The isothermal linear and volume compression of pentaerythritol tetranitrate (PETN) to 10 GPa (100 kbar) and the calculated shock compression

The isothermal linear and volume compressions of the explosive pentaerythritol tetranitrate (PETN) were measured to 10 GPa using a high pressure x-ray diffraction technique. The fits to the data are a/a0 = 1−2.052×10−2P + 2.230×10−3P2 − 1.041×10−4P3, and c/c0 = 1−2.832×10−2P + 3.295×10−3P2 − 1.458×10−4P3, for P<10 GPa, and ust = 2.16 + 3.007 upt − 0.682 upt2, for upt < 0.95 km/s, and ust = 2.76 + 1.71 upt, for upt ≳ 0.95 km/s, where ust = [PV0/ (1 − V/V0)]1/2, upt = [PV0(1 − V/V0)]1/2, and ρ0 = 1/V0 = 1.774 g/cm3. The shock compression Hugoniot of PETN calculated from the isothermal compression fit is us = 2.24 + 2.95 up − 0.605 up2, for up < 1.00 km/s, and us = 2.81 + 1.75 up, for up ≳ 1.00 km/s, where us is the shock velocity and up is the particle of mass velocity behind the shock wave. The isothermal compression fit and the Hugoniot are initially quadratic because of the rapid change in the strength of repulsive forces between the PETN molecules during initial compression.