HfB2-coated SiC powder with core-shell structure, preparation method and application

Abstract

The invention provides HfB2-coated SiC powder with a core-shell structure as well as a preparation method and application thereof, and belongs to the technical field of ceramic powder. According to the preparation method, a gas phase reaction and catalytic impregnation secondary coating method is adopted, firstly, rod-shaped HfB2 powder is subjected to heat treatment in the N2 atmosphere, the outermost layer of the rod-shaped HfB2 powder is subjected to chemical reaction coating to generate HfN, then the rod-shaped HfB2-coated HfN powder is catalyzed by nickel nitrate, then placed into a silicon source solution to be impregnated, dried and subjected to heat treatment, and the rod-shaped HfB2-coated HfN powder is obtained. And enabling Si-O-C to replace the HfN site in the chemical reaction process, so as to prepare the rod-like HfB2-coated SiC powder with the core-shell structure. According to the method, the reaction process is easy to control, the method is suitable for large-scale preparation, and the prepared rod-like HfB2-coated SiC powder of the core-shell structure has high purity and uniform morphology, can be applied in a high-temperature environment, and synergistically enhances the oxidation resistance / ablation resistance and mechanical properties of materials.

Description

Technical Field

[0001] The present application belongs to the field of ceramic powders, and specifically relates to a core-shell structure HfB2@SiC powder, a preparation method and an application thereof. Background Art

[0002] In the Chinese invention patent application published with the publication number CN115286396A, the applicant disclosed a hafnium boride ceramic powder with a micro-nano topological structure and a preparation method thereof. The hafnium boride powder (HfB2) has high purity and good micromorphology. Each hafnium boride with a micro-nano topological structure has approximately eight branches. The rod-shaped hafnium boride branches are more than ten microns long, with an average diameter of approximately 300 to 600 nm. The angles between the short rods are distributed in the range of 10° to 60°. The hafnium boride ultra-high temperature ceramics and composite materials obtained by sintering the hafnium boride powder with a micro-nano topological structure have excellent mechanical properties such as impact resistance and bending resistance while maintaining the original good thermal protection performance.

[0003] However, due to the brittleness of the ceramic itself, carbon fiber, silicon carbide (SiC), etc. are usually added for toughening during use. The coating of SiC on the surface of HfB2 powder mainly includes sol-gel method, chemical vapor deposition method (CVD), chemical vapor reaction method (CVR), embedding method, brushing method, plasma spraying method and fluidized bed coating method. On the one hand, these methods have problems such as high equipment cost and complex operation; on the other hand, because the micro-nano topological structure of hafnium boride ceramic powder is different from conventional commercial HfB2 powder (usually in granular form), this powder and ordinary commercial powder have differences in exposed crystal surfaces, and conventional coating methods cannot achieve uniform and effective coating. Summary of the Invention

[0004] 1. Problem to be solved

[0005] In response to the defects of the existing SiC coating technology on the surface of HfB2 powder, this application provides a method for preparing core-shell structured HfB2@SiC powder, especially a method for preparing SiC-coated rod-shaped HfB2 powder with a micro-nano topological structure.

[0006] On the other hand, the present application provides the prepared SiC-coated rod-shaped HfB2 powder with a micro-nano topological structure and its application. The core-shell structured rod-shaped HfB2@SiC powder has high purity and uniform morphology, can be used in high-temperature environments, and synergistically enhances the material's antioxidant / anti-ablation properties and mechanical properties.

[0007] 2. Technical solution

[0008] In order to solve the above problems, the technical solutions adopted in this application are as follows:

[0009] The present application provides a method for preparing a core-shell structured HfB2@SiC powder, the method comprising:

[0010] HfN is generated on the outer layer of HfB2 powder to obtain HfB2@HfN powder;

[0011] The HfB2@HfN powder was immersed in a silicon source solution and then taken out for heat treatment, so that SiC replaced the original site of HfN, thereby achieving SiC coating on the surface of the HfB2 powder and obtaining a core-shell structure HfB2@SiC.

[0012] Furthermore, the method for preparing the core-shell structure HfB2@SiC powder comprises the following steps:

[0013] Step A: heat-treating HfB2 powder in an N2 atmosphere to cause a chemical reaction in its outermost layer to form HfN, and then cooling it to room temperature to obtain HfB2@HfN powder;

[0014] Step B: dissolving nickel nitrate in ethanol and deionized water to prepare a nickel nitrate solution, and placing the HfB2@HfN powder prepared in step A in the nickel nitrate solution under ultrasonication and stirring; the effect of ultrasonication is to uniformly disperse the HfB2@HfN powder in the nickel nitrate solution; the effect of stirring is to uniformly mix the HfB2@HfN powder and the nickel nitrate solution;

[0015] Step C: Filter and retain the lower layer of powder, add the silicon source solution to the retained powder, and continue stirring;

[0016] Step D, filtering out the powder soaked in the silicon source solution in Step C and drying it;

[0017] Step E: Grind the powder dried in step D, and perform high-temperature heat treatment under an argon (Ar) atmosphere, and obtain HfB2@SiC powder with a core-shell structure after cooling.

[0018] Furthermore, in the above step A, the HfB2 powder is a rod-shaped HfB2 powder with a micro-nano topological structure. The HfB2 powder has about eight short rod branches, each branch is more than ten microns long, with an average diameter of about 300 to 600 nm, and the angle distribution range between the short rod branches is 10° to 60°, as recorded in the Chinese invention patent application with publication number CN115286396A. As a further explanation of the present application, the rod-shaped HfB2 powder with a micro-nano topological structure has multiple short rod branches, which is different from ordinary commercial powders in terms of exposed crystal surfaces. Conventional coating methods cannot achieve uniform and effective coating. Therefore, a method is adopted to first generate HfN on its outer layer, and then immerse it in a silicon source solution and heat treat it to replace the original site of HfN with SiC, thereby achieving SiC coating on the surface of the rod-shaped HfB2 powder.

[0019] Furthermore, in the above step A, the heat treatment includes a treatment at 1400-1600° C. for 1.5-2.5 hours. Furthermore, in the above step A, the heat treatment includes a treatment at 1500° C. for 2 hours.

[0020] Furthermore, in the above step A, the temperature rise program of the heat treatment includes: heating from room temperature to 950-1050°C at a rate of 4-6°C / min, and then heating to 1400-1600°C at a rate of 1-3°C / min. Furthermore, in the above step A, the temperature rise program of the heat treatment includes: heating from room temperature to 1000°C at a rate of 5°C / min, and then heating from 1000°C to 1500°C at a rate of 2°C / min.

[0021] Furthermore, in the above step A, the cooling procedure to room temperature includes: cooling to 950-1050°C at a rate of 1-3°C / min, then cooling to 250-350°C at a rate of 4-6°C / min, and finally cooling naturally to room temperature. Furthermore, in the above step A, the cooling procedure to room temperature includes: cooling to 1000°C at a rate of 2°C / min, then cooling to 300°C at a rate of 5°C / min, and finally cooling naturally to room temperature.

[0022] Furthermore, in the above step B, the volume ratio of ethanol to deionized water is 1:1.

[0023] Furthermore, in the above step B, the mass fraction of the nickel nitrate solution is 2 to 8 wt%.

[0024] Furthermore, in the above step B, the mass fraction of the nickel nitrate solution is 4-8 wt%.

[0025] Furthermore, in the above step B, the mass fraction of the nickel nitrate solution is 4-6 wt%.

[0026] Furthermore, in the above step B, the mass fraction of the nickel nitrate solution is 4 wt%.

[0027] Furthermore, in the above step B, the ultrasonic time is 1.5 to 2.5 hours. Furthermore, in the above step B, the ultrasonic time is 2 hours.

[0028] Furthermore, in the above step B, the ultrasonic power is 30-40 kHz. Furthermore, in the above step B, the ultrasonic power is 35 kHz.

[0029] Furthermore, in the above step B, the stirring speed is 400-600 rpm, and the stirring time is 10-15 hours. Furthermore, in the above step B, the stirring speed is 450 rpm, and the time is 12 hours.

[0030] Furthermore, in the above step C, the silicon source solution includes: a mixed solution of methyltrimethoxysilane, ethanol and deionized water.

[0031] Furthermore, in the above step C, the volume ratio of methyltrimethoxysilane, ethanol and deionized water is 1:1:8; the silicon source solution in this ratio has a good coating effect.

[0032] Furthermore, in the above step C, the stirring time after the silicon source solution is added is 10 to 15 hours, and the purpose of stirring is to uniformly mix the powder and the silicon source solution.

[0033] Furthermore, in the above step C, the stirring time after the silicon source solution is added is 12 hours.

[0034] Furthermore, in the above step D, the drying temperature is 75-85° C., and the drying time is 2-4 hours. Still further, in the above step D, the drying temperature is 80° C., and the drying time is 3 hours.

[0035] Furthermore, in step E, the high-temperature heat treatment is performed at a temperature of 1400-1600°C for 1-3 hours. Furthermore, in step E, the heat treatment is performed at a temperature of 1500°C for 2 hours. As a further illustration of the present application, this temperature facilitates the formation and growth of SiC.

[0036] Furthermore, in the above step E, the temperature rise program of the high temperature heat treatment includes: heating from room temperature to 950-1050°C at a rate of 4-6°C / min, and then heating to 1400-1600°C at a rate of 1-3°C / min. Furthermore, in the above step A, the temperature rise program of the heat treatment includes: heating from room temperature to 1000°C at a rate of 5°C / min, and then heating from 1000°C to 1500°C at a rate of 2°C / min.

[0037] Furthermore, in the above step E, the cooling procedure includes: cooling to 950-1050°C at a rate of 1-3°C / min, then cooling to 250-350°C at a rate of 4-6°C / min, and finally cooling naturally to room temperature. Furthermore, in the above step A, the cooling procedure to room temperature includes: cooling to 1000°C at a rate of 2°C / min, then cooling to 300°C at a rate of 5°C / min, and finally cooling naturally to room temperature.

[0038] The present application also provides a core-shell structure HfB2@SiC powder prepared by the above-mentioned method for preparing the core-shell structure HfB2@SiC powder.

[0039] This application also provides a core-shell HfB2@SiC powder, which comprises a rod-shaped HfB2 powder with a micro-nanoscale topological structure and SiC coated on its surface. While maintaining the inherent toughening properties of the high aspect ratio powder, the outer SiC coating further enhances the powder's antioxidant properties, giving the powder both toughening and antioxidant properties. Furthermore, the prepared core-shell rod-shaped HfB2@SiC powder has a high purity and can be used in complex and extreme thermal-mechanical coupling environments, synergistically enhancing the material's antioxidant / ablation resistance and mechanical properties.

[0040] The present application also provides the application of the above-mentioned core-shell structure HfB2@SiC powder in the preparation of ceramic materials.

[0041] The present application also provides a ceramic material, which includes the above-mentioned core-shell structure HfB2@SiC powder.

[0042] 3. Beneficial effects

[0043] Compared with the prior art, the present application has the following advantages:

[0044] (1) The present application provides a method for preparing a core-shell structure HfB2@SiC powder, which is prepared by adopting a gas phase reaction and catalytic impregnation secondary coating method, wherein SiC is coated on the surface of the HfB2 powder, especially on the surface of the rod-shaped HfB2 powder with a micro-nano topological structure. Specifically, HfB2 powder, nickel nitrate hexahydrate, methyltrimethoxysilane, ethanol, and deionized water are used as raw materials. The HfB2 powder is first heat-treated in an N2 atmosphere so that its outermost layer undergoes a chemical reaction and is coated to generate HfN to obtain HfB2@HfN powder. The HfB2@HfN powder is then catalyzed by nickel nitrate and then immersed in a silicon source solution. The powder is then dried and heat-treated so that Si-OC replaces the HfN site during the chemical reaction, and SiC replaces the original site of HfN, thereby achieving SiC coating on the surface of the HfB2 powder to obtain HfB2@SiC powder with a core-shell structure. The preparation method is easy to control, especially for rod-shaped powders (rod-shaped HfB2 powders with micro-nano topological structures). The preparation method has uniform coating, and the prepared core-shell structured HfB2@SiC powder has high purity and does not show any impurity peaks in the X-ray diffraction pattern. No further impurity removal treatment is required, making it suitable for large-scale preparation.

[0045] (2) The present application provides a core-shell structure HfB2@SiC powder, especially a SiC-coated rod-shaped HfB2 powder with a micro-nano topological structure. The outer SiC coating further improves the powder's antioxidant properties, allowing the powder to have both toughening and antioxidant properties. At the same time, the core-shell structure HfB2@SiC powder has high purity, a high aspect ratio, and a uniform micromorphology (length of about 10 μm, average diameter of about 2 μm). The HfB2@SiC powder greatly improves the antioxidant properties of the initial powder, raising its intense oxidation temperature from about 750°C to about 1120°C. It can be used in complex extreme thermal-mechanical coupling environments to synergistically enhance the material's antioxidant / anti-ablation properties and mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 are the analysis results of the initial rod-shaped HfB2 powder and the rod-shaped HfB2@HfN powder, where: (a) is the scanning electron microscope image of the initial rod-shaped HfB2 powder; (b) is the scanning electron microscope image of the rod-shaped HfB2@HfN powder; (c) is the X-ray diffraction pattern of the initial rod-shaped HfB2 powder and the rod-shaped HfB2@HfN powder; (d) is the morphology of the HfB2@HfN powder under a transmission electron microscope; (e) is the high-resolution image of the HfB2@HfN powder under a transmission electron microscope; and (f) is the diffraction ring of the HfB2@HfN powder.

[0047] Figure 2 3 is a scanning electron microscope image of the rod-shaped HfB2@SiC powder with a core-shell structure prepared in Examples 1-4.

[0048] Figure 3 This is the X-ray diffraction pattern of the rod-shaped HfB2@SiC powder with a core-shell structure prepared in Example 2.

[0049] Figure 4 3 and 4 are thermogravimetric curves of the initial rod-shaped HfB2 powder and the rod-shaped HfB2@SiC powder with a core-shell structure obtained in Examples 1-4 oxidized in air. DETAILED DESCRIPTION

[0050] The present application is further described below with reference to specific embodiments.

[0051] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0052] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents or instruments used, if the manufacturer is not specified, are commercially available conventional products.

[0053] As used herein, the term "about" is used to provide flexibility and imprecision associated with a given term, measurement, or value. One skilled in the art can readily determine the degree of flexibility for a particular variable.

[0054] As used herein, the term "at least one of" is intended to be synonymous with "one or more of." For example, "at least one of A, B, and C" explicitly includes only A, only B, only C, and combinations of each thereof.

[0055] Concentration, amount and other numerical data can be presented in range format in this article.Should be understood that such range format is only used for convenience and brevity, and should be flexibly interpreted as not only including the numerical value clearly described as range limit, but also including all independent numerical values ​​or subranges encompassed within the scope, just as each numerical value and subrange are clearly described.For example, the numerical range of about 1 to about 4.5 should be interpreted as not only including the limit value of 1 to about 4.5 clearly described, but also including independent numerals (such as 2,3,4) and subranges (such as 1 to 3,2 to 4 etc.).The same principle is applicable to the scope of only narrating a numerical value, such as "less than about 4.5", which should be interpreted as including all above-mentioned values ​​and scopes.In addition, no matter how the breadth of described scope or feature is, this explanation should be applicable.

[0056] Example 1

[0057] This embodiment provides a method for preparing a core-shell structured HfB2@SiC powder and the core-shell structured HfB2@SiC powder prepared thereby.

[0058] In this embodiment, the HfB2 powder is a rod-shaped HfB2 powder with a micro-nano scale topological structure, and the HfB2 powder is the hafnium boride powder prepared in Example 1 of the Chinese invention patent application with publication number CN115286396A.

[0059] In this embodiment, a method for preparing HfB2@SiC powder having a core-shell structure includes the following steps:

[0060] Step A, weighing 5g of rod-shaped HfB2 powder with a micro-nano scale topological structure into a graphite crucible, placing it in a high-temperature tube furnace, using high-purity nitrogen (N2≥99.999%) as a protective gas, heating from room temperature to 1000°C at a rate of 5°C / min, then heating from 1000°C to 1500°C at a rate of 2°C / min, heat treating for 120min, cooling to 1000°C at a rate of 2°C / min, then cooling to 300°C at a rate of 5°C / min, and finally naturally cooling to room temperature to obtain rod-shaped HfB2@HfN powder;

[0061] Step B: 1.0 g of nickel nitrate hexahydrate was dissolved in 25 mL of ethanol and 25 mL of deionized water to prepare a 2 wt% nickel nitrate solution. The rod-shaped HfB2@HfN powder prepared in step A was placed in the nickel nitrate solution, ultrasonicated at 35 kHz for 2 h, and stirred at 450 rpm for 12 h.

[0062] Step C: Filter out the upper layer solution in step B, prepare a silicon source solution by taking 5 mL of methyltrimethoxysilane, 5 mL of ethanol, and 40 mL of deionized water, inject the silicon source solution into the retained powder, and continue stirring at 450 rpm for 12 h;

[0063] Step D: Filter out the powder soaked in the silicon source solution in step C and dry it in an oven at 80° C. for 3 h;

[0064] Step E: Grind the powder dried in step D lightly, put it into a graphite crucible, and place it in a high-temperature tube furnace. Use high-purity argon (Ar≥99.999%) as a protective gas, heat it from room temperature to 1000°C at a rate of 5°C / min, and then heat it from 1000°C to 1500°C at a rate of 2°C / min. Heat it for 120 minutes, reduce it to 1000°C at a rate of 2°C / min, and then reduce it to 300°C at a rate of 5°C / min. Finally, cool it naturally to room temperature to obtain rod-shaped HfB2@SiC powder with a core-shell structure.

[0065] Example 2

[0066] This embodiment provides a method for preparing a core-shell structured HfB2@SiC powder and the core-shell structured HfB2@SiC powder prepared thereby.

[0067] In this embodiment, the HfB2 powder is a rod-shaped HfB2 powder with a micro-nano scale topological structure, and the HfB2 powder is the hafnium boride powder prepared in Example 1 of the Chinese invention patent application with publication number CN115286396A.

[0068] In this embodiment, a method for preparing HfB2@SiC powder having a core-shell structure includes the following steps:

[0069] Step A, weighing 5g of rod-shaped HfB2 powder with a micro-nano scale topological structure into a graphite crucible, placing it in a high-temperature tube furnace, using high-purity nitrogen (N2≥99.999%) as a protective gas, heating from room temperature to 1000°C at a rate of 5°C / min, then heating from 1000°C to 1500°C at a rate of 2°C / min, heat treating for 120min, cooling to 1000°C at a rate of 2°C / min, then cooling to 300°C at a rate of 5°C / min, and finally naturally cooling to room temperature to obtain rod-shaped HfB2@HfN powder;

[0070] Step B: 2.0 g of nickel nitrate hexahydrate was dissolved in 25 mL of ethanol and 25 mL of deionized water to prepare a nickel nitrate solution with a mass fraction of 4 wt%. The rod-shaped HfB2@HfN powder prepared in step A was placed in the nickel nitrate solution, ultrasonicated at 35 kHz for 2 h, and stirred at 450 rpm for 12 h.

[0071] Step C: Filter out the upper layer solution in step B, prepare a silicon source solution by taking 5 mL of methyltrimethoxysilane, 5 mL of ethanol, and 40 mL of deionized water, inject the silicon source solution into the retained powder, and continue stirring at 450 rpm for 12 h;

[0072] Step D: Filter out the powder soaked in the silicon source solution in step C and dry it in an oven at 80° C. for 3 h;

[0073] Step E: Grind the powder dried in step D lightly, put it into a graphite crucible, and place it in a high-temperature tube furnace. Use high-purity argon (Ar≥99.999%) as a protective gas, heat it from room temperature to 1000°C at a rate of 5°C / min, and then heat it from 1000°C to 1500°C at a rate of 2°C / min. Heat it for 120 minutes, reduce it to 1000°C at a rate of 2°C / min, and then reduce it to 300°C at a rate of 5°C / min. Finally, cool it naturally to room temperature to obtain rod-shaped HfB2@SiC powder with a core-shell structure.

[0074] Example 3

[0075] This embodiment provides a method for preparing a core-shell structured HfB2@SiC powder and the core-shell structured HfB2@SiC powder prepared thereby.

[0076] In this embodiment, the HfB2 powder is a rod-shaped HfB2 powder with a micro-nano scale topological structure, and the HfB2 powder is the hafnium boride powder prepared in Example 1 of the Chinese invention patent application with publication number CN115286396A.

[0077] In this embodiment, a method for preparing HfB2@SiC powder having a core-shell structure includes the following steps:

[0078] Step A, weighing 5g of rod-shaped HfB2 powder with a micro-nano scale topological structure into a graphite crucible, placing it in a high-temperature tube furnace, using high-purity nitrogen (N2≥99.999%) as a protective gas, heating from room temperature to 1000°C at a rate of 5°C / min, then heating from 1000°C to 1500°C at a rate of 2°C / min, heat treating for 120min, cooling to 1000°C at a rate of 2°C / min, then cooling to 300°C at a rate of 5°C / min, and finally naturally cooling to room temperature to obtain rod-shaped HfB2@HfN powder;

[0079] Step B: 3.0 g of nickel nitrate hexahydrate was dissolved in 25 mL of ethanol and 25 mL of deionized water to prepare a nickel nitrate solution with a mass fraction of 6 wt%. The rod-shaped HfB2@HfN powder prepared in step A was placed in the nickel nitrate solution, ultrasonicated at 35 kHz for 2 h, and stirred at 450 rpm for 12 h.

[0080] Step C: Filter out the upper layer solution in step B, prepare a silicon source solution by taking 5 mL of methyltrimethoxysilane, 5 mL of ethanol, and 40 mL of deionized water, inject the silicon source solution into the retained powder, and continue stirring at 450 rpm for 12 h;

[0081] Step D: Filter out the powder soaked in the silicon source solution in step C and dry it in an oven at 80° C. for 3 h;

[0082] Step E: Grind the powder dried in step D lightly, put it into a graphite crucible, and place it in a high-temperature tube furnace. Use high-purity argon (Ar≥99.999%) as a protective gas, heat it from room temperature to 1000°C at a rate of 5°C / min, and then heat it from 1000°C to 1500°C at a rate of 2°C / min. Heat it for 120 minutes, reduce it to 1000°C at a rate of 2°C / min, and then reduce it to 300°C at a rate of 5°C / min. Finally, cool it naturally to room temperature to obtain rod-shaped HfB2@SiC powder with a core-shell structure.

[0083] Example 4

[0084] This embodiment provides a method for preparing a core-shell structured HfB2@SiC powder and the core-shell structured HfB2@SiC powder prepared thereby.

[0085] In this embodiment, the HfB2 powder is a rod-shaped HfB2 powder with a micro-nano scale topological structure, and the HfB2 powder is the hafnium boride powder prepared in Example 1 of the Chinese invention patent application with publication number CN115286396A.

[0086] In this embodiment, a method for preparing HfB2@SiC powder having a core-shell structure includes the following steps:

[0087] Step A, weighing 5g of rod-shaped HfB2 powder with a micro-nano scale topological structure into a graphite crucible, placing it in a high-temperature tube furnace, using high-purity nitrogen (N2≥99.999%) as a protective gas, heating from room temperature to 1000°C at a rate of 5°C / min, then heating from 1000°C to 1500°C at a rate of 2°C / min, heat treating for 120min, cooling to 1000°C at a rate of 2°C / min, then cooling to 300°C at a rate of 5°C / min, and finally naturally cooling to room temperature to obtain rod-shaped HfB2@HfN powder;

[0088] Step B: 4.0 g of nickel nitrate hexahydrate was dissolved in 25 mL of ethanol and 25 mL of deionized water to prepare a nickel nitrate solution with a mass fraction of 8 wt%. The rod-shaped HfB2@HfN powder prepared in step A was placed in the nickel nitrate solution, ultrasonicated at 35 kHz for 2 h, and stirred at 450 rpm for 12 h.

[0089] Step C: Filter out the upper layer solution in step B, prepare a silicon source solution by taking 5 mL of methyltrimethoxysilane, 5 mL of ethanol, and 40 mL of deionized water, inject the silicon source solution into the retained powder, and continue stirring at 450 rpm for 12 h;

[0090] Step D: Filter out the powder soaked in the silicon source solution in step C and dry it in an oven at 80° C. for 3 h;

[0091] Step E: Grind the powder dried in step D lightly, put it into a graphite crucible, and place it in a high-temperature tube furnace. Use high-purity argon (Ar≥99.999%) as a protective gas, heat it from room temperature to 1000°C at a rate of 5°C / min, and then heat it from 1000°C to 1500°C at a rate of 2°C / min. Heat it for 120 minutes, reduce it to 1000°C at a rate of 2°C / min, and then reduce it to 300°C at a rate of 5°C / min. Finally, cool it naturally to room temperature to obtain rod-shaped HfB2@SiC powder with a core-shell structure.

[0092] Example 5

[0093] In this example, purity testing, morphology observation and thermogravimetric analysis were performed on the rod-shaped HfB2@SiC powder with a core-shell structure prepared in Examples 1-4 of the present application and the powder in the process.

[0094] (1) Rod-shaped HfB2@HfN powder

[0095] The scanning electron microscopy images of the initial rod-shaped HfB2 powder (rod-shaped HfB2 powder with micro-nano topological structure) and the rod-shaped HfB2@HfN powder prepared by preliminary coating are shown in Figure 2. Figure 1 As shown in (a) and (b), they all have uniform morphology, and the surface of the rod-shaped HfB2@HfN powder is evenly coated.

[0096] The X-ray diffraction patterns of the initial rod-shaped HfB2 powder and the rod-shaped HfB2@HfN powder prepared by preliminary coating are shown in Figure 2. Figure 1 As shown in (c), X-ray diffraction analysis shows that the powders are all pure phases without any other impurities.

[0097] The morphology of rod-shaped HfB2@HfN powder under transmission electron microscopy is as follows: Figure 1 As shown in (d), high-resolution image analysis under transmission electron microscopy ( Figure 1(e)) and diffraction rings ( Figure 1 (f)) is calibrated to determine that its outer layer is HfN.

[0098] (2) Rod-shaped HfB2@SiC powder with core-shell structure

[0099] The scanning electron microscopy images of the rod-shaped HfB2@SiC powder with core-shell structure prepared in Examples 1-4 are as follows: Figure 2 As shown in (a) to (d), after being impregnated with silicon source solution and heat treated, SiC particles are generated on the surface of the powder and are arranged relatively evenly on the surface. It can be seen that as the concentration of nickel nitrate solution increases, the generated SiC particles gradually become smaller.

[0100] The X-ray diffraction pattern of the rod-shaped HfB2@SiC powder with core-shell structure prepared in Example 2 is as follows: Figure 3 As shown, X-ray diffraction analysis shows that the powder is a pure phase without any other impurities.

[0101] (3) Antioxidant performance test

[0102] The thermogravimetric curves of the initial rod-shaped HfB2 powder and the rod-shaped HfB2@SiC powder with core-shell structure obtained in Examples 1-4 oxidized in air are shown in Figure 2. Figure 4 As shown in Figure 2, it can be seen that the antioxidant performance of the coated powder (HfB2@SiC powder) is better than that of the initial powder ( Figure 4 Among them, the SiC coating on the surface of the powder treated with 4wt% nickel nitrate solution is more uniform and has the best antioxidant performance.

[0103] In summary, the present invention prepares a rod-shaped HfB2@SiC powder with a core-shell structure by innovatively adopting a method of gas phase reaction and catalytic impregnation secondary coating. On the basis of maintaining the intrinsic toughening properties of the original powder, SiC is uniformly coated on its surface, so that the powder inherently has both toughening properties and antioxidant properties. The provided method process is easy to control, the coating is uniform, and it is suitable for large-scale preparation. The prepared rod-shaped HfB2@SiC powder with a core-shell structure has high purity and uniform morphology. There is no preparation of similar powders in related reports. The powder can be used in complex and extreme thermal-mechanical coupling environments to synergistically enhance the antioxidant / anti-ablation properties and mechanical properties of the material.

[0104] Those skilled in the art will appreciate that the foregoing descriptions are merely specific embodiments of the present invention, and not exhaustive examples. It should be noted that numerous variations and modifications are possible for those skilled in the art, and all such variations and modifications that do not exceed the scope of the claims should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a core-shell structured HfB2@SiC powder, characterized in that: The method comprises: HfN is generated on the outer layer of HfB2 powder to obtain HfB2@HfN powder; The HfB2@HfN powder was immersed in a silicon source solution and then taken out for heat treatment, so that SiC replaced the original site of HfN, achieving SiC coating on the surface of the HfB2 powder and obtaining a core-shell structure HfB2@SiC.

2. The preparation method according to claim 1, characterized in that The method comprises the following steps: Step A: heat-treating HfB2 powder in a N2 atmosphere and cooling it to room temperature to obtain HfB2@HfN powder; the heat treatment comprises treating at 1400-1600°C for 1.5-2.5 hours; Step B: dissolving nickel nitrate in ethanol and deionized water to prepare a nickel nitrate solution, placing the HfB2@HfN powder prepared in step A in the nickel nitrate solution and stirring under ultrasonication; Step C: Filter and retain the lower layer of powder, add the silicon source solution to the retained powder, and continue stirring; Step D, filtering out the powder soaked in the silicon source solution in Step C and drying it; Step E: Grind the powder dried in step D, perform high-temperature heat treatment under an argon atmosphere, and obtain HfB2@SiC powder with a core-shell structure after cooling; the temperature of the high-temperature heat treatment is 1400-1600°C, and the heat treatment time is 1-3 hours.

3. The preparation method according to claim 2, characterized in that The mass fraction of the nickel nitrate solution is 2-8 wt %.

4. The preparation method according to claim 3, characterized in that The mass fraction of the nickel nitrate solution is 4 wt%.

5. The preparation method according to claims 1-4, characterized in that The silicon source solution includes a mixed solution of methyltrimethoxysilane, ethanol and deionized water.

6. The preparation method according to claim 5, characterized in that In step A, the heating program of the heat treatment includes: heating from room temperature to 950-1050°C at a rate of 4-6°C / min, and then heating to 1400-1600°C at a rate of 1-3°C / min; the cooling program to room temperature includes: cooling to 950-1050°C at a rate of 1-3°C / min, and then cooling to 250-350°C at a rate of 4-6°C / min, and finally cooling naturally to room temperature; and / or In step E, the heating program of the high-temperature heat treatment includes: heating from room temperature to 950-1050°C at a rate of 4-6°C / min, and then heating to 1400-1600°C at a rate of 1-3°C / min; the cooling program includes: cooling to 950-1050°C at a rate of 1-3°C / min, and then cooling to 250-350°C at a rate of 4-6°C / min, and finally naturally cooling to room temperature.

7. The preparation method according to claim 6, characterized in that The HfB2 powder is a rod-shaped HfB2 powder with a micro-nano topological structure.

8. A core-shell structure HfB2@SiC powder, characterized in that: The powder comprises rod-shaped HfB2 powder with a micro-nano scale topological structure and SiC coated on the surface of the rod-shaped HfB2 powder.

9. Use of the core-shell structured HfB2@SiC powder according to claim 8 in the preparation of ceramic materials.

10. A ceramic material, characterized in that: The ceramic material includes the core-shell structure HfB2@SiC powder according to claim 8.

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