Punin Ripening and the Classification of Solution-Mediated Recrystallization Mechanisms

Abstract

Ripening (also called recrystallization) is a process that occurs commonly in nature and industry that shifts the size distribution of an ensemble of crystals toward a smaller number of larger crystals. Ostwald ripening is by far the best known recrystallization mechanism and sometimes is mistakenly considered as the only mechanism for shifting the crystal size distribution. Ostwald ripening accounts for recrystallization under thermodynamic control and is driven only by the well-known size dependence of solubility. There are, however, other recrystallization mechanisms that can be observed on laboratory timescales for crystals of any size under certain conditions. Internal stress dispersion is a thermodynamic ripening mechanism that depends not on surface energies but rather on crystal defects. In addition, there are two other mechanisms that are kinetic in nature. The most efficient is driven by the size dependence of growth and dissolution rates at low supersaturation. Finally, a mechanism proposed by Punin is driven by the difference between growth and dissolution rates due to crystal defects. All the four mechanisms can be at work simultaneously. The efficiency of ripening can be enhanced by temperature oscillations, but only the thermodynamic mechanisms can work at constant temperature. In this paper, we discuss the fundamentals of these four ripening mechanisms and revisit in detail Punin’s mechanism because it is the least well articulated in the literature.

Dissolution enables dolomite crystal growth near ambient conditions

“…By deliberately introducing periods of mild undersaturation, one can facilitate the dissolution of defects, whose dissolution would otherwise proceed very slowly under constant high supersaturation. Beyond low solute concentrations, undersaturation can also be driven by temperature oscillations ( 60 ), etching ( 61 ), voltage in electrodeposition ( 62 ), redox potential in natural soils ( 63 ), and so on ( 64 ), which can all serve as viable control handles to accelerate the kinetics of ripening.…”

A Novel Strategy for Deracemization Using Periodic Fluctuations of Concentration

“…Key factors in the solid-state deracemization process are ripening mechanisms which lead to dissolution-recrystallization phenomena, and racemization in the solution phase allowing for interconversion between the two enantiomers. In addition, there are different driving forces to induce the ripening mechanisms such as Oswald ripening, internal stress dispersion, size-dependent growth, and dissolution rates in bulk solution, and Punin ripening [6].…”

Efficient Conversion of Threonine to Allothreonine Using Immobilized Amino Acid Racemase and Temperature Cycles

“…Presently, temperature cycling-induced deracemization is an outstanding technique which can successfully produce enantiopure crystals from a suspension of conglomerate-forming compounds. − Temperature fluctuations allow dissolution and recrystallization of the crystal phase of an enantiomeric suspension, where very small changes in the stability or kinetics of growth of the two enantiomorphs, potentially due to differences in crystal size or structural quality, can lead to one of the enantiomorphs being enriched at the expense of the second enantiomorph. − Moreover, temperature fluctuations can produce a mechanism where the size dependence of growth and dissolution rates results in a ripening mechanism, which allow the enriched enantiomeric crystals to consume the counter enantiomorph, leading to an enantiopure phase. This process leads to deracemization of the crystal phase of the suspension.…”