Capabilities for Dielectric-Constant Gas Thermometry in a Special Large-Volume Liquid-Bath Thermostat

Dielectric-constant gas thermometry is being further developed at PTB to measure thermodynamic temperature and the Boltzmann constant at the triple point of water. For this purpose, a huge liquid-bath thermostat with a liquid volume of about 800 L has been built to provide a suitable thermal environment in the central working volume (diameter 0.5 m, height 0.65 m), in which the vacuum chamber containing the measuring system is placed. Measurements of the temperature field in the working volume have been performed with and without the chamber using a mesh of 12 platinum resistance thermometers at appropriate positions. The results verify that the temperature inhomogeneity in the bath is well below 1 mK as necessary. The uncertainty of the temperature measurement inside the measuring system must be of the order of 0.1 mK. Its thermal conditions have been, therefore, investigated in detail, too. Special emphasis was given to the thermalization after temperature changes.     

Design and Capabilities of the Temperature Control System for the Italian Experiment Based on Precision Laser Spectroscopy for a New Determination of the Boltzmann Constant

This article reports on the construction details of an isothermal cell, referenced to the triple point of water (TPW), together with characterization of its temperature uniformity and stability. The traceability of the temperature measurements is also defined and reported. The cell has an inner chamber of 15 mm diameter, and it is 150 mm long. Its temperature is actively controlled and maintained stable within 0.1 mK, for an unlimited time. The temperature gradient is limited to less than one millikelvin over the length of the cell which is kept in a horizontal position. This accurate temperature control is achieved by means of a series of three vacuum chambers, one inside the other. A special heater, reflectors, standard platinum resistance thermometers, several feedthroughs, an auxiliary thermostat, specific electronics, and dedicated software are used for the active control. The device represents a mixture of cryogenic and contact thermometry techniques, and it has been designed, assembled, and characterized at the Istituto Nazionale di Ricerca Metrologica. This temperature-stabilized cell is a part of a more complex experimental setup, based on near-infrared precision laser spectroscopy, devoted to the experimental determination of the Boltzmann constant.     

PVTx Measurements for a H2O + Methanol Mixture in the Subcritical and Supercritical Regions

PVTx relationships for a H₂O + CH₃OH mixture (0.36 mole fraction of methanol) were measured in a range of temperatures from 373 to 673 K and pressures between 0.042 and 90.9 MPa. The density ranged from 37.76 to 559.03 kg · m^–3. Measurements were made with a constant-volume piezometer surrounded by a precision thermostat. The temperature inside the thermostat was maintained uniform within 5 mK. The volume of the piezometer (32.68 ± 0.01 cm³) was previously calibrated from well-established PVT values of pure water (IAPWS), and was corrected for both temperature and pressure expansions. Uncertainties of the density, temperature, and pressure measurements are estimated to be 0.16%, 30 mK, and 0.05%, respectively. The uncertainty in composition is 0.001 mole fraction. The method of isochoric and isothermal break points was used to extract the phase transition temperatures, pressures, and densities for each measured isochore and isotherm. The values of the critical temperature, pressure, and density of the mixture were also determined from PVTx measurements in the critical region.     

Radiation Thermometry Toward the Triple Point of Water?

The article describes and evaluates the possibility of using a high-temperature blackbody of accurately known thermodynamic temperature as a reference source for the determination of lower thermodynamic temperatures by spectral radiation thermometry. By applying various intermediate steps, this approach will allow spectral radiation thermometry to be used for the determination of the thermodynamic temperature of the triple point of water with a low uncertainty. The procedure for such an attempt is outlined, theoretical, and practical limits of the resulting uncertainty in thermodynamic temperature are given. The described experimental approach also provides a framework to calculate the uncertainties in determining the thermodynamic temperatures of the defining high-temperature fixed points of the International Temperature Scale of 1990 down to the triple point of water. The estimation of uncertainties is based on current and future values of the relevant contributing components. The uncertainty anticipated in determining the thermodynamic temperature of the triple point of water is 24 mK with current uncertainties and 1.9 mK in the future. Thus, the described approach yields uncertainties that are slightly higher, but comparable to, the tentative uncertainties of other methods—e.g., dielectric constant gas thermometry developed and applied within the framework of the new determination of the Boltzmann constant.     

Investigation of TiC–C Eutectic and WC–C Peritectic High-Temperature Fixed Points

TiC–C eutectic (2,761°C) and WC–C peritectic (2,749°C) fixed points were investigated to compare their potential as high-temperature thermometric reference points. Two TiC–C and three WC–C fixed-point cells were constructed, and the melting and freezing plateaux were evaluated by means of radiation thermometry. The repeatability of the TiC–C eutectic within a day was 60 mK with a melting range roughly 200 mK. The repeatability of the melting temperature of the WC–C peritectic within 1 day was 17 mK with a melting range of ∼70 mK. The repeatability of the freezing temperature of the WC–C peritectic was 21 mK with a freezing range less than 20 mK. One of the TiC–C cells was constructed from a TiC and graphite powder mixture. The filling showed the reaction with the graphite crucible was suppressed and the ingot contained less voids, although the lack of high-purity TiC powder poses a problem. The WC–C cells were easily constructed, like metal–carbon eutectic cells, without any evident reaction with the crucible. From these results, it is concluded that the WC–C peritectic has more potential than the TiC–C eutectic as a high-temperature reference point. The investigation of the purification of the TiC–C cell during filling and the plateau observation are also reported.     

The New KRISS Low Frost-Point Humidity Generator

A new low frost-point humidity generator (LFPG) has been designed, and its performance has been tested, in order to extend the calibration capabilities to the low frost-point range at KRISS. The water vapor–gas mixture is generated by saturating air with water vapor over a surface of an ice-coated saturator under the conditions of constant temperature and pressure. This LFPG covers a range of frost point from  − 99 °C to  − 40 °C. The temperature of the saturator, which is controlled by thermoelectric devices and a two-stage mechanical refrigeration system, is stable within 5 mK, and the difference between the saturator temperature and the frost point generated at the saturator outlet is less than 20 mK. This stability is achieved by using oxygen-free high-conductivity copper materials as the saturator body, and applying a precision PID temperature control system. The performance of this new LFPG system is compared with the KRISS standard two-temperature generator in the frost-point range ( − 80 to  − 40) °C, and its performance is tested with a quartz crystal microbalance (QCM), which was built at KRISS, to  − 91 °C.     

Characterizing the NRC Blackbody Sources for Radiation Thermometry from 150 °C to 962 °C

Validation of the various NRC blackbody sources below 962 °C has been hampered by the lack of a radiation thermometer with sufficient sensitivity and adequately small target size. Recently, progress was made in this area by having access to a NIST RT1550, a radiation thermometer operating at 1.55 μm with a thermoelectrically cooled InGaAs detector, a 3 mm nominal target size, a measuring range of 150 °C to 1064 °C, and a noise-equivalent temperature of 0.5 mK at 420 °C. Having the RT1550 for several months allowed sufficient time to intercompare our various blackbodies, both fixed-point and variable-temperature. It is these intralaboratory comparison results that are reported here.     

System for Realizing the Triple Point of Mercury to Calibrate Industrial-Type Platinum Resistance Thermometers

Most platinum resistance thermometers (PRTs) sent to CENAM for calibration are of the industrial type (IPRT). The cells used to calibrate both standard PRTs (SPRTs) and IPRTs form part of the national standard of temperature. In order to reduce their use, we built a set of fixed-point cells, furnaces, and baths to calibrate IPRTs using fixed points, including an apparatus and cells to reproduce the Hg triple point. To realize the triple point of mercury (TP-Hg), an apparatus that operates from room temperature to  − 45 ^◦C using a CENAM-constructed heat pipe was designed and built. With the heat pipe, it is unnecessary to use a recirculation bath to provide a temperature-controlled environment, the temperature gradient is reduced, and the system is more efficient because its thermal mass is reduced. In this way, it is possible to reproduce the TP-Hg for long periods of time to facilitate IPRT calibration, using cells of smaller size than is conventional and without using expensive liquid baths. The system was tested with cells having 400 g and 800 g of mercury, and a reproducibility of about 0.1 mK was obtained.     

Realization of the Triple Point of Water in Metallic Sealed Cells at the LNE-INM/CNAM: A Progress Report

A miniature metallic cell for the water triple point (TPW, temperature 273.16 K) was developed for capsule-type thermometer calibrations for realizations with adiabatic calorimetry techniques. The LNE-INM/Cnam previously developed a copper cell for the water triple point and the techniques for cleaning, filling, and sealing. On the basis of previous work, a new copper cell prototype for the TPW was developed and filled at the LNE-INM/Cnam. Measurements were performed using an appropriate calorimeter and a comparison block containing several thermometers. Preliminary results show a scatter of the temperatures measured at the phase transition of the order of 0.2 mK when measurements are repeated over a short-term period (1 month). A positive drift in the phase transition temperature of about 30μK·month⁻¹ was observed over several months. Studies are in progress to improve the cell, to reduce the reproducibility uncertainty to less than 0.1 mK and to have a phase transition with better temporal stability.     

Electrical and thermal conductivities of porous SiC/SiO2/C composites with different morphology from carbonized wood

Porous SiC/SiO₂/C composites exhibiting a wide range of high thermal and electrical conductivities were developed from carbonized wood infiltrated with SiO₂. As a pre-treatment, the samples were either heated at 100 °C or kept at room temperature followed by sintering in the temperature range 1200–1800 °C. The microstructure, the morphology, and the electrical and thermal conductivities of the composites were investigated. Pre-treatment at room temperature followed by sintering up to 1800 °C produced composites exhibiting a greater size of carbon crystallites, a higher ordering of the microstructure of carbon and β-SiC and a smaller amount of SiO₂, resulting in electrical and thermal conductivities of 1.17 × 10⁴ Ω⁻¹ m⁻¹ and 25 W/mK, respectively. The thermal conductivity could be further improved to 101 W/mK by increasing the density of the composite to 1.82 g/cm³. In contrast, the pre-treatment at 100 °C produced composites possessing a lower thermal conductivity of 2 W/mK.     

The Limits of a Rayleigh-Scattering Primary Thermometer

Progress in the development of an apparatus to compare the thermodynamic temperature of a gas with the temperature as determined by the International Temperature Scale of 1990 (ITS-90) is reported. The apparatus uses the Rayleigh scattering of light from a gas to provide an intensive measure of gas density, thus avoiding the need for corrections for dead volumes or wall adsorption required by conventional gas thermometry. A laser beam is shone through gas in two cells that are at the same pressure but different temperatures, and the measured ratio of the Rayleigh scattering signals from the two cells can be related to the ratio of the gas density in the cells. From the density ratio, the thermodynamic temperature of one cell can be inferred if the other cell is held close to the triple point of water. However, the Rayleigh scattering is weak and signals are small, making measurements with sufficiently small uncertainty extremely challenging. Since previous reports, the apparatus has been significantly modified, and these changes are described along with indicative results. In this paper, results of measurements in the range from 211 K to 292 K using both argon and xenon are reported. The results suffer from large systematic errors due to contamination in one of the measurement cells. Although the results do not provide reliable estimates of T  − T ₉₀, they indicate that measurements with uncertainties below 1 mK are feasible.     

Dielectric-Constant Gas-Thermometry Measuring System for the Determination of the Boltzmann Constant at PTB

Dielectric-constant gas thermometry is being further developed at PTB to measure thermodynamic temperature and the Boltzmann constant k at the triple point of water. Due to the small electric susceptibility of gases, the targeted relative uncertainty of k of the order of 2 ppm can be achieved only if gas pressures up to 7 MPa and special 10 pF capacitors for the susceptibility measurements, including very large multi-ring toroidal cross capacitors, are used. This required development of a huge measuring system having a large heat capacity. Since the temperature measurement must be traceable to the triple point of water at a level of the order of 0.1 mK, a corresponding stability and homogeneity of the thermal conditions has to be realized. The design of the system and data characterizing its thermal parameters is described. The experimental results are compared with estimations based both on simple models and finite-element calculations.     

Isotopic Effects on the Temperature of the Triple Point of Water

An investigation into the effects of isotopic composition on the triple point temperature of water has been carried out at the National Institute of Metrology (NIM), China, since redefinition of the kelvin with respect to Vienna Standard Mean Ocean Water (V-SMOW) was officially proposed by the Consultative Committee for Thermometry (CCT) in 2005. In this paper, a comparison of four cells with isotopic analyses and relevant results corrected for isotopic composition, employing the isotope correction algorithm recommended by the CCT, is described. The results indicate that, after application of the corrections, the maximum temperature difference between the cells drops from 0.10 mK to 0.02 mK and that these cells are in good agreement within 0.02 mK. Also, temperature deviations arising from isotopic variations fall in the range from −55.9 μK to + 40.7 μK. We consider that the distillation temperature and degassing time of the production procedure lead to isotopic variations.     

Thermophysical Properties of the Refrigerant Mixtures R417A and R417B from Dynamic Light Scattering (DLS)

Dynamic light scattering (DLS) has been used for the measurement of several thermophysical properties of the refrigerant mixtures R417A (50 % by mass 1,1,1,2-tetrafluoroethane—R134a, 46.6 % pentafluoroethane—R125, 3.4 % n-butane—R600) and R417B (79 % by mass R125, 18.25 % R134a, 2.75 % R600). Both refrigerant mixtures are designed for a replacement of R22 (chlorodifluoromethane) in existing refrigeration systems. Thermal diffusivity and sound speed have been obtained by light scattering from the bulk fluid for the liquid phase under saturation conditions over a temperature range from about 283 K up to the liquid–vapor critical point with estimated uncertainties between 1 % and 3 % and between 0.5 % and 2 %, respectively. By applying the method of DLS to a liquid–vapor interface, also called surface light scattering, the saturated liquid kinematic viscosity and surface tension have been determined simultaneously. These properties have been measured from 253.15 K up to the liquid–vapor critical point with estimated uncertainties between 1 % and 3 % for kinematic viscosity and between 1 % and 2 % for surface tension. The measured thermal diffusivity, sound speed, kinematic viscosity, and surface tension are represented by interpolating expressions with differences between the experimental and calculated values that are comparable with but always smaller than the uncertainties. The results are discussed in detail in comparison with literature data and with various prediction methods.     

SAFARI engineering model 50 mK cooler

SAFARI is an infrared instrument developed by a European based consortium to be flown in SPICA, a Japanese led mission. The SAFARI detectors are transition edge sensors (TES) and require temperatures down to 50 mK for their operation. For that purpose we have developed a hybrid architecture based on the combination of a 300 mK sorption stage and a small adiabatic demagnetization stage. An engineering model has been designed to provide net heat lifts of 0.4 and 14 μW respectively at 50 and 300 mK, with an overall cycle duration of 48 h and a duty cycle objective of over 75%. The cooler is self-contained, fits in a volume of 156 × 312 × 182 mm and is expected to weigh 5.1 kg. It has been designed to withstand static loads of 120 g and a random vibration level of 21 g RMS.     

Giant carbon solubility in Au nanoparticles

Variable temperature transmission electron microscopy of individual 5 nm Au nanoparticles shows a striking increase in the particle size on raising the temperature from room temperature to 500 °C in the presence of carbon from amorphous carbon support. Using the assembly of ordered graphene shells on the surface of individual nanoparticles at elevated temperatures—and the high pressures induced by such shells—as an experimental tool to study the origins of this swelling, we find that the volume increase is associated with the uptake of carbon to concentrations exceeding the bulk solubility by more than four orders of magnitude. The formation of stable metal–carbon nanostructures that have no bulk equivalent may have important implications on the functional properties of metal nanoparticles.     

PVT Measurements for Pure Ethanol in the Near-Critical and Supercritical Regions

The PVT properties of pure ethanol were measured in the near-critical and supercritical regions. Measurements were made using a constant-volume piezometer immersed in a precision thermostat. The uncertainty of the density measurements was estimated to be 0.15%. The uncertainties of the temperature and pressure measurements were, respectively, 15 mK and 0.05%. Measurements were made along various near-critical isotherms between 373 and 673 K and at densities from 91.81 to 497.67 kg · m⁻³. The pressure range was from 0.226 to 40.292 MPa. Using two-phase PVT results, the values of the saturated-liquid and -vapor densities and the vapor pressure for temperatures between 373.15 and 513.15 K were obtained by means of an analytical extrapolation technique. The measured PVT data and saturated properties for pure ethanol were compared with values calculated from a fundamental equation of state and correlations, and with experimental data reported by other authors. The values of the critical parameters (T _C,P _C,ρ _C) were derived from the measured values of saturated densities and vapor pressure near the critical point. The derived values of the saturated densities near the critical point for ethanol were interpreted in term of the “complete scaling” theory.     

Experimental Investigation of the Cr3C2–C Peritectic Fixed Point

The Cr₃C₂–C (1,826°C) peritectic point was investigated for its performance as a high-temperature fixed point. Dependence on the impurity content was observed, although it was less severe for the higher of the two equilibrium temperatures obtained with the same cell, the Cr₃C₂–C peritectic point, than for the lower, the Cr₇C₃–Cr₃C₂ eutectic point. Thermal history had an effect on the melting plateau duration, but not on the point-of-inflection temperature nor on the melting range. The melting rate had no apparent effect. The repeatability evaluated as the standard deviation of the repeated melting plateaux within a day was 20 mK for the Cr₃C₂–C peritectic point, while for the Cr₇C₃–Cr₃C₂ eutectic point, this was 210 mK. For both the Cr₃C₂–C peritectic and the Cr₇C₃–Cr₃C₂ eutectic, the freezing plateaux often showed deep supercools, which made them unsuitable for use. The observed good repeatability shows the peritectic-point performance to be comparable to the best MC-eutectic high-temperature fixed points investigated so far. The insensitivity to thermal history constitutes an important and practical advantage. The low price of chromium is a clear benefit as compared to Pt–C (1,738°C) or Ru–C (1,953°C) eutectic points, the M–C eutectic points in this temperature range.     

Fixed point on the basis of Ga-In eutectic alloy for rapid monitoring of thermometers and temperature measurement systems

A fixed point based on Ga-In eutectic alloy with a phase transition temperature of 288.798 K (15.648°C) is proposed and studied. This temperature makes it possible to accomplish a phase transition without the use of external thermostat devices. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 26–30, May, 2008.