Characterization of hydroxyapatite/titania composite coatings codeposited by a hydrothermal-electrochemical method on titanium

Hydroxyapatite (HA)/titania (TiO2) composite coatings were successfully prepared in an electrolyte solution contain Ca2+ and H2PO4- ions with added TiO2 particles, between 100 degrees C and 200 degrees C in an autoclave through a hydrothermal-electrochemical codeposited method under galvanostatic conditions. The effect of TiO2 additions on the phase composition, microstructure, thermal stability, corrosion behavior and the bonding strength of the HA/TiO2 Composite coatings were studied. The results show that the crystallinity of HA in HA/TiO2 composite coatings increased continuously with the electrolyte temperature and became close to stoichiometric HA. The n(Ca)/n(P) ratio for coatings prepared at 200 degrees C is about 1.67 in accordance with stoichiometric HA. TiO2 particles were imbedded uniformly between HA crystals and the addition of TiO2 reduced the HA crystallite size. After heating at 800 degrees C, HA in the HA/TiO2 composite coating partially decomposes into beta-tri-calcium phosphate (beta-TCP) due to the incorporation of TiO2. After heating at 1200 degrees C, HA tended to react with TiO2 to form CaTiO3, and beta-TCP converted to alpha-tri-calcium phosphate (alpha-TCP), anatase TiO2 transformed to rutile TiO2. The bonding strength of the HA/TiO2 composite coatings increased with the addition of TiO2, and the bonding strength of the TiO2 reinforced HA increased with increases TiO2 content in the coatings. (c) 2005 Elsevier B.V. All rights reserved.