Progress in INRiM Experiment for the Determination of the Boltzmann Constant with a Quasi-spherical Resonator

Current progress in the INRiM experiment for the determination of the Boltzmann constant k _B by means of acoustic thermometry is reported. Particularly, the microwave determination of the volume of a triaxial ellipsoidal resonator with an inner radius of 5 cm which was designed at LNE-CNAM is discussed. For the same cavity, acoustic measurements in helium at T _w over the extended pressure range between 50 kPa and 1.4 MPa are reported and these results are compared with the predictions of a model which accounts for several perturbing effects. The procedures, methods, and results obtained in the calibration of several capsule-type SPRTs used in the experiment are briefly illustrated, together with the estimate of the temperature uniformity of the experiment.     

Progress Report on NMIJ Acoustic Gas Thermometry at the Triple Point of Water

Herein, progress in the development of an acoustic gas thermometry (AGT) system at the National Metrology Institute of Japan is reported. This AGT system is an initial low-cost version that uses a 1-l quasi-spherical resonator (QSR) made of oxygen-free copper. The system was tested by measuring the speed of sound in argon at the temperature of triple point of water. Measurements were conducted at ten different pressures, ranging from 60 kPa to 420 kPa. The ideal gas limit of the squared speed of sound was obtained through extrapolation, and a preliminary calculation of the Boltzmann constant, which was 12 ppm below the CODATA2014 value, was made. Large inconsistencies among microwave and acoustic modes were observed, which are dominant sources of uncertainty in speed of sound measurements. The system will be improved by replacing the present QSR with another one that is more precisely fabricated.     

Effect of rf power on the structural properties of indium tin oxide thin film prepared for application in hydrogen gas sensor

Indium tin oxide films were grown on glass substrate by rf magnetron sputtering at 648 K. Influence of rf power on structural properties of the ITO films was studied. XRD measurements showed (222) preferred orientation under the optimized deposition conditions. The surface morphology of ITO films analyzed by scanning electron microscope appears to be uniform over the entire surface area, the film exhibited dense layers with fine grains. Finally, ITO sensor device was fabricated and the sensing properties of the device towards hydrogen gas were investigated. The variation in sensitivity of the ITO sensor with operating temperature and with concentration of hydrogen gas was studied. The maximum response was found to be 1.6 at 400 K, for 1,000 ppm of hydrogen gas, and the response of the sensor was found to decrease with increase in concentration of H₂ gas.     

Progress Towards an Acoustic Measurement of the Molar Gas Constant at INRIM

Progress in developing an experiment for the determination of the molar gas constant R and the Boltzmann constant k at INRIM is reported. The experiment involves simultaneous measurements of the acoustic and microwave resonance frequencies of a stainless steel spherical resonator for which its hemispheres were deliberately misaligned. For the present work, these frequencies were measured in helium near 273.16 K, in the pressure range from 100 to 800 kPa. From microwave data, the radius of the resonator was determined as a function of pressure with an estimated uncertainty of 6.0 ppm. Using acoustic data and the microwave determination of the resonator radius, the speed of sound in helium was deduced, and these values were compared with those predicted by recent accurate ab initio calculations. Over most of the pressure range, the present values agreed with the ab initio values within the uncertainty of the measurements (standard uncertainty of approximately 7.0 ppm). Many suggestions for reducing the uncertainty are provided.     

On the retrograde condensation behavior of lean natural gas

The occurrence of liquid dropout in natural gas pipelines may cause operational problems during storage, transport, and processing. Therefore, the availability of a model that accurately predicts the amount of liquid formed is of great importance for the natural gas industry. The objective of this study is to develop a thermodynamic model for the accurate prediction of the amount of liquid formed in natural gas pipelines at transportation conditions. As input, the model requires an accurate gas analysis. A modified Peng-Robinson equation of state was selected for the phase equilibrium calculations. Interaction parameters were optimized from experimental data at conditions of practical interest, i.e., at pressures 10 < p < 70 bar and at temperatures 250 < T < 290 K. For a number of keysystems, the interaction parameters were calculated from new accurate solubility data of heavy hydrocarbons in some of the main constituents of natural gas like methane and nitrogen. Also, an extensive experimental program was carried out to study the influence of minute amounts of nitrogen, ethane and carbon dioxide in methane on the solubility behavior of decane in these gas mixtures. From a sensitivity analysis, it could be concluded that the liquid dropout is influenced mainly by the concentration and characterization of C₇-C₁₃ fractions. In this work, two characterization procedures to represent these fractions are compared. For two types of lean natural gas, the model predictions are compared with field measurement data, recently supplied by the Dutch natural gas industry.Invited paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

NRC Microwave Refractive Index Gas Thermometry Implementation Between 24.5 K and 84 K

The implementation of microwave refractive index gas thermometry at the National Research Council between 24.5 K and 84 K is reported. A new gas-handling system for accurate control and measurement of experimental gas pressure has been constructed, and primary thermometry measurements have been taken using a quasi-spherical copper resonator and helium gas at temperatures corresponding to three defining fixed points of the International Temperature Scale of 1990 (ITS-90). These measurements indicate differences between the thermodynamic temperature T and ITS-90 temperature \(T_{90}\) of \(\left( T - T_{90} \right) = -0.60 \pm 0.56\) mK at \(T_{90} = 24.5561\) K, \(\left( T - T_{90} \right) = -2.0 \pm 1.3\) mK at \(T_{90} = 54.3584\) K, and \(\left( T - T_{90} \right) = -4.0 \pm 2.9\) mK at \(T_{90} = 83.8058\) K. The present results at \(T_{90} = 24.5561\) K and \(T_{90} = 83.8058\) K agree with previously reported measurements from other primary thermometry techniques of acoustic gas thermometry and dielectric constant gas thermometry, and the result at \(T_{90} = 54.3584\) K provides new information in a temperature region where there is a gap in other recent data sets.     

Microwave Determination of Water Mole Fraction in Humid Gas Mixtures

A small volume (65?cm³) gold-plated quasi-spherical microwave resonator has been used to measure the water vapor mole fraction x _w of H₂O/N₂ and H₂O/air mixtures. This experimental technique exploits the high precision achievable in the determination of the cavity microwave resonance frequencies and is particularly sensitive to the presence of small concentrations of water vapor as a result of the high polarizability of this substance. The mixtures were prepared using the INRIM standard humidity generator for frost-point temperatures T _fp in the range between 241?K and 270?K and a commercial two-pressure humidity generator operated at a dew-point temperature between 272?K and 291?K. The experimental measurements compare favorably with the calculated molar fractions of the mixture supplied by the humidity generators, showing a normalized error lower than 0.8.     

Experimental Measurement and Thermodynamic Modeling of the Solubility of Carbon Dioxide in Aqueous Alkanolamine Solutions in the High Gas Loading Region

The solubility of carbon dioxide in aqueous alkanolamine solutions was investigated in the high gas loading region based on experimental measurements and thermodynamic modeling. An experimental phase equilibrium study was performed to evaluate the absorption of carbon dioxide in aqueous solutions of five representative alkanolamines, including monoethanolamine, diethanolamine, N-methyldiethanolamine, 2-amino-2-methyl-1-propanol and piperazine. The carbon dioxide loadings of these solutions were determined for a wide range of pressures (62.5 kPa to 4150 kPa), temperatures (303.15 K to 343.15 K) and alkanolamine concentrations (2 M to 4 M). The results were found to be largely consistent with those previously reported in the literature. Furthermore, a hybrid Kent–Eisenberg model was developed for the correlation of the experimental data points. This new model incorporated an equation of state/excess Gibbs energy model for determining the solubility of carbon dioxide in the high-pressure–high gas loading region. This approach also used a single correction parameter, which was a function of the alkanolamine concentration. The results of this model were in excellent agreement with our experimental results. Most notably, this model was consistent with other reported values from the literature.     

Force Transmission Error Analysis for a High-Pressure Single-Sinker Magnetic Suspension Densimeter

The magnetic suspension densimeter (MSD) is a sophisticated, state-of-the-art device that provides extremely accurate results for density measurements. The MSD uses a magnetic technique to couple a mass inside a measurement cell with an external mass balance for mass measurement. This article presents a force transmission error (FTE) analysis for a high-pressure, single-sinker MSD. Due to the magnetic working principle of the apparatus, magnetic properties of the high-pressure cell and external magnetic fields affect the measurements slightly. For the analysis, McLinden et al. suggest making measurements using two different sinkers, a titanium sinker and a copper sinker, having the same mass. The measurements cover densities for methane, ethane, carbon dioxide and nitrogen over the temperature range from 265 K to 450 K (±5 mK stability) up to 180 MPa (uncertainty of 0.01 % full scale: 200 MPa). Comparing and manipulating the measurements permit determination of apparatus and fluid specific effects that contribute to the FTE. For this MSD, the apparatus effect is about 200 ppm, which effectively masks any fluid specific effect. A comprehensive analysis of the FTE produces a uniform deviation for density values of about 0.05 % at 2σ across the full range of pressure.     

Design and Capabilities of a Custom-Made Thermostat for a High-Accuracy Adiabatic Calorimeter

A high-accuracy adiabatic calorimeter is being developed at the Italian Istituto Nazionale di Ricerca Metrologica (INRiM) to investigate thermodynamic properties of small amounts of solids and fluids, including bio-diesels and biological materials. The designed apparatus is intended to perform absolute heat-capacity measurements in the temperature range between 240 K and 420 K. Such a kind of investigations requires accurate temperature measurements and controls. Therefore, a dedicated thermostat has been studied and assembled at INRiM to obtain temperature stability and uniformity within 1 mK over the complete application range of temperature. The accuracy of the temperature measurements is obtained by means of a capsule standard platinum resistance thermometer calibrated at the national temperature fixed points. This paper describes the AC calorimeter project and the dedicated thermostat design. The temperature automatic control principle is reported, together with the preliminary results obtained in terms of thermal conditions and measurements.     

Thermal Conductivity of Humid Air

In this article, measurements of the thermal conductivity of humid air as a function of pressure, temperature, and mole fraction of water, for pressures up to 5 MPa and temperatures up to 430 K, for different water contents (up to 10 % vapor mole fraction) are reported. Measurements were performed using a transient hot-wire apparatus capable of obtaining data with an uncertainty of 0.8 % for gases. However, as moist air becomes corrosive above 373 K and at pressures >5 MPa, the apparatus, namely, the pressure vessel and the cells had to be modified, by coating all stainless-steel parts with a titanium nitride thin film coating, about 4 μm thick, obtained by physical vapor deposition. The expanded uncertainty (coverage factor k = 2) of the present experimental thermal conductivity data is 1.7 %, while the uncertainty in the mole fraction is estimated to be better than 0.0006. Experimental details regarding the preparation of the samples, the precautions taken to avoid condensation in the tubes connected to the measuring cell, and the method developed for obtaining reliable values of the water content for the gas mixtures are discussed. A preliminary analysis of the application of the kinetic theory of transport properties in reacting mixtures to interpret the complex dependence of the thermal conductivity of humid air on water composition is addressed.     

One-Step Synthesis and Sintering of MgB2 by Spark Plasma Sintering

We have studied the one-step procedure for simultaneous synthesis and sintering of SiC-doped MgB₂ by the spark plasma sintering technique. Two types of composition, one in which Mg is strongly deficient, with the atomic ratio $\mathrm{B/Mg} = 3.75$ , and one in which Mg content is slightly higher than the stoichiometric value, specifically $\mathrm{B/Mg} = 1.87$ , were investigated. The amount of SiC was 12 wt.% and 9 wt.%, respectively. For comparison we also studied the way the deficit of Mg can be compensated in a second process of sintering. The sample with Mg deficit shows that SiC is left almost unreacted but the results are spectacular: the highest critical temperature, 36.5 K, the highest upper critical field and the highest self-field critical current density 6.7×10⁵ A/cm² at 10 K. In the sample with overstoichiometric Mg, SiC is decomposed, carbon diffuses within MgB₂ but the critical temperature is only of 35.8 K and the zero-field critical current density is one order of magnitude lower. The compensation of the deficit of Mg in the two-step procedure is not efficient. The critical temperature is even lower, 35.8 K, the upper critical field is also lower despite SiC decomposition and C diffusion within MgB₂ and the critical current density is slightly above 10⁵ A/cm². However, at low temperatures and fields of order 7 T the sample with overstoichiometric Mg and the sample prepared by the two-step procedure have higher critical current density.     

Measurement of the Calorific Value of Methane by Calorimetry Using Metal Burner

With the diversification of natural gas origins and variations in natural gas compositions, the accurate measurement of the calorific value of natural gas has become a very important issue for the gas industry and standardization. Korea Research Institute of Standards and Science is developing a standard gas calorimeter based on the isoperibolic technique. This work describes the details of the experimental apparatus and procedures of the developed gas calorimeter along with the measurement results for the superior calorific value of methane at \(25\,^{\circ }\hbox {C}\). A burner made of stainless steel was used for the first time in this type of calorimeter, and the potential application of a metal burner to a gas calorimeter was investigated. Eight measurements were performed, and the deviation from international standards was 0.16 %. The deviation was mainly caused by the measurement of the burned methane gas. The measurement results show that the metal burner may potentially be employed in a gas calorimeter.     

The Russian National Standard of Gases Humidity and Traceability System of Humidity Measurements

The Russian national humidity standard of gases has been modernized in order to increase the number of reproducible quantities of humidity (relative humidity, dew/frost-point temperature, mole fraction) and to extend the humidity and operating temperature ranges. The basis of the standard comprises two humidity generators with operating temperature ranges from \(5\,^{\circ }\hbox {C}\) to \(90\,^{\circ }\hbox {C}\) and from \(-60\,^{\circ }\hbox {C}\) to \(15\,^{\circ }\hbox {C}\). The common working range (from \(5\,^{\circ }\hbox {C}\) to \(15\,^{\circ }\hbox {C}\)) allows comparison of the generators. The generators use the two-pressure method to generate humid gas defined in terms of the relative humidity (from 5 %rh to 98 %rh at temperatures from \(90\,^{\circ }\hbox {C}\) to \(-60\,^{\circ }\hbox {C}\)) and the one-pressure (or phase equilibrium) method to generate humid gas defined in terms of the vapor mole fraction (from 0.6 ppm to \(700\times 10^{3}\) ppm) and dew/frost-point temperature (from \(-79\,^{\circ }\hbox {C}\) to \(90\,^{\circ }\hbox {C}\)). The expanded uncertainty in the relative humidity is no more than 0.2 %rh, no more than 1.2 % in the vapor mole fraction, and no more than \(0.12\,^{\circ }\hbox {C}\) in the dew/frost-point temperature. The ordinary hygrometers are traceable to the national primary standard in accordance with the state hierarchical chain for measuring means of gas humidity. The state hierarchical chain consists of three branches for means of measurements: (a) mole fraction, (b) dew/frost-point temperature, and (c) relative humidity with each branch represented as the scheme: primary standard–secondary standard–working standard–ordinary hygrometer. Calibration and verification of working standards and ordinary hygrometers, and their traceability to the primary standard use methods of (i) direct measurements, (ii) direct comparison, or (iii) comparison with a comparator.     

Indium oxide thin film based ammonia gas and ethanol vapour sensor

A sensor for ammonia gas and ethanol vapour has been fabricated using indium oxide thin film as sensing layer and indium tin oxide thin film encapsulated in poly(methyl methacrylate) (PMMA) as a miniature heater. For the fabrication of miniature heater indium tin oxide thin film was grown on special high temperature corning glass substrate by flash evaporation method. Gold was deposited on the film using thermal evaporation technique under high vacuum. The film was then annealed at 700 K for an hour. The thermocouple attached on sensing surface measures the appropriate operating temperature. The thin film gas sensor for ammonia was operated at different concentrations in the temperature range 323–493 K. At 473 K the sensitivity of the sensor was found to be saturate. The detrimental effect of humidity on ammonia sensing is removed by intermittent periodic heating of the sensor at the two temperatures 323K and 448 K, respectively. The indium oxide ethanol vapour sensor operated at fixed concentration of 400 ppm in the temperature range 293–393 K. Above 373 K, the sensor conductance was found to be saturate. With various thicknesses from 150–300 nm of indium oxide sensor there was no variation in the sensitivity measurements of ethanol vapour. The block diagram of circuits for detecting the ammonia gas and ethanol vapour has been included in this paper.     

Sensitive Spectroscopic Analysis of Biomarkers in Exhaled Breath

We have developed a novel optical setup which is based on a high finesse cavity and absorption laser spectroscopy in the near-IR spectral region. In pilot experiments, spectrally resolved absorption measurements of biomarkers in exhaled breath, such as methane and acetone, were carried out using cavity ring-down spectroscopy (CRDS). With a 172-cm-long cavity, an efficient optical path of ~?132 km was achieved. The CRDS technique is well suited for such measurements due to its high sensitivity and good spectral resolution. The detection limits for methane of ~?8 ppbv and acetone of ~?2.1 ppbv with spectral sampling of 0.005 cm^?1 were achieved, which allowed to analyze multicomponent gas mixtures and to observe absorption peaks of ¹²CH₄ and ¹³CH₄. Further improvements of the technique have the potential to realize diagnostics of health conditions based on a multicomponent analysis of breath samples.     

Cryostat for Fixed-Point Calibration of Capsule-Type SPRTs

A cryostat for fixed-point calibration of capsule-type SPRTs (standard platinum resistance thermometers) was developed. Using this system, cryogenic fixed points defined on the International Temperature Scale of 1990 (ITS-90) were realized. The cryogenic cells were argon, oxygen, neon, and two equilibrium-hydrogen (e-H₂) cells, made by INRiM, Italy. The uncertainty of the realization of each fixed point was estimated to range from 0.53 mK to 0.43 mK (k = 2). The realizations of the triple point of e-H₂ using two sealed cells coincided within 0.1 mK. Therefore, we are able to calibrate capsule-type SPRTs down to 24.5561 K within an uncertainty of 1 mK (k = 2) by this system. A closed-cycle helium gas refrigerator was used for the cryostat. Each sealed cell was designed so that it could accommodate three sealed cells in the thermometer wells made within the cell. Therefore, the cryostat was designed to accommodate only one sealed cell at a time. The base temperature of this liquid-free cryostat, when one sealed cell and three capsule-type SPRTs were attached for calibration, was ~17 K. For the realization of the triple point of e-H₂, we used liquid helium for additional cooling. Adiabatic melting of the triple point was realized by controlling the inner-most radiation shield at a temperature very close to that of the triple point, and by applying a heat pulse by a heater directly wound to the cell. The amount of the heater power and the waiting time for the thermal equilibrium after each heat pulse were chosen in a way that the adiabatic melting could be finished within ~6 h for each cell. The triple point of each cryogenic fixed point was deduced from the equilibrium temperatures between the heat pulses and subsequent extrapolation to the liquidus point. For the oxygen cell, temperatures of two solid?Csolid transitions (???C?? and ???C?? transitions) were also measured, and the results were consistent with values reported in the literature within the designated uncertainty.     

Structural, optical and gas sensing properties of spin coated nanocrystalline zinc oxide thin films

Synthesis of nanocrystalline zinc oxide thin films by sol gel spin coating technique and its application as ammonia gas sensor is presented in this paper. The synthesized sample is pure zinc oxide with hexagonal wurtzite structure. The lattice parameters are: a = 3.2568 Å and c = 5.210 Å. Average crystallite size is of the order of 58 nm. SEM studies show that growth of the film takes place with folded structure, increasing the open surface area of the film. Optical study revealed that band gap of ZnO is 3.25 eV with direct band to band transitions. Gas sensing characteristics showed that ZnO film is sensitive as well as fast responding to ammonia gas at 573 K. A high sensitivity for ammonia gas indicates that the ZnO films are selective for this gas. The rise time and recovery time are 25 and 80 s, respectively. The mechanism of gas sensing is explained adequately.     

Thermal conductivity of methane for temperatures between 110 and 310 K with pressures to 70 MPa

The paper presents new experimental measurements of the thermal conductivity of methane for 14 temperatures between 110 and 310 K with pressures to 70 MPa and densities from 0 to 30 mol · L^–1. The measurements were made with a transient hot-wire apparatus and they cover a wide range of physical states including the dilute gas, the moderately dense gas, the near-critical region, the compressed liquid states, and the vapor at temperatures below the critical temperature. The new measurements are closely spaced in temperature and density to describe the thermal conductivity surface, in particular the critical enhancement which extends to the highest temperature measured. A fit of the thermal conductivity surface allows comparison of the present results to those of others. The comparison reveals several discrepancies inherent in the results of others and in an earlier correlation. The precision (2) of the methane measurements is between 0.5 on 0.8 % for wire temperature transients of 4 to 5 K, while the accuracy is estimated to be 1.6%.     

Performance Characterization of Capacitance Diaphragm Gauges with Different Diaphragm Materials Below 10% of Full Capacity

The capacitance diaphragm gauge (CDG) is one of the most accurate transfer standards for use in atmospheric to medium vacuum regions. Currently, it is practical to cover a wide range of measurements with the least amount of equipment possible. In this study, one CDG with a metal membrane and two CDGs with a ceramic membrane are characterized through calibrations using a reference standard, in this case a force-balanced piston gauge system, through repeated measurements ranging from about 500 Pa to 13.3 kPa, below 10% of their full capacities (133 kPa). Performance characterizations such as repeatability, long-term instability and zero-pressure instability assessments were conducted. According to repeatability and long-term instability measurements of 133 kPa CDGs tested below 10% of their full-scale (FS) capacities, the metal membrane CDG was found to be somewhat superior compared to the ceramic membrane CDG due to the inherent material stiffness of this type of CDG. However, the difference was negligible, and both membrane-type CDGs could be used at 3 kPa (about 2% of the FS). The responses to heater effects and the results of the zero-pressure instability tests were also evaluated and presented. As shown from these results, the zero-pressure instability is major concerns for the metal membrane CDG, while it has little effect for the ceramic membrane CDG. CDGs in either case have their own advantages and can be used depending on the user’s discretion.