Preparation method of Mo-toughened boride-based ultra-high temperature ceramics

Abstract

A preparation method of Mo-toughened boride-based ultra-high temperature ceramics. In this method, a carbonyl complex of metal Mo is mixed with boride powder and heated in a solution to decompose the metal complex by heating. Under the action of a surfactant, metal Mo particles are generated and grow on the surface of boride particles. After centrifuging and drying the heated mixture, a boride powder wrapped with refractory metal Mo is obtained. Then, by using an appropriate sintering process, a boride-based ultra-high temperature ceramic material with improved performance is prepared. The technical solution of the present invention introduces a refractory metal Mo additive by a chemical method, providing a new idea and solution for the introduction of a refractory metal toughening phase in the research of ultra-high temperature ceramics.

Description

Technical Field

[0001] The technical solution of the present invention is used for preparing refractory metal Mo-modified boride ceramic powder, and then preparing Mo-toughened boride-based ultra-high temperature ceramic materials through rapid sintering, belonging to the field of ultra-high temperature ceramic preparation. Background Art

[0002] Metal borides, such as ZrB2, HfB2, TiB2 and other ceramics, have extremely high melting temperatures, high thermal conductivity and electrical conductivity, high strength, high hardness and chemical inertness, and belong to typical ultra-high temperature ceramic (UHTC) materials. Ultra-high temperature ceramics can withstand extremely high heat fluxes, thermo-mechanical loads and high temperature oxidation that are difficult for traditional structural materials to bear, meet the requirements of hypersonic aircraft and rockets for extreme environment structural materials, and are one of the most promising materials in the ultra-high temperature field. However, boride-based ceramics also have problems such as difficult sintering and poor fracture toughness.

[0003] In the past few decades, different methods and additives have been adopted to promote the sintering of borides and improve their properties. So far, the most commonly used additive for improving boride ceramics is SiC, which removes oxide impurities on the surface of borides through chemical reactions, promotes densification and reduces the sintering temperature. Although the addition of SiC significantly improves the properties of boride-based ceramics, especially mechanical properties, oxidation resistance and ablation resistance, the problems of poor toughness and thermal shock resistance still limit its practical applications. Other non-metallic additives, such as borides, carbides, silicides, etc., have not completely solved the problems of low fracture toughness and poor thermal shock resistance.

[0004] In order to improve the fracture toughness of boride-based ceramics, in-depth exploration has also been carried out on whisker and fiber toughening, among which carbon fiber is the most concerned toughening material. The toughening mechanism of carbon fiber mainly includes crack deflection, crack bifurcation, fiber pull-out and bridging, which changes the fracture mode from brittle fracture to non-brittle fracture mode. It should be noted that only when the fiber / matrix interface is appropriate can a high fracture toughness be obtained. However, the introduction of carbon fiber is likely to provide a channel for the diffusion of oxygen, which is not conducive to the improvement of oxidation resistance. In addition, carbon fiber is prone to oxidation at high temperatures, resulting in performance deterioration, affecting the toughening effect and the high-temperature performance of the composite material.

[0005] Non-metallic additives have not completely solved the toughness and thermal shock resistance problems that restrict the application of boride ceramics. Due to the high melting point and good ductility of refractory metals, theoretically, refractory metal additives can improve the densification process of boride-based ceramic materials and enhance the toughness and thermal shock resistance of the materials. Refractory metals have a high melting point and good high-temperature mechanical properties, and have little influence on the high-temperature properties of boride-based ceramics. However, the toughening effect of refractory metal additives is not significant. This is because in traditional methods, the second-phase metal is often introduced by mechanical mixing or in-situ reaction, and then the boride-refractory metal composite material is obtained by sintering. This preparation method is difficult to obtain a uniformly dispersed metal phase, easy to cause agglomeration, and the size of the metal phase is large, which affects the improvement of material properties.

[0006] Mo has a high melting point (2623 °C), a relatively low density (10.2 g / cm 3 ), a high thermal conductivity (138 W / (m·K)), high toughness (>20 MPa·m 1 / 2 ), a low thermal expansion coefficient (6×10 -6 / °C) close to that of borides, a low ductile-brittle transition temperature (-20 °C), and good wettability to ceramic materials. At high temperatures, ZrB2 and Mo will undergo solid solution, increasing the sintering driving force, reducing the sintering temperature, and promoting densification. Above 1200 °C, ZrB2 and Mo can react to form ZrB and MoB, forming pinning centers at grain boundaries to inhibit grain coarsening and enhance interface strength. The introduction of plastic Mo can also reduce the sensitivity to cracks and improve fracture toughness. In the preparation process of Mo-toughened boride-based ceramics, the possible Mo-containing substances have a high melting point and good high-temperature properties, which can improve the high-temperature stability of the SiO2-rich glass phase on the surface after ceramic oxidation and enhance its thermal protection ability at high temperatures. Therefore, the combination of Mo and boride-based ceramics is expected to simultaneously improve the mechanical properties and thermal protection ability of the materials.

[0007] At present, the problems of the large intrinsic brittleness of boride-based ceramics and the resulting poor thermal shock resistance have not been effectively solved, making it difficult to meet the multiple requirements of the aerospace field for the thermal shock resistance and reliability of thermal protection materials, and restricting its application in service environments with drastic temperature changes and high heat fluxes. Traditional refractory metals, such as Mo, are difficult to achieve uniform introduction of the metal phase due to the limitations of the introduction method and sintering process, and have not achieved significant improvement in the properties of boride-based ceramics. Therefore, developing new toughening phase introduction technologies to improve the toughness and thermal shock resistance of boride-based ceramics is of great significance for realizing the application of boride-based ceramics. Summary of the Invention

[0008] The object of the present invention is to provide a new scheme for introducing refractory metal Mo additive into ceramic materials, to solve the problems such as easy agglomeration and over-large metal phase size caused by the existing methods for introducing refractory metals, so as to solve the problem that refractory metals cannot significantly improve the mechanical properties of ultra-high temperature ceramics in traditional preparation methods. In the traditional method, the second-phase metal is introduced into the boride-based ceramic material by means of mechanical mixing or in-situ carbothermal reduction reaction method combined with sintering. The metal phase is unevenly distributed and seriously agglomerated, and the grain size is relatively large, which affects the improvement of material properties. The present invention overcomes the problems of uneven metal phase and easy agglomeration existing in the traditional method.

[0009] The present invention uses the solvothermal method to introduce metal Mo, making the prepared metal Mo phase more evenly distributed, enhancing the bonding strength between metal Mo and ceramics, and significantly improving the green density, which is very suitable for preparing Mo-toughened ceramic matrix composites. The ceramic powder is controllably modified by the solvothermal method. Using the carbonyl complex of Mo as the precursor, it is mixed with the boride powder, solvent and surfactant in the reaction kettle and then heat-treated at a certain temperature; the metal complex undergoes thermal decomposition during heating to generate refractory metal Mo, which grows on the surface of the boride particles. Then the heated mixture is centrifuged and dried to obtain the boride powder modified with refractory metal Mo. Using this Mo-modified ceramic powder, by controlling the sintering process, the preparation of high-performance Mo-toughened boride-based ceramics can be realized.

[0010] Compared with the prior art, the technical solution of the present invention has the advantage that by introducing refractory metal additives through chemical methods, the problems such as over-large metal phase size and easy agglomeration existing in the existing methods for introducing refractory metals are solved, thus putting forward a new idea and scheme for the introduction of refractory metal toughening phases in the research of ultra-high temperature ceramics.

[0011] The present invention relates to a method for preparing Mo-modified boride powder by the solvothermal method and preparing Mo-toughened boride-based ultra-high temperature ceramics, which is carried out according to the following steps:

[0012] (1)A preparation method of Mo - toughened boride - based ultra - high temperature ceramics, the preparation process includes the following steps: Add boride powder and Mo carbonyl complex into a solvent, then add a surfactant, and mix the Mo carbonyl complex, solvent and surfactant evenly; The boride is one of ZrB2, HfB2, TiB2, TaB2, NbB2; The Mo carbonyl complex is one or more of Mo(CO)6, Na2[Mo(CO)5], Mo(CO)3PPh3, Mo(CO)4Cl2, Mo(CO)4Br2, HMo(CO)3(Cp) (Cp = cyclopentadienyl); The surfactant can be one or two of sodium dodecyl sulfate, sodium oleate, tetraoctylammonium bromide, phospholipid, polyacrylic acid, polyethylene glycol, polyvinylpyrrolidone, cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, oleylamine, oleic acid and sodium dodecylbenzenesulfonate; The solvent is one or a mixture of two of water, methanol, ethanol, ethylene glycol, glycerol, toluene, hexane, tetrahydrofuran, chloroform, dimethylformamide, dimethyl sulfoxide, octadecene, oleylamine, ethylenediamine; By mass percentage, the boride powder, Mo carbonyl complex and surfactant account for 50% - 99.8%, 0.1% - 50% and 0.0001% - 10% of the total mass of the three respectively; The mass ratio of the total mass of the boride powder, Mo carbonyl complex and surfactant to the solvent mass is 0.01:1 - 2:1; The mass ratio range of the Mo carbonyl complex to the boride powder is 0.001:1 - 2:1; The molar ratio of the surfactant to the Mo carbonyl complex is 0.001:1 - 100:1; The mass ratio range of the boride powder to the solvent is 0.01:1 - 10:1; The mass ratio of the Mo carbonyl complex to the solvent is 0.0001:1 - 0.5:1; When adding the boride powder, other ceramic components or additives can be added simultaneously. These additives are one or more of silicon carbide, zirconium carbide, hafnium carbide, boron carbide, titanium carbide, titanium nitride, hafnium nitride, boron nitride, zirconium nitride, silicon nitride, molybdenum disilicide, graphite. After introducing the additives, the mass ratio range of the ceramic phase powder to the solvent is still 0:1 - 10:1;

[0013] (2)Add the mixed solution into a reaction vessel, and under a protective atmosphere, heat the reaction solution to the reaction temperature and then keep it warm; The pressure range that the reaction vessel can withstand is 1 - 50 MPa; The protective atmosphere in the vessel is argon, nitrogen or vacuum atmosphere; The heating rate is 1 °C / min - 100 °C / min, the reaction temperature range is 200 - 400 °C, and the holding time is 0.01 - 48 h; During the reaction process, the solution needs to be continuously stirred, and the stirring rate is 1 - 2000 r / min;

[0014] (3)After the heat preservation is completed, collect the powder and carry out washing, centrifugation and drying to obtain Mo - modified boride powder;

[0015] (4) The obtained powder is rapidly sintered to obtain Mo-toughened boride-based ultra-high temperature ceramics; during sintering, the applied pressure is 1 - 50 MPa, the protective atmosphere is argon, nitrogen or vacuum, the heating rate is 5 °C / min - 2000 °C / min, the sintering temperature is 1200 - 2200 °C, and the holding time is 0.01 - 10 h.

[0016] The advantages of the present invention over the prior art are as follows:

[0017] First, the present invention uses a solvothermal method to prepare Mo-modified ceramic powders. The Mo content, particle size, and distribution state on the surface of the ceramic powders can be adjusted by regulating the reaction temperature, type of surfactant, reaction time, etc., solving the problems of too large metal phase size and easy agglomeration existing in the existing refractory metal introduction methods.

[0018] Second, the solvothermal method and rapid sintering process adopted in the present invention can achieve uniform coating of Mo on the boride ceramic powders and ultimately achieve uniform distribution in the sintered ceramic materials.

[0019] Third, the introduced Mo in the present invention can effectively promote the sintering of the boride ceramic materials and significantly improve the mechanical and thermal shock resistance properties of the ceramic materials. Description of the Drawings

[0020] Figure 1 SEM photographs of ZrB2@Mo powders prepared in Example 1 and EDS elemental surface distribution maps of different elements: (a) SEM photograph, (b) Zr and Mo element distributions, (c) Zr element distribution, (d) Mo element distribution;

[0021] Figure 2 SEM photographs of ZrB2-SiC@Mo powders prepared in Example 2 and EDS elemental surface distribution maps of different elements: (a) SEM photograph, (b) Si, Zr and Mo element distributions, (c) Si element distribution, (d) Zr element distribution, (e) Mo element distribution;

[0022] Figure 3 Scanning electron micrographs of the microstructures of ZrB2-Mo and ZrB2-SiC-Mo ceramics prepared in Example 1 and Example 2: (a) ZrB2-Mo ceramic, (b) ZrB2-SiC-Mo ceramic. Specific Embodiments

[0023] The present invention will be further described below in conjunction with the embodiments. However, the scope of the present invention is not limited to the following embodiments. Those skilled in the art can understand that various changes and modifications can be made to the present invention without departing from the spirit and scope of the present invention.

[0024] For the instruments, reagents, and materials involved in the following examples, unless otherwise specified, they are all conventional instruments, reagents, and materials existing in the prior art and can be obtained through regular commercial channels. For the experimental methods, detection methods, etc. involved in the following examples, unless otherwise specified, they are all conventional experimental methods and detection methods existing in the prior art.

[0025] Example 1:

[0026] (1) Add 2.73 g of ZrB2 and 1.32 g of Mo(CO)6 to 30 mL of octadecene, then add 33 mL of oleylamine, mix in a glass bottle, and then transfer the mixture to a magnetic stirring reactor.

[0027] (2) Evacuate the reactor, heat it to 120 °C at a rate of 10 °C / min under vacuum and hold for 30 min; then introduce argon and heat it to 300 °C and hold for 2 h. After the holding is completed, cool it naturally to room temperature; during this process, keep stirring the reaction solution at a rate of 600 r / min all the time.

[0028] (3) Transfer the mixture obtained after the reaction to a 50 mL centrifuge tube, then add a mixed solution of 30 mL of n-hexane and acetone to the centrifuge tube, and then place the centrifuge tube in a centrifuge and run it at a speed of 10000 r / min for 10 min to separate the solid and liquid phases obtained from the reaction; repeat this step 3 times, and then dry the centrifuged solid in a vacuum at 70 °C to obtain ZrB2 powder wrapped with nano-Mo.

[0029] (4) Put the dried powder into a graphite mold and sinter it for 30 min under the conditions of a loading pressure of 30 MPa, a protective atmosphere of argon, and a sintering temperature of 1800 °C.

[0030] For the Mo-modified ZrB2 powder prepared in this example, Mo particles successfully grow on the surface of the ZrB2 powder, realizing the modification of the refractory metal Mo to ZrB2. The scanning photos of the Mo-modified ZrB2 powder and the distribution of different elements are as Figure 1 shown. According to Figure 1 the distribution of Zr and Mo elements in it, as well as the coincidence with the powder particles in the SEM photos, it can be known that the Mo prepared in this example is nano-scale particles, and the Mo element is evenly distributed on the surface of the ZrB2 powder. The density, relative density, flexural strength, and fracture toughness of the ZrB2-Mo ceramic obtained after sintering are 6.20 g / cm 3 ³, 98.4%, 350.8 MPa, and 4.75 MPa·m 1 / 2 ¹ / ², respectively. The microscopic structure photos of the sintered ceramic are as Figure 3As shown in Fig. (a), the ceramic structure is uniform and dense with small grains, indicating that the introduction of Mo effectively inhibits grain growth, promotes sintering densification, and is beneficial to improving the material properties.

[0031] Example 2:

[0032] (1) Add 2.73 g of nano-ZrB2 powder, 0.358 g of nano-SiC powder, and 1.32 g of Mo(CO)6 into 30 mL of octadecene and 33 mL of oleylamine solution, mix them in a glass bottle, and then transfer the mixture into a magnetic stirring reactor.

[0033] (2) Evacuate the reactor, heat it to 120 °C at a rate of 10 °C / min under vacuum and hold for 30 min; then introduce argon, heat it to 300 °C, hold for 2 h, and cool it to room temperature naturally after the holding ends; during this process, keep stirring the reaction solution at a rate of 600 r / min all the time.

[0034] (3) Transfer the mixture obtained after the reaction into a 50 mL centrifuge tube, add 30 mL of a mixed solution of n-hexane and acetone into the centrifuge tube, then place the centrifuge tube in a centrifuge and run it at a speed of 10000 r / min for 10 min to separate the solid and liquid phases obtained from the reaction; repeat this step 3 times, and then dry the centrifuged solid in vacuum at 70 °C to obtain nano-Mo-coated ZrB2 and SiC powders.

[0035] (4) Put the dried powder into a graphite mold, sinter it for 30 min under the conditions of a loading pressure of 30 MPa, a protective atmosphere of argon, and a sintering temperature of 1800 °C.

[0036] For the Mo-modified ZrB2 and SiC powders prepared in this example, Mo particles have successfully grown on the surfaces of the ZrB2 and SiC powders, realizing the modification of refractory metal Mo on ZrB2 and SiC. The scanning photos and element distribution of the Mo-modified ZrB2 and SiC powders are as shown in shown. According to the distribution of Si, Zr, and Mo elements in Figure 2 and the coincidence with the powder particles in the SEM photos, it can be seen that the ZrB2 and SiC powders in this example are evenly distributed, and the Mo particles are nano-scale particles and are evenly distributed on the surfaces of the ceramic powders. The density, relative density, and flexural strength of the sintered ZrB2-SiC-Mo ceramic are 5.52 g / cm 3 , 96.0%, and 380.5 MPa respectively. The microscopic structure photo of the sintered ceramic is as shown in Figure 2 Figure 3 Fig. (b). The ceramic structure is uniform and the grains are small. The introduction of Mo effectively inhibits grain growth.

[0037] Example 3:

[0038] (1) Add 4.92 g HfB2 powder and 0.23 g Mo(CO)4Cl2 to 50 mL dimethylformamide, then add 0.05 g polyvinylpyrrolidone. Mix all the raw materials in a glass bottle, and then transfer the mixture to a magnetic stirring reactor.

[0039] (2) The reactor was evacuated and heated to 150 °C at a rate of 10 °C / min under vacuum, and kept warm for 10 min; nitrogen was then introduced, and the temperature was raised to 300 °C, and kept warm for 2 h. After the end of the heat preservation, the reactor was naturally cooled to room temperature; during this process, the reaction solution was stirred at a rate of 1000 r / min;

[0040] (3) The mixture obtained after the reaction was transferred to a 50 mL centrifuge tube, and 30 mL of a mixed solution of n-hexane and acetone was added to the centrifuge tube. The centrifuge tube was then placed in a centrifuge and run at a speed of 10,000 r / min for 10 min to separate the solid obtained from the reaction from the liquid phase. After repeating this step three times, the solid obtained by centrifugation was vacuum-dried at 70 °C to obtain nano-Mo-coated HfB2 powder.

[0041] (4) The dried powder was placed in a graphite mold, heated to 1900 °C at a rate of 100 °C / min under a loading pressure of 30 MPa and an argon atmosphere, and then sintered at 1900 °C for 5 min.

[0042] The Mo-modified HfB2 powder prepared in this example has Mo particles successfully grown on the surface of the HfB2 powder. The density and flexural strength of the HfB2-Mo ceramic obtained after sintering are 10.60 g / cm 3 , 470.3 MPa and 6.04 MPa·m 1 / 2 .

[0043] Example 4:

[0044] (1) 4.22 g ZrB2 powder, 1.12 g Si3N4 powder, 0.02 g graphite, and 0.26 g Na2[Mo(CO)5] were added to 50 mL ethylenediamine, followed by 0.02 g sodium dodecylbenzenesulfonate. All the raw materials were mixed evenly in a glass bottle, and the mixture was then transferred to a magnetic stirring reactor.

[0045] (2) Evacuate the reaction kettle, heat it up to 150 °C at a rate of 10 °C / min under vacuum, and keep it at this temperature for 10 min; then introduce nitrogen gas, heat it up to 300 °C, and keep it at this temperature for 2 h. After the heat preservation is completed, cool it naturally to room temperature; during this process, keep stirring the reaction solution at a rate of 1000 r / min all the time;

[0046] (3) Transfer the mixture obtained after the reaction into a 50 mL centrifuge tube, then add 30 mL of ethanol into the centrifuge tube, and then put the centrifuge tube into a centrifuge and run it at a speed of 10000 r / min for 10 min to separate the solid and liquid phases obtained from the reaction; after repeating this step 3 times, dry the centrifuged solid at 90 °C to obtain the ceramic mixed powder wrapped with nano-Mo;

[0047] (4) Put the dried powder into a graphite mold, under a loading pressure of 30 MPa, with an argon protective atmosphere, heat it up to 1900 °C at a rate of 100 °C / min, and then sinter it at 1900 °C for 5 min;

[0048] For the Mo-modified ceramic mixed powder prepared in this example, Mo particles successfully grew on the surface of the mixed powder; the density and flexural strength of the ZrB2-Si3N4-graphite-Mo ceramic obtained after sintering are 5.80 g / cm 3 , 270.7 MPa and 5.89 MPa·m 1 / 2 .

[0049] Example 5:

[0050] (1) Add 4.99 g of nano-ZrB2 powder and 0.1 g of Mo(CO)6 into 500 mL of aqueous solution, then add 0.1 g of polyvinylpyrrolidone, mix all the raw materials evenly in a glass bottle, and then transfer the mixture into a magnetic stirring reaction kettle;

[0051] (2) Evacuate the reaction kettle, heat it up to 200 °C at a rate of 1 °C / min under vacuum, and keep it at this temperature for 30 min; then introduce argon gas, heat it up to 360 °C, and keep it at this temperature for 1 h. After the heat preservation is completed, cool it naturally to room temperature; during this process, keep stirring the reaction solution at a rate of 100 r / min all the time;

[0052] (3) Transfer the mixture obtained after the reaction into a centrifuge tube, mix every 10 mL of the reacted solution with 30 mL of a mixed solution of n-hexane and acetone, and then put the centrifuge tube into a centrifuge and run it at a speed of 10000 r / min for 10 min to separate the solid and liquid phases obtained from the reaction; after repeating this step 3 times, dry the centrifuged solid under vacuum at 70 °C to obtain the nano-Mo-wrapped ZrB2 powder;

[0053] (4) The dried powder is placed in a graphite mold. Under a loading pressure of 30 MPa, with a nitrogen protective atmosphere, it is heated to 2200 °C at a rate of 100 °C / min, and then sintered at 2200 °C for 5 min;

[0054] For the Mo-modified ZrB2 powder prepared in this example, Mo particles successfully grow on the surface of the ZrB2 powder; the density and flexural strength of the sintered ZrB2-Mo ceramic are 6.0 g / cm 3 、272.8 MPa and 3.67 MPa·m 1 / 2 .

[0055] Example 6:

[0056] (1) 4.5 g of nano-ZrB2 powder and 0.49 g of Mo(CO)6 are added to 3 mL of methanol, and then 0.01 g of oleic acid is added. All the raw materials are mixed evenly in a glass bottle, and then the mixture is transferred into a magnetic stirring reactor;

[0057] (2) The reactor is evacuated, heated to 200 °C at a rate of 1 °C / min under vacuum, and held for 30 min; then argon is introduced, heated to 360 °C, and held for 1 h. After the holding is completed, it is naturally cooled to room temperature; during this process, the reaction solution is continuously stirred at a rate of 100 r / min;

[0058] (3) The mixture obtained after the reaction is transferred into a centrifuge tube. Every 10 mL of the reaction solution is mixed with 30 mL of a mixed solution of n-hexane and acetone, and then the centrifuge tube is placed in a centrifuge and run at a speed of 10000 r / min for 10 min to separate the solid obtained from the reaction from the liquid phase; after repeating this step 3 times, the centrifuged solid is vacuum dried at 70 °C to obtain nano-Mo-coated ZrB2 powder;

[0059] (4) The dried powder is placed in a graphite mold. Under a loading pressure of 30 MPa, with a nitrogen protective atmosphere, it is heated to 2200 °C at a rate of 100 °C / min, and then sintered at 2200 °C for 5 min;

[0060] For the Mo-modified ZrB2 powder prepared in this example, Mo particles successfully grow on the surface of the ZrB2 powder; the density and flexural strength of the sintered ZrB2-Mo ceramic are 6.07 g / cm 3 、335.1 MPa and 6.29 MPa·m 1 / 2 .

[0061] Example 7:

[0062] (1) Add 4.0 g of nano-ZrB2 powder and 0.5 g of Mo(CO)6 to 5 mL of methanol, then add 0.5 g of sodium dodecylbenzenesulfonate. Mix all the raw materials evenly in a glass bottle, and then transfer the mixture into a magnetic stirring reactor;

[0063] (2) Evacuate the reactor, heat it to 200 °C at a rate of 1 °C / min under vacuum and hold for 30 min; then introduce argon, heat it to 360 °C and hold for 1 h. After the holding is completed, cool it naturally to room temperature; during this process, keep stirring the reaction solution at a rate of 100 r / min;

[0064] (3) Transfer the mixture obtained after the reaction into a centrifuge tube. Mix every 10 mL of the reaction solution with 30 mL of a mixed solution of n-hexane and acetone, and then place the centrifuge tube in a centrifuge and run it at a speed of 10000 r / min for 10 min to separate the solid and liquid phases obtained from the reaction; repeat this step 3 times, and then dry the centrifuged solid in a vacuum at 80 °C to obtain nano-Mo-coated ZrB2 powder;

[0065] (4) Put the dried powder into a graphite mold, under a loading pressure of 30 MPa, with a protective atmosphere of nitrogen, heat it to 2200 °C at a rate of 100 °C / min, and then sinter at 2200 °C for 5 min;

[0066] For the Mo-modified ZrB2 powder prepared in this example, Mo particles successfully grew on the surface of the ZrB2 powder; the density and flexural strength of the ZrB2-Mo ceramic obtained after sintering are 6.4 g / cm 3 、368.1 MPa and 6.75 MPa·m 1 / 2 .

[0067] Comparative Example 1:

[0068] Different from Example 1, Mo was not prepared on the surface of the ceramic powder through steps (1) to (3), but ZrB2 was directly sintered, and the sintering conditions were the same as those in step (4) of Example 1; the density of the ZrB2 ceramic prepared in this comparative example is 5.87 g / cm 3 、the relative density is 96.4%, and the flexural strength is 219.1 MPa.

[0069] Comparative Example 2:

[0070] Different from Example 2, Mo was not prepared on the surface of the ceramic powder through steps (1) to (3), but ZrB2 and SiC were mixed and then sintered, and the sintering conditions were the same as those in step (4) of Example 2; the density of the ZrB2-SiC ceramic prepared in this comparative example is 5.41 g / cm3 , with a relative density of 98.0%, a flexural strength of 268.9 MPa, and a fracture toughness of 4.19 MPa·m 1 / 2 .

[0071] In Examples 1 to 7, the modification of Mo on the surface of ceramic powder was achieved, and uniform distribution in the mixed powder was realized, which is beneficial to the uniform distribution of Mo in the ceramic after sintering and the exertion of the toughening effect. This method provides a new and feasible solution for the preparation and structure control of Mo-toughened boride-based ceramics.

Claims

1. A preparation method of Mo-toughened boride-based ultra-high temperature ceramics, characterized in that The preparation process includes the following steps: (1) Add boride powder and carbonyl complex of Mo into a solvent, then add a surfactant, and mix the carbonyl complex of Mo, the solvent and the surfactant evenly; the boride is one of ZrB2, HfB2, TiB2, TaB2, NbB2; the carbonyl complex of Mo is one or more of Mo(CO)6, Na2[Mo(CO)5], Mo(CO)3PPh3, Mo(CO)4Cl2, Mo(CO)4Br2, HMo(CO)3(Cp) (Cp = cyclopentadienyl); the surfactant is one or two of sodium dodecyl sulfate, sodium oleate, tetraoctylammonium bromide, phospholipid, polyacrylic acid, polyethylene glycol, polyvinylpyrrolidone, cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, oleylamine, oleic acid and sodium dodecylbenzenesulfonate; the solvent is one or a mixture of two of water, methanol, ethanol, ethylene glycol, glycerol, toluene, hexane, tetrahydrofuran, chloroform, dimethylformamide, dimethyl sulfoxide, octadecene, oleylamine, ethylenediamine; by mass percentage, the boride powder, the carbonyl complex of Mo and the surfactant account for 50% - 99.8%, 0.1% - 50% and 0.0001% - 10% of the total mass of the three respectively; the mass ratio of the total mass of the boride powder, the carbonyl complex of Mo and the surfactant to the solvent mass is 0.01:1 - 2:1; (2) Add the mixed solution into a reaction vessel, heat up the reaction solution to the reaction temperature under a protective atmosphere and then keep it warm; the pressure range that the reaction vessel can withstand is 1 - 50 MPa; the protective atmosphere in the vessel is argon, nitrogen or vacuum atmosphere; the heating rate is 1 °C / min - 100 °C / min, the reaction temperature range is 20°C - 400 °C, and the holding time is 0.01 - 48 h; during the reaction process, the solution needs to be continuously stirred, and the stirring rate is 1 - 2000 r / min; (3) After the heat preservation is completed, collect the powder and carry out washing, centrifugation and drying to obtain Mo-modified boride powder; (4) Rapidly sinter the obtained powder to obtain Mo-toughened boride-based ultra-high temperature ceramics; the pressure applied during sintering is 1 - 50 MPa, the protective atmosphere is argon, nitrogen or vacuum, the heating rate is 5 °C / min - 2000 °C / min, the sintering temperature is 1200 - 2200 °C, and the holding time is 0.01 - 10 h.

2. The preparation method of a Mo-reinforced boride-based ultra-high temperature ceramic according to claim 1, wherein: [[ID=S]] In step (1), the mass ratio range of the carbonyl complex of Mo to the boride powder is 0.001:1 - 2:

1.

3. The preparation method of a Mo-toughened boride-based ultra-high temperature ceramic according to claim 1, characterized in that: In step (1), the molar ratio of the surfactant to the carbonyl complex of Mo is 0.001:1 - 100:

1.

4. The preparation method of a Mo-toughened boride-based ultra-high temperature ceramic according to claim 1, characterized in that: In step (1), the mass ratio range of the boride powder to the solvent is 0.01:1 - 10:

1.

5. The preparation method of a Mo-toughened boride-based ultra-high temperature ceramic according to claim 1, characterized in that: In step (1), the mass ratio of the carbonyl complex of Mo to the solvent is 0.0001:1 - 0.5:

1.

6. The preparation method of a Mo-toughened boride-based ultra-high temperature ceramic according to claim 1, characterized in that: In step (1), when adding the boride powder, it is allowed to add other ceramic components or additives simultaneously. These additives are one or more of silicon carbide, zirconium carbide, hafnium carbide, boron carbide, titanium carbide, titanium nitride, hafnium nitride, boron nitride, zirconium nitride, silicon nitride, molybdenum disilicide, and graphite. After introducing the additives, the mass ratio range of the ceramic phase powder to the solvent is still 0:1 to 10:1.

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