Preparation of needle-like hydroxyapatite by homogeneous precipitation under hydrothermal conditions.

Preparation of hydroxyapatite was carried out by a homogeneous precipitation technique using hydrothermal reactions of Ca(EDTA)2- and PO4(3-) at 130-250 degrees C and pH 4-10. Hydroxyapatite and monetite were formed above pH 6 and below pH 4, respectively. Needle-like hydroxyapatite was formed at high temperatures above 130 degrees C. The length of the needle-like hydroxyapatite crystal increased with increasing working solution pH and temperature.