Investigation of hydration phases in the system CaO–SiO₂-P₂O₅-H₂O

Hydration reactions and their rates have been studied qualitatively in CaO-and P₂O₅-rich compositional regions of the system CaO–SiO₂-P₂O₅-H₂O. Using aqueous solutions of Ca (NO₃)₂–4H₂O, Ludox, and H₃PO₄ as starting materials, amorphous powders made by the sol-gel process were reacted with water. Some “curing” reactions were carried out at several temperatures: room temperature, 90 °C, and under hydrothermal conditions. Some glasses in the phosphate-rich region of the system were also made and hydrated. The hydration products are OH–Ap [OH–Ap = Ca₁₀(PO₄)₆-(OH)₂], Ca(OH)₂ [CH = Ca(OH)₂],C–S–H crystalline, C–S–P–H (C = CaO,S = SiO₂,P = P₂O₅,H = H₂O) crystalline, C–S–H gel, C–S–P–H gel, Ca(H₂PO₄)₂·H₂O, and CaHPO₄. All phases have been identified and characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray analysis (EDAX). The reactivities of the precursor materials and the compositional-structural nature of the hydration products formed are discussed. Some new compositions for “cementlike behavior” have been discovered.