Abstract
This study reports effects of horn diameter and suspension concentration on specific surface area of hydroxyapatite (HAp) synthesized by ultrasound irradiation. HAp was synthesized by Ca(OH)_2-H_3PO_4-H_2O system with ultrasound. The frequency of ultrasound was 20 kHz. Amorphous calcium phosphate (ACP) was formed just after a reaction, and then ACP crystallized sequentially in HAp. In the case of horn diameter 16 mm, the optimum condition of initial temperature was 30 ℃, and the suspension concentration was 12.25 mass%. The optimum amplitude was 70 %. In the case of horn diameter 6 mm, the optimum condition of initial temperature was 30 ℃, and suspension concentration was 8.75 mass%. The optimum amplitude was 30 %. The specific surface area of sample rose over time because ACP crystallized to HAp. When HAp became single phase, the specific surface area showed maximum value. However, the specific surface area of HAp decreased when reaction time became longer. The reason was for the crystal growth of HAp. The maximum specific surface area of HAp with horn diameter 16 mm and 9 mm were 330, 298 m^2・g^<-1>, respectively. However, if horn diameter was thin, the sound at the time of the synthesis was not too loud.
