A quantitative analysis of dicalcium silicate synthesized via different sol-gel methods

In this paper, the synthesis of dicalcium silicate (C₂S) via sol-gel (acid-catalyzed) process including aqueous route, non-aqueous route, and the Pechini method is reported. The composition of C₂S (α, β, and γ) polymorphs, by-products, and amorphous content is established by employing QXRD (quantitative X-ray diffraction) studies. The attention has been focused to comprehend assay-amorphous relationships of C₂S yield. The intermediate dried gels have been investigated via thermal analysis to monitor changes in the gel structures and precursors at low temperatures. The synthetic parameters including calcination time and temperature, Ca/Si molar ratio and mode of cooling have been optimized to get pure β-C₂S with low amorphous content. The dependency of β → γ C₂S polymorphic transformation on mean crystallite size (Dcryst) is studied. Overall, the Pechini method exhibits the most promising results for the purity and tuning of β-C₂S polymorph. Moreover, the non-aqueous and aqueous routes require calcining the dried gel at a temperature higher than 1200 ℃ due to the presence of CaO precursors as CaCO3. The theoretical calculations of amorphous content have revealed that the change in the stoichiometry from 2.0 to 1.7 Ca/Si ratio is not a viable solution to improve the C₂S product yield.