Jw. Zhang et Gh. Nancollas, KINK DENSITY AND RATE OF STEP MOVEMENT DURING GROWTH AND DISSOLUTION OF AN AB CRYSTAL IN A NONSTOICHIOMETRIC SOLUTION, Journal of colloid and interface science, 200(1), 1998, pp. 131-145
Despite the fact that the growth and dissolution of sparingly soluble
minerals in aquatic and biological systems usually occur under nonstoi
chiometric conditions, little attention has been paid to the effect of
solution ionic ratio on the rates. Equations for kink density along a
n atomic step of an AB crystal with NaCl lattice in super-and undersat
urated solutions have been derived using a kinetic approach previously
developed for a Kossel crystal. The equations reduce to that obtained
thermodynamically at solubility equilibrium. The rate of step movemen
t can subsequently be calculated. For growth and dissolution controlle
d by integration and detachment, respectively, it is shown that the ra
te cannot be defined solely in terms of the ionic activity product; it
also depends upon the activity ratio and the relative integration fre
quencies of the lattice ions. At a given thermodynamic driving force,
a maximum rate occurs at a certain ratio of lattice ion activities,The
present theory is expected to be applicable to sparingly soluble salt
s, which are characterized by a low kink density, The effect of soluti
on stoichiometry is also discussed for diffusion-controlled crystal gr
owth and dissolution. (C) 1998 Academic Press.