Estimating the influence of impurities on the freezing point of tin

Fellmuth, B.; Hill, Kathryn

doi:10.1088/0026-1394/43/1/011

Cited by 54 publications

(86 citation statements)

References 49 publications

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“…The shapes of the freezing and melting plateaux realized for a fixed-point cell are not recommended as a means to assess its impurity content [2,10], but such freezing and melting ranges may give an approximate idea of what might be expected. Comparing the slow melting plateau realized following a fast freeze with one following a slow freeze (provided no liquid-solid interface formed around the thermometric well) enables a qualitative analysis of this source of uncertainty.…”

Section: Characterization Of the Cellsmentioning

confidence: 99%

Assembly and Study of Different Mercury Cells with Known Impurity Content and Isotopic Composition

et al. 2008

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The "Centro Español de Metrología" is carrying out a project to improve the knowledge of the influence of impurities and isotopic composition on the temperature of the mercury triple point. High-purity mercury from the Almaden mine (stated purity of 99.9998%) was further purified by vacuum distillation. Three mercury fractions, the original mercury from Almaden and two distilled fractions, were characterized in terms of both impurities and isotopic composition and used to measure the mercury triple point. The original mercury sample contained silver at 560 ng · g −1 as the main impurity while the impurity levels were much lower (silver < 1 ng · g −1 ) in the two distilled fractions. The isotopic composition of the distilled fractions showed delta values, expressed as 1,000×( 198/202 Hg sample − 198/202 Hg reference )/ 198/202 Hg reference , of 1.37 ± 0.07 (1σ ) for the first distilled sample and −1.55 ± 0.03 (1σ ) for the second distilled sample with reference to the original Almaden mercury. For the measurement of the mercury triple point, an alcohol stirred bath was used that allowed two cells to be compared nearly simultaneously. It was observed that the presence of the silver impurities in the high-purity mercury modified slightly the mercury triple point while the effect of variations in the isotopic composition can be considered negligible.

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Section: Characterization Of the Cellsmentioning

confidence: 99%

Assembly and Study of Different Mercury Cells with Known Impurity Content and Isotopic Composition

et al. 2008

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“…If the temperature depression of the uncorrected data, which is mostly due to thermal effects, is treated as induced by impurities, an extrapolation could obviously mislead to an overestimation of the impurity content of a fixed-point cell, different from that [10]. Hence, if the slope of a temperature plateau is to be used, the influence of heat conduction has to be considered first.…”

Section: Correction and Quasi-adiabatic Conditionsmentioning

confidence: 99%

“…2, influences of impurities and diffusion cannot be treated properly. Different melting and freezing rates induce different impurity distributions in the region near the phase boundary due to slow diffusion [9] in the liquid phase, which causes temperatures at the phase boundary to depend on the interfacial velocity [10]. In terms of the equations above, in particular, Eq.…”

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confidence: 99%

A New Method for the Quantification and Correction of Thermal Effects on the Realization of Fixed Points

Fahr

Rudtsch

2008

Int J Thermophys

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The temperature and flatness (shape) of a fixed-point plateau depend on both the amount and nature of specific impurities and on thermal effects that are influenced by the fixed-point cell design and furnace properties. A better understanding and experimental proof of the influence of specific impurities on fixed-point realizations require the separation of impurity influences from thermal effects. In this paper the influence of heat exchange between the thermometer and furnace is quantified via a method based on changing the furnace temperature during the fixed-point measurement. It will be shown that the corresponding correction of this thermal effect has a dominant influence on the plateau shape compared to the influence of impurities. This leads to an explanation for why the maximum of an induced freeze is the most reproducible temperature. A secondary outcome is an explanation of why natural freezes have less flat plateaux compared to induced freezes, resulting in fixed-point temperatures that are too low. Furthermore, the suggested procedure is the basis of the direct and quantitative comparison of fixed-point cells and the detection of weak points within a specific design. It allows optimization of fixed-point cells and furnaces, and helps to deepen the common understanding of the phase transition in fixed-point cells.

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“…The estimate of the uncertainty in the realization of the aluminum fixed point was obtained using the "sum of individual estimates (SIE)" for those impurities for which the concentration and the liquidus slope are known and the "overall maximum estimate (OME)" for the remainder [3][4][5][6]. ( T SIE = 0.15 mK; T OME = 0.15 mK, with a cryoscopic constant of 0.00149 K −1 ).…”

Section: Quantitative Effect Of Impuritiesmentioning

confidence: 99%

Influence of Impurities and Filling Protocol on the Aluminum Fixed Point

2008

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To improve the uncertainty of the aluminum fixed point, a study was launched by LNE-INM/CNAM in the framework of the EUROMET Project 732 "Toward more accurate temperature fixed points" (Coordinating laboratory: LNE-INM/CNAM, 17 partner countries). A new open cell was filled with aluminum of 99.99995% purity. A French laboratory carried out elemental analysis of the sample using glow discharge-mass spectrometry (GD-MS). The values of the equilibrium distribution coefficient k and of the derivative δT l /δc i l of the temperature of the liquidus line with respect to the concentration of impurity i will be obtained through collaboration with a French physical and chemical laboratory. In the past, some aluminum cells were opened after several melts and freezes. The aluminum ingot was sticking to the graphite crucible, indicating that physicochemical reactions had likely occurred between Al and C. To avoid this reaction, an effort was made to draw benefit from the Al 2 O 3 film that appears immediately on the surface of the aluminum ingot when it is exposed to oxygen. The open aluminum cell was tested in different furnaces and with different thermal insulator arrangements inside the fixed-point assembly. The observed drifts of the plateaux were always larger than the expected values. The cell was opened to inspect the aluminum ingot. The ingot was extracted easily, since no sticking to the crucible had occurred. The aluminum showed a very bright surface, but the presence of many "craters" throughout the thickness of the ingot was surprising. In some cases, the thermometer well was even apparent.

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Estimating the influence of impurities on the freezing point of tin

Cited by 54 publications

References 49 publications

Assembly and Study of Different Mercury Cells with Known Impurity Content and Isotopic Composition

Assembly and Study of Different Mercury Cells with Known Impurity Content and Isotopic Composition

A New Method for the Quantification and Correction of Thermal Effects on the Realization of Fixed Points

Influence of Impurities and Filling Protocol on the Aluminum Fixed Point

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