Large-sized hydroxyapatite whiskers derived from calcium tripolyphosphate gel

Hydrothermal methods using calcium phosphate gels as precursor have an advantage in high production efficiency of hydroxyapatite (HAp), but almost no large-sized HAp has been obtained so far. In the present work, large-sized HAp whiskers were prepared by a hydrothermal treatment of calcium tripolyphosphate gel controlled at pH 4–6 using various alcohols at 140 °C for 24 h. Long HAp whiskers of 30–50 μm in length were successfully prepared using 2-propanol; their sizes were several ten times larger than those prepared via conventional gel processes. The whisker length and aspect ratio were controlled by content of additive solvents with high specific dielectric constant.