Naomichi Nakamura1, Hiroyuki Baba1,2, Yasuhiko Sakaguchi1, Shoichi Hiwasa2 and Yoshiei Kato1,
1Steel Research Laboratory, JFE Steel Corporation, Chiba 260-0835
Boron removal in molten silicon with a steam added plasma melting method was investigated as an important part of the sequential metallurgical process to produce highly purified solar grade silicon (SOG-Si) from commercially available metallurgical grade silicon (MG-Si). Experiments were carried out from laboratory to industrial scale and silicon amount used per charge was varied from 0.6 to 300 kg. Boron was stably removed to permissible boron content for SOG-Si of [B]<0.1 massppm. Deboronization rate was proportional to steam content, 3.23th power of hydrogen content in plasma gas, boron content in molten silicon and area of dimple formed by plasma gas jet, and inversely proportional to the mass of molten silicon. An application of the thermodynamics leads to preferential boron oxidation in molten silicon due to higher temperature, which showed that this plasma method capable of locally heightening the temperature of the reaction surface was advantageous in principle.}
(Received July 1, 2003)
boron, silicon, plasma, steam, hydrogen, solar grade silicon, metallurgical grade silicon, photovoltaic cell
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