Growth of broken crystals tracked in 4D using X-ray computed tomography and its influence on impurity incorporation

Crystallization is a commonly used unit operation for separation and purification. During processing, crystals may break due to mechanical stress, e.g., intentionally by milling or unintentionally through collision with stirrers. This study investigates the growth of broken crystals in three dimensions using X-ray micro-computed tomography. The results show that damaged regions of crystals grow faster than faceted regions, and crystals become faceted through growth. Initially, this happens on a microscale, producing faceted but concave regions on the crystal surface. Eventually, crystals become convex. Shape-healing through growth incorporates inclusions in the crystals. These findings have important implications for designing and optimizing crystallization processes in the pharmaceutical, food, and chemical industries, as purity is often a critical quality criterion adversely affected by inclusions. In addition, the kinetics in crystallization processes are likely to be strongly affected by the growth of non-faceted and concave crystals.