Refining of Metallurgical-Grade Silicon by Thermal Plasma Arc Melting

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The refining of MG-silicon (MG-Si) is closely related to the cost and purity of solar-grade silicon (SoG-Si) as well as semiconductor-grade silicon (SeG-Si). Plasma arc refining of MG-silicon is one of the alternative and effective route to remove the impurities in silicon. In this study, a 60KW transfer-arc plasma melting furnace operated in105Pa was used to purify the MG-Si by different kinds of working gas, which was composed of 100%Ar, 95%Ar+5%O2, 95%Ar+5%H2, and 70%Ar+30%H2 respectively. During the processing, an optical spectrometer was used to monitor the changes of compositions. The experimental results show that the removal rate of impurities of aluminum, calcium, sodium, barium...etc. in silicon with plasma working gas containing oxygen, and hydrogen are higher than pure Ar plasma. Especially with 30% H2 plasma, the removal rate of the Na and Ba could reach 100% and the removal rate of Ca and Al could also achieve to 99.5% and 89.5% respectively. For the impurities of boron in the MG-Si, the elimination rate of hydrogen-mixed plasma could be as high as 76%.The in-situ monitoring of plasma refining is accomplished with the monochromators in the range of visible light’s wavelength. From the results of chemical analysis and optical spectrograph, it revealed that elimination rate of Fe and Al was higher in hydrogen-contained plasma arc than in pure Ar plasma, As to the refining of carbon, the hydrogen and oxygen mixed plasma arc are also efficient to reduce the carbon content in silicon, which could be decreased from 310 ppm to 60~70 ppm.

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Periodical:

Materials Science Forum (Volumes 475-479)

Main Theme:

Edited by:

Z.Y. Zhong, H. Saka, T.H. Kim, E.A. Holm, Y.F. Han and X.S. Xie

Pages:

2595-2598

Citation:

S. Tsao and S. S. Lian, "Refining of Metallurgical-Grade Silicon by Thermal Plasma Arc Melting", Materials Science Forum, Vols. 475-479, pp. 2595-2598, 2005

Online since:

January 2005

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$38.00

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[5] min 4178 2249 702 9 9 53 280.

[10] min 3981 1802 499 6 6 52 271.

[15] min 3880 1598 325 3 4 48 231 Pure Ar.

[20] min 3850 903 165 2 2 47 207.

[5] min 3970 1600 510 6 7 45 265.

[10] min 3841 1097 290 2 4 36 218.

[15] min 3792 503 98 1 2 30 162 Ar + 0. 5%O2.

[20] min 3725 499 83 1 1 29 100.

[5] min 3911 1504 470 5 6 40 220.

[10] min 3810 702 231 2 3 32 165.

[15] min 3749 398 60 1 1 28 92 Ar + 1. 0%O2.

[20] min 3680 396 31 1 1 26 80.

[5] min 3975 1948 380 4 6 47 169.

[10] min 3610 751 146 0 1 38 94 Ar + 5%H2 15 min 3403 450 42 0 0 22 77.

[5] min 3859 1752 275 3 5 44 155.

[10] min 3447 649 100 0 0 34 75 Ar + 30%H2.

[15] min 2951 349 8 0 0 14 70 Fig. 1 Schematic diagram of the experimental DC-plasma arc facility Fig. 2 (a)Ar (b)5%H2 and (c)30%H2 plasma arc in silicon melting Fig. 3 Comparison the removal rate with Fe and Al under different plasma atmosphere Fig. 4 Comparison the removal rate with B and C under different plasma atmosphere Fig. 5 The collected signals of in-situ plasma arc spectrum with Ar and Ar+5%H2 atmosphere Fig. 6 The collected signals of in-situ plasma arc spectrum with Ar+30%H2 atmosphere.

DOI: https://doi.org/10.1088/1009-0630/9/2/07