Metal emissivity under dynamic compression

Temperature measurements of dynamically compressed materials provide stronger equation of state constraint than purely mechanical data. However, practical challenges prevent widespread use of temperature diagnostics, and there is long standing skepticism about the reliability of these measurements. For example, sample emissivity is needed for the analysis of optical pyrometry signals, but this property is rarely known for the conditions of interest.

Although emissivity is physically constrained between unity (perfect blackbody) and zero (perfect reflector), the corresponding temperature range calculated from a pyrometry measurement is infinite. Ideally, sample emissivity should be as large as possible with minimal spectral variation. Metals are particularly challenging because the free electrons that make samples opaque also lead to high reflectivity: good metals are usually strong reflectors and thus weak emitters. This presentation discusses general trends in metal emissivity, examining different empirical models and their effect on pyrometry analysis. Material and geometric changes during dynamic compression are also considered.