Abstract
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.
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