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

• Formation and decomposition of calcium sulphoaluminate were studied.
• Decomposition of calcium sulphoaluminate combined CaO and yielded C3A.
• Activation energy for formation was 231 ± 42 kJ/mol.
• Activation energy for decomposition was 792 ± 64 kJ/mol.
• Both the formation and decomposition were controlled by diffusion.

The formation kinetics of tricalcium aluminate (C3A) and calcium sulfate yielding calcium sulfoaluminate (C4A3$) and the decomposition kinetics of calcium sulfoaluminate were investigated by sintering a mixture of synthetic C3A and gypsum. The quantitative analysis of the phase composition was performed by X-ray powder diffraction analysis using the Rietveld method. The results showed that the formation reaction 3Ca3Al2O6 + CaSO4 → Ca4Al6O12(SO4) + 6CaO was the primary reaction < 1350 °C with and activation energy of 231 ± 42 kJ/mol; while the decomposition reaction 2Ca4Al6O12(SO4) + 10CaO → 6Ca3Al2O6 + 2SO2 ↑ + O2 ↑ primarily occurred beyond 1350 °C with an activation energy of 792 ± 64 kJ/mol. The optimal formation region for C4A3$ 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. Ca2 + and SO42 − were the diffusive species in both the formation and decomposition reactions.