How crystallization equipment works

- Nov 04, 2019-

Crystals are precipitated from the unsaturated solution of the solid substance, generally through the following steps: unsaturated solution → saturated solution → supersaturated solution → occurrence of crystal nuclei → crystal growth.

There are two ways to precipitate crystals:

 

(1) Evaporation at a constant temperature to reduce the amount of the solvent, and the solution represented by the P point becomes a saturated solution, that is, a solution represented by the point A on the S curve. At this time, if the evaporation is stopped and the temperature does not change, the solution at point A is in a dissolved equilibrium state, and the solute is not precipitated from the solution. If evaporation continues, as the amount of solvent continues to decrease, the solution originally indicated by point A must be indicated by the point A'. The solution at this time is a supersaturated solution, and the solute can naturally precipitate crystals from the solution.

 

(2) If the amount of the solvent remains the same, the temperature of the solution is lowered. If the temperature of the unsaturated solution indicated by the P point is lowered from t1 ° C to t 2 ° C, the solution represented by the original P point becomes S. A saturated solution indicated by point B on the curve. At this time, if the temperature is stopped, the solution at point B is in a dissolved equilibrium state, and the solute is not precipitated from the solution. If the temperature is lowered, from t2 °C to t3 °C, the solution originally indicated by point B must be changed to B' point. The solution at this time is a supersaturated solution, and the solute can naturally precipitate crystals from the solution.


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