Hydrothermal Synthesis of Hydroxyapatite Whisker from Amorphous Calcium Phosphate and the Effect of Carboxylic Acid

(SEM). The shape of the products changed by kinds of carboxylic acid used, and the largest HAp whisker was obtained under conditions such as acetic acid of concentration 1.0mol•Edm-3, hydrothermal temperature of 200•Ž, and holding time of 3h; the resulting whisker was hexagonal prismatic with 100ƒÊm in length and 4ƒÊ m in diameter, and had Ca/P atomic ratio of 1.56•}0.02. The formation of HAp whisker is ascribed to ad sorption of dimer-carboxylic acid on the a-plane of HAp. Accordingly, carboxylic acid promoted growth toward the c-axis. The existence of dimer-carboxylic acid was also influenced by the acid dissociation con stant of carboxylic acid. Synthesis conditions for HAp whisker was calculated from the dissociation con stant. [Received July 18 , 2000; Accepted November 13, 2000]