Page 7 of 9
Slim Mercury Triple Point Cell Model 17724M Iss.05 – 01/13
THE PERFORMANCE OF A SLIM MERCURY CELL IN THE EUROPA-6 APPARATUS
INTRODUCTION
The purpose of this evaluation is to assess the performance of a Slim Mercury Triple Point Cell in the Europa-6
compared to the Large Mercury Triple Point Cell in its larger apparatus (ITL-M-17725).
METHOD
A True Temperature Indicator 2 (TTI 2) with a resolution of 10uΩ together with a 670 Standard Platinum Resistance
Thermometer (SPRT) serial number 080 was used for this evaluation.
The Slim Mercury Triple Point Cell was placed in the well of the Europa-6. A cushion of Insulating foam 1cm thick
(520-03-03) was placed between the cell and the bottom of the well.
Above the cell were placed two blue insulation pieces (951-02-30) (these are provided with the cell).
The temperature of the Europa-6 was initially set to –37°C and the system was allowed to stabilise for 30 minutes.
Next the controller temperature was set some 0.5°C below the freeze temperature. The cell’s well temperature was
monitored until it showed super-cool. At this point the thermometer was removed and a 6mm copper rod pre-
cooled in liquid nitrogen was inserted into the well to initiate nucleation. After two minutes the thermometer, which
had also been placed in liquid nitrogen, was returned to the re-entrant tube.
To aid thermal conduction the re-entrant well was filled with acetone to a level where the metal re-entrant tube
meets the glass fibre extension tube (520-03-01).
Graph 1 shows the complete freeze.
The apparatus was left overnight and next morning the Europa-6’s temperature was set to –45°C for 30 minutes,
then to –37°C until the mercury began to melt, at which time the controller was set to 0.3°C above the melt
temperature.
A melt of over three hours was obtained, see Graph 2. Longer or shorter plateaus can be obtained by setting the
controller closer or further from the Triple Point Temperature.
Lastly the TTI 2 and 670/080 were calibrated in our Large Mercury Triple Point Cell and apparatus.
RESULTS
Summarising, all results were within 100uK.
In detail: setting a freeze 0.5°C lower than the Triple Point and initiating the freeze with a cold rod and the cold
thermometer resulted in a 2 hour freeze. 50% of the freeze occurred within 100uK. The freeze will be extended if
thermometers are calibrated during the freeze, since each thermometer will melt some of the frozen mercury, thus
elongating the freeze time.
The freeze plateau can also be lengthened by setting the Europa-6 to, for instance, 0.25°C below its Triple Point
which would double the plateau time.
Melting the cell: setting a temperature about 0.3°C above the melt resulted in a melt of three hours with a flatness of
better than 100uK over 80% of the melt.