A Comparative Study of Pressureless Sintered Nanostructured Hydroxyapatite/TiO₂ Composites Prepared by Different TiO₂ Addition Methods.

Two methods of TiO₂ addition were applied to prepare hydroxyapatite/TiO₂ (HA/TiO₂) composite, i.e., hydrolysis TiO₂ in HA powders (N-HA/TiO₂) and mixing commercial nano-sized HA and TiO₂ powder (C-HA/TiO₂). Effects of TiO₂ addition methods and sintering temperatures on phase, microstructure and microhardness were investigated for pressureless sintered HA/TiO₂ composites, and pure HA was investigated for comparison. Results show that TiO₂ from both hydrolysis and mixing commercial powder presented similar effects on phase structures and composition, and trended to chemically react with HA in the HA/TiO₂ composites at high sintering temperature. Weight loss for different composites was investigated by thermal analysis. Sintering behavior for two different composite was also discussed. The TiO₂ from hydrolysis can effectively enhance the TiO₂ distribution and densification for the N-HA/TiO₂ composites. Both two different composites showed typical grain growth and pore formation with the increase of sintering temperature. The N-HA/TiO₂ composite had a lower porosity, higher shrinkage and microhardness than that of C-HA/TiO₂ composite at sintering temperature from 700 °C to 1100 °C.