*3.3. Crystals on the Titanium Surfaces after Immersion in the Calcium Phosphate Solution*

Figure 6 shows the SEM photographs of the polished titanium after immersion in the calcium phosphate solution at 37 ◦C (Ti-IT37◦) and after 5 M NaOH treatment and subsequent immersion in the calcium phosphate solution at 37 ◦C (Ti-AT-IT37◦). No crystals were deposited on the Ti-IT37◦ for up to 7 days of immersion. In contrast, spherical particles consisting of plate-like HA crystals were deposited on part of the Ti-AT-IT37◦ after 1 day of immersion. These crystals grew with time and covered almost all of the surface of the titanium after immersion for 7 days. These results were consistent with those reported previously [5].

Figure 7 shows the SEM photographs of the polished titanium after immersion in the calcium phosphate solution at 60 ◦C (Ti-IT60◦) and after 5 M NaOH treatment and subsequent immersion in the calcium phosphate solution at 60 ◦C (Ti-AT-IT60◦). No spherical particle precipitation was observed on the Ti-IT60◦ after immersion in the solution for 30 min. Precipitated crystals between 5 and 40 μm in diameter were found on the Ti-IT 60◦ after immersion for 6 h, and these HA spherical particles grew into large size spherical particles between 40 and 100 μm in diameter after immersion for 24 h. On the Ti-AT-IT60◦, small crystals precipitated after immersion for 30 min. The density of the crystals increased due to the growth of crystals with time. From the results shown in Figures 6 and 7, it was observed that the crystal formation and its growth rate were markedly enhanced with 5 M NaOH treatment as well as an increase in the temperature of the calcium phosphate solution.

**Figure 6.** SEM images of the Polished-Ti and Ti-AT after immersion in the meta stable calcium phosphate solution at 37 ◦C (Ti-IT37◦ and Ti-AT-IT37◦). No HA spherical particles were deposited on the Ti-IT37◦ for up to 7 days of immersion. In contrast, spherical particles consisting of plate-like HA were deposited on the part of the Ti-AT-IT37◦ after immersion for 1 day.

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**Figure 7.** SEM images of the Polished-Ti and Ti-AT after immersion in the calcium phosphate solution at 60 ◦C (Ti-IT60◦ and Ti-AT-IT60◦). There was no HA precipitation observed on the Ti-IT60◦ after immersion in the solution for 30 min. HA spherical particles were found on the Ti-IT60◦ after immersion for 6 h and they grew into large spherical particles after immersion for 24 h. On the Ti-AT-IT60◦, small HA spherical particles precipitated after immersion for 30min. The spherical particles grew larger with time and covered the entire surface of a titanium after immersion for 24 h.
