Synthesis and characterization of hydrogarnet Ca₃(AlxFe₁ - x)₂(SiO₄)y(OH)₄(₃ - y)

C₃AH₆ is a stable phase in the CaO–Al₂O₃–H₂O system at temperatures 20 °C and above. The presence of SiO₂ results in the formation of C₃AH₆ and C–S–H phases at room temperature. At 110 °C crystalline C₃ASyH₂(₃ - y) phases form. Two solid solutions: C₃AH₆–C₃AS0.41H5.18 and C₃AS0.84H4.32–C₃AS₃ are found with log Ks₀ = - 20.50, - 25.35, - 26.70 and - 39.7 at 20 °C, respectively. In the CaO–Fe₂O₃–H₂O system, only traces of C₃FH₆ and C₄FH₁₃ phases are formed due to the high stability of FH phase. The presence of silica leads between 20 and 110 °C to the formation of C₃FS0.84H4.32 and C₃FS1.34H3.32 phases with log Ks₀ = - 32.50 and - 34.20 at 25 °C. No significant solid solution formation occurred between C₃AH₆ and C₃FH₆ end members, but between C₃AS0.84H4.32 and C₃FS0.84H4.32 solid solution formation is observed. The determined solubility products indicate that C₃FS0.84H4.32 is the most stable iron-containing phase in hydrated Portland cements.