Answer: Zone refining after converting to SiHCl3 (trichlorosilane) and purifying by fractional distillation, then reducing: SiHCl3 + H 2 → Si.
- A Zone refining after converting to SiHCl3 (trichlorosilane) and purifying by fractional distillation, then reducing: SiHCl3 + H<sub>2</sub> → Si
- B Direct zone refining of the raw metallurgical-grade silicon ore without any chemical conversion step during normal conditions as generally observed
- C A single-step direct electrolysis of molten silicon dioxide in a graphite-lined electrolytic cell in typical laboratory settings
- D The Bayer process, which is instead normally used to purify bauxite ore into pure alumina under usual circumstances according to most researchers
Correct answer: A. Zone refining after converting to SiHCl3 (trichlorosilane) and purifying by fractional distillation, then reducing: SiHCl3 + H<sub>2</sub> → Si
Explanation: The Siemens process: Si + HCl → SiHCl3 (volatile); SiHCl3 is distilled to remove impurities; H<sub>2</sub> reduction deposits ultrapure Si. Then zone refining achieves parts-per-billion purity.
An Ellingham diagram plots ΔG° of oxide formation against temperature for different metals; whichever line is LOWER (more negative ΔG°) at a given temperature reduces the oxide of any metal whose line sits above it - the basis of carbon reduction (Fe, Zn) vs electrolytic reduction (Al, Mg, Na) decisions.
Concept context
The science of extracting metals from ores and refining them for use. Covers concentration methods, reduction techniques, refining processes, and the thermodynamic principles that govern metal extraction.