THERMAL CONDUCTIVITY OF H2O UP TO 11 GPa USING TIME-DOMAIN THERMOREFLECTANCE METHOD IN DIAMOND ANVIL CELL: INSIGHTS INTO ICY PLANETARY BODIES

As a planetary body ages, the heat trapped and generated in its interior escapes to the surface. Thermal conductivity is a fundamental parameter that governs the thermal evolution and internal dynamics of the planetary body. Due to exceedingly small sample size under high pressure, measuring the thermal conductivity of compressed materials is challenging. Here we report new experimental data on the thermal conductivity of liquid H₂O and ice VII up to 11 GPa and at 300 K in the diamond anvil cell, using the time-domain thermoreflectance technique. Molecular-pure liquid water and a thermally insulating muscovite sheet are loaded into a sample chamber, which is drilled in a rhenium metal gasket. A thin film of aluminum (Al) is coated on the muscovite sheet and serves as a transducer (Antonelli et al. 2006, MRS Bulletin). Ruby balls are included as the pressure marker. Upon compression, liquid H₂O crystallizes into multiple grains of tetragonal ice VI, and then transforms to the cubic ice VII. A pulsed "pump" beam, focused to a ~10 micron-diameter spot, heats the Al film and raises its temperature by several degrees Kelvin. Between pulses, the Al film cools via heat conduction, across the interfaces and then through the muscovite sheet and the sample. A slight change in the reflectivity of the film, resulting from repeated heating and cooling, is measured by a pulsed "probe" beam. The thermal conductivity of H₂O is extracted from the measured time spectra, on the basis of one-dimensional heat flow model. At 300 K, the thermal conductivity of liquid water at 0.2 GPa is 0.8 W/m-K. From 3.3 to 11 GPa, the thermal conductivity of ice VII increases from 1.6 to 7.0 W/m-K, by a factor of ~ 4. The high-pressure thermal conductivity data helps constrain the internal structure and thermal evolution of large icy bodies in the Solar System.