Thermal Stability of Iron- and Silicon-Substituted Hydroxyapatite Prepared by Mechanochemical Method

In this study, hydroxyapatite with the substitution of calcium cations by iron and phosphate by silicate groups was synthesized via a mechanochemical method. The as-prepared compounds have the general formula Ca10−xFex(PO4)6−x(SiO4)x(OH)2−xOx/2 with x = 0–1.5. The thermal stability of the as-prepared compounds was studied by ex situ annealing of powders in a furnace. It has been established that, at 800 °C for x ≤ 0.5, a partial decomposition of the substituted apatites occurs with the formation of the β–Ca3(PO4)2 phase. At high “x” values, the formation of this phase starts at the lower temperature of 700 °C, followed by the formation of Fe2O3 at 900 °C. The introduction of iron and silicate ions into the hydroxyapatite lattice was shown to decrease its thermal stability.