In situ TEM imaging of CaCO ₃ nucleation reveals coexistence of direct and indirect pathways

TLDR

The initial stage of calcite crystallization—nucleus formation—is critical yet difficult to observe due to its length and time scales, as noted by Nielsen et al. The study aimed to investigate calcium carbonate crystallization, addressing competing nucleation theories. The authors mixed calcium and carbonate solutions in a fluid cell and imaged the process with a liquid‑cell transmission electron microscope. They observed both direct ion association into nuclei and transformation of amorphous calcium carbonate into various crystalline polymorphs during nucleation. Science, p.

Abstract

Watching nucleation pathways in calcite The initial stage of crystallization, the formation of nuclei, is a critical process, but because of the length and time scales involved, is hard to observe. Nielsen et al. explored the crystallization of calcium carbonate, a well-studied material but one with multiple nucleation theories. Different calcium and carbonate solutions were mixed inside a fluid cell and imaged using a liquid cell inside a transmission electron microscope. Competing pathways operated during nucleation, with both the direct association of ions into nuclei from solution and the transformation of amorphous calcium carbonate into and between different crystalline polymorphs. Science , this issue p. 1158