Microwave (2.45 GHz)-assisted rapid sintering of SiO₂-rich rice husk ash

The as-received SiO₂-rich material, rice husk ash (RHA), was ground to a specific surface area (Blaine) of 4800 cm²/g and then was rapidly sintered by 2.45 GHz microwave energy using a multi-mode system. The sintering temperatures were in a range of 800-1200 °C. The morphology, phase composition, microstructure and reactivity were investigated by SEM, XRD, and hydration heat evolution and strength index. Results show that the sintered ground RHAs (SgRHAs) contain SiO₂-cristolbalite and α-SiO₂ as major phases. The bulk density is up to 0.98 kg/l, and strength index at 28 days of the 800 °C microwave-sintered RHA paste are up by 30% when comparing to the as-received ground RHA (gRHA).