Crystallization

The general idea is to avoid too high a driving force because that will force crystals to grow too rapidly. There must be time for the correct atom, ion, or molecule to find a place in the crystal lattice where it can fit perfectly. Intense driving force may force an impurity into the lattice. The following graph indicates an acceptable operating region.

A concentration in solution that falls in the bluish region is below saturation, and no crystals can form.
The red/purple region indicates where the concentration in solution is higher than saturation, and there is a driving force for deposition of crystals. The exact transition to the yellow region cannot be measured; this line is indistinct and depends on the conditions of the experiment.
A concentration in the yellow region is far above saturation. Too much driving force means that we can expect crystallization to be spontaneous and fast.

In the red/purple region, especially close to the lower line, nothing may happen unless something such as nucleation sites or seed crystals initiates crystallization.

  • A reason for violating rules for good crystallization.
    30-May-96