Novel Method for Hydroxyapatite Coating by Hydrothermal Hot-Pressing via Double Layered Capsule
A new hydrothermal method is proposed which enables us to prepare thin hydroxyapatite (HA) ceramic coatings on Ti substrates with a curved surface at low temperatures. The method uses double layered capsules in order to produce a suitable hydrothermal condition; the inner capsule encapsulates the coating materials and a Ti substrate, and the outer capsule is subjected to isostatic pressing under the hydrothermal condition. In this study, it is demonstrated that a pure HA ceramic layer with the thickness of 50 µm could be coated to a Ti cylindrical rod at the low temperature as low as 135°C under the confining pressure of 40 MPa. Pull-out tests were conducted to obtain an estimate for the adhesion properties of the HA coating prepared by the double layered capsule method. The shear strength obtained from the pull-out tests was in the range of 4.0-5.5 MPa. It was also shown that the crack propagation occurred within the HA coating layer, not along the HA/Ti interface in the pull-out tests.
Takashi Nakamura, Kimihiro Yamashita and Masashi Neo
T. Onoki and T. Hashida, "Novel Method for Hydroxyapatite Coating by Hydrothermal Hot-Pressing via Double Layered Capsule ", Key Engineering Materials, Vols. 309-311, pp. 647-650, 2006