INTERFACIAL PROPERTIES AND EQUILIBRIA IN THE APATITE-AQUEOUS SOLUTION SYSTEM

Thermodynamic calculations of the solubility of hydroxyapatite have been carried out and the results are presented in different types of equilibrium diagrams in order to interpret observed interfacial behavior in this system. For predicting the electrical double-layer properties, especially the conditions for zero surface charge, diagram with activities of predominant calcium and phosphorous species as the axes and pH as the third independent variable have been found to be most useful. Conditions for zero charge at the surface are predicted based on the assumption that the affinity for the surface of all the lattice ions in solution is nearly equal. The different kinds of equilibrium diagrams have been found useful to explain some hitherto unexplained observations in the literature. Calculations have also been made to determine the effect of fluoride ions on the thermodynamic properties of the system. Experimental data are presented to support the calculations. © 1979.