What other known reductants for SiO₂ could potentially be used for producing silicon from silica in an arc furnace?
Read more: http://www.madehow.com/Volume-6/Silicon.html#ixzz6uKynirns
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$\begingroup$ Industrial or laboratory scale ? $\endgroup$– PoutnikMay 9, 2021 at 8:46
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$\begingroup$ The wikipedia article on “silicon” lists several methods used to produce silicon for semiconductor production. No mention of using hydrogen gas as reductant, possibly because combining arc furnaces with high pressure hydrogen gas is a glaringly obvious disaster waiting to happen. $\endgroup$– Ed VMay 10, 2021 at 15:21
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$\begingroup$ @EdV More likely because H₂ is reasonably expensive (ATM) and there's no price on polluting the atmosphere with CO₂ emissions. Several steel production facilities are now trialling injection of Hydrogen to eventually replace coking coal entirely. e.g. in Sweden h2greensteel.com/newsroom/h2greensteel and Germany steelguru.com/steel/… If it can be safely done in iron ore and steel smelting with arc furnaces can it be done in silica processing to produce pure Is I wonder? $\endgroup$– wide_eyed_pupilMay 11, 2021 at 6:33
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$\begingroup$ I did find one patent application for use of H₂ as a reductant in silicon production but it's only in the final stage of reducing a silicon halide that is to made by furnacing SiO2 + C in a chlorination process, so it's not the full process just the end point using H₂ in an arc furness where the gases are separated using a vortex apparatus. $\endgroup$– wide_eyed_pupilMay 11, 2021 at 6:37
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1$\begingroup$ Glad to hear hydrogen can be safely used in steel smelting! I had a colleague who worked in a steel mill before becoming a professor. The stories he told made me happy to never visit a working steel mill. $\endgroup$– Ed VMay 11, 2021 at 12:15
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1 Answer
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On a small scale, hydrogen gas is certainly an option. Here is a paper: Reduction Kinetics of Metal Oxides by Hydrogen. High temperatures induce the formation of monoatomic hydrogen as the active agent.
However, on a practical note, explosive mixtures of hydrogen with air exist over a wide range (Wikipedia has a good discussion on this topic), so this path is clearly not without danger.
[EDIT] To address a question on trials, not that am aware of, however, here is an interesting experiment one may conduct at a seemingly much lower temperature that is likely safe. For reducing, it is known that in situ creation of the hydrogen atom radical (cited as the major reducing species by Buxton, see Eq 3 on page 2 here). Suggestively, the chemisorption of the hydrogen radical on the surface of metals like Zn, Al and Mg (albeit, effective for a limited lifespan) may be an interesting trial path.
So, as an experiment, proceed to imbue the surface of Mg or Al metal with the hydrogen atom radical (from the traditional nascent hydrogen generation methods based on say Al/NaOH). Place the SiO2 on the imbued metal surface and heat.
As to the reaction mechanics, the •H radical functional behaves based on the equation:
$\ce{ e- + H+ <=> •H }$
where this seemingly reversible formation reaction apparently acts as (e-,H+) pair on ions. For an example, citing a work in Hydrometallurgy 2008: Proceedings of the Sixth International Symposium on p. 818, a suggested commercial reductive leaching equation, to quote:
$\ce{PbS + 2 •H = Pb + H2S (5) }$
Now, could a related reaction path exist with SiO2 at a much lower temperature? To answer, this suggested trial could be quite interesting.
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$\begingroup$ thanks @AJKOER. I'm aware of several pilots for injecting hydrogen into steel furnesses and intentions to transfer the production process to entirely avoid coal eventually. Are there any such trials you're aware of for the production of silicon? And disadvantages other than the cost and flammability of hydrogen? $\endgroup$ May 9, 2021 at 12:22
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$\begingroup$ Thanks again for the additional information @AJKOER. I did locate one patient claim using hydrogen as the reductant, but it only uses it on a silicon halide and carbon is used in the chlorinator and results in CO₂ production, not sure if its the typical ratio of C to SiO2 but would seem so if the oxygen is all captured in a resulting CO₂ stream. freepatentsonline.com/4102985.pdf $\endgroup$ May 10, 2021 at 3:59