A modified milling system, using a bimodal distribution of highly resistant ceramics. Part 1. A natural hydroxyapatite study

A careful combination of the main parameters controlling natural hydroxyapatite (NHA: Ca10(PO4)6(OH)2) production such as milling techniques, sintering temperature and holding time may lead to an interesting NHA based bio-ceramics without any foreign oxide additions. In this way, an original wet milling setup has been proposed to obtain sub-micron sized NHA powders. In order to avoid any possible NHA decomposition, a precise Ca/P ratio of NHA derived from animals was selected accordingly. Also, an alternative direct visual approach of the bone age classification was also proposed. A relative density of about 95% was obtained for powders sintered at 1300 °C for 2 h. The best Vickers micro-hardness and 3 point bending strength values for these sintered samples, using this proposed milling system and without any additions, were 4.7 ± 0.3 GPa and 37 MPa, respectively. Finally, a complete correlation between the powder microstructure and the final product properties has been established.