Exploring High-Pressure Melt Curves using X-Ray Diffraction

Richard Kraus, Lawrence Livermore National Laboratory

The melting curve represents a tremendous rheological transition, from a material with strength to one without. This transition is critical to the evolution of the Earth, as latent heat from solidification of the planet’s inner core helps drive the magneto-dynamo in the liquid outer core. Efforts to use diamond anvil cell measurements to constrain the melting curves of important engineering and planetary materials often are limited in pressure and temperature. The sound velocity along the shock Hugoniot has been used as a diagnostic of melting, however interpretation of the data has sometimes come into question. I will present initial results and the development of techniques to constrain the ultra high-pressure melting curve using tailored pressure drives and in situ X-ray diffraction. I will discuss how we use X-ray diffraction as a diagnostic of melting along the principal Hugoniots of iron and tantalum. I also will present the first evidence for recrystallization of tin on the nanosecond timescale after recompression from the molten Hugoniot state. Finally, I will discuss our plan for using in situ X-ray diffraction at the National Ignition Facility to constrain the ultra high-pressure melting curve of iron at super-Earth core conditions, which will help constrain the types of exoplanets that could be habitable.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Abstract Author(s): Richard Kraus