Sound velocity measurements in liquid iron by ultrasonic interferometry

Abstract

Compressional wave velocity Vp has been measured in liquid iron in the temperature range 1823–1883 K and in the frequency range 5.4–11.8 MHz for the first time using ultrasonic interferometry. The value of Vp at the melting temperature is 3820±3 ms−1 which is comparable to previous measurements all using time‐of‐flight methods. The temperature derivative of velocity, dVp/dT, in this temperature range (−0.72±0.07 m s−1 K−1 ) and the lack of dispersion observed in this frequency range are in agreement with previous studies. Our calculated value of the relaxed (adiabatic) bulk modulus K0 at the melting temperature is 102 GPa. Estimate of the average longitudinal relaxation time τl indicates that the liquid iron is in a relaxed state in the present frequency range. Accurate measurement of attenuation is not yet possible with our present apparatus, but typical interferograms indicate a very low attenuation, which is qualitatively consistent with the prediction from viscoelastic theory and seismological determinations of attenuation of Earth's outer core.