Kinetic model for ye’elimite polimorphs formation during clinkering production of CSA cement

Abstract

The calcium sulfoaluminate, orthorhombic (OY) and pseudo- cubic (CY) ye’elimite polymorphs, were synthesized by solid state reaction from SiO2, Al2O3, Fe2O3, CaCO3, Na2CO3, CaSO4·2H2O in specific oxide relationships. Thermal gravimetric analysis (TGA) was made before sintering the raw mixes in an electrical furnace. Laboratory X-Ray Powder Diffraction (LXRPD) and Rietveld quantitative phase analysis (RQPA) and amorphous and crystalline non-quantified (ACn) quantification were made on each sample. Kinetic were analyzed isothermally between 1150 °C and 1300 °C. The kinetic model who best fitted each OY and CY polymorph was the geometrical and diffusional model proposed by Jander (D3 model). The activation energy, Ea (kJ/mol), values obtained for OY and CY were 420 and 275 respectively. The activation energy is lower in CY due to the presence of minor elements that reduce the sintering temperature. The frequency factor or compensation factor A is higher for OY than CY, meaning the need for a higher collision frequency. As founded by previous authors, the coexistence of both polymorphs must be considered into the kinetic study as a fundamental condition of these results. For this reason, this research proposes the inclusion of αmodified. OY always is present at the reaction beginning. But as higher the temperature and reaction time, in the presence of some minor elements, CY appears mainly at lower temperatures regarding OY, it means requiring lesser energy. Knowing the kinetic model proposed by this work would allow a better control or tailor of the ratio OY/CY, to produce CSA with different performances.