Novel synthesis and crystallographic results of zinc substituted hydroxyapatite with high thermal stability

Abstract

Hydroxyapatite (CaHap) doped with different amounts of Zn(II) has been studied by complementary techniques, X-ray powder diffraction (XRPD), thermogravimetry (TGA) and infrared spectroscopy (FTIR), the latter including the examination of samples treated at different temperatures. The studied samples have been synthesized at 98 °C by a precipitation method by a reaction of solutions of Ca(OH)2, H3PO4 and ZnCl2. The analysis of FTIR and XRPD data by Rietveld method suggests that at low Zn(II) concentration, the Zn(II) ions exhibits some preference to occupy the Ca2 site of the apatite structure. However, to increasing concentrations up to 6.2 wt % of Zn(II), XRPD and FTIR data as well as those from thermal treated samples indicate that Zn(II) ions would exhibit some preference to occupy the Ca1 site, together with an appreciable amount of water incorporated in the structure, with the consequent reduction of crystallinity.The information obtained in the present work suggests that (Ca,Zn)Hap doped with zinc below 6.2 wt % has a thermal stability over 800 °C which results in ceramic formed by a single phase of zinc-hydroxyapatite. It should be noted that, to our knowledge, the zinc-doped ceramic biomaterials obtained at the present time are a mixture of β-(Zn,Ca)3(PO4)2 and CaHap. Thus, the studies in this work allow obtaining a (Ca,Zn)Hap apatite stable above 800 °C that could potentially be used as a biomaterial useful in bone repair applications.