Pyrometry measurements on shock-heated bismuth using PMMA and sapphire windows

Lithium fluoride (LiF) is the most popular window material for temperature measurements under shock loading. But it can be interesting also to use polymethylmethacrylate (PMMA) and sapphire as transparent anvils, since their shock impedances are, respectively, lower and higher than that of LiF. In the case of bismuth, this makes it possible to investigate under dynamic excitation a part of its (pressure, temperature) diagram. In the present experiments, the metallic plate is glued onto the window and the interpretation is somewhat complicated by extra phenomena occurring at the bismuth-glue interface. Fortunately, on the basis of theoretical considerations, a thorough analysis of the experimental results can be given and their accuracy greatly improved by using data on bismuth emissivity from previous measurements. This allowed us to plot experimental release isentropes and second-shock Hugoniot curves, which proved in good agreement with theoretical predictions.