Metallurgical and Materials Transactions B

, Volume 44, Issue 2, pp 244–251 | Cite as

Trace Elements in the Si Furnace-Part II: Analysis of Condensate in Carbothermal Reduction of Quartz

  • Elena Dal Martello
  • Gabriella Tranell
  • Oleg Ostrovski
  • Guangqing Zhang
  • Ola Raaness
  • Rune Berg Larsen
  • Kai Tang
  • Pramod Koshy
Article

Abstract

Silicon feedstock for production of solar-grade silicon should be as pure as possible to decrease the cost of manufacturing of solar cells. Impurities in quartz, carbonaceous materials, electrodes, and refractories are mostly present in the form of oxides. These oxides can be reduced to volatile gaseous compounds in presence of SiO(g) and CO(g) atmosphere and potentially leave the furnace or stay in the condensed reaction products, metal, and slag. This work investigates the conditions under which volatile impurities report to the gas phase in laboratory experiments with lumpy and pelletized mixtures of SiO2, SiC, and Si at 1923 K and 2123 K (1650 °C and 1850 °C), respectively, were carried out. The volatile compounds were generated by the reduction of quartz and collected in the form of condensate. The effects of the reaction temperature, quartz type, charge composition, pellets, and lumps on the composition of the condensate were studied. The trace elements in the charge input, reacting charge, and condensate were analyzed using inductively coupled plasma (ICP)-mass spectroscopy (MS) and X-ray diffraction (XRD). CO(g) and SiO(g), which are the major components in reduction reactions, formed four types of condensate: white, brown, green, and orange. The condensate constituents were amorphous SiO2, 3C:SiC, Si, and α-quartz. Each impurity present in the quartz charge entered the gas phase during quartz reduction and was detected in the condensate. Al and Fe show limited volatility. The volatility of Mn, P, and B depends on the charge mix: a higher PCO enhances the concentration of these elements in the gas phase. Fluid inclusions, common in hydrothermal quartz, enhance the distribution of the contaminants to the gas phase. Industrial campaigns on Si and Fe-Si production confirm the experimental results.

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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2012

Authors and Affiliations

  • Elena Dal Martello
    • 1
  • Gabriella Tranell
    • 1
  • Oleg Ostrovski
    • 2
  • Guangqing Zhang
    • 3
  • Ola Raaness
    • 4
  • Rune Berg Larsen
    • 5
  • Kai Tang
    • 4
  • Pramod Koshy
    • 2
  1. 1.Department of Materials Science and EngineeringNTNUTrondheimNorway
  2. 2.UNSW Materials Science and EngineeringSydneyAustralia
  3. 3.UOWWollongongAustralia
  4. 4.SINTEF Materials and ChemistryTrondheimNorway
  5. 5.Department of Geology and Mineral Resources EngineeringNTNUTrondheimNorway

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