Investigations of spherulitic growth in industrial crystallization

The discrimination between crystal growth and aggregation is of crucial importance for the control of morphology and particle size in crystallization processes, as they are influenced in very different ways by the industrial processing environment. A collection of resembling solution-grown polycrystalline particles that differ widely in chemical nature, like elemental nickel, calcium and sodium carbonate, l-glutamic acid and an aromatic amine have been identified to grow by a spherulitic growth mechanism usually only associated with the crystallization of polymers or melts. The particles are not growing by agglomeration of small individual crystals, as often claimed in the literature. The effect of initial supersaturation, temperature and solvent composition on the spherulitic growth of calcium carbonate (vaterite) has been used to demonstrate how spherulites can grow from solution both by central multidirectional growth (in water) and by unidirectional growth followed by low angle branching (in 90 wt% ethylene glycol). The progression of non-crystallographic branching could be monitored as a function of time at intermediate initial supersaturation values, supplying direct visual evidence for spherulitic growth in this system. A reduction in initial supersaturation and temperature resulted in insufficient branching and dumbbell particles, whereas increased levels of supersaturation rapidly produced fully grown spherulites.