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. 31P 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 31P 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. Copyright 1998 Kluwer Academic Publishers