HYDROTHERMAL-ELECTROCHEMICAL DEPOSITION OF HYDROXYAPATITE

Hydroxyapatite crystals were formed on a titanium electrode using the hydrothermal-electrochemical method in an autoclave with two electrode s. The electrolyte dissolving NaCl, K2HPO4, CaCl2 . 2H(2)O, trishydrox yaminomethane, and hydrochloric acid was maintained at 80 degrees-200 degrees C. After loading of a constant current at 12.5 mA/cm(2) for 1 h, the deposited amounts were measured through the weight gain of the electrode. The deposits were characterized by X-ray diffractometry, Fo urier transform infrared spectroscopy, field emission-type scanning el ectron microscopy, field emission-type transmission electron microscop y, and energy dispersive X-ray spectroscopy. The deposited amount incr eased with electrolyte temperatures up to 150 degrees C and slightly d ecreased above that temperature. The deposits were identified as hydro xyapatite crystal rods grown along the c axis and perpendicular to the substrate. The crystallinity of the deposited hydroxyapatite increase d continuously with the electrolyte temperature and closed to stoichio metric hydroxyapatite. At 150 degrees-160 degrees C, the hydroxyapatit e rod grew very homogeneously perpendicular to the substrate, and the edge of the needle had a flat hexagonal plane. (C) 1998 John Wiley & S ons, Inc.