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The Crystal Growth of Sparingly Soluble Salts

G. H. Nancollas ; Chemistry Department, State University of New York at Buffalo, Buffalo, New York, U.S. A.

Puni tekst: engleski pdf 8.537 Kb

str. 225-231

preuzimanja: 307



The mechanism of crystal growth of sparingly soluble salts
from their supersaturated solutions is discussed in the light of a
number of available growth theories. It is shown that in the case
of both calcium sulphate and calcium carbonate, the observed
quadratic dependence of the rate of crystallization upon the
relative supersaturation is consistent with a surface controlled
reaction. The reaction rates are unaffected by changes in the fluid
dynamics within the crystallization cell, and the activation energy
for both seeded growth and the linear growth of calcium sulphate
is 15.0 ± 0.5 kcal mo1e-1• Evidence is discussed for a screw dislocation
mechanism for calcium sulphate crystal growth. Under
conditions of relatively high supersaturation, secondary nucleation
of both calcium sulphate and calcium carbonate crystals is observed
upon the addition of seed crystals. The striking effect of certain
additives in reducing the rate of crystal growth is discussed in
terms of the important factors involved and in a number of
instances it is shown that a simple adsorption isotherm of the
Langmuir type satisfactory describes the growth data.

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