Ramp EOS measurements through phase transitions in tin up to 10 Mbar*

An equation of state (EOS) for a material is constrained through pressure and density measurements across a wide range. Static compression experiments under ‘quasi-hydrostatic’ conditions are typically used in combination with in situ X-ray diffraction to determine the pressure-volume relationship of a material (room temperature isotherms). Pressure-volumes are fit with an appropriate EOS equation, e.g. Birch-Murnaghan or Vinet, with extrapolations to very high pressure often used to compare against shockwave or ramp derived data.

 

Tin is a material that undergoes several solid-solid phase transitions between 0 and 200 GPa at room temperature, with large regions of coexistence observed between phases. Consequently, the experimental data used to define the EOS for each phase covers a relatively small range. Ramp compression experiments are now a well-established technique to derive a room temperature isotherm from longitudinal stress measurements via velocimetry.

 

In this talk, I will present ramp compression data on Sn from the National Ignition Facility. A reduced isotherm determined from low adiabat (solid tin) ramp compression shows good agreement with experimental static compression data (that are corrected using a more up-to-date ruby pressure scale). The implications of adiabatic pathways that traverse the bcc to hcp phase transition in tin will be discussed. An update to the phase diagram, based on recently published experimental data, will also be compared against existing EOS models, alongside high adiabat ramp compression experiments on NIF that begin in the liquid phase.

 

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