Influence of temperature, [Ca2+], Ca/P ratio and ultrasonic power on the crystallinity and morphology of hydroxyapatite nanoparticles prepared with a novel ultrasonic precipitation method

Nanocrystalline hydroxyapatite was prepared by a precipitation method with the aid of ultrasonic irradiation using Ca(NO3)2 and NH4H2PO4 as source material and carbamide (NH2CONH2) as precipitator. The influence of Ca/P molar ratio, precipitation temperature, concentration of Ca2+ ([Ca2+]) and ultrasonic power on the crystallinity of the nanopowder were systematically investigated by XRD analysis. The size of the as-prepared particles was analyzed using TEM and XRD methods. The results revealed that the monophase hydroxyapatite could be obtained at the following technological conditions: [Ca2+] = 0.01-0.1 mol/L, ultrasonic power = 300 W, Ca/P (mol) = 1.2-2.5 and T = 313-353 K. In addition, the acicular and spherical particles could be prepared at different ultrasonic powers of 300 and 200 W, respectively.