Melting of Tantalum at Multimegabar Pressures on the Nanosecond Timescale

Measuring the melting curve of iron at super-Earth core conditions

“…As the shock transits from the iron into a lithium fluoride (LiF) window, the iron decompresses isentropically to pressures between 120 and 160 GPa, ensuring a completely liquid iron sample for all but the lowest shock pressure experiment. Then we precisely increase the laser power to isentropically compress the sample to the desired peak pressure, up to 1000 GPa in ~10 ns, where the initial shock pressure and peak pressure in the sample are accurately determined from the measured interface velocity between the iron sample and LiF window ( 14 ). To document the atomic structure of the iron while it is at peak pressure, another 24 beams of the NIF laser illuminate a germanium or zirconium foil, producing a hot plasma.…”

“…( 8 ) refutes predictions of body-centered cubic stability in pure iron at core conditions ( 18 , 19 ), where it is noted that substantial alloying can affect phase stability and the mode of core solidification ( 20 ). Finally, the solidification into a mixed phase suggests that the nanosecond time scale of the experiments is not causing the transition to be substantially overdriven, where we might only expect to see a liquid or completely solidified system ( 14 , 15 ). This observation provides confidence in our measurement of the equilibrium melt curve.…”

Toward better understanding of the high-pressure structural transformation in beryllium by the statistical moment method

“…Combining eqn (14) and (15) yieldswhereNext, to minimize the number of empirical inputs for WHEP calculations, we constrain T 1 ( P 1 ) and T 2 ( P 2 ) by T 1 ( P 1 ) = T m (0),Interestingly, the initial melting gradient can be linked to the bulk modulus via the Lindemann criterion as 58 Entering eqn (20)–(22) into eqn (18) provides us with the final expression for the melting profile asUnlike eqn (17) and (23) only requires empirical information about the zero-pressure melting temperature T m (0). To verify the reliability and flexibility of eqn (23), we perform numerical calculations for tantalum, 59–62 iron, 63–66 and magnesium oxide 67–70 because their melting behaviors have been thoroughly measured by modern DAC and SW methods. As presented in Section II and Fig.…”

“…Unlike eqn ( 17) and ( 23) only requires empirical information about the zero-pressure melting temperature T m (0). To verify the reliability and flexibility of eqn (23), we perform numerical calculations for tantalum, [59][60][61][62] iron, [63][64][65][66] and magnesium oxide [67][68][69][70] because their melting behaviors have been thoroughly measured by modern DAC and SW methods. As presented in Section II and Fig.…”

Femtosecond Diffraction and Dynamic High Pressure Science

“…3. Indeed, such a knowledge of the energy budget, along with other experimental parameters, has recently been used to constrain the melting temperature of Ta under shock compression 181 One method that has been pursued for many years in the field of shock physics is optical pyrometery 182 , whereby the thermal emission from the rear surface of a sample is recorded (often through a window that is transparent). However, it has been shown that these experiments are hampered by small optical depths and thermal conduction effects, such that the surface temperature observed may not be representative of the bulk temperature 183 .…”