Adiabatic release measurements in aluminum from 240- to 500-GPa states on the principal Hugoniot

Adiabatic release measurements were performed on aluminum (6061-T6) from similar to 240- to500-GPa(similar to 2.4-5 Mbar) states on the principal Hugoniot. Using a magnetically accelerated flyer plate technique, capable of launching macroscopic aluminum flyer plates (approximately 12x25 mm in lateral dimension and similar to 300 mu m in thickness) to velocities in excess of 20 km/s, direct impact experiments were performed on a low shock impedance, 200-mg/cc silica aerogel to determine the aerogel Hugoniot in the pressure range of similar to 30-75 GPa. Release experiments were then performed in which the aerogel was mounted onto an aluminum base plate, and the initial shock in the base plate was transmitted to the aerogel sample. Given the measured aerogel shock velocities from the release experiments and the measured aerogel Hugoniot from the direct impact experiments, release states on release adiabats of aluminum were ascertained. The results were compared to several equation of state models for aluminum, and a rigorous statistical analysis was performed. The statistical analysis enabled the suitability of these various models in describing the release response of hot, liquid states to be determined. This study enhances our understanding of the release response of aluminum for high-pressure states on the Hugoniot and lends confidence to the use of aluminum as a standard material in impedance-matching experiments. (C) 2005 American Institute of Physics.