Effect of Na₂O on transition and stability of dicalcium silicate based on sintering process

Abstract

The phase transition, morphology, stability and pulverization performance of dicalcium silicate (C₂S) with different Na₂O additions during the high-temperature sintering process were studied using XRD, SEM-EDS, FT-IR, and Raman spectra methods. When the CaO to SiO₂ molar ratio is 2.0 and the Na₂O to SiO₂ molar ratio is below 0.20, the crystalline calcium silicate compounds include γ-C₂S and β-C₂S. As the Na₂O addition increases, the proportion, crystallinity and grain size of β-C₂S in the sintered products increase, those parameters of β-C₂S decrease, and the content of amorphous phase increases. Na₂O mainly forms solid solutions in β-C₂S and inhibits the transition of β-C₂S to γ-C₂S, resulting in the sintered products unpulverized. The stability of sintered products in alkali solution decreases significantly with the increasing Na₂O additions, and the β-C₂S solid solution with Na₂O is less stable than γ-C₂S. The mechanism that Na₂O affects the transition of C₂S as well as its stability was also discussed, which can give actual guidance for the treatment of low-grade alumina-containing resources by the sintering process.

Keywords

dicalcium silicate / Na₂O / crystal structure / stability / sintering

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