Triple Point Of Water Cells Research Articles

Totally frozen water triple point cells: a comparison between the INTI (Argentina) and the ICAITI (Guatemala)

A water triple point (WTP) cell maintained for the past three years at the Instituto Nacional de Tecnología Industrial (INTI, Argentina) in a totally frozen state, was compared on three consecutive Mondays with a WTP cell from the Instituto Centroamericano de Investigación y Tecnología Industrial (ICAITI, Guatemala). The latter was prepared by letting it freeze slowly and completely over a period of one month in an ice bath at 0 °C, under the influence of the 0,01 °C temperature difference. Preparation an measuring techniques are described. Since measurements were performed using four polarizing currents (5 mA, □2 × 5 mA, 10 mA, and □2 × 10 mA), results are compared using two, three, and four currents, in order to extrapolate to zero power.The main results were the following. By comparing the temperatures measured on the same day, the WTP temperatures realized using the two cells differed by less than ±24 µK (±5 µK when using only three currents for extrapolation). These differences do not depend on the long-term stability of the measuring system. By comparing the temperatures measured over the two-week period, the maximum temperature difference measured within a single cell was 129 µK (82 µK when using only three currents for extrapolation). These differences reflect the long-term instability of the measuring system, but should have a limited effect on precision thermometry.

Effects of different methods of preparation of ice mantles of triple point of water cells on the temporal behaviour of the triple-point temperatures

We report results of an investigation of the temporal variation of the temperature of triple point of water (TPW) cells, in which the ice mantles were prepared by four different techniques using: (i) solid CO2, (ii) an immersion cooler, (iii) liquid-nitrogen-cooled rods, and (iv) liquid nitrogen (LN), first passing cold nitrogen vapours and then LN directly into the wells of the cells. The temperature of the TPW cell water was either approximately 274 K or 295 K when the freezing of the ice mantle was started. No visible cracks formed during the preparation of any of the mantles using the crushed solid-CO2 or the immersion cooler method, but all of the ice mantles cracked when prepared using the LN-cooled-rod and LN techniques. The cracked mantles, however, soon healed. Initially, the temperatures of the mantles prepared by the four methods varied, but after about three or four days they agreed to within 0,1 mK; after one week they agreed to within 0,03 mK, except for mantles prepared by the LN technique, for which nine days were once required for one of the mantles; after eleven days, the results were practically the same. It appears that the temperature variations observed during the first few days following the preparation of mantles could be caused by a combination of (i) temperature decrease due to introduction of strains in the ice and to formation of fine ice crystals during the preparation of the mantle and (ii) temperature increase due to the relief of strains and the gradual conversion of fine ice crystals to larger ice crystals. Mantles that underwent severe cracking thereby released most of the energy associated with the large strains introduced during preparation of the mantle.

A practical method of realizing the triple point of water using totally frozen cells

A simple, economical and time-saving procedure is described for maintaining water triple point cells (WTPCs) ready for use for indefinite periods, based on storing the WTPCs totally frozen. The uncertainty of reproducibility of the triple point temperature does not exceed 0,1 mK.The WTPC is kept in direct contact with crushed ice in a Dewar flask. Under such conditions the natural tendency of the cell is to solidify completely over a period of several weeks, but it will not break as long as the crushed ice is made of deionized water. The procedure for inducing the initial appearance of the ice phase seems irrelevant within the stated uncertainty. This may indicate that the impurities in the cell attain a stationary quasi-two-dimensional distribution in the ice phase, having migrated to the interfaces between the individual crystals, some of which can be observed with the naked eye (linear dimensions 1 cm to 3 cm). This final state is only slightly perturbed during use, since a very small fraction of ice is melted when forming the inner and outer ice/water interfaces. The triple point temperature is mainly determined by the bulk properties of the pure crystals. Reduced lixiviation and unattended shipping of the WTPCs are possible by-products of the method.

Isotopic composition of water used for triple point of water cells

Measurements of the isotopic composition of water used in the production of triple point of water cells show that state-of-the-art triple point realizations must consider corrections and uncertainties due to variations in the isotopic composition of water. Triple point cell production processes yield cells with triple point temperatures 60 µK below that implied by the definition, with a similar sized uncertainty in the value. The use of isotopically impure water for the triple point leads to a fundamental uncertainty in the definition of the kelvin of around 14 µK because of the equilibrium isotope fractionation between the ice and liquid water in the triple point cell.

‘‘Tray’’ type calorimeter for the 15–300 K temperature range: Copper as a specific heat standard in this range

A calorimeter is described in which thermal contact with the sample is made via a grease film. Radiation shields built into the calorimeter minimize the effect of temperature gradients. Used in an adiabatic shield system the apparatus gives results of high precision and accuracy. The new design permits easy sample changing but there is a small specific heat anomaly owing to melting of the grease film. An all-metal water triple point cell can be installed in place of the sample to check the temperature measuring equipment. The adiabatic shield system used had four independently controlled elements. Experiment showed that a single controlled element is sufficient for discontinuous heating calorimetry. The apparatus could be run in both continuous and discontinuous heating modes. There was no significant difference in results. Measurements on pure copper are reported and the use of this material as a specific heat standard up to 300 K is discussed.

A simple method of filling water triple-point cells

A simple method of filling water triple-point cells is described. The triple-point temperatures of cells prepared in this way were found to differ no more than 0.1 mK from the temperatures yielded by cells used in this laboratory for reference purposes.

Realization of the triple point of water

A method of making triple point of water cells has been developed. The water is purified using ion-exchange techniques followed by vacuum sublimation, and the cell is filled under vacuum. Measurements have shown the cells produced in this way to be of a consistently high standard. The technique described keeps the ice mantle in good condition for a month or more

RADIATION EFFECTS IN PRECISION RESISTANCE THERMOMETRY: II. ILLUMINATION EFFECT ON TEMPERATURE MEASUREMENT IN WATER TRIPLE-POINT CELLS PACKED IN CRUSHED ICE

The heating effect of normal laboratory illumination on the sensors of standard platinum resistance thermometers immersed in a standard water triple-point cell packed in crushed ice has been investigated. This study shows that the absorption by the platinum sensors of luminous and near-infrared radiation transmitted through the ice pack could easily amount to temperature errors as large as 0.000 5 °C. Any illumination error must be eliminated by making all measurements in the dark or under adequate radiation shielding.

An isothermal microcalorimeter operated in a water triple point cell and designed for radioactivity measurements

The construction and operation of an isothermal microcalorimeter are described. The instrument relies on the triple point of water for the maintenance of the constant temperature envelope. This ensures a temperature stability to ±0.0001 degC. Thermistor thermometry is used and the smallest detectable temperature change in the calorimeter is 0.00012 degC corresponding to a power change of 0.5 μW. The microcalorimeter has been employed for the measurement of alpha and beta emitting radioactivities; for example, an activity of about 4 Ci of tritiated water was measured with an estimated accuracy to ±2.5%.

THE FREEZING POINTS OF HIGH-PURITY METALS AS PRECISION TEMPERATURE STANDARDS: VII. THERMAL ANALYSES ON SEVEN SAMPLES OF BISMUTH WITH PURITIES GREATER THAN 99.999 + %

An investigation has been made of the freezing and melting temperatures of seven samples of high-purity bismuth (analyzed impurity contents <0.5 to 7 ppm) including zone-refined metal. Using a controlled outside nucleation technique, freezing curves having plateaux of essentially constant (< ±0.0001 °C) temperature with long durations are readily obtained. A standard deviation in plateau temperature (liquidus point) of ±0.00025 °C was obtained from a series of 34 freezes on a particular sample. The pressure effect on the freezing temperature of bismuth was determined as −0.0035 °C for 1 atmosphere. A value of 271.375 °C (Int. 1948) was determined for the standard liquidus point of pure bismuth.The liquidus points of the samples were intercompared with a precision of about 0.0002 °C and their alloy melting ranges were measured for selection of the purest samples. Ingot morphologies and solute redistributions during melting and freezing were investigated using decanting, quenching, and tracer techniques.Appendix I gives the results of the latest intercomparison of temperatures realized in a grid of water triple-point cells that is maintained by this laboratory for use in the precision temperature measurements. Appendix II lists the values and pressure–temperature dependencies of the liquidus points of the purest samples of Zn, Pb, Cd, Bi, Sn, and In that have been determined at this laboratory.

Triple Point of Water Cell, a New Temperature Standard

Triple Point of Water Cell, a New Temperature Standard

THE FREEZING POINTS OF HIGH PURITY METALS AS PRECISION TEMPERATURE STANDARDS:V. THERMAL ANALYSES ON 10 SAMPLES OF TIN WITH PURITIES GREATER THAN 99.99+%

Extensive thermal analyses have been made on 10 samples (suppliers' analyzed impurity contents <0.2 to <100 p.p.m.) of high purity tin, including zone-refined metal; liquidus points have been intercompared with a precision of about 0.0002 °C and alloy melting ranges have been examined following different types of freezing with and without overnight anneals near the solidus temperature. Samples of nominal 99.9999% purity tin were found to have such narrow alloy melting ranges that any ambiguity, arising from unknown impurity concentrations, in specifying the liquidus point of pure tin is well inside 0.001 °C; a value of 231.913 °C (Int. 1948) was found for the standard liquidus point of pure tin. An account is given of the supercooling that was observed on the bulk samples and of anomalous structures that were found on melting curves. An appendix gives the results of long-term intercomparisons of the temperatures realized in four water triple point cells.