Effect of temperature on nano-crystalline silica and carbon composites obtained from rice-husk ash

Rice husk (RH), an agricultural waste, was used to produce nano-crystalline silica and carbon composite powder. The rice-husk ash enriched with carbon was obtained in N(2) atmosphere after pyrolysing at 700 degrees C/2 h. This pyrolysed product enriched with carbon, hence named as black ash (BA), was heat-treated at different temperatures (400-1200 degrees C)/2 h in a temperature-controlled muffle furnace, in the presence of static air. Different phases of silica obtained from charred BA were observed with respect to changes in temperature. Changes in phase transitions of silica and carbon were studied by using X-ray diffractometry (XRD). Crystallite sizes of silica and carbon obtained from charred BA at each temperature were worked out using Scherer's relation. Nano-crystalline silica of various crystallite sizes was obtained from charred black ash at different temperatures (400-1200 degrees C). A comparative study between raw rice husk (RH) as received, BA (prepared by pyrolysing RH at 700 degrees C/2 h in N(2) atm.) and BA charred in air was done by using scanning electron microscopy (SEM), X-ray diffractometry (XRD) and Fourier transform infra-red (FTIR) spectroscopy. TG/DSC of RH was also done to study the decomposition process. (C) 2011 Elsevier Ltd. All rights reserved.