Wilhelm Ostwald notable work Ostwald ripening
Crystallization
Ostwald studied the crystallization behavior of solids, especially those solids that are capable of crystallizing in different forms, in the phenomenon known as polymorphism. He discovered that solids do not necessarily crystallize in their most thermodynamically stable form but instead sometimes crystallize preferentially in other forms dependent on the relative rates of crystallization of each polymorphic form. Ostwald found that the relative rates were dependent on the surface tension between the solid polymorph and the liquid form. Many common materials exhibit this type of behavior, including minerals and various organic compounds. This finding came to be known as Ostwald's rule.Ostwald realized that solid or liquid solutions can continue to evolve over time. While the a non-thermodynamically preferred polymorph may crystallize first, more thermodynamically stable forms can continue to develop as the solution ages. Often this results in large crystals forming, since they are more thermodynamically stable than are large numbers of small crystals. This phenomenon came to be known as Ostwald Ripening and is observed in many situations. An everyday example is the gritty texture that ice cream develops as it ages. On a geologic timescale, many minerals exhibit Ostwald Ripening as their crystal forms evolve as the mineral ages.Related to solubility and crystallization was Ostwald's finding that dissolution of a solid depends on the size of the crystal. When the crystals are small, typically less than a micron, the solubility of the solid in the solution phase is increased. Ostwald quantified this effect mathematically in a relationship that became known as the Ostwald-Freundlich equation. Ostwald first published his finding in 1900, and his mathematical equation was refined by German chemist Herbert Freundlich in 1909. This mathematical relationship also applies to the partial pressure of substance in the system. The Ostwald-Freundlich equation takes into account the surface tension of the particle in the system, in addition to curvature and temperature. The size dependence of solubility is sometimes utilized in the formulation of pharmaceuticals that have low solubility so as to enhance their uptake by the patient. The size dependence also has a role in Ostwald Ripening.
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