Oxidative Removal of Boron from Molten Silicon by CaO-based Flux Treatment with Oxygen Gas Injection

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Vol. 45; no. 2; pp. 629 - 642
• Main Authors: Tanahashi, Mitsuru, Fujisawa, Toshiharu, Yamauchi, Chikabumi
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.04.2014; Springer; Springer Nature B.V
• Subjects: Applied sciences; Boron; Characterization and Evaluation of Materials; Chemistry and Materials Science; Concentration (composition); Exact sciences and technology; Flux; Gas injection; Gases; Injections; Materials Science; Melts; Metallic Materials; Metals. Metallurgy; Nanotechnology; Optimization; Oxidation; Oxygen; Partial pressure; Production of metals; Silicon; Structural Materials; Surfaces and Interfaces; Thin Films; Boron Concentration; Boron Removal; Boron; Molten Silicon; High Oxygen Partial Pressure; Removal; Gas injection
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-013-9966-x

Oxidative removal of boron from molten silicon has been investigated at 1773 K (1500 °C) by CaO-based flux treatment with oxygen gas injection. Since oxygen gas is injected into the silicon melt after adding CaO- or CaCO 3 -CaF 2 flux onto the melt, high oxygen partial pressure is maintained at the flux-O 2 -Si interface and the removal of boron proceeds under nonequilibrium conditions. The experimental results clarified that the behavior of boron removal from molten silicon depends on the competition between the oxidation reactions of boron and silicon. On the basis of the results obtained, optimum operating conditions for boron removal by the flux treatment were examined from the viewpoints of initial flux composition, reaction time, oxygen gas flow rate, and orifice size of gas injection nozzle. By repeating the batch operation for 120 seconds three times under the optimum conditions determined in the present study, boron concentration in metallurgical-grade silicon could be reduced from 14 to 7.6 mass ppm efficiently.