Effect of temperature and time on purity, morphology and phase transformations of silica from rice husk

Abstract

Silica (SiO₂) is the most abundant substance in the earth's crust. Rice husk (RH) is an excellent silica source and can replace conventional silica sources. In this work, Thermal and chemical treatment methods to synthesize silica from rice husks. The multiple properties of silica sources depend on various calcination temperatures (500–1000 ​°C) and time (1–6 ​h) in temperature-controlled muffle furnaces. X-ray Diffraction (XRD) data indicated that rice husk ash produced silica of different silica phases such as amorphous and crystalline such as quartz, tridymite, cristobalite, wollastonite phase, etc. The purity of silica from rice husk is increased at higher calcination temperatures examined by X-ray Fluorescence (XRF). The highest purity of silica was above 97 ​% at 1000 ​°C. Fourier transform infrared spectroscopy (FTIR) revealed that the stretching and bending vibration of siloxane and silanol group of silica is similar to commercial grade silica. The surface morphological structure of rice husk ash, which is observed by Scanning Electronic Microscope (SEM) result, confirms that the highest amount of silica content is in the outer layer of the husk, which is in the amorphous form. The removal of organic residues such as hemicellulose, cellulose, and lignin from rice husk, as well as the stability of silica up to 650 ​°C, were indicated by thermal analysis (TGA, DTA). These studies optimize the identification of temperature and time for the calcination process.