Fabrication and characterization of sol-gel derived hydroxyapatite/zirconia composite nanopowders with various yttria contents

Homogeneous composite nanopowders of hydroxyapatite/30 wt% yttria-stabilized zirconia (HA-YSZ) containing 0, 3, 5, and 8 mol% Y ₂O₃ (namely; HA-0YSZ, HA-3YSZ, HA-5YSZ, and HA-8YSZ) were successfully synthesized using the sol-gel method. Simultaneous thermal analysis (STA), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Fourier transformed infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques were utilized to characterize the prepared nanopowders. Analyses of HA-YSZ composite nanopowders showed the successful formation of desirable phases. HA unit cell volume in the composites increased as a result of ion exchange of calcium and zirconium between HA and zirconia. Results revealed the formation of HA particles with irregular morphology (40-80 nm) and spherical yttria-stabilized zirconia particles (20-30 nm). Segregation of yttrium ions at the grain boundaries of ZrO₂ particles retarded the grain growth of zirconia particles and the presence of ZrO₂ nanoparticles among the hydroxyapatite particles resulted in grain growth inhibition of HA particles. This process can be used to synthesize HA-YSZ composite nanopowders with improved properties, which are much needed for hard tissue repair and biomedical applications.