SOL-GEL SYNTHESIS OF SILICA FROM RICE HUSK ASH FOR GLASS CERAMICS PRODUCTION
This study is an experimental research on the possible use of rice husk ash silica for the Production of glass ceramics utilising the abundant agricultural waste. Rice husk was pre-treated, carbonised to drive out volatile matter and ash at 700oC. The brown ash (BA) obtained was characterised by X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) to determine the chemical composition and to know the crystal phases present in the ash. The XRF result contained 79.98% SiO2 and the rest 20.02% included 1.80% P2O3, 0.42% Na2O, 1.54% CaO, 0.05% BaO, 0.11% TiO2. XRD result of the RHA showed a broad peak zone centred near
2θ 22.2o signifying the amorphous nature of silica. A solution of the ash was prepared with Sodium hydroxide, titre against a solution of Calcium trioxonitrate(iv) tetrahydrate and Trioxonitrate (v) acid, after some minutes the gel was formed and dried to powder. Fourteen samples were compacted and sintered at 700oC. The products were characterised by XRD, Scanning Electron Microscopy (SEM) and the physicochemical properties were tested. The XRD Pattern of the product showed the presence of sodium calcium silicate phase (Na4Ca4SiO6O18) combeite which belong to the bioactive ceramics family. The SEM showed a circular morphology of glass ceramics in glassy matrix with Energy Dispersive X-ray analysis (EDS) elemental spectra showing Si, Ca, P and Na. Physicochemical test also showed the material having 0.2% water absorption below the convectional range of between 5-10% making it better by being less porous and good resistance to alkali attack than acid attack. Above all, a glass ceramics product has been produced highlighting the importance of utilising an agricultural waste RHA in the glass and glass ceramics industry for production. It also, goes to show that RHA is an alternative raw material to silica sand. The sol-gel route employed proves that it is a high energy saving technique when compared with the conventional methods and powder processing through sinter-crystallisation.
1.1 Background of the Study
Rice is a major crop grown in some states in Nigeria. After rice grain milling, rice husks remain as an agricultural waste material. Many people have tried to use this waste to produce useful materials such as silica, silicon carbide, silicon nitride or silicon for solar cells (Yalcin and Sevinc, 2001). Rice husk is one of the largest readily available but most unutilised biomass resources and has long been an ideal fuel for electricity generation (kumar and Venugopal, 2013).
Numerous silicate based wastes, such as coal ash, slag from steel production, fly ash and filter dusts from waste incinerators, mud from metal hydrometallurgy, different types of sludge as well as glass cullet or mixtures of them have been considered for the production of glass ceramics (Rawlings et al., 2009).