COMPRESSION IN MULTIPLE REGIMES: STUDIES OF COPPER AND MGO (Invited Presentation)

Geoscience problems, from meteorite impacts to exoplanet interiors, require study of timescales that span orders of magnitude. However, the shock and static experiments required to examine these processes occur over limited timescales, strain-rates, and temperatures compared to natural systems. The effects of kinetics and strain-rate are relatively unconstrained. It is therefore important to understand their effects during the experiments used to determine phase diagrams and equation of state models. For exoplanetary systems and the deep Earth, temperature, kinetics and strain-rate studies are important because rheological properties, such as viscosity, are dependent on phase identities and deformation mechanisms. In this presentation, I will discuss high pressure deformation and phase relations in copper and MgO across compression regimes. In copper, we study the face-centered cubic (fcc) to body centered cubic (bcc) phase transition using two techniques, computational modeling and through in situ X-ray diffraction during shock experiments. Two types of thermodynamic integration models are utilized. We completed the series of laser shock experiments using the Dynamic Compression Sector at Argonne National Laboratory. Using texture analysis, the orientation relationship between the fcc and bcc phases is analyzed and found to be indicative a martensitic phase transition via the Pitsch distortion. To examine MgO, we completed ramp compression experiments with in situ X-ray diffraction at the OMEGA Laser Facility at University of Rochester Laboratory for Laser Energetics. We study the effect of temperature on the B1-B2 transition. We compare our ramp experiments to shock data collected along the Hugoniot and find differences in texture. These studies allow us to more accurately examine geological events with timescales from microseconds to billions of years.