Temperature measurements in cerium shocked from 8.4 to 23.5 GPa

摘要

Shock temperature, stress, and dynamic emissivity for cerium shocked from 8.4 to 23.5 GPa were measured. In addition, the isentropic shock release temperature as a function of release stress was determined at a window interface. Cerium samples were shock compressed by plate impact on a single-stage gun. We made time-resolved measurements of thermal radiance, reflectance, and interface velocity of samples glued to lithium fluoride windows. Reflectance was measured with an integrating sphere and velocity with photonic Doppler velocimetry. From these measurements, we determined the temperature, emissivity, and stress at the interface. For shock stresses below 10.24 GPa, the samples were shocked from the γ phase into the α phase; at higher stresses, the cerium presumably melted or entered a mixed phase upon shock. The shock Hugoniot temperature as a function of stress follows a straight line over the entire range of our measurements, disagreeing with previously published predictions that the Hugoniot would follow the melt boundary from 10.24 up to around 16-18 GPa. Between 11.9 and 16.8 GPa, all the release isentropes converged (within experimental uncertainty) to a point around 4 GPa and 900 K, near the published melt curve. For experiments shocked above ～16GPa, the release isentropes behave differently. This suggests that within this 12-16 GPa range, there is a phase transition taking place, probably melt, and that it is occurring somewhere along the shock and release path. We could not identify a single-valued phase boundary from our experiments. Potential reasons for this are discussed.