Abstract
We fielded experiments to compare temperatures measured simultaneously by pyrometry and Raman spectroscopy in toluene shocked to 9 GPa. A 0.5 mm thick toluene sample was compressed between sapphire windows by plate impact from a gas gun. As the shock wave reverberated between the windows, the pressure increased stepwise to about 9 GPa. While the sample was near its peak pressure, we measured the Raman spectrum and determined temperature from the ratio of the Stokes and anti-Stokes intensities. Simultaneously, we measured the sample thermal radiance from the C-H vibration bands that occur between 3.2 and 3.6 μm to determine temperature pyrometrically. The pyrometer used a biased indium antimonide detector paired with a custom transimpedance amplifier, a system capable of temperature measurements as low as about 400 K. The Raman measurements gave a temperature of 530 ± 25 K in the bulk volume of toluene. Pyrometry gave a temperature of 496 + 15/−20 K, which is in reasonable agreement with the Raman measurement. Comparisons of this type are necessary to validate pyrometry as a temperature diagnostic in dynamic experiments.
Highlights
Temperature measurements are a critical ingredient in understanding and modeling the equation of state (EOS) of a shocked material.1 Recently, researchers have made substantial improvements in the ability to determine the temperature of a shocked metal sample using optical pyrometry with accompanying reflectivity measurements to identify the emissivity at similar shock stresses.2–6 Pyrometry involves measuring the optical emission from a shock-heated sample in one or more visible or infrared (IR) bands
Comparisons are needed between pyrometry and some other dynamic temperature diagnostic, such as neutron resonance spectroscopy7,8 or Raman spectroscopy
A sapphire impactor moving at 400 m/s caused a 0.5 mm thick toluene sample to undergo multiple shock compressions between sapphire windows to raise the toluene pressure stepwise to around 9 GPa
Summary
Temperature measurements are a critical ingredient in understanding and modeling the equation of state (EOS) of a shocked material. Recently, researchers have made substantial improvements in the ability to determine the temperature of a shocked metal sample using optical pyrometry with accompanying reflectivity measurements to identify the emissivity at similar shock stresses. Pyrometry involves measuring the optical emission from a shock-heated sample in one or more visible or infrared (IR) bands. With pyrometry of an opaque sample, the temperature is determined at its surface, i.e., at its interface with the window needed to maintain shock stress in the sample It is, the bulk temperature (in the sample interior) that is required for EOS calculations. Time-resolved Raman spectroscopy has been used as a temperature diagnostic in shocked materials.9–12 It utilizes the temperature dependence of the intensity ratios of anti-Stokes to Stokes Raman-scattered line pairs for various vibration modes. One value of T should fit all the Raman spectral lines, so it is advantageous to use a Raman spectrum with several lines if possible Confidence in both diagnostics, pyrometry and Raman spectroscopy, would be improved if they were shown to agree for some material
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