A multifunctional Al-doped core-shell structured SiC nanowire, its preparation method and application

Abstract

This invention discloses a multifunctional Al-doped core-shell SiC nanowire, its preparation method, and its applications. Using SiO powder and Al powder as precursors, a large quantity of Al-doped core-shell SiC nanowires can be synthesized on various substrate surfaces at relatively low temperatures through grinding and mixing. This method can prepare a large quantity of uniformly sized Al-doped core-shell SiC nanowires at low temperatures, at low cost, and with high efficiency. The prepared nanowires exhibit good photoluminescence properties and promote the self-healing properties of coatings at high temperatures. The synthesized nanowires have the following characteristics: a diameter distribution between 100 and 130 nm; a crystalline Al-doped SiC core at the center with a diameter of approximately 50–80 nm; and an outer layer of amorphous Al-doped SiO2 with a thickness of approximately 30–50 nm. The nanowires are composed of Si, O, C, and Al, and their length can reach the millimeter scale.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation technology, specifically relating to a multifunctional Al-doped core-shell structure SiC nanowire, its preparation method, and its application. Background Technology

[0002] One-dimensional nanomaterials possess high aspect ratios, excellent mechanical properties, strong quantum size effects, and good electrical and optical properties, making them valuable for applications in aerospace and optoelectronic materials. Compared to other one-dimensional materials, SiC nanowires have attracted widespread attention from scholars both domestically and internationally due to their superior physical and chemical properties, such as strong radiation resistance, excellent chemical and high-temperature stability, high specific strength, low dielectric constant, high critical breakdown electric field, and thermal conductivity.

[0003] Elemental doping or core-shell structure design of nanowires can adjust their band structure, thereby effectively improving the luminescence efficiency of semiconductor nanowires. Studies have shown that introducing Al into SiC nanowires improves their luminescence efficiency by altering the SiC bandgap structure. Compared to SiC nanowires, SiC@SiO2 core-shell nanowires exhibit superior photoluminescence performance due to the SiO2 layer on their surface, which can adjust the band structure of SiC. Therefore, doping core-shell nanowires can enhance their photoluminescence properties. Furthermore, introducing self-healing components, such as Al, into nanowires and incorporating them into SiC coatings is expected to improve the self-healing properties of nanowire-toughened SiC coatings. Therefore, core-shell structure design and elemental doping modification of SiC nanowires will broaden their application areas.

[0004] Currently, some progress has been made in the preparation of doped SiC nanowires or core-shell structured SiC nanowires. For example, reference 1, "Z.Li,K.Li,G.Song et al.Al-Doped SiC nanowires wrapped by the nanowirenetwork:excellent field emission property and robust stability at high current density[J],Journal of Materials Chemistry C,2018,6(24):6565-6574," introduces a method for preparing Al-doped SiC nanowires using polycarbosilane (PCS) as the Si and C source, Al(NO3)3 as the Al source, and Ni(NO3)2 as the catalyst, employing polymer pyrolysis. This method successfully achieved Al doping in SiC nanowires at 1400℃, and an amorphous SiO2 layer existed on the surface of the nanowires. However, this method requires a high preparation temperature, resulting in disordered nanowire morphology, uneven size distribution, and severe interconnections between nanowires, which is detrimental to the subsequent multifunctional applications of the nanowires. Reference 2, "H.Cui, L.Gong, GZYang et al. Enhanced field emission property of a novel Al2O3 nanoparticle-decorated tubular SiC emitter with low turn-on and threshold field[J], Physical Chemistry Chemical Physics, 2011, 13(3): 985-990," uses a single-crystal Si substrate as both the base and the silicon source. 60Using Al as the carbon source and Al powder as the Al source, Al2O3-coated SiC nanowires were prepared by placing the three raw materials at different temperature ranges. The nanowires prepared by this method have high purity, but their aspect ratio is small, and the placement of the powder needs to be strictly controlled during the preparation process, allowing the nanowires to grow on only one surface of the substrate. Patent 1, "Li Hejun, Chu Yanhui, Fu Qiangang, Li Kezhi, Li Lu. A method for preparing Al-doped silicon carbide nanowires, ZL201210206341.5 [P]. 2012," provides a method for preparing Al-doped SiC nanowires, but this method requires a high preparation temperature (>1600℃), resulting in non-core-shell SiC nanowires. Furthermore, the raw materials require long-term ball milling and mixing, and the nanowire size distribution is extremely uneven, which is detrimental to the stable performance of the nanowires. Therefore, to maximize the effectiveness of nanowires, it is necessary to prepare uniformly sized nanowires at lower temperatures to maintain the structural stability of the core-shell structure, prevent nanowire interconnection or structural alteration, and thus improve the luminescence efficiency and performance stability of SiC nanowires. However, the above work is limited to the application of materials in the field of optoelectronics and does not consider the conditions required for nanowire applications in other fields, such as how to uniformly prepare them on the surface of irregularly shaped components. Considering and meeting the conditions for nanowire applications in other fields will enhance their application value. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a multifunctional Al-doped core-shell structured SiC nanowire, its preparation method and application, so as to solve the technical problems of the prior art, such as high preparation temperature, complex operation, strict requirements on the placement of powder, which leads to low purity, non-uniform size and poor structural stability of the prepared product, thus limiting its application range.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] This invention discloses a method for preparing multifunctional Al-doped core-shell structured SiC nanowires, comprising:

[0008] The mixed powder obtained by thoroughly mixing SiO powder and Al powder is used as the precursor powder;

[0009] A catalyst-loaded matrix is ​​suspended above precursor powder, then sealed, and subjected to negative pressure heat treatment at 1250–1400 °C to prepare multifunctional Al-doped core-shell SiC nanowires.

[0010] Preferably, the preparation method of the above-mentioned multifunctional Al-doped core-shell structure SiC nanowires disclosed in this invention includes the following steps:

[0011] 1) Select SiO powder and Al powder, grind them evenly, and prepare a mixed powder as a precursor powder;

[0012] 2) Spread the mixed powder evenly on the bottom of the crucible, suspend the catalyst-loaded matrix above the precursor powder using molybdenum wire, and seal the crucible;

[0013] 3) The crucible processed in step 2) is suspended in the constant temperature zone of a vertical tube furnace. After testing the sealing performance (vacuum pressure treatment until the pressure inside the furnace does not change significantly), inert gas is introduced, the vacuum pump is turned on, and the temperature is raised to 1250-1400℃. Then, the inert gas is stopped and the vacuum pump is turned off. The temperature is maintained in this closed environment for 2-5 hours. Then, inert gas is introduced again and the vacuum pump is turned on. The temperature is naturally cooled to room temperature to obtain Al-doped core-shell structured SiC nanowires.

[0014] More preferably, the particle size of SiO powder is 5-10 μm, and the particle size of Al powder is 30-50 μm.

[0015] More preferably, the mass ratio of SiO powder to Al powder is (8:1) to (3:1).

[0016] More preferably, the mixed powder is prepared by grinding, and the mixing time is 30 to 60 minutes.

[0017] More preferably, SiO powder and Al powder of appropriate particle size are weighed in proportion, and the SiO powder and Al powder are placed together in an agate mortar and ground for 30 min to 60 min to obtain a mixed powder, which is used as the precursor powder.

[0018] Preferably, the catalyst-supported matrix is ​​prepared by the following method:

[0019] After cleaning the substrate, it is immersed in a nickel nitrate ethanol solution for 10–30 minutes, and then dried to obtain the final product.

[0020] More preferably, the substrate is a carbon / carbon composite material, graphite, SiC ceramic, or a SiC coating prepared by CVD.

[0021] More preferably, the cleaning is performed using anhydrous ethanol; the molar concentration of the nickel nitrate ethanol solution is 0.2–1 mol / L; and the drying process is performed at 70–90°C.

[0022] More preferably, in step 2), a molybdenum wire is used to suspend the catalyst-loaded matrix 1 to 3 cm above the precursor powder.

[0023] More preferably, in step 3), the pressure inside the furnace is maintained at 5 to 7 kPa during the vacuum pressure holding process.

[0024] More preferably, the inert gas is argon.

[0025] The present invention also discloses a multifunctional Al-doped core-shell structured SiC nanowire prepared by the above preparation method, wherein the diameter of the multifunctional Al-doped core-shell structured SiC nanowire is distributed between 100 and 130 nm.

[0026] The center of this multifunctional Al-doped core-shell structured SiC nanowire is a crystalline Al-doped SiC core with a diameter of 50–80 nm, and the outer layer is an amorphous Al-doped SiO2 layer with a thickness of 30–50 nm.

[0027] The constituent elements of this multifunctional Al-doped core-shell structured SiC nanowire are Si, O, C, and Al.

[0028] The length of these multifunctional Al-doped core-shell SiC nanowires reaches the millimeter level.

[0029] This invention discloses the application of the above-mentioned multifunctional Al-doped core-shell structure SiC nanowires in the preparation of semiconductor materials, optoelectronic materials, ceramic coating materials or aerospace substrate materials.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] This invention discloses a method for preparing multifunctional Al-doped core-shell SiC nanowires. Using SiO powder and Al powder as precursors, the nanowires are ground and mixed to synthesize large quantities of Al-doped core-shell SiC nanowires on various substrate surfaces at relatively low temperatures. The advantages of this method are: First, the precursors are low-cost SiO powder and Al powder, which do not need to be stored separately, thus effectively solving the problem of poor nanowire growth caused by temperature fluctuations in the equipment. Second, the Al-doped core-shell SiC nanowires have a good promoting effect on the self-healing properties of SiC coatings. This is mainly because the introduction of Al reduces the viscosity of SiO2 and improves the fluidity of SiO2 glass. Compared with SiC nanowire-toughened SiC coatings, the self-healing efficiency is improved by about 100% in an oxygen-rich environment at 1500℃. The Al-doped core-shell SiC nanowires, due to... The enhanced resonance results in high photoluminescence efficiency, approximately 2.5 times higher than pure SiC nanowires and 36% higher than core-shell SiC@SiO2 nanowires. Furthermore, the prepared Al-doped core-shell SiC nanowires exhibit uniform diameter with a core-to-shell diameter ratio of approximately 1:2. Simultaneously, due to the low preparation temperature (below 1400℃), the nanowires are free from interconnections, resulting in high structural stability and facilitating multifunctional applications such as light-emitting devices or coating toughening. Therefore, this method enables the high-efficiency and low-cost preparation of large quantities of uniformly sized Al-doped core-shell SiC nanowires at relatively low temperatures.

[0032] The multifunctional Al-doped core-shell SiC nanowires prepared by the above method of this invention exhibit strong adaptability to substrate types and shapes, meeting the needs of nanowire fabrication on substrate surfaces in optoelectronics and aerospace fields. They possess good photoluminescence properties and promote self-healing of coatings at high temperatures. The Al-doped core-shell SiC nanowires, due to... The enhanced resonance results in higher photoluminescence efficiency, approximately 2.5 times and 36% higher than pure SiC nanowires and core-shell SiC@SiO2 nanowires, respectively. Compared to SiC nanowire-toughened SiC coatings, the self-healing efficiency is approximately doubled in an oxygen-rich environment at 1500°C.

[0033] Furthermore, the Al element is uniformly distributed in the prepared Al-doped core-shell structure SiC nanowires. The Al element content can be adjusted by adjusting the mass fraction of Al powder, and the nanowire length can be adjusted by controlling the holding time. Attached Figure Description

[0034] Figure 1 XRD pattern of Al-doped core-shell SiC nanowires on the surface of C / C composite material;

[0035] Figure 2 SEM image of Al-doped core-shell SiC nanowires;

[0036] Figure 3 TEM images and Al energy spectrum results for Al-doped core-shell SiC nanowires;

[0037] Figure 4 Photoluminescence spectra of core-shell SiC nanowires and Al-doped core-shell SiC nanowires;

[0038] Figure 5 Photos of SiC nanowire-toughened SiC coating and Al-doped core-shell structure SiC nanowire-toughened SiC coating before and after crack healing: (a) and (c) are before crack healing; (b) and (d) are after crack healing.

[0039] Figure 6 The images shown are SEM images of the nanowires in the comparative examples; (a) is comparative example 1; (b) is comparative example 2; and (c) is comparative example 3. Detailed Implementation

[0040] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0041] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0042] The present invention will now be described in further detail with reference to the accompanying drawings:

[0043] This invention discloses a method for low-temperature preparation of multifunctional Al-doped core-shell structured SiC nanowires, comprising the following steps:

[0044] Step 1: Clean the substrate with anhydrous ethanol, immerse it in nickel nitrate ethanol solution for 10-30 minutes, then remove it and place it in an oven at 70-90℃ for drying; the molar concentration of the nickel nitrate ethanol solution is 0.2-1 mol / L.

[0045] Step 2: Weigh out SiO powder and Al powder of appropriate particle size according to the ratio, place them in an agate mortar, and grind for 30 min to 60 min to obtain a mixed powder.

[0046] The particle sizes of the SiO powder and Al powder are 5-10 μm and 30-50 μm, respectively; the mass ratio of SiO powder to Al powder is (8:1) to (3:1).

[0047] Step 3: Spread the mixed powder obtained in Step 2 evenly on the bottom of the graphite crucible, use a molybdenum wire to suspend the substrate treated in Step 1 about 1 to 3 cm above the mixed powder, and then seal the crucible.

[0048] Step 4: Suspend the graphite crucible prepared in Step 3 in the isothermal zone of a vertical tube furnace and maintain vacuum pressure for approximately 1 hour, during which no significant pressure change occurs. Then, introduce Ar and turn on the vacuum pump. Raise the furnace temperature from room temperature to 1250–1400°C at a rate of 5–10°C / min. After reaching the specified temperature, turn off the Ar and vacuum pumps to create a sealed environment and maintain the temperature for 2–5 hours, keeping the furnace pressure at 5–7 kPa. Then, turn on the Ar and vacuum pumps again, turn off the heating power, and allow the furnace to cool naturally to room temperature. Remove the graphite crucible, clean the molybdenum wires from the sample surface, and you will obtain Al-doped core-shell SiC nanowires.

[0049] The substrate is a carbon / carbon (C / C) composite material, graphite, SiC ceramics, or a SiC coating prepared by CVD (CVD-SiC).

[0050] Example 1

[0051] The C / C composite material (matrix) was cleaned with anhydrous ethanol and dried in an oven at 80°C. A nickel nitrate ethanol solution with a molar concentration of approximately 0.3 mol / L was prepared, and the C / C composite material was immersed in the nickel nitrate solution for approximately 10 minutes, and then dried in an oven at 70°C.

[0052] Weigh 3g of SiO powder and 1g of Al powder, and grind them in an agate mortar for about 40 minutes to obtain a mixed powder as a precursor powder. Spread the mixed powder in a graphite crucible, and use a molybdenum wire to suspend the C / C composite material loaded with the catalyst about 2cm above the mixed powder, and then seal the crucible.

[0053] The sealed crucible was suspended in the isothermal zone of a vertical tube furnace, and a vacuum was drawn to 4 kPa, then maintained at that pressure for 1 hour. After the pressure showed no significant change, the temperature was increased to 1250℃ at a rate of 5℃ / min, with Ar as the protective gas introduced at a flow rate of approximately 300 sccm. Once the temperature was reached, the vacuum pump and Ar were turned off, and the sealed environment was maintained for 3 hours. After the maintenance period, the vacuum pump and Ar were turned on, and the heating power was turned off. The sample was cooled with the furnace, with the Ar flow rate remaining at 300 sccm. After cooling to room temperature, the sample was removed, yielding a large number of Al-doped core-shell SiC nanowires.

[0054] The XRD pattern of the Al-doped core-shell structured SiC nanowires prepared in this embodiment is as follows: Figure 1 As shown in the figure, the phase remains predominantly SiC, with no new phase appearing, indicating that Al mainly enters the SiC nanowires in a solid solution form. SEM images of the fabricated Al-doped core-shell SiC nanowires are shown below. Figure 2As shown in the figure, the nanowires exhibit a well-defined linear structure, and the nanowire tips contain a catalyst. TEM images and Al energy dispersive spectroscopy results of the fabricated Al-doped core-shell SiC nanowires are shown below. Figure 3 As shown in the figure, the nanowires have a core-shell structure. Energy dispersive spectroscopy results indicate that Al has dissolved into SiC and SiO2, forming an Al-doped SiC structure coated with Al-doped SiO2.

[0055] Example 2

[0056] The CVD-SiC coated sample (substrate) was cleaned with anhydrous ethanol and dried in an oven at 80°C. A nickel nitrate ethanol solution with a molar concentration of approximately 0.4 mol / L was prepared. The CVD-SiC coated sample was immersed in the nickel nitrate solution for approximately 10 minutes, and then dried in an oven at 80°C.

[0057] Weigh 3g of SiO powder and 0.5g of Al powder, and grind them in an agate mortar for about 40 minutes to obtain a mixed powder as a precursor powder. Spread the mixed powder in a graphite crucible, and suspend the CVD-SiC coating sample loaded with the catalyst about 3cm above the powder using a molybdenum wire, and then seal the crucible.

[0058] The sealed crucible was suspended in the isothermal zone of a vertical tube furnace, and a vacuum was drawn to 4 kPa, then held at that pressure for 1 hour. After the pressure showed no significant change, the temperature was increased to 1300℃ at a rate of 5℃ / min, with Ar as the protective gas introduced at a flow rate of approximately 400 sccm. Once the temperature was reached, the vacuum pump and Ar were turned off, and the sealed environment was maintained for 2 hours. After the holding period, the vacuum pump and Ar were turned on, and the heating power was turned off. The sample was then cooled with the furnace, with the Ar flow rate remaining at 400 sccm. After cooling to room temperature, the sample was removed, yielding a large quantity of Al-doped core-shell SiC nanowires.

[0059] Example 3

[0060] The C / C composite material (matrix) was cleaned with anhydrous ethanol and dried in an oven at 80°C. A nickel nitrate ethanol solution with a molar concentration of approximately 0.5 mol / L was prepared, and the C / C composite material was immersed in the nickel nitrate solution for approximately 20 minutes, followed by drying in an oven at 70°C.

[0061] Weigh 6g of SiO powder and 1.5g of Al powder, and grind them in an agate mortar for about 50 minutes to obtain a mixed powder as a precursor powder. Spread the mixed powder in a graphite crucible, and use a molybdenum wire to suspend the C / C composite material loaded with the catalyst about 3cm above the powder, and then seal the crucible.

[0062] The sealed crucible was suspended in the isothermal zone of a vertical tube furnace. A vacuum was evacuated to 4 kPa and held for 1 hour. After no significant pressure change, the temperature was increased to 1350℃ at a rate of 5℃ / min, with Ar as the protective gas introduced at a flow rate of approximately 200 sccm. Upon reaching the desired temperature, the vacuum pump and Ar were turned off, and the furnace was kept in a sealed environment for 4 hours. After this period, the vacuum pump and Ar were turned on, and the heating power was turned off. The sample was then cooled with the furnace, with the Ar flow rate remaining at 200 sccm. After cooling to room temperature, the sample was removed, yielding a large quantity of Al-doped core-shell SiC nanowires.

[0063] Example 4

[0064] The C / C composite material (matrix) was cleaned with anhydrous ethanol and dried in an oven at 80°C. A nickel nitrate ethanol solution with a molar concentration of approximately 0.6 mol / L was prepared, and the C / C composite material was immersed in the nickel nitrate solution for approximately 10 minutes, and then dried in an oven at 70°C.

[0065] Weigh 4g of SiO powder and 1g of Al powder, and grind them in an agate mortar for about 40 minutes to obtain a mixed powder as a precursor powder. Spread the mixed powder in a graphite crucible, and use a molybdenum wire to suspend the C / C composite material loaded with the catalyst about 1cm above the powder, and then seal the crucible.

[0066] The sealed crucible was suspended in the isothermal zone of a vertical tube furnace. A vacuum was evacuated to 4 kPa and held for 1 hour. After no significant pressure change, the temperature was increased to 1400℃ at a rate of 5℃ / min, with Ar as the protective gas introduced at a flow rate of approximately 300 sccm. Upon reaching the desired temperature, the vacuum pump and Ar were turned off, and the furnace was kept in a sealed environment for 2 hours. After the holding period, the vacuum pump and Ar were turned on, and the heating power was turned off. The sample was cooled with the furnace, with the Ar flow rate remaining at 300 sccm. After cooling to room temperature, the sample was removed, yielding a large quantity of Al-doped core-shell SiC nanowires.

[0067] Comparative Example 1

[0068] Unlike Example 1, the ratio of SiO powder to Al powder is approximately 1:1, which is higher than the ratio specified in the example. The presence of a large amount of Al will inhibit the volatilization of SiO powder, reduce the gas concentration required for nanowire growth, and is not conducive to nanowire growth.

[0069] The C / C composite material (matrix) was cleaned with anhydrous ethanol and dried in an oven at 70°C. A nickel nitrate ethanol solution with a molar concentration of approximately 0.2 mol / L was prepared. The C / C composite material was immersed in the nickel nitrate solution for approximately 20 minutes, and then dried in an oven at 90°C.

[0070] Weigh 3g of SiO powder and 3g of Al powder, and grind them in an agate mortar for about 30 minutes to obtain a mixed powder as a precursor. Spread the mixed powder in a graphite crucible, and use a molybdenum wire to suspend the C / C composite material loaded with the catalyst about 1cm above the powder, and then seal the crucible.

[0071] The sealed crucible was suspended in the isothermal zone of a vertical tube furnace. A vacuum was evacuated to 4 kPa and held for 1 hour. After no significant pressure change, the temperature was increased to 1250℃ at a rate of 5℃ / min, with Ar as the protective gas flowing through at a flow rate of approximately 300 sccm. Once the temperature was reached, the vacuum pump and Ar were turned off, creating a sealed environment and holding for 2 hours. After the holding period, the vacuum pump and Ar were turned on, and the heating power was turned off. The sample was cooled with the furnace, with the Ar flow rate remaining at 300 sccm. After cooling to room temperature, the sample was removed. Only a small number of nanowires appeared on the surface of the C / C composite material. The nanowires were short in length and uneven in thickness, exhibiting a mixture of nanowires and whiskers. Figure 6 As shown in (a).

[0072] Comparative Example 2

[0073] Unlike Example 1, the particle size of the SiO powder used in this comparative example is different from that in the aforementioned examples.

[0074] The C / C composite material (matrix) was cleaned with anhydrous ethanol and dried in an oven at 80°C. A nickel nitrate ethanol solution of approximately 0.3 mol / L was prepared, and the C / C composite material was immersed in the nickel nitrate solution for about 10 minutes, then dried in an oven at 70°C.

[0075] Subsequently, nanowires were prepared using powders of different particle sizes. Specifically, 3g of SiO powder with a particle size of 1-3μm and 1g of Al powder were weighed and ground in an agate mortar for about 40 minutes to obtain a mixed powder. The mixed powder was then spread in a graphite crucible, and a C / C composite material loaded with a catalyst was suspended about 2cm above the powder using a molybdenum wire. The crucible was then sealed.

[0076] The sealed crucible was suspended in the isothermal zone of a vertical tube furnace. A vacuum was evacuated to 4 kPa and held for 1 hour. After no significant pressure change, the temperature was increased to 1250℃ at a rate of 5℃ / min, with Ar as the protective gas purging at a flow rate of approximately 300 sccm. Upon reaching the desired temperature, the vacuum pump and Ar were turned off, and the furnace was kept in a sealed environment for 4 hours. After the holding period, the vacuum pump and Ar were turned on, and the heating power was turned off. The sample was cooled with the furnace, with the Ar flow rate remaining at 300 sccm. After cooling to room temperature, the sample was removed. The nanowire growth on the sample surface was minimal. Figure 6As shown in (b), the main reason is that the SiO powder has a fine particle size and is not mixed evenly with the Al powder. At high temperature, the molten Al powder inhibits the generation of SiO gas. If ball milling is used for mixing, it will lead to the deterioration of the SiO powder.

[0077] Comparative Example 3

[0078] Unlike the technical solution of this invention, the temperature of the negative pressure heat treatment is 1500℃.

[0079] Clean the C / C composite material with anhydrous ethanol and dry it in an oven at 70°C. Prepare a nickel nitrate ethanol solution of approximately 0.2 mol / L. Immerse the C / C composite material in the nickel nitrate solution for about 20 minutes, and then dry it in an oven at 90°C.

[0080] Weigh 3g of SiO powder and 1g of Al powder, and grind them in an agate mortar for about 30 minutes to obtain a mixed powder. Spread the mixed powder in a graphite crucible, and use a molybdenum wire to suspend the C / C composite material loaded with the catalyst about 1cm above the powder, and then seal the crucible.

[0081] The sealed crucible was suspended in the isothermal zone of a vertical tube furnace. A vacuum was evacuated to 4 kPa and held for 1 hour. After no significant pressure change, the temperature was increased to 1500℃ at a rate of 5℃ / min, with Ar as the protective gas introduced at a flow rate of approximately 300 sccm. Upon reaching the desired temperature, the vacuum pump and Ar were turned off, creating a sealed environment and holding for 2 hours. After holding, the vacuum pump and Ar were turned on, and the heating power was turned off. The sample was cooled with the furnace, with the Ar flow rate remaining at 300 sccm. After cooling to room temperature, the sample was removed. The nanowires on the C / C composite surface were interconnected, and the amorphous layer on the surface fractured into spherical shapes due to surface tension. The integrity and uniformity of the nanowire morphology were disrupted. Figure 6 As shown in (c).

[0082] Furthermore, the photoluminescence properties of the Al-doped core-shell SiC nanowires prepared in Example 1 and the undoped core-shell SiC nanowires were also tested. First, the nanowires were dissolved in pure water (1 mg / ml) and a suspension was formed by ultrasonication and vortexing. Two ml of the nanowire suspension was placed in a four-sided transparent quartz cuvette, then placed in a fluorescence spectrophotometer with a filter to eliminate the influence of the overtone peak. The excitation wavelength was 325 nm during the test. The test results are as follows: Figure 4 As shown, from Figure 4 As can be seen, compared with SiC nanowires and SiC@SiO2 nanowires, the photoluminescence intensity of Al-doped nanowires is increased by about 2.5 times and 36%, respectively, proving that the Al-doped core-shell structured SiC nanowires prepared in this invention have application value in the field of optoelectronics.

[0083] This invention also tested the self-healing properties of the Al-doped core-shell SiC nanowires prepared in Example 1 and the undoped core-shell SiC nanowires. First, an Al-doped SiC nanowire layer was prepared on the surface of a C / C composite material. Then, a SiC coating was prepared using chemical vapor deposition to densify the nanowire network. Next, a Vickers hardness tester was used to create a pre-crack in the coating cross-section, and the initial state of the crack was observed and recorded under a scanning electron microscope. Finally, the pre-cracked coating was oxidized in a muffle furnace at 1500℃ for 5 min, and the state of the healed crack was observed and recorded under a scanning electron microscope. The test results are as follows: Figure 5 As shown in the figure, the crack healing effect of the Al-doped core-shell SiC nanowire-toughened SiC coating is better, proving that the Al-doped core-shell SiC nanowire is also suitable for the field of ceramic coatings. This also demonstrates the multifunctionality of the Al-doped core-shell SiC nanowire prepared by the method of this invention.

[0084] In summary, this invention proposes a method for preparing multifunctional Al-doped core-shell SiC nanowires. Using SiO powder and Al powder as precursors, a large quantity of Al-doped core-shell SiC nanowires can be synthesized on various substrate surfaces at relatively low temperatures through grinding and mixing. This method can prepare a large quantity of uniformly sized Al-doped core-shell SiC nanowires at low temperatures, at low cost, and with high efficiency. The prepared nanowires exhibit good photoluminescence properties and promote the self-healing properties of the coating at high temperatures. The synthesized nanowires have the following characteristics: diameter distribution between 100 and 130 nm; a crystalline Al-doped SiC core with a diameter of approximately 50–80 nm at the center; and an outer layer of amorphous Al-doped SiO2 with a thickness of approximately 30–50 nm. The constituent elements of the nanowires are Si, O, C, and Al. The nanowire length can reach the millimeter scale.

[0085] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing multifunctional Al-doped core-shell structured SiC nanowires, characterized in that, include: The mixed powder obtained by thoroughly mixing SiO powder and Al powder is used as the precursor powder; A catalyst-loaded matrix is ​​suspended above the precursor powder, then sealed, and then subjected to negative pressure heat treatment at 1250~1400 °C to prepare multifunctional Al-doped core-shell structured SiC nanowires. The diameter of the multifunctional Al-doped core-shell SiC nanowires is between 100 and 130 nm. The multifunctional Al-doped core-shell SiC nanowire has a crystalline Al-doped SiC core at its center, with a diameter of 50-80 nm, and an outer layer of amorphous Al-doped SiO2 with a thickness of 30-50 nm. The multifunctional Al-doped core-shell SiC nanowire has no interconnections.

2. The method for preparing multifunctional Al-doped core-shell structured SiC nanowires according to claim 1, characterized in that, Includes the following steps: 1) Select SiO powder and Al powder, grind them evenly, and prepare a mixed powder as a precursor powder; 2) Spread the mixed powder evenly on the bottom of the crucible, suspend the catalyst-loaded matrix above the precursor powder using molybdenum wire, and seal the crucible; 3) The crucible processed in step 2) is suspended in the constant temperature zone of a vertical tube furnace. After confirming the airtightness, inert gas is introduced and the vacuum pump is turned on. The temperature is raised from room temperature to 1250~1400 ℃. Then, the inert gas is stopped and the vacuum pump is turned off. The temperature is maintained in this closed environment for 2~5 h. Then, inert gas is introduced again and the vacuum pump is turned on. The temperature is naturally cooled to room temperature to obtain Al-doped core-shell structured SiC nanowires.

3. The method for preparing multifunctional Al-doped core-shell structured SiC nanowires according to claim 1 or 2, characterized in that, The particle size of SiO powder is 5~10 μm, the particle size of Al powder is 30~50 μm, the mass ratio of SiO powder to Al powder is (8:1)~(3:1), and the mixed powder is prepared by grinding for 30~60 min.

4. The method for preparing multifunctional Al-doped core-shell structured SiC nanowires according to claim 1 or 2, characterized in that, The catalyst-supported matrix was prepared by the following method: After cleaning the substrate, it is immersed in a nickel nitrate ethanol solution for 10-30 minutes and then dried to obtain the final product.

5. The method for preparing multifunctional Al-doped core-shell structured SiC nanowires according to claim 4, characterized in that, The substrate is made of carbon / carbon composite material, graphite, SiC ceramic, or SiC coating prepared by CVD method.

6. The method for preparing multifunctional Al-doped core-shell structured SiC nanowires according to claim 4, characterized in that, The cleaning process uses anhydrous ethanol; the molar concentration of the nickel nitrate ethanol solution is 0.2~1 mol / L; the drying process is performed at 70~90 ℃.

7. The method for preparing multifunctional Al-doped core-shell structured SiC nanowires according to claim 2, characterized in that, In step 2), the catalyst-loaded matrix is ​​suspended 1-3 cm above the precursor powder using molybdenum wire.

8. The method for preparing multifunctional Al-doped core-shell structured SiC nanowires according to claim 2, characterized in that, In step 3), the pressure inside the furnace is maintained at 5~7 kPa during the vacuum pressure holding process.

9. Multifunctional Al-doped core-shell structured SiC nanowires prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The diameter of the multifunctional Al-doped core-shell SiC nanowires is between 100 and 130 nm. The center of this multifunctional Al-doped core-shell structured SiC nanowire is a crystalline Al-doped SiC core with a diameter of 50-80 nm, and the outer layer is an amorphous Al-doped SiO2 layer with a thickness of 30-50 nm. The constituent elements of this multifunctional Al-doped core-shell structured SiC nanowire are Si, O, C, and Al.

10. The application of the multifunctional Al-doped core-shell structure SiC nanowires of claim 9 in the preparation of semiconductor materials, optoelectronic materials, ceramic coating materials or aerospace substrate materials.

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