Synthesis and nanocomposite sintering of hydroxyapatite-coated zirconia nanopowders

Hydroxyapatite (HAP), Ca10(PO4)6(OH)2, is a well-known and a valuable implant material with biocompatibility and bioactive properties. Full utilisation of the unique properties of hydroxyapatite bulk ceramics is, however, enhanced by a proper reinforcement, i.e. by preparation of composites. The goal of this study was to synthesize a HAP-coated zirconia composite powder by the precipitation of HAP in presence of zirconia. The idea was to avoid uncontrolled agglomeration of the zirconia nanostructured reinforcement during the sintering step. ZrO2 nanopowders, previously synthesized by hydrothermal crystallisation, were added in an appropriate amount to an intensively stirred aqueous suspension of Ca(OH)2. HAP was precipitated by addition of H2PO4 at controlled pH in order to obtain a 50:50 composite powders. The obtained powders, fully characterized by TEM, XRD, TG-DTA and BET, were used for the preparation of the nanostructured composite speciments. The sintered materials were characterized in order to evaluate their structural and morphological properties.