| http://www.w3.org/ns/prov#value | - The impurities such as carbon, oxygen, Na, K and else, contained in the Si powder have been adhered to the powder surface during Si crashing steps, and reduction of these impurities can be attempted by subjecting the impurity-contaminated Si powder to a heating process of from 1200??? to 1300??? C. under a vacuum lower than 104 Torr for 2 to 6 hours.
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