Silicon carbide nanowire combined silicon carbide ceramic and preparation method thereof

Abstract

The invention relates to the technical field of ceramics, in particular to a method for combining silicon carbide nanowires with silicon carbide ceramics. The preparation method comprises the following steps: 1, putting an ethanol solution into a container, adding acrylamide and N, N-methylene bisacrylamide, and dissolving to form a premixed solution; 2, Si powder and activated carbon are ground, and mixed powder is obtained; step 3, adding the mixed powder in the step 2 into the premixed solution in the step 1, then adding an ammonium persulfate solution and N, N, N, N-tetramethylethylenediamine, immediately pouring into a silica gel mold, and standing at room temperature; and step 4, after demolding, placing the product in a nitriding furnace for heat treatment to obtain the silicon carbide nanowire combined silicon carbide porous ceramic. The product has high porosity of 60%, compressive strength of 2.6 MPa, good electromagnetic wave absorption performance, minimum reflection loss (RLmin) of 50.2 dB, maximum effective absorption bandwidth (EABmax) of 9.6 GHz and low heat conductivity coefficient of 0.074 W / (m.K).

Description

Technical Field

[0001] The present invention relates to the technical field of ceramics, and particularly relates to a silicon carbide nanowire-bonded silicon carbide ceramic and a preparation method thereof. Background Art

[0002] Silicon carbide nanowires (SiC nw ) have received extensive attention due to their unique properties that combine those of nanomaterials and ceramic materials. As a one-dimensional nanomaterial, it has properties such as a wide bandgap, high thermal conductivity, and high dielectric loss, which endow it with great application potential in advanced functional material fields such as semiconductors, optoelectronics, wave absorption, electromagnetic shielding, and catalysis. On the other hand, SiC nanowires also possess some properties of ceramic materials, such as low density, high heat conductivity, low coefficient of thermal expansion, stable chemical properties, excellent physical and chemical properties such as heat and corrosion resistance, and excellent comprehensive properties such as strength, toughness, friction, creep resistance, and heat insulation under high-temperature or extreme usage conditions, and are widely used in environments such as aerospace, petrochemical industry, space mirrors, and radars.

[0003] Silicon carbide is currently a very important third-generation wide-bandgap semiconductor material. The resistivity of β-SiC is greater than 103 Ω·cm. It not only has wave absorption potential but also can weaken infrared signals, making it one of the wave absorption materials that have developed rapidly at home and abroad. Due to its chemical stability at high temperatures, SiC nanowires have received more attention in the field of high-temperature wave absorption. The silicon carbide materials prepared by traditional processes have too high resistivity and a low imaginary part of the dielectric, resulting in poor wave absorption performance and cannot be directly used as wave absorption materials. They need to be further doped and modified or compounded with other materials. Due to the special properties of one-dimensional nanomaterials of SiC nanowires, the wave absorption performance has been greatly improved, which is the focus of research in recent years.

[0004] Silicon carbide nanowires (SiC nanowires, SiC NWs) have advantages such as low density, a large number of stacking faults and defects inside, and a high aspect ratio, which have attracted extensive attention in the research and application in the field of wave absorption.

[0005] However, the currently prepared silicon carbide materials are mostly silicon carbide nanofiber aerogels or silicon carbide porous ceramics. The fiber aerogels have a low thermal conductivity and an effective wave absorption bandwidth but too low mechanical strength, which limits their wide use. While the silicon carbide porous ceramics can achieve an increase in strength, but the pore size of the pores is large, which has an impact on properties such as heat insulation and wave absorption. Summary of the Invention

[0006] To comprehensively solve the above problems, the present invention uses low-cost raw materials and a simple preparation method to achieve silicon carbide nanowire combined with silicon carbide ceramic in one step, significantly improving the mechanical strength, heat preservation performance, wave absorption performance, etc. of the material. The preparation method is simple and can be produced on a large scale.

[0007] To achieve the above object, in the first aspect of the present invention, there is provided a preparation method of silicon carbide nanowire combined with silicon carbide ceramic, including Step 1: Place an ethanol solution in a container, add acrylamide and N,N-methylenebisacrylamide and dissolve them to form a premixed solution; Step 2: Grind Si powder and activated carbon to obtain a mixed powder; Step 3: Add the mixed powder in Step 2 to the premixed solution in Step 1, then add ammonium persulfate solution and N,N,N,N-tetramethylethylenediamine, and immediately pour it into a silica gel mold and let it stand at room temperature; Step 4: After demolding, place it in a nitriding furnace for heat treatment to obtain silicon carbide nanowire combined with porous silicon carbide ceramic.

[0008] Preferably, in Step 1, the mass ratio of acrylamide to N,N-methylenebisacrylamide is 20:1.

[0009] Preferably, in Step 2, the mass ratio of Si powder to activated carbon is 1:1.

[0010] Preferably, the standing time in Step 3 is 5 hours.

[0011] Preferably, the heat treatment process in Step 3 is: heat to 1500 °C at a heating rate of 5 / min in argon, hold for 6 hours, and finally cool to room temperature.

[0012] In the second aspect of the present invention, there is provided a silicon carbide nanowire combined with silicon carbide ceramic prepared by the above method.

[0013] Compared with the prior art, the beneficial effects of the present invention are: The present invention uses low-cost raw materials and a simple preparation method to achieve silicon carbide nanowire combined with silicon carbide ceramic in one step. The porous structure and nanowire intertwined structure of the product prepared by the present invention form more interfaces, realizing more polarization loss of electromagnetic waves and showing excellent wave absorption performance; the highly wound silicon carbide nanowires delay the crack propagation during the compression of the porous ceramic, increasing the strength of the composite material; the intertwined nanowires formed in the pores of the porous ceramic make its pore size much lower than the average free path of air molecules under normal pressure, and the air molecules in the voids are approximately stationary, thus restricting the convective heat transfer of the gas and further reducing the thermal conductivity of the material. Therefore, the mechanical strength, heat preservation performance and wave absorption performance of the material are significantly improved. The porosity of the product of the present invention is 60%, the compressive strength is 2.6 MPa, it has good electromagnetic wave absorption performance, the minimum reflection loss (RLmin) is -50.2 dB, the maximum effective absorption bandwidth (EABmax) is 9.6 GHz and the low thermal conductivity is 0.074 W / (m·K). And the preparation method is simple and can be produced on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification, and are used to explain the present invention together with the embodiments of the present invention, and do not constitute a limitation to the present invention.

[0015] In the drawings: Figure 1 is the XRD pattern of the product prepared by the present invention.

[0016] Figure 2 is the SEM pattern of the product prepared by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The following is described in conjunction with Figure 1 - Figure 2 the preferred embodiments of the present invention; it should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0018] Example 1: A preparation method of silicon carbide nanowire combined with silicon carbide ceramic, comprising Step 1: Take 10 ml of ethanol solution and place it in a container, add 1 g of acrylamide and 0.05 g of N,N-methylenebisacrylamide and dissolve to form a premixed solution; Step 2: Ball-mill 2 g of Si powder and 2 g of activated carbon at 300 r / min for 3 hours, then add 1 g of rice husk powder and continue ball-milling for 1 h to obtain a mixed powder; Step 3: Add the mixed powder from Step 2 in batches (5 times, 1 g each time) with continuous stirring into the premixed solution from Step 1, then add 0.5 ml of ammonium persulfate solution and 0.5 ml of N,N,N,N-tetramethylethylenediamine, and immediately pour it into a silica gel mold with dimensions of 20 mm × 20 mm × 40 mm, and let it stand at room temperature for 5 hours; Step 4: After demolding, place it in a nitriding furnace for heat treatment, heat it to 1500 °C at a heating rate of 5 °C / min in argon, and hold for 6 hours to obtain silicon carbide nanowire-bonded silicon carbide porous ceramics.

[0019] Example 2: A silicon carbide nanowire-bonded silicon carbide ceramic prepared by the method described in Example 1.

[0020] Result analysis: Crystal structure: As Figure 1 is the XRD of the product prepared in this invention, showing that SiC was successfully prepared.

[0021] 2. Scanning electron microscope images is the scanning electron microscope result of this example. The silicon carbide nanowire-bonded silicon carbide porous ceramics prepared by this method show an approximately spherical pore structure. However, the diameters of these pores are significantly different, including large pores formed by mechanical foaming and small pores formed by particle packing. And between the small pores, due to the close packing of the powder, with a large surface area and high surface energy, a large number of silicon carbide nanowires were in-situ formed.

[0022] Observing the morphology of the polished and calcined sample, the pores show an irregular structure. Among them, many pores existing in the microstructure mainly come from the following two aspects: (i) pores left by the thermal decomposition of rice husk powder and (ii) pores generated by the stacking of multiple particles. And between the pores, there are a large number of in-situ generated silicon carbide nanowires.

[0023] 3. Performance test results: Thermal conductivity test: Tested by a Hot Disk thermal constant analyzer, the test atmosphere is air, and the 5465 probe is selected.

[0024] The silicon carbide nanowire-bonded silicon carbide porous ceramics prepared in this example have a porosity of 60%, a compressive strength of 2.6 MPa, good electromagnetic wave absorption performance, a minimum reflection loss (RLmin) of -50.2 dB, a maximum effective absorption bandwidth (EABmax) of 9.6 GHz, and a low thermal conductivity of 0.074 W / (m·K).

[0025] Comparative example: Different from Example 1, in this example, 1 g of Si powder and 1 g of activated carbon are used, the porosity of the porous ceramic is 700%, the compressive strength is 0.8 MPa, and the low thermal conductivity is 0.066 W / (m·K). The improvement of the thermal conductivity is not high, but the compressive strength decreases significantly.

[0026] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments; the above embodiments and the descriptions in the specification only illustrate the principles of the present invention; without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements; these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A method for preparing silicon carbide nanowires combined with silicon carbide ceramics, characterized in that: include Step 1: Place an ethanol solution in a container, add acrylamide and N,N-methylenebisacrylamide to dissolve, and form a premixed solution; Step 2: Grind Si powder and activated carbon to obtain mixed powder; Step 3: Add the mixed powder of step 2 to the premixed solution of step 1, then add ammonium persulfate solution and N,N,N,N-tetramethylethylenediamine, immediately pour into a silicone mold, and let stand at room temperature; Step 4: After demolding, place in a nitriding furnace for heat treatment to obtain silicon carbide nanowires combined with silicon carbide porous ceramics.

2. The method for preparing silicon carbide nanowires combined with silicon carbide ceramics according to claim 1, characterized in that: The mass ratio of acrylamide to N,N-methylenebisacrylamide in step 1 is 20:

1.

3. The method for preparing silicon carbide nanowires combined with silicon carbide ceramics according to claim 2, characterized in that: In step 2, the mass ratio of Si powder to activated carbon is 1:

1.

4. The method for preparing silicon carbide nanowires combined with silicon carbide ceramics according to claim 3, characterized in that: The standing time in step 3 is 5 hours.

5. The method for preparing silicon carbide nanowires combined with silicon carbide ceramics according to claim 3, characterized in that: The heat treatment process in step 3 is: heating to 1500° C. at a heating rate of 5° C. / min in argon gas, maintaining the temperature for 6 hours, and finally cooling to room temperature.

6. Silicon carbide nanowire-bonded silicon carbide ceramics prepared by the method according to any one of claims 1 to 5.

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