Apatite formation on zirconium metal treated with aqueous NaOH.

Previous studies by the authors have shown that titanium metal, titanium alloys and tantalum metal which were subjected to aqueous NaOH solution and subsequent heat treatments form an apatite surface layer upon immersion in a simulated body fluid (SBF) with ion concentrations nearly equal to those in human blood plasma. These metals form the apatite surface layer even in living body, and bond to living bone through the apatite layer. In the present study, the apatite-forming ability of NaOH-treated zirconium metal in SBF has been investigated. A hydrated zirconia gel layer was formed on the surface of the zirconium metal on exposure to 1-15 M NaOH aqueous solutions at 95 degrees C for 24h. It was observed that the metals treated in NaOH aqueous solutions with concentrations above 5 M form an apatite layer on their surface in SBF. This indicates that the Zr-OH group of the zirconia gel induces apatite nucleation. The present study points to the possibility of obtaining bioactive zirconium after treatment by NaOH.