Transmission electron microscopic observation of a metastable phase on the thermal decomposition process of Ca-deficient hydroxyapatite |
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Authors: | Masato Tamai Toshiyuki Isshiki Koji Nishio Mitsuhiro Nakamura Atsushi Nakahira Hisamitsu Endoh |
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Affiliation: | (1) Department of Chemistry and Materials Technology, Kyoto Institute of Technology, Gosho-kaido-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan;(2) Department of Electronics and Information Science, Kyoto Institute of Technology, Gosho-kaido-cho, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan |
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Abstract: | Calcium-deficient hydroxyapatite (Ca-def HAp) decomposes to stoichiometric hydroxyapatite (HAp) and β-tricalcium phosphate
(β-TCP) at high temperature. In a previous study, we reported that a metastable phase with a high Ca/P molar ratio appeared
in the temperature range from 700 to 800°C. In the present study, the formation process of a metastable phase and the crystallographic
relationship between the Ca-rich metastable phase and HAp matrix were investigated by high-resolution transmission electron
microscopy (HRTEM). Ca-def HAp was annealed at 600–850°C for 2 or 6 h in air. TEM observations were performed before and after
annealing Ca-def HAp. Based on analysis of image of Ca-def HAp before annealing, several HAp crystals with different aspect
ratios agglomerated. The metastable phases grew thicker by long-term annealing. HRTEM image suggested that the Ca-rich metastable
phase was formed by migration to the interface and continuous accumulation of calcium ions from HAp crystals with a small
aspect ratio. From HRTEM images and results of the analysis of selected area electron diffraction patterns along the 010],
110] and 001] zone axes, lattice constants of the metastable phases were determined to be a = 2.86 nm, b = 0.94 nm, and c = 0.69 nm with orthorhombic crystals system. |
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