Further improvement of the carbothermic reduction process requires an understanding in real time of the reactions occurring and the weight change during heating. However, this process is very complicated and SiO and SiC form as by-products. The starting point of the processes is to produce raw silicon materials from a natural resource via mostly carbothermic reduction. As well as we proposed the acetylene assisted Mg-thermal method where C 2 H 2 is added to the stream of the inert gas flow and used for creation of the gas atmosphere appropriate for simultaneous covering of the created material by a thin carbon film at the same time as reduction of silica.įor many years the production of solar-grade silicon remained a costly process resulting in a large amount of carbon gas being emitted, and so the process still requires improvement to suppress carbon emission. We put forward a method of thermal reduction of bulky micronized SiO 2 powder followed by acid rinsing in solutions contained HF in order to produce the hollow porous Si particles in a highly scalable manner. We analysed and discussed the challenges the used highly scalable Mg-thermal reduction method may present in getting por-Si materials suitable for energy conversion applications and proposed simple and inexpensive improvements for its optimization. The characterizations have been done by different methods: SEM, EDEX, FTIR, Raman, BET and BJH.
The Mg-reduction process brings deep changes in not only chemical composition of initial por-SiO 2 material, but also, and primary, it determines the geometrical structuring and crystallinity of the obtained products. We confirm the incomplete reduction of initial silica into final por-Si in all experimental conditions, even at the 700 o C and 2 hr treatment. We also explore the possibility for an additional covering of the obtained porous silicon (por-Si) by a thin carbon layer in a successive independent treatment with employment of the acetylene gas to enhance the material's conductivity and improve its suitability as perspective anodes in Li-ion batteries.
ELLINGHAM DIAGRAMS SERIES
In this report we present a series of assays on Mg-thermal reduction of porous silica (por-SiO 2) in inert argon atmosphere under different thermal and time conditions. The study indicated significant potential for industrial application of the process. A quartz-anthracite mixture with 90 pct of the particles < 350.9 µm carbothermically treated at 1873.15 K (1600 ☌) resulted in almost complete conversion of quartz to SiC in both nitrogen and air atmospheres. The influences of quartz and anthracite particle size, treatment temperature, and gaseous atmosphere (nitrogen or air) on SiC formation were investigated. SiC can partially replace conventional carbonaceous reductants used to produce alloys such as ferrochromium. In this study, an alternative method to partially capture the thermal energy associated with off-gas combustion, in the form of silicon carbide (SiC) generated from waste materials (quartz and anthracite fines), is proposed. Flaring of CO-rich off-gas results in significant wastage of energy. Most of the CO-rich off-gas is cleaned and flared on stacks, since the storing of large volumes is problematic due to the associated toxic and explosive risks. Carbothermic smelting of ores to produce metals or alloys in alternating current open/semiclosed and closed submerged arc furnaces, or in closed direct current furnaces, results in large volumes of CO-rich off-gas being generated.
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