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Title: Updated determination of the molar gas constant R by acoustic measurements in argon at UVa-CEM.
Authors: Segovia, José Juan
Lozano-Martín, Daniel
Martín, María del Carmen
Chamorro, Cesar Rubén
Villamañán, Miguel Ángel
Pérez, Eduardo
García Izquierdo, Carmen
del Campo, Dolores
Issue Date: 2017
Description: Producción Científica
Citation: Metrologia 54 (2017) 663-673
Abstract: A new determination of the molar gas constant was performed from measurements of the speed of sound in argon at the triple point of water and extrapolation to zero pressure. A new resonant cavity was used. This is a triaxial ellipsoid whose walls are gold-coated steel and which is divided into two identical halves that are bolted and sealed with an O-ring. Microwave and electroacoustic traducers are located in the northern and southern parts of the cavity, respectively, so that measurements of microwave and acoustic frequencies are carried out in the same experiment. Measurements were taken at pressures from 600 kPa to 60 kPa and at 273.16 K. The internal equivalent radius of the cavity was accurately determined by microwave measurements and the first four radial symmetric acoustic modes were simultaneously measured and used to calculate the speed of sound. The improvements made using the new cavity have reduced by half the main contributions to the uncertainty due to the radius determination using microwave measurements which amounts to 4.7 parts in 106 and the acoustic measurements, 4.4 parts in 106, where the main contribution (3.7 parts in 106) is the relative excess half-widths associated with the limit of our acoustic model, compared with our previous measurements. As a result of all the improvements with the new cavity and the measurements performed, we determined the molar gas constant R = (8.314449  0.000056) J·K-1·mol-1 which corresponds to a relative standard uncertainty of 6.7 parts in 106. The value reported in this paper lies -1.3 parts in 106 below the recommended value of CODATA 2014, although still within the range consistent with it.
Keywords: Termodinámica
Classification: Molar gas constant
Triaxial ellipsoid resonator
Microwave resonance
Speed of sound
Acoustic resonance
ISSN: 1681-7575
Peer Review: SI
DOI: 10.1088/1681-7575/aa7c47
Sponsor: MEC ENE2013-47812-R
Junta de Castilla y León VA035U16
Language: eng
Rights: info:eu-repo/semantics/embargoedAccess
Appears in Collections:DEP46 - Artículos de revista

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