Preparation of hydroxyapatite ceramics by hydrothermal hot-pressing method at 300 °C

Hydroxyapatite (HA) ceramics were prepared by a hydrothermal hot-pressing (HHP) method at a low temperature (300 °C). DCPD (CaHPO4·2H2O) + Ca(OH)2, OCP (Ca8H2(PO4)6·5H2O) + Ca(OH)2, DCPD + NH3·H2O, OCP + NH3·H2O or α-TCP (Ca3(PO4)2) + NH3·H2O were used as the precursors. The mixture was treated by HHP under a condition of 300 °C/40 MPa. In sample DCPD + Ca(OH)2 and OCP + Ca(OH)2, the HA ceramics obtained showed a porous and homogenous microstructure, and the bending strength were 9.9 MPa and 10.9 MPa, respectively. In sample α-TCP+NH3·H2O, rod-like HA crystals produced. When the starting materials were DCPD + NH3·H2O, OCP + NH3·H2O, the HA particles produced exhibited plate-like features. It appeared that the plate-like HA particles stacked into a lamellar structure. The formation of the lamellar structure leads to a noticeable improvement in fracture property of the HA ceramic. The bending strength and the fracture toughness of the sample prepared from OCP and ammonia water reach 90 MPa and 2.3 MPam1/2, respectively.