Study of Pellets and Lumps as Raw Materials in Silicon Production from Quartz and Silicon Carbide |
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Authors: | E Dal Martello G Tranell S Gaal O S Raaness K Tang L Arnberg |
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Affiliation: | (1) Department of Materials Science and Engineering, NTNU, 7491 Trondheim, Norway;(2) SINTEF Materials and Chemistry, 7465 Trondheim, Norway |
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Abstract: | The use of high-purity carbon and quartz raw materials reduces the need for comprehensive refining steps after the silicon
has been produced carbothermically in the electric reduction furnace. The current work aims at comparing the reaction mechanisms
and kinetics occurring in the inner part of the reduction furnace when pellets or lumpy charge is used, as well as the effect
of the raw material mix. Laboratory-scale carbothermic reduction experiments have been carried out in an induction furnace.
High-purity silicon carbide and two different high-purity hydrothermal quartzes were charged as raw materials at different
molar ratios. The charge was in the form of lumps (size, 2–5 mm) or as powder (size, 10–20 μm), mixed and agglomerated as pellets (size, 1–3 mm) and reacted at 2273 K (2000 °C). The thermal properties of the quartzes
were measured also by heating a small piece of quartz in CO atmosphere. The investigated quartzes have different reactivity
in reducing atmosphere. The carbothermal reduction experiments show differences in the reacted charge between pellets and
lumps as charge material. Solid–gas reactions take place from the inside of the pellets porosity, whereas reactions in lumps
occur topochemically. Silicon in pellets is produced mainly in the rim zone. Larger volumes of silicon have been found when
using lumpy charge. More SiO is produced when using pellets than for lumpy SiO2 for the same molar ratio and heating conditions. The two SiC polytypes used in the carbothermal reduction experiments as
carbon reductants presented different reactivity. |
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