Thermal stability assessment of calcium monosulfoaluminate 12-hydrate by applying the in-situ X-ray diffraction method at 25–1250 °C

In this study, the stability of synthetic calcium monosulfoaluminate and the reaction mechanism of its conversion into ye`elimite during the thermal treatment were examined. The monosulfoaluminate was produced referring to ye`elimite stoichiometry by applying the mechanochemical treatment (dry grinding at 900 rpm with 3 on–off cycles of 10 min) followed by the hydrothermal synthesis (for 8 h at 110 °C). The data indicated that the prepared sample consists of Ms12 (~ 54.8%), CaCO(3) (~ 1.9%), Ms10.5/Hc (~ 0.7%) and amorphous content (~ 42.6%). Meanwhile, the thermal stability assessment by in-situ XRD analysis reveals that the dehydration of monosulfoaluminate interlayer water proceeds at 25–370 °C, where four different hydration states of monosulfoaluminate are identified. Additionally, the results suggest that the removal of water molecules from the main (octahedral) layers begins at ~ 200 °C. Finally, at 700–1250 °C, the solid-state reactions between CŜ, CA and CaO are observed, generating the formation of ye`elimite.