Analysis of the nucleation and growth of amorphous CaCO3 by means of time-resolved static light scattering

The formation of amorphous calcium carbonate particles from supersaturated aqueous solution is relevant to many processes in nature and industry. The present work introduces time-resolved static light scattering as a new tool to investigate the initial stage of this process. The process is initiated by mixing a solution of Na2CO3 with a CaCl2 solution or, alternatively, by mixing solutions of the dimethyl ester of carbonic acid and CaCl2 with solutions of NaOH. Particle formation was analyzed by recording scattering curves as a function of time. Scattering data indicate the formation of compact spheres with diameters close to 360 run. In the case of particle formation induced by ester hydrolysis, nucleation sets in after a certain lag time. Particle size is homogeneous, and the growth mechanism corresponds to an addition of ions or small constituent particles to a constant number of growing spheres. An increase of the NaOH concentration, which triggers ester hydrolysis, decreases the lag period prior to the onset of particle formation. An increase of the solution temperature also decreases this lag period. The temperature and NaOH dependent duration of the lag time could successfully be interpreted in terms of the kinetics of the ester hydrolysis. The work establishes time-resolved static light scattering as an efficient tool to investigate the particle formation process of amorphous calcium carbonate.