title: Early homogenous amorphous precursor stages of calcium carbonate and subsequent crystal growth in levitated droplets.
abstract: An in situ study of the contact-free crystallization of calcium carbonate in acoustic levitated droplets is reported. The levitated droplet technique allows an in situ monitoring of the crystallization while avoiding any foreign phase boundaries that may influence the precipitation process by heterogeneous nucleation. The diffusion-controlled precipitation of CaCO3 at neutral pH starts in the initial step with the homogeneous formation of a stable, nanosized liquid-like amorphous calcium carbonate phase that undergoes in a subsequent step a solution-assisted transformation to calcite. Cryogenic scanning electron microscopy studies indicate that precipitation is not induced at the solution/air interface. Our findings demonstrate that a liquid-liquid phase separation occurs at the outset of the precipitation under diffusion-controlled conditions (typical for biomineral formation) with a slow increase of the supersaturation at neutral pH.
authors: Institute for Inorganic Chemistry, Johannes Gutenberg-University, Duesbergweg 10-14, D-55099 Mainz, Germany.
authors: Stephan E
authors: SE
authors: Wolf
authors: Jork
authors: J
authors: Leiterer
authors: Michael
authors: M
authors: Kappl
authors: Franziska
authors: F
authors: Emmerling
authors: Wolfgang
authors: W
authors: Tremel