Carbothermic Reduction of Amorphous Silica Refined from Diatomaceous Earth
- PDF / 808,902 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 34 Downloads / 203 Views
RGE-SCALE power generation with solar cells is one of the most attractive and desired routes for the global environmental issue because solar energy is inexhaustible and free from CO2 emission. The dominant material used in solar cells is silicon, which is the second-most abundant element in the crust of the earth. However, many problems must be solved to realize the solar-cell power generation in a large scale. One of the most serious problems is the unstable supply route of solar-grade Si (SOG-Si) whose purity is required to be 6–7 N. Currently, SOG-Si is produced from a nonstandard product of semiconductor-grade Si (SEG-Si) for electronic devices, with a product purity of 11 N. The production rate of SOG-Si by this route, thus, is seriously influenced by the market trend in SEG-Si.[1] Another problem is the exhaustion of high-quality quartz (>99.5 pct), which is reduced carbothermically to metallurgical-grade Si. Therefore, the development of a novel SOG-Si supply route independent of SEG-Si has been eagerly anticipated.
Diatomaceous earth, or diatomite, is one of the most promising high-purity silica resources. It mainly contains amorphous silica (AS) in frustules of fossil diatoms with impurities such as aluminum, iron, and potassium in clay minerals. The reserves of diatomaceous earth are huge (estimated to be more than 900 million tons[2]), and the deposits are distributed extensively across the world. The primary use of diatomaceous earth is currently filtration, filler, and adsorption.[2] However, no research has been reported to recognize diatomaceous earth as a raw material for high-purity silica or SOG-Si. Thus, a possibility of 5-N silica purification from diatomaceous earth has been proposed in Kyoto University.[3,4] If the purified silica is reduced to Si without contamination, then diatomaceous earth can become a suitable resource for SOG-Si. Crystalline silica (quartz or quartzite) conventionally is reduced carbothermically to metallurgical-grade Si in submerged arc furnaces. The overall reduction reaction is expressed as follows: SiO2 þ 2C ¼ Si þ 2COðgÞ
MASATAKA HAKAMADA, Graduate Student, YASUHIRO FUKUNAKA, Professor, and HIROMU KUSUDA, Associate Professor, are with the Department of Energy Science and Technology, Graduate School of Energy Science, Kyoto University, Yoshidahonmachi, Sakyo, Kyoto 606-8501, Japan. Contact e-mail: fukunaka@ energy.kyoto-u.ac.jp TOSHIO OISHI, Professor, is with the Department of Materials Science and Engineering, Faculty of Engineering, Kansai University, 3-3-35 Yamate-cho, Suita, Osaka 564-8680, Japan. TAKASHI NISHIYAMA, Researcher, is with the Thinktank Kyoto Institute of Natural History, 14 Yoshida-kawaramachi, Sakyo, Kyoto 606-8305, Japan. Manuscript submitted April 23, 2009. Article published online January 6, 2010. 350—VOLUME 41B, APRIL 2010
½1
However, the actual reduction process includes the formation of intermediate species, such as SiO(g) and SiC, which make the reduction process more complicated than is shown in Eq. [1] (Appendix A). Molten SiO2 is reduced
Data Loading...
