Method for preparing silicon carbide by using waste granite stone powder and conductive carbon black

Abstract

This invention provides a method for preparing silicon carbide using waste granite powder and conductive carbon black, comprising the following steps: S1, mixing waste granite powder and conductive carbon black evenly to form a mixture; S2, ball milling the mixture and sieving it to obtain a refined mixture; S3, placing the refined mixture into a Joule apparatus and sintering it to prepare a multiphase composite powder; S4, calcining the multiphase composite powder at high temperature and then alkali washing to obtain silicon carbide powder. This invention achieves high-value recycling of waste granite powder, solving the problems of high energy consumption and long cycle time in traditional silicon carbide preparation processes, and avoiding the problems of large land occupation and significant pollution from the accumulation of building material waste. This invention aligns with the concept of green and low-carbon development, turning waste into treasure. By designing different raw material ratios and sintering parameters, different types of silicon carbide products can be prepared, creating economic benefits while controlling pollution.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic materials technology, specifically to a method for preparing silicon carbide using waste granite powder and conductive carbon black. Background Technology

[0002] Silicon carbide, as a typical representative of third-generation wide-bandgap semiconductor materials, has a bandgap of 3.2 eV, which is three times that of silicon, and possesses a high breakdown electric field strength (2.5 × 10⁻⁶ eV). 6 V / cm), high thermal conductivity (4.9 W / cm·K), and high electron saturation drift velocity (2×10⁻⁶). 7 Silicon carbide possesses superior properties such as high speed (cm / s). These unique properties give silicon carbide a significant advantage in high-temperature, high-frequency, and high-power electronic devices, leading to its widespread application in cutting-edge technology fields such as electric vehicle inverters, 5G base station radio frequency devices, and aerospace high-temperature sensors.

[0003] Traditional silicon carbide preparation technologies mainly include the Atchison process, chemical vapor deposition (CVD), and physical vapor transport (PVT). The Atchison process, as the primary method for industrial production, requires a long reaction time of 50–100 hours at 2400–2500℃, consuming 3000–4000 kWh / t of energy, and producing a product purity of only 95–98%, necessitating complex subsequent purification processes. While CVD can produce high-purity silicon carbide films, the growth rate is only 1–10 μm / h, requiring huge equipment investment, and the raw materials (such as SiH4 and CH4) are toxic and explosive, posing serious safety hazards. Although PVT produces high-quality silicon carbide single crystals, the crystal size is limited (currently the largest diameter is only 150 mm), and the crystal defect density remains as high as 10-1. 3 ~10 4 cm -2 This makes it difficult to meet the demand for high-end components.

[0004] In recent years, Joule heating technology, as a revolutionary rapid heating technology, can heat materials to over 3000°C within milliseconds by directly applying a pulsed high current to conductive materials, with a heating rate reaching 10-1. 5 The rapid Joule flash evaporation technique, with a speed of ℃ / s, provides a novel approach for the preparation of ultra-high temperature materials. A research team at Rice University in the United States has successfully prepared nanomaterials such as graphene and carbon nanotubes using this technique, but its application in the preparation of silicon carbide is still in its early stages.

[0005] During stone processing, approximately 20-30% of granite powder waste is generated, with a global annual production of 300 million tons. Current landfill disposal methods not only consume vast amounts of land resources, but the heavy metals contained in granite powder can also easily pollute soil and groundwater through leaching, causing a huge environmental burden. It is worth noting that the main chemical components of granite powder are SiO2 (55-75%) and Al2O3 (12-15%), which are precisely the silicon source and doping elements required for the synthesis of silicon carbide; while conductive carbon black, as an industrial byproduct, has a resistivity of only 0.89-1.12 Ω·mm, making it an ideal Joule heating medium. Therefore, developing a new technology for in-situ Joule heating of silicon carbide using granite powder and conductive carbon black as precursors not only achieves high-value resource utilization of industrial solid waste but also significantly reduces raw material costs, which has profound strategic significance for promoting the low-cost, large-scale application of silicon carbide materials. Summary of the Invention

[0006] To address the shortcomings and deficiencies of the existing technologies, this invention provides a simple, energy-efficient, and low-cost method for preparing silicon carbide from waste granite powder and conductive carbon black. This method enables the high-value recycling of waste granite powder, solving the problems of high energy consumption and long production cycles in traditional silicon carbide preparation processes, and avoiding the problems of large land occupation and significant pollution caused by the accumulation of building material waste. This invention aligns with the concept of green and low-carbon development, turning waste into treasure. By designing different raw material ratios and sintering parameters, different types of silicon carbide products can be prepared, creating economic benefits while controlling pollution.

[0007] One object of the present invention is to provide a method for preparing silicon carbide using waste granite powder and conductive carbon black, wherein the method for preparing silicon carbide using waste granite powder and conductive carbon black includes the following steps: S1. Mix waste granite powder and conductive carbon black evenly to prepare a mixture; S2. The mixture is ball-milled and then sieved to obtain a refined mixture; S3. Place the refined mixture into a Joule apparatus and sinter to prepare multiphase composite powder; S4. The multiphase composite powder is calcined at high temperature and then alkali washed to obtain silicon carbide powder.

[0008] Furthermore, the waste granite powder and conductive carbon black undergo a pre-drying treatment at a temperature of 50-70°C for 2-5 hours.

[0009] Furthermore, the mass ratio of the waste granite powder to the conductive carbon black is (20-50):(50-80).

[0010] Furthermore, the granite powder, by mass percentage, has the following composition: SiO2: 50-70 wt%, Al2O3: 20-30 wt%, Na2O+K2O: 5-10 wt%, CaO+MgO: 1-5 wt%, Fe2O3: 0-3 wt%.

[0011] Furthermore, in the granite powder of this invention, Al2O3 can participate in the construction of a silicon-aluminum-oxygen network structure, regulating the structural stability of the reaction system at high temperatures, which is beneficial to the continuous progress of the carbothermic reduction reaction. On the other hand, CaO and alkali metal oxides (K2O, Na2O) can act as fluxing components, forming a low-melting-point liquid phase during the reaction process, reducing the activation energy of SiO2, improving its contact and reaction efficiency with the carbon source, thereby promoting the formation of SiC. In addition, the above-mentioned alkali metal and alkaline earth metal oxides can also improve the overall electrical conductivity of the material in the Joule heating system, making the current distribution more uniform, thereby improving the heating efficiency and reducing local overheating, which is beneficial to obtaining silicon carbide products with uniform particle size distribution.

[0012] Furthermore, the resistivity of the conductive carbon black is 0.89-1.12 Ω·mm.

[0013] Furthermore, the particle size of the refined mixture is 100-200 mesh.

[0014] Furthermore, the Joule device is an HTS Joule ultrafast heating device.

[0015] Furthermore, the sintering temperature is 1600-2000℃, the voltage is 25-32 V, and the current is 80-150 A.

[0016] Furthermore, the vacuum degree of the sintering is 10-100 Pa.

[0017] Furthermore, the high-temperature calcination temperature is 500-800℃, and the time is 3-5 h.

[0018] Furthermore, the reagent for alkaline washing is a 30-50 wt% NaOH solution.

[0019] Furthermore, the reaction mechanism of this invention is based on a carbothermic reduction reaction: SiO₂ + 3C → SiC + 2CO↑ SiO2 in granite powder undergoes a reduction reaction with conductive carbon black at high temperatures to produce SiC. The conductive carbon black not only participates in the reaction as a reactant but also acts as a heating element in Joule heating, enabling rapid temperature rise.

[0020] Further, step S3 includes: The refined mixture is placed in a graphite carrier and compacted, then placed in a vacuum Joule furnace. The preset voltage and current parameters are applied through the control system to execute a rapid sintering process.

[0021] This invention utilizes the moderate resistivity of a graphite carrier to generate a strong Joule heating effect upon the application of electricity, achieving a temperature jump from room temperature to 1600-2500℃ within 1-10 seconds. Up to 10 4 K s -1 The ultra-high heating rate provides a non-equilibrium thermal shock to the reaction system, which not only breaks through the heating rate bottleneck of traditional thermal equipment, but also facilitates the induction of rapid carbothermic reduction and crystallization of the precursor. At the same time, the high-temperature chemical stability of the graphite matrix effectively blocks the side reaction pathways with Si / SiO / CO, ensuring product purity and significantly reducing the level of lattice defects.

[0022] The present invention has the following beneficial effects: The method for preparing silicon carbide using waste granite powder and conductive carbon black provided by this invention has advantages such as high ecological value and good economic benefits. (1) Utilize granite powder solid waste as a silicon source to realize resource utilization and turn waste into treasure; (2) Joule heating technology reduces the reaction time from several hours to 1-10 seconds, making the process fast and efficient; (3) It saves more than 75% energy compared to traditional methods, making it more energy-efficient and environmentally friendly; (4) The prepared silicon carbide has high purity and good crystallinity, and has excellent electrical properties. Attached Figure Description

[0023] Figure 1 The appearance of the high-purity silicon carbide prepared in Example 1 is shown.

[0024] Figure 2 A flowchart of the method for preparing silicon carbide using waste granite powder and conductive carbon black is shown.

[0025] Figure 3 The X-ray diffraction (XRD) analysis results of the product of Example 1 are shown.

[0026] Figure 4 The scanning electron microscope (SEM) results of the product of Example 1 are shown. Detailed Implementation

[0027] To more clearly illustrate the technical solution of the present invention, the following embodiments are provided. Unless otherwise stated, the raw materials, reactions, and post-processing methods appearing in the embodiments are all commercially available raw materials and technical methods well known to those skilled in the art.

[0028] The terms "preferred," "more preferably," and "more suitable" used in this invention refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this invention.

[0029] It should be understood that, except in any operational instance or otherwise indicated, the amounts or all figures representing ingredients used, for example, in the specification and claims, should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise stated, the numerical parameters set forth in the following specification and appended claims are approximate values ​​varying according to the desired performance to be obtained according to the invention.

[0030] The main chemical composition of the waste granite powder in this embodiment of the invention, by mass percentage, is as follows: SiO2 61.80 wt%, Al2O3 26.57 wt%, Na2O 2.29 wt%, K2O 4.60 wt%, CaO 3.87 wt%, MgO 0.15 wt%, and Fe2O3 0.13 wt%.

[0031] The resistivity of the conductive carbon black in this embodiment of the invention is 1.02 Ω·mm.

[0032] Example 1 A method for preparing silicon carbide using waste granite powder and conductive carbon black, the method comprising the following steps: S1. Dry waste granite powder and conductive carbon black at 60℃ for 5 h, then mix them evenly at a mass ratio of 30:70 to prepare a mixture. S2. Add the mixture to a ball mill and dry ball mill for 5 hours, then pass it through a 100-mesh sieve to obtain a refined mixture; S3. Place the refined mixture into the HTS Joule ultrafast heating device, with a vacuum degree of 10. -2 A 30 V pulse voltage was applied under Pa to raise the temperature of the powder to 1800℃ within 2 seconds. The pulse was repeated 4 times to obtain a multiphase composite powder. S4. The multiphase composite powder was calcined at 500°C for 3 h, then washed with an excess sodium hydroxide aqueous solution (concentration 30wt%), and dried to obtain silicon carbide powder with a yield of 94.4%.

[0033] Figure 1 The appearance of the high-purity silicon carbide prepared in Example 1 is shown.

[0034] Figure 2A flowchart of the method for preparing silicon carbide using waste granite powder and conductive carbon black is shown.

[0035] Figure 3 The X-ray diffraction (XRD) analysis results of the product of Example 1 are shown. It can be seen that the main component of the product of Example 1 is SiC, and the purity reaches more than 96%.

[0036] Figure 4 The scanning electron microscope (SEM) results of the product of Example 1 are shown. It can be seen that the product has a linear structure with a diameter of 50-100 nm and a length of 5-20 μm.

[0037] Example 2 A method for preparing silicon carbide using waste granite powder and conductive carbon black, the method comprising the following steps: S1. Dry waste granite powder and conductive carbon black at 60℃ for 5 h, then mix them evenly at a mass ratio of 30:70 to prepare a mixture. S2. Add the mixture to a ball mill and dry ball mill for 5 hours, then pass it through a 100-mesh sieve to obtain a refined mixture; S3. Place the refined mixture into the HTS Joule ultrafast heating device, with a vacuum degree of 10. -2 A 20 V pulse voltage was applied under Pa to raise the temperature of the powder to 1800℃ within 2 seconds. The pulse was repeated 4 times to obtain a multiphase composite powder. S4. The multiphase composite powder was calcined at 500°C for 3 h, then washed with an excess sodium hydroxide aqueous solution (concentration 30wt%), and dried to obtain silicon carbide powder with a yield of 88.1%.

[0038] XRD analysis showed that the main component of the product in Example 2 was β-SiC, with a purity of over 95%. SEM observation revealed that the product had a linear structure with a diameter of 50-100 nm and a length of 5-20 μm.

[0039] Comparative Example 1 The difference between this comparative example and Example 1 is that in step S3, the pulse is changed to once, while the other materials and preparation methods are the same as in Example 1.

[0040] Comparative Example 1 showed a yield of 64.4%. XRD analysis revealed that the main component of the product was β-SiC, with a purity exceeding 86%. SEM observation showed that the product had a linear structure with a diameter of 20-40 nm and a length of 2-10 μm. Due to insufficient pulse counts under the same conditions, the reaction was incomplete, resulting in a low yield and poor sample morphology.

[0041] Comparative Example 2 The difference between this comparative example and Example 1 is that in step S3, the pulse is changed to 10 times, while the other materials and preparation methods are the same as in Example 1.

[0042] Comparative Example 2 showed a yield of 84.4%. XRD analysis revealed that the main component of the product was β-SiC, with a purity exceeding 90%. SEM observation showed that the product had a linear structure with a diameter of 20-80 nm and a length of 5-15 μm. Excessive pulse frequency under the same conditions damaged the sample structure, leading to a decrease in the content of the target product.

[0043] Comparative Example 3 The difference between this comparative example and Example 1 is that in step S1, the waste granite powder is replaced with SiO2, while the other materials and preparation methods are the same as in Example 1.

[0044] Comparative Example 3 showed a yield of 65.3%. XRD analysis revealed that the main component of the product was β-SiC, with a purity exceeding 55%. SEM observation showed that the product was an irregular mass with significant agglomeration, ranging from 1-5 μm in diameter and 5-15 μm in length. Analysis suggests that the granite powder, in addition to SiO2, contains various components such as Al2O3, CaO, and alkali metal oxides. These components synergistically improve the reaction interface state and promote the carbothermic reduction reaction during Joule heating, thus benefiting the formation and growth of silicon carbide crystals. In contrast, pure silica reagent, due to its single component, lacks the aforementioned synergistic promoting effect, resulting in incomplete reaction, reduced yield, and poorer morphology.

[0045] Test case The silicon carbide samples prepared in the examples and comparative examples were subjected to performance tests.

[0046] Test method: The silicon carbide prepared in the examples and comparative examples was used as the negative electrode active material of lithium-ion batteries. The electrochemical performance was tested in accordance with GB / T 24533-2019, GB / T 30836-2014 and SJ / T 11793-2022.

[0047] The specific steps are as follows: A silicon carbide sample, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 80:10:10. N-methylpyrrolidone (NMP) was added to prepare a uniform slurry, which was then coated onto the surface of a copper foil current collector. The loading of the active material was controlled at 1.0 mg / cm³. 2 The corresponding coating thickness is 50 μm. After vacuum drying at 100℃ for 10 h, the working electrode is obtained by rolling and stamping.

[0048] CR2032 coin cell half-cells were assembled in an argon-filled glove box, with lithium metal sheet as counter electrode, polypropylene membrane as separator, and 1 mol / L LiPF6 electrolyte (solvent EC:DMC:EMC=1:1:1, volume ratio).

[0049] Within the voltage range of 0.01–3.0 V (vs. Li / Li) + Constant current charge-discharge tests were performed under constant current conditions, and cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests were also performed.

[0050] Table 1. Specific capacitance test results As shown in Table 1, compared with the use of pure silica reagent as silicon source, silicon carbide-based materials prepared with granite powder exhibit higher reversible specific capacity, better first coulombic efficiency, and significantly improved cycle stability and rate performance.

[0051] Analysis suggests that granite powder, in addition to SiO2, contains various oxide components such as Al2O3, CaO, K2O, and Na2O. These components synergistically improve the reaction interface and conductive network structure during Joule heating, promoting the formation of silicon carbide and optimizing its microstructure, thereby enhancing electrochemical reactivity and structural stability. In contrast, pure SiO2, due to its single composition and lack of the aforementioned synergistic effects of multiple components, results in materials with poor conductivity and insufficient structural uniformity, leading to capacity decay during cycling and exhibiting lower capacity and poorer cycling performance.

[0052] Therefore, granite powder not only participates in the reaction as a silicon source, but its complex components also play a crucial role in regulating the material structure and improving electrochemical performance. In summary, this invention utilizes the multi-component synergistic effect of granite powder to simultaneously optimize the structure and performance of silicon carbide-based anode materials under Joule heating conditions, demonstrating promising application prospects.

[0053] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0054] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing silicon carbide using waste granite powder and conductive carbon black, characterized in that, The method for preparing silicon carbide using waste granite powder and conductive carbon black includes the following steps: S1. Mix waste granite powder and conductive carbon black evenly to prepare a mixture; S2. The mixture is ball-milled and then sieved to obtain a refined mixture; S3. Place the refined mixture into a Joule apparatus and sinter to prepare multiphase composite powder; S4. The multiphase composite powder is calcined at high temperature and then alkali washed to obtain silicon carbide powder.

2. The method for preparing silicon carbide using waste granite powder and conductive carbon black according to claim 1, characterized in that, The waste granite powder and conductive carbon black undergo a pre-drying treatment at a temperature of 50-70°C for 2-5 hours.

3. The method for preparing silicon carbide using waste granite powder and conductive carbon black according to claim 1, characterized in that, The mass ratio of the waste granite powder to the conductive carbon black is (20-50):(50-80).

4. The method for preparing silicon carbide using waste granite powder and conductive carbon black according to claim 1, characterized in that, The resistivity of the conductive carbon black is 0.89-1.12 Ω·mm.

5. The method for preparing silicon carbide using waste granite powder and conductive carbon black according to claim 1, characterized in that, The particle size of the refined mixture is 100-200 mesh.

6. The method for preparing silicon carbide using waste granite powder and conductive carbon black according to claim 1, characterized in that, The Joule device is an HTS Joule ultrafast heating device.

7. The method for preparing silicon carbide using waste granite powder and conductive carbon black according to claim 1, characterized in that, The sintering temperature is 1600-2000℃ and the voltage is 25-32 V.

8. The method for preparing silicon carbide using waste granite powder and conductive carbon black according to claim 1, characterized in that, The vacuum degree during sintering is 0.01-10 Pa.

9. The method for preparing silicon carbide using waste granite powder and conductive carbon black according to claim 1, characterized in that, The high-temperature calcination is carried out at a temperature of 500-800℃ for 3-5 hours.

10. The method for preparing silicon carbide using waste granite powder and conductive carbon black according to claim 1, characterized in that, The reagent used for alkaline washing is a 30-50 wt% NaOH solution.

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