One of the easy ways to prepare nanocrystalline hydroxyapatite (nano-HAp) is the sol-gel method that due to its uniqueadvantages compared to conventional methods, has raised research interest among scientists. The purpose of this study wasto investigate the properties of nano-HAp powders which were synthesized by ethanol-based sol-gel method withstoichiometric ratio of Ca/P = 1.67 and comparing it with closer ratios of 1.5 and 1.6. To do so, we used the aqueous solutionof phosphorus pentoxide (p205, MERCK) and four-watered calcium nitrate (Ca (NO3)2.4H2O, MERCK) in ethanol. Theresulted nano-powders and sintered pellets made of it were analysed and compared with X-ray diffraction analysis (XRD). Also, the sintered pellets' bioactivity in simulated body fluid (SBF) solution was examined by SEM. In powders which werecalcined at the temperature of 600 oC, the most amorphous phase (49%) in comparison to Ca/P = 1.5 was observed. Aftersintering, the main phase of 1.67 ratio was hydroxyapatite (HAp) and the main phase of 1.5 ration was β-TCP, although in1.6 ration a composite of HAp and β-TCP was observed. According to the results, sol-gel method for producing nanocrystallineHAp was an appropriate method; in addition, compared with the different ratios of Ca/P, the stoichiometric nanocrystallinemay have better bioactivity.

Keywords: Hydroxyapatite, Sol-gel, tricalcium phosphate, Bioactivity