Size-Dependent Crystalline to Amorphous Uphill Phase Transformation of Hydroxyapatite Nanoparticles

详细信息    查看全文

• 作者：Christina Mossaad ; Mei-Chee Tan ; Matthew Starr ; E. Andrew Payzant ; Jane Y. Howe ; Richard E. Riman
• 刊名：Crystal Growth & Design
• 出版年：2011
• 出版时间：January 5, 2011
• 年：2011
• 卷：11
• 期：1
• 页码：45-52
• 全文大小：1099K
• 年卷期：v.11,no.1(January 5, 2011)
• ISSN：1528-7505

文摘

The room temperature Ca(C₂H₃O₂)₂鈭扠₃PO₄鈭扝₂O equilibrium system was examined for the preparation of hydroxyapatite nanopowder with sizes less than 10 nm. The reaction products were characterized with X-ray diffraction, transmission electron microscopy (TEM), nitrogen-adsorption surface area, helium pycnometry, thermogravimetric analysis, and Karl Fisher titration methods. TEM revealed that 5 nm nanopowders could be successfully prepared with this synthesis approach. However, the vast instability of these powders brought upon by the method of sample separation or the characterization method itself made it impossible to use other conventional methods of characterization to validate TEM data. This study has identified key processing steps that control the order and disorder of these nanomaterials, as well as the conditions that lead to surface area reduction. The most unique phenomenon from this work is the observed crystalline to amorphous phase transformation when washed or unwashed nanopowders are aged for 5 months in 30% relative humidity. This transformation, the first of its kind to be reported in the literature, is accompanied by a surface area loss by a factor of 3 or greater. The uphill phase transformation from the nanocrystalline to amorphous state appears to be driven by the reduction of the large positive surface energy inherent in the as-crystallized 5 nm nanopowder.