SYNTHESIS OF ULTRAFINE HYDROXYAPATITE IN A Ca(OH)2-H3PO4-H2O REACTION SYSTEM USING ULTRASOUND IRRADIATION

This paper reports the application of ultrasound irradiation in the synthesis of ultrafine hydroxyapatite (HAp) with a high specific surface area of 300 m2/g. We examined the effects of initial temperature, horn diameter and suspension concentration on the powder properties, especially specific surface area, of ultrafine HAp. Amorphous calcium phosphate (ACP), which is a precursor of HAp, was formed in the early stage of the reaction, and then rapidly crystallized to form HAp. In the case of an initial temperature at 30°C, the largest specific surface areas of 250 m2/g and 300 m2/g were obtained using horn diameters of 19 mm and 6 mm, respectively. Based on particle size distribution measurements, the mode and average diameters of the HAp powders were found to be 5.0 and 6.3 nm, respectively. These values were well-agreed with the average diameter calculated from the specific surface area.