Croatica Chemica Acta, Vol. 56 No. 4, 1983.
Conference paper
Thermodynamics of Hydroxyapatite Surfaces
Walter E. Brown
; American Dental Association Health Foundation Research Unit, National Bureau of Standards, Washington, DC 20234, USA
Lawrence C. Chow
; American Dental Association Health Foundation Research Unit, National Bureau of Standards, Washington, DC 20234, USA
M. Mathew
; American Dental Association Health Foundation Research Unit, National Bureau of Standards, Washington, DC 20234, USA
Abstract
A new model for equilibria at the interface of a sparingly
soluble crystal is reviewed. It provides that several kinds of equilibria
are present and each type is characterized by (i) a set of
species that are transported across the phase boundary, (ii) a set ·
of chemical reactions which describe this transport process, and
(iii) a set of thermodynamic expressions which define equilibrium.
Three types are envisaged: 1. Stoichiometric equilibrium provides
the thermodynamic communication between the lattice and the
bulk solution, occurs at a kink site, preserves the composition of
the solid phase, defines a solubility product, leads to an isotherm
in the phase diagram, and is unaffected by Galvani potentials. The
equilibrium is defined by a single equation. 2. Gibbsian equilibrium
in which the chemical potential of each component is stated to be
equal across the phase boundary, but does not define an actual
chemical process. There is one such equation for each component
in the system. 3. Electrochemical equilibrium provides thermodynamic
communication between ions in the bulk phase and those
in the outer layer of the crystal, is nonstoichiometric, is profoundly
affected by Galvani potentials, does not lead to a solubility product
constant nor to an isotherm, and requires one more equilibrium
condition than there are components in the system. Equilibrium
between the lattice and the surface is limited to reactions via the
aqueous phase, one of which is stoichiometric and the other nonstoichiometric.
This model provides a clarity of description of
interfacial events heretofore unattainable.
Keywords
Hrčak ID:
194197
URI
Publication date:
9.11.1983.
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