Transmission electron microscopic observation of a metastable phase on the thermal decomposition process of Ca-deficient hydroxyapatite
- 72 Downloads
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 ,  and  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.
KeywordsHydroxyapatite Select Area Electron Diffraction Electron Diffraction Pattern HRTEM Image Transmission Electron Microscopic Observation
Unable to display preview. Download preview PDF.
- 2.H. MONMA, S. UENO, Y. TSUTSUMI and K. KANAZAWA, J. Ceram. Soc. Jpn. (Yogyo-Kyokai-shi) 86 (1978) 590.Google Scholar
- 11.M. TAMAI, M. NAKAMURA, T. ISSHIKI, K. NISHIO, H. ENDOH and A. NAKAHIRA, J. Mater. Sci: Mater. Med. 14 (2003) 617.Google Scholar
- 13.J. C. ELLIOTT, in “Structure and Chemistry of the Apatite and Other Calcium Orthophosphates” (Elsevier, Tokyo, 1994) p. 1.Google Scholar