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

Beta-dicalcium silicate (beta-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 beta-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 beta-C2S are still blank. Herein, crystal information analysis, including atomic structure and active oxygen atoms of lab-scale synthesized beta-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 beta-C2S structure. The exact positions of Ca and Si columns in beta-C2S crystal lattice were obtained from STEM images, which is consistent with the visualization results. The hydration heat evolution of beta-C2S within 30 d was investigated by isothermal calorimetry, showing that beta-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 beta-C2S, have a significant contribution to the crystal structure foundation data base, which is beneficial to understanding the intrinsic relationship between beta-C2S hydration and its atomic structure.