EFFECT OF HEAT-TREATMENT ON APATITE-FORMING ABILITY OF TI METAL-INDUCED BY ALKALI TREATMENT

The present authors previously showed that titanium metal forms a bone -like apatite layer on its surface in a simulated body fluid (SBF), wh en it has been treated with a NaOH solution to form a sodium titanate hydrogel layer on its surface. This indicates that the NaOH-treated Ti metal bonds to living bone. The gel layer as-formed is, however, mech anically unstable. In the present study, the NaOH-treated Ti metal was heat treated at various temperatures in order to convert the gel laye r into a more mechanically stable layer. The gel layer was dehydrated and transformed into an amorphous sodium titanate layer at 400-500 deg rees C, fairly densified at 600 degrees C and converted into crystalli ne sodium titanate and rutile above 700 degrees C. The induction perio d for the apatite formation on the NaOH-treated Ti metal in SBF increa sed with the transformation of the surface gel layer by the heat treat ment. Ti metal heat treated at 600 degrees C, however, showed a fairly short induction period as well as high mechanical stability, since it was covered with a fairly densified amorphous layer.