot because the ceramic powder can form a solid solution with stable high mixed entropy after being sintered.
The high entropy boride ceramic is an emerging single-phase solid solution ceramic material formed of 5 or more metal borides of nearly equimolar ratio, having a hexagonal crystal structure of two-dimensional boron layers and metal layers alternately arranged. The high-entropy boride ceramic further improves the performance of the ceramic through the high-entropy effect and the fine component regulation and control on the basis of enriching the variety of the ceramic field.
2016, gild et al (Scientific Reports 2016,6,1-10) were successful for the first time with ZrB 2 、HfB 2 、TaB 2 、TiB 2 、MoB 2 、NbB 2 And CrB 2 The transition metal diboride is used as a raw material and is prepared by adopting a Spark Plasma Sintering (SPS) process to prepare (Hf) 0.2 Zr 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 、(Hf 0.2 Zr 0.2 Ta 0.2 Mo 0.2 Ti 0.2 )B 2 、(Hf 0.2 Zr 0.2 Mo 0.2 Nb 0.2 Ti 0.2 )B 2 A series of high entropy ceramics, transition metal elements and boronThe element distribution is more uniform, and compared with the single-phase boride ceramic prepared by the same method, the single-phase boride ceramic has the advantages of optimizing the hardness, oxidation resistance and the like. However, since the grinding step is involved in the preparation process of the commercial boride raw material, impurities such as oxides and the like are easily introduced, so that sintering densification is difficult, and the highest density is only 92.4%. To solve the problem of densification, gild et al (Scripta Materialia,2019,170,106-110) improved the above method by adding a small amount of C to the original boride powder, pre-sintering at 1600 ℃ and 30MPa for 5min, and then heat treating the powder by lightning spark plasma sintering under different power conditions without using a die to obtain a dense (Hf) of 99.3% 0.2 Zr 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 High entropy ceramics, but still with small amounts of oxide and carbide impurities in the system.
To avoid the introduction of oxide impurities from the feedstock, the borothermal/carbothermic reduction process began to be one of the research hotspots for preparing high entropy ceramics. Zhang et al (Journal ofthe European Ceramic Society,2019, 39, 3920-3924) produced corresponding boride powders of metal oxide, boron carbide and carbon powder by a borocarbothermic reaction at 1600℃and SPS was successfully employed to produce (Hf) 0.2 Zr 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 、(Hf 0.2 Zr 0.2 Mo 0.2 Nb 0.2 Ti 0.2 )B 2 、(Hf 0.2 Mo 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 The hardness and the compactness of the high-entropy ceramic prepared by the method are greatly improved, in particular (Hf) 0.2 Zr 0.2 Mo 0.2 Nb 0.2 Ti 0.2 )B 2 The density of the high-entropy ceramic of the system reaches 98.5%, and the hardness also reaches 27GPa. However, oxide impurities still exist in the obtained high-entropy ceramic, and uniformity of distribution of Nb and Hf elements is poor. Liu et al (Scripta Materialia,2019, 167, 110-114) prepared (Hf) at 1700 ℃ by a boron thermal reduction reaction using a metal oxide and boron powder as raw materials 0.2 Zr 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 The high entropy powder had a particle size of about 310nm and was shown to have no significant oxide impurity peaks by XRD analysis. The Friedel-crafts team (Gu, science ChinaMaterials,2019, 62, 1898-1909) of the university of Wuhan uses boron carbide to reduce metal oxide to obtain fine and high-purity boride powder at 1700 ℃, the oxygen content and the carbon content are respectively 0.64% and 0.04%, and then the fine and high-purity dense (Hf) is obtained by SPS and heat preservation at 2050 ℃ for 5min 0.2 Zr 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 High entropy boride ceramic.
In addition to the above several methods, tallarita et al (Script materials,2019, 158, 100-104) reported that Hf, mo, ta, nb, ti, B powder was uniformly reacted by self-propagating reaction (SHS), after which the SHS powder was prepared by Spark Plasma Sintering (SPS) at 1950deg.C (Hf) 0.2 Mo 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )B 2 High entropy ceramic, however, oxide impurities still exist in the prepared high entropy ceramic, and the sintering densification and the hardness improvement of the ceramic are affected.
At present, the reported high-entropy boride ceramic is prepared by adopting an inorganic method, has the advantage of easily available raw materials, but also has the problems of impure product and larger particle size, so that innovation of a preparation method of the high-entropy boride is urgent.
Disclosure of Invention
In order to solve the technical problems, the invention provides a high-entropy boride ceramic precursor, ceramic powder, and preparation methods and applications of the high-entropy boride ceramic precursor and the ceramic powder.
The high-entropy boride ceramic precursor is a polymer connected by a metal source-boron carbon source through a bridging oxygen bond, and comprises a metal element M and boron elements, wherein the metal element M is selected from at least 4 of Ti, zr, hf, V, nb, ta, mo, W.
According to an embodiment of the present invention, the amount of the substance of each metal element is 5 to 35% of the amount of the total metal substance of the high entropy boride ceramic precursor, respectively.
According to an embodiment of the present invention, the amounts of the substances of the respective metal elements are the same or different, preferably the same.
According to an embodiment of the invention, the ratio of the amount of the substance of the boron element to the total amount of the substance of the metal element is 2.2 to 5:1, preferably 3 to 4:1, for example 3:1.
According to the embodiment of the invention, the metal-carbon-boron elements in the high-entropy boride ceramic precursor are uniformly distributed at the molecular level, and the metal elements, boron and carbon elements are uniformly distributed in a short range.
The invention also provides a preparation method of the high-entropy boride ceramic precursor, which comprises the following steps:
(1) Preparing a metal alkoxide copolymer solution;
(2) Preparing a boron carbon source solution: mixing a boron source and a carbon source in C1-C4 organic acid, and raising the temperature to 50-100 ℃ to react for 0.5-3 h;
(3) Mixing the metal alkoxide copolymer solution in the step (1) with the boron carbon source solution in the step (2), heating to 80-100 ℃ for a first heating reaction, heating to 110-150 ℃ for a second heating reaction after the reaction to the system gel, and drying and cooling to obtain the high-entropy boride ceramic precursor.
According to an embodiment of the invention, in step (3), the C1-C4 organic acid comprises at least one of formic acid, acetic acid, propionic acid or butyric acid, for example acetic acid.
According to an embodiment of the invention, in step (3), the ratio of the amount of the substance of the boron element to the total amount of the substances of the metal element in the boron carbon source is 2.2 to 5:1, preferably 3 to 4:1, for example 3:1.
According to an embodiment of the present invention, in step (3), the temperature of the first heating reaction is 85 to 95 ℃, the reaction time is 0.5 to 3 hours, preferably the reaction time is 1 to 2 hours.
According to an embodiment of the present invention, in step (3), the temperature of the second heating reaction is 120 to 130 ℃, the reaction time is 3 to 10 hours, preferably the reaction time is 4 to 6 hours.
According to an embodiment of the invention, the mixing in step (3) is carried out at a temperature of 40 to 80 ℃, preferably 50 to 70 ℃, e.g. maintaining the temperature of the boron carbon source at 45 ℃, and the metal alkoxide copolymer is added for mixing.
According to an embodiment of the invention, the boron source in step (3) is boric acid and the carbon source is a polyol, such as sorbitol.
According to an embodiment of the invention, the ratio of the amounts of the substances of the boron source, the carbon source and the acetic acid in step (3) is 1:0.2 to 1.5:0.4 to 4, preferably 1:0.5 to 1:1 to 3, for example 1:0.5:1.
According to an embodiment of the present invention, the drying in step (3) is vacuum drying, the drying temperature is 80-150 ℃, the drying time is 3-8 hours, preferably the drying temperature is 100-120 ℃, and the drying time is 4-6 hours.
According to an embodiment of the present invention, the metal alkoxide copolymer solution includes the steps of:
a. adding complexing agent into metal alkoxide M (OR) n to react at room temperature-80 ℃ to obtain metal alkoxide complex;
b. and d, selecting at least 4 metal alkoxide complexes containing different metal elements prepared in the step a, uniformly mixing, slowly dropwise adding a mixed solution of water and monohydric alcohol at the temperature of between room temperature and 90 ℃, and completely refluxing for 1 to 5 hours to prepare a metal alkoxide copolymer solution.
According to an embodiment of the invention, said M in step M (OR) n has the definition as described above.
As an example, when the M is selected from Hf, V, nb, ta, mo or W, the metal alkoxide is prepared as follows: dispersing the metal salt of M in an organic solvent, dripping monohydric alcohol at the temperature of-10-5 ℃, then dripping triethylamine, heating and refluxing for 1-5 h after the dripping is finished, and filtering to obtain a metal alkoxide solution.
According to an embodiment of the invention, the metal salt of M is selected from MCln or M (NO 3 )n。
According to an embodiment of the invention, n is determined according to the valence of M, for example when M is selected from Ti, zr or Hf, n is 4; when M is selected from V, nb, ta or Mo, n is 5; when M is W, n is 6.
According to an embodiment of the invention, the ratio of metal alkoxide, monohydric alcohol and triethylamine is 1: (1-2) n: (1-1.5) n.
According to an embodiment of the present invention, the organic solvent is one or more of n-hexane, n-heptane, toluene, xylene, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and tert-butyl methyl ether.
According to an embodiment of the present invention, the monohydric alcohol is selected from one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol methyl ether, and ethylene glycol ethyl ether.
According to an embodiment of the invention, the molar ratio of metal alkoxide to complexing agent in step b is 1 (0.12 to 0.4) n, preferably 1 (0.2 to 0.3) n.
According to an embodiment of the invention, the complexing agent in step b is one or a mixture of two of acetylacetone and ethyl acetoacetate.
According to an embodiment of the invention, the reaction time in step b is 0.1 to 5 hours, preferably 1 to 3 hours.
According to an embodiment of the invention, the molar ratio of water to total metal in step c is 0.9-1.5:1, the mass ratio of monohydric alcohol to water is 3-8:1, preferably the molar ratio of water to total metal is 1-1.2:1, and the mass ratio of monohydric alcohol to water is 5-7:1.
According to an embodiment of the present invention, the monohydric alcohol in step c is selected from one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol methyl ether, ethylene glycol ethyl ether.
The invention also provides application of the high-entropy boride ceramic precursor in preparing high-entropy boride ceramic powder.
The invention also provides high-entropy boride ceramic powder, which is obtained by the high-entropy boride ceramic precursor through glue discharging and cracking.
According to an embodiment of the invention, the high entropy boride ceramic powder has the chemical formula MB y For example (Ti 1 Zr 0.99 Hf 1.02 Nb 1.02 Ta 1.00 )B 10.06 。
According to an embodiment of the invention, the high entropy boride ceramic powder is a solid solution.
According to an embodiment of the present invention, the solid solution is a crystal having a hexagonal crystal phase.
According to an embodiment of the present invention, the high entropy boride ceramic powder particles have a size of 100nm to 1 μm, preferably 300nm to 800nm, for example 300 to 500nm.
According to an embodiment of the present invention, the metallic element in the solid solution is the same as the metallic element in the high entropy boride ceramic precursor.
According to the embodiment of the invention, the metallic elements and the boron elements in the solid solution are uniformly distributed at the molecular level.
The invention also provides a preparation method of the high-entropy boride ceramic powder, which comprises the following steps: and (3) performing glue discharging and cracking on the high-entropy boride ceramic precursor to obtain high-entropy boride ceramic powder.
According to the embodiment of the invention, the glue discharging temperature is not higher than 500 ℃, and the glue discharging time is 0.5-4 h; preferably, the glue discharging temperature is 400-500 ℃, the glue discharging time is 1-3 hours, for example, the glue discharging is 2 hours at 400 ℃.
According to the embodiment of the invention, the cracking temperature is not lower than 1500 ℃, and the cracking time is 0.5-5 h; preferably, the cleavage temperature is 1700 to 2000℃and the cleavage time is 1 to 4 hours, for example 4 hours at 1800 ℃.
According to an embodiment of the invention, the evacuation is performed under an inert atmosphere, the pyrolysis is performed under vacuum or under an inert atmosphere, the inert atmosphere is selected from argon, helium or a gas mixture of the two.
The invention also provides high-entropy boride ceramic, which is prepared from the high-entropy boride ceramic powder.
The invention also provides the application of the high-entropy boride ceramic in heat protection, such as the application in aircrafts and rockets.
The invention also provides a heat-proof product, the surface of which is provided with the high-entropy boride ceramic or is made of the high-entropy boride ceramic.
In the above-described scheme, the researchers of the present invention found that there is a difference in reactivity in forming complexes with respect to different types of metal elements, and if complexing agents are added in a proportion outside the scope of the present invention, although complexes can be formed, in the subsequent mixed hydrolysis of alkoxide complexes of various metal elements, a precursor having uniformly distributed molecules cannot be formed due to a reaction equilibrium inclination caused by the difference in the addition amount of the complexing agents. In addition, the addition amount of the complexing agent can influence the amount of residual active groups of the obtained metal alkoxide copolymer, so that the reactivity of the metal alkoxide copolymer and the boron carbon source is influenced.
In the scheme, the proportion of the alkoxide to the water is obtained on the basis of considering the mixture of metal alkoxides with different reactivity, so that the reactivity of various metal alkoxides in cohydrolysis tends to be similar, thus obtaining alkoxide copolymers with uniformly distributed metal element molecular levels, and simultaneously retaining the reactivity of the metal alkoxide copolymers with boron carbon sources.
In order to further improve the reactivity of the metal alkoxide copolymer and the boron carbon source, on the basis of controlling the dosage of the ligand and the water, the metal alkoxide copolymer is mixed and reacted with the boron carbon source in a solution form (instead of the metal alkoxide copolymer with the solvent removed by distillation), and the metal alkoxide copolymer is added in the solution form, so that the reduction of active groups in the metal alkoxide copolymer due to the continuous reaction in the distillation process can be avoided, and the problem of unmatched reactivity of the metal alkoxide copolymer and the boron carbon source is avoided.
In the preparation method, the boron source and the carbon source need to be prepared into the boron carbon source through polymerization reaction, which mainly aims to solve the problem that the reaction speed of the boron source boric acid and the reaction speed of the carbon source polyol and the metal polymer are not matched, specifically, the boron source boric acid reacts with the metal copolymer slowly due to poor solubility and low reaction activity, the reaction speed of the carbon source polyol and the metal polymer is too fast, if the boron source boric acid and the carbon source polyol react with the metal copolymer respectively, the polyol and the metal copolymer are easy to react rapidly, precipitation occurs, the reaction activity of the metal copolymer is reduced, and boric acid cannot participate in the reaction, so that a precursor with target element content and uniformly distributed elements in molecular level cannot be obtained.
Firstly, a boron source reacts with a carbon source to prepare a boron carbon source, then, a metal source and the boron carbon source are subjected to polymerization reaction, the metal source and the boron carbon source are connected through a bridging oxygen bond, so that a polymer with metal-carbon-boron elements uniformly distributed in molecular level is formed, the metal elements and B, C elements in the polymer are uniformly distributed in short range, the boron carbon thermal reduction reaction in the precursor cracking process is facilitated, and the high-entropy boride ceramic with uniformly distributed elements is prepared at a relatively low temperature.
The reactivity of the metal alkoxide is reduced after the metal alkoxide is copolymerized to form the metal alkoxide copolymer, and the reactivity of the carbon source and the boron source is also reduced after the reaction, so that the proper activity reduction treatment is beneficial to the control of the reaction process to obtain a more uniform precursor.
When the boron carbon source is prepared by reacting the carbon source with the boron source, the boron source boric acid cannot be guaranteed to be completely reacted with the carbon source due to excessive boric acid, and in order to prevent the unreacted boric acid from being separated out after the temperature is reduced in the step (3), the reaction activity of the boric acid is affected, and the element uniformity of a product is further affected, wherein the mixing temperature of the metal copolymer and the boron carbon source is 40-80 ℃.
The precursor is subjected to a carbothermic reaction during the whole cracking process, so that the metal source, the boron source and the carbon source are fed in a proper proportion range, or the metal carbide impurity phase occurs due to insufficient boron or excessive carbon, or the boron carbide impurity phase occurs due to excessive boron.
The high-entropy boride ceramic precursor is a polymer formed by connecting a metal source and a boron carbon source through a metal bridge oxygen bond, the metal source is prepared by the way of cohydrolysis of metal alkoxide, and the boron carbon source is prepared by reacting a boron-containing compound with polyalcohol. Therefore, firstly, the metal alkoxide is prepared into a metal source through cohydrolysis, on one hand, the proportion change of metal elements caused by the reactivity difference between the metal alkoxides is avoided, and on the other hand, the various metals are uniformly distributed in the precursor in molecular level. Meanwhile, in order to avoid element loss or element uneven distribution caused by unmatched reactivity between a boron source and a carbon source and a metal copolymer, the boron source and the carbon source are subjected to pre-reaction to prepare the boron carbon source, and then the boron carbon source and the metal polymer react, so that each element in the precursor is ensured to be uniformly distributed in molecular level.
Advantageous effects
In the prior art, boride high-entropy ceramic is mostly prepared by an inorganic powder reaction sintering method, the purity of the obtained solid solution is not high (impurity peaks exist on XRD), and the element distribution is uneven. The boride high-entropy boride ceramic precursor is prepared by adopting the polymer precursor method, and elements in the polymer precursor are uniformly dispersed at a molecular level, so that the uniform distribution of the elements is maintained in the solidification and cracking processes, and the uniform distribution of the elements of the boride solid solution is facilitated, and therefore, the high-purity and completely chemically uniform solid solution can be obtained at a relatively low temperature (1700-2000 ℃ for example 1800 ℃), and each element in the solid solution is uniformly distributed at the molecular level.
Drawings
FIG. 1 is an XRD pattern of the high entropy boride ceramic powder obtained in example 2.
Fig. 2 is an SEM and EDS image of the high entropy boride ceramic powder obtained in example 2.
Fig. 3 is an XRD pattern of the ceramic powder obtained in comparative example 1.
Fig. 4 is an XRD pattern of the ceramic powder obtained in comparative example 2.
Fig. 5 is an XRD pattern of the ceramic powder obtained in comparative example 3.
FIG. 6 is an XRD pattern of the ceramic powder obtained in comparative example 5.
Detailed Description
The high-entropy ceramic precursor, the preparation method and the application of the high-entropy ceramic precursor according to the present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are illustrative only and are not to be construed as limiting the scope of the invention. All techniques implemented based on the above description of the invention are intended to be included within the scope of the invention.
Unless otherwise indicated, the starting materials and reagents used in the following examples were either commercially available or may be prepared by known methods.
Example 1 preparation of high entropy boride ceramic precursor:
(1) Obtaining metal alkoxide: ti (OPr) 4 、Zr(OPr) 4 、Hf(OPr) 4 、Nb(OCH 2 CH 2 OCH 2 CH 3 ) 5 And Ta (OCH) 2 CH 3 ) 5
Ti(OPr) 4 、Zr(OPr) 4 Is obtained by direct purchase, hf (OPr) 4 And Nb (OCH) 2 CH 2 OCH 2 CH 3 ) 5 、Ta(OCH 2 CH 3 ) 5 The preparation method comprises the following steps:
wherein Hf (OPr) 4 And Nb (OCH) 2 CH 2 OCH 2 CH 3 ) 5 Is prepared by adding metal salt HfCl 4 And NbCl 5 Dispersing in n-heptane respectively, respectively dripping monohydric alcohol n-propanol and ethylene glycol diethyl ether at-10deg.C, then dripping triethylamine respectively, heating and refluxing for 1 hr after dripping, and filtering to obtain metal alkoxide solution; wherein HfCl 4 The mol ratio of the n-propanol to the triethylamine is 1:4:4, nbCl 5 The molar ratio of the ethylene glycol diethyl ether to the triethylamine is 1:5:6.
Ta(OCH 2 CH 3 ) 5 Is prepared from metal salt TaCl 5 Dispersing in ethylene glycol dimethyl ether, firstly dripping monohydric alcohol ethanol at-5 ℃, then dripping triethylamine, heating and refluxing for 1h after dripping, and filtering to obtain a metal alkoxide solution; wherein TaCl 5 The molar ratio of ethanol to triethylamine is 1:5:5.
(2) Preparation of metal alkoxide complexes: at 40 ℃, to the metal alkoxides Ti (OPr) 4 、Zr(OPr) 4 、Hf(OPr) 4 、Nb(OCH 2 CH 2 OCH 2 CH 3 ) 5 And Ta (OCH) 2 CH 3 ) 5 Adding acetylacetone serving as a complexing agent dropwise, and continuously stirring for 0.1h after completing the dropwise addition to obtain a metal alkoxide complex; metal alkoxide Ti (OPr) 4 、Zr(OPr) 4 、Hf(OPr) 4 、Nb(OCH 2 CH 2 OCH 2 CH 3 ) 5 、Ta(OCH 2 CH 3 ) 5 And acetylacetone in a molar ratio of 1:0.48, 1:0.8, 1:1, 1:2, and 1:2, respectively.
(3) Co-hydrolysis: uniformly mixing the metal alkoxide complex obtained in the step (2) according to the equimolar ratio of metal, slowly dropwise adding a mixed solution of water and n-propanol into the system at room temperature, wherein the molar ratio of water to total metal is 1.5:1, the mass ratio of n-propanol to water is 4:1, and completely refluxing for 5 hours to obtain the metal alkoxide copolymer solution.
(4) Preparing a boron carbon source: uniformly mixing boric acid and sorbitol in acetic acid, and then reacting at 60 ℃ for 2 hours to obtain a boron carbon source solution; the ratio of the amounts of boric acid, sorbitol and acetic acid was 1:0.5:1.
(5) Preparing a precursor: maintaining the temperature of the boron carbon source solution prepared in the step (4) at 45 ℃, adding the metal alkoxide copolymer solution obtained in the step (3) into the boron carbon source solution, heating to 80 ℃ to perform a first heating reaction, reacting for 1h to obtain a system gel, and heating to 120 ℃ to perform a second heating reaction for 5h; finally, drying the gel in a vacuum oven at 120 ℃ for 4 hours, and cooling to obtain a high-entropy boride ceramic precursor;
the ratio of the total amount of the metal in the metal alkoxide copolymer to the amount of the boron element in the boron carbon source was 1:3.
EXAMPLE 2 preparation of high entropy boride ceramic powder
The high-entropy boride ceramic precursor prepared in example 1 was discharged at 400 ℃ under argon for 2 hours, and then the discharged gel product was cracked at 1800 ℃ under vacuum for 4 hours to prepare high-entropy boride ceramic powder (hereinafter referred to as ceramic).
As shown in FIG. 1, the XRD pattern of the ceramic shows only one group of diffraction peaks, which indicates that solid solution occurs, metal atoms are completely dissolved into one lattice, and impurity peaks of metal oxide or metal carbide or boron carbide are not contained in the system.
The metal element content of the ceramic was tested using inductively coupled plasma spectroscopy, with the following results: ti-6.6%, zr-2.4%, hf-25.1%, nb-13.1%, ta-25%, B-15%, in an empirical formula (Ti) 1 Zr 0.99 Hf 1.02 Nb 1.02 Ta 1.00 )B 10.06 It can be seen that the contents of the five metals and boron element are close to the theoretical values.
The oxygen content of the ceramic is only 0.8% by adopting an oxygen-nitrogen analyzer, which shows that the ceramic prepared by the method has lower oxygen content.
As shown in fig. 2, which shows SEM of the ceramic and its EDS, the average particle size of the ceramic is 300nm, and the EDS shows that the metal elements are uniformly distributed, which indicates that element segregation does not occur in the cracking process, and thus, fine and uniform high-entropy boride ceramic powder is formed by the above method.
Comparative example 1 preparation of high entropy boride ceramic precursor
This comparative example was carried out by adjusting the ratio of the total amount of the metal substances to the amount of the boron element substances in the boron carbon source in the step (4) to 1:6 on the basis of example 1; other conditions were the same as in example 1.
As shown in fig. 3, two diffraction peaks appear in the XRD pattern of the ceramic precursor obtained in comparative example 1, one being a high-entropy boride and the other being a boron carbide peak (impurity peak), indicating that the high-entropy boride ceramic precursor obtained in this comparative example contains boron carbide impurities, i.e., when the boron-carbon source amount exceeds the range defined in the present invention (the ratio of the amount of boron element substance to the total amount of metal element substance is 2.2 to 5:1), a pure-phase high-entropy boride ceramic precursor cannot be obtained.
Comparative example 2 preparation of high entropy boride ceramic precursor
This comparative example was based on example 1, with the molar ratio of boric acid, sorbitol and acetic acid adjusted to 1:2:1; other conditions of the comparative example were the same as in example 1.
As shown in FIG. 4, the XRD patterns of the ceramic precursor obtained in this comparative example show that when two groups of diffraction peaks, one group being high-entropy boride and the other group being impurity peaks of high-entropy carbide, the amount of carbon source is beyond the limit of the present invention (the ratio of the amounts of boron source, carbon source and acetic acid is 1:0.2-1.5:0.4-4), the pure-phase high-entropy boride ceramic precursor cannot be obtained.
Comparative example 3
This comparative example was based on example 1, wherein Hf (OPr) in step (2) was used 4 And the molar ratio of acetylacetone was adjusted to 1:4, and the other conditions of this comparative example were the same as in example 1.
As shown in FIG. 5, the XRD patterns of the ceramic precursor obtained in this comparative example show two diffraction peaks, one being boride obtained by solid solution of quaternary metal and the other being HfB 2 The peaks of (2) show that the metal Hf cannot participate in solid solution, which is mainly because the hydrolysis process is slow when the content of the complexing agent is high, so that the metal Hf cannot participate in cohydrolysis, and the precursor cannot keep short-range distribution with other metal elements in the cracking process, so that the diffusion difficulty is high, and the precursor cannot participate in solid solution.
Comparative example 4
This comparative example was based on example 1, wherein Hf (OPr) in step (2) was used 4 And the molar ratio of acetylacetone was adjusted to 1:0.25, and the other conditions of this comparative example were the same as in example 1.
Precipitation occurs during the co-hydrolysis process due to too low an amount of complexing agent resulting in too fast a hydrolysis of the hafnium alkoxide complex.
Comparative example 5
On the basis of the example 1, the reflux system in the step (3) is subjected to normal pressure distillation to remove the solvent to obtain a metal alkoxide copolymer, and the metal alkoxide copolymer is added into the boron carbon source solution prepared in the step (4); other conditions of the comparative example were the same as in example 1. It was found in experiments that no gelling of the system occurred during the whole process, since the reactive groups of the metal alkoxide copolymer continued to react during the atmospheric distillation, affecting their reactivity with the boron carbon source. The resulting precursor was cleaved as in example 2.
As shown in FIG. 6, which shows the XRD pattern of the ceramic precursor obtained in this comparative example, diboride (MB) 2 ) Boride (MB), oxide (MO) 2 ) And multiple groups of diffraction peaks such as carbide (MC), and the like, because the metal copolymer cannot react with the boron carbon source, the metal copolymer and the boron carbon source are separated in the solidification and cracking processes, so that metal and carbon boron atoms are distributed remotely, and the metal copolymer and the boron carbon source are not easy to react to generate high-entropy boride solid solution.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. The high-entropy boride ceramic precursor is a polymer connected by a metal source-boron carbon source through a bridge oxygen bond, and comprises a metal element M and boron elements, wherein the metal element M is at least 4 selected from Ti, zr, hf, V, nb, ta, mo, W.
Preferably, the amount of the substances of the respective metal elements is 5 to 35% of the amount of the total metal substances of the high-entropy boride ceramic precursor, respectively.
Preferably, the ratio of the amount of the substance of the boron element to the total amount of the substances of the metal element is 2.2 to 5:1.
2. A method of preparing the high entropy boride ceramic precursor of claim 1, comprising the steps of:
(1) Preparing a metal alkoxide copolymer solution;
(2) Preparing a boron carbon source solution: mixing a boron source and a carbon source in organic acid, heating to 50-100 ℃ and reacting for 0.5-3 h;
(3) Mixing the metal alkoxide copolymer solution in the step (1) with the boron carbon source solution in the step (2), heating to 80-100 ℃ for a first heating reaction, heating to 110-150 ℃ for a second heating reaction after the reaction to the system gel, and drying and cooling to obtain the high-entropy boride ceramic precursor.
3. The method according to claim 2, wherein in the step (3), the temperature of the first heating reaction is 85 to 95 ℃ and the reaction time is 0.5 to 3 hours.
Preferably, in the step (3), the temperature of the second heating reaction is 120-130 ℃, and the reaction time is 3-10 h.
Preferably, the mixing in step (3) is carried out at a temperature of 40 to 80 ℃.
Preferably, the ratio of the amounts of the boron source, carbon source and acetic acid in step (3) is 1 (0.2 to 1.5): 0.4 to 4.
4. A method of preparing as claimed in claim 2 or 3, wherein the metal alkoxide copolymer solution comprises the steps of:
a. adding complexing agent into metal alkoxide M (OR) n to react at room temperature-80 ℃ to obtain metal alkoxide complex;
b. and d, selecting at least 4 metal alkoxide complexes containing different metal elements prepared in the step a, uniformly mixing, slowly dropwise adding a mixed solution of water and monohydric alcohol at the temperature of between room temperature and 90 ℃, and completely refluxing for 1 to 5 hours to prepare a metal alkoxide copolymer solution.
Preferably, when the M is selected from Hf, V, nb, ta, mo or W, the metal alkoxide is prepared as follows: dispersing the metal salt of M in an organic solvent, dripping monohydric alcohol at the temperature of-10-5 ℃, then dripping triethylamine, heating and refluxing for 1-5 h after the dripping is finished, and filtering to obtain a metal alkoxide solution.
5. The process according to claim 4, wherein the ratio of the metal alkoxide, the monohydric alcohol and the triethylamine is 1: (1-2) n: (1-1.5) n.
Preferably, the molar ratio of metal alkoxide to complexing agent in step b is 1 (0.12 to 0.4) n, preferably 1 (0.2 to 0.3) n.
Preferably, the complexing agent in step b is one or a mixture of two of acetylacetone and ethyl acetoacetate.
Preferably, the reaction time in step b is 0.1 to 5 hours.
6. The process according to claim 4 or 5, wherein the molar ratio of water to total metal in step c is 0.9-1.5:1 and the mass ratio of monohydric alcohol to water is 3-8:1.
Preferably, the monohydric alcohol in the step c is one or more selected from methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, ethylene glycol methyl ether and ethylene glycol ethyl ether.
7. The high-entropy boride ceramic powder is characterized by being obtained by the steps of discharging glue and cracking the high-entropy boride ceramic precursor according to claim 1.
8. The high entropy boride ceramic powder of claim 7, wherein the high entropy boride ceramic powder is a solid solution.
Preferably, the solid solution is a crystal having a hexagonal crystal phase.
Preferably, the high-entropy boride ceramic powder particles have a size of 100 nm-1 μm.
9. A method for preparing the high-entropy boride ceramic powder according to claim 7 or 8, comprising the steps of: the high-entropy boride ceramic precursor according to claim 1 is subjected to glue discharging and cracking to obtain high-entropy boride ceramic powder.
Preferably, the glue discharging temperature is not higher than 500 ℃, and the glue discharging time is 0.5-4 h.
Preferably, the cracking temperature is not lower than 1500 ℃, and the cracking time is 0.5-5 h.
Preferably, the discharging of the gel is performed under an inert atmosphere, and the cracking is performed under vacuum or under an inert atmosphere.
10. A high entropy boride ceramic produced using the high entropy boride ceramic powder of claim 7 or 8.
CN202111566900.9A 2021-12-20 2021-12-20 High-entropy boride ceramic precursor, ceramic powder, and preparation methods and applications thereof Pending CN116284804A (en)

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