Comprehensive evaluation of formation kinetics in preparation of ternesite from different polymorphs of Ca2SiO4

Ca 2 SiO 4 is an essential intermediate phase in the formation process of Ca 5 (SiO 4 ) 2 SO 4 , and the polymorph change of Ca 2 SiO 4 would seriously influence the relevant reaction kinetics. Herein, the reaction activities of three Ca 2 SiO 4 polymorphs ( α L ’ , β and γ phases) in preparation of Ca 5 (SiO 4 ) 2 SO 4 are studied in detail. The results indicate there is almost no generation of Ca 5 (SiO 4 ) 2 SO 4 from α L ’ -Ca 2 SiO 4 , and by contrast, β - and γ -Ca 2 SiO 4 phases can successfully form the target product. Moreover, β -Ca 2 SiO 4 manifests a higher reactivity than that of the γ one, and the relevant reaction rate constant is about 1.6 times larger than that of the γ one. Meanwhile, the ion activation mechanism is investigated in the formation process of Ca 5 (SiO 4 ) 2 SO 4 by Eu 3+ fluorescence labeling. The reaction sites containing Eu 3+ ions preferentially form Ca 5 (SiO 4 ) 2 SO 4 due to the introduced oxygen defects or calcium vacancies by doping Eu 3+ ions, especially for the low-temperature sintering. In combination with the polymorph influence, the activation effect from ion doping further contributes to the formation of Ca 5 (SiO 4 ) 2 SO 4 . The findings in this research provide a guidance for the synthesis and application development of Ca 5 (SiO 4 ) 2 SO 4 and offer a deeper understanding of the ion doping effect in cement minerals.