Chemical and thermal stability of multiple ions doped nonstoichiometric nanoapatite heat-treated in CO2 and air atmospheres

Nanostructured apatite has been widely used as a bone substitute material due to its close resemblance to human bone mineral. To further mimic biological apatites, multiple ions doped nonstoichiometric nanoapatite has been studied. A nanosized apatite (NAp-2) containing Mg (1.09 wt%), Na (0.15 wt%), K (0.008 wt%) and CO3 2- (5.18 wt%) was synthesized by a wet precipitation technique. The presence of these ions in NAp-2 was detected using ICP. Broad diffraction peaks of XRD results indicated the presence of nanocrystalline phase-pure NAp-2. The primary particle size of the resulted powder was ~ 20 nm, typical of bone crystal size, estimated using Scherrer's equation. Based on CHN results, the NAp-2 powders showed a total loss of 51 and 78% of carbonate ions when heat-treated at 900°C in both CO2 and air atmospheres, respectively. This indicates that the heat-treatment in CO2 flux has reduced the carbonate ions lost from the NAp-2. A highly crystalline HA phase was formed in the ionic doped NAp-2 without secondary phases, indicating a thermal stability of this powder at 900°C in CO2 and air atmospheres. Thus, this study demonstrated that a phase-pure multiple ions doped nanoapatite was synthesized using a wet precipitation technique