The influence of sucrose on the crystallization behaviour in the system CaO–SiO2–C12H22O11–H2O under hydrothermal conditions

Hydrothermal synthesis in the presence of sucrose has been carried out at 200 °C and autogeneous pressure in the system CaO–SiO2–C12H22O11–H2O to investigate the influence of C12H22O11 on phase formation and the crystal habit of calcium silicate hydrates (CSH-phases). A sucrose/lime ratio of 0.5 was utilized in all experiments and the reactivity of the SiO2 source was varied using educts of different grain size of ∼40 mesh and >230 mesh. CaO/SiO2 concentration ratios of 0.5 and 0.8 have been selected, the latter with respect to the composition of the important CSH-phase 11 Å tobermorite. The results were compared with experiments under similar but sucrose-free conditions. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX-analysis) as well as Fourier transform infrared spectroscopy (FTIR-spectroscopy) have been applied for analyses.A retarding effect of sucrose on CSH-phase formation has been observed. Only minor amount of CSH without regular morphology was observed instead of typically fibrous 11 Å tobermorite formed in the sucrose-free system. Sucrose altered the reaction mechanism in the CSH-system and hydrothermal process started with rapid reaction of sucrose and lime. The further course of crystallization was dominated by an extended precipitation of calcium carbonate and small amounts of calcium oxalate hydrate. Formation of these stable hydrothermal decomposition products of saccharated lime is strongly suppressing the CSH-crystallization.