Investigation of the furnace effect in cobalt-carbon high-temperature fixed-point cells

• Published in: Measurement : journal of the International Measurement Confederation Vol. 106; pp. 88 - 94
• Main Authors: Dong, W., Lowe, D., Machin, G., Bloembergen, P., Wang, T., Lu, X.
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.08.2017; Elsevier Science Ltd
• Subjects: Blackbody; Carbon; Cobalt; Eutectic; Eutectics; Fixed point; Furnace effect; Furnaces; High temperature; Holes; HTFP; Melt temperature; Melting; Radiation; Radiation thermometry; Temperature profiles; Uncertainty; Radiation thermometry; Eutectic; Furnace effect; HTFP; Fixed point
• ISSN: 0263-2241; 1873-412X
• DOI: 10.1016/j.measurement.2017.04.005

•Discrepancy in melting temperature of high-temperature fixed-point observed.•Evidence for an unaccounted for effect.•Additional uncertainty values proposed. Temperatures with associated uncertainties are to be assigned to high-temperature fixed-points. It is important that those uncertainties are large enough to cover the sources of error but not so overstated as to unnecessarily reduce the usefulness of the fixed-points. Concerns have been raised about unexplained differences between the same fixed-point measured in different furnaces; here we investigate the effect of using three different furnaces on the freezing and melting behaviour of two Co-C eutectic fixed point blackbody cavities. Each furnace had significantly different temperature profiles. The results indicate that the most uniform furnace yielded a higher melting temperature by over 100mK. Investigation of possible confounding effects: the effect of furnace uniformity on melting curve shape, the micro-structure of the ingot, the temperature drop across the cavity wall, the cavity emissivity and the size-of-source effect show that these factors together are too small to account for the overall observed difference.