Structure analysis of beta dicalcium silicate via scanning transmission electron microscope (STEM)

Beta-dicalcium silicate (β-C₂S), one of the main phases in Portland cement clinker, offers some promising overviews regarding CO₂ and energy savings potential compared to alite. Understanding the crystalline structure and reactive sites on β-C₂S surface is critical to enable further optimization of its use. There is a lack of such studies available in the literature. Particularly, regarding the atomic structure and reactive oxygen species of β-C₂S are still blank. Herein, crystal information analysis, including atomic structure and active oxygen atoms of lab-scale synthesized β-C₂S was achieved by spherical aberration-corrected scanning transmission electron microscope (STEM). Detailed compositions and accurate element distributions of atomic layers were thus presented. Results show that a number of (0 0 1) twin crystal planes are present in the β-C₂S structure. The exact positions of Ca and Si columns in β-C₂S crystal lattice were obtained from STEM images, which is consistent with the visualization results. The hydration heat evolution of β-C₂S within 30 d was investigated by isothermal calorimetry, showing that β-C₂S was almost unhydrated for 28 d, only with a weakly exothermic activity in the early stage (1–2 h). Finally, visualization, simulation and experiment results of atomic structure analysis, as well as the hydration behavior of β-C₂S, have a significant contribution to the crystal structure foundation data base, which is beneficial to understanding the intrinsic relationship between β-C₂S hydration and its atomic structure.