Crystallization of calcium silicate at elevated temperatures in highly alkaline system of Na2O-CaO-SiO2-H2O

In Na2O-CaO-SiO2-H2O system, systematic investigations of phase and morphology of calcium silicate in hydrothermal conditions were concisely conducted for high-value utilization of silicon resource in high-alumina fly ash (HAFA). The results show that crystal composition and phase may be affected by relatively low concentration of NaOH, and sodium ions are rearranged into the structure to form NaCaHSiO4 and Na2Ca3H8Si2O12 with different C/S ratio at high concentration of NaOH. In addition, phases in wollastonite group possess the morphology of nanofiber. Formation of nanofiber is attributed to the difference of surface energies between axial and radial direction, and higher temperatures lead to easier growth along radial direction. The preparation of C-S-H with different phases and morphologies can guide for the application of silicate solution with high alkalinity with different purposes.