Direct conversion of eggshell to hydroxyapatite ceramic by a sintering method

Nanocrystalline hydroxyapatite derived from eggshell (HA-Es) was successfully prepared via a direct solid-state sintering method. The process involved mixing calcined eggshell powder and dicalcium hydrogen phosphate di-hydrate followed by a heat treatment at 800 degrees C. The resulting flower-like HA-Es powder was sintered at various temperatures ranging from 1050 degrees C to 1350 degrees C for 2 h in air atmosphere. The material was characterized to determine the thermal stability and the effect of sintering on the microstructure as well as properties of the resulting HA derived from eggshell. The results showed that sintering beyond 1250 degrees C resulted in the HA phase decomposition to tricalcium phosphate and tetra calcium phosphate. However, these secondary phases did not disrupted the densification process as the samples exhibited densities above 98% when sintered at 1300-1350 degrees C. A maximum fracture toughness of 1.51 MPam(1/2) was measured for HA-ES sample sintered at 1250 degrees C with a concomitant small grain size, below 1 pm coupled with high hardness of 5.62 GPa and high relative density of 98% being measured. The study also revealed that the relative density and grain size played a significant role in governing the properties of the HA-Es samples. (C) 2016 Elsevier Ltd and Techna Group S.r.1. All rights reserved.