Microstructural Characterization of Thermally Treated Fluorapatite-Titanium Composites

Objectives: This study investigated the crystallinity and phase transformation of thermally treated Fluorapatite-Titanium (FAP-Ti) composites synthesized through the calcium phosphate cement (CPC) method.
Methods: FAP-Ti discs (6 mm D × 3 mm H) were synthesized by mixing a cement powder consisting of 19.89 wt% Ca(OH)₂, 73.12 wt% CaHPO₄, 6.99 wt% CaF₂, and four levels of Ti powder (0%, 10%, 25%, and 40%) with a cement liquid (0.5 mol/L (NH₄)₂HPO₄ solution) at powder to liquid ratios of 1.8, 2.0, 2.3, and 3.3, respectively. The hardened FAP-Ti discs were thermally treated at 900°C and 1200°C. The samples were analyzed for their crystallinity and phase composition using XRD diffractometry, FTIR spectroscopy, SEM/EDS microscopy.
Results: The XRD pattern of pure FAP cement demonstrated the presence of FAP as the only phase formed in the discs. The FAP degree of crystallinity improved with the thermal treatment at 900°C and 1200°C, indicating the stability of the FAP phase under high-temperature conditions. The XRD of the FAP-Ti discs processed at 900 °C showed the FAP maintained a high degree of crystallinity. However, at 1200 °C, the increase of Ti in the FAP matrix gave rise to a phase transformation of 80% of FAP to calcium titanate (CaTiO₃). Further, the FTIR analysis demonstrated a decrease of PO₄ peaks associated with an increase in the OH^– peak at 3240 cm^-1, indicating the dissociation of FAP crystal and the release of fluoride ions. The SEM and EDS analyses showed the formation of FAP microtubes-like shapes covering the surface under 1200 °C.
Conclusions: Apatite formed via the CPC method is a pure FAP phase with solid stability in high-temperature conditions. The transformation of FAP to CaTiO₃ was observed as Ti content increased in the matrix and the treatment temperature rose. Further studies are underway to evaluate the composite’s properties for dental implant applications.