Crystal Formation in the Presence of Ostwald Ripening Agents


Crystal Formation (Nucleation) in the Presence of Ostwald Ripening Agents

Ingo H. Leubner, Journal of Imaging Science, 31(4): 145-148 (1987)

Ripeners provide the most potent effect to increase the crystal size through nucleation control in solution.

Significantly fewer and thus larger crystals are obtained when certain compounds are added before the beginning of crystallization, than without these compounds. These compounds generally also increase Ostwald ripening (Kelvin-Thomson effect) of the crystals. Thus, they are referred to as ripeners.

The BNG theory of crystal formation (nucleation) was extended to predict the effect of Ostwald ripening agents (‘ripeners’) on the nucleation of crystals. It is predicted that below a limiting concentration, nucleation is independent of the ripener concentration. Above this concentration, it is predicted that the number of crystals, Z decreases with increasing ripener concentration, R0. In this concentration range, a linear logZ/logR0 correlation is predicted. The predictions were experimentally confirmed by double-jet precipitations of cubic and octahedral silver bromide crystals in the presence of an Ostwald ripening agent, 1, 10-dithia-4,7,13,16-tegraoxacyclooctadecane.

The crystal number decreased for cubic AgBr crystals from 54.2E15 to 0.072E15, while the size increased from 0.070 to 0.637 µm from zero to 1000mg/liter. For the precipitation of octahedral crystals, the crystal number decreased from 15.4E15 to 0.406E15 crystals, and the size increased from 0.137 t0 0.460 µm between zero and 500 mg/liter.