Further Findings of Impurity Precipitation in Metal Fixed Points

Fahr, Martin; Rudtsch, Steffen; Aulich, A.

doi:10.1007/s10765-011-1132-6

Cited by 11 publications

(11 citation statements)

References 17 publications

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“…As a result of their different densities, some of these compounds will float, some of them will sink. A series of doping experiments has supported this, showing no indication of a change of the indium melting point due to added sulfur [7].…”

Section: Resultsmentioning

confidence: 90%

“…This is a well-known behavior used in industrial metal-purification processes where oxides and other insoluble compounds are skimmed off the top of the molten metal. Particularly for Ga and Zn in indium, this precipitation process have been substantiated by performing doping experiments that allowed observing how these two elements would initially dissolve causing the melting point to drop, but subsequently precipitate until the fixed-point temperature eventually approached the original value after a few days [7].…”

Section: Resultsmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 90%

Section: Resultsmentioning

confidence: 99%

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

et al. 2011

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“…The phase diagrams in Figure 1 show the effect of oxygen on the In-Li system, where the oxygen clearly inhibits the effect of impurity Li (solute) on the fixed-point metal (solvent). This is due to the formation of insoluble oxides [12,13]. Once the compounds are formed, they have no effect on the freezing temperature of the fixedpoint metal.…”

Section: Resultsmentioning

confidence: 99%

“…It is therefore of interest to know how the binary (impurity-metal) phase diagram looks for a given 'starting' amount of oxygen. Two further points are that the oxides of noble elements (present or added to fixed-point metal) will reduce to elemental form, and elements which are highly reactive with oxygen will always precipitate as an oxide [13].…”

Section: Methodsmentioning

confidence: 99%

Effect of oxygen on trace impurities in extremely pure metal ingots used for realising ITS-90 fixed point temperatures

Chowdhury

Pearce

2023

J. Phys.: Conf. Ser.

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The International Temperature Scale of 1990 (ITS-90) provides a scheme for calibrating thermometers which is largely based on the freezing points of pure metals such as indium, tin, zinc, aluminium and silver. The existence of trace impurities in pure metals results in uncertainties in the realization of these freezing points. Several methods such as the sum of individual estimates (SIE) and overall maximum estimate (OME) are used to assess the uncertainties due to the presence of impurities. However, it is becoming evident that the oxidation of impurities results in their precipitation, which means that these insoluble oxides no longer play a significant role in the elevation or depression of the freezing temperature. Hence the conventional correction techniques may overestimate the magnitude of the effect. In this study, the thermodynamic modelling software MTDATA was used to evaluate the effect of oxygen on selected impurities in In, Sn, Zn, Al and Ag by calculating the binary impurity-metal phase diagram in the presence of specific amounts of oxygen. It was found that oxygen has a significant effect on many of the systems studied. The most significant effect was observed in the Ag system, and then, in decreasing order of significance, In, Sn, Zn and Al.

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“…Since they have measurement uncertainties comparable to those of standard cells, slim cells are appropriate for several kinds of investigations, such as the analysis of the homogeneity of large batches of fixed-point material, and doping experiments to estimate the influence of impurities on the fixed-point temperature [4,7,13].…”

Section: Resultsmentioning

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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Further Findings of Impurity Precipitation in Metal Fixed Points

Cited by 11 publications

References 17 publications

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

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

Effect of oxygen on trace impurities in extremely pure metal ingots used for realising ITS-90 fixed point temperatures

Fixed-Point Comparison Uncertainties for Two Cell Geometries

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