Metallurgical and Materials Transactions B

, Volume 41, Issue 6, pp 1268–1273

Mass Transfer of Phosphorus in Silicon Melts Under Vacuum Induction Refining

  • Song-Sheng Zheng
  • Wen-Hui Chen
  • Jing Cai
  • Jin-Tang Li
  • Chao Chen
  • Xue-Tao Luo
Article

DOI: 10.1007/s11663-010-9422-0

Cite this article as:
Zheng, SS., Chen, WH., Cai, J. et al. Metall and Materi Trans B (2010) 41: 1268. doi:10.1007/s11663-010-9422-0

Abstract

An experimental investigation into the mass transfer of phosphorus in molten silicon under vacuum induction refining has been carried out. In a pilot-scale experiment, in the temperature range 1773 K (1500 °C) to 1873 K (1600 °C) and a vacuum of 0.1 to 0.035 Pa smelting for 7200 seconds (2 hours), phosphorus is decreased from 15 ppmw to 0.08 ppmw, which achieved the target for solar-grade silicon of less than 0.1 ppmw. Lab-scale experiments are used to determine the effects of vacuum, refining time, and temperature on the rate of mass transfer of phosphorus during vacuum refining. Hardly any phosphorus was removed when the vacuum pressure is greater than 100 Pa. Mass-transfer coefficients are nearly independent of pressure at 1783 K (1510 °C) when pressures are below 0.1 Pa and are highly correlated with vacuum pressures above 0.1 Pa. A model of vacuum refining of inductively stirred silicon melts is discussed to explain the transfer path of phosphorus out of the melt.

Nomenclature

A

Surface area exposed to the vacuum, m2

fP

Henry activity coefficient of solute phosphorus

\( P_{i}^{0} \)

Vapor pressure of pure solute I, Pa

patm

Atmospheric pressure, 101, 325 Pa

△G0

Gibbs energy change, J/mol

R

Gas constant, 8.31541 J/mol × K

\( {\text{K}}_{F}^{0} \)

Reaction equilibrium constant of phosphorus

T

Temperature, K

K

Overall mass transfer coefficient, m/s

t0

Starting time for vacuum refining, s

MSi

Molecular weight of silicon, g/mol

T

Current time during vacuum refining, s

Mi

Molecular weight of solute i, g/mol

V

Volume of metal, m3

mSi

Mass of silicon, kg

[wt pct P]0

Phosphorus content of silicon at time t0, ppmw

P

Element phosphorus

[wt pct P]t

Phosphorus content of silicon at time t, ppmw

\( P_{\text{Si}}^{ 0} \)

Vapor pressure of silicon, Pa

xP

Mole fraction of solute phosphorus

pP

Dimensionless pressure of phosphorus

xi

Mole fraction of solute i

\( p_{P}^{{^{e} }} \)

Equilibrium partial pressure of solute phosphorus, Pa

A

Evaporation coefficient

\( p_{i}^{e} \)

Equilibrium partial pressure of solute i, Pa

γi

Raoultian activity coefficient of solute i

Copyright information

© THE MINERALS, METALS & MATERIALS SOCIETY and ASM INTERNATIONAL 2010

Authors and Affiliations

  • Song-Sheng Zheng
    • 1
  • Wen-Hui Chen
    • 1
  • Jing Cai
    • 1
  • Jin-Tang Li
    • 1
  • Chao Chen
    • 2
  • Xue-Tao Luo
    • 1
  1. 1.Department of Materials Science and EngineeringXiamen UniversityXiamenP.R. China
  2. 2.Department of PhysicsXiamen UniversityXiamenP.R. China

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