Alkali Counterions Impact Crystallization Kinetics of Apatite Nanocrystals from Amorphous Calcium Phosphate in Water at High pH

摘要

Crystallization from amorphous precursors emerges as a major principle in biomineralization, but the mechanisms and kinetics involved remain unclear for many materials. Herein, we used in situ synchrotron X-ray diffraction to study crystallization of apatite from amorphous calcium phosphate at a pH where the solution is dominated by phosphate to circumvent the formation of acidic calcium phosphates. The initial crystals were almost isometric. Highly anisotropic growth resulted in needle shaped crystals at later times. Changing the counterion from sodium to potassium lead to changes in nucleation time, growth speed, and nanocrystal shape but preserved the overall crystallization mechanism.