Abstract
We have developed a new technique to measure the melt curve of a shocked metal sample and have used it to measure the high-pressure solid-liquid phase boundary of tin from 10 to 30 GPa and 1000 to 1800 K. Tin was shock compressed by plate impact using a single-stage powder gun, and we made accurate, time-resolved radiance, reflectance, and velocimetry measurements at the interface of the tin sample and a lithium fluoride window. From these measurements, we determined temperature and pressure at the interface vs time. We then converted these data to temperature vs pressure curves and plotted them on the tin phase diagram. The tin sample was initially shocked into the high-pressure solid γ phase, and a subsequent release wave originating from the back of the impactor lowered the pressure at the interface along a constant entropy path (release isentrope). When the release isentrope reaches the solid-liquid phase boundary, melt begins and the isentrope follows the phase boundary to low pressure. The onset of melt is identified by a significant change in the slope of the temperature-pressure release isentrope. Following the onset of melt, we obtain a continuous and highly accurate melt curve measurement. The technique allows a measurement along the melt curve with a single radiance and reflectance experiment. The measured temperature data are compared to the published equation of state calculations. Our data agree well with some but not all of the published melt curve calculations, demonstrating that this technique has sufficient accuracy to assess the validity of a given equation of state model.
Highlights
The high-pressure phase diagram of materials is important in many disciplines, including earth and planetary science, materials science, astrophysics, armor penetration, and other military and defense applications
We suggest that other metals, too, often have reflectance values that differ for different phase states
We have developed a method to measure the high-pressure melt curve of a metal by combining reflectance, pyrometry, and velocimetry measurements to determine temperatures and pressures during dynamic shock compression and release experiments
Summary
The high-pressure phase diagram of materials is important in many disciplines, including earth and planetary science, materials science, astrophysics, armor penetration, and other military and defense applications. They reported the pyrometric temperature of shock-compressed tin measured at the interface between a tin sample and lithium fluoride window They measured a melt temperature of 2110 ± 200 K at a pressure of 39 GPa, which agrees well with their model. Our technique uses pyrometry and reflectance to measure the temperatures of shock-compressed tin across a large segment of the melt curve at the interface between the tin sample and a transparent window. The highexplosive drive was not one-dimensional, which complicated the analysis, and the pressures did not drop low enough to observe melting We applied these diagnostics to better-characterized loading conditions using tin targets impacted by flyer plates accelerated with a single-stage powder gun. History in the samples so that we can create the temperature and pressure conditions necessary for melting to occur
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