Study on the Realization of Zinc Point and the Zinc-Point Cell Comparison

Continuing our study on aluminum, tin, and silver points, a study on the realization of the zinc point was conducted. Zinc-point cells were newly fabricated using 6N-nominal grade zinc samples, impurity elements of which were analyzed extensively based on glow-discharge mass spectrometry (GDMS). The present paper reports the temperature measurements done using the newly fabricated cells during the zinc freezing process, under which the zinc fixed point is defined, and the analysis of the freezing curve obtained. Comparisons of zinc-point temperatures realized by the newly fabricated cells (cell-to-cell comparisons) were also conducted. Zinc-point depression due to impurity elements was calculated based on the sum of individual estimates and the impurity element analysis. One of the cells evaluated was drawn out from its crucible and analyzed by GDMS at four points, namely, at around the center of the top, of the middle, of the bottom, and around the outer part of the middle area. The purpose of this cell disassembly is to see whether or not there has been some difference before and after cell fabrication, as well as difference in impurity element distribution within the ingot. From the aforementioned studies, some findings were obtained. First finding is that the homogeneity of the zinc ingot was within 30%, except for Pb, which was more concentrated in the center part. Second finding is that the cell-to-cell temperature difference changes along with the progressing solidification process. As a consequence, for an accurate cell-to-cell comparison, the locus in the freezing plateau where the comparison is done should be determined. Third finding is that the slope analysis estimates accurately the cell-to-cell comparison, and is consistent with the impurity analysis. This shows that the slope analysis gives extensive information about the effect of impurity to the zinc-point realization, especially after the cell fabrication.     

New SMU Gallium Fixed-Point Cells

In the framework of the European research project EURAMET 732, the Slovak Institute of Metrology (SMU) built three primary gallium fixed-point cells of different designs. The cells are designed for the calibration of the long-stem SPRT. In regard to the procedure commonly used at SMU when realizing the gallium point, the cells are designed for use in a stirred liquid bath. This article provides information about the cell designs, materials used, method of filling, and results of the performed experiments. The experiments were focused on the study of the cells?? metrological characteristics, some effects that could influence the melting-point temperature and the effect of the melted metal fraction on the immersion profile. New cells were compared with the SMU reference gallium cell.     

Realization of the Temperature Scale in the Range from 234.3 K (Hg Triple Point) to 1084.62°C (Cu Freezing Point) in Croatia

This article describes the realization of the International Temperature Scale in the range from 234.3 K (mercury triple point) to 1084.62°C (copper freezing point) at the Laboratory for Process Measurement (LPM), Faculty of Mechanical Engineering and Naval Architecture (FSB), University of Zagreb. The system for the realization of the ITS-90 consists of the sealed fixed-point cells (mercury triple point, water triple point and gallium melting point) and the apparatus designed for the optimal realization of open fixed-point cells which include the gallium melting point, tin freezing point, zinc freezing point, aluminum freezing point, and copper freezing point. The maintenance of the open fixed-point cells is described, including the system for filling the cells with pure argon and for maintaining the pressure during the realization.     

Bilateral Comparison of Mercury and Gallium Fixed-Point Cells Using Standard Platinum Resistance Thermometer

The objective of project EURAMET 1127 (Bilateral comparison of triple point of mercury and melting point of gallium) in the field of thermometry is to compare realization of a triple point of mercury (?38.8344 °C) and melting point of gallium (29.7646 °C) between the Slovenian national laboratory MIRS/UL-FE/LMK and the Croatian national laboratory HMI/FSB-LPM using a long-stem 25 ?? standard platinum resistance thermometer (SPRT). MIRS/UL/FE-LMK participated in a number of intercomparisons on the level of EURAMET. On the other hand, the HMI/LPM-FSB laboratory recently acquired new fixed-point cells which had to be evaluated in the process of intercomparisons. A quartz-sheathed SPRT has been selected and calibrated at HMI/LPM-FSB at the triple point of mercury, the melting point of gallium, and the water triple point. A second set of measurements was made at MIRS/UL/FE-LMK. After its return, the SPRT was again recalibrated at HMI/LPM-FSB. In the comparison, the W value of the SPRT has been used. Results of the bilateral intercomparison confirmed that the new gallium cell of the HMI/LPM-FSB has a value that is within uncertainty limits of both laboratories that participated in the exercise, while the mercury cell experienced problems. After further research, a small leakage in the mercury fixed-point cell has been found.     

Establishment of NIMT Zinc Fixed-Point Cell

One of the research programs for the Thermometry Metrology Department at the National Institute of Metrology (Thailand), NIMT, is establishment of its own fixed-point cells. Among the fixed-point cells adopted for the realization of the International Temperature Scale of 1990 (ITS-90), NIMT has chosen the zinc fixed point to start the program. The fabrication and the initial evaluation of the zinc fixed-point cell were conducted at the National Metrology Institute of Japan, NMIJ. The cell fabrication was following the design and procedures developed by the NMIJ. In the cell fabrication, a 6N nominal purity zinc metal cylinder ingot was used. The metal ingot was collected in a graphite crucible under an argon gas atmosphere. The new fixed-point cell was compared with the old fixed-point cells already owned by NIMT, namely, one open-type cell and one sealed-type cell by direct cell comparisons. Since the ingot was equipped with a detail impurity element analysis, it is possible to calculate the effect coming from the existence of the impurities based on, for example, the sum of individual estimates (SIE) method. This effect can then be used to correct for the influence impurities on the realization of the temperature fixed point.     

Construction of Gallium Point at NMIJ

Two open-type gallium point cells were fabricated using ingots whose nominal purities are 7N. Measurement systems for the realization of the melting point of gallium using these cells were built. The melting point of gallium is repeatedly realized by means of the measurement systems for evaluating the repeatability. Measurements for evaluating the effect of hydrostatic pressure coming from the molten gallium existing during the melting process and the effect of gas pressure that fills the cell were also performed. Direct cell comparisons between those cells were conducted. This comparison was aimed to evaluate the consistency of each cell, especially related to the nominal purity. Direct cell comparison between the open-type and the sealed-type gallium point cell was also conducted. Chemical analysis was conducted using samples extracted from ingots used in both the newly built open-type gallium point cells, from which the effect of impurities in the ingot was evaluated.     

镓熔点温坪复现研究

镓熔点是ITS-90国际温标中重要的定义固定点,在温度计量研究中起着重要作用。由于高纯镓从液态转化为固态时,体积膨胀约3.1%,传统玻璃外壳的镓熔点容器在冻制过程中很容易造成损坏。为了解决这一难题,设计了一种具有金属外壳的镓熔点装置,以该装置为对象,开展了2种不同镓熔点复现方法和2种不同复现装置对镓相变温坪影响方面的研究,并与国外同类型装置的性能进行了比较。实验结果表明:不同镓点容器复现的镓熔点温度在0.02 mK范围内一致,高纯镓中的微量杂质是造成差异的主要原因;外液-固界面复现方法比双液-固界面复现方法得到的温坪值低0.09 mK;不同复现装置对镓熔点温坪的影响较小。     

A New Generation of Open Zinc Freezing Point Cells at TUBITAK UME

The Temperature Laboratory at TUBITAK UME initiated a study which focused on the construction of freezing point cells of ITS-90 as primary temperature standards. The first cell constructed within the scope of this study was an open tin freezing point cell and the results were in good agreement with the reference tin fixed point cell of UME. The second set of cells constructed was two open zinc freezing point cells. The design of these cells is similar to the tin freezing point cell. After construction, all the home-made cells were evaluated by analyzing their melting and freezing curves. Finally comparison measurements were performed between the current laboratory reference zinc cell and all newly constructed cells.     

Realization of the Indium Fixed Point by an Adiabatic Technique

This work investigates the effect of heating techniques on the realization of the ITS-90 fixed points above room temperature. For that purpose, LNE has constructed a new apparatus to realize the indium fixed point under adiabatic conditions using the “calorimetric” method. The adiabatic condition, in general, is established by maintaining a temperature difference between the fixed-point cell and its surroundings that is as small as possible. In this work, the indium fixed-point cell is located within thermally controlled heat shields whose walls also contain indium. Thus, the shields themselves are also indium cells. The experiments realizing the melting and freezing temperatures of indium using the calorimetric method are described. The results revealed the existence of thermal effects in the realization of the indium fixed-point cell by the conventional “continuous heat flux” method. The advantages of the “cell-within-cell” technique are presented.     

二级校准用温度固定点

近年来出现了一种新的温度固定点校准技术。这种新技术不同于经典的固定点技术，所用设备简单，操作方便，工作效率高，主要适用于二级和工业温度计的校准。本文简要介绍了若干应用例子：一种不需用液氮或干冻冻制及杜瓦瓶保存的复现水三相点的新方法，自动金属固定点装置和不锈饮固定点容器及其复现装置等。     

Fixed-Point Comparison Uncertainties for Two Cell Geometries

To realize the ITS-90 according to its definition, among others, the melting and freezing temperatures of ideally pure metals are needed. Therefore, many national metrology institutes (NMIs) utilize a group of cells instead of one single cell as the national reference for each temperature. With direct fixed-point cell comparisons on a regular basis, it is feasible to account for the small differences between the individual fixed-point temperatures and to detect possible temperature drifts of the cells. At PTB (the German NMI), in recent years, these groups of national standard cells and the so-called transfer cells for calibrations have been complemented by newly developed slim fixed points. These cells typically contain 75% to 80% less fixed-point material compared with standard cells. Slim cells are used for homogeneity investigations of large batches of fixed-point material, for doping experiments to determine the influence of very small amounts of impurities on the fixed-point temperature with very small uncertainties, and for the investigation of contamination or purification effects after the manufacture of a fixed-point cell. These investigations have shown that the main limitation of slim cells is the quality of the phase boundary. The small dimensions of the cell do not allow the formation of a closed phase boundary (or even two of them). However, this can be compensated using a quasi-adiabatic realization procedure, and in this way, uncertainties comparable to those of standard fixed-point cells can be achieved. In this article, the design of the cells as well as typical measurement results and uncertainties for the direct comparison of fixed-point cells of both types, the standard size and slim design, are presented.     

Effect of Ultra-Trace Impurities on the Freezing Point of Zinc

Impurities are the most significant source of uncertainty in most metal fixed points for the realization of the International Temperature Scale of 1990 (ITS-90). The methods for the estimation of uncertainties and corrections of fixed-point temperatures attributable to the influence of chemical impurities were summarized in 2005, and the sum of individual estimates (SIE) method was recommended to be used with the known concentration and liquidus slope of each impurity. This method requires the concentrations and the liquidus slopes of all impurities. For applying the SIE method, efforts still need to be made to solve a series of problems including the unsatisfactory chemical analysis, inadequate data of the liquidus slopes, and information about the dissolution and precipitation of impurities during the filling and the operation of a fixed-point cell. In the present work at the National Institute of Metrology (NIM), great attention is paid to the effect of ultra-trace impurities on the freezing point of zinc. Five slim graphite crucibles were filled with the same batch of zinc with a nominal purity of 6 N for this research. One of them was used to investigate the concentration and distribution of the impurities in the freezing point of zinc by chemical analysis. The remaining crucibles were used to carry out the ultra-trace impurity doping experiments. The liquidus slopes of Ag–Zn, Pb–Zn, Fe–Zn, and Ni–Zn were measured. All results are reported and discussed.     

Measuring Systems for Thermometer Calibration in Low-Temperature Range

The national temperature standard for the low-temperature range between 13.8033 K and 273.16 K has been established in Poland at the Institute of Low Temperature and Structure Research (INTiBS). The standard consists of sealed cells for realization of six fixed points of the International Temperature Scale of 1990 (ITS-90) in the low-temperature range, an adiabatic cryostat and Isotech water and mercury triple-point baths, capsule standard resistance thermometers (CSPRT), and AC and DC bridges with standard resistors for thermometers resistance measurements. INTiBS calibrates CSPRTs at the low-temperature fixed points with uncertainties less than 1 mK. In lower temperature range??between 2.5 K and about 25 K ?? rhodium?Ciron (RhFe) resistance thermometers are calibrated by comparison with a standard which participated in the EURAMET.T-K1.1 comparison. INTiBS offers a calibration service for industrial platinum resistance thermometers and for digital thermometers between 77 K and 273 K. These types of thermometers may be calibrated at INTiBS also in a higher temperature range up to 550°C. The Laboratory of Temperature Standard at INTiBS acquired an accreditation from the Polish Centre for Accreditation. A management system according to EN ISO/IEC 17025:2005 was established at the Laboratory and presented on EURAMET QSM Forum.     

Realization of the ITS-90 at IMGC in the range of long stem PRTS

IMGC has established the fixed points required by the International Temperature Scale of 1990 (ITS-90) for long-stem platinum resistance thermometers (PRTs) at the highest accuracy level. The present paper describes the fixed point apparatus and the measuring procedures used at IMGC for the accurate realization of each fixed point, and gives some data on the typical phase transitions thereby obtained. Moreover, since IMGC has developed both traditional and sealed cells for the realization of the freesing or melting points of metals, the different types of cells and the procedure used for their construction and preparation are also supplied. Finally, the reproducibilities of the freezing points of Sn, Zn, Al, and Ag were evaluated by means of several determinatiaons with one standard thermometer.Translated from Izmeritel'naya Tekhnika, No. 12, 58–62, December, 1993.     

SF6及CO2三相点替代Hg三相点内插方法可行性探究

在不改变90国际温标内插方程形式的基础上,针对83.8058 K到273.16 K温区,分析了六氟化硫(SF6)和二氧化碳(CO2)三相点替代汞(Hg)三相点后,导致的内插方程变化带来的温度偏差以及传播不确定度变化规律.研究结果表明:SF6和CO2三相点替代Hg三相点后,该方程在该温区仍具有适用性;在复现不确定度相同的...     

Some Curious Results with a Gallium Fixed-Point Cell

In 2009, most of the gallium fixed-point cells in use in different INRIM laboratories were compared with Italy??s national standard. The comparison has uncovered problems with one of the commercial devices, realizing a temperature about 0.7 mK too low which initially was even changing linearly with time. An additional series of measurements was undertaken to find out the reason for this behavior, but not being allowed to open the cell, only a suspicion on the possible cause has remained. A way is suggested that might give users an indication of such misbehavior of their cell. The results underline the importance for those NMIs with only a single cell, for any fixed point, to undertake regular comparisons with another cell as a check on its behavior.     

复现90温标定义固定点时杂质引起的偏差估算

本通过介绍一种计算杂质在复现各定义固定点温度时引起的偏差的方法,从实验及理论分析计算的角度讨论了在高纯金属凝固（或熔化）过程中,样品中的杂质对相变温度的影响。     

A Comparison of the ITS-90 Among NPL, NIM, and CEM, Above the Silver Point Using High-Temperature Fixed Points

A prototype comparison of the ITS-90, as realized by NPL, NIM, and CEM, using high-temperature fixed points (HTFPs) of Co-C (1324 °C), Pt-C (1738 °C), and Re-C (2474 °C), is reported. The local realizations of ITS-90 temperatures were assigned by NPL, NIM, and CEM to their own set of HTFPs. NIM and CEM then transported their cells to NPL, and the ITS-90 temperatures of all three sets of cells were measured using a linear pyrometer. From these measurements, a comparison reference value (CRV) was derived. At the Co-C and Pt-C points, the deviation from the CRV was <0.1 °C for all three institutes; at the Re-C point, the deviation was <0.4 °C. These deviations are significantly less than the scale realization uncertainties ascribed by the individual institutes indicating that these uncertainty estimates are conservative and could be revised to smaller values. In addition, thermodynamic temperatures were determined for these HTFPs using the current value of the thermodynamic temperature for the copper point, namely, 1357.82 K. Given the consistent performance of the HTFPs, they should be seriously considered as scale comparison artifacts of choice when comparing primary realizations of the ITS-90 and of the thermodynamic temperature.     

Long Term Performance of Mercury Triple-Point Cells Realized at NIS-Egypt

The triple point of mercury is one of the defining fixed-points of the International Temperature Scale of 1990 (ITS-90). Its value was assigned to be 231.3456 K (?38.8344 °C) by ITS-90 and has a unique importance since it is the only fixed-point suggested by ITS-90 between 0.01 °C and ?190 °C. The thermal metrology laboratory of the National Institute for Standards has chosen, several decades ago, to realize this fixed point through batch of thermometric cells. In the present work, four cells, composing the batch of reference, are inter-compared. The results of these inter-comparisons, over a period of time that may reach a dozen of years, showed the excellent reliability of these cells. One cell of the batch, that is constructed thirty years ago, is still able to materialize a fixed point with an expanded uncertainty of 0.44 mK.