Crystallization and phase transition of tobermorite synthesized by hydrothermal reaction from dicalcium silicate

Abstract In this paper, tobermorite was hydrothermally synthesized from the dicalcium silicate (C ₂ S) in sodium silicate solution, and the crystallization and phase transition process were investigated in detail using XRD, Raman spectra, and SEM. The tobermorite is difficult to synthesize when the temperature is lower than 160°C because it gets converted into xonotlite (without Na ₂ O) or pectolite (with Na ₂ O) when the temperature is higher than 180°C. The crystallization process of tobermorite shows “S” trend with the increase in time, which can be divided into three stages: the nucleation stage, rapid crystal growth stage, and perfect crystal forming stage. During the crystallization, 90% of the crystallization of tobermorite is completed in the stage of rapid crystal growth. Raman spectra and SEM analysis show that with the increase in hydrothermal time, the C ₂ S of monomer (Q ⁰ ) is first converted into the calcium silicate hydrate of sheet (Q ² and Q ³ ), and then continues to convert into tobermorite of chain (Q ² ).