Effect of the combustion process on the structure of rice hull silica

Abstract

The study was carried to clarify the effect of thermal decomposition of rice hulls on the amorphous structure of silica ash. The ash obtained by thermal decomposition of hulls at temperatures in the range 500–1150°C for one hour was evaluated by X-ray diffraction. The ash prepared at comparatively lower temperatures (500–600°C) still consists of amorphous silica. Cristobalite was detected at 800°C. At 1150°C, both cristobalite and tridymite were present. The ash produced by combustion of rice hulls in a fixed bed at different air rates was evaluated. The amorphous structure of silica was present in the case of combustion at low air rates. At comparatively higher air rates, crystallization of silica takes place. The results obtained clarify the optimum conditions for production of amorphous silica by combustion of rice hulls in fixed beds.