EELS characterisation of β-tricalcium phosphate and hydroxyapatite

Hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) are of great interest due to their potential application as bone-replacement materials. In particular, composites made of a mixture of these Ca-phosphates revealed improved mechanical properties; however, the reason for this improvement is unknown. Future development and properties enhancement of such bioceramics is linked to the possibility to characterise their particular microstructure. In this context, the ability to quickly identify individual grains of HA and β-TCP within these composites will allow acquiring information about the phase distributions and the phase-boundary microstructure. The aim of the present study is, therefore, to demonstrate that electron energy-loss spectroscopy (EELS) can be successfully employed to differentiate between individual grains of HA and β-TCP. In particular, the analysis of the near-edge structure of the oxygen K-ionisation edge allows detection of a characteristic signal at ca. 536 eV that can be employed as an identification tool for HA. EELS investigations were performed first on as-received and calcined (1000 °C) HA and β-TCP powders and subsequently on pure bulk HA and β-TCP samples sintered at 1250 °C. Finally, this method was successfully applied to a HA/β-TCP (50/50 wt.%) composite sintered at 1250 °C.