Mg-substituted hydroxyapatite nanopowders: Synthesis, thermal stability and sintering behaviour

This paper reports a systematic investigation on Mg-substituted hydroxyapatite (Ca10−xMgx(PO4)6(OH)2) nanopowders produced by precipitation of Ca(NO3)2·4H2O and Mg(NO3)2. The Mg content ranged between 0.6 and 2.4 wt%. Semicrystalline Mg-substituted hydroxyapatite powders made up of needle-like nanoparticles were obtained, the specific surface area ranged between 87 and 142 m2/g. Pure hydroxyapatite nanopowder decomposed around 1000 °C. Mg-substituted hydroxyapatites were thermally stable up to 660 °C (x = 1.0), 760 °C (x = 0.5) and 840 °C (x = 0.25) showing a distinct decreased thermal stability with respect to the pure sample. A relevant displacement of the sintering curve at lower temperature as a function of Mg content was observed, comparing to the behaviour of a pure HAp material, synthesized following the same procedure, and ascribed to the β-TCP formation.