Hydrothermal growth of hydroxyapatite single crystals under natural convection

Whiskerlike-shaped hydroxyapatite single crystals with the calcium-deficient nature were hydrothermally grown under natural convection by using a temperature-gradient-applied pressure vessel. With this method, crystals grew thinner with a smaller tapering angle than those grown under the nonconvection. Maximum length of the crystals grown under natural convection was 8.3 nm. The grown crystals survived without fracture through at least ten times maximum indentation (25 µm) of the three-point bending tests, showing the maximum bending angle of 62°. Average tensile strength of the crystals was 410.0 MPa.