Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 1, pp. 12−15.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.G. Vodop’yanov, G.N. Kozhevnikov, V.G. Kuz’min, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 1, pp. 14−18.
INORGANIC SYNTHESIS AND INDUSTRIAL
Study of a Subﬂ uoride Process for Production
of High-Purity Silicon
A. G. Vodop’yanov
, G. N. Kozhevnikov
, and V. G. Kuz’min
Institute of Metallurgy, Ural Branch, Russian Academy of Sciences, Yekaterinburg, Russia
Kyshtym Mining and Processing Combine, Open Joint-Stock Company,
Kyshtym, Chelyabinsk oblast, Russia
Received December 7, 2010
Abstract—Process was studied in which high-purity silicon (1.07–1.35 ppm) is obtained from powdered technical-
grade silicon (99.81–99.86% Si) produced by acid reﬁ ning to remove impurities by its treatment with gaseous
at a temperature of 1200°C to give pure SiF
(gas), with its subsequent decomposition at temperatures lower
than 800°C into silicon and SiF
(gas) circulating in the system.
Silicon is the main raw material for manufacture of
photoelectric devices. It is produced by the chlorosilane
method , which includes processing of technical-grade
silicon into trichlorosilane, followed by its reduction
with hydrogen to silicon containing impurities in an
amount not exceeding 10 ppm (n × 10–4%).Therefore,
new less expensive techniques for production of silicon
are being intensively developed in the world. To these
belong methods for carbothermal reduction of silicon
from high-purity quartz and carbon . However,
silicon melted in a 150-kW furnace contained 0.09%
impurities. It can be puriﬁ ed in 2–3 stages by directed
crystallization, but this method is low-productive and
requires intricate and expensive equipment.
Also known is the subﬂ uoride technique for produc-
tion of silicon . It is based on the transport reaction
Si(s) + SiF
(g) = 2SiF
which occurs to the right at temperatures higher than
950°C, and in the reverse direction below 950°C.
The process was performed in a tubular quartz
reactor (d = 76 mm) ﬁ lled with a mixture of technical
grade silicon and quartz of a 0.5–25 mm fraction. The
quartz served as catcher of aluminum ﬂ uoride vapor by
+ 3 SiO
(g) formed was delivered into a unit in
whose upper part it was condensed as (SiF
in a condenser coil cooled by liquid nitrogen and then
was melted on being heated to 150–300°C. Liquid
polymers ﬂ owed down to the lower part of the unit onto
lumps of high-purity silicon heated to 400–950°C and
decomposed there into silicon and SiF
(g), which was
recycled. This method has not been implemented in the
industry because of its complexity.
The goal of our study was to develop a simpler
method for production of high-purity silicon by the
subﬂ uoride process.
For this purpose we assembled an experimental
setup including a heated steel retort for synthesis of
(g), quartz tube with an inner diameter of 24 mm
and length of 1000 mm, tubular furnace with a 100-mm-
long isothermal zone, piston-type circulation pump,
rotameter, and calibrated vacuum gage.
As raw material served technical-grade silicon of
composition (%): Si 98, Fe 0.7, Al 0.8, Ca 0.5, and
quartz for catching of AlF
vapor by reaction (2).
Prior to an experiment, the isothermal zone of the
quartz tube was charged with a mixture of 20 g of
technical-grade silicon and 10 g of quartz of fraction