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 Å) 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, -Ca₂SiO₄ ↔ -Ca₂SiO₄ from 1170 to 1230 K, and -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 -Ca₂SiO₄ ↔ α-Ca₂SiO₄ has decreased with the addition of activators. Finally, active belite clinkers were produced as the final samples contained α-belite phases.