Purification of silicon for mfr. of solar heating fuel cell - by melting, solidifying and treating with an acid mixt.

摘要

Metallurgical grade silicon of >95% purity is purified by (a) melting, (b) solidifying at a rate of crystallisation growth of 50 cm/hr (10 cm/hr) and (c) leaching with an aq. HCl-HF acid mixt. Pref. the 95% pure Si is molten in a crucible of quartz, carbon or Si nitride and the melt is contacted for up to 1 hr. with fused salt such as Ca-, or Mg fluoride or a mixt. of Ca fluoride and K silicate, Mg fluoride and Mg silicate, or K silicate and Mg silicate, pref. K fluoride-K silicate at a ratio of fused salt to Si 2 : 1 to 4 : 1, in an oxidising atm., for example air. The melt may be stirred. Si si sepd. from the fused salt mixt. and allowed to solidify very slowly as specified. It is then ground to a size 500 mu and leached with an aq. acid soln. about 2-5 times the wt. of Si, at 10-90 degrees C for 12 hr. to 4 days. The purified Si is sepd. by filtering, washed and dried.