Preparation of hydroxyapatite–ferrite composite particles by ultrasonic spray pyrolysis

Bio-compatible composite particles composed of hydroxyapatite (Ca10(PO4)6(OH)2, HAp) and ferrite (maghemite (γ-Fe2O3) or magnetite (Fe3O4)) were synthesized by two-step synthesis. In this work, co-precipitation method using aqueous solution of FeSO4 and FeCl3 was employed to synthesize γ-Fe2O3 and Fe3O4 particles. It was found that the resultant phase was changed by the molar ratio of FeSO4 and FeCl3, and optimal molar ratio to suppress the coexistence of α-FeOOH was FeSO4/FeCl3 = 2. The suspension composed of crushed ferrite particles, Ca(NO3)2 and H3PO4 aqueous solution with surfactant ultrasonically nebulized into mist and the mist was pyrolyzed at 500 °C to synthesize HAp–ferrite composite particles. The shape of the synthesized composite particle was round with dimple, and the particle size was around 0.5–3 μm in diameter. The composite particle showed saturation magnetization of 0.833 emu/g. Net saturation magnetization of the ferrite component was calculated to be 46.4 or 48.0 emu/g under the assumption that the ferrite was composed of γ-Fe2O3 or Fe3O4, respectively.