Use of Different Furnaces to Study Repeatability and Reproducibility of Three Pd-C Cells

Abstract

Three different Pd-C eutectic fixed-point cells were prepared and investigated at INRIM. Several tens of phase transition runs were carried out and recorded with both a Si-based radiation thermometer at 950 nm and a precision InGaAs-based thermometer at 1.6 μm. Two of the cells were of the same design with an inner volume of 12 cm3. The third one was smaller with a useful inner volume of 3.6 cm3. The three cells were filled with palladium powder 4N5 or 4N8 pure and graphite powder 6N pure. The repeatability and stability of the inflection point were investigated over a period of 1 year. The noticeably different external dimensions of the two cells, namely, 110 mm and 40 mm in length, allowed the influence of the longitudinal temperature distribution to be investigated. For this purpose, two different furnaces, a single-zone with SiC heaters and a three-zone with MoSi2 heaters, were used. Different operative conditions, namely, temperature steps, melting rate, longitudinal temperature distributions, and position of cells within the furnace, were tested to investigate the reproducibility of the cells. Effects on the duration and shape of the plateaux were also studied. This article gives details of the measurement setup and analyses of the melting plateaux obtained with the different conditions

Influence of the Cavity Length on the Behavior of Hybrid Fixed-Point Cells Constructed at INRIM

“…A single-zone furnace equipped with six heating elements made from silicon carbide for operation up to 1600 • C (Carbolite STF 16/450) was instead used with both Cu and Co-C cells [8]. The heated chamber (length of 450 mm) was equipped with a singleend closed ceramic working tube 800 mm long with an inner diameter of 43 mm.…”

Investigations at INRIM on a Pd–C cell manufactured by NPL

“…The cell was sent to INRIM where it was investigated and characterized for the temperature of the inflection point of the melting curve. The measurement setup was part of that already described elsewhere and used for the determination of the thermodynamic temperature of the Co-C point [7] and for investigations of INRIM-constructed Pd-C points [8].…”

“…To perform a direct measurement of the temperature profile of both the furnaces, a setup with a dummy crucible and graphite insulators specifically designed to allow scans with a thermocouple was arranged. The longitudinal temperature profiles inside the furnace tubes were measured with a Pt/Pd thermocouple and a uniformity of 1 K over the length of the cell was obtained with both the furnaces [8].…”