Preparation of hydroxyapatite–ferrite composite particles by ultrasonic spray pyrolysis

Bio-compatible composite particles composed of hydroxyapatite (Ca 10(PO 4) 6(OH) 2, HAp) and ferrite (maghemite (γ-Fe 2O 3) or magnetite (Fe 3O 4)) were synthesized by two-step synthesis. In this work, co-precipitation method using aqueous solution of FeSO 4 and FeCl 3 was employed to synthesize γ-Fe 2O 3 and Fe 3O 4 particles. It was found that the resultant phase was changed by the molar ratio of FeSO 4 and FeCl 3, and optimal molar ratio to suppress the coexistence of α-FeOOH was FeSO 4/FeCl 3 = 2. The suspension composed of crushed ferrite particles, Ca(NO 3) 2 and H 3PO 4 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-Fe 2O 3 or Fe 3O 4, respectively.