TRANSMISSION ELECTRON-MICROSCOPIC OBSERVATION OF HETEROGENEOUS FLUORIDATED HYDROXYAPATITES

Two different types of heterogeneous fluoridated hydroxyapatites previ ously synthesized at 80 degrees C and pH 7.4, which might be composed of hydroxyapatite covered with fluorapatite (H-FAp) and fluorapatite c overed with hydroxyapatite (F-HAp), were observed by high-resolution t ransmission electron microscopy. The transverse-sectional shapes of bo th apatites were clearly hexagonal. This confirmed that both apatites were highly crystallized. However, their shapes differed slightly from each other in detail:H-FAp was more slender and F-HAp was typically h exagonal, probably reflecting the shapes of the original core apatites , hydroxyapatite and fluorapatite. The portions thought to be synthesi zed with fluoride-free solution showed clear electron beam damage. The expanded lattice image observed at the edge of the F-HAp crystal coin cided approximately with the a-axis dimension of 0.9443 nm obtained fr om the X-ray diffraction data of synthetic hydroxyapatite. After incub ation in 0.5 mol l(-1) acetate buffer solution (37 degrees C, pH 4.0) for one month, the fluorapatite-covered H-FAp maintained its sharp cor ners, while the hydroxyapatite-covered F-HAp showed rounded corners.