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

Abstract

• STEM was used to identify the atomic structure of β-C 2 S. • TEM results confirmed the (0 0 1) twin crystal planes in β-C 2 S lattice. • Doping 1 wt% Ca 3 (PO 4 ) 2 stabled the β-C 2 S in room temperature. • The intrinsic difference of β-C 2 S inherent reactivity was reveled. Beta-dicalcium silicate (β-C 2 S), one of the main phases in Portland cement clinker, offers some promising overviews regarding CO 2 and energy savings potential compared to alite. Understanding the crystalline structure and reactive sites on β-C 2 S 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-C 2 S are still blank. Herein, crystal information analysis, including atomic structure and active oxygen atoms of lab-scale synthesized β-C 2 S 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-C 2 S structure. The exact positions of Ca and Si columns in β-C 2 S crystal lattice were obtained from STEM images, which is consistent with the visualization results. The hydration heat evolution of β-C 2 S within 30 d was investigated by isothermal calorimetry, showing that β-C 2 S 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-C 2 S, have a significant contribution to the crystal structure foundation data base, which is beneficial to understanding the intrinsic relationship between β-C 2 S hydration and its atomic structure.