Equations of state and phase transformation of depleted uranium DU-238 by high pressure-temperature diffraction studies

摘要

We have conducted in situ high-pressure diffraction experiments on depleted uranium (DU-238) at pressures up to 8.5 GPa and temperatures up to 1123 K. From the pressure (P)-volume (V)-temperature (T) measurements, thermoelastic parameters were derived for α-uranium based on a modified high-T Birch-Murnaghan equation of state and a thermal-pressure approach. With the pressure derivative of the bulk modulus K′_0 fixed at 4.0, we obtained ambient bulk modulus K_0= 117(2) GPa, temperature derivative of bulk modulus at constant pressure ((partial deriv K)/(partial derivd T))_P=-3.4(4)X 10~(-2) GPa/K and at constant volume ((partial deriv K)/(partial derivd T))_V=-1.1(6) X 10~(-2) GPa/K, volumetric thermal expansivity α_T=a+bT, with a=1.2(±0.4) X 10~(-5) K~(-1) and b=8.0(±0.7) X 10~(-8) K~(-2), and the pressure derivative of thermal expansion ((partial deriv K)/(partial derivd T))_T=-2.5(5) X 10~(-6) GPa~(-1) K~(-1). Within the experimental errors, the ambient bulk modulus and volumetric thermal expansion derived from this work are in good agreement with previous experimental results, whereas all other thermoelastic parameters represent the first determinations for the α phase of uranium. We also studied the α-γ phase transformation and obtained a phase boundary described by T (in K) = 1032+7.4P (in GPa). Although the γ-phase uranium cannot be pressure quenched to ambient conditions, it was observed to be stable upon cooling from 1123 to 300 K at pressures of 7-8 GPa. These observations indicate that pressure, in addition to the commonly utilized alloying techniques, provides an alternative route for stabilizing the γ-uranium at room temperature.