Method for efficiently preparing SiC whiskers at low temperature

Abstract

The invention relates to a method for efficiently preparing SiC whiskers at low temperature, and belongs to the technical field of material preparation. According to the method, polycrystalline silicon waste is selected as a silicon source, organic acid coating activation treatment is carried out, a renewable biomass material with a wide source is selected as a carbon source, trace nitrate is combined for catalysis assistance and reaction atmosphere regulation and control, and synthesis of the SiC crystal whiskers with controllable size, high crystallinity and uniform distribution is realized at a relatively low temperature of 1100-1300 DEG C. According to the method, the polycrystalline silicon waste is used for preparing the SiC crystal whiskers for the first time, the advantage of high reaction activity of the biomass charcoal is fully played, the gas-solid interface reaction process is enhanced, the generation and growth temperature of the SiC crystal whiskers is effectively reduced, and the reaction efficiency is improved. The whole process provided by the invention is green and environment-friendly, is simple and convenient to operate, has the characteristics of energy conservation, emission reduction and high-value utilization of solid wastes, has good industrial application potential, and is particularly suitable for the fields of green preparation of high-performance ceramic reinforced phases, functional composite materials and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of material preparation, and in particular relates to a method for preparing SiC whiskers at low temperature and high efficiency. Background Art

[0002] Silicon carbide (SiC) is an important structural ceramic material with excellent mechanical properties, thermal stability, high-temperature oxidation resistance, electrical properties, and corrosion resistance. It is widely used in aerospace, automotive, metallurgy, chemical engineering, and electronic devices. SiC whiskers, as one-dimensional nanomaterials, possess a high aspect ratio, excellent mechanical strength, high modulus, and good thermal shock resistance. They are valuable in reinforcing ceramic-, metal-, and polymer-based composites, significantly improving their fracture toughness, strength, and wear resistance. Conventional SiC whisker preparation methods require high raw materials, such as carbon sources (such as graphite and carbon black) and silicon sources (such as high-purity Si powder and SiO2). These processes also face challenges such as high cost, low yield, and limited or non-renewable raw material sources, hindering the industrial preparation and widespread application of SiC whiskers. Therefore, there is an urgent need to develop a novel method for preparing morphology-controlled SiC whiskers at lower temperatures using low-cost, green raw materials.

[0003] Polysilicon, a crucial building block for the electronics and photovoltaic industries, generates significant amounts of waste scrap and cutting powder (containing micron-sized, high-purity silicon particles) during its slicing and processing. Currently, much of this waste is not efficiently utilized, with crude disposal methods resulting in resource waste and environmental risks.

[0004] Biomass is a renewable resource with a wide range of sources in my country. It has large surface area and high reactivity, making it a potential high-quality carbon source. However, its high-value utilization rate is low. Therefore, the efficient use of biomass resources not only solves my country's ecological and environmental problems, but also enables the resource utilization of waste. Currently, the technology for the low-temperature and efficient synthesis of SiC whiskers by the synergistic reaction of polysilicon waste and biochar has not yet been developed. Summary of the Invention

[0005] The present invention aims to provide a method for producing SiC whiskers at low temperature and high efficiency. The method utilizes inexpensive, renewable biochar as a carbon source and polysilicon waste as a silicon source, and achieves in-situ growth of SiC whiskers by controlling temperature and atmosphere.

[0006] The innovation of this technology lies in: for the first time, polycrystalline silicon waste is used as a silicon source after activation treatment for the preparation of SiC whiskers, effectively reducing waste and increasing its utilization value. At the same time, waste biomass materials are selected and activated to prepare biochar with a large specific surface area and high reactivity as a carbon source. Under carbon burial conditions, the reaction atmosphere is regulated to promote the generation of CO(g) and SiO(g), thereby optimizing the growth environment of SiC whiskers. Compared with traditional carbon sources and silicon sources, this method can prepare SiC whiskers at a lower synthesis temperature. The synthesized SiC whiskers have the characteristics of high crystallinity, large aspect ratio, and uniform distribution. They have broad application prospects in the field of green preparation of high-performance ceramic reinforcement phases and functional composite materials. In addition, this method achieves high-value utilization of solid waste resources, and at the same time has the advantages of simple process, energy conservation and emission reduction, resource sustainability and environmental friendliness, providing a new technical path for the large-scale preparation of SiC whiskers.

[0007] To achieve the above object, the technical solution adopted by the present invention is: A method for preparing SiC whiskers at low temperature and high efficiency comprises the following steps: (1) Soak the polysilicon waste in an organic acid solution for 30 to 60 minutes and then dry it at 120 to 150°C; (2) After washing the biomass material, soak it in a nitrate solution for 30 to 60 minutes, then dry it at 120 to 150°C, and carbonize it in an argon atmosphere to obtain biochar; (3) mixing the biochar and the polysilicon waste treated in step (1) in a mass ratio of 1.2:1 to 1.5:1, ball-milling the mixture until uniform, and granulating the mixture to obtain precursor particles; (4) placing the precursor particles in a graphite crucible, and placing the graphite crucible in an alumina crucible, and covering it with carbon powder to form a carbon-buried system to create a reducing atmosphere; (5) Place the crucible in a high-temperature furnace, heat it to 1100-1300°C at a rate of 5-10°C / min, and keep it at that temperature for 1-3 hours to obtain SiC whisker products.

[0008] Furthermore, the polysilicon waste in step (1) is scraps and cutting powder generated during the production process of polysilicon cells, with a particle size of ≤20μm.

[0009] Furthermore, the organic acid solution in step (1) is a citric acid solution or an oxalic acid solution, and the concentration is 0.5-1 mol / L.

[0010] Furthermore, the biomass material in step (2) is selected from one or more of coconut shells, corn cobs, corn stalks, and bamboo.

[0011] Furthermore, the nitrate solution in step (2) is one of Fe(NO3)3, Co(NO3)2 and Ni(NO3)2 solutions, with a concentration of 0.5-1 mol / L.

[0012] Furthermore, in step (2), the temperature of the carbonization treatment is 600-800° C., the carbonization time is 1-3 h, and the argon flow rate is 50 mL / min.

[0013] Furthermore, in step (3), the ball milling speed of the biomass charcoal and polysilicon waste mixture is 200 r / min, and the ball milling time is 1-2 h.

[0014] Furthermore, the particle size of the precursor particles in step (3) is 1-2 mm.

[0015] Furthermore, in step (4), the precursor particles occupy 1 / 2-2 / 3 of the volume of the graphite crucible.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses organic acid to perform surface activation treatment on polysilicon waste to form a surface complexing layer, thereby enhancing its specific surface area and reactivity and solving the problem of polysilicon waste disposal.

[0017] 2. The present invention uses nitrate to catalyze biomass to prepare biochar with large specific surface area and high reaction activity, providing a basis for the efficient utilization of biomass resources.

[0018] 3. The present invention uses activated polysilicon waste as the silicon source and biochar as the carbon source. By regulating the raw material ratio and reaction atmosphere, efficient synthesis of SiC whiskers is achieved under low temperature conditions of 1100~1300℃.

[0019] 4. The biochar in the present invention has a developed microporous structure, which is conducive to the generation and diffusion of SiO(g) and CO(g) gases, optimizing the growth environment of SiC whiskers. At the same time, nitrate catalyzes the growth of SiC whiskers. The prepared SiC whiskers have the characteristics of smooth surface, high aspect ratio, and excellent crystallinity.

[0020] 5. The process of the present invention is simple, easy to operate, and the raw materials are extensive and low-cost, making it suitable for large-scale production and providing a new technical approach for the commercial application of SiC whiskers. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the X-ray diffraction pattern of the SiC whisker prepared in Example 3 of the present invention; Figure 2 This is a scanning electron microscope image of SiC whiskers prepared in Example 3 of the present invention; Figure 3for Figure 2 A partial enlarged view of Figure 4 This is a transmission electron microscope image of the SiC whisker prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0023] In the following embodiments, polysilicon waste is derived from cutting residues generated by the polysilicon ingot slicing process in the photovoltaic industry, wherein Si accounts for 86 wt%, SiO2 accounts for 9 wt%, SiC accounts for 3 wt%, Fe accounts for 1.2 wt%, and the remaining components account for 0.8 wt%. Example 1

[0024] The method for preparing SiC whiskers in this embodiment is as follows: (1) Soak the polysilicon waste in 1 mol / L oxalic acid solution for 30 min and then dry it at 120°C; (2) After washing, the coconut shell was soaked in a 0.5 mol / L ferric nitrate solution for 30 min, then dried at 120 °C, and carbonized at 800 °C for 3 h in an argon atmosphere with a gas flow rate of 50 mL / min; (3) Coconut shell charcoal and polysilicon waste treated in step (1) were weighed in a mass ratio of 1.2:1, uniformly mixed in a ball mill at a speed of 200 r / min for 1 h, and granulated to obtain precursor particles with a particle size of 1-2 mm; (4) Placing the precursor particles in a graphite crucible, with the precursor particles occupying 2 / 3 of the volume of the graphite crucible, and placing the graphite crucible in an alumina crucible, covering it with carbon powder to form a buried carbon system, creating a reducing atmosphere; (5) Place the crucible in a high-temperature furnace, heat it to 1200°C at a rate of 5°C / min, and keep it at that temperature for 2 h to obtain SiC whisker products.

[0025] In this embodiment, the surface area of ​​the treated coconut shell charcoal reached 1854m 2 / g, the prepared SiC whisker product is mainly composed of β-SiC with a purity of more than 99%, a length of 20-30 μm, a diameter of 30-50nm, and a smooth surface and uniform distribution. Example 2

[0026] The method for preparing SiC whiskers in this embodiment is as follows: (1) Soak the polysilicon waste in 1 mol / L citric acid solution for 30 min and then dry it at 120°C; (2) After washing, the coconut shells and corn cobs were soaked in a 0.5 mol / L cobalt nitrate solution for 30 min, dried at 120 °C, and carbonized at 800 °C for 2 h in an argon atmosphere with a gas flow rate of 50 mL / min; (3) Coconut shell charcoal, corn cob charcoal and polysilicon waste treated in step (1) were weighed in a mass ratio of 0.6:0.6:1, uniformly mixed in a ball mill at a speed of 200 r / min for 1 h, and granulated to obtain precursor particles with a particle size of 1-2 mm; (4) Placing the precursor particles in a graphite crucible, with the precursor particles occupying 2 / 3 of the volume of the graphite crucible, and placing the graphite crucible in an alumina crucible, covering it with carbon powder to form a buried carbon system, creating a reducing atmosphere; (5) Place the crucible in a high-temperature furnace, heat it to 1200°C at a rate of 5°C / min, and keep it at that temperature for 2 h to obtain SiC whisker products.

[0027] In this embodiment, the specific surface area of ​​the treated coconut shell charcoal reached 1963m 2 / g, the specific surface area of ​​corn cob charcoal is 2117m 2 / g, the prepared SiC whisker product is mainly composed of β-SiC with a purity of more than 99.5%, a length of 30-40µm, a diameter of 25-40nm, and a smooth surface and uniform distribution. Example 3

[0028] The method for preparing SiC whiskers in this embodiment is as follows: (1) Soak the polysilicon waste in 1 mol / L citric acid solution for 30 min and then dry it at 120°C; (2) After washing, corn cobs and corn stalks were soaked in a 0.5 mol / L nickel nitrate solution for 30 min, dried at 120 °C, and carbonized at 600 °C for 2 h in an argon atmosphere with a gas flow rate of 50 mL / min; (3) corn cob charcoal, corn straw charcoal and polysilicon waste treated in step (1) were weighed in a mass ratio of 0.8:0.7:1, uniformly mixed in a ball mill at a speed of 200 r / min for 1 h, and granulated to obtain precursor particles with a particle size of 1-2 mm; (4) Placing the precursor particles in a graphite crucible, with the precursor particles occupying 2 / 3 of the volume of the graphite crucible, and placing the graphite crucible in an alumina crucible, covering it with carbon powder to form a buried carbon system, creating a reducing atmosphere; (5) Place the crucible in a high-temperature furnace, heat it to 1200°C at a rate of 5°C / min, and keep it at that temperature for 2 h to obtain SiC whisker products.

[0029] In this embodiment, the specific surface area of ​​the treated corn cob charcoal reached 2258m 2 / g, the specific surface area of ​​corn straw charcoal is 2536m 2 / g, the prepared SiC whisker product is mainly composed of β-SiC with a purity of more than 99.8%, a length of 40-50µm, a diameter of 20-35nm, and a smooth surface and uniform distribution.

[0030] See also Figure 1 , which is the X-ray diffraction pattern of SiC whiskers prepared in Example 3 of the present invention. Figure 1 It can be seen that the SiC whiskers are mainly composed of β-SiC, and no other diffraction peaks appear, indicating that the SiC whiskers are of high purity.

[0031] See also Figure 2 and Figure 3 , which is a scanning electron microscope image of SiC whiskers prepared in Example 3 of the present invention. Figure 2 and Figure 3 It can be seen that the SiC whiskers are evenly distributed, curved, about tens of microns in length, and have a high aspect ratio, which can reach 1500-2500.

[0032] See also Figure 4 , which is a transmission electron microscope image of SiC whiskers prepared in Example 3 of the present invention. Figure 4 It can be seen that the SiC whiskers have a smooth surface, are well developed, and have a diameter of about 20-35 nm.

[0033] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the invention, and the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing SiC whiskers at low temperature and high efficiency, characterized in that: The method comprises the following steps: (1) Soak the polysilicon waste in an organic acid solution for 30 to 60 minutes and then dry it at 120 to 150°C; (2) After washing the biomass material, soak it in a nitrate solution for 30 to 60 minutes, then dry it at 120 to 150°C, and carbonize it in an argon atmosphere to obtain biochar; (3) mixing the biochar and the polysilicon waste treated in step (1) in a mass ratio of 1.2:1 to 1.5:1, ball-milling the mixture until uniform, and granulating the mixture to obtain precursor particles; (4) placing the precursor particles in a graphite crucible, and placing the graphite crucible in an alumina crucible, and covering it with carbon powder to form a carbon-buried system to create a reducing atmosphere; (5) Place the crucible in a high-temperature furnace, heat it to 1100-1300°C at a rate of 5-10°C / min, and keep it at that temperature for 1-3 hours to obtain SiC whisker products.

2. The method for preparing SiC whiskers at low temperature and high efficiency according to claim 1, wherein The polysilicon waste in step (1) is scraps and cutting powder generated during the production process of polysilicon cells, with a particle size of ≤20 μm.

3. The method for preparing SiC whiskers at low temperature and high efficiency according to claim 1, wherein The organic acid solution in step (1) is a citric acid solution or an oxalic acid solution with a concentration of 0.5-1 mol / L.

4. The method for preparing SiC whiskers at low temperature and high efficiency according to claim 1, wherein In step (2), the biomass material is selected from one or more of coconut shells, corn cobs, corn stalks, and bamboo.

5. The method for preparing SiC whiskers at low temperature and high efficiency according to claim 1, wherein The nitrate solution in step (2) is one of Fe(NO3)3, Co(NO3)2 and Ni(NO3)2 solutions, with a concentration of 0.5-1 mol / L.

6. The method for preparing SiC whiskers at low temperature and high efficiency according to claim 1, wherein: The temperature of the carbonization treatment in step (2) is 600-800°C, the carbonization time is 1-3h, and the argon flow rate is 50mL / min.

7. The method for preparing SiC whiskers at low temperature and high efficiency according to claim 1, wherein: In the step (3), the ball milling speed of the biomass charcoal and polysilicon waste mixture is 200 r / min, and the ball milling time is 1-2 h.

8. The method for preparing SiC whiskers at low temperature and high efficiency according to claim 1, wherein: The particle size of the precursor particles in step (3) is 1-2 mm.

9. The method for preparing SiC whiskers at low temperature and high efficiency according to claim 1, wherein: In step (4), the precursor particles occupy 1 / 2-2 / 3 of the volume of the graphite crucible.

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