Pressure-volume-temperature equation of state and high-pressure melting of zirconium

Robust modeling of shock phenomena requires accurate and precise experimental measurements of equations of state and phase diagrams. Zirconium is of particular interest in nuclear applications because of its low neutron cross section. Here, we present the thermal equation of state and melting curve of ultra-high purity Zr in the body-centered cubic (bcc) phase measured using the laser-heated diamond-anvil cell (LHDAC) coupled with in situ synchrotron-based X-ray diffraction (XRD). From quasi-hydrostatic room-temperature compression to pressure (P) = ~70 GPa using helium as a pressure transmitting medium, we constrain the bcc-Zr bulk modulus, K₀ = 120(7) GPa and its pressure derivative, K₀’ = 3.0(1). Additionally, we have collected LHDAC XRD data over a range of P = ~10 – 40 GPa and temperature (T) = ~1400 – 2200 K to further constrain the bcc-Zr thermal equation of state parameters. Within a separate set of experiments, we have observed melting of bcc-Zr between P = ~10 – 20 GPa based on plateaus in the T versus laser-power curves coupled with diffuse X-ray scattering and visual changes in the sample before and after laser-heating. At P = ~10 GPa, initial results suggest a melting temperature, T_m = 2270(50), that implies a melting curve slope of ~14 K/GPa.