Boron carbide and silicon carbide composite nano-powder and preparation method thereof

Abstract

The invention relates to boron carbide and silicon carbide composite nano powder and a preparation method thereof. The average particle size of the silicon carbide in the composite nano powder is 50-100 nm, the average particle size of the boron carbide in the composite nano powder is 70-120 nm, and the silicon carbide and the boron carbide are uniformly mixed together according to the mass ratio of 1: 1 to 5: 1. The particles in the nano powder have good dispersity, and no obvious agglomeration phenomenon exists among the particles. The invention further discloses a method for preparing the boron carbide and silicon carbide composite nano-powder through the in-situ reaction method, the method is used for preparing the boron carbide and silicon carbide composite nano-powder with the edible carbon source powder and the silica sol solution as raw materials, and the method has the advantages of being low in equipment requirement, low in preparation cost, high in product purity, beneficial to achieving large-scale industrial preparation and the like.

Description

Technical Field

[0001] The present invention belongs to the field of inorganic non-metallic materials, and in particular relates to the technical field of composite nanopowders and their preparation. Background Art

[0002] Silicon carbide has a low density (3.21g / cm 3 ), high melting point (>2700℃), high strength (tensile strength is 2100kg / cm 2 ), high modulus (elastic modulus is 4.9×104kg / cm 2 ), low thermal expansion coefficient and corrosion resistance, and is widely used in many fields such as machinery, electronics, chemical industry, energy, aerospace and environmental protection. However, when used as a structural material, silicon carbide has the disadvantages of poor toughness and high brittleness, and usually requires the addition of a high-performance flexible phase to enhance toughness so that it can be suitable for different applications. The preparation methods of silicon carbide include direct reaction method, chemical degradation method, vapor deposition method, liquid phase crystallization method, carbon thermal reduction method, sol-gel method, molten salt method, hydrothermal method, microwave-assisted heating method, etc. However, the above-mentioned known methods for preparing silicon carbide have the disadvantages of high production cost, low yield and long cycle, and the prepared silicon carbide often has the disadvantages of poor toughness and high brittleness.

[0003] Boron carbide is an ideal material for reinforcing and toughening silicon carbide. Boron carbide boasts excellent properties such as high hardness, lightweight, wear resistance, corrosion resistance, high temperature resistance, and neutron absorption. Its bulk modulus and thermal expansion coefficient are similar to those of silicon carbide, making it widely used in the machinery, metallurgy, chemical industry, and nuclear industry. As a specialty ceramic material, boron carbide requires a small particle size to increase the driving force for sintering, thereby increasing density, refining the grain size, and enhancing strength and toughness. Furthermore, boron carbide must be of high purity to prevent impurities from accumulating at grain boundaries during sintering, thereby reducing strength and toughness. Boron carbide is a covalently bonded compound with excellent chemical stability, making it difficult to sinter during ceramic production. The commonly used process, both domestically and internationally, is hot-pressing sintering at temperatures around 2200°C. This high manufacturing cost and inapplicability to the processing of special shapes and specialized products have limited its development.

[0004] The common methods for strengthening and toughening silicon carbide with boron carbide in the prior art involve mixing the two raw materials through ball milling or ultrasonic mixing. However, both methods have certain limitations. The former may introduce a certain amount of impurities (usually from the ball mill or grinding balls), while the latter makes it difficult to achieve uniform mixing of the two raw materials. Furthermore, the composite nanopowders produced by these methods also suffer from large grain size, poor uniformity, low purity, and high production costs.

[0005] Therefore, obtaining high-performance boron carbide-silicon carbide composite nanopowders with both high hardness and high toughness remains a difficult challenge. Summary of the Invention

[0006] In order to overcome the shortcomings and deficiencies of the prior art, the present invention proposes a new method for preparing boron carbide-silicon carbide composite nanopowder by in-situ reaction, and obtains a new high-performance boron carbide-silicon carbide composite nanopowder.

[0007] Specifically, the present invention uses an edible carbon source, adopts liquid phase molecular mixing, and a continuous high-temperature vacuum reaction preparation technology, giving full play to the refinement and homogenization advantages of the liquid phase evaporation method, solving the problems of carbon source pollution and subsequent impurity removal, achieving uniform mixing of silicon carbide and boron carbide at the nanometer scale, and simplifying the preparation process of the boron carbide and silicon carbide composite nanopowder prepared by the in-situ reaction method. The method uses pollution-free, non-toxic and side-effect-free raw materials and adopts a low-energy consumption, low-emission preparation process, etc., and is therefore a green preparation process for mixed powders that meets the requirements of environmental friendliness and sustainable development. In addition, compared with the existing technology, the composite nanopowder prepared by the in-situ reaction method has a smaller grain size (and can be more precisely controlled), good uniformity, higher purity, and lower cost.

[0008] Therefore, the technical solution of the first aspect of the present application is a boron carbide-silicon carbide (B4C-SiC) composite nanopowder, wherein the average particle size of the silicon carbide is 50-100 nm, and the average particle size of the boron carbide is 70-120 nm, respectively, and the two are uniformly mixed together at a mass ratio of silicon carbide to boron carbide of 1:1 to 5:1. It has been observed that the particles in the nanopowder have good dispersion and no obvious agglomeration between the particles.

[0009] The technical solution of the second aspect of the present application is a method for preparing boron carbide silicon carbide composite nanopowder, which comprises the following steps:

[0010] 1) Weighing edible carbon source powder and silica sol solution, adding them to water, stirring and dissolving them, and evaporating water in the resulting solution by heating to obtain a dry solid;

[0011] 2) grinding the obtained solid into a fine powder, then adding the fine powder into a graphite crucible, then calcining the graphite crucible at a high temperature in a vacuum heating device to obtain an amorphous carbon and silicon carbide composite intermediate, and then grinding the composite intermediate into a fine powder again;

[0012] 3) adding the composite intermediate fine powder to water, then adding boric acid or boric acid ester, mixing uniformly, and drying to remove moisture to obtain a mixed powder;

[0013] 4) placing the mixed powder obtained after drying in a graphite crucible, and then placing the graphite crucible in a vacuum heating device for high-temperature calcination to obtain boron carbide and silicon carbide composite nanopowder.

[0014] In the boron carbide and silicon carbide (BC-SiC) composite nanopowder prepared according to the above method, the average particle size of silicon carbide is 50 to 100 nm, and the average particle size of boron carbide is 70 to 120 nm, respectively. The two are uniformly mixed in a mass ratio of silicon carbide to boron carbide of 1:1 to 5:1. The particles in the resulting composite nanopowder have been observed to be well dispersed, with no significant agglomeration between the particles.

[0015] The third aspect of the present application also relates to boron carbide silicon carbide (B4C-SiC) composite nanopowder obtained by the preparation method according to the second aspect of the present application.

[0016] Compared with the prior art, the present invention has the following characteristics and advantages:

[0017] 1. The present invention introduces the second phase boron carbide in situ, so that the boron carbide and silicon carbide are mixed evenly, thereby improving the comprehensive mechanical properties of the composite powder.

[0018] 2. The edible carbon source powder used in the present invention has the characteristics of sufficient raw materials, low price, and no harm to the environment and human health.

[0019] 3. Unlike ball milling and ultrasonic methods, the present invention can achieve nano-sized mixing of silicon carbide and boron carbide through an in-situ reaction method. In addition, homogenous mixing is achieved through liquid phase reaction, and the reactants are refined and uniformed by stirring the solution, so that the nano-sized mixing of silicon carbide and boron carbide in the final product is very uniform.

[0020] 4. Different from chemical vapor deposition and laser-induced pyrolysis, the preparation method adopted in the present invention has the advantages of low equipment requirements and low preparation cost, which is conducive to large-scale industrial preparation.

[0021] The boron carbide-silicon carbide composite nanopowder and the preparation method thereof of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The scanning electron microscope (SEM) image of the boron carbide-silicon carbide composite nanopowder obtained in Example 1 of the present invention is shown.

[0023] Figure 2 The X-ray diffraction pattern (XRD) of the boron carbide-silicon carbide composite nanopowder obtained in Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0024] Therefore, the technical solution of the first aspect of the present application is a boron carbide-silicon carbide (B4C-SiC) composite nanopowder, wherein the average particle size of the silicon carbide is 50-100 nm, and the average particle size of the boron carbide is 70-120 nm, respectively, and the two are uniformly mixed together at a mass ratio of silicon carbide to boron carbide of 1:1 to 5:1. It has been observed that the particles in the nanopowder have good dispersion and no obvious agglomeration between the particles.

[0025] The average particle size of the silicon carbide in the B4C-SiC composite nanopowder of the present application is 50 to 100 nm, for example, it can be about 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or any particle size within a particle size interval consisting of any two of the above particle sizes as endpoints. A preferred average particle size of the silicon carbide is 70 to 90 nm. The average particle size of the silicon carbide can be measured by those skilled in the art based on scanning electron microscopy or transmission electron microscopy data.

[0026] The average particle size of the boron carbide in the B4C-SiC composite nanopowder of the present application is respectively 70~120nm, for example, can be about 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, 105nm, 110nm, 115nm, 120nm, or is any particle size within the particle size interval consisting of any two of the above particle sizes as endpoints. A preferred average particle size of boron carbide is respectively 90~100nm. The average particle size of boron carbide can be obtained by those skilled in the art according to scanning electron microscopy or transmission electron microscopy data measurement.

[0027] The mass ratio of silicon carbide to boron carbide in the B4C-SiC composite nanopowder of the present application is 1:1 to 5:1, for example, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or any ratio within a ratio interval consisting of any two of the above ratios as endpoints. A preferred mass ratio of silicon carbide to boron carbide is 1:1 to 3:1.

[0028] In this application, unless otherwise specified or defined, all terms should be interpreted as having the meaning as commonly understood by those skilled in the art.

[0029] In the context of this application, "boron carbide silicon carbide composite nanopowder" refers to a powder that is basically composed of silicon carbide (SiC) and boron carbide (B4C) in terms of phase composition, and from a microscopic perspective, the powder is composed of numerous nanometer-sized particles.

[0030] The boron carbide-silicon carbide composite nanopowder of the present invention is a high-purity nanopowder, typically having a purity greater than or equal to 98%, preferably greater than or equal to 99%, preferably greater than or equal to 99.5%, and most preferably greater than or equal to 99.9%. In the context of this application, "purity" is a dimensionless value that measures the content of impurities (phases other than silicon carbide and boron carbide) in the nanopowder, and refers to the mass ratio of the sum of the silicon carbide and boron carbide phases in the powder. The higher the purity, the lower the impurity content in the composite nanopowder.

[0031] Those skilled in the art will appreciate that various techniques are available for obtaining microstructural information about a material (e.g., the average particle size of silicon carbide or boron carbide). For example, direct observation can be performed using a scanning electron microscope or transmission electron microscope, or analysis can be performed using X-ray spectrometry. For accurate characterization, analysis is preferably performed on samples from within the material. Furthermore, to avoid interference from small amounts of contaminants that may be present in the nanopowder, multiple (e.g., three or more or five) random samples of the material can be analyzed.

[0032] A second aspect of the present application provides a method for preparing boron carbide-silicon carbide composite nanopowder, the preparation method comprising the following steps:

[0033] 1) Weighing edible carbon source powder and silica sol solution (as a silicon source), adding them to water, stirring and dissolving them, and evaporating water in the resulting solution by heating to obtain a dry solid;

[0034] 2) grinding the obtained solid into a fine powder, then adding the fine powder into a graphite crucible, and then calcining the graphite crucible at a high temperature in a vacuum heating device (such as a vacuum tube furnace, a vacuum carbon tube furnace, etc.) to obtain an amorphous carbon-silicon carbide composite intermediate, and then grinding the composite intermediate into a fine powder again;

[0035] 3) adding the composite intermediate fine powder to water, then adding boric acid or boric acid ester (as a boron source), mixing well, and drying to remove moisture to obtain a mixed powder;

[0036] 4) placing the mixed powder obtained after drying in a graphite crucible, and then placing the graphite crucible in a vacuum heating device (such as a vacuum tube furnace, a vacuum carbon tube furnace, etc.) for high-temperature calcination to obtain boron carbide and silicon carbide composite nanopowder.

[0037] The raw materials used in step 1) are edible carbon source powder and silica sol solution.

[0038] In the present invention, the edible carbon source can be various common carbohydrates, preferably carbohydrates soluble in water, such as sucrose, glucose, fructose, arabinose, galactose, lactose, maltose, soluble starch or modified starch, soluble dextrin or modified dextrin and other common carbon sources, or any mixture of these substances.

[0039] In this application, the term "silica sol solution" as a silicon source has the meaning commonly understood by those skilled in the art, i.e., refers to a colloidal solution formed by uniformly dispersing silicon dioxide (SiO2) particles in water or an organic solvent. The present invention has no special requirements for the silica sol solution used as a raw material, and various commercially available silica sol solutions can be used, such as silica sol solutions of various specifications sold by Shandong Better New Materials Co., Ltd. and Linyi Kehan Silicon Products Co., Ltd. The concentration of the silica sol solution can be selected as needed, and can generally be 20 to 50 wt%, such as 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, or any concentration within a concentration range consisting of any two of the above concentration values as endpoints, preferably 25 to 35 wt%.

[0040] In step 1), the mass ratio of the edible carbon source to the silica sol is 0.5:1 to 5:1, for example, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or any ratio within a ratio interval consisting of any two of the above ratios as endpoints. A preferred mass ratio of the edible carbon source to the silica sol is 0.8:1 to 3:1.

[0041] In step 1), the temperature and time of heating evaporation can be selected by technicians according to needs, for example, the temperature can be 70-90° C. or 75-85° C., and the heating time can be 24-72 hours, for example, 24-48 hours or 40-50 hours.

[0042] In step 1), the obtained dry solid is usually brown-red.

[0043] In step 2), both the operation of grinding the obtained solid and the operation of grinding the obtained composite intermediate can be carried out in conventional grinding equipment, for example, a mortar can be used.

[0044] In step 2), when the obtained solid fine powder is added into the graphite crucible, the amount of solid fine powder added is usually no more than 2 / 3 of the volume of the graphite crucible.

[0045] In step 2), the high temperature calcination temperature can generally be 1200-1800°C, such as 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, 1700°C, 1800°C, or any temperature within the temperature range consisting of any two of the above temperature values as endpoints, and the high temperature calcination time can be appropriately selected as needed, for example, it can be 0.2-1 hour, such as 0.2 hour, 0.3 hour, 0.4 hour, 0.5 hour, 0.6 hour, 0.7 hour, 0.8 hour, 0.9 hour, 1.0 hour, or any time within the time range consisting of any two of the above values as endpoints. The system vacuum during high temperature calcination is generally required to be higher than 8.0×10 -3 , for example, higher than 8.0×10 -3 , higher than 7.0×10 -3 , higher than 6.0×10 -3 , higher than 5.0×10 -3 , higher than 4.0×10 -3 , higher than 3.0×10 -3 , higher than 2.0×10 -3 , higher than 1.0×10 -3 , higher than 8.0×10 -3 , higher than 5.0×10 -3 , higher than 2.0×10 -3 , even higher than 1.0×10 -3 .

[0046] In step 2), a schematic calcination temperature program is: the heating and cooling rate is 5°C / min below 300°C, 10°C / min at 300-1200°C, and 5°C / min at 1200-1500°C.

[0047] In step 3), the amorphous carbon-silicon carbide composite intermediate fine powder is added to water and then mixed evenly with boric acid (or borate), wherein the mass ratio of the composite intermediate fine powder to boric acid (or borate) can be selected as needed, but is usually greater than 0.2, for example, greater than 0.3, greater than 0.4, greater than 0.5, greater than 0.6, greater than 0.8, greater than 1.0; the mass ratio is usually also less than 5.0, for example, less than 4.0, less than 3.0, less than 2.5, less than 2.0, less than 1.5, less than 1.2.

[0048] The boric acid (or boric acid ester) used in step 3) is preferably of high purity, for example, its purity is preferably higher than 98%, more preferably higher than 99% or 99.5%.

[0049] In step 3), boric acid or a boric acid ester is used as a boron source, preferably boric acid or an alkyl borate. As the alkyl borate, a lower alkyl borate (i.e., a lower alkyl borate having 1 to 6 carbon atoms) is preferred, such as trimethyl borate or triethyl borate.

[0050] The process conditions for the drying operation in step 3) can be selected by technicians according to needs, for example, the same or similar process conditions as those for the heating evaporation operation in step 1) can be adopted.

[0051] The process conditions for high-temperature calcination in step 4) can be the same or similar to those for high-temperature calcination in step 2). That is, the temperature for high-temperature calcination can generally be 1200-1800°C, such as 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, 1700°C, 1800°C, or any temperature within the temperature range consisting of any two of the above temperature values as endpoints; the time for high-temperature calcination can be appropriately selected as needed, such as 0.2-1 hour, such as 0.2 hour, 0.3 hour, 0.4 hour, 0.5 hour, 0.6 hour, 0.7 hour, 0.8 hour, 0.9 hour, 1.0 hour, or any time within the time range consisting of any two of the above values as endpoints; the system vacuum during high-temperature calcination is generally required to be higher than 8.0×10 -3 , for example, higher than 8.0×10 -3 , higher than 7.0×10 -3 , higher than 6.0×10 -3 , higher than 5.0×10 -3 , higher than 4.0×10 -3 , higher than 3.0×10 -3 , higher than 2.0×10 -3 , higher than 1.0×10 -3 , higher than 8.0×10 -3 , higher than 5.0×10 -3 , higher than 2.0×10 -3 , even higher than 1.0×10 -3 .

[0052] In step 4), when the mixed powder is placed in a graphite crucible, the amount of the mixed powder added is usually no more than 2 / 3 of the volume of the graphite crucible.

[0053] In step 4), a schematic calcination temperature program is: the heating and cooling rates are 5°C / min below 300°C, 10°C / min from 300 to 1200°C, and 5°C / min from 1200 to 1500°C.

[0054] The above preparation method can produce high-purity (purity greater than or equal to 98%) boron carbide and silicon carbide (BC-SiC) composite nanopowders. The average particle size of the silicon carbide is 50 to 100 nm, and the average particle size of the boron carbide is 70 to 120 nm, respectively. The two phases are uniformly mixed together. The mass ratio of silicon carbide to boron carbide can be adjusted as needed, typically within a range of 1:1 to 5:1 (preferably 1:1 to 3:1). Furthermore, it has been observed that the particles in the nanopowder have good dispersion and no obvious agglomeration between the particles.

[0055] The inventors discovered that: in steps 1) and 3), liquid phase homogenization mixing is used, and stirring the solution can refine and homogenize the reactants, ensuring the uniformity of the final product; the product of step 2) is silicon carbide and amorphous carbon, wherein the generated amorphous carbon encapsulates the silicon carbide, presenting a semi-encapsulated or fully encapsulated state; this ensures that in the subsequent step 4), the carbon can fully react with boric acid (or boric acid ester), increasing the reaction efficiency; this not only solves the problems of carbon source contamination and subsequent impurity removal, but also achieves uniform mixing of boron carbide and silicon carbide at the nanometer scale. Therefore, the preparation method of the present invention has the advantages of low equipment requirements, low preparation cost, high product purity, and is conducive to large-scale industrial production.

[0056] In a preferred embodiment of the present invention, the method for preparing the boron carbide-silicon carbide composite nanopowder of the present invention comprises the following steps:

[0057] 1') Weigh the edible carbon source powder and silica sol solution in a specific mass ratio, pour them into a beaker filled with deionized water, and stir with a glass rod to fully dissolve. The beaker is then placed on a heating plate to evaporate the water from the solution, ultimately yielding a dry, brownish-red solid mass.

[0058] 2′) grinding the brown-red solid block into a fine powder using a mortar, then placing the fine powder into a graphite crucible, and then placing the graphite crucible in a vacuum heating apparatus for high-temperature calcination to obtain an amorphous carbon-silicon carbide composite intermediate, and then grinding the composite intermediate into a fine powder using a mortar;

[0059] 3') The amorphous carbon-silicon carbide composite intermediate is poured into a beaker filled with deionized water, and then a certain amount of boric acid (or boric acid ester) is added and ultrasonicated using an ultrasonic machine to mix uniformly, and then dried to remove moisture to obtain a mixed powder.

[0060] 4') placing the mixed powder obtained after drying in a graphite crucible, and finally placing the graphite crucible in a vacuum heating device for high-temperature calcination to obtain boron carbide and silicon carbide composite nanopowder.

[0061] The nanocrystalline silicon carbide bulk material and preparation method of the present application are further described below with reference to examples.

[0062] Example

[0063] The embodiments described below are some embodiments of the present invention, rather than all embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but merely represents specific embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without departing from the principles of the present invention and without making creative efforts are within the scope of protection of the present invention.

[0064] For the sake of clarity, some materials, equipment, and methods commonly used in the art are not listed in the examples. Any process methods and analytical testing procedures (and related parameters) not specifically noted in the examples were performed according to those commonly employed by those skilled in the art. Materials and equipment not specifically sourced are from conventional laboratories.

[0065] Raw materials, equipment and material analysis and testing methods

[0066] The raw materials and equipment used in each embodiment are as follows:

[0067] 1. Edible carbon source powder: Beijing Yinuokai Technology Co., Ltd.; sucrose, BioReagent,

[0068] =99.5% (GC)

[0069] 2. Silica sol solution: Henan Zhuangwei New Materials Co., Ltd.; silica sol, 30.63%

[0070] 3. Boric acid: Beijing Yinuokai Technology Co., Ltd.; Boric acid, 99.5%

[0071] 4. Tubular vacuum furnace: Micro-x Shanghai MGX1750-60

[0072] The main analytical methods and instruments used in each embodiment are as follows:

[0073] X-ray diffraction: XRD patterns were measured using a Rigaku DMAX-2500 / P with a scanning speed of 2 degrees per minute and a range of 20 to 90 degrees.

[0074] SEM: Thermo Fisher Scientific Scios DualBeam was used for fracture analysis of the samples. The voltage was 5 kV and the current was 0.1 nA.

[0075] TEM: TEM samples (5 × 10 × 0.06 μm) were prepared using a focused ion beam (FIB) and measured using a Thermo Fisher Scientific Talos F200X scanning transmission electron microscope (STEM) and a JEOL JEM-ARM300F2 scanning transmission electron microscope (STEM) at accelerating voltages of 200 kV and 300 kV, respectively.

[0076] The particle size test methods for boron carbide and silicon carbide are as follows: the particle size is measured by SEM photos; to ensure accuracy, 5 SEM photos are randomly taken and selected, 100 particle sizes are measured in each photo, and the average value is finally taken.

[0077] Method for determining the mass ratio of silicon carbide to boron carbide (SiC / B4C): The mass ratio of boron carbide to silicon carbide produced is indirectly calculated by measuring the mass ratio of amorphous carbon contained in the amorphous carbon-silicon carbide composite intermediate during the preparation process. The specific method is to first perform the first step of the reaction to produce silicon carbide and amorphous carbon, and then measure the mass ratio of amorphous carbon by thermogravimetric analysis; then, using the reaction equation:

[0078] 4C+4H3BO3=B4C+3CO2+6H2O

[0079] Calculate the mass ratio of boron carbide to silicon carbide in the final product.

[0080] Example 1

[0081] A) Weigh edible carbon source powder and silica sol solution in a 1:1 mass ratio, pour them into a beaker filled with deionized water, and stir with a glass rod to fully dissolve. The beaker is then placed on a heating plate and dried at 80°C for 45 hours to evaporate the water in the solution, ultimately yielding a dry, brownish-red solid.

[0082] B) Grind the brownish-red solid block into a fine powder using a mortar and pestle, then add the fine powder into a graphite crucible, with the amount of brownish-red solid added not exceeding 2 / 3 of the volume of the graphite crucible. Then, place the graphite crucible in a vacuum tube furnace for high-temperature calcination, with the calcination temperature and time being 1500°C and 0.5 hours, respectively. The heating and cooling rates are 5°C / min below 300°C, 10°C / min between 300 and 1200°C, and 5°C / min between 1200 and 1500°C. The vacuum degree inside the tube furnace is higher than 5.0×10 -3 , obtaining an amorphous carbon-silicon carbide composite intermediate, and then grinding the composite intermediate into a fine powder using a mortar;

[0083] C) pouring the amorphous carbon and silicon carbide composite intermediate into a beaker filled with deionized water, then adding a certain amount of boric acid and ultrasonically mixing them uniformly using an ultrasonic machine, wherein the mass ratio of the composite powder (the composite powder of amorphous carbon and silicon carbide) to the boric acid is 1.0, and then drying to remove the moisture therein to obtain a mixed powder, the drying temperature and time being 80° C. and 45 hours, respectively;

[0084] D) placing the dried mixed powder in a graphite crucible, and finally placing the graphite crucible in a vacuum tube furnace for high-temperature calcination, wherein the reaction temperature and time are 1500°C and 0.5 hour respectively, the heating and cooling rates are 5°C / min below 300°C, 10°C / min from 300 to 1200°C, and 5°C / min from 1200 to 1500°C, and the vacuum degree is higher than 5.0×10 -3 , boron carbide silicon carbide composite nanopowder can be obtained.

[0085] The SEM images and XRD patterns of the obtained boron carbide silicon carbide composite nanopowders are shown in Figure 1 and Figure 2 .

[0086] Example 2

[0087] A) Weigh edible carbon source powder and silica sol solution in a mass ratio of 2:1, pour them into a beaker filled with deionized water, and stir with a glass rod to fully dissolve. The beaker is then placed on a heating plate and dried at 80°C for 40 hours to evaporate the water in the solution, ultimately yielding a dry, brownish-red solid mass.

[0088] B) Grind the brownish-red solid block into a fine powder using a mortar and pestle, then add the fine powder into a graphite crucible, wherein the amount of brownish-red solid added does not exceed 2 / 3 of the volume of the graphite crucible, and then place the graphite crucible in a vacuum tube furnace for high-temperature calcination, wherein the calcination temperature and time are 1500°C and 0.6 hours, respectively, and the heating and cooling rates are 5°C / min below 300°C, 10°C / min between 300-1200°C, and 5°C / min between 1200-1500°C. The vacuum degree inside the tube furnace is higher than 5.0×10 -3 , obtaining an amorphous carbon-silicon carbide composite intermediate, and then grinding the composite intermediate into a fine powder using a mortar;

[0089] C) pouring the amorphous carbon-silicon carbide composite intermediate into a beaker filled with deionized water, then adding a certain amount of boric acid and ultrasonically mixing it to obtain a uniform mixture, wherein the mass ratio of the composite powder (composite powder of amorphous carbon and silicon carbide) to the boric acid is 1.0, and then drying to remove the water therein to obtain a mixed powder, wherein the drying temperature and time are 80° C. and 45 hours, respectively;

[0090] D) placing the dried mixed powder in a graphite crucible, and finally placing the graphite crucible in a vacuum tube furnace for high-temperature calcination, wherein the reaction temperature and time are 1400°C and 0.5 hours respectively, the heating and cooling rates are 5°C / min below 300°C, 10°C / min from 300 to 1200°C, and 5°C / min from 1200 to 1500°C, and the vacuum degree is higher than 5.0×10 -3 , boron carbide silicon carbide composite nanopowder can be obtained.

[0091] Example 3

[0092] A) Weigh edible carbon source powder and silica sol solution in a mass ratio of 1.5:1, pour them into a beaker filled with deionized water, and stir with a glass rod to fully dissolve. The beaker is then placed on a heating plate and dried at 80°C for 45 hours to evaporate the water in the solution, ultimately yielding a dry, brownish-red solid mass.

[0093] B) Grind the brownish-red solid block into a fine powder using a mortar, and then charge the fine powder into a graphite crucible. The amount of brownish-red solid added does not exceed 2 / 3 of the volume of the graphite crucible. Then, place the graphite crucible in a vacuum tube furnace for high-temperature calcination. The calcination temperature and time are 1450°C and 0.5 hours, respectively. The heating and cooling rates are 5°C / min below 300°C, 10°C / min between 300 and 1200°C, and 5°C / min between 1200 and 1500°C. The vacuum degree inside the tube furnace is higher than 5.0×10 -3 , obtaining an amorphous carbon-silicon carbide composite intermediate, and then grinding the composite intermediate into a fine powder using a mortar;

[0094] C) pouring the amorphous carbon-silicon carbide composite intermediate into a beaker filled with deionized water, then adding a certain amount of boric acid and ultrasonically mixing it to obtain a uniform mixture, wherein the mass ratio of the composite powder (composite powder of amorphous carbon and silicon carbide) to the boric acid is 1.0, and then drying to remove the water therein to obtain a mixed powder, wherein the drying temperature and time are 80° C. and 45 hours, respectively;

[0095] D) placing the dried mixed powder in a graphite crucible, and finally placing the graphite crucible in a vacuum tube furnace for high-temperature calcination. The reaction temperature and time are 1450°C and 0.5 hours, respectively. The heating and cooling rates are 5°C / min below 300°C, 10°C / min between 300 and 1200°C, and 5°C / min between 1200 and 1500°C. The vacuum degree is higher than 5.0×10 -3 , boron carbide silicon carbide composite nanopowder can be obtained.

[0096] Example 4

[0097] A) Weigh edible carbon source powder and silica sol solution in a 1:1 mass ratio, pour them into a beaker filled with deionized water, and stir with a glass rod to fully dissolve. The beaker is then placed on a heating plate and dried at 79°C for 47 hours to evaporate the water in the solution, ultimately yielding a dry, brownish-red solid.

[0098] B) Grind the brownish-red solid block into a fine powder using a mortar and pestle, then add the fine powder into a graphite crucible, with the amount of brownish-red solid added not exceeding 2 / 3 of the volume of the graphite crucible. Then, place the graphite crucible in a vacuum tube furnace for high-temperature calcination, with the calcination temperature and time being 1550°C and 0.5 hours, respectively. The heating and cooling rates are 5°C / min below 300°C, 10°C / min between 300 and 1200°C, and 5°C / min between 1200 and 1500°C. The vacuum degree inside the tube furnace is higher than 5.0×10 -3 , obtaining an amorphous carbon-silicon carbide composite intermediate, and then grinding the composite intermediate into a fine powder using a mortar;

[0099] C) pouring the amorphous carbon-silicon carbide composite intermediate into a beaker filled with deionized water, then adding a certain amount of boric acid and ultrasonically mixing it to obtain a uniform mixture, wherein the mass ratio of the composite powder (composite powder of amorphous carbon and silicon carbide) to the boric acid is 1.0, and then drying to remove the water therein to obtain a mixed powder, wherein the drying temperature and time are 80° C. and 46 hours, respectively;

[0100] D) placing the dried mixed powder in a graphite crucible, and finally placing the graphite crucible in a vacuum tube furnace for high-temperature calcination, wherein the reaction temperature and time are 1500°C and 0.5 hour respectively, the heating and cooling rates are 5°C / min below 300°C, 10°C / min from 300 to 1200°C, and 5°C / min from 1200 to 1500°C, and the vacuum degree is higher than 5.0×10 -3 , boron carbide silicon carbide composite nanopowder can be obtained.

[0101] Example 5

[0102] A) Weigh edible carbon source powder and silica sol solution in a mass ratio of 2:1, pour them into a beaker filled with deionized water, and stir with a glass rod to fully dissolve. The beaker is then placed on a heating plate and dried at 80°C for 45 hours to evaporate the water in the solution, ultimately yielding a dry, brownish-red solid mass.

[0103] B) Grind the brownish-red solid block into a fine powder using a mortar, and then charge the fine powder into a graphite crucible. The amount of brownish-red solid added does not exceed 2 / 3 of the volume of the graphite crucible. Then, place the graphite crucible in a vacuum tube furnace for high-temperature calcination. The calcination temperature and time are 1450°C and 0.5 hours, respectively. The heating and cooling rates are 5°C / min below 300°C, 10°C / min between 300 and 1200°C, and 5°C / min between 1200 and 1500°C. The vacuum degree inside the tube furnace is higher than 5.0×10 -3 , obtaining an amorphous carbon-silicon carbide composite intermediate, and then grinding the composite intermediate into a fine powder using a mortar;

[0104] C) pouring the amorphous carbon-silicon carbide composite intermediate into a beaker filled with deionized water, then adding a certain amount of boric acid and ultrasonically mixing it to obtain a uniform mixture, wherein the mass ratio of the composite powder (composite powder of amorphous carbon and silicon carbide) to the boric acid is 1.0, and then drying to remove the water therein to obtain a mixed powder, wherein the drying temperature and time are 78° C. and 45 hours, respectively;

[0105] D) placing the dried mixed powder in a graphite crucible, and finally placing the graphite crucible in a vacuum tube furnace for high-temperature calcination, wherein the reaction temperature and time are 1500°C and 0.6 hours respectively, the heating and cooling rates are 5°C / min below 300°C, 10°C / min from 300 to 1200°C, and 5°C / min from 1200 to 1500°C, and the vacuum degree is higher than 5.0×10 -3 , boron carbide silicon carbide composite nanopowder can be obtained.

[0106] The key parameters of the preparation methods in Examples 1 to 5 and the measured data of the grain size and SiC / B4C mass ratio of the obtained boron carbide-silicon carbide composite nanopowders are summarized in the following table:

[0107] Table 1: Reaction parameters and product characteristics of Examples 1 to 5

[0108]

[0109] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A boron carbide and silicon carbide (B4C-SiC) composite nanopowder, wherein the average particle size of silicon carbide is 50-100 nm, and the average particle size of boron carbide is 70-120 nm, respectively, and the two are uniformly mixed together at a mass ratio of silicon carbide to boron carbide of 1:1 to 5:

1.

2. The boron carbide-silicon carbide (B4C-SiC) composite nanopowder according to claim 1, characterized in that Silicon carbide The average particle size of quartz is 70-90 nm, and the average particle size of boron carbide is 90-100 nm.

3. The boron carbide-silicon carbide composite nanopowder according to claim 1 or 2, which is prepared by a method comprising the following steps: 1) Weighing edible carbon source powder and silica sol solution, adding them to water, stirring and dissolving them, and evaporating water in the resulting solution by heating to obtain a dry solid; 2) grinding the obtained solid into a fine powder, then adding the fine powder into a graphite crucible, then calcining the graphite crucible at a high temperature in a vacuum heating device to obtain an amorphous carbon and silicon carbide composite intermediate, and then grinding the composite intermediate into a fine powder again; 3) adding the composite intermediate fine powder to water, then adding boric acid or boric acid ester, mixing uniformly, and drying to remove moisture to obtain a mixed powder; 4) placing the mixed powder obtained after drying in a graphite crucible, and then placing the graphite crucible in a vacuum heating device for high-temperature calcination to obtain boron carbide and silicon carbide composite nanopowder.

4. A method for preparing boron carbide and silicon carbide (B4C-SiC) composite nanopowder, the preparation method comprising the following steps: 1) Weighing edible carbon source powder and silica sol solution, adding them to water, stirring and dissolving them, and evaporating water in the resulting solution by heating to obtain a dry solid; 2) grinding the obtained solid into a fine powder, then adding the fine powder into a graphite crucible, then calcining the graphite crucible at a high temperature in a vacuum heating device to obtain an amorphous carbon and silicon carbide composite intermediate, and then grinding the composite intermediate into a fine powder again; 3) adding the composite intermediate fine powder to water, then adding boric acid or boric acid ester, mixing uniformly, and drying to remove moisture to obtain a mixed powder; 4) placing the mixed powder obtained after drying in a graphite crucible, and then placing the graphite crucible in a vacuum heating device for high-temperature calcination to obtain boron carbide and silicon carbide composite nanopowder.

5. The method for preparing boron carbide and silicon carbide composite nanopowder according to claim 4, characterized in that: In step 1), the edible carbon source powder used is selected from sucrose, glucose, fructose, arabinose, galactose, lactose, maltose, soluble starch or modified starch, soluble dextrin or modified dextrin, or any mixture of these substances, the concentration of the silica sol solution used is 20-50wt%, and the mass ratio of the edible carbon source to the silica sol is 0.5:1 to 5:

1.

6. The method for preparing boron carbide and silicon carbide composite nanopowder according to claim 4 or 5, characterized in that: In step 2), the temperature and time of high-temperature calcination are 1200-1800° C. and 0.2-1 hour respectively.

7. The method for preparing boron carbide and silicon carbide composite nanopowder according to claim 6, characterized in that: During the calcination process in step 2), the vacuum degree inside the tube furnace is higher than 8.0×10 -3 , preferably higher than 5.0×10 -3 .

8. The in-situ preparation method of boron carbide and silicon carbide composite nanopowder according to claim 4 or 5, characterized in that: In step 4), the temperature and time of high-temperature calcination are 1200-1800° C. and 0.2-1 hour, respectively.

9. The method for preparing boron carbide and silicon carbide composite nanopowder according to claim 8, characterized in that: During the calcination process in step 4), the vacuum degree inside the tube furnace is higher than 8.0×10 -3 , preferably higher than 5.0×10 -3 .

10. The method for preparing boron carbide and silicon carbide composite nanopowder according to any one of claims 4 to 9, characterized in that: In step 3), the mass ratio of the composite intermediate to the boric acid or boric acid ester is 0.2 to 1.2, preferably 0.4 to 1.0.

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