Internal friction and dynamic modulus of polycrystalline ceramics prepared from stoichiometric and Ca-deficient hydroxyapatites

Internal frictions and the dynamic moduli were measured by a forced torsional vibrational method at 1 Hz in the range of −150–400°C on the specimens sintered at 1200°C from hydroxyapatite (HAp) particles with molar ratios of Ca/P≒1.7 and 1.5. A peak of internal friction appeared at ∼110°C on the sintered Ca/P≒1.7, however, the peak shifted to ∼−40C° on the sintered Ca/P≒1.5. The dynamic moduli of both specimens with Ca/P≒1.7 and 1.5 reached the minimum values in the dynamic modulus–temperature curves.