Kinetics of calcium sulfoaluminate with 1% iron oxide by isothermal and isoconversional methods

The influence of iron oxide (Fe₂O₃) on the formation and decomposition kinetics of calcium sulfoaluminate (C₄A₃$) formed from tricalcium aluminate and calcium sulfate was investigated by both isothermal and isoconversional methods. Rietveld quantitative analysis was used to determine the mineral compositions. The results showed that the addition of 1 wt% iron oxide accelerated both the formation and decomposition of C₄A₃$ at a given temperature. The formation and decomposition activation energies obtained by the isothermal method using the Jander diffusion model were 184 ± 25 kJ/mol and 523 ± 17 kJ/mol, respectively. The isoconversional methods yielded formation and decomposition activation energies of 191 kJ/mol and 509 kJ/mol, respectively. The isoconversional results were thus in agreement with the isothermal results. This confirmed the validity of the diffusion model, which revealed that both reactions were diffusion mechanisms. With 1 wt% iron oxide, the optimal region for the formation of C₄A₃$ was found to be in the temperature range 1150–1300°C for sintering times of 8 h to 1 h.