Thin film heating and cooling technique to measure high pressure phase transition temperature and enthalpy*

We present theoretical and experimental studies of a novel method for measuring dynamic phase transition temperatures and enthalpies at high pressure in plate impact experiments. Traditional shock temperature (T) experiments measure T at a radiant interface to infer bulk shock T and thermodynamic properties. We instead measure the behavior of a thin—roughly one micron—film coated onto a lithium fluoride optical window. The film is held at steady stress by a supported shock, but experiences varying T as heat diffuses between the film, window, and impactor. We look for a change or interruption in the T-vs-time trajectory of the film at the interface. The interruption T directly indicates phase transition temperature, while its shape allows estimation of enthalpy and entropy of the transition. We explore phase transitions in different metals, including measurements of melt in Al and Ce, a design for Fe melt, and potential studies of refractory metals (Mo, Ta, W).