78 research outputs found
A determination of the molar gas constant R by acoustic thermometry in helium
We have determined the acoustic and microwave frequencies of a misaligned spherical resonator
maintained near the temperature of the triple point of water and filled with helium with carefully
characterized molar mass M = (4.002 6032 ± 0.000 0015) g mol-1, with a relative standard uncertainty
ur(M) = 0.37×10-6. From these data and traceable thermometry we estimate the speed of sound in our
sample of helium at TTPW = 273.16 K and zero pressure to be u0
2 = (945 710.45 ± 0.85) m2 s-2 and
correspondingly deduce the value R = (8.314 4743 ± 0.000 0088) J mol-1 K-1 for the molar gas
constant. We estimate the value k = R/NA = (1.380 6508 ± 0.000 0015) × 10-23 J K-1 for the Boltzmann
constant using the currently accepted value of the Avogadro constant NA. These estimates of R and k,
with a relative standard uncertainty of 1.06 × 10-6, are 1.47 parts in 106 above the values recommended
by CODATA in 2010
Further confirmation of the value 22T(90)-20T(90) at INRIM
Values are given for the difference 22T-20T of a new sample with a dedicated isotopic and chemical assay. The new value changes the overall average by only 3 microK
Production of a new Tin Cell at INRIM
Over the years some of the INRIM metal fixed-point cells, ≥20 years old,
have shown a variable deterioration consisting in the leaking of some of the metal
through the walls of the crucible. The variation in the deterioration is assumed to be
connected with the frequency with which the cells have been used. New cells are
therefore being produced at INRiM as substitutes for the older cells. A description
of the new cells and their preparation is given, along with a preliminary comparison
between the new cell and the older cell(s)
Reanalysis of Possible effects due to Gold-plating on the Thermal Expansion of Copper on Constant-volume Gas Thermometry at Low Temperatures
Constant-volume gas thermometry below the triple point of water (TPW) with reference to TPW gives temperature values higher than the correct ones when the thermal expansion coefficient of the bulb assumed in the calculation is smaller than the real one. Therefore, in order to attribute this temperature difference to a change in the thermal expansion coefficient of copper due to gold-plating, it is necessary that gold-plating increases the thermal expansion coefficient of copper even though that of gold is smaller than that of copper
Some Curious Results with a Gallium Fixed Point Cell
In 2009, most of the gallium fixed-point cells in use in different
INRIM laboratories were compared with Italy’s national standard. The comparison
has uncovered problems with one of the commercial devices, realizing a temperature
about 0.7mK too low which initially was even changing linearly with time. An additional
series of measurements was undertaken to find out the reason for this behavior,
but not being allowed to open the cell, only a suspicion on the possible cause has
remained. A way is suggested that might give users an indication of such misbehavior
of their cell. The results underline the importance for those NMIs with only a single
cell, for any fixed point, to undertake regular comparisons with another cell as a check
on its behavior
Preliminary Measurements of the Xenon Triple Point
Ever since the construction and definition of the highly successful International
Temperature Scale of 1990 (ITS-90), one severe deficiency of the scale has been recognized, without a reliable remedy. The problem is the fact that the only then
available high-quality fixed point between the argon triple point and the water triple
point was the mercury triple point, which unfortunately is situated rather closely to
the water triple point, thus having an extremely strong influence on the interpolation
function of SPRTs in the Ar−H2O range. Already before 1990, measurements on possible
fixed points better placed in this temperature range have been investigated, such
as the triple points of krypton and xenon. However, results have been rather elusive,
mainly regarding the rather large melting range of their transition. A turning point
was the 2005 paper from the National Research Council (NRC, Canada), where it
was established that the relatively high content of krypton was the culprit for the large melting range of the xenon transitions published previously. Indeed, measurements on a xenon sample with very low krypton content produced a very high-quality plateau,
of the same level as other ITS-90 fixed points. However, no follow-up measurements
have been reported, and thus neither have comparison measurements been reported.
Shortly, after the appearance of the NRC paper, Istituto Nazionale di Ricerca Metrologica (INRIM, Italy) acquired a batch of the same high-purity xenon as used by NRC
with the aim of preparing a few sealed cells with it and trying to reproduce the NRC
results. However, with the start of the Neon Project (Euromet Project 770), the realization of these intentions had to be postponed until now. Last December, three cells of different design have been filled with this high-quality xenon and preliminary results of the measurements on the triple point are reported
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