Development and investigation of WC–C fixed-point cells

Abstract

Three cells of the WC–C peritectic fixed point with a temperature of about 3021 K were built and investigated. Two different sources of tungsten with nominal purities of 5N and 3N were used, and two different filling techniques were applied. There was no difference in plateau shapes between the cells. The 3N purity cell showed a small difference (0.22 K) in the melting temperature from the 5N cell, which indicates significant purification of initially contaminated tungsten. The typical melting range and repeatability of the observed peritectic melting plateaux were 100 mK and 15 mK, respectively. The melting point was stable and reproducible within 25 mK per two weeks. T90 temperature of the WC–C melting point was found to be (2747.6 ± 1.1) °C (k = 2). The observed freezing plateaux were flat and repeatable within 50 mK and 15 mK, respectively. The WC1−x–WC eutectic transition showed a melting temperature about 29 K lower than the peritectic one with a repeatability of about 0.2 K. The problem of deep supercooling is discussed and a method for its solution is shown and tested.

Development of large-area high-temperature fixed-point blackbodies for photometry and radiometry

“…At the POI it is 2747.84 K with standard uncertainty of 0.18 K for an average small cell [4]. The temperature of WC-C was measured at VNIIOFI [7] and some other national Taking into account the differences presented in table 3, the temperatures of the large-area HTFP blackbodies based on the cells Re-C25 and WC-C16 are 2747.64 K and 3020.15 K, respectively. In estimating the uncertainty of HTFPs we have to take into account the uncertainty of a small-cell realisation, i.e.…”

“…One of them, Re-C (2747.91 K), could be very valuable for applications in radiometry and photometry because of its high temperature. Other attractive HTFPs in this field are WC-C and δ(MoC)-C [6,7]. WC-C, with a temperature (3021 K) close to the distribution temperatures of quartz-halogen lamps, could be useful for spectral irradiance measurements, while the δ(MoC)-C blackbody with its temperature of 2856 K could be ideal as a photometric type-A source.…”

Spectral irradiance scale realization and uncertainty analysis based on a 14 mm diameter WC–C fixed point blackbody from 250 nm to 2500 nm

“…The temperature differences measured were −0.51 K, −0.50 K and −0.46 K, respectively. The average difference was −0.49 K. The melting temperature of the large-cell WC-C fixed point blackbody was defined as 3020.11 K using the average value of the WC-C fixed point, 3020.60 K, based on available measured values for small cells [17,18,27,28]. In future, after the Real-K project [12], the value of the WC-C fixed point might be updated.…”

“…The 3 mm diameter WC-C HTFP blackbodies are generally used in radiation thermometry [13,14], or in radiometry for traceability to temperature scale [15,16]. After development and investigation of small WC-C cells with cavity diameters of 3 mm and 5 mm [17,18], VNIIOFI developed a large area fixed-point cell blackbody with the cavity diameter of 14 mm [19]. The large-area cell has longer phase-transition melting plateau and relatively high radiation flux compared to a small-area HTFP cell of the same type (figure 1).…”

Development of High-Temperature Blackbodies and Furnaces for Radiation Thermometry

“…The BB3500YY, with a larger cavity and improved temperature uniformity, is used at NMIJ to study HTFPs above 2500 • C [6]. The latest PG blackbody developed, the BB3500MP, with the largest cavity diameter of 58 mm is used at VNIIOFI for the investigation of Re-C and WC-C (2748 • C) [7,8] and the fabrication of large-area HTFPs.…”