Fabrication of porous SiO2/C composite from rice husks

Porous SiO2/carbon composites were fabricated by heating pellets composed of rice husk (RH) powders in small (<74 μm), medium(74–175 μm) and large(150–300 μm) sizes. The contents of the small RH were fixed at 30 mass% and the RH pellets molded at 10, 15, and 30 MPa were heated at 800–1150 °C in an inert atmosphere. The weight loss due to the thermal decomposition of the organic materials in the pellet peaked at 1000 °C, whereas the specimen heated at 1000 °C showed the lowest carbon content and density, 29 mass% and 0.40 g cm−3, respectively. The SiO2 phase of the specimens were amorphous at 800 and 1150 °C, but a cristobalite phase was visible at 1000 °C. The specimen fire at 1000 °C showed a higher compressive strength than the others, and the large RH particles were seen to increase the strength of the product while an increase in molding pressure decreased the medium pore size, from 17 to 7 μm, and increased the strength, from 0.25 to 3.52 MPa. The specific surface area (SSA) of the specimen peaked at 450 m2 g−1, at 1000 °C and finally, the mesopore size of the specimens was similar throughout, at ∼2 nm.