High Pressure and High Temperature Equation-of-State of Gamma and Liquid Iron
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t. Res. Soc. Symp. Proc. Vol. 499 ©1998 Materials Research Society
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Figure 1: Sound velocity measurements. Present data indicate 7-iron melts at about 70-_2GPa. Abbreviations: B&H: Barker and Hollenbach [5]; B&M: Brown and McQueen [3]. EXPERIMENTAL PREPARATION The pure iron targets are in the shape of a single machined disk, the "driver plate" is 2mm thick and 38 mm in diameter, the central "top hat" is 4 mm thick and 13 mm in diameter [6]. The target is heated via an induction coil (see Chen and Ahrens [6]) placed around the top hat. The temperature is monitored until just before impact with a two-color infrared pyrometer (Williamson 8120S-C-WD2) which in turn was calibrated against a thermocouple (Figure 2). Two dual-color pyrometers (Williamson 8120S-C-WD2 (temperature range: 10002000°C), and Ircon R-20C10-0-0-0-00-0/000) were used in the experiments. These were calibrated in a Deltech furnace using a Pt-Pt/l 0%Rh thermocouple as a standard. The pure iron target was placed in a mixture of CO 2 and H2 gas. The iron was thus stable in a the temperature range of the measurements (1306-1673 K measured by the thermocouple data), except when the target was deliberately oxidized to observe the effect of surface oxidation on thermal radiation
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detected by the pyrometer. The thermocouple was calibrated at melting point of gold (1337.4 K) and was found to read 2.7 K low. The accuracy of the thermocouple is estimated +1 K. Several factors that may contribute to errors in the pyrometer temperature were investigated during the calibrations, including non-normal pyrometer viewing angle, surface oxidation, and IR absorption of CO 2 in gas flow (through which the samples were observed by the pyrometers). Systematic errors in the pyrometer data, may result from incomplete knowledge of the IR transmission and reflection properties of windows and mirrors in the pyrometer light path. The last two factors were found to be the major causes of uncertainty. Thin quartz or Pyrex windows
Two Color Pyrometer
W (Pyrex) 40 mm Gun Tank M (Au)
Projectile Gun
Target and
Heating Coil
Xenon Flash Lamp
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Streak Camera
Figure 2. Experimental assemblies for EOS experiments. Iron target is preheated with RF induction coils and temperature is monitored by pyrometer. Abbreviations: W: window; L: lens; M: mirror; M (Au): gold mirror; T: EOS turning mirror. About 1 second before launching projectile, EOS turning mirror is inserted in front of the target free-surface via a compressed airoperated piston [7].
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