In situ synchrotron powder diffraction study of active belite clinkers

The clinkerization processes to form belite clinkers, with theoretical compositions close to 60 wt% of Ca2SiO4, have been studied in situ by high-resolution high-energy (λ = 0.30 A) synchrotron X-ray powder diffraction. In order to obtain active belite cements, different amounts of K2O, Na2O and SO3 have been added. The existence range of the high-temperature phases has been established and, furthermore, Rietveld quantitative phase analyses at high temperature have been performed for all patterns. The following high-temperature reactions have been investigated: (i) polymorphic transformations of dicalcium silicate, \alpha_{\rm L}'-Ca2SiO4 ↔ \alpha_{\rm H}'-Ca2SiO4 from 1170 to 1230 K, and \alpha_{\rm H}'-Ca2SiO4 ↔ α-Ca2SiO4 from 1500 to 1600 K; (ii) melting of the aluminates phases, Ca3Al2O6 and Ca4(Al2Fe2)O10, above ∼1570 K; and (iii) reaction of Ca2SiO4 with CaO to yield Ca3SiO5 above ∼1550 K. Moreover, in all the studied compositions the temperature of the polymorphic transformation \alpha_{\rm H}'-Ca2SiO4 ↔ α-Ca2SiO4 has decreased with the addition of activators. Finally, active belite clinkers were produced as the final samples contained α-belite phases.