Conversion of Calcium Fluorapatiteinto Calcium Hydroxyapatite under Alkaline Hydrothermal Conditions
✍ Scribed by J.C. Rendón-Angeles; K. Yanagisawa; N. Ishizawa; S. Oishi
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 296 KB
- Volume
- 151
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
The exchange of F ؊ ions in synthetic calcium 6uorapatite single crystals with OH ؊ was investigated under alkaline hydrothermal conditions. Experiments were performed at various temperatures from 600 to 8003C at 100 MPa, for intervals between 6 and 192 h, in 5 and 10 M KOH solutions. The 6uorapatite single crystals were sluggishly dissolved at temperatures over 7003C, which resulted in the ion exchange of F ؊ with OH ؊ . The rate of conversion was accelerated by increasing the reaction temperature or concentration of the alkaline solution. The ion-exchange reaction started from the prismatic ends of the 6uorapatite single crystals to form acicular small crystals and holes in the original crystal along the c-axis. The acicular crystals had a lower content of F ؊ resulting from the ion exchange, and they broke away from the original crystal as the ion exchange proceeded. This phenomenon may be due to the accumulation of residual stress, which was generated by the lattice expansion along the a-axis caused by the ion exchange. The ion-exchange reaction proceeds by a dissolution and precipitation process. The in6uence of the apatite structure on the conversion mechanism developed under alkaline hydrothermal conditions is proposed.