Critical ageing of hydroxyapatite sol-gel solutions

It has been established that hydroxyapatite coatings can be produced using an alkoxide based sol-gel technique. Previous work showed that in addition to hydroxyapatite other phases including CaO were observed. A critical fact or in determining the composition of the final coating is the period betwee n solution preparation and coating deposition. The current study addresses how the ageing time affects the composition of the coating and the time req uired before a solution can be used to deposit monophasic coatings. Powders and coatings were produced with ageing times up to one week and exa mined with X-ray diffraction, thermal gravimetric analysis and differential thermal analysis. By depositing coatings after various ageing times, it wa s found that a solution ageing time of at least 1 day was required before m onophasic hydroxyapatite coatings could be deposited. Thermogravimetric ana lysis showed that heating of the gel in air or in nitrogen both produced hy droxyapatite. Thermogravimetric analysis could be used as a simple and effe ctive tool for identifying the critical ageing time required to produce hig h-purity hydroxyapatite coatings. (C) 1998 Published by Elsevier Science Lt d. All rights reserved.