Abstract
The elastic velocities of nano-polycrystalline diamond were measured by an ultrasound pulse method and resonance method in high pressure and high temperature. Both sound velocities for longitudinal and transverse waves of samples can be obtained from sound signals waves both with QE mode 100 MHz fundamental frequency and with S mode 50 MHz frequency LiNbO_3 transducers. Elastic constants of bulk modulus, rigidity, Young's modulus, Poisson's number and elastic constants of C_<11>,C_<12> are derived from these velocities data. Elastic constants of sphere-nano polycrystalline diamond were measured by resonance method in helium gas. Velocities of sphere samples of nano-polycrystalline diamond were compered with cylindrical nano-polycrystalline diamond and sintered diamond samples.
