ORIGINAL PAPER Determination of Silica Activity Index and XRD, SEM and EDS Studies of Amorphous SiO 2 Extracted from Rice Husk Ash Pallavi Deshmukh • Jatin Bhatt • Dilip Peshwe • Shailkumar Pathak Received: 2 July 2011 / Accepted: 2 November 2011 / Published online: 1 December 2011 Ó Indian Institute of Metals 2011 Abstract Rice husk ash (RHA) contains 20% SiO 2 in hydrated amorphous form (Si–OH). On thermal treatment, the SiO 2 converts to cristobalite, the crystalline form which is not reactive. However under controlled conditions, amorphous SiO 2 with high reactivity is produced. There- fore rice husk has been one of the useful bio-mass. The silica activity index was determined to be equal to 97.73 which was used to determine the percentage of amorphous SiO 2 in RHA. The values of the soluble fraction and silica activity index were also stated. Comparative study of amorphous and crystalline SiO 2 done by X-ray diffraction revealed the total amorphous nature of SiO 2 . The scanning electron microscopy (SEM) images displayed the com- parative morphological features of the rice husk and RHA. The energy dispersive spectroscopy analysis of rice husk was done to determine the presence of SiO 2 on the upper portion of rice husk and to determine the percentage of SiO 2 in RHA. The SiO 2 particles in an agglomerated form was found to be of micron size when observed under SEM. Keywords EDS  SEM  Soluble fraction  Silica activity index  XRD analysis 1 Introduction Many plants during their growth take up SiO 2 from the earth. When plants residues are burned, organic materials are broken down as carbon dioxide, water vapors etc. The remaining ash contains inorganic residues, notably the SiO 2 . Examples are rice husk ash (RHA), rice straw ash, bagasse ash etc. Of all plant residues, the ash of rice husks contains the highest percentage of SiO 2 . Rice husk, a form of agricultural biomass, is generated in large quantities as a major by-product in the rice milling industry. The esti- mated world-wide rice husk production is about 100 mil- lion tons, of which about 90% is generated in developing countries. Disposal of these vast amounts of rice husk has been one of the major problems facing the rice milling industry. By burning rice husk, 20% ash is obtained from it [1, 2]. The SiO 2 present in ash has a purity of 94–96% with major impurities like K 2 O, Na 2 O and Fe 2 O 3 . It has been shown that purity of SiO 2 obtained by incineration of rice husk can be further extended to 98–99%, if rice husk is subjected to pre treatments like washing with distilled water and boiling with acid such as HCl which helps in removing above mentioned impurities. The SiO 2 obtained by burning rice husk is amorphous and can be transformed to quartz, tridymite and cristobalite by heating it at high temperature over 900°C. The crystal phase, to which form the amorphous SiO 2 transform depends on the purity of the SiO 2 [3, 4]. The ‘‘SiO 2 ’’ powder is widely used as raw material for cement, glass, porcelain, refractory, the filler for plastic, rubber and tire and so on. Comparison of natural ‘‘SiO 2 ’’ and rice husk SiO 2 exhibits two main differences. The first one is that use of natural ‘‘SiO 2 ’’, destroys nature more or less. On the other hand, rice husk SiO 2 is one of the bio- logical resources. Secondly, the crystal phase of ‘‘SiO 2 ’’ is quartz while that of rice husk SiO 2 is amorphous. Trans- forming quartz to tridymite and cristobalite needs high temperature of about 1,400°C. On the other hand rice husk SiO 2 can transform to cristobalite at low temperature of 1,000°C. Rice husk SiO 2 can be crushed to very fine P. Deshmukh (&)  J. Bhatt  D. Peshwe  S. Pathak Department of Metallurgical and Materials Engineering, Visvesvaraya National Institute of Technology, South Ambazari Road, Nagpur 440 010, Maharashtra, India e-mail: pallavi_yd@yahoo.com 123 Trans Indian Inst Met (February 2012) 65(1):63–70 DOI 10.1007/s12666-011-0071-z