Calcium Carbonate Nucleation Investigated in a Double Pulse Experiment

The nucleation rate is essential in a number of research fields in order to control crystal formation. The purpose of this study is to test and optimize the double pulse procedure as a method to investigate nucleation of calcium carbonate. The induction time, interpreted as time of formation of postcritical nuclei, was used to separate a stage in which nucleation is the main process from a stage in which formed nuclei mainly grow. The induction time was defined for a model mineralization solution by recording the pH profile of the supersaturated solution representing the desaturation curve. In the double pulse procedure nucleation was quenched during the induction time at several time points, and existing nuclei could grow until a size detectable by scanning electron microscopy. It was observed, under applied supersaturation conditions S = 4, that postcritical nuclei formed directly when the saturation level of the solution was achieved. It is proposed here that the growth of crystals occurs due to the agglomeration of nuclei.