High-Purity Fixed Points of the ITS-90 with Traceable Analysis of Impurity Contents

Rudtsch, Steffen; Fahr, Martin; Fischer, Julian; Gusarova, Tamara; Kipphardt, Heinrich; Matschat, Ralf

doi:10.1007/s10765-007-0358-9

Cited by 12 publications

(9 citation statements)

References 12 publications

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“…Moreover, the freeze peaks of the Al 298, compared with the reference Al cell plateau, are much lower (by (11.3 ± 3.9) mK); therefore, the Al 298 ingot contained considerable initial impurities which affected its freezing and melting temperatures. (We use the freeze peak as a comparison point as this is considered the most reproducible part of the curve [6].) The presence of background impurities can be seen from the GD-MS analysis as reported in Table 1.…”

Section: Resultsmentioning

confidence: 99%

The Influence of Titanium on the Aluminum Fixed-Point Temperature

Petchpong¹,

Head²

2011

Int J Thermophys

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This work describes the deliberate doping of high purity (99.9999 %) aluminum with titanium (99.8 %) impurity and the effect of this on the temperature of the aluminum liquid-solid phase transition (660.323 • C). The aluminum sample was in the form of an ∼0.3 kg ingot (that would normally be used to realize an ITS-90 fixed point) which was doped at ∼0.9 ppmw Ti and ∼1.8 ppmw Ti (mass fraction in parts per million by mass). Measurements were made with procedures and equipment normally used in a metrological thermometry laboratory, rather than using special arrangements. Samples cut from the aluminum ingot were chemically analyzed by glow discharge mass spectrometry (GD-MS) before doping and after the second doping (to 1.8 ppmw). The experimental temperature offsets were compared with those calculated by interpolation from a reference book value using the mass of dopant introduced, or the chemical analysis data. The results showed that the aluminum temperature increased after adding 0.9 ppmw Ti, but apparently the temperature did not change after further doping to 1.8 ppmw Ti; which was unexpected. The first result suggested that titanium impurity increases the Al transition temperature by +5.1 mK·ppmw −1 . However, using the (total) temperature offset and the GD-MS value for the (total) added Ti impurities, then one calculates a value of 3.4 mK · ppmw −1 (much closer to a reference book value). The experimental undoped liquid-solid transition curves were also compared against theoretical curves (calculated using a theoretical model "MTDATA"). This suggested that GD-MS may not be "exposing" all the active impurities (some of which may be "hidden" in the carbon background).

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Section: Resultsmentioning

confidence: 99%

The Influence of Titanium on the Aluminum Fixed-Point Temperature

Petchpong¹,

Head²

2011

Int J Thermophys

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“…An SI-traceable GD-MS calibration was achieved by means of synthetic standards [3][4][5], yielding uncertainties smaller than 30 % for the majority of the detected impurities. This is a considerable improvement compared to typical uncertainties of GD-MS, which are of the order of (300 to 500) %.…”

Section: Chemical Analysismentioning

confidence: 99%

“…2. Chemical analysis of the graphite crucible and other parts of the fixed-point cell that possibly contaminate the fixed-point metal [3]. 3.…”

Section: Introductionmentioning

confidence: 99%

Procedure for the Impurity-Related Correction at the Indium Fixed-Point

et al. 2011

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Determining the influence of impurities on the fixed-point temperatures of the ITS-90 requires the completion of several tasks. In this paper, the progress made at Physikalisch-Technische Bundesanstalt (PTB) and BAM Federal Institute for Materials Research and Testing is presented and remaining questions are discussed. The projected characterization procedure at PTB, which is based on the established SIE method (sum of the individual estimates), using a new indium fixed-point cell is described as an example. This procedure includes an SI-traceable chemical analysis of the material in the fixed-point cell with sufficiently low uncertainties, the individual experimental determination of the influence of the quantified impurities on the fixed-point temperature, and the establishment of direct links to the phase-transition temperatures of the national standard and of an assumed material of ideal purity. A characteristic difference to the common practice is the chemical analysis of the fixed-point metal being done after determining the cell's freezing temperature. This allows for the detection and consideration of contamination and purification effects due to the filling process, or due to the contact with the carbon crucible and other parts 123 294 Int J Thermophys (2011) 32:293-302 of the fixed-point cell. A chemical analysis of an indium fixed-point was carried out by BAM with relative measurement uncertainties below 30 % which have not been previously achieved. The results provide evidence for the precipitation of some impurities, which is apparently inconsistent with the corresponding binary phase diagrams, but was explained in a recent publication. Implications for the use of the SIE method shall be described briefly at the end.

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“…The fixed-point metal is contained in a crucible made of graphite of the highestavailable purity (specified ash content <5 µg/g, please see [5] for the detailed chemical analysis); this graphite crucible is enclosed in a quartz tube. The thermometer is inserted in the quartz thermometer well, which in turn fits into the graphite well.…”

Section: Cell Designmentioning

confidence: 99%

“…Therefore, it is certainly desirable to carry out these investigations with small sample masses, provided that the temperaturemeasurement uncertainties are not compromised. Two different setups for smaller sample masses have been developed [5]; this article covers the slim type of fixedpoint cells, which are to be used with standard fixed-point equipment and feature a reduction of the necessary amount of fixed-point metal by more than 75 % compared with standard cells.…”

Section: Introductionmentioning

confidence: 99%

Fixed-Point Comparison Uncertainties for Two Cell Geometries

2011

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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.

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High-Purity Fixed Points of the ITS-90 with Traceable Analysis of Impurity Contents

Cited by 12 publications

References 12 publications

The Influence of Titanium on the Aluminum Fixed-Point Temperature

The Influence of Titanium on the Aluminum Fixed-Point Temperature

Procedure for the Impurity-Related Correction at the Indium Fixed-Point

Fixed-Point Comparison Uncertainties for Two Cell Geometries

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