In-situ transmission electron microscopy of calcium carbonate formation

Abstract

Calcium Carbonate (CaCO$_3$) has been studied for industrial and medical usage. For increasing efficiency, the enlargement of the surface area has been challenged. In previous studies, concentration, pressure, temperature, and additive addition have all been considered as the main parameter to manipulate the shape of CaCO$_3$. For direct observation of the effect of these parameters, liquid phase Transmission Electron Microscopy (LP-TEM) has been efficiently utilized. However, the initial phase of CaCO$_3$, Amorphous Calcium Carbonate (ACC) has not yet discovered all the mysteries like the hollowing mechanism of ACC. Here, by utilizing LP-TEM, the crystallization process of CaCO$_3$ in high pH (9.75) conditions is observed. Furthermore, based on the analysis of the Selected Area Electron Diffraction (SAED) pattern and Electron Energy Loss Spectroscopy (EELS) data, the initial phase is determined to ACC-H2O and ACC. In conclusion, dehydration and solid-state phase transformation at the surface of ACC-H2O construct the ACC shell around the particle. And then, sequential process of dissolution / (re)precipitation of ACC-H2O fabricate hollow shape of ACC.