Effect of Ti ion substitution on the structure of hydroxylapatite

In order to increase the understanding of the interaction of titanium (Ti) ions with hydroxylapatite (HA) structure, two different kinds of experiments were carried out. In the first, titanium ion containing HA was made via a precipitation method. Tetraethyl orthotitanate were added to precipitating HA to incorporate Ti ions into HA structure. The precipitates were dried and sintered in air at 500 °C, 700 °C, 900 °C, 1100 °C, and 1300 °C for 2 h. X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy analysis were used to characterize the samples. In the second, rather as the complementary experiments to the first set, powder mixtures of HA/CaTiO₃, tri-calcium phosphate/CaTiO₃ were sintered in air at 900 °C, 1100 °C, and 1300 °C for 2 h, and characterized with X-ray diffraction technique. Lattice parameters from X-ray diffraction spectra showed that Ti incorporation into the apatite structure caused lattice shrinkage. The grain sizes of substituted HAs were smaller than those of pure HA. Increasing the amount of the Ti ions in HA caused the decomposition of HA associated with the formation of α-tricalcium phosphate and CaTiO₃. This enhanced the porosity in titanium containing HA compared to pure HA. As also verified by the results of complementary experiments, α-tricalcium phosphate (TCP) and CaTiO₃ reacted at 1300 °C in the expense of both phases in the presence of HA. No reaction products in the form of new phases could be identified. On the other hand, the same reaction was not observed in the samples that did not have stable HA phase.