Thermophysical Properties of Nitrogen Trifluoride, Ethylene Oxide, and Trimethyl Gallium from Speed-of-Sound Measurements |
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Authors: | J. J. Hurly |
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Affiliation: | (1) Process Measurements Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Mail Stop 8363, Gaithersburg, Maryland, 20899-8363, U.S.A |
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Abstract: | The speed of sound was measured in gaseous nitrogen trifluoride, ethylene oxide, and trimethyl gallium using a highly precise acoustic resonance technique. The measurements span the temperature range 200 to 425 K and reach pressures up to the lesser of 1500 kPa or 80% of the sample vapor pressure. The speed-of-sound measurements have a relative standard uncertainty of less than 0.01%. The data were analyzed to obtain the constant-pressure ideal-gas heat capacity C0p as a function of temperature with a relative standard uncertainty of 0.1%. The values of C0p are in agreement with those determined from spectro- scopic data. The speed-of-sound data were fitted by virial equations of state to obtain temperature-dependent density virial coefficients. Two virial coefficient models were employed, one based on square-well intermolecular potentials, and the second based on a hard-core Lennard-Jones intermolecular potential. The resulting virial equations reproduced the sound-speed data to within ±0.02%, and may be used to calculate vapor densities with relative standard uncertainties of 0.1% or less. |
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Keywords: | C2H4O ethylene oxide equation of state Ga(CH3)3 ideal-gas heat capacity intermolecular potential NF3 nitrogen trifluoride speed of sound thermodynamic properties trimethyl gallium virial coefficients |
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