Construction, Characterization and Measurement of Fe–C and Pd–C HTFPs at CEM

Abstract

The current state of the art for temperature realization and dissemination above 1300 K is through the MeP-K-19 [1]. A limited set of high-temperature fixed points (HTFPs), an essential component of the MeP-K-19, has their temperature determined (Co–C (1597 K), Pt–C (1011 K) and Re–C (2747 K)). It is really a need to increase the HTFPs available for realization and dissemination of the high-temperature MeP-K. Fe–C (1426 K) and Pd–C (1765 K) has been less investigated, their thermodynamic temperature hasn’t been definitively determined, and they have been considered good candidates for their inclusion in the MeP-K in the EMPIR project “Real-K” [2]. This paper describes the construction, characterization, and measurement of HTFPs of Fe–C and Pd–C at Centro Español de Metrología as part of its contribution to the EMPIR project “Real-K”. Cells made have hybrid-type crucibles and they have been filled applying the piston method. A series of 6 HTFPs has been constructed: 3 Fe–C and 3 Pd–C. Points of inflection of the melting plateaux are repeatable after several initial measurement cycles. Their corresponding International Temperature Scale (ITS-90) temperatures (t90), referenced to a Cu fixed point, and thermodynamic temperatures (t), by means of the spectral responsivity calibration, have been calculated. Additionally, the influence of the furnace in the temperature assigned to the cells has been determined for different furnaces types (one zone and three zone) and different temperature profiles.

Large-area Fe–C eutectic fixed-points for radiation and contact thermometry

“…In these realizations, the melting temperature of the cell gradually increased and reached a stable value. A similar behavior was observed for the 6 mm aperture cell in [22]. For technical reasons, it was not possible to repeat these measurements in the 1ZF furnace or realize the C1 cell in the HUF furnace.…”

“…The nominal purity of the Fe powder was 99.995+% (American Elements, USA). The metal powder was mixed and packaged in a clean environment with graphite powder at 1% below the carbon composition of the eutectic composition [22], that is, 4.2% hypoeutectic metal-carbon mixtures. All graphite pieces, CC-sheets, and holders were baked in a vacuum at approximately 1100 • C for more than 3 h. Additionally, the parts of the crucibles were baked in an argon gas environment under similar conditions before the filling.…”

“…The final uncertainty evaluations for the melting temperature assignment for the investigated cells are listed in table 4 for LP5 and Pt/Pd TC. In both evaluations, similar to [22], the uncertainty value for the 'Structure effect' was directly adopted from [31]. As described above, three different methods were employed to determine and compare the POI values.…”

“…Many researchers have focused on the use of the Fe-C cells to improve the calibration possibilities of TCs by reducing interpolation or extrapolation uncertainties in the temperature range of 1100 • C to about 1600 • C [15][16][17][18][19][20]. In [21,22], Fe-C cells were studied using radiation thermometers. In addition, in [22], the ITS-90 and thermodynamic melting temperatures of Fe-C cells were determined and compared using the same radiation thermometer.…”

“…In [21,22], Fe-C cells were studied using radiation thermometers. In addition, in [22], the ITS-90 and thermodynamic melting temperatures of Fe-C cells were determined and compared using the same radiation thermometer. In [23], a miniature Fe-C graphite crucible was designed, constructed, and successfully used to calibrate a Type R thermocouple.…”