Shock compression of liquefied gases: Molecular dissociation and radiance change at the sample/LiF interface

Abstract

This study investigates the behavior of nitrogen and other liquefied gases under shock compression, with a focus on temperature variations and molecular dissociation. Through dynamic compression experiments on liquefied Ar, O2, CO, and N2, we aimed to understand shock-induced cooling and radiance changes at the sample/lithium fluoride (LiF) interface. The experiments were conducted using a setup involving a Doppler pin system and pyrometer to measure shock velocities, pressures, and temperatures across the interface between shocked liquids and LiF. Under the first-shock, molecular liquids experienced partial dissociation due to a rapid rise in pressure, density, and temperature within nanoseconds. Upon re-shocking at the sample/LiF interface, a radiance drop was observed for all liquids except Ar. Our data analysis suggests that the cooling effect is likely due to a chemical reaction occurring at the interface between reactive species, produced during the initial shock, and the layer of LiF at the surface under re-shock conditions. One probable interpretation is that this reaction formed a thin, partially transparent layer on the LiF, which absorbed a significant portion of the radiation emitted by the shocked fluid. Thus, the observed temperature drop in re-shocked liquid nitrogen is likely attributable to radiation reduction.