Fabrication of Silica (SiO<sub>2</sub>) Foam from Rice Husk Ash (RHA): Effects of Solid Loadings

Silica (SiO2) foams have been widely applied in numerous fields, mainly filters and catalysts supports, due to their characteristics of high permeability, high porosity and specific surface area. In this study, foams of SiO2 from rice husk ash (RHA) was fabricated via polymeric sponge replication method. Polymeric foam initially was used as template and dipped into SiO2 slurry followed by drying and sintering to yield the replica of the original polymeric foam. Different solid loadings of SiO2 as-derived from RHA (20 to 35 wt. %) slurry and sintering temperature of 1150 °C were applied. Phase identification and chemical composition of the green and sintered foams were conducted using X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF). Morphological observations were performed using Scanning Electron Microscopy (SEM). Density and porosity of the SiO2 foams were characterized using Archimedes method. Compressive strengths of the foams were determined as per ASTM C773-88 (1999). XRD analyses confirmed that the SiO2 as derived from the RHA were of tridymite and cristobalite phases with as high as 93% purity, as confirmed by XRF analyses. The density of SiO2 foams fabricated was in the range of 0.614 to 0.989 g/cm3, whereas the porosity values was in the range of 70% to 82%%. Compressive strengths were found to increase from 0.05 to 0.30 MPa respectively, proportionate with the increased SiO2 solid loading. Excellent properties of the SiO2 foams definitely signifies that the polymeric replication method is indeed a promising technique for SiO2 as derived from RHA foam fabrication.