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Abstract: The kinetics of sintering of nanosized (20 nm) and microsized (0.7-0.9 μm) hydroxyapatite (HA) powders with continuously increasing temperature at a constant rate was studied by dilatometry. The sintering of the HA micropowders within the temperature range 1100-1300°C occurred by the mechanism of diffusion-viscous flow of crystalline particles. The kinetics of the process was described by a power-law function of time; i.e., the process rate depended on current shrinkage. The shrinkage of the nanopowders within the sintering temperature range was directly proportional to temperature, occurred by the law of viscous flow of amorphous particles, and was independent of the temperature increase rate. The apparent sintering activation energies of the studied micro- and nanopowders were 180 and 60 kJ/mol, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The high-temperature solid-phase interaction of hydroxyapatite (HA) with magnesium, strontium, and zinc nitrates at the stage of annealing of ceramics was investigated. The phase composition and unit cell parameters of the obtained materials were studied for various metals introduced into the structure to different concentrations. The introduction of Mg led to partial decomposition of HA to tricalcium phosphate and tetracalcium phosphate, the addition of Sr caused partial formation of tetracalcium phosphate from HA, and the doping with Zn gave rise to single-phase HAs. [ABSTRACT FROM AUTHOR]