Synthesis and sintering of hydroxyapatite derived from eggshells as a calcium precursor

In the present work, phase pure hydroxyapatite (HA) was successfully prepared using calcined eggshells as a calcium precursor via the wet chemical precipitation method. The sintering of eggshell-derived HA (EHA) compacts was carried out in air over a temperature range of 800-1400 degrees C. The sintered HA samples were evaluated in terms of phase stability, relative density, grain size, Vickers hardness and fracture toughness. The results showed that phase pure HA was obtained and remained stable after sintering at 1250 degrees C. However, secondary phases such as alpha-TCP and TTCP were obtained at 1300-1350 degrees C and melted upon further sintering at 1400 degrees C. A relatively high density of 97.4% was achieved in pure HA at 1250 degrees C whilst a maximum fracture toughness of 1.14 MPa m(1/2) was attained at 1000 degrees C due to the small grain size of 0.33 mu m obtained at this temperature. The study found that a combination of relative density, the reverse Hall-Petch relationship and grain growth affected the hardness of the HA samples, where the highest value of 4.96 GPa was achieved at a sintering temperature of 1250 degrees C. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.