Nucleation and growth of hydroxyapatite on titanium pretreated in NaOH solution: Experiments and thermodynamic explanation

Titanium was submitted to chemical attack with sodium hydroxide solution un der hydrothermal (SBF) conditions and then kept for 4 weeks in simulated bo dy fluid after heat treatment. The resultant coating titanium samples were characterized regarding nucleation and growth of hydroxyapatite on their su rfaces using scanning electron microscopy and energy dispersive spectroscop y, as well. as low angle X-ray diffraction. fn order to obtain a thermodyna mic explanation of same results, Eh-pH diagrams of Na-Ti-H2O and Ca-Ti-H2O systems at 25, 100, 200, and 300 degrees C were built for selected activiti es of the species in aqueous solutions. Values of pairs corresponding to th e predominance limit of the species in solution at equilibrium with 0.21 at m of oxygen pressure were taken from these Eh-pH diagrams for subsequent bu ilding of the pNa-pH and pCa-pH diagrams of the same systems at each referr ed temperature (pi = -log(10)a(i)). Ln addition, the titanate-apatite free energy of formation was estimated and then a pCa-pH diagram of the Ca-P-Ti- H2O system at 25 degrees C was built. Examination of the resultant diagrams could elucidate the thermodynamic viability of the process. (C) 1999 John Wiley & Sons, Inc.