The Effects of Calcium‐to‐Phosphorus Ratio on the Densification and Mechanical Properties of Hydroxyapatite Ceramic

In this work, hydroxyapatite ( HA ) powders were synthesized using calcium hydroxide Ca( OH ) ₂ and orthophosphoric acid H ₃ PO ₄ via wet chemical precipitation method in aqueous medium. Calcium‐to‐phosphorus (Ca/P) ratio was set to 1.57, 1.67, 1.87 that yield calcium‐deficient HA , stoichiometric HA , and calcium‐rich HA , respectively. These synthesized HA powders (having different Ca/P ratio) were characterized in terms of particle size and microstructural examination. Then, the densification and mechanical properties of the calcium‐deficient HA , stoichiometric HA , and calcium‐rich HA were evaluated from 1000 to 1350°C. Experimental results have shown that no decomposition of hydroxyapatite phase was observed for stoichiometric HA (Ca/P = 1.67) and calcium‐deficient HA (Ca/P = 1.57) despite sintered at high temperature of 1300°C. However, calcium oxide (CaO) was detected for calcium‐rich HA (Ca/P = 1.87) when samples sintered at the same temperature. The study revealed that the highest mechanical properties were found in stoichiometric HA samples sintered at 1100–1150°C, having relative density of ~99.8%, Young's modulus of ~120 GP a, Vickers hardness of ~7.23 GP a, and fracture toughness of ~1.22 MP am ^1/2 .