The vapour pressure of sodium between 660  C and 962  C

Abstract

Marcarino and Bassani have proposed the sodium liquid-vapour equilibrium as a means to approximate the ITS-90 between 660 C and 962 C with an accuracy of about 10 mK. We have also measured the sodium vapour pressure over this temperature range using a pressure-controlled heat pipe. Our results differ from those of Marcarino and Bassani by approximately 34 mK at 660 C and 21 mK at 962 C with a linear temperature dependence of the difference between these values. This relationship may be explained very satisfactorily by a difference in the impurity content of the two samples. We show that an additional 200 10 -6 mass fraction of potassium in our sample as compared with theirs is sufficient to explain the discrepancy. As sodium of sufficient purity to ensure repeatability of its use as a temperature standard at the millikelvin level is not commercially available, it appears necessary to characterize the pressure/temperature relationship for each sample prior to relying on a measurement of the pressure to determine the temperature of the heat pipe. The alternative is to rely on the heat pipe as an intercomparison device with the temperature given by a calibrated thermometer.

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“…First, this instrument is much less complicated than any other system adopted for similar investigations, such as the previous one operating at INRiM [1] or the one used by Hill and Gotoh [4]. It involves fewer devices, and no extra bath is required to keep the temperature of a reference volume as stable as possible.…”

Implementation of Ethanol Heat Pipe at Cetiat

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“…From equation (1) it appears that any variations in pressure lead to a direct temperature change in the system. Thus, the internal temperature of the heat pipe can be regulated by a pressure variation.…”

“…The CETIAT is working on the implementation of a Gas Controlled Heat Pipe (GCHP) temperature generator to replace the thermometric baths in order to increase productivity and in order to improve temperature stability in the working volume of the generator. Many studies [1,2], explain the advantage of this method. For this purpose, the new system must have better thermal performance and produce the same temperature range than the stirred baths.…”

A New Mercury Gas-Controlled Heat Pipe for Temperature Amplifier and as Calibration Facility

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