Method for preparing wide band gap SiC from waste fan blades

Abstract

The application discloses a method for preparing wide-bandgap silicon carbide by using waste fan blades, and belongs to the technical field of solid waste resource utilization and semiconductor material preparation. The method comprises the following steps in sequence: carrying out crushing and separation pretreatment on the waste fan blades; carrying out pyrolysis carbonization on the blade particles after the pretreatment, so as to obtain a composite precursor rich in amorphous carbon and glass fibers; carrying out activation treatment on the composite precursor by using a mechanical ball milling method, so as to obtain a high-reactivity precursor; carrying out high-temperature carbon thermal reduction reaction on the high-reactivity precursor in an inert atmosphere, so as to generate silicon carbide crystals; and carrying out impurity removal and purification treatment on the reaction product, so as to obtain wide-bandgap SiC powder. The application takes the waste fan blades as the only carbon source and silicon source, realizes high-value utilization of the solid waste, and the prepared SiC is a wide-bandgap semiconductor material, has high purity and good crystal form, and is suitable for high-frequency and high-voltage electronic devices. The method has the advantages of low cost, green environmental protection and simple process.

Description

Technical Field

[0001] This invention relates to the interdisciplinary field of solid waste resource utilization and advanced inorganic non-metallic material preparation, and more specifically, to a method for preparing wide-bandgap semiconductor material silicon carbide using waste wind turbine blades as raw materials. Background Technology

[0002] Silicon carbide, as a core material for third-generation wide-bandgap semiconductors, exhibits enormous application potential in high-temperature, high-frequency, and high-voltage fields such as new energy vehicles, smart grids, and 5G communications due to its high breakdown electric field, high saturated electron drift velocity, high thermal conductivity, and excellent chemical stability. However, current industrial production of silicon carbide primarily employs the Atcheson process, using high-purity petroleum coke and quartz sand as raw materials, and carrying out a carbothermic reduction reaction at temperatures exceeding 2000℃. This process suffers from significant energy consumption, high raw material costs, and environmental impact.

[0003] On the other hand, with the booming development of the wind power industry, early-installed wind turbines are gradually entering their decommissioning period. Wind turbine blades are mainly made of glass fiber reinforced epoxy resin or polyester resin composite materials, which are chemically stable and extremely difficult to degrade naturally. Currently, the vast majority of waste wind turbine blades are disposed of through landfill or simple incineration, which not only occupies a large amount of land resources but also causes environmental pollution and resource waste. The resin in wind turbine blades is a rich carbon source, while glass fiber is rich in silicon dioxide, which is precisely the key element required for the synthesis of silicon carbide. Therefore, developing a technology that can convert waste wind turbine blades into high-value-added SiC materials has both environmental and economic value.

[0004] Currently, several studies have proposed different methods for preparing silicon carbide (SiC). For example, patent CN120987656A (a method for preparing SiC by silicon nitride-assisted sintering) uses oxygen-containing silicon nitride as a sintering aid to prepare high-purity silicon carbide through high-temperature sintering (2000-2200℃). This method improves the sintering density and mechanical properties to some extent, but it suffers from problems such as excessively high sintering temperature, high energy consumption, and demanding equipment requirements. Another patent, CN120441322A (a method for preparing SiC ceramic powder by combining precursor conversion with microwave heating), innovatively combines precursor conversion with microwave heating. It utilizes the SiOC system precursor and carbon powder to rapidly react and synthesize SiC under microwave action. This method has the advantages of fast heating speed and relatively low energy consumption, but it still relies on high-purity precursor raw materials, resulting in higher costs, and the controllability of microwave plasma effects needs to be improved. In addition, patent CN121083952A (a method for preparing and applying a SiC / SiC composite V-shaped structural component) uses a precursor impregnation pyrolysis (PIP) process to prepare SiC / SiC composite materials. By alternating densification treatment with and without mold, internal stress accumulation is reduced, resulting in a structural component with good shape stability. This method has advantages in the molding of complex structural components, but the process is complex, the cycle is long, and it also faces the problem of high raw material costs.

[0005] Despite the progress made by the above technologies in improving the properties of SiC materials and optimizing the preparation process, the following challenges remain:

[0006] (1) Existing methods generally rely on high-purity fossil-based raw materials (such as petroleum coke, quartz sand, polycarbosilane, etc.), which are expensive and contradict the current concept of circular economy;

[0007] (2) Most preparation processes require high temperature (>1500℃ or even >2000℃) or long time processing, resulting in huge energy consumption, which does not meet the requirements of green and low-carbon development.

[0008] (3) Solid wastes such as waste wind turbine blades, which are rich in carbon and silicon sources, have not been effectively utilized for high-value purposes. A large number of retired blades face landfill or incineration, resulting in serious waste of resources and environmental pollution.

[0009] Therefore, this invention proposes an innovative method for preparing wide-bandgap SiC from waste wind turbine blades. Through a synergistic process of "pyrolytic carbonization-mechanical activation-carbothermic reduction," it utilizes waste wind turbine blades as the sole carbon and silicon source for the first time, achieving high-value utilization of solid waste. Compared with existing technologies, this invention has the following significant advantages:

[0010] (1) Raw material innovation and environmental value: Using waste wind turbine blades as raw materials, the cost is extremely low or even negative (processing fee), while solving the solid waste pollution problem caused by the retirement of wind turbine blades, realizing "using waste to treat waste and turning waste into treasure";

[0011] (2) Energy saving and consumption reduction: Mechanical ball milling activation significantly reduces the temperature of the carbothermic reduction reaction (1400-1600℃, which is more than 20% lower than the >2000℃ of the traditional Atchison method), thus greatly saving energy consumption;

[0012] (3) Simple and controllable process: No complicated equipment and high-purity reagents are required. The process is simple and easy to scale up. It has good economic benefits and industrialization prospects.

[0013] (4) High added value of products: The SiC obtained is a wide bandgap semiconductor material (bandgap width ≥ 2.2eV), with high purity and good crystal form. It can be widely used in the field of high frequency and high voltage power electronic devices, realizing a perfect closed loop from "green waste" to "high value material". Summary of the Invention

[0014] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing wide bandgap SiC from waste wind turbine blades that is reasonable in process flow, low in cost, and environmentally friendly, so as to realize the high-value utilization of solid waste resources.

[0015] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0016] A method for preparing wide bandgap silicon carbide using waste wind turbine blades includes the following steps:

[0017] S1. Pretreatment: The waste wind turbine blades are mechanically crushed, and then metal connectors and other impurities are removed by magnetic separation and air separation to obtain clean blade particles with a particle size of 0.1-10mm.

[0018] S2. Pyrolysis and Carbonization: The blade particles obtained in step S1 are heated to 500-800℃ at a rate of 5-10℃ / min under an inert atmosphere (such as nitrogen or argon) and held at this temperature for 1-5 hours. During this process, the organic resin undergoes pyrolysis, generating volatile gases and leaving behind a porous carbon skeleton rich in amorphous carbon, which together with the glass fiber forms a composite precursor.

[0019] S3. Mechanical Activation: The composite precursor obtained in step S2 is subjected to high-energy mechanical ball milling for 2-12 hours at a ball-to-material ratio of 10:1 to 30:1. This process, through mechanochemical action, significantly reduces particle size, increases specific surface area, disrupts the stable structure of SiO2 in the glass fiber, and ensures thorough mixing and contact with amorphous carbon, thereby significantly improving reactivity and yielding a highly reactive precursor. Optionally, a small amount of magnesium powder or similar additives can be added as reaction aids to further reduce the subsequent reaction temperature.

[0020] S4. Carbothermic Reduction: The highly reactive precursor obtained in step S3 is placed in a high-temperature furnace and heated to 1400-1600℃ at a rate of 5-15℃ / min under an inert atmosphere or vacuum, and held for 1-6 hours. More preferably, the temperature is increased to 1500-1550℃ at a rate of 5-15℃ / min and held for 2-4 hours. At this high temperature, the core carbothermic reduction reaction occurs: SiO2(s) + 3C(s) → SiC(s) + 2CO(g), generating β-SiC crystals.

[0021] S5. Purification Treatment: Besides SiC, the reaction product also contains unreacted carbon, SiO2, and other impurities. The purification steps include: first, calcination in air at 600-700℃ for 1-3 hours to remove excess carbon; then washing with hot hydrochloric acid or nitric acid to dissolve metal oxide impurities; and finally soaking in 10-40wt% hydrofluoric acid to remove unreacted SiO2. After washing and drying, high-purity wide-bandgap SiC powder is obtained.

[0022] Preferably, the rotational speed of the mechanical ball mill in step S3 is 300-500 rpm.

[0023] Preferably, the inert atmosphere in step S4 is high-purity argon.

[0024] The present invention also claims protection for the wide bandgap silicon carbide material prepared by the above method, which is mainly β-SiC crystal form, has a purity of not less than 95%, a bandgap width of not less than 2.2 eV, and is suitable for the preparation of high frequency and high voltage power devices.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention systematically proposes to use waste wind turbine blades, a specific solid waste, as the sole carbon and silicon source to prepare high-value SiC, realizing "using waste to treat waste and turning waste into treasure", opening up a new path for the high-value utilization of waste wind turbine blades, and has significant environmental and social benefits.

[0027] 2. By combining "pyrolysis carbonization" and "mechanical ball milling activation," the problems of complex composition and low reactivity of wind turbine blades were synergistically solved. The mechanical activation step effectively reduced the reaction temperature of subsequent carbothermic reduction (from the traditional >1700℃ to 1400-1600℃), significantly reducing energy consumption.

[0028] 3. The prepared SiC is a wide bandgap semiconductor material with high purity and good crystal form. It can be directly used as an abrasive, ceramic reinforcement phase, or as a raw material for preparing semiconductor devices. Its economic value is far higher than that of traditional recycling methods.

[0029] 4. The raw material cost is extremely low, even negative (processing fee), and the process is relatively simple, making it easy to scale up production and giving it strong market competitiveness. Attached Figure Description

[0030] Figure 1 A process flow diagram for preparing wide bandgap silicon carbide using waste wind turbine blades. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0032] Example 1

[0033] S1. Take waste wind turbine blades, crush them, remove iron by magnetic separation, and air classify them to obtain particles with a diameter of about 1-3mm.

[0034] S2. Place the above particles in a tube furnace, heat to 600°C at 5°C / min under a nitrogen atmosphere, hold for 2 hours, and after natural cooling, obtain black blocky pyrolysis residue, which is then crushed and passed through a 100-mesh sieve.

[0035] S3. Take the above pyrolysis powder and put it into a high-energy ball mill jar at a ball-to-powder ratio of 20:1. Mill the powder at 400 rpm for 6 hours to obtain a highly reactive precursor.

[0036] S4. Place the precursor in an alumina crucible, put it into a vacuum atmosphere sintering furnace, evacuate the furnace, and then fill it with high-purity argon. Heat the furnace to 1500℃ at a rate of 10℃ / min, hold for 3 hours, and then cool it with the furnace.

[0037] S5. The reaction product was calcined at 650°C for 2 hours in air to remove carbon; then washed with 1M hydrochloric acid at 70°C for 1 hour and filtered; finally, it was soaked in 20wt% hydrofluoric acid at room temperature for 4 hours to remove residual SiO2. After washing with deionized water until neutral, it was dried to obtain gray-green SiC powder.

[0038] X-ray diffraction analysis revealed the product to be β-SiC, with a distinct main peak and few impurity peaks. Calculations showed the product purity to be approximately 96.5%.

[0039] Example 2

[0040] S1. Take waste wind turbine blades, crush them, remove iron by magnetic separation, and air classify them to obtain particles with a diameter of about 1-3mm.

[0041] S2. Place the above particles in a tube furnace, heat to 600°C at 5°C / min under a nitrogen atmosphere, hold for 2 hours, and after natural cooling, obtain black blocky pyrolysis residue, which is then crushed and passed through a 100-mesh sieve.

[0042] S3. Take the above pyrolysis powder and put it into a high-energy ball mill jar at a ball-to-powder ratio of 20:1. During ball milling, add 5% magnesium powder by weight of the pyrolysis powder as a reaction aid. Ball mill at 400 rpm for 6 hours to obtain a highly reactive precursor.

[0043] S4. Place the precursor in an alumina crucible, put it into a vacuum atmosphere sintering furnace, evacuate the furnace, and then fill it with high-purity argon. Heat the precursor to 1450℃ at 10℃ / min under an argon atmosphere, hold for 3 hours, and then cool it with the furnace.

[0044] S5. The reaction product was calcined at 650°C for 2 hours in air to remove carbon; then washed with 1M hydrochloric acid at 70°C for 1 hour and filtered; finally, it was soaked in 20wt% hydrofluoric acid at room temperature for 4 hours to remove residual SiO2. After washing with deionized water until neutral, it was dried to obtain gray-green SiC powder.

[0045] The obtained SiC powder was tested and found to have a purity of approximately 97.1%, with more uniform grain size. Compared to Example 1, the addition of magnesium powder as an additive enabled the synthesis of high-quality SiC at a lower temperature.

[0046] Example 3

[0047] S1. Take waste wind turbine blades, crush them, remove iron by magnetic separation, and air classify them to obtain particles with a particle size of about 0.5-2mm.

[0048] S2. Place the above particles in a tube furnace, heat to 700°C at 8°C / min under an argon atmosphere, hold for 1.5 hours, and after natural cooling, obtain the pyrolysis residue, which is then crushed and passed through a 100-mesh sieve.

[0049] S3. Take the above pyrolysis powder and put it into a high-energy ball mill jar at a ball-to-powder ratio of 15:1. Mill the powder at 450 rpm for 10 hours to obtain a highly reactive precursor.

[0050] S4. Place the precursor in a graphite crucible, put it into a vacuum atmosphere sintering furnace, evacuate the furnace, and then fill it with high-purity argon. Heat the furnace to 1550℃ at a rate of 12℃ / min, hold for 2 hours, and then cool it with the furnace.

[0051] S5. The reaction product was calcined at 680°C for 1.5 hours in air to remove carbon; then washed with 1.5M nitric acid at 75°C for 1.5 hours, and filtered; finally, it was soaked in 15wt% hydrofluoric acid at room temperature for 5 hours. After washing with deionized water until neutral, it was dried to obtain SiC powder.

[0052] The obtained SiC powder was tested and found to have a purity of approximately 97.8%. This example demonstrates the optimization effect under different pretreatment particle sizes, pyrolysis temperatures, ball milling parameters, and maximum reaction temperatures, proving the wide adaptability and adjustability of the process parameters. X-ray diffraction analysis confirmed the product to be β-SiC.

[0053] Example 4

[0054] S1. Take waste wind turbine blades, crush them, remove iron by magnetic separation, and air classify them to obtain particles with a diameter of about 1-3mm.

[0055] S2. Place the above particles in a tube furnace, heat to 600°C at 5°C / min under a nitrogen atmosphere, hold for 2 hours, and after natural cooling, obtain black blocky pyrolysis residue, which is then crushed and passed through a 100-mesh sieve.

[0056] S3. Take the above pyrolysis powder and put it into a high-energy ball mill jar at a ball-to-powder ratio of 20:1. During ball milling, add an additional 3% NaCl and 2% iron powder mixture as an auxiliary agent by mass of the pyrolysis powder. Ball mill at 400 rpm for 6 hours to obtain a highly reactive precursor.

[0057] S4. Place the precursor in an alumina crucible, put it into a vacuum atmosphere sintering furnace, evacuate the furnace, and then fill it with high-purity argon. The precursor is heated to 1480℃ at 10℃ / min under an argon atmosphere, held at that temperature for 3.5 hours, and then cooled with the furnace.

[0058] S5. The reaction product was calcined at 650°C for 2 hours in air to remove carbon; then washed with 1M hydrochloric acid at 70°C for 1 hour and filtered; finally, it was soaked in 20wt% hydrofluoric acid at room temperature for 4 hours to remove residual SiO2. After washing with deionized water until neutral, it was dried to obtain gray-green SiC powder.

[0059] The obtained SiC powder was tested and found to have a purity of approximately 96.9%. This example demonstrates that the mixed additives also have the effect of promoting the reaction and reducing the synthesis temperature.

[0060] Example 5

[0061] S1. Take waste wind turbine blades, crush them, remove iron by magnetic separation, and air classify them to obtain particles with a diameter of about 1-3mm.

[0062] S2. Place the above-mentioned blade particles in a tube furnace, heat to 500°C at 5°C / min under a nitrogen atmosphere, hold for 4 hours, and after natural cooling, obtain black blocky pyrolysis residue, which is then crushed and passed through a 100-mesh sieve.

[0063] S3. Take the above pyrolysis powder and put it into a high-energy ball mill jar at a ball-to-powder ratio of 25:1. Mill the powder at 350 rpm for 8 hours to obtain a highly reactive precursor.

[0064] S4. Place the precursor in an alumina crucible, put it into a vacuum atmosphere sintering furnace, evacuate the furnace, and then fill it with high-purity argon. Heat the precursor to 1520℃ at 8℃ / min under an argon atmosphere, hold for 4 hours, and then cool it with the furnace.

[0065] S5. The reaction product was calcined at 650°C for 2 hours in air to remove carbon; then washed with 1M hydrochloric acid at 70°C for 1 hour and filtered; finally, it was soaked in 20wt% hydrofluoric acid at room temperature for 4 hours to remove residual SiO2. After washing with deionized water until neutral, it was dried to obtain gray-green SiC powder.

[0066] The obtained SiC powder was tested and found to have a purity of approximately 95.2%. This example demonstrates that SiC can still be effectively prepared at relatively low pyrolysis temperatures by adjusting ball milling and reaction parameters.

[0067] Comparative Example 1

[0068] Without performing mechanical ball milling activation in step S3, the pyrolysis powder obtained in S2 is directly subjected to carbothermic reduction reaction in S4. The reaction temperature needs to be increased to 1600℃ and held for 4 hours to complete the reaction. Moreover, the content of unreacted SiO2 and C in the obtained SiC product is relatively high, and the purity is only 89.3%.

[0069] Comparative Example 2

[0070] Instead of using discarded wind turbine blades, this method uses a traditional ratio of quartz sand and anthracite powder as raw materials, reacting them at 1550℃ for 3 hours. Although the resulting SiC purity is as high as 98.5%, this method has high raw material costs and does not possess the environmental benefits of this invention.

[0071] Comparative Example 3

[0072] Without performing the pyrolysis carbonization step S2, the raw wind turbine blade particles after crushing and sorting in S1 were directly subjected to mechanical ball milling activation in S3, followed by carbothermic reduction in S4. The product after the reaction was severely agglomerated, and XRD analysis showed that it mainly consisted of cristobalite and a small amount of SiC. The carbothermic reaction was incomplete, and the SiC yield and purity were extremely low.

[0073] Comparative Example 4

[0074] In step S3, instead of high-energy ball milling, a conventional drum ball mill was used for low-speed ball milling at 60 rpm for 24 hours. The precursor was then subjected to carbothermic reduction at 1550°C. The resulting product contained significantly higher levels of unreacted SiO2 and C than in Example 1, with a SiC purity of only 90.1%, demonstrating that the mechanochemical activation effect of high-energy ball milling is crucial for improving the precursor's reactivity.

[0075] Comparative Example 5

[0076] By modifying the process in step S4, the highly reactive precursor was subjected to a carbothermic reduction reaction at 1300℃ for 6 hours. XRD analysis showed that the product mainly consisted of amorphous carbon and SiO2, with only a weak SiC diffraction peak detected, indicating that the reaction could not proceed effectively at this temperature, thus demonstrating the necessity of the temperature range selected in this invention.

[0077] Test Example 1

[0078] The products prepared in Examples 1-5 and Comparative Examples 1-5 were characterized in terms of performance, and the results are shown in Table 1 below.

[0079] Table 1

[0080]

[0081] The foregoing examples are merely illustrative, used to explain some features of the method described in this invention. The appended claims are intended to claim the broadest possible scope, and the embodiments presented herein are demonstrated by the applicant's actual experimental results. Therefore, the applicant intends that the appended claims are not limited by the selection of examples illustrating the features of the invention. Some numerical ranges used in the claims also include sub-ranges within them, and variations within these ranges should also be interpreted as being covered by the appended claims where possible.

Claims

1. A method for preparing wide bandgap silicon carbide using waste wind turbine blades, characterized in that, Includes the following steps: S1. Pretreatment: The waste wind turbine blades are crushed and sorted to obtain blade particles with a particle size of 0.1-10mm; S2. Pyrolysis and carbonization: The blade particles obtained in step S1 are pyrolyzed at 500-800℃ under an inert atmosphere and kept at that temperature for 1-5 hours to obtain pyrolysis residue, i.e., composite precursor. S3. Mechanical activation: The composite precursor obtained in step S2 is mechanically activated by ball milling for 2-12 hours to obtain a highly reactive precursor. S4. Carbothermic reduction: The highly reactive precursor obtained in step S3 is placed in a reactor and heated to 1400-1600℃ at a rate of 5-15℃ / min under an inert atmosphere or vacuum, and held for 1-6 hours to carry out the carbothermic reduction reaction and obtain the reaction product. S5. Purification treatment: The reaction product obtained in step S4 is subjected to carbon removal, acid washing and hydrofluoric acid washing in sequence to obtain purified wide bandgap SiC powder.

2. The method according to claim 1, characterized in that, In step S1, the sorting includes magnetic separation and air separation to remove metal impurities.

3. The method according to claim 1 or 2, characterized in that, In step S2, the heating rate of the pyrolysis treatment is 5-10℃ / min, and the inert atmosphere is nitrogen or argon.

4. The method according to claim 1, characterized in that, In step S3, the mechanical ball milling activation is performed using a high-energy ball mill with a ball-to-material ratio of 10:1 to 30:1 and a rotation speed of 300-500 rpm.

5. The method according to claim 1 or 4, characterized in that, In step S3, a reaction aid is added during mechanical ball milling. The reaction aid is one or more of magnesium powder, iron powder, or sodium chloride, and the amount added is 1%-10% of the mass of the composite precursor.

6. The method according to claim 1, characterized in that, In step S4, the optimal temperature for the carbothermic reduction reaction is 1500-1550℃, and the optimal holding time is 2-4 hours.

7. The method according to claim 1, characterized in that, In step S5, the carbon removal involves calcining the reaction product in air at 600-700°C for 1-3 hours; the acid washing involves washing with hydrochloric acid or nitric acid at 60-80°C for 1-2 hours; and the hydrofluoric acid washing involves soaking in 10-40wt% hydrofluoric acid at room temperature for 2-6 hours.

8. A wide bandgap silicon carbide material, characterized in that, The silicon carbide is prepared by the method described in any one of claims 1-7, wherein the silicon carbide is of β-SiC crystal form, has a purity ≥95%, and a band gap ≥2.2 eV.

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