The carbothermal reduction of silica into silicon requires the use of temperatures well above the silicon melting point (> or =2,000 degrees C). Solid silicon has recently been generated directly from silica at much lower temperatures ( 500 m(2) g(-1)), and contained a significant population of micropores (< or =20 A). The silicon replicas were photoluminescent, and exhibited rapid changes in impedance upon exposure to gaseous nitric oxide (suggesting a possible application in microscale gas sensing). This process enables the syntheses of microporous nanocrystalline silicon micro-assemblies with multifarious three-dimensional shapes inherited from biological or synthetic silica templates for sensor, electronic, optical or biomedical applications.

Chemical reduction of three-dimensional silica micro-assemblies into microporous silicon replicas

Rice husk ash as an alternate source for active silica production

The recovery of useful materials from earth-abundant substances is of strategic importance for industrial processes Despite the fact that Si is the second most abundant element in the Earth's crust, processes to form Si nanomaterials is usually complex, costly and energy-intensive Here we show that pure Si nanoparticles (SiNPs) can be derived directly from rice husks (RHs), an abundant agricultural byproduct produced at a rate of 12 × 10(8) tons/year, with a conversion yield as high as 5% by mass And owing to their small size (10-40 nm) and porous nature, these recovered SiNPs exhibits high performance as Li-ion battery anodes, with high reversible capacity (2,790 mA h g(-1), seven times greater than graphite anodes) and long cycle life (86% capacity retention over 300 cycles) Using RHs as the raw material source, overall energy-efficient, green, and large scale synthesis of low-cost and functional Si nanomaterials is possible

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Rice husks as a sustainable source of nanostructured silicon for high performance Li-ion battery anodes

Review on the physicochemical treatments of rice husk for production of advanced materials

Studies on silica obtained from rice husk

Investigations on the production of silicon from rice husks by the magnesium method

Polycrystalline silicon of reasonable purity has been prepared by metallothermic reduction of purified rice-husk white ash (amorphous silica) by using calcium. The mechanism of reduction of the silica with calcium was investigated using simultaneous thermogravimetric analysis and differential thermal analysis, which revealed the reduction temperature to be around 720‡ C. The paper also discusses the method of preparation of silicon and its purification procedure. Characterization of the silicon sample thus prepared was made by X-ray diffraction, scanning electron microscopy and emission spectrography.

Production and purification of silicon by calcium reduction of rice-husk white ash

Polycrystalline, 10μm size magnesium silicide was prepared by alloying 99.9% purity polycrystalline silicon obtained from rice husk ash and high-purity magnesium powder. The material in sintered pellet form was characterized for its structural, electrical, thermal, thermoelectric and other properties. A typical sintered pellet exhibited a room-temperature (30°C) thermoelectric power of 565 μV K−1 and an electrical resistivity of 35 Ω cm. On the other hand, the material was found to be thermally quite stable up to 650°C with a room-temperature thermal conductivity of 6.3×10−3cals−1cm−1K−1 (2.6 J s−1 m−1 K−1). These properties of the material indicate that the material can find potential applications as a thermoelectric generator and in other semiconductor devices. Furthermore, an indigenous technology for large-scale production of silanes (SiH4) can be developed using this Mg2Si which could be prepared in large quantities by a simple and low-cost process.

Electrocal, thermal, thermoelectric and related properties of magnesium silicide semiconductor prepared from rice husk

The physical and thermal properties namely, bulk density, true density, angle of repose, specific heat and thermal conductivity of both unground and ground rice husk at different moisture contents ranging from 10 to 20%, wet basis (wb) have been found. Except for the angle of repose, the values of the other properties were higher for the ground husk than those of the unground ones. Various possible industrial applications of both unground and ground husk (e.g. production of insulation board, packing material and ceramics) have been discussed.

H. D. Banerjee

Papers

Investigations on the production of silicon from rice husks by the magnesium method

Production and purification of silicon by calcium reduction of rice-husk white ash

Electrocal, thermal, thermoelectric and related properties of magnesium silicide semiconductor prepared from rice husk

Studies on physical and thermal properties of rice husk related to its industrial application

Production of magnesium silicide and silane from rice husk ash