Internal friction of hydroxyapatite and fluorapatite

Internal friction was measured by a forced torsional vibration method at 0.1–10 Hz in the temperature range of −100 to 400 °C on both hydroxyapatite (HAp) sintered at 1300 °C for 3 h under fluent H2O vapor and fluorapatite (FAp) sintered at 1200 °C for 3 h in the F2 atmosphere. Three peaks of internal friction appeared at approximately −40, 80 and 130 °C for HAp. However, for the FAp, no internal friction peak was obtained in the measured temperature range. It is considered that the difference of F− and OH− positions in each FAp and HAp structure greatly influences internal friction.