FLUORAPATITE GROWTH-KINETICS AND THE INFLUENCE OF SOLUTION COMPOSITION

Although the rates of dissolution and growth of crystals are usually e xpressed as a function of the thermodynamic driving forces, the actual stoichiometry of the solutions may be an important factor. The kineti cs of fluorapatite (FAP) growth on FAP seed crystals has been investig ated using the constant composition (CC) method in supersaturated solu tions containing both stoichiometric and nonstoichiometric crystal lat tice ion molar ratios. The rate of reaction varies with the zeta-poten tial of the crystal surfaces, decreasing as the latter approaches zero . Flocculation is also shown to be an important factor determining the reaction rates. Rate data as a function of supersaturation is interpr eted in terms of the Burton-Cabrera-Frank model. Calculated interfacia l free energies of the FAP crystals are compared to the values obtaine d by independent experiments.