Chemistry of hydrogrossular

Hydrogrossular is the solid solution between Katoite (Ca 3 Al 2 (OH) 12 ) and Grossular (Ca 3 Al 2 (SiO 4 ) 3 ). The hydrogrossular series are major hydration products of calcium (sulfo)aluminate cement and are also present in traditional cement systems hydrated at elevated temperature. Hydrogrossular is also important to the Earth's hydrosphere under different hydrothermal conditions. However, the formation kinetics and possible existence of a miscibility gap in hydrogrossular remains poorly understood. In this paper, we hydrothermally synthesized hydrogrossular under different Si concentrations, temperatures and durations. We were able to synthesize hydrogrossular with continuous chemical composition within the miscibility gap proposed in literature. We hypothesized a kinetic-driven multi-step crystallization process to explain the coexistence behavior rather than equilibrium immiscibility proposed in previous studies. Under our investigated hydrothermal synthesis conditions, the maximum Si 4+ replacement to 4H + in hydrogrossular showed a linear increasement trend with synthesis temperature, data from previous literature with different synthesis conditions are broadly consistent with this empirical correlation. These findings provide updated insights into the (thermo)chemistry of the hydrogrossular series and its formation in cement systems.