Phase states of dynamically compressed cerium

This paper presents a multiphase equation of state for cerium, which includes the gamma, alpha, epsilon, and liquid phases. The a and gamma phases are described with the Aptekar-Ponyatovsky model for pseudobinary solutions, while the epsilon and liquid phases are treated as pure phases. The Hugoniot and release isentropes are calculated for the solid gamma, alpha, liquid, and mixed phases. Based on the model developed, the Hugoniot does not cross the line of the alpha-epsilon transition and melting occurs directly from the alpha phase. The equation of state developed shows reasonable agreement with the static measurements, the experimentally determined phase diagram, and the shock experimental data. Cerium compresses isentropically through the gamma-alpha transition as a result of cerium's abnormal compressibility in the region of the gamma-alpha transition. The inclusion of the Aptekar-Ponyatovsky model assists in providing a way to handle both the abnormal compressibility and the anomalous melt boundary simultaneously. Experimentally under dynamic loading conditions, a three-wave structure is observed at stresses above the phase transition: an elastic wave, a phase transition wave (which appears as an isentropic compression wave), followed by a shock wave. For our model development we consider only the hydrostatic response and thus a two-wave structure would be anticipated. No phase precursor would be observed for melting. Sound velocity behind the shock front dramatically decreases in the region of the gamma-alpha transition and smoothly varies through the region of melting.