Method for synthesizing calcium hexaboride micro-nano powder by electric field and magnetic field coupling assisted combustion

Abstract

The invention relates to a method for synthesizing calcium hexaboride micro-nano powder by electric field and magnetic field coupling auxiliary combustion, which mainly comprises the following steps: by taking calcium hydroxide, boric oxide and magnesium powder as raw materials, carrying out electric field and magnetic field coupling auxiliary combustion synthesis to obtain a reaction product; and then, carrying out acid pickling on a reaction product to obtain the unique calcium hexaboride micro-nano material with the hollow cubic structure. In the process of combustion synthesis of calcium hexaboride, under the coupling influence of an electric field and a magnetic field, the prepared calcium hexaboride micro-nano powder shows unique hollow cubic structural characteristics, and the structural characteristics enable the calcium hexaboride micro-nano powder to have the advantages of high specific surface area, light weight, porous neutron absorption and the like; the method has important application prospects in the fields of aerospace, high-end manufacturing, nuclear industry and the like.

Description

Technical Field

[0001] This invention belongs to the field of inorganic materials, specifically relating to a method for synthesizing calcium hexaboride micro / nano powders by combustion assisted by electric and magnetic field coupling. Background Technology

[0002] Calcium hexaboride, as an important boride ceramic material, has extremely high hardness and wear resistance, high melting point, good chemical stability and excellent resistance to neutron radiation, making it of great application potential and research value in functional materials such as wear-resistant parts, high-temperature applications, special electrodes and thermoelectric conversion.

[0003] There are many reported methods for preparing calcium hexaboride in the prior art, such as solid-state reaction, borothermic reduction, and mechanical ball milling. Among these, the solid-state reaction method utilizes elemental calcium and boron to directly synthesize calcium hexaboride in a high-temperature, inert, or vacuum environment. This method is simple in principle and theoretically can obtain high-purity products, but it requires stringent reaction conditions, and because the reactants are all solid, the mass transfer efficiency is low, resulting in uneven product composition and coarse grains. The borothermic reduction method uses elemental boron to reduce calcium oxide in a vacuum environment. This method can obtain high-purity CaB6 powder, but it requires demanding equipment, consumes a lot of energy, has a slow reaction rate, and is costly. The mechanical ball milling method uses elemental calcium and boron oxide as raw materials, directly generating calcium hexaboride powder after high-energy ball milling, but the operation time is long, the reaction rate is slow, and the product purity is low. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for synthesizing calcium hexaboride micro / nano powder by electric field and magnetic field assisted combustion, which addresses the shortcomings of the prior art. By controlling the nucleation, growth and crystal orientation during the crystal growth process through electric field and magnetic field, calcium hexaboride micro / nano powder with a hollow cubic structure is obtained.

[0005] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: A method for synthesizing calcium hexaboride micro / nano powders by electric field and magnetic field coupled combustion involves using calcium hydroxide, boron oxide, and magnesium as raw materials, and synthesizing them through electric field and magnetic field assisted combustion to obtain reaction products. The reaction products are then acid-washed to obtain calcium hexaboride micro / nano powders. The specific steps include: (1) Raw material mixing: Grind magnesium powder, calcium hydroxide and boron oxide into powder, mix evenly, and then press into blocks; (2) External field assisted combustion synthesis reaction: The block obtained in step (1) is placed in the reaction chamber of the Joule heating device. After the reaction chamber is evacuated, an inert protective gas is filled in and maintained at a predetermined pressure. Then, the electric field and magnetic field are activated, and the combustion synthesis reaction is carried out by ignition. The ignition reaction will affect the gas pressure in the device. Therefore, the inert protective gas is kept in a circulating state throughout the combustion synthesis reaction process to ensure that the atmospheric pressure of the combustion synthesis reaction is always within the predetermined pressure range. (3) Post-processing: After the combustion reaction in step (2) is completed, the mixture is naturally cooled to room temperature, and the pressure in the reaction chamber is reduced to atmospheric pressure to obtain a block product. The obtained block product is ground into fine powder, acid washed, and dried to obtain calcium hexaboride micro-nano powder.

[0006] According to the above scheme, in step (1), the molar ratio of calcium hydroxide and boron oxide is 1:2 to 1:5.

[0007] According to the above scheme, in step (1), the amount of magnesium powder added is 0.8 to 1.5 times the total mass of calcium hydroxide and boron oxide.

[0008] According to the above scheme, in step (1), the raw material powder is pressed into blocks by holding the pressure at 5~10MPa for 10~20 minutes.

[0009] According to the above scheme, in step (2), the pressure of the inert protective gas is maintained in the range of 0.003~0.008MPa; the purity of the inert protective gas is not less than 99.99%, preferably argon or the like.

[0010] According to the above scheme, in step (2), the electric field strength is 5V / mm~40V / mm and the magnetic field strength is 1.5T~15T.

[0011] According to the above scheme, in step (3), the block product is ground into powder and then dispersed in 4~7 mol / L hydrochloric acid and heated to 40~60℃ and stirred for 4~8 h to achieve acid washing; after acid washing, the drying temperature is 50~70℃ and the time is 8~12 h.

[0012] The calcium hexaboride micro / nano powder synthesized by the above method exhibits a hollow cubic structure in its microstructure. The size of the cubic particles ranges from 0.1 to 1 μm, and the wall thickness of the hollow cubes ranges from 10 to 50 nm.

[0013] The following chemical reactions may occur during the synthesis of calcium hexaboride micro / nano powders in this invention:

[0014] Ca(OH)₂ = CaO + H₂O Mg + CaO = Ca* + MgO 3Mg + B₂O₃ = 2B* + 3MgO Ca* + 6B* = CaB6 The possible reaction mechanism of the above synthesis process is as follows: as the reaction temperature gradually increases after ignition, calcium hydroxide decomposes into calcium oxide and water. Then, magnesium undergoes a violent reduction reaction, reducing boron oxide and calcium oxide into active boron atoms and calcium atoms. Under the influence of magnetic and electric fields, the diffusion path and mass transfer process of calcium and B atoms change, inducing crystal orientation growth and particle directional assembly. This results in crystal growth preferentially occurring on the outer surface. At the same time, the external field provides non-uniform energy input, causing different reaction rates inside and outside. Finally, a hollow cubic structure of calcium hexaboride micro / nano powder with a unique microstructure appears.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention employs an electric and magnetic field-assisted combustion synthesis technique, using magnesium powder, calcium hydroxide, and boron oxide as reactants, to synthesize hollow cubic calcium hexaboride micro / nano powders under a protective atmosphere. This invention utilizes electric and magnetic fields to influence nucleation, growth, and crystal orientation during crystal growth, ultimately synthesizing hollow cubic calcium hexaboride micro / nano materials.

[0016] The combustion synthesis method employed in this invention requires readily available external fields, exhibits rapid reaction, short production cycle, low cost, low product impurities, and is energy-efficient, providing a new method for the synthesis of inorganic materials. Furthermore, the unique hollow cubic structure of the calcium hexaboride micro / nano powder prepared by this invention endows it with high specific surface area, lightweight properties, and excellent neutron absorption performance, making it a promising candidate for applications in cutting-edge fields such as aerospace, high-end manufacturing, and the nuclear industry. Attached Figure Description

[0017] Figure 1 This is a scanning electron microscope (SEM) image of the CaB6 sample obtained in Comparative Example 1.

[0018] Figure 2 This is a transmission electron microscope (TEM) image of the CaB6 sample obtained in Comparative Example 1.

[0019] Figure 3 The image shows the X-ray diffraction (XRD) pattern of the CaB6 sample obtained in Comparative Example 1.

[0020] Figure 4 This is a scanning electron microscope (SEM) image of the CaB6 sample obtained in Comparative Example 2.

[0021] Figure 5 Scanning electron microscope (SEM) image of the CaB6 sample obtained in Comparative Example 3. Figure 6This is a scanning electron microscope (SEM) image of the CaB6 sample obtained in Example 1.

[0022] Figure 7 The images shown are scanning electron microscope (SEM) images and EDS spectra of the CaB6 sample obtained in Example 1.

[0023] Figure 8 This is a transmission electron microscope (TEM) image of the CaB6 sample obtained in Example 1.

[0024] Figure 9 The image shows the X-ray diffraction (XRD) pattern of the CaB6 sample obtained in Example 1.

[0025] Figure 10 This is a high-resolution transmission electron microscope (HR-TEM) image of the CaB6 sample obtained in Example 1.

[0026] Figure 11 This is a transmission electron microscope (TEM) selected area electron diffraction pattern (SEEP) image of the CaB6 sample obtained in Example 1. Detailed Implementation

[0027] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0028] In the following examples, the morphology was observed using a scanning electron microscope (SEM) of an SM8600 Hitachi and a transmission electron microscope (TEM) of a JEM-2100F; X-ray diffraction analysis (XRD) was performed using a Rigaku D / MAX-LLIA X-ray powder diffractometer (λ = 1.5406 Å) with 2θ ranging from 5 to 80°.

[0029] Comparative Example 1 A method for preparing calcium hexaboride by combustion synthesis includes the following steps: (1) Raw material mixing: Magnesium powder, calcium hydroxide and boron oxide are used as raw materials. The molar ratio of calcium hydroxide and boron oxide is 1:3. The amount of magnesium powder added is 1.2 times the total mass of calcium hydroxide and boron oxide. The three raw materials are ground in a mortar for 1 hour and mixed thoroughly. The resulting mixed powder is placed in a tableting mold and pressed at 10 MPa for 10 minutes to obtain a block. (2) Combustion synthesis reaction: The block obtained in step (1) is placed in the reaction chamber of the Joule heating device. After the reaction chamber is closed, a vacuum is drawn, and then high-purity argon gas is introduced. The purity of the high-purity argon gas is >99.99%. The gas is vented twice, and then argon gas is introduced to the predetermined pressure and always maintained at 0.005MPa. The reaction is ignited by tungsten wire to carry out the combustion synthesis reaction. (3) Product processing: After the combustion reaction is completed, the product is naturally cooled to room temperature, the pressure of the reaction chamber is released, the block product is taken out from the chamber, further ground into powder, dispersed in 6 mol / L hydrochloric acid, heated to 40°C, stirred for 8 hours, then washed three times with deionized water and three times with ethanol, and finally dried at 70°C for 8 hours to obtain calcium hexaboride micro-nano powder.

[0030] Figure 1 The SEM image of the CaB6 sample prepared in this comparative example shows that the CaB6 sample is cubic with a particle size in the range of 0.15~0.6μm. The microstructure is not very uniform and is relatively disordered. There are also a small amount of impurities attached to the surface, indicating poor dispersibility.

[0031] Figure 2 The TEM image of the CaB6 sample prepared in this comparative example shows that the CaB6 sample is a solid cube.

[0032] Figure 3 The XRD pattern of the CaB6 sample prepared in this comparative example shows several obvious diffraction peaks located at 2θ = 30.47°, 37.53°, 43.61°, 49.06°, and 67.68°, respectively. These peaks correspond to the crystal planes (110), (111), (200), (210), and (300) of the CaB6 crystal, indicating that the sample has no obvious impurity phases and has high purity.

[0033] Comparative Example 2 A method for synthesizing calcium hexaboride by electric field-assisted combustion includes the following steps: (1) Raw material mixing: Magnesium powder, calcium hydroxide and boron oxide are used as raw materials. The molar ratio of calcium hydroxide and boron oxide is 1:3. The amount of magnesium powder added is 1.2 times the total mass of calcium hydroxide and boron oxide. The three raw materials are ground in a mortar for 1 hour and mixed thoroughly. The resulting mixed powder is placed in a tableting mold and pressed at 10 MPa for 10 minutes to obtain a block. (2) Combustion synthesis reaction: The block obtained in step (1) is placed in the cavity of the Joule heating device. After the cavity is closed, a vacuum is drawn, and then high-purity argon gas is introduced. The purity of the high-purity argon gas is >99.99%. The gas is vented twice, and then argon gas is introduced to a predetermined pressure of 0.005MPa and maintained at this pressure during the subsequent combustion synthesis process. The reaction is ignited by tungsten filament to carry out the combustion synthesis reaction. (3) Product processing: After the combustion reaction is completed, the product is naturally cooled to room temperature, the chamber pressure is released, and a block product is obtained. After further grinding, it is dispersed in 6 mol / L hydrochloric acid, heated to 40°C, stirred for 8 hours, washed three times with deionized water and three times with ethanol, and finally dried at 70°C for 8 hours to obtain a calcium hexaboride micro-nano powder.

[0034] Figure 4 The image shown is the SEM image of the CaB6 sample prepared in this comparative example. It can be seen that the CaB6 sample is a solid cube or cuboid with poor uniformity and the sample size is in the range of 0.1~0.6μm.

[0035] Comparative Example 3 A method for synthesizing calcium hexaboride by magnetic field-assisted combustion includes the following steps: (1) Raw material mixing: Magnesium powder, calcium hydroxide and boron oxide are used as raw materials. The molar ratio of calcium hydroxide and boron oxide is 1:3. The amount of magnesium powder added is 1.2 times the total mass of calcium hydroxide and boron oxide. The three raw materials are ground in a mortar for 1 hour and mixed thoroughly. The resulting mixed powder is placed in a tableting mold and pressed at 10 MPa for 10 minutes to obtain a block. (2) Combustion synthesis reaction: The block obtained in step (1) is placed in the cavity of the Joule heating device. After the cavity is closed, a vacuum is drawn, and then high-purity argon gas is introduced. The purity of the high-purity argon gas is >99.99%. The gas is vented twice, and then argon gas is introduced to a predetermined pressure of 0.005MPa and maintained at this pressure during the subsequent combustion synthesis process. The reaction is ignited by tungsten filament to carry out the combustion synthesis reaction. (3) Product processing: After the combustion reaction is completed, the product is naturally cooled to room temperature, the chamber pressure is released, and a block product is obtained. After further grinding, it is dispersed in 6 mol / L hydrochloric acid, heated to 40°C, stirred for 8 hours, washed three times with deionized water and three times with ethanol, and finally dried at 70°C for 8 hours to obtain a calcium hexaboride micro-nano powder.

[0036] Figure 5 The SEM image of the CaB6 sample prepared in this comparative example shows that the CaB6 sample is a solid cubic shape with poor homogeneity and a particle size in the range of 0.15~0.7μm.

[0037] Example 1 A method for synthesizing calcium hexaboride micro / nano powders by combustion assisted by electric and magnetic field coupling, comprising the following steps: (1) Raw material mixing: Magnesium powder, calcium hydroxide and boron oxide are used as raw materials. The molar ratio of calcium hydroxide and boron oxide is 1:3. The amount of magnesium powder added is 1.2 times the total mass of calcium hydroxide and boron oxide. These three raw materials are ground in a mortar for 1 hour and mixed thoroughly. The resulting mixed powder is placed in a tableting mold and pressed at 10 MPa for 10 minutes to obtain a block. (2) Combustion synthesis reaction: The block obtained in step (1) is placed in the cavity of the Joule heating device. After closing the cavity, a vacuum is drawn, and then high-purity argon gas is introduced. The purity of the high-purity argon gas is >99.99%. The gas is vented twice, and then argon gas is introduced to a predetermined pressure of 0.005MPa. The electric field is set to 10V / mm and the magnetic field is set to 3.16T. The reaction is ignited by tungsten filament to carry out the combustion synthesis reaction. Argon gas is kept in a flowing state throughout the combustion synthesis reaction process to ensure that the atmospheric pressure of the combustion synthesis reaction is maintained at the predetermined pressure. (3) Product processing: After the combustion reaction is completed, the product is naturally cooled to room temperature, the chamber pressure is released, and a block product is obtained. After further grinding, it is dispersed in 6 mol / L hydrochloric acid, heated to 40°C, stirred for 8 hours, washed three times with deionized water and three times with ethanol, and finally dried at 70°C for 8 hours to obtain a calcium hexaboride micro-nano powder.

[0038] Figure 6 The image shows a SEM image of the CaB6 sample prepared in Example 1. It can be seen that the CaB6 sample has a hollow cubic structure with a particle size mainly in the range of 0.2~0.65μm and an inner wall thickness in the range of about 15~30nm.

[0039] Figure 7 The image shown is a SEM image and EDS spectrum of the CaB6 sample prepared in Example 1. The sample is composed of Ca and B.

[0040] Figure 8 The image shown is a transmission electron microscope (TEM) image of the CaB6 sample obtained in Example 1, which shows that the CaB6 sample has a hollow structure.

[0041] Figure 9 The figure shows the XRD pattern of the CaB6 sample prepared in Example 1. Several obvious diffraction peaks are present in the figure, located at 2θ = 30.47°, 37.53°, 43.61°, 49.06° and 67.68° respectively. The peaks correspond to the crystal planes (110), (111), (200), (210) and (300) of CaB6 crystal, respectively. It can be seen that the sample has no impurity phase and has high purity.

[0042] Figure 10The high-resolution transmission electron microscope (HR-TEM) image of the CaB6 sample obtained in Example 1 shows that the lattice fringe spacing of the sample is 0.415 nm, and the crystal grows along the

[001] crystal orientation.

[0043] Figure 11 The selected area electron diffraction pattern (SEAD) image of the CaB6 sample obtained in Example 1 shows that the sample has good crystallinity, and the zone axis in this region is a face-centered cubic structure. 00).

[0044] Example 2 A method for synthesizing calcium hexaboride micro / nano powders by combustion assisted by electric and magnetic field coupling includes the following steps: (1) Raw material mixing: Magnesium powder, calcium hydroxide and boron oxide are used as raw materials. The molar ratio of calcium hydroxide and boron oxide is 1:3. The amount of magnesium powder added is 1.2 times the total mass of calcium hydroxide and boron oxide. These three raw materials are ground in a mortar for 1 hour and mixed thoroughly. The resulting mixed powder is placed in a tableting mold and pressed at 10 MPa for 10 minutes to obtain a block. (2) Combustion synthesis reaction: The block obtained in step (1) is placed in the cavity of the Joule heating device. After closing the cavity, a vacuum is drawn, and then high-purity argon gas is introduced. The purity of the high-purity argon gas is >99.99%. The gas is vented twice, and then argon gas is introduced to a predetermined pressure of 0.005MPa. The electric field is set to 20V / mm and the magnetic field is set to 6.33T. The reaction is ignited by tungsten filament to carry out the combustion synthesis reaction. Argon gas is kept in a flowing state throughout the combustion synthesis reaction process to ensure that the atmospheric pressure of the combustion synthesis reaction is maintained at the predetermined pressure. (3) Product processing: After the combustion reaction is completed, the product is naturally cooled to room temperature and the chamber pressure is released to obtain a block product. After further grinding, it is dispersed in 6 mol / L hydrochloric acid, heated to 40°C, stirred for 8 hours, washed three times with deionized water and three times with ethanol, and finally dried at 70°C for 8 hours to obtain a hollow cubic calcium hexaboride micro-nano powder.

[0045] Example 3 A method for synthesizing calcium hexaboride micro / nano powders by combustion assisted by electric and magnetic field coupling includes the following steps: (1) Raw material mixing: Magnesium powder, calcium hydroxide and boron oxide are used as raw materials. The molar ratio of calcium hydroxide and boron oxide is 1:3. The amount of magnesium powder added is 1.2 times the total mass of calcium hydroxide and boron oxide. The three raw materials are ground in a mortar for 1 hour and mixed thoroughly. The resulting mixed powder is placed in a tableting mold and pressed at 10 MPa for 10 minutes to obtain a block. (2) Combustion synthesis reaction: The block obtained in step (1) is placed in the cavity of the Joule heating device. After closing the cavity, a vacuum is drawn, and then high-purity argon gas is introduced. The purity of the high-purity argon gas is >99.99%. The gas is vented twice, and then argon gas is introduced to a predetermined pressure of 0.005MPa. The electric field is set to 40V / mm and the magnetic field is set to 12.66T. The reaction is ignited by tungsten filament to carry out the combustion synthesis reaction. Argon gas is kept in a flowing state throughout the combustion synthesis reaction process to ensure that the atmospheric pressure of the combustion synthesis reaction is maintained at the predetermined pressure. (3) Product processing: After the combustion reaction is completed, the product is naturally cooled to room temperature and the chamber pressure is released to obtain a block product. After further grinding, it is dispersed in 6 mol / L hydrochloric acid, heated to 40°C, stirred for 8 hours, washed three times with deionized water and three times with ethanol, and finally dried at 70°C for 8 hours to obtain a hollow cubic calcium hexaboride micro-nano powder.

[0046] Example 4 A method for synthesizing calcium hexaboride micro / nano powders by combustion assisted by electric and magnetic field coupling includes the following steps: (1) Raw material mixing: Magnesium powder, calcium hydroxide and boron oxide are used as raw materials. The molar ratio of calcium hydroxide and boron oxide is 1:3. The amount of magnesium powder added is 1.2 times the total mass of calcium hydroxide and boron oxide. These three raw materials are ground in a mortar for 1 hour and mixed thoroughly. The resulting mixed powder is placed in a tableting mold and pressed at 5 MPa for 20 minutes to obtain a block. (2) Combustion synthesis reaction: The block obtained in step (1) is placed in the cavity of the Joule heating device. After closing the cavity, a vacuum is drawn, and then high-purity argon gas is introduced. The purity of the high-purity argon gas is >99.99%. The gas is vented twice, and then argon gas is introduced to a predetermined pressure of 0.005MPa. The electric field is set to 10V / mm and the magnetic field is set to 3.16T. The reaction is ignited by tungsten filament to carry out the combustion synthesis reaction. Argon gas is kept in a flowing state throughout the combustion synthesis reaction process to ensure that the atmospheric pressure of the combustion synthesis reaction is maintained at the predetermined pressure. (3) Product processing: After the combustion reaction is completed, the product is naturally cooled to room temperature and the chamber pressure is released to obtain a block product. After further grinding, it is dispersed in 6 mol / L hydrochloric acid, heated to 40°C, stirred for 8 hours, washed three times with deionized water and three times with ethanol, and finally dried at 70°C for 8 hours to obtain a hollow cubic calcium hexaboride micro-nano powder.

[0047] Example 5 A method for synthesizing calcium hexaboride micro / nano powders by combustion assisted by electric and magnetic field coupling, comprising the following steps: (1) Raw material mixing: Magnesium powder, calcium hydroxide and boron oxide are used as raw materials. The molar ratio of calcium hydroxide and boron oxide is 1:3. The amount of magnesium powder added is 1.2 times the total mass of calcium hydroxide and boron oxide. These three raw materials are ground in a mortar for 1 hour to mix them thoroughly.

[0048] (2) Combustion synthesis reaction: The block obtained in step (1) is placed in the cavity of the Joule heating device. After closing the cavity, a vacuum is drawn, and then high-purity argon gas is introduced. The purity of the high-purity argon gas is >99.99%. The gas is vented twice, and then argon gas is introduced to a predetermined pressure of 0.008MPa. The electric field is set to 10V / mm and the magnetic field is set to 3.16T. The reaction is ignited by tungsten filament to carry out the combustion synthesis reaction. Argon gas is kept in a flowing state throughout the combustion synthesis reaction process to ensure that the atmospheric pressure of the combustion synthesis reaction is maintained at the predetermined pressure. (3) Product processing: After the combustion reaction is completed, the product is naturally cooled to room temperature and the chamber pressure is released to obtain a block product. After further grinding, it is dispersed in 6 mol / L hydrochloric acid, heated to 40°C, stirred for 8 hours, washed three times with deionized water and three times with ethanol, and finally dried at 70°C for 8 hours to obtain a hollow cubic calcium hexaboride micro-nano powder.

[0049] Example 6 A method for synthesizing calcium hexaboride micro / nano powders by combustion assisted by electric and magnetic field coupling includes the following steps: (1) Raw material mixing: Magnesium powder, calcium hydroxide and boron oxide are used as raw materials. The molar ratio of calcium hydroxide and boron oxide is 1:3. The amount of magnesium powder added is 1.5 times the total mass of calcium hydroxide and boron oxide. The three raw materials are ground in a mortar for 1 hour and mixed thoroughly. The resulting mixed powder is placed in a tableting mold and pressed at 10 MPa for 10 minutes to obtain a block. (2) Combustion synthesis reaction: The block obtained in step (1) is placed in the cavity of the Joule heating device. After closing the cavity, a vacuum is drawn, and then high-purity argon gas is introduced. The purity of the high-purity argon gas is >99.99%. The gas is vented twice, and then argon gas is introduced to a predetermined pressure of 0.005MPa. The electric field is set to 10V / mm and the magnetic field is set to 3.16T. The reaction is ignited by tungsten filament to carry out the combustion synthesis reaction. Argon gas is kept in a flowing state throughout the combustion synthesis reaction process to ensure that the atmospheric pressure of the combustion synthesis reaction is maintained at the predetermined pressure. (3) Product processing: After the combustion reaction is completed, the product is naturally cooled to room temperature and the chamber pressure is released to obtain a block product. After further grinding, it is dispersed in 6 mol / L hydrochloric acid, heated to 40°C, stirred for 8 hours, washed three times with deionized water and three times with ethanol, and finally dried at 70°C for 8 hours to obtain a hollow cubic calcium hexaboride micro-nano powder.

[0050] The calcium hexaboride micro / nano powders prepared in the above examples all showed a hollow cubic structure as observed by scanning electron microscopy, with a particle size in the range of 0.1~1μm and an inner wall thickness in the range of 10~50nm. XRD characterization showed no obvious impurity phases.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for synthesizing calcium hexaboride micro-nano powder assisted by electric field and magnetic field coupling combustion, characterized in that, The calcium hexaboride micro-nano powder is prepared by using calcium hydroxide, boron oxide and magnesium as raw materials and through the process of electric field and magnetic field assisted combustion synthesis.

2. The method for synthesizing CaB6 micro-nano powder by electric field and magnetic field coupling auxiliary combustion according to claim 1, characterized in that, The micro-nano powder has a hollow cubic structure, the cubic particle size is in the range of 0.1-1 μm, and the hollow cubic wall thickness is in the range of 10-50 nm.

3. The method for electric field and magnetic field assisted combustion synthesis of calcium hexaboride micro-nano powder according to claim 1, characterized in that, The method comprises the following steps: (1) mixing raw materials: grinding magnesium powder, calcium hydroxide and boron oxide into powder, uniformly mixing, and then pressing into a block; (2) external field assisted combustion synthesis reaction: placing the block obtained in step (1) into a joule heating device, vacuumizing, then filling with inert protective gas, starting electric field and magnetic field, igniting, and then performing combustion synthesis reaction; (3) post-treatment: grinding the blocky product obtained after the combustion reaction in step (2) into powder, acid washing, and then obtaining the calcium hexaboride micro-nano powder.

4. The method for synthesizing CaB6 micro-nano powder by electric field and magnetic field assisted combustion according to claim 3, characterized in that, In step (1), the molar ratio of calcium hydroxide to boron oxide is 1:2-1:

5.

5. The method for synthesizing CaB6 micro-nano powder by electric field and magnetic field assisted combustion according to claim 3, characterized in that, In step (1), the added amount of magnesium powder is 0.8-1.5 times of the total mass of calcium hydroxide and boron oxide.

6. The method for synthesizing CaB6 micro-nano powder by electric field and magnetic field assisted combustion according to claim 3, characterized in that, In step (2), the pressure of the inert protective gas in the whole combustion synthesis reaction process is maintained in the range of 0.003-0.008 MPa.

7. The method for synthesizing CaB6 micro-nano powder by electric field and magnetic field assisted combustion according to claim 3, characterized in that, In step (2), the electric field intensity is 5-40 V / mm, and the magnetic field intensity is 1.5-15 T.

8. The method for synthesizing CaB6 micro-nano powder by electric field and magnetic field assisted combustion according to claim 3, characterized in that, In step (1), the raw material powder is pressed into a block by using a pressure of 5-10 MPa for 10-20 minutes.

9. The method for synthesizing CaB6 micro-nano powder by electric field and magnetic field assisted combustion according to claim 3, characterized in that, In step (3), after the blocky product is ground into powder, the powder is dispersed in 4-7 mol / L hydrochloric acid and heated and stirred for 4-8 h for acid washing.

10. The calcium hexaboride micro-nano powder synthesized by the method of any one of claims 1 or 3-8, characterized in that, The micro-nano powder has a hollow cubic structure, the cubic particle size is in the range of 0.1-1 μm, and the hollow cubic wall thickness is in the range of 10-50 nm.

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