Ultrasonic measurements of Q-1p and Vp for An and Di.64An.36 melts are reported in the frequency range 3--20 MHz and in the temperature range from melting to 1934 K and 1831 K, respectively. When Q-1p and shear viscosity are normalized to their respective liquidus temperature values, they have the same linear dependence on reciprocal homologous temperature. From the Arrhenius temperature dependence of Q-1p, the activation energies calculated for An and Di.64An.36 melts are on the order of 216 and 302 kJ/mol, respectively. Although there is insufficient data for An, the activation energy of Q-1 for Di.64An.36 is in excellent agreement with its activation energy of viscosity.

The relaxed adiabatic bulk modulus, derived from relaxed velocities, for an at 1893 K is 20.4¿0.2 GPa and for Di.64An.36 at 1677K is 23.0¿0.1 GPa. These values fall into a general trend of decreasing bulk modulus with increasing Al2O3. ¿American Geophysical Union 1991