3.2. Synthesis of Hydroxyapatite (HAp)

Hydroxyapatite was obtained via the wet precipitation method wherein the ammonium phosphate monobasic and calcium nitrate tetrahydrate were used as the main reagents. In the first stage, 20 mL of NH₄H₂PO₄ solution (0.36 mol/L) were introduced into the flasks in Carousel Plus Reaction Station (Radleys, United Kingdom) containing 130 mL of distilled water. Then, the ammonia water was added until the pH of the reaction mixture was >10. Next, 50 mL of Ca(NO₃)₂∙4H₂O (0.60 mol/L) was added dropwise (1 drop/s) to the mixture. Process was performed at constant stirring (350 rpm) and at 25 °C. After adding the whole volume of the calcium nitrate solution, the reaction mixture was mixed for further 30 min and remained for 24 h. Then, the ripening and the sedimentation of the precipitate formed took place. After 24 h, the precipitate was filtrated and washed with distilled water to the neutral pH. The equipment applied as well as the scheme of the hydroxyapatite synthesis is presented in Figure 10.

The equipment used (left) and the scheme (right) of the preparation of hydroxyapatite.

The hydroxyapatite obtained has been investigated via XRD technique and FT-IR analysis. Next, its stability in PVP solutions at various concentrations has also been determined. In further step of the research, the HAp powder prepared was used for preparation of polymer-ceramic composites.