4:30 PM - 4:45 PM
[PCG22-11] Study on transport properties of liquid iron and iron alloy under high temperature and high pressure using the laser shock technique
Target assemblies containing polypropylene (CH), aluminum, quartz, iron or iron-silicon alloy and magnesium oxide (MgO) window were shock compressed by laser ablation at the GEKKO XII laser facility, the Institute of Laser Engineering, Osaka University. Iron and iron-silicon alloy were formed by electron beam evaporation on the MgO window. Laser beams with a wavelength of 527 nm were focused onto the target. A focal spot was 1 mm in diameter with a flat-top spatial intensity distribution resulting in a planar shock front. Temporal shape of the laser pulse was approximately a flat-top with a full-width at half-maximum of 2.5 ns. The velocity interferometer system for any reflector (VISAR) measure a particle velocity and a reflectivity at the interface between iron or iron-silicon alloy and MgO. The Ppressure was evaluated using measured particle velocity and a known equation of state of MgO. The optical pyrometer measures the temperature at the interface through the MgO window.
The pressures determined from the measurement results were from 200 to 400 GPa, and the temperatures were up to 15000 K. In the pressure range exceeding 200 GPa, in the case of iron, a decrease in reflectivity was observed as the pressure increased, whereas in the case of the iron-silicon alloy, a continuous increase following a discontinuous decrease in the reflectivity was observed. The decrease in reflectivity of iron suggests a decrease in electronic conductivity due to temperature rise with increasing pressure. On the other hand, the continuous rise seems to indicate an increase in the density of free electrons derived from silicon.
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 S. Root, L. Shulenburger, R. W. Lemke et al.: Phys. Rev. Lett, 115, 198501 (2015).