Core-shell structure ceramic powder, preparation method and application

Abstract

The invention relates to the technical field of ceramic material preparation, in particular to core-shell structure ceramic powder and a preparation method and application thereof.The surface of boride ceramic powder is coated with a uniform carbon layer, then the carbon layer is mixed with silicon powder, thermal treatment is conducted through Joule thermal equipment, and the boride ceramic powder coated with a silicon carbide layer is obtained; the prepared composite ceramic powder has good sinterability and oxidation resistance, a composite ceramic block or a ceramic-based composite material is prepared by sintering the composite ceramic powder as a raw material, and the long-acting oxidation / ablation resistance can be effectively improved, so that the composite ceramic powder can be used as a thermal structure component on a remote high-speed aircraft; the preparation process is simple, the reaction condition is mild, the period is short, the cost is low, and the problems that in the prior art, the boride and silicon carbide composite ceramic powder preparation process is complex, and the service requirement in an extreme environment cannot be met are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic material preparation, in particular to a core-shell structure ceramic powder, a preparation method and an application thereof. Background Art

[0002] Currently, refractory metal borides are excellent candidates for ultra-high-temperature thermal protection systems in spacecraft due to their high melting point, high elastic modulus, high hardness, high thermal conductivity, good high-temperature stability, and excellent oxidation resistance and ablation resistance. However, studies have shown that when refractory metal borides are exposed to air, when the temperature exceeds 1200°C, the low-melting-point oxidation product of the boride ultra-high-temperature ceramic, boron oxide (B2O3), begins to volatilize, forming oxygen diffusion channels within the boride ceramic, intensifying oxidation and significantly reducing its oxidation protection performance.

[0003] In the prior art, the oxidation resistance of boride ceramics is usually improved by adding SiC. This is because the transition metal oxides produced by the oxidation of the boride can react with the oxidation product of SiC, SiO2, to form silicate glass with strong oxygen barrier ability and good thermal stability, which inhibits the further oxidation of the boride. In addition, the refractory oxidation products of boride ceramics can increase the viscosity of borosilicate glass, inhibit the volatilization of the glass layer, and still achieve good oxidation protection at temperatures above 1600°C. By coating the boride ceramic powder with a silicon carbide layer, a dense protective layer is formed on the surface of the boride ceramic powder in extreme service environments, which significantly improves its oxidation resistance. The tight interface bonding reduces interface defects, thereby increasing the overall mechanical properties. For example, in the paper "HAN JS, AN GS, CHOI SC. Synthesis of ZrB2@SiC composite particle through sol-gel and carboxylic acid Bothermal reduction [J]. Materials Today Communications, 2022, 33: 104646," core-shell ZrB2@SiO2 powders were prepared by a sol-gel process using tetraethyl orthosilicate as a silicon source. Subsequently, ZrB2@SiO2 was converted to ZrB2@SiC by heat treatment at 1400°C in a tube furnace by adding 7 wt% carbon powder. However, this method has a high heat treatment temperature, a long cycle, high energy consumption, and a relatively cumbersome preparation process. Reference 2 "ZHU S, FAHRENHOLTZ WG, HILMAS GE. Enhanced densification and mechanical properties of ZrB2-SiC processed by a preceramic polymer coating route [J]. ScriptaMaterialia, 2008, 59 (1): 123-6." Polycarbosilane and ZrB2 were mixed and pyrolyzed, and the polycarbosilane was in situ converted into carbon and silicon carbide. ZrB2-SiC ceramic blocks were then prepared by a pressureless sintering process, with silicon carbide particles uniformly distributed in the ZrB2 matrix. The process of obtaining silicon carbide by pyrolysis of polycarbosilane is difficult to control, and the discontinuous SiC distribution causes the oxidation protection of ZrB2 directly exposed to high-temperature oxygen-containing environments to fail when the temperature exceeds 1200°C. The porous structure of ZrO2, the oxidation product of ZrB2, is difficult to resist high-temperature erosion, thereby weakening its antioxidant and anti-ablation properties.Reference 3, "LYU Y, HAO J, CHENG Y, et al. Ultrahigh temperature aBlation resistant HfB2-SiC composites: From liquid SiHfCB precursor synthesis to light weight Bulk preparation and characterization [J]. Journal of Materials Science & Technology, 2025, 212: 1-16.", first prepares the ceramic precursor SiHfCB, which is then converted into HfB2-SiC composite ceramic powder by pyrolysis. This method can produce ceramic powders with uniform element distribution and good sintering properties, but the process is relatively cumbersome, and the synchronous loss of HfB2 and SiC under extreme dynamic ablation conditions may accelerate the overall failure of the material, reducing its resistance to melt erosion during the ablation process.

[0004] In summary, the existing processes for preparing boride and silicon carbide composite ceramic powders have some limitations, such as high heat treatment temperature, cumbersome preparation process, and limited service performance of the prepared materials in extreme environments. Therefore, there is an urgent need to develop a simple, feasible, and process-controllable method to prepare silicon carbide-coated boride ultrafine powder with a core-shell structure, so as to significantly improve the long-term antioxidant and anti-ablation properties of boride ceramics, and lay the theoretical and technical support for its application in high-speed aircraft thermal protection systems. Summary of the Invention

[0005] In response to the problems in the prior art that the preparation process of boride and silicon carbide composite ceramic powder is complicated and cannot meet the service requirements in extreme environments, the present invention provides a core-shell structure ceramic powder, a preparation method and application.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for preparing a core-shell structured ceramic powder, comprising:

[0008] Performing surface functionalization treatment on ceramic powder to introduce hydroxyl groups on the surface of ceramic particles to obtain pretreated ceramic powder;

[0009] placing the pretreated ceramic powder in a water-soluble carbon source solution and performing a hydrothermal reaction to obtain carbon-coated ceramic powder;

[0010] The carbon-coated ceramic powder and silicon powder are ground and mixed, and subjected to a temperature-raising treatment to obtain a core-shell structure ceramic powder.

[0011] Optionally, the ceramic powder is one or more of ZrB2, HfB2, TiB2, TaB2 and NB2.

[0012] Optionally, the method of performing surface functionalization treatment on the ceramic powder and introducing hydroxyl groups on the surface of the ceramic particles to obtain the pretreated ceramic powder is:

[0013] The ceramic powder is placed in a mixed solution of hydrochloric acid and nitric acid, and reacted at 70° C. to 90° C. for 0.5 to 2 hours to obtain a pretreated ceramic powder; wherein the molar ratio of hydrochloric acid to nitric acid in the mixed solution of hydrochloric acid and nitric acid is 1:1, and the total molar concentration is 1% to 5%.

[0014] Optionally, the water-soluble carbon source solution is sucrose solution, glucose solution, fructose solution, maltose solution or lactose solution; the mass concentration of the water-soluble carbon source solution is 3% to 5%, and the mass ratio of the pretreated ceramic powder to the water-soluble carbon source is 1:(2 to 4).

[0015] Optionally, the process of removing residual silicon powder is also included, specifically:

[0016] The carbon-coated ceramic powder and silicon powder are ground and mixed, and subjected to a temperature treatment to react to obtain a prefabricated core-shell structure ceramic powder;

[0017] The prefabricated core-shell structure ceramic powder is placed in an alkaline solution, heated to remove residual silicon powder in the prefabricated core-shell structure ceramic powder, washed to neutrality, and dried to obtain the core-shell structure ceramic powder.

[0018] Optionally, the reaction temperature of the hydrothermal reaction is 160° C. to 180° C., and the reaction time is 7 to 9 hours.

[0019] Optionally, the mass ratio of the carbon-coated ceramic powder to the silicon powder is 1:(0.2-0.3), and the grinding time is 0.5-1 h.

[0020] Optionally, the method of grinding and mixing the carbon-coated ceramic powder and silicon powder and subjecting the mixture to a temperature treatment to obtain the core-shell structure ceramic powder is:

[0021] After grinding and mixing carbon-coated ceramic powder and silicon powder, vacuuming to a pressure below -0.1 MPa, heating to 1300-1350°C at a heating rate of 100-200°C / s and keeping the temperature for 20-40s to obtain core-shell structure ceramic powder.

[0022] A core-shell structure ceramic powder is prepared using the above-mentioned method for preparing core-shell structure ceramic powder.

[0023] For example, the application of the core-shell structure ceramic powder mentioned above in the thermal protection system of aerospace vehicles.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides a method for preparing a core-shell structured ceramic powder. The method comprises the following steps: performing surface functionalization treatment on ceramic powder, introducing hydroxyl groups on the surface of ceramic particles, and obtaining pretreated ceramic powder; then placing the pretreated ceramic powder in a water-soluble carbon source solution, and performing a hydrothermal reaction, to obtain carbon-coated ceramic powder; finally, grinding and mixing the carbon-coated ceramic powder with silicon powder, and subjecting the mixture to an in-situ reaction by heating treatment to form a core-shell structured ceramic powder having an outer layer of silicon carbide and an inner core of ceramic particles. The introduction of hydroxyl groups onto the ceramic particle surface allows hydrogen or covalent bonds between the hydroxyl groups and oxygen-containing functional groups in the carbon source, providing anchoring sites for the subsequent uniform adsorption of the carbon source, enhancing chemical adsorption and ensuring uniform nucleation of the subsequent carbon layer on the ceramic particle surface. A water-soluble carbon source decomposes under hydrothermal conditions and deposits on the ceramic particle surface to form a continuous and dense carbon coating. This carbon coating then reacts with silicon powder during high-temperature treatment to form a silicon carbide layer. This coating is tightly bonded to the core ceramic particle through chemical bonds, forming a gradient structure of "core (ceramic particle)-intermediate layer (carbon)-shell (SiC)." This not only significantly improves interfacial bonding strength and reduces the risk of spalling during use, but also significantly enhances the material's high-temperature thermal stability and thermal shock resistance, better meeting service requirements in extreme environments. The preparation method is simple, involving only conventional hydrothermal and heat treatment processes, without tedious machining processes. It offers a short preparation cycle, high efficiency, and low cost. Furthermore, the thickness of the silicon carbide can be regulated by adjusting the hydrothermal reaction and heat treatment conditions during the preparation process.

[0026] The present invention provides a core-shell ceramic powder, which is prepared using the above-mentioned method for preparing core-shell ceramic powder. The core-shell ceramic powder constructs a gradient structure of "core (ceramic particles)-intermediate layer (carbon)-shell (SiC)" through a unique preparation process (hydroxyl functionalization pretreatment → carbon layer coating → silicon-carbon reaction). The SiC on the surface of the core-shell structure can form a dense and continuous SiO2 film under high temperature conditions. The SiO2 film has an extremely low oxygen diffusion coefficient and can effectively block the inward diffusion of oxygen, giving the core-shell ceramic powder good sintering and oxidation resistance. At the same time, during the oxidation / ablation process, the oxidation product B2O3 of the boride in the inner layer of the structure further reacts with SiO2 to form borosilicate glass, forming a composite glass layer with lower viscosity and higher fluidity. This can fill microcracks in the oxide film and dynamically repair defects in the protective layer. In addition, SiO2 reacts with transition metal oxides to form a dense and stable composite oxide layer, which significantly improves thermal shock resistance and ablation resistance.

[0027] For example, the aforementioned core-shell ceramic powders are used in thermal protection systems for aerospace vehicles. Sintering these core-shell ceramic powders to produce composite ceramic blocks or ceramic-based composite materials overcomes the challenge of material performance degradation in ultra-high temperature, strong oxidation, and high ablation coupled environments. These materials can effectively enhance long-term antioxidant / ablative performance and can be used as thermal structural components on long-range, high-speed aircraft, providing a revolutionary thermal protection solution for next-generation aerospace equipment such as hypersonic vehicles and reusable spacecraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The figure is a schematic flow chart of a method for preparing a core-shell structure ceramic powder according to the present invention.

[0029] Figure 2 These are the SEM and EDS images of the core-shell structure ceramic powder prepared in Example 1 of the present invention; wherein a is the SEM image and B is the EDS image.

[0030] Figure 3 This is the XRD pattern of the core-shell structure ceramic powder prepared in Example 1 of the present invention.

[0031] Figure 4 This is the XRD pattern of the prefabricated ceramic powder prepared in Example 1 of the present invention.

[0032] Figure 5 This is the XRD pattern of the ceramic powder prepared in Comparative Example 1 of the present invention.

[0033] Figure 6 This is the XRD pattern of the ceramic powder prepared in Comparative Example 2 of the present invention.

[0034] Figure 7 This is a comparison chart of the isothermal antioxidant performance tests of the prefabricated ceramic powder in Example 1 of the present invention (Example 1 (not alkali washed)), the core-shell structure ceramic powder prepared in Example 1 (Example 1 (alkali washed)), and the comparative document 1 and the ceramic powder prepared in Comparative Document 1. DETAILED DESCRIPTION

[0035] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0036] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0037] Herein, all features such as values, amounts, amounts, and concentrations defined in numerical ranges or percentage ranges are for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to include and specifically disclose all possible subranges and individual values within the range (including integers and fractions).

[0038] In this document, unless otherwise specified, “include,” “including,” “contains,” “has” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0039] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0040] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0041] The following examples were prepared using conventional instruments and equipment in the art. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the manufacturer. The various raw materials used in the following examples, unless otherwise specified, were conventional commercially available products, with specifications conventional in the art. In the present specification and the following examples, unless otherwise specified, "%" indicates percentage by weight, "part" indicates parts by weight, and "ratio" indicates weight ratio.

[0042] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0043] See also Figure 1 The present invention discloses a method for preparing a core-shell structure ceramic powder, comprising:

[0044] S1: Performing surface functionalization treatment on the ceramic powder to introduce hydroxyl groups on the surface of the ceramic particles to obtain pretreated ceramic powder, specifically:

[0045] The ceramic powder is placed in a mixed solution of hydrochloric acid and nitric acid, and reacted at 70°C to 90°C for 0.5 to 2 hours to obtain pretreated ceramic powder; wherein the molar ratio of hydrochloric acid to nitric acid in the mixed solution of hydrochloric acid and nitric acid is 1:1, and the total molar concentration is 1% to 5%; preferably, the ceramic powder is one or more of ZrB2, HfB2, TiB2, TaB2 and NB2; the purity of the ceramic powder is ≥99.5%, and the particle size is 0.5 to 1 μm.

[0046] By introducing oxygen-containing functional groups such as hydroxyl (-OH), the hydrophilicity of the particle surface is enhanced, making it easier for water-soluble carbon to undergo chemical adsorption.

[0047] S2: placing the pretreated ceramic powder in a water-soluble carbon source solution and performing a hydrothermal reaction to obtain carbon-coated ceramic powder, specifically:

[0048] The pretreated ceramic powder is placed in a water-soluble carbon source solution, and hydrothermally reacted at 160°C to 180°C for 7 to 9 hours to coat the surface of the ceramic powder particles with a carbon layer, and then dried to obtain carbon-coated ceramic powder; wherein the water-soluble carbon source solution is a sucrose solution, a glucose solution, a fructose solution, a maltose solution or a lactose solution; the mass concentration of the water-soluble carbon source solution is 3% to 5%, and the mass ratio of the pretreated ceramic powder to the water-soluble carbon source is 1:(2 to 4).

[0049] S3: Grinding and mixing the carbon-coated ceramic powder and the silicon powder, and subjecting the mixture to a temperature-raising treatment to obtain a core-shell structure ceramic powder, specifically:

[0050] The carbon-coated ceramic powder and silicon powder were mixed and ground at a mass ratio of 1:(0.2-0.3) for 0.5-1h, rolled into a cylinder with graphite paper, placed in a Joule heating device, evacuated to a pressure below -0.1Mpa, and heated to 1300-1350°C at a heating rate of 100-200°C / s and kept at that temperature for 20-40s to obtain a prefabricated core-shell structure ceramic powder;

[0051] The prefabricated core-shell structure ceramic powder is placed in an alkaline solution, heated to 60°C to 80°C, and reacted for 0.5 to 1.5 hours to remove the residual silicon powder in the prefabricated core-shell structure ceramic powder, wash it to neutrality, and dry it to obtain the core-shell structure ceramic powder; wherein the alkaline solution is a NaOH solution or a KOH solution; the concentration of the alkaline solution is 4 to 6 mol / L. The residual silicon is removed because free Si will preferentially oxidize to form SiO2 in a high-temperature service environment. Excessive SiO2 may cause a mismatch in the oxide layer composition (such as a local Si-rich area), forming a loose or porous structure, which weakens its ability to block oxygen diffusion. In addition, during the sintering process, free Si may react with ZrB2 to form ZrSi2, causing pores or cracks in the sintered body, which directly affects the mechanical properties of the material.

[0052] During the preparation process described above, a carbon layer is coated on the boride powder via a hydrothermal reaction, followed by mixing with silicon powder. During heat treatment, the silicon carbide coating is generated in situ. The process is simple, and heat treatment in a Joule heating device takes only tens of seconds, making the preparation process fast and efficient. Furthermore, in a low-pressure environment, the sublimation temperature of the Si powder can be reached at 1300°C, where the gaseous silicon reacts with the carbon layer on the surface of the boride particles through a gas-solid reaction, achieving a uniform coating. At 1400°C, the volatilization rate of Si may exceed its reaction rate with the carbon layer, resulting in more unreacted Si powder impurities remaining. Therefore, compared to the traditional sol-gel method, which produces a SiC coating by carbothermal reduction of SiO2 colloid with a carbon source, this preparation method significantly reduces energy consumption and effectively reduces costs. Furthermore, the post-treatment method of removing residual Si powder by alkaline washing avoids the negative impact of Si impurities on the material's oxidation resistance, ablation resistance, and mechanical properties in extreme service environments, further improving the high-temperature and ablation resistance of the prepared ceramic powder.

[0053] Example 1

[0054] 5g of ZrB2 powder was dispersed in 250mL of a mixed solution of hydrochloric acid and nitric acid (the molar ratio of hydrochloric acid to nitric acid was 1:1, and the total molar concentration was 1%), stirred at 300rpm at 80°C for 1h, centrifuged and washed with water until neutral, and vacuum dried at 50°C for 12h for later use to obtain pretreated ceramic powder. The pretreated ceramic powder, sucrose, and deionized water were mixed in a mass ratio of 1:3:70 and placed in a 100mL polytetrafluoroethylene-lined stainless steel autoclave, placed in a high-temperature oven at 170°C for reaction for 8h, centrifuged and washed with water, and then vacuum dried to obtain carbon-coated ceramic powder.

[0055] The carbon-coated ceramic powder and Si powder were weighed at a mass ratio of 1:0.25, and the weighed mixed powder was placed in an agate mortar and ground for 30 minutes. Then, it was rolled into a tube with graphite paper and placed in a Joule heating device for rapid heating treatment. The mixture was evacuated to a pressure below -0.1 MPa, heated to 1300°C at 150°C / s, kept warm for 30 seconds, and cooled naturally to obtain a prefabricated core-shell structure ceramic powder.

[0056] The prefabricated core-shell structure ceramic powder was dispersed in 5 mol / L NaOH solution, reacted at 60°C for 1 hour under magnetic stirring, and residual Si powder and other impurities were removed. The powder was washed with water by centrifugation until neutrality was achieved, and dried to obtain the core-shell structure ceramic powder.

[0057] Example 2

[0058] 5g of NB2 powder was dispersed in 250mL of a mixed solution of hydrochloric acid and nitric acid (molar ratio of hydrochloric acid to nitric acid was 1:1, total molar concentration was 2%), stirred at 300rpm at 70°C for 1.5h, centrifuged and washed with water until neutral, and vacuum dried at 60°C for 12h to obtain pretreated ceramic powder. The pretreated ceramic powder, maltose, and deionized water were mixed in a mass ratio of 1:4:80 and charged into a 100mL polytetrafluoroethylene-lined stainless steel autoclave. The mixture was placed in a high-temperature oven at 180°C for 7h, centrifuged and washed with water, and vacuum dried to obtain carbon-coated ceramic powder.

[0059] The carbon-coated ceramic powder and Si powder were weighed at a mass ratio of 1:0.2, and the weighed mixed powder was placed in an agate mortar and ground for 30 minutes. Then, it was rolled into a tube with graphite paper and placed in a Joule heating device for rapid heating treatment. The mixture was evacuated to a pressure below -0.1 MPa, heated to 1350°C at 100°C / s, kept warm for 20 seconds, and cooled naturally to obtain a prefabricated core-shell structure ceramic powder.

[0060] The prefabricated core-shell structure ceramic powder was dispersed in 6 mol / L NaOH solution, reacted at 70°C for 1 hour under magnetic stirring, and residual Si powder and other impurities were removed. The powder was washed with water by centrifugation until neutral, and dried to obtain the core-shell structure ceramic powder.

[0061] Example 3

[0062] 5g of TiB2 powder was dispersed in 250mL of a mixed solution of hydrochloric acid and nitric acid (the molar ratio of hydrochloric acid to nitric acid was 1:1, and the total molar concentration was 3%), stirred at 300rpm at 70°C for 1.5h, centrifuged and washed with water until neutral, and vacuum dried at 60°C for 12h to obtain pretreated ceramic powder. The pretreated ceramic powder, fructose, and deionized water were mixed in a mass ratio of 1:2:60 and charged into a 100mL polytetrafluoroethylene-lined stainless steel autoclave, placed in a high-temperature oven at 160°C for reaction for 7h, centrifuged and washed with water, and then vacuum dried to obtain carbon-coated ceramic powder.

[0063] The carbon-coated ceramic powder and Si powder were weighed at a mass ratio of 1:0.3, and the weighed mixed powder was placed in an agate mortar and ground for 50 minutes. Then, it was rolled into a tube with graphite paper and placed in a Joule heating device for rapid heating treatment. The mixture was evacuated to a pressure below -0.1 MPa, heated to 1350°C at 200°C / s, kept warm for 30 seconds, and naturally cooled to obtain a prefabricated core-shell structure ceramic powder.

[0064] The prefabricated core-shell structure ceramic powder was dispersed in 4 mol / L NaOH solution, reacted at 80°C for 0.5 h under magnetic stirring, and the residual Si powder and other impurities were removed. The powder was washed with water by centrifugation until neutral, and dried to obtain the core-shell structure ceramic powder.

[0065] Example 4

[0066] 5g of HfB2 powder was dispersed in 250mL of a mixed solution of hydrochloric acid and nitric acid (the molar ratio of hydrochloric acid to nitric acid was 1:1, and the total molar concentration was 5%), stirred at 300rpm at 80°C for 0.5h, centrifuged and washed with water until neutral, and vacuum dried at 60°C for 12h to obtain pretreated ceramic powder. The pretreated ceramic powder, glucose, and deionized water were mixed in a mass ratio of 1:3:60 and charged into a 100mL polytetrafluoroethylene-lined stainless steel autoclave. The mixture was placed in a high-temperature oven at 170°C for 7h, centrifuged and washed with water, and then vacuum dried to obtain carbon-coated ceramic powder.

[0067] The carbon-coated ceramic powder and Si powder were weighed at a mass ratio of 1:0.2, and the weighed mixed powder was placed in an agate mortar and ground for 50 minutes. Then, it was rolled into a tube with graphite paper and placed in a Joule heating device for rapid heating treatment. The powder was evacuated to a pressure below -0.1 MPa, heated to 1300°C at 180°C / s, kept warm for 30 seconds, and cooled naturally to obtain a prefabricated core-shell structure ceramic powder.

[0068] The prefabricated core-shell structure ceramic powder was dispersed in 5 mol / L NaOH solution, reacted at 80°C for 0.5 h under magnetic stirring, and the residual Si powder and other impurities were removed. The powder was washed with water by centrifugation until neutral, and dried to obtain the core-shell structure ceramic powder.

[0069] Example 5

[0070] 5g of TaB2 powder was dispersed in 250mL of a mixed solution of hydrochloric acid and nitric acid (the molar ratio of hydrochloric acid to nitric acid was 1:1, and the total molar concentration was 3%), stirred at 300rpm at 70°C for 1.5h, centrifuged and washed with water until neutral, and vacuum dried at 60°C for 12h for later use to obtain pretreated ceramic powder. The pretreated ceramic powder, sucrose and deionized water were mixed in a mass ratio of 1:2.1:70 and charged into a 100mL polytetrafluoroethylene-lined stainless steel autoclave, placed in a high-temperature oven at 180°C for reaction for 7h, centrifuged and washed with water, and then vacuum dried to obtain carbon-coated ceramic powder.

[0071] The carbon-coated ceramic powder and Si powder were weighed at a mass ratio of 1:0.3, and the weighed mixed powder was placed in an agate mortar and ground for 50 minutes. Then, it was rolled into a tube with graphite paper and placed in a Joule heating device for rapid heating treatment. The mixture was evacuated to a pressure below -0.1 MPa, heated to 1300°C at 100°C / s, kept warm for 30 seconds, and naturally cooled to obtain a prefabricated core-shell structure ceramic powder.

[0072] The prefabricated core-shell structure ceramic powder was dispersed in 4 mol / L NaOH solution, reacted at 60°C for 1.5 h under magnetic stirring, and residual Si powder and other impurities were removed. The powder was washed with water to neutrality by centrifugation and dried to obtain the core-shell structure ceramic powder.

[0073] Comparative Example 1

[0074] 5g of ZrB2 powder was dispersed in 250mL of a mixed solution of hydrochloric acid and nitric acid (the molar ratio of hydrochloric acid to nitric acid was 1:1, and the total molar concentration was 1%), stirred at 300rpm at 80°C for 1h, centrifuged and washed with water until neutral, and vacuum dried at 50°C for 12h for later use to obtain pretreated ceramic powder. The pretreated ceramic powder, sucrose, and deionized water were mixed in a mass ratio of 1:1:70 and placed in a 100mL polytetrafluoroethylene-lined stainless steel autoclave, placed in a high-temperature oven at 170°C for reaction for 8h, centrifuged and washed with water, and then vacuum dried to obtain carbon-coated ceramic powder.

[0075] The carbon-coated ceramic powder and Si powder were weighed at a mass ratio of 1:0.25. The weighed mixed powder was placed in an agate mortar and ground for 30 minutes. Then, it was rolled into a tube with graphite paper and placed in a Joule heating device for rapid heating treatment. The powder was evacuated to a pressure below -0.1 MPa, heated to 1300°C at 150°C / s, kept warm for 30 seconds, and naturally cooled to obtain a core-shell structured ceramic powder.

[0076] Comparative Example 2

[0077] 5g of ZrB2 powder was dispersed in 250mL of a mixed solution of hydrochloric acid and nitric acid (the molar ratio of hydrochloric acid to nitric acid was 1:1, and the total molar concentration was 1%), stirred at 300rpm at 80°C for 1h, centrifuged and washed with water until neutral, and vacuum dried at 50°C for 12h for later use to obtain pretreated ceramic powder. The pretreated ceramic powder, sucrose, and deionized water were mixed in a mass ratio of 1:3:70 and placed in a 100mL polytetrafluoroethylene-lined stainless steel autoclave, placed in a high-temperature oven at 170°C for reaction for 8h, centrifuged and washed with water, and then vacuum dried to obtain carbon-coated ceramic powder.

[0078] The carbon-coated ceramic powder and Si powder were weighed at a mass ratio of 1:0.25. The weighed mixed powder was placed in an agate mortar and ground for 30 minutes. Then, it was rolled into a tube with graphite paper and placed in a Joule heating device for rapid heating treatment. The powder was evacuated to a pressure below -0.1 MPa, heated to 1400°C at 150°C / s, kept warm for 30 seconds, and naturally cooled to obtain a core-shell structured ceramic powder.

[0079] To further illustrate the beneficial effects of the present invention, the core-shell structure ceramic powder prepared in Example 1 was subjected to SEM and EDS tests. Figure 2 , it can be clearly observed that the core-shell structure of ZrB2 particles as the core and nano-scale SiC as the coating layer. The core-shell structure ceramic powder prepared in Example 1 was also subjected to XRD testing. The XRD pattern is shown in Figure 3, it can be seen that the Si peak in the XRD spectrum almost completely disappears, indicating that there is no Si powder remaining in the core-shell structure ceramic powder. The prefabricated core-shell structure ceramic powder prepared in Example 1 was subjected to XRD testing, see Figure 4 , there is a small amount of Si peak in the prefabricated core-shell structure ceramic powder, indicating that there is indeed Si residual in the prefabricated core-shell structure ceramic powder. Free Si will be preferentially oxidized to form SiO2 in a high-temperature service environment. Excessive SiO2 may cause a mismatch in the oxide layer composition (such as a local Si-rich area), forming a loose or porous structure, which weakens its ability to block oxygen diffusion. In addition, during the sintering process, free Si may react with ZrB2 to form ZrSi2, causing pores or cracks in the sintered body, which directly affects the mechanical properties of the material. It can be seen that in the method of the present invention, the silicon residue in the ceramic powder can be effectively removed by washing with alkaline solution, further improving the oxidation resistance and high-temperature ablation resistance of the prepared core-shell structure ceramic powder.

[0080] See also Figure 5 The ceramic powder prepared in Comparative Example 1 was subjected to XRD testing, and the intensity of the SiC peak in the spectrum decreased significantly. This is because the insufficient amount of carbon source added resulted in a low content of in-situ generated SiC, which is not conducive to the effective coating of the SiC layer on the surface of the ZrB2 particles. Therefore, a sufficient amount of water-soluble carbon source needs to be provided when coating the carbon layer.

[0081] See also Figure 6 XRD analysis of the ceramic powder prepared in Comparative Example 2 revealed no significant change in the SiC peak intensity compared to Example 1, but an increase in the Si peak intensity. This suggests that at 1400°C, the volatilization rate of Si may exceed its reaction rate with the carbon layer, leading to an incomplete reaction and an increase in the residual Si powder content. Simultaneously, the high-temperature densification of the carbon layer forms a kinetic barrier, preventing subsequent diffusion of gaseous silicon into the unreacted carbon layer. This demonstrates that an appropriate amount of water-soluble carbon source and high-temperature treatment temperature can significantly enhance the oxidation resistance and high-temperature ablation resistance of ceramic powders.

[0082] The powders prepared in Example 1 and Comparative Examples 1 and 2 were subjected to isothermal oxidation tests at 1700°C. Figure 7, the ceramic powders of Example 1 and Comparative Examples 1 and 2 that were not alkali-washed experienced severe oxidation, reaching the maximum weight gain in 20 to 40 minutes, and then continuously losing weight as time went on, corresponding to the oxidation of the boride phase at high temperature. The weight loss of the ceramic powder in Comparative Example 1 was the most serious, because the insufficient carbon source affected the uniform coating of the SiC layer, causing the exposed ZrB2 particles to rapidly oxidize to generate volatile B2O3. Although the weight loss of Comparative Example 2 was slower, the residual Si impurities may have led to uneven distribution of components, forming non-protective oxidation areas, resulting in intense oxidation in the initial stage. In comparison, the ceramic powder after alkali washing to remove Si in Example 1 not only had the lowest initial oxidation degree, but also had a relatively slow weight loss, further illustrating that the removal of residual Si powder promoted the formation of a continuous oxide layer with excellent protective capabilities on the surface of the ZrB2 particles, thereby improving the oxidation resistance of the ceramic powder.

[0083] The present invention provides a core-shell ceramic powder, which is prepared using the above-mentioned method for preparing core-shell ceramic powder. The core-shell ceramic powder constructs a gradient structure of "core (ceramic)-intermediate layer (carbon)-shell (SiC)" through a unique preparation process (hydroxyl functionalization pretreatment → carbon layer coating → silicon-carbon reaction). The SiC on the surface of the core-shell structure can form a dense and continuous SiO2 film under high temperature conditions. The SiO2 film has an extremely low oxygen diffusion coefficient and can effectively block the inward diffusion of oxygen, giving the core-shell ceramic powder good sintering and oxidation resistance. At the same time, during the oxidation / ablation process, the oxidation product B2O3 of the boride in the inner layer of the structure further reacts with SiO2 to form borosilicate glass, forming a composite glass layer with lower viscosity and higher fluidity, which can fill microcracks in the oxide film and dynamically repair defects in the protective layer. In addition, SiO2 reacts with transition metal oxides to form a dense and stable composite oxide layer, which significantly improves thermal shock resistance and ablation resistance.

[0084] For example, the aforementioned core-shell ceramic powders are used in thermal protection systems for aerospace vehicles. Sintering these core-shell ceramic powders to produce composite ceramic blocks or ceramic-based composite materials overcomes the challenge of material performance degradation in ultra-high temperature, strong oxidation, and high ablation coupled environments. These materials can effectively enhance long-term antioxidant / ablative performance and can be used as thermal structural components on long-range, high-speed aircraft, providing a revolutionary thermal protection solution for next-generation aerospace equipment such as hypersonic vehicles and reusable spacecraft.

[0085] In summary, the present invention provides a core-shell structure ceramic powder, preparation method and application. In view of the problems of the existing process for preparing boride and silicon carbide composite ceramic powder, such as complicated process, high preparation temperature, and difficulty in obtaining a specific morphology, the preparation method disclosed in the present invention is to coat a uniform carbon layer on the surface of the boride ceramic powder, then mix it with silicon powder, and use Joule heat equipment to heat treat it to obtain a boride ultra-high temperature ceramic powder coated with a silicon carbide layer. The process is simple, the preparation temperature is low, the cycle is short, and the cost is low. The prepared core-shell structure ceramic powder has good sintering and oxidation resistance. It is used as a raw material to sinter and prepare a composite ceramic block or ceramic-based composite material, which can effectively improve the long-term antioxidant / ablation performance, and can be used as a thermal structure component on a long-range high-speed aircraft.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to impose any limitation on the technical solution of the present invention. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and replacements, and these modifications and replacements are also within the scope of protection covered by the claims.

Claims

1. A method for preparing a core-shell structure ceramic powder, characterized in that: include: Performing surface functionalization treatment on ceramic powder to introduce hydroxyl groups on the surface of ceramic particles to obtain pretreated ceramic powder; placing the pretreated ceramic powder in a water-soluble carbon source solution and performing a hydrothermal reaction to obtain carbon-coated ceramic powder; The carbon-coated ceramic powder and silicon powder are ground and mixed, and subjected to a temperature-raising treatment to obtain a core-shell structure ceramic powder.

2. The method for preparing core-shell structure ceramic powder according to claim 1, characterized in that: The ceramic powder is one or more of ZrB2, HfB2, TiB2, TaB2 and NB2.

3. The method for preparing core-shell structure ceramic powder according to claim 1, characterized in that: The method of performing surface functionalization treatment on ceramic powder and introducing hydroxyl groups on the surface of ceramic particles to obtain pretreated ceramic powder is as follows: The ceramic powder is placed in a mixed solution of hydrochloric acid and nitric acid, and reacted at 70° C. to 90° C. for 0.5 to 2 hours to obtain a pretreated ceramic powder; wherein the molar ratio of hydrochloric acid to nitric acid in the mixed solution of hydrochloric acid and nitric acid is 1:1, and the total molar concentration is 1% to 5%.

4. The method for preparing core-shell structure ceramic powder according to claim 1, characterized in that: The water-soluble carbon source solution is sucrose solution, glucose solution, fructose solution, maltose solution or lactose solution; the mass concentration of the water-soluble carbon source solution is 3% to 5%, and the mass ratio of the pretreated ceramic powder to the water-soluble carbon source is 1:(2 to 4).

5. The method for preparing core-shell structure ceramic powder according to claim 1, characterized in that: It also includes the removal process of residual silicon powder, specifically: The carbon-coated ceramic powder and silicon powder are ground and mixed, and subjected to a temperature treatment to react to obtain a prefabricated core-shell structure ceramic powder; The prefabricated core-shell structure ceramic powder is placed in an alkaline solution, heated to remove residual silicon powder in the prefabricated core-shell structure ceramic powder, washed to neutrality, and dried to obtain the core-shell structure ceramic powder.

6. The method for preparing core-shell structure ceramic powder according to claim 1, characterized in that: The reaction temperature of the hydrothermal reaction is 160° C. to 180° C., and the reaction time is 7 to 9 hours.

7. The method for preparing core-shell structure ceramic powder according to claim 1, characterized in that: The mass ratio of the carbon-coated ceramic powder to the silicon powder is 1:(0.2-0.3), and the grinding time is 0.5-1h.

8. The method for preparing core-shell structure ceramic powder according to claim 1, characterized in that: The method of grinding and mixing carbon-coated ceramic powder and silicon powder and performing a temperature treatment to obtain a core-shell structure ceramic powder is as follows: After grinding and mixing carbon-coated ceramic powder and silicon powder, vacuuming to a pressure below -0.1 MPa, heating to 1300-1350°C at a heating rate of 100-200°C / s and keeping the temperature for 20-40s to obtain core-shell structure ceramic powder.

9. A core-shell structure ceramic powder, characterized in that: The core-shell structure ceramic powder is prepared using the preparation method of any one of claims 1 to 8.

10. Use of the core-shell structure ceramic powder according to claim 9 in a thermal protection system of an aerospace vehicle.

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