Mechanism of boron removal from Si-Al melt by Ar-H2 gas mixtures
(Key Laboratory of Novel Thin Film Solar Cells, Institute of Applied Technology,
Chinese Academy of Science, Hefei 230031, China)
Chinese Academy of Science, Hefei 230031, China)
Abstract: A new method about purification of metallurgical grade silicon (MG-Si) by a combination of Si-Al solvent refining and gas blowing treatment was proposed. The morphologies and transformation of impurity phases, especially for boron and iron in Si-Al melt were investigated during Ar-H2 gas blowing treatment. The mechanism of boron removal was discussed. The results indicate that gas blowing can refine grain size and increase nucleation of the primary Si. Boron can be effectively removed from MG-Si using the Ar-H2 gas blowing technique during the Si-Al solvent refining. Compared with the sample without gas blowing, the removal efficiency of boron increases from 45.83% to 74.73% after 2.5 h gas blowing. The main impurity phases containing boron are in the form of TiB2, AlB2 and VB compounds and iron-containing one is in the form of β-Al5FeSi intermetallic compound. Part of boron combines [H] to transform into gas BxHy (BH, BH2) and diffuses towards the surface of the melt and is volatilized by Ar-H2 gas blowing treatment under electromagnetic stirring.
Key words: metallurgical grade silicon; Si-Al melt; gas blowing; boron removal