研究目的
To investigate the removal of boron from silicon melt by incorporating water vapor during electron beam melting, addressing the challenges posed by boron's large segregation coefficient and low vapor pressure.
研究成果
Boron can be effectively removed from silicon melt with an average efficiency of 28% using water vapor-added electron beam melting. The process involves oxidation to volatile BO, facilitated by high temperature and vacuum conditions. An oxygen self-circulating path is established, involving chemical reactions, evaporation, gas-phase transport, and ionization, enabling continuous boron removal. Higher temperatures improve removal efficiency, but decreasing boron content reduces the driving force, making further purification challenging.
研究不足
The study is conducted on an industrial scale, which may limit control over experimental variables. The removal efficiency of boron is only 28% on average, indicating room for improvement. The process relies on high vacuum and temperature, which could be energy-intensive. Potential areas for optimization include enhancing the oxidation and evaporation mechanisms or scaling down for better precision.
1：Experimental Design and Method Selection:
The study uses electron beam melting with added water vapor to oxidize and evaporate boron from silicon melt. Thermodynamic models and kinetic equations are employed to analyze the process.
2：Sample Selection and Data Sources:
Raw silicon material with an average boron content of 0.55 × 10^{-4} wt.% is used, sourced from the top of a casting ingot. Samples are pretreated by washing with acid and deionized water.
3：55 × 10^{-4} wt.% is used, sourced from the top of a casting ingot. Samples are pretreated by washing with acid and deionized water.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Industrial-scale electron beam melting furnace with a 300 kW electron beam gun, water-cooled copper crucible (diameter 68 cm, depth 30 cm), vacuum systems, hydrochloric acid, hydrofluoric acid, deionized water, and water vapor source.
4：Experimental Procedures and Operational Workflow:
Raw material is placed in the crucible, chambers are evacuated, electron beam is applied to melt silicon, water vapor is added, beam power is maintained at 250 kW for 30 minutes, then decreased. For comparison, an experiment without water vapor is conducted. After melting, silicon ingots are cut and analyzed.
5：Data Analysis Methods:
Boron content is measured using inductively coupled plasma mass spectrometry (ICP-MS), condensate is analyzed by X-ray diffraction (XRD), oxygen content is characterized by electron probe microstructure analysis (EPMA), and thermodynamic calculations are performed using Factsage database.
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