阅读说明：本技术 高熵碳化物超高温陶瓷粉体及其制备方法 (High-entropy carbide ultra-high temperature ceramic powder and preparation method thereof ) 是由 刘红霞 宋伟豪 梁腾飞 吴东升 陈伟东 白玉 于 2021-11-12 设计创作，主要内容包括：本发明提供了一种高熵碳化物超高温陶瓷粉体及其制备方法,所述陶瓷粉体分子式为(M1-(x1)M2-(x2)……Mn-(xn))C,M为Zr、Ti、Hf、V、Nb、Ta、Mo或W中的至少四种,具有单一面心立方结构,呈单一相固溶体。所述方法：将至少四种金属氧化物和碳粉制成阴极,熔盐电解得到纳米陶瓷粉体。本发明能够在电解过程中同时实现多种金属氧化物混合电脱氧和原位碳化以及固溶,具有工艺流程短、原料价格低廉、合成温度低、设备要求低、工艺过程简单,易于产业化及经济价值高等优点；能够为制备高质量的高熵碳化物纳米粉体提供一条经济和可行的新路线；还能够被作为半成品用于宇航部件、涂层材料和特种功能陶瓷等方面。(The invention provides high-entropy carbide ultra-high temperature ceramic powder and a preparation method thereof, wherein the molecular formula of the ceramic powder is (M1) x1 M2 x2 ……Mn xn ) And C and M are at least four of Zr, Ti, Hf, V, Nb, Ta, Mo or W, have a single face-centered cubic structure and are single-phase solid solutions. The method comprises the following steps: preparing at least four metal oxides and carbon powder into a cathode, and electrolyzing molten salt to obtain the nano ceramic powder. The method can simultaneously realize the mixed electro-deoxidation, in-situ carbonization and solid solution of various metal oxides in the electrolytic process, and has the advantages of short process flow, low raw material price, low synthesis temperature, low equipment requirement, simple process, easy industrialization, high economic value and the like;an economic and feasible new route can be provided for preparing high-quality high-entropy carbide nano powder; can also be used as a semi-finished product for aerospace parts, coating materials, special functional ceramics and the like.)

1. A preparation method of high-entropy carbide ultrahigh-temperature ceramic powder is characterized by comprising the following steps:

mixing a metal oxide mixture with carbon powder, and pressing and forming the mixture into a solid piece, wherein the metal oxide mixture consists of more than four selected from metal oxides of IVB, VB and VIB elements, the metal oxide mixture at least comprises four different metal elements, the molar weight of all the metal elements in the metal oxide mixture is calculated according to an equimolar ratio or a nearly equimolar ratio, and the sum of the molar weight of all the metal elements is equal to the molar weight of the carbon powder;

and (3) carrying out constant-pressure electrolysis in a molten salt at the temperature of 800-950 ℃ in an inert atmosphere by taking the solid sheet as a cathode and graphite as an anode until the reaction is complete to obtain the high-entropy carbide ultrahigh-temperature ceramic powder, wherein the molten salt is calcium chloride or a mixed halide containing the calcium chloride.

2. The method for preparing high-entropy carbide ultrahigh-temperature ceramic powder according to claim 1, wherein the IVB group elements are Ti, Zr and Hf, the VB group elements are V, Nb and Ta, and the VIB group elements are Mo and W.

3. The method for preparing the high-entropy carbide ultrahigh-temperature ceramic powder according to claim 1, wherein the voltage of the constant-voltage electrolysis is 2.8-3.1V.

4. The preparation method of the high-entropy carbide ultrahigh-temperature ceramic powder body according to claim 1, wherein the temperature is 855-895 ℃.

5. The high-entropy carbide ultra-high temperature ceramic powder is characterized by being prepared by the preparation method of any one of claims 1 to 4.

6. High entropy carbide hyper-entropy according to claim 5The high-temperature ceramic powder is characterized in that the structural formula of the high-entropy carbide ultra-high-temperature ceramic powder is (M1)_x1M2 _x2……Mn _xn) C, wherein 4 ≦ n ≦ 8, and x1, x2, … … xn are equal or substantially equal to each other, x1+ x2+ … … xn ═ 1, and M1, M2, … … Mn correspond to all the metal elements described in the metal oxide mixture.

7. The high-entropy carbide ultra-high-temperature ceramic powder according to claim 6, wherein the high-entropy carbide ultra-high-temperature ceramic powder is a single-phase solid solution and has a single-phase face-centered cubic structure.

8. An aerospace component comprising the high-entropy carbide ultra-high-temperature ceramic powder of claim 6 or 7, or produced using the high-entropy carbide ultra-high-temperature ceramic powder of claim 6 or 7.

9. A coating material, which is characterized by containing the high-entropy carbide ultra-high-temperature ceramic powder as claimed in claim 6 or 7 or being prepared by using the high-entropy carbide ultra-high-temperature ceramic powder as claimed in claim 6 or 7.

10. A special functional ceramic, which is characterized by containing the high-entropy carbide ultra-high-temperature ceramic powder as claimed in claim 6 or 7 or being prepared by using the high-entropy carbide ultra-high-temperature ceramic powder as claimed in claim 6 or 7.

Technical Field

The invention relates to the technical field of carbide ceramics, in particular to high-entropy carbide ultra-high temperature ceramic powder and a preparation method thereof, and an aerospace component, a coating material and a special functional ceramic containing the high-entropy carbide ultra-high temperature ceramic powder.

Background

The transition metal carbide has the characteristics of ultrahigh hardness, high strength, excellent corrosion resistance, oxidation resistance, ablation resistance and the like, and can be widely used in protective materials and supporting structural components of parts such as high-temperature nuclear reactors, jet engines, nose cones, leading edges and the like of latest-generation supersonic aircraft. However, with the increasing demand of the major national strategies such as aerospace, national defense and military industry on the performance of transition metal carbide materials, the conventional transition metal carbide materials (such as ZrC, HfC, TaC, (Ta, Hf) C, etc.) have been unable to meet the use requirements. Therefore, a novel transition metal carbide material applicable to the future extreme service environment is in urgent need of development.

Based on the traditional superhigh temperature complex phase ceramic system, with the inspiration of the design concept of 'high entropy' materials in the alloy field, researchers at home and abroad begin to try to prepare high entropy transition metal carbide ceramics in recent years. Research shows that the high entropy causes the transition metal carbide ceramic to have hardness and elastic modulus which are obviously higher than the average value of all components, thermal conductivity which is lower than all the components, more excellent oxidation resistance and high-temperature creep resistance, and good radiation damage resistance. The material has oxidation resistance and ablation resistance far superior to binary ultrahigh-temperature ceramic, so that the material is an important development direction of a new-generation thermal protection system material. Currently, High Entropy Carbides (HECs) are produced by mechanical grinding and subsequent spark plasma sintering or carbothermic reduction at temperatures around 2000 ℃, the products being almost bulk or coarse micron-sized powders.

However, the inventor analyzes and shows that the synthesis of the high-purity ultrafine ceramic powder can not only reduce the sintering temperature of the bulk ceramic, but also reduce the grain size of the bulk ceramic and improve the compactness of the ceramic material, thereby improving the performance of the ceramic material. In addition, the superfine high-entropy metal carbide ceramic powder with uniform tissue structure can be used for preparing a compact block, a coating or a matrix phase of a ceramic matrix composite material, can also be applied to a powder metallurgy process, can replace high-temperature alloy powder used under other special conditions, and is applied to 3D printing, laser reconstruction technology, three-dimensional rapid prototyping technology and the like. Therefore, it is of great significance to prepare high entropy metal carbide materials in large quantities and in the form of nanopowders.

At present, the preparation methods of high-entropy transition metal carbide powder mainly comprise a solid-phase synthesis method, a liquid-phase precursor synthesis method, a molten salt synthesis method and the like.

The solid-phase synthesis methods can be classified into three types according to the raw material powder.

The first method uses commercial metal carbide powder as raw material, and makes atoms diffuse to form single-phase solid solution of multiple metal carbides through ball milling mixing and high-temperature discharge plasma sintering (SPS). Synthesized by Zhou et al at 1950 ℃ (Ti)_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2) C high-entropy ceramic powder with the grain diameter of 2 mu m. This method is simple and efficient, but the particle size of the synthesized powder is large because the required temperature is high and the particle size of the raw material powder is large. Moreover, oxide impurities or free carbon inevitably exist in the raw material powder, and these impurities adversely affect the subsequent densification of the ceramic, and finally it is difficult to obtain a high-entropy carbide ceramic bulk with high density.

The second method uses metal oxide and graphite powder as raw materials, and high-entropy carbide powder is obtained through high-temperature vacuum carbothermic reduction reaction. Ye et al directly heat the raw material mixed powder after ball milling in a vacuum furnace to 2200 ℃ for heat preservation, and prepare (Ti) by a one-step method_0.25Zr_0.25Nb_0.25Ta_0.25) C powder with a particle size of 0.5 to 2 μm. Feng et al ball-mill the raw material powder with high energy, press it into a disc, and then reduce and mix it with 1600 deg.C carbothermalSolid solution at 2000 deg.C, and two-step synthesis (Ti)_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2) C powder with a particle size of about 0.55 μm and an oxygen content of 0.2 wt.% is obtained. The method has low cost of raw materials, and can effectively reduce the content of oxide impurities in the synthetic powder by regulating and controlling the vacuum degree. But the carbothermic process requires a vacuum environment and high temperatures.

In the third method, metal coarse powder (40-60 mu m) and graphite powder are used as raw materials, and high-entropy carbide powder can be directly obtained in an inert atmosphere by a mechanochemical synthesis mode. Chicard et al prepared (Ti) by ball-milling raw material powder for 50-70 h at room temperature (300rmp)_0.2Zr_0.2Hf_0.2V_0.2Nb_0.2)C、(Ti_0.2Zr_0.2Hf_0.2V_0.2Ta_0.2)C、(Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2) C and six kinds of high-entropy ceramic powder with the grain size of about 100-300 nm. Moskovskiikh et al synthesized the raw material powder by high-energy ball milling for 1h (Ti)_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2Ti_0.2Nb_0.2) C and (Ti)_0.2Hf_0.2Nb_0.2Ta_0.2Mo_0.2) C high-entropy ceramic powder with the grain size of about 1-10 μm. This method is simple and does not require high temperatures. However, the high activity of the metal powder makes it very easy to introduce oxygen impurities during the ball milling process; also, trace amounts of grinding media residue inevitably enter the product and are difficult to remove thoroughly in subsequent steps. In addition, the raw material is metal powder, which is expensive and difficult to handle.

The liquid-phase precursor synthesis method obtains a polymer precursor solution with uniformly dispersed element molecular levels in a mode of metal-containing monomer polymerization, and then the precursor is decomposed and chemically reacted through high-temperature heat treatment to form high-entropy carbide powder with a single structure. Du et al first dissolve the transition metal chloride and the acetyl methane in butanol, then obtain a liquid phase precursor by polymerization at 200 ℃ and then prepare (Hf) by heat treatment at 2000 ℃_0.25Nb_0.25Zr_0.25Ti_0.25) C powder with average particle size of 800nm, oxygen content of 0.51 wt.% and free carbon impurity content of 2.56 wt.%. Li et al firstly dissolve transition metal chloride in ethanol, then add furfuryl alcohol to prepare liquid phase precursor through 60 ℃ polymerization, and then obtain (Ti) through 1400 ℃ vacuum carbothermal reduction and 2000 ℃ heat treatment_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2) C ceramic powder, particle size (132 +/-5) nm, oxygen content 0.22 wt.%. The method can realize the mixing of all the components on the molecular level, and is beneficial to the mutual diffusion and the uniform distribution of all the elements in the later high-temperature solid solution process. However, the method has the disadvantages of long process flow, high cost, adoption of an organic solvent and high environmental protection pressure.

The molten salt synthesis method mainly takes low-melting-point salts as reaction media, and metal and carbon powder react in high-temperature molten salt. Ning et al synthesized (Ta) at 1300 ℃ by using metal fine powder (1-3 mu m) and carbon powder as raw materials and potassium chloride as a molten salt medium_0.25Nb_0.25Ti_0.25V_0.25) C powder with the particle size of 50-110 nm. The method has simple process flow and lower synthesis temperature, and can obtain the nano powder. However, the raw material cost is high; also, fine metal powders can cause operational problems such as spontaneous combustion or high oxygen contamination. Furthermore, some fine metal powders (e.g., zirconium powders) can even be dangerous to handle in air.

The patent application with the publication number of CN107059063A of 8 and 18 in 2017 discloses a method for preparing AlFeMnTiZr high-entropy alloy, and TiO is added in the method₂、MnO₂、ZrO₂、Fe₂O₃Mixing, pressing and sintering oxide powders to obtain a cathode in NaF-AlF₃～CaF₂～Al₂O₃In a molten salt system, the AlFeMnTiZr high-entropy alloy is prepared by electrolysis at 900-1100 ℃. The method has the advantages that the cathode needs to be sintered for 4-10 h at 800-1000 ℃ in a heat preservation manner during the preparation process, the energy consumption is high, and the product is only AlFeMnTiZr high-entropy alloy and does not relate to the preparation of high-entropy carbide.

Special publication with publication number of CN 108950286A and publication number of 12, 7 and 2018The application discloses a method for preparing ZnAlCrMnNbB high-entropy alloy, which adopts ZnO₂、Al、Cr₂O₃、MnO₂Nb powder and B powder as raw material, ball milling, pressing and sintering to obtain cathode, and mixing with NaF and CaF₂Electrolyzing in molten salt at 900-1200 ℃ to obtain the ZnAlCrMnNbB high-entropy alloy. In the preparation process of the cathode, the cathode needs to be sintered for 5-8 hours at 700-950 ℃, the raw materials comprise pure metals Al and Nb, the raw materials are a mixture of pure metals and oxides, and the product is only ZnAlCrMnNbB high-entropy boride and does not relate to the preparation of high-entropy carbides.

A patent application published as 6 and 7 in 2019 and published as CN 109851367A discloses a rod-shaped (Zr, Hf, Ta, Nb) B₂High-entropy nano powder and preparation method thereof, wherein ZrO is adopted in the method₂、HfO₂、Ta₂O₅、Nb₂O₅And B powder as raw material, in NaCl and KCl fused salt, carrying out boron thermal reduction reaction at 1200 ℃ to obtain (HfZrNbTa) B₂A method of high entropy nano powder. The product of the method is only (HfZrNbTa) B₂High entropy boride, does not relate to the preparation of high entropy carbide.

The patent application with publication number CN 110923750A, 3.27.2020 discloses a preparation method of high-entropy alloy, and the method adopts Al₂O₃、CoO、Cr₂O₃、Fe₂O₃Mixing with NiO powder, putting into container as cathode, adding into CaCl₂Electrolyzing in molten salt at 900 deg.C to obtain Al_xAnd (3) carrying out high-entropy CoCrFeNi alloy powder, and then carrying out vacuum hot-pressing sintering on the high-entropy alloy powder at 1100 ℃ to obtain a high-entropy alloy block. The method is characterized in that the mixed powder is required to be placed into a special container in the process of preparing the high-entropy alloy powder, the container is made of stainless steel, a plurality of small holes are formed in the wall of the container, a stainless steel wire net is wrapped outside the container, and the product is only an AlFeMnTiZr high-entropy alloy block and does not relate to the preparation of high-entropy carbide.

In summary, the inventors have analyzed that the above preparation methods all have their advantages, but mainly have the following disadvantages: (1) the method has the problems that the high-purity ceramic powder is difficult to obtain, the prepared high-entropy carbide powder contains impurities such as oxygen, free carbon or grinding medium residues, the sintering activity of the high-entropy carbide powder is reduced due to the presence of the oxygen and other impurities, the coarsening of pores and crystal grains is promoted, the high-density high-entropy carbide ceramic block is difficult to obtain, the situation of uneven distribution of micro-area elements is easy to occur, and finally, the performance of the material is adversely affected. (2) There is a problem in controlling the particle size of the high-entropy carbide powder, especially in the nanometer scale. Since most of the methods involve high temperature and are influenced by the size of raw material particles, the obtained high-entropy carbide ceramic powder is usually coarse micron-sized powder and is not uniformly distributed, and uniform nano ceramic powder is difficult to prepare, which seriously hinders the wide application of the method.

Disclosure of Invention

The present invention aims to address at least one of the above-mentioned deficiencies of the prior art. For example, in view of one or more of the above disadvantages in the prior art, the inventors of the present invention have conducted analytical studies and propose that a high-entropy carbide powder is prepared in situ by one-step electrochemical reduction using inexpensive metal oxide and elemental carbon as raw materials, so as to achieve short-flow, low-cost, low-energy consumption and low-carbon preparation of the high-entropy carbide powder, and no impurity is introduced during the process.

In order to achieve the above object, one aspect of the present invention provides a method for preparing high-entropy carbide ultra-high temperature ceramic powder, the method comprising the following steps: mixing a metal oxide mixture with carbon powder, and pressing and forming the mixture into a solid piece, wherein the metal oxide mixture consists of more than four selected from metal oxides of IVB, VB and VIB elements, the metal oxide mixture at least comprises four different metal elements, the molar weight of all the metal elements in the metal oxide mixture is calculated according to an equimolar ratio or a nearly equimolar ratio, and the sum of the molar weight of all the metal elements is equal to the molar weight of the carbon powder; and (3) carrying out constant-pressure electrolysis in a molten salt at the temperature of 800-950 ℃ in an inert atmosphere by taking the solid sheet as a cathode and graphite as an anode until the reaction is complete to obtain the high-entropy carbide ultrahigh-temperature ceramic powder, wherein the molten salt is calcium chloride or a mixed halide containing the calcium chloride.

The invention also provides high-entropy carbide ultra-high temperature ceramic powder, which is prepared by the preparation method. The structural formula of the high-entropy carbide ultrahigh-temperature ceramic powder is (M1)_x1M2_x2……Mn_xn) C, wherein 4 ≦ n ≦ 8, and x1, x2, … … xn are equal or substantially equal to each other, x1+ x2+ … … xn ═ 1, and M1, M2, … … Mn correspond to all the metal elements described in the metal oxide mixture.

The invention further provides a component, a coating material and/or a special functional ceramic for space navigation, which respectively contain or are prepared from the high-entropy carbide ultra-high-temperature ceramic powder.

Compared with the prior art, the beneficial effects of the invention comprise one or more of the following:

(1) the high-entropy carbide ultra-high temperature ceramic powder is a single-phase solid solution, has a single-phase face-centered cubic structure, is high in purity, and has a nano-scale particle size.

(2) The preparation method has the characteristic of short flow, needs cheaper raw materials and is beneficial to greatly saving the cost.

(3) The method efficiently removes oxygen in various metal oxides in a molten salt liquid medium by an electrochemical method; meanwhile, the released metal particles are subjected to in-situ carbonization reaction under the protection of cathodic polarization. The in-situ carbonization breaks through the main kinetic barrier of the traditional solid-solid carbonization reaction, reduces the activation energy of the reaction, can reduce the preparation temperature of the solid-phase synthesis method of the high-entropy carbide powder to 800-950 ℃, reduces the energy consumption, is beneficial to controlling the particle size of the powder to be nano-scale, and has low oxygen content.

(4) The method realizes electro-deoxidation, in-situ carbonization and solid solution in one step in the cathode polarization process, and establishes an electrochemical approach for preparing the high-entropy carbide ultra-high temperature ceramic powder for the first time.

(5) The high-entropy carbide ultra-high temperature ceramic powder has good sintering performance and high oxidation resistance, and can be used for various aspects such as aerospace parts, coating materials, special functional ceramics and the like.

Drawings

The above and other objects and/or features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

figure 1 shows an X-ray diffraction (XRD) pattern of a solid sheet of an exemplary embodiment of the present invention;

FIG. 2 shows an X-ray diffraction (XRD) pattern of an exemplary embodiment of the high entropy carbide ultra high temperature ceramic powder of the present invention;

FIG. 3 shows a Scanning Electron Microscope (SEM) image of an exemplary embodiment of the high entropy carbide ultra high temperature ceramic powder of the present invention;

FIG. 4 shows an X-ray spectral analysis (EDS) of an exemplary embodiment of the high entropy carbide ultra high temperature ceramic powder of the present invention;

FIG. 5 shows a Transmission Electron Microscope (TEM) image of an exemplary embodiment of the high entropy carbide ultra high temperature ceramic powder of the present invention;

FIG. 6 shows a Scanning Transmission Electron Microscope (STEM) image of an exemplary embodiment of the high entropy carbide ultra high temperature ceramic powder of the present invention and its EDS surface distribution;

FIG. 7 shows an X-ray diffraction (XRD) pattern of a ceramic powder of a comparative example of the present invention;

fig. 8 shows an X-ray diffraction (XRD) pattern of an exemplary embodiment of the high entropy carbide ultra high temperature ceramic powder of the present invention.

Detailed Description

Hereinafter, the high-entropy carbide ultra-high temperature ceramic powder and the preparation method thereof according to the present invention will be described in detail with reference to the exemplary embodiments.

In an exemplary embodiment of the invention, the preparation method of the high-entropy carbide ultrahigh-temperature ceramic powder is realized by the following steps:

(1) preparation of cathode materials

The metal oxide mixture is mixed with carbon powder and is pressed into a solid piece. Specifically, the metal oxide mixture is composed of four or more selected from metal oxides of group IVB, VB and VIB elements, and the metal oxide mixture contains at least four different metal elements, and the molar amounts of all the metal elements in the metal oxide mixture are calculated in an equimolar ratio or a nearly equimolar ratio, while the sum of the molar amounts of all the metal elements is equal to the molar amount of the carbon powder. The step does not need sintering, can reduce energy consumption, and the pressed and formed solid sheet is beneficial to the subsequent electrochemical reduction process and has a beneficial effect on generating uniform nano particles. Here, the "near equimolar ratio" can be understood as: when each metal element in the metal oxide mixture is represented as M1, M2, … … Mn, then one or more of the dosed molar amounts of metal oxide corresponding to the M1, M2, … … Mn elements may have a value not equal to 1/n and between 0.9 x 1/n and 1.1 x 1/n.

That is, here, a raw material composed of a carbon powder and a metal oxide of IVB (Ti, Zr, Hf), VB (V, Nb, Ta), or VIB group (Mo, W) is mixed and press-molded into a solid sheet, and the solid sheet is used as a cathode material for subsequent electrolytic reduction. The amount of the metal oxide and the carbon powder with corresponding stoichiometric ratio can be calculated according to the equimolar or nearly equimolar ratio of the metal elements in the target high-entropy carbide ultra-high temperature ceramic powder product to form the raw material for manufacturing the cathode sheet. Preferably, the carbon powder is nanoscale amorphous carbon.

Here, each metal oxide and carbon powder may also be subjected to ball milling wet milling, for example, in a planetary ball mill, prior to the mixing. The press forming may be performed by isostatic pressing.

(2) Electrochemical reduction

And (3) carrying out constant-pressure electrolysis in a molten salt at the temperature of 800-950 ℃ in an inert atmosphere by taking the solid sheet as a cathode and graphite as an anode until the reaction is complete to obtain the high-entropy carbide ultrahigh-temperature ceramic powder, wherein the molten salt is calcium chloride or a mixed halide containing the calcium chloride. Here, the graphite as the anode may include a carbon rod, a graphite rod, and the like.

Specifically, the cathode material obtained in the step (1) is used for forming a cathode to be electrolyzed, graphite is used as an anode, and a mixed halide containing calcium chloride is used as a molten salt medium to form an electrolysis system. And electrolyzing in molten salt at 800-950 ℃ under an inert atmosphere by adopting a constant voltage of 2.8-3.1V until the reaction is complete to obtain the high-entropy carbide powder. Here, a constant voltage range of 2.8 to 3.1V is used to ensure no decomposition of the electrolyte and a high electrochemical reduction rate. For example, the time of constant-voltage electrolysis (which may be simply referred to as electrolysis time) may be 4 to 20 hours, preferably not less than 6 hours, so as to form pure, impurity-phase-free high-entropy carbides. As another example, the electrolysis time may be a piecewise function of where t_rElectrolysis time, T_cRepresents the molten salt temperature.

The electrolysis process is preferably carried out at a molten salt temperature of 800-950 ℃. Preferably, the molten salt temperature may be 855-895 ℃. If the temperature is too high, the volatilization loss of the molten salt is severe, and side reactions (e.g., corrosion of graphite anode during the reaction, etc.) are aggravated to lower the current efficiency. If the temperature of the molten salt is too low, the theoretical decomposition voltage of the oxide in the cathode is higher, and under the condition that the working voltage is not changed, the overvoltage is lower, and the driving force of the reaction is relatively reduced; on the other hand, when the temperature of the molten salt is low, the viscosity thereof also increases, and O^2-The diffusion rate in the molten salt system becomes slow, resulting in a large reduction rate of the electrochemical reduction, possibly resulting in too long reaction time or even incomplete oxygen removal from the cathode material.

The molten salt medium may employ calcium chloride, or may employ a mixed halide containing calcium chloride. Because of calcium chloride O^2-Has a greater solubility, which is not only favorable for O^2-The transmission of the molten salt can also increase the conductivity of the molten salt system, thereby being beneficial to the proceeding of the electrochemical reduction process of the molten salt. In addition, for reducing electrolytesMelting point, two or more salts can be selected to form the electrolyte system. The molten salt medium may be a single or mixed alkali or alkaline earth metal halide molten salt system, and the mixed salt contains calcium chloride. For example, the molten salt may be a eutectic mixed molten salt of calcium chloride and sodium chloride.

In another exemplary embodiment of the invention, the high-entropy carbide ultra-high temperature ceramic powder is obtained by adopting the preparation method, and the structural formula of the high-entropy carbide ultra-high temperature ceramic powder is (M1)_x1M2_x2……Mn_xn) C, wherein n is from [4,8 ]]And all natural numbers 4, 5, 6, 7 and 8 therebetween, and x1, x2, … … xn are equal or substantially equal to each other, x1+ x2+ … … xn ═ 1, and M1, M2, … … Mn correspond to all the metal elements described in the metal oxide mixture. I.e. M1, M2, … … Mn correspond to all the metallic elements in the metal oxide mixture selected from IVB (Ti, Zr, Hf), VB (V, Nb, Ta) or VIB (Mo, W). The inventors have only found experimentally that when the metal oxides are dosed in equimolar proportions, the entropy of the resulting equimolar ratio (i.e. x1, x2, … … xn are equal to each other) product (also referred to as sample) is the largest and more stable.

Through detection and analysis of products of a plurality of embodiments, the high-entropy carbide ultra-high temperature ceramic powder (which can be called high-entropy carbide nano powder for short) is a single-phase solid solution and has a single-phase face-centered cubic structure. For example, transition metal elements such as Ti, Zr, Hf, Nb, Ta, V, Mo, W and the like and C elements in the high-entropy carbide ultra-high-temperature ceramic powder are uniformly distributed on a micrometer scale to form a single-phase solid solution. In addition, the high-entropy carbide ultrahigh-temperature ceramic powder is composed of approximately equiaxial particles with uniform particle sizes and about 10-50 nm.

In addition, the high-entropy carbide ultra-high temperature ceramic powder is also suitable for forming parts for space navigation, coating materials and materials of special functional ceramics. For example, the aerospace component, the coating material or the special functional ceramic may respectively contain the high-entropy carbide ultra-high temperature ceramic powder or be prepared by respectively using the high-entropy carbide ultra-high temperature ceramic powder.

Exemplary embodiments of the present invention are described in further detail below with reference to specific examples.

Example 1

TiO calculated by molar ratio of Ti, Zr, Hf, Nb, Ta, etc₂、ZrO₂、HfO₂、Nb₂O₅、Ta₂O₅Mixing with carbon powder in stoichiometric ratio, and pressing to obtain solid tablet; placing the solid sheet in a porous stainless steel cup to prepare a cathode, taking graphite as an anode, and connecting the cathode with a constant voltage power supply; the mass ratio of the components is 7: 3 CaCl₂And (4) taking the NaCl mixed salt as a molten salt medium to form an electrolysis system.

Electrolyzing for 15h in fused salt at 850 ℃ by adopting a 3.1V constant voltage under an inert atmosphere to obtain an electrolysis product.

The electrolysis products were cleaned and then subjected to XRD, SEM, TEM and SAED detection.

As shown in FIG. 1, the solid sheet of the present example is made of TiO₂、ZrO₂、HfO₂、Nb₂O₅、Ta₂O₅And amorphous carbon powder.

As shown in FIG. 2, the electrolysis product of this example consists of (Ti)_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2) C single phase composition, and has a single phase face center cubic structure.

As can be seen from FIG. 3, (Ti) of this example_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2) The C high entropy carbide product is in powder form, consisting of approximately equiaxed particles of size less than 50nm, typically agglomerated into clusters. The results show that the high entropy carbide powder particles synthesized by electrochemical reduction of the present invention do not coarsen, mainly due to the absence of any significant in situ sintering at a temperature of 850 ℃, which is 2500 ℃ or more below the assumed melting point.

As can be seen from FIG. 4, six elements of Ti, Zr, Hf, Nb, Ta and C in the synthesized high-entropy carbide nano-powder are uniformly distributed on a micrometer scale to form a single-phase solid solution.

A in FIG. 5 is a synthesized high entropy carbide powder sampleTypical TEM image and SAED pattern of the product (inset), it can be seen that the high entropy carbide powder sample is composed of particles with a particle size of about 10-30 nm. The SAED plot shows the annular pattern of the poly features. The rings observed in the SAED pattern can be indexed Fm to 3m and correspond to the (111), (200), (220), and (311) crystallographic planes of the fcc structure. High Resolution Transmission Electron Microscope (HRTEM) image (b in FIG. 5) shows a typical periodic lattice structure with a set of interplanar spacings d ofCorresponding to the {111} plane of the metal carbide, the lattice parameter of the synthesized nano-powder can be calculated asThis indicates that the synthesized nanopowder is a single-phase solid solution of metal carbide with a face-centered cubic structure. Figure 6 shows a Scanning Transmission Electron Microscope (STEM) image and corresponding EDS composition map of the synthesized nanopowder. It can be clearly seen that the distribution of the five metal elements on the nanoscale is very uniform. TG-DSC results show that the temperature rise rate is 10 ℃/min under the air atmosphere, the exothermic peak value in the oxidation process is remarkably increased at 762 ℃ and 600 ℃, and the oxidation resistance of the composite carbide is superior to that of single-component carbide. In addition, tested (Ti) of the present example_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2) The oxygen content of sample C was 3200 ppm.

Comparative example 1

This comparative example, which is also one of the examples of the present invention, has exactly the same parameters and conditions as example 1 except that the electrolytic time was 8 h. As shown in FIG. 7, the ceramic powder prepared was composed mainly of (Ti)_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2) C high entropy carbide composition, and a small amount of oxide and single component carbide impurities. The powder is proved to have incomplete electro-deoxidation and carbonization reaction due to short electrolysis time, and can not form single-phase high-entropy carbide.

Example 2

Ti, Zr, Hf,Calculated TiO of mole ratio of Nb to Ta₂、ZrO₂、HfO₂、Nb₂O₅、Ta₂O₅Mixing with carbon powder in stoichiometric ratio, and pressing to obtain solid tablet; placing the solid sheet in a porous stainless steel cup to prepare a cathode, taking graphite as an anode, and connecting the cathode with a constant voltage power supply; the mass ratio of the components is 7: 3 CaCl₂And (4) taking the NaCl mixed salt as a molten salt medium to form an electrolysis system.

Electrolyzing for 10h in molten salt at 900 ℃ by adopting a 3.1V constant voltage under an inert atmosphere to obtain an electrolysis product. And then, cleaning the electrolysis product for multiple times by adopting ethanol, deionized water and the like to obtain a sample to be detected.

The sample to be detected is detected to be a (Ti) cubic structure with a single phase surface center_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2) C, the particle size is about 10-40 nm, and the oxygen content is 2900 ppm.

Example 3

TiO calculated by mole ratio of Ti, Hf, Nb, V, Ta₂、HfO₂、Nb₂O₅、V₂O₅、Ta₂O₅Mixing with carbon powder in stoichiometric ratio, and pressing to obtain solid tablet; placing the solid sheet in a porous stainless steel cup to prepare a cathode, taking graphite as an anode, and connecting the cathode with a constant voltage power supply; the mass ratio of the components is 7: 3 CaCl₂And (4) taking the NaCl mixed salt as a molten salt medium to form an electrolysis system.

Electrolyzing for 15h in molten salt at 885 ℃ under an inert atmosphere by adopting a 2.9V constant voltage to obtain an electrolysis product. And then, cleaning the electrolysis product for multiple times by adopting ethanol, deionized water and the like to obtain a sample to be detected.

As shown in FIG. 8, the sample to be measured is of a single phase plane-centered cubic structure (Ti)_0.2V_0.2Hf_0.2Nb_0.2Ta_0.2) C, the particle size of which is within the range of about 10-35 nm. The oxygen content of the sample is 3000ppm by detection.

Table 1 below shows relevant experimental parameters and product characteristics such as phase, particle size and oxygen content of the samples produced in examples 4 to 9.

TABLE 1 relevant reaction conditions and sample parameters for examples 4-9

Through detection and statistical analysis of a plurality of groups of samples, transition metal elements such as Ti, Zr, Hf, Nb, Ta, V, Mo, W and the like and C elements in the high-entropy carbide ultra-high temperature ceramic powder prepared by the invention are uniformly distributed on a micrometer scale to form a single-phase solid solution; the high-entropy carbide ultrahigh-temperature ceramic powder has a single-phase face-centered cubic structure, is high in purity (for example, the oxygen content is less than 3500ppm), is composed of approximately equiaxial particles, and has a nanoscale particle size of, for example, about 10-50 nm.

In conclusion, the high-entropy carbide ultrahigh-temperature ceramic powder can be prepared, the molecular formula of the high-entropy carbide ultrahigh-temperature ceramic powder is MC, M is at least four of Zr, Ti, Hf, V, Nb, Ta, Mo or W, the high-entropy carbide ultrahigh-temperature ceramic powder has a single face-centered cubic structure, is a single-phase solid solution, is high in purity, is nano-sized in particle size, and is beneficial to later-stage processing and application. In addition, the preparation method of the invention realizes the mixed electro-deoxidation, in-situ carbonization and solid solution of a plurality of metal oxides simultaneously in the electrolytic process, has the advantages of short process flow, low raw material price, low synthesis temperature, low equipment requirement, simple process, easy industrialization, high economic value and the like, and provides a simple, economic and feasible new idea and method for preparing high-quality high-entropy carbide nano powder.

Although the present invention has been described above in connection with the exemplary embodiments and the accompanying drawings, it will be apparent to those of ordinary skill in the art that various modifications may be made to the above-described embodiments without departing from the spirit and scope of the claims.