Kinetics of crystal growth and dissolution of calcium and magnesium fluorides

Kinetic results of the crystal growth and dissolution of seed crystals of calcium fluoride and magnesium fluoride, obtained conductimetrically and potentiometrically, indicate that both processes are controlled by a surface reaction mechanism. An initial reaction surge in the case of magnesium fluoride is consistent with a concomitant secondary nucleation process. The activation energies for the growth and dissolution of calcium fluoride, 14.5 and 1.4 kcal mole-1, also point to surface reaction control. The heat of solution of this salt, obtained calorimetrically, was 2.9 +/- 0.1 kcal mole-1.