Thin hydroxyapatite coatings via sol-gel synthesis

Production of hydroxyapatite coatings using an alkoxide-based sol-gel route requires control of solution aging time and heating schedule. P-31 nuclear magnetic resonance spectroscopy was used to investigate the changes during aging of the sol and thermal gravimetric analysis employed to study the behavior of the xerogels as a function of temperature, while final products were determined using X-ray diffraction. Results from P-31 nuclear magnetic resonance spectroscopy and thermal analysis revealed that sols must be aged for at least 24 h to complete the reaction of the two reactants. Deposition of the sol for coating production will then yield monophasic hydroxyapatite. Coatings produced from sols aged for less than 24 h yielded calcium oxide in addition to hydroxyapatite. Prefiring is necessary to remove most of the residual organic materials. Final heating up to 800 degrees C produces crystallization at 550 degrees C and removal of the remaining organic constituents for the formation of a thin hydroxyapatite layer. (C) 1998 Kluwer Academic Publishers.