modification of hydroxyapatite during transmission electron microscopy

The structure of hydroxyapatite compacts was examined using TEM, and hydroxyapatite powder and sintered compacts were characterised by XRD. TEM samples were prepared using both an ion-beam thinner and mechanical grinding in order to distinguish the effect of the techniques used to produce electron-transparent foils for TEM. It can be seen from the TEM micrographs that the hydroxyapatite prepared by both methods is polycrystalline with Ca-rich phases. Diffraction patterns taken from both samples showed that the hydroxyapatite is converted to alpha-Ca3(PO4)2 under the electron beam. The occurrence of this transformation may be due to the release of H2 gas by electron bombardment in a high vacuum, or it may take place in the sample when it is subjected to such conditions in a modern transmission electron microscope. 4 refs.