Rokhmistrov D. Structural changes in hydroxyapatite samples with various impurity contents at annealing in the temperature range of 20-1200С

Object of study: highly disperse hydroxyapatite powders. The aim of study: an establishment of interrelation between structural changes in hydroxyapatite samples which contain impurities, and the synthesis conditions at room temperature and 100С, and also at annealing in an interval of temperatures 20-1200С. Methods: XRD, electron diffraction study, scanning and transmission electron microscopy, IR-spectroscopy, energy-dispersive analysis, X-ray microanalysis, mass-spectrometry, thermogravimetry and differential thermal analysis, Archimedes' method. Results: It has been shown, that the calcium phosphate known earlier as amorphous (ACP), actually is a mixture of true ACP and nanocrystalline HA with particle sizes of some lattice constants. The ACP to HA transformation scheme which is in a good agreement with the experimental data has been offered. The nature and the origin of impurities and the lattice replacements which influenced on the lattice constants of highly disperse HA have been established. The temperature dependence of the lattice constants at annealing of highly disperse HA in an interval 20-1200C, which assigned with interaction of the impurity particles and release of yields from the lattice obtained and explained. Non-monotonic curves of shrinkage at sintering of highly dispersive HA pressings are found, They caused by the thermal decomposition of the carbonate ions which substitute phosphate groups in the crystal lattice (В-type of replacement). Field of use: solid state physics, bioactive material science.