Ostwald ripening

The Ostwald ripening is a disperse of self-running colloid chemical ripening matter, which was in 1900 by the polymath and later Nobel laureate in chemistry, Wilhelm Ostwald, discovered and named after him.

Ostwald ripening due to the curvature function of the vapor pressure and the solubility of a fine powder, in terms of Ostwald " as according to known principles of fine powder must be soluble as a coarse as well as fine droplets have a larger vapor pressure than large " ( Gibbs -Thomson effect). The vapor pressure or concentration difference is compensated in a closed system by a stream of material from the small to the large flows colloids. Consequently shrink the small, the large but still growing. When the radius of a small colloid is below a critical value, it is energetically unstable and dissolves completely ( Kelvin instability). Consequently the number of colloids decreases with progressive evolution (coarsening ), and there is a phase separation. During Ostwald ripening, the free energy (surface tension ) of the system is minimized. This is important for practical application in the production of emulsions or creams, wherein the evaluation of the stability of foams or the cloud -point extraction. The Ostwald ripening is measured by nephelometry on the Tyndall effect.

A similar effect occurs in the metallurgy at About Aging and the grain growth in polycrystalline solids on, especially during the grain growth after the grain growth is complete. The aging results from the Ausscheidungsvergröberung precipitated particles of a second phase in metallic alloys by Ostwald ripening, which is described quantitatively by Carl Wagner theory of Ostwald ripening. Analogously, Mats Hillert described the grain coarsening in a lot of crystalline metals and alloys.