A study of hydration reaction on the MgO-MgSO4-H2O system

This study systematically investigated the hydration process and phase evolution of MgO-MgSO₄-H₂O (M-M-H) systems with and without chemical additive at different hydration stages using X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), hydration heat measurement, and microstructural characterization. The results demonstrate that the formation of magnesium oxysulfate cement (MOSc) product phases is intrinsically governed by Mg²⁺ concentration in the liquid phase, which is co-regulated by both raw material molar ratios and phase regions. At low Mg²⁺ concentrations, the primary hydration products in chemical additive-free MOSc are 3Mg(OH)₂·MgSO₄·8H₂O (3–1–8 phase) and Mg(OH)₂. When Mg²⁺ concentration reaches a critical threshold, 5Mg(OH)₂·MgSO₄·7H₂O (5–1–7 phase) additionally forms in the system. Chemical additive significantly alter the hydration process by enhancing Mg²⁺ concentration and promoting MgO particle participation, ultimately shifting the dominant product phases to 5–1–7 and Mg(OH)₂. These findings provide deeper mechanistic understanding of hydration reactions in M-M-H systems and offer important guidelines for research and applications of chemically modified MOSc.