Structural evolution of amorphous calcium sulfate nanoparticles into crystalline gypsum phase

Abstract

The involvement of amorphous calcium sulfate (ACS) as a precursor to calcium sulfate crystallization remains an important but poorly understood phenomenon, especially the mechanism by which ACS evolves into crystalline phase. Here, we captured the ACS nanoparticles as a precursor to calcium sulfate crystallization in a concentrated CaCl₂ solution at 90 °C and observed several stages of its evolution. The ACS nanoparticles grew by simultaneous fusion and internal structural evolution. Aggregation of the ACS nanoparticles gave birth to bulk ACS particles within which nanocrystalline domains sprouted and developed into crystalline gypsum. This work deepens the understanding of the evolution of ACS nanoparticles and its role in multistage crystallization of calcium sulfate.