Kinetics of calcium sulfoaluminate formation from tricalcium aluminate, calcium sulfate and calcium oxide

The formation kinetics of tricalcium aluminate (C₃A) and calcium sulfate yielding calcium sulfoaluminate (C₄A₃$) and the decomposition kinetics of calcium sulfoaluminate were investigated by sintering a mixture of synthetic C₃A and gypsum. The quantitative analysis of the phase composition was performed by X-ray powder diffraction analysis using the Rietveld method. The results showed that the formation reaction 3Ca₃Al₂O₆ + CaSO₄ → Ca₄Al₆O₁₂(SO₄) + 6CaO was the primary reaction < 1350 C with and activation energy of 231 ± 42 kJ/mol; while the decomposition reaction 2Ca₄Al₆O ₁₂(SO₄) + 10CaO → 6Ca₃Al₂O ₆ + 2SO₂ ↑ + O₂ ↑ primarily occurred beyond 1350 C with an activation energy of 792 ± 64 kJ/mol. The optimal formation region for C₄A₃$ was from 1150 C to 1350 C and from 6 h to 1 h, which could provide useful information on the formation of C₄A₃$ containing clinkers. The Jander diffusion model was feasible for the formation and decomposition of calcium sulfoaluminate. Ca^{2 +} and SO₄^{2 -} were the diffusive species in both the formation and decomposition reactions.