The effect of Cr2O3 and P2O5 additions on the phase transformations during the formation of calcium sulfoaluminate C4A3S¯

The study describes the influence of chromium and phosphorus additions on the phase transformations during the formation of the calcium sulfoaluminate Ca₄Al₆SO₁₆ from CaCO₃-Al₂O₃-CaSO₄ mixtures. The temperatures of decarbonation reaction were measured by means of differential thermal analysis. The enthalpy variations at different heating temperatures were determined by isothermal calorimetry. The results show that the Cr₂O₃ and P₂O₅ additions lower the onset temperature of decarbonation. The energy requirement at high temperature of the doped mixtures is less, compared to that of mixtures without dopants. The formation of solid solutions is followed by X-ray diffraction. The higher concentrations of additives hinder the formation of the C₄A₃S¯ phase.