In this study, calcined eggshells were combined with phosphoric acid solutions having various concentrations and pH levelsin order to examine the hydroxyapatite (HA) or β-tricalcium phosphate (β-TCP) synthesis behavior and their powdermorphology change. While mixing the calcined eggshell powder and the solution at room temperature, a vigorous exothermicreaction was observed with the formation of crystalline phases of Ca3(PO4)2 and tetra-calcium phosphate (Ca4O(PO4)2). In thesample prepared from a 40 wt% phosphoric acid solution, HA was successfully synthesized at 800 oC while the 60 wt%solution showed β-TCP. The pH of the solution influenced the microstructure of the room temperature reactants and heattreated powders. The powder morphology was changed to rod-, plate- and spherical-shaped particles according to the solutionpH. The samples synthesized at pH of 0.69 showed whisker-shaped particles after being heat treated at 800 oC.

Keywords: Biomaterials, Powder processing, Calcium Phosphate, Eggshell, Solution pH