Effect of B2O3 on mechanical properties of porous natural hydroxyapatite derived from cortical bovine bones sintered at 1,050°C

Abstract

Due to its close physical and chemical properties to the mineral part of bone and teeth, hydroxyapatite (Ca10(PO4)6(OH)2) is one of the most attractive materials for human hard-tissue implants. However, its poor mechanical properties are one of the most serious obstacles for wider applications of hydroxyapatite. Optimizing the main parameters controlling a natural hydroxyapatite (NHA) production such as milling techniques, compacting pressure, sintering temperature, holding time and B2O3 additions may lead to better NHA-based bioceramics. Consequently, different percentages of B2O3 (0.5–5.0 wt.%) have been added to NHA powders in order to promote densification and to lower the sintering temperature of porous NHA. Afterwards, these powders were uniaxially cold compacted at 75 MPa and sintered at 1,050°C for 2 h. The porosity ratio was ranged between 27 and 43%. The best Vickers micro-hardness value was 2.1 GPa (using 300 g). This value is much higher than those of NHA (0.6–0.9 GPa) prepared using other usual techniques even with foreign oxide additions such as ZrO2. As far as three point bending strength is concerned, a strength of about 57 MPa was also obtained using this proposed process. This value is significantly higher than that reported by others (35 MPa) using the sol–gel method.