Billy W. Mangum

Determination of the Triple-Point Temperature of Gallium

We have determined the triple-point temperature of high-purity gallium to be 29.77406°C using three standard platinum resistance thermometers (SPRTs) calibrated on the IPTS-68 and using samples of gallium from three commercial sources. All data obtained on the highest purity sample have a standard deviation of ±0.00011°C. The overall systematic uncertainty is estimated to be +0.6-1.1 m°C. The day-to-day irreproducibility of a single melt of each gallium cell was found to be < ±15 μ°C, while over a period of 7 months the irreproducibility among melts of each gallium cell was ≤ ±0.00011°C. These limits on the reproducibility appear to be largely instrumental since every time an SPRT was left in a gallium cell for several days there was no change in the indicated temperature of the triple-point to within the instrumental resolution of ±1.5 μ°C. The pressure dependence was measured and determined to be dT/dP = -2.011 ± 0.001 m°C/atm.

On the International Temperature Scale of 1990 (ITS-90). Part I: Some definitions

In this paper, we specify the purpose of an international temperature scale and present some definitions that are basic to the International Temperature Scale of 1990. These definitions include those for non-uniqueness and for the temperature fixed points underlying the scale. Three types of non-uniqueness are identified.

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.

The Platinum Resistance Thermometer Range of the International Temperature Scale of 1990

Within the International Temperature Scale of 1990 (ITS-90) the platinum resistance thermometer (PRT) is used to realize the scale from approximately 13,8 K to 1 235 K. Such a temperature range is wider than the corresponding range in the International Practical Temperature Scale of 1968 (IPTS-68) because the PRT is used up to the freezing point of silver (1 234,93 K). In this way, the ITS-90 can be realized with much more precision than the IPTS-68, particularly between 901 K and 1 235 K where the standard Pt-10% Rh vs Pt thermocouple was previously used. This paper describes some important steps in the construction of the PRT reference function and the criteria for the selection of the PRT interpolating equations of the ITS-90. In contrast to previous international scales, the PRT range of the ITS-90 is based on two reference functions, one from 13,8 K to 273,16 K and the other from 273,15 K to 1 234,93 K. The two reference functions were obtained from two real PRTs. A set of interpolating equations is used to account for the differences of other real PRTs from those on which the reference functions are based. They provide flexibility of calibration and high precision as expressed, for instance, by non-uniqueness and sub-range inconsistency not exceeding 0,5 mK over the range from 13,8 K to 693 K. Such good properties are the consequence of the choice of suitable forms for the interpolating equations and of fine adjustments in the values assigned to some defining fixed points.

Determination of the Indium Freezing-point and Triple-point Temperatures

The freezing-point temperatures of two samples of 99.9999% pure indium in cells constructed such that the indium was in contact only with Teflon were measured with four standard platinum resistance thermometers and two resistance bridges, one bridge operating at 400 Hz and the other with square-wave dc. Although nominally of the same purity, one sample was purer than the other, with a difference in freezing-point temperature of 0.2 to 0.4 mK, the value depending on the bridge used for the measurements. The temperature, t68, of the purer sample as determined from dc measurements is (156.6342 ± 0.0004) °C and as determined from ac measurements is (156.6345 ± 0.0004) °C. The pressure dependence was determined to be (4.92 ± 0.05) mK/(std. atm). Consequently, the triple-point temperatures are (4.92 ± 0.05) mK lower than the freezing-point values. The indium freezing-point temperature would be a suitable defining fixed point for a temperature scale.

Evaluation of the triple point of 1,3-dioxolan-2-one

The temperature characteristics of the same two glass triple-point cells containing well purified samples of 1,3-dioxolan-2-one have been studied at NPL and NBS. Triple-point temperatures measured on mushes under near-equilibrium conditions were found to be more reproducible than those measured during continuous cooling or heating through the phase transition. The results from the mush experiments, using measurements taken with a variety of standard platinum resistance thermometers, proved that realizations of IPTS-68 in the two national laboratories agree to within 0.3 mK at 36 °C, in accord with the expectations of the Comite Consultatif de Thermometrie. After being corrected for the effect of residual impurities in the sample and of the hydrostatic head, the mean value of the triple-point temperature of the substance is 36.3238 °C, with an overall uncertainty (1 σ) of 0.0004 °C.

On the International Temperature Scale of 1990 (ITS-90), Part II: Recommended Techniques for Comparisons, at the Highest Level of Accuracy, of Fixed-Point Cells Used for Contact Thermometry

Techniques are recommended for comparisons, at the highest levels of accuracy, of fixed-point cells of the defining fixed points, excluding the vapour-pressure points, of the ITS-90, which are used for contact thermometry. The authors are the members of Working Group 1 of the Consultative Committee for Thermometry (CCT) of the Comit´ e International des Poids et Mesures, dealing with Defining Fixed Points and Interpolating Instruments underlying the realization of the ITS-90.

Comparisons of some NIST fixed-point cells with similar cells of other standards laboratories

In this paper we present results of international comparisons of fixed-point cells of some of the defining fixed-point materials of the International Temperature Scale of 1990. These comparisons involved cells from seven national laboratories, although in some cases only one type of fixed-point material was compared. Except for silver cells, the agreement among cells of the same defining fixed-point material from the various laboratories was to within 1 mK. The expanded uncertainties (k = 2) of the comparison measurements were 12 µK for Ga, 18 µK for H2O, 27 µK for Sn, 35 µK for In, 37 µK for Zn, 42 µK for Al, and 55 µK for Ag.

Report on the Sixth International Symposium on Temperature

This is a report on the Sixth International Symposium on Temperature which was held in Washington, DC, USA. March 15-18, 1982. It includes a brief introduction indicating the timeliness of the Symposium, its sponsors and the publication of its proceedings. The remainder of the report is devoted to a summary of the Plenary and Technical Sessions of the Symposium.