研究目的
To recycle polysilicon waste from diamond wire cutting by preparing α-Si3N4 via direct nitridation, investigating the effects of additives (FeCl3, NaCl, Cu) on the nitridation process, and achieving high conversion and α-phase content to reduce environmental pollution and production costs.
研究成果
Cu is an effective additive for nitridation of polysilicon waste, enabling high overall conversion and α-Si3N4 content (92.37%) at 1250°C for 8 h with 5 wt.% Cu. The α-Si3N4 fibers form via VLS and VS mechanisms, with Cu-Si liquid phase facilitating nucleation and growth. This method successfully recycles waste, reduces environmental impact, and lowers production costs, with potential for further optimization in impurity control.
研究不足
FeCl3 and NaCl additives are not ideal for achieving high α-Si3N4 content. Trace SiO2 formation occurs due to oxygen in N2 gas or from raw materials, which may affect product purity. Residual Cu in products requires acid leaching for removal to avoid impurities in high-temperature applications. The calculations of conversion and phase content are approximate due to potential weight loss during nitridation.
1：Experimental Design and Method Selection:
The study uses direct nitridation method to convert polysilicon waste into α-Si3N4. Additives (FeCl3, NaCl, Cu) are tested to enhance nitridation and α-phase formation. Theoretical models include vapor-liquid-solid (VLS) and vapor-solid (VS) mechanisms for fiber growth.
2：Additives (FeCl3, NaCl, Cu) are tested to enhance nitridation and α-phase formation. Theoretical models include vapor-liquid-solid (VLS) and vapor-solid (VS) mechanisms for fiber growth.
Sample Selection and Data Sources:
2. Sample Selection and Data Sources: Ultrafine polysilicon waste from diamond wire cutting is the raw material, with chemical composition analyzed (e.g., Si 93.69%, O 4.44%). High-purity N2 (>99.999%) is used as nitrogen source.
3：69%, O 44%). High-purity N2 (>999%) is used as nitrogen source.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes electric resistance furnace with MoSi2 heating elements, alumina crucible, FE-SEM (ZEISS SUPRA 55), XRD (TTR III, Rigaku), TEM, ICP-AES, vacuum drying cabinet. Materials include polysilicon waste, FeCl3, NaCl, Cu powders, N2 gas.
4：Experimental Procedures and Operational Workflow:
Polysilicon waste is dried at 120°C for 8 h. Mixed powders (10 g) with additives are heated in furnace from room temperature to 1200-1400°C at 5°C/min in flowing N2 (0.4 L/min) for various times. After reaction, samples are furnace-cooled and analyzed by XRD and FE-SEM.
5：4 L/min) for various times. After reaction, samples are furnace-cooled and analyzed by XRD and FE-SEM.
Data Analysis Methods:
5. Data Analysis Methods: XRD data is used to calculate mass fractions and conversion using integrated intensities of peaks (e.g., Si (111), α-Si3N4 (102,210,201), β-Si3N4 (101,210)). Formulas from Jovanovic and Kimura are applied. Morphology is analyzed via FE-SEM and TEM.
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