Ultrasonic Measurements of Sound Velocity of Iron-nickel (Fe0.9Ni0.1) Alloy up to 8 GPa and 773K

Earth's solid inner core is widely believed to mainly compose of iron-nickel (Fe-Ni) alloys, with 5-15 wt.% Ni, as well as some light elements (including Si, S, O, C, and H), based on cosmochemical, geochemical and geophysical investigations. Studying the elasticity of iron and its alloys under high pressure and temperature conditions is critical for geoscientists to constrain the composition of Earth's core as well as the interior of other telluric planetary bodies . While the sound velocity of pure iron (Fe) has been measured using various techniques, experimental study on the sound velocity of iron-nickel (Fe-Ni) alloys is still limited, especially for shear wave under simultaneous high pressure and high temperature conditions. In this study, we conducted measurements on an Fe-Ni alloy with 10 wt.% of Ni up to ~8 GPa and 773 K, using ultrasonic interferometry techniques in the 2000-ton uniaxial split-cylinder apparatus (USCA-2000) in the High Pressure Laboratory at Stony Brook University. We report here the results for the compressional and shear wave velocities as a function of pressure, as well as the bulk and shear moduli and their pressure and temperature derivatives by fitting the experimental data to finite strain equations. These new data not only allow us to compare with previous sound velocity data on pure Fe and its light elements alloys, but also enable us to further explore the effects of temperature on its elasticity. Implications for planetary cores will be discussed.