Ostwald Ripening Crystal Growth

Ostwald ripening is the result of the difference in solubility S between small and large particles. Typically, smaller particles have a larger solubility than larger particles, and the effect of particle size on solubility can be described by the Kelvin equation [9], 

To obtain a measure of the rate of crystal growth, the particle size distribution of the suspension is followed as a function of time, using either a Coulter counter, a Master Sizer or an optical disc centrifuge. Usually, the cube of the average radius is plotted versus time this gives a straight Hne from which the rate of crystal growth can be determined (the slope of the linear curve). 

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At equilibrium, crystal growth and dissolving rates become equal, and the process of Ostwald ripening may now appear, in which the larger crystals grow at the expense of the smaller ones. The kinetics of the process has been studied (see Ref. 103). 

Another mechanism for crystal growth is known as Ostwald ripening. If a small nucleus or embryo is close to a larger crystal, the ions formed by (partial) dissolution of the smaller, less stable crystal can be incorporated into the larger crystal. As the smaller crystal becomes even smaller, its dissolution will become ever more favorable and eventually it will disappear. The result is that the larger crystals grow at the expense of the smaller ones. 

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