Structural Changes of Bioapatite during Heat Treatment

Bovine bones heated to 1100 °C under air atmosphere were studied using transmission electron microscopy. During heating, bone bioapatite was transformed into hydroxylapatite (HAp). Energy-dispersive spectroscopy did not indicate the presence of A-type CO3 substitution, it showed a near-ideal Ca/P ratio of 1.67 during heating. In the present study, the structure of the formed HAp was determined using automated electron diffraction tomography, a 3D electron diffraction method, space group P63 a = 9.42 Å and c = 6.89 Å at 700 °C. The position of the OH hydrogen sitting in the channel position was determined, confirming the lack of the mirror plane perpendicular to the c-axis in the P63/m space group.