Realization of Ru–C Eutectic Point for Evaluation of W–Re and IrRh/Ir Thermocouples

Autor: S. Masuyama, H. Ogura, M. Izuchi, Kazuaki Yamazawa, M. Arai
Rok vydání: 2015
Předmět:
Zdroj: International Journal of Thermophysics. 36:385-398
ISSN: 1572-9567
0195-928X
DOI: 10.1007/s10765-014-1825-8
Popis: Tungsten–rhenium (W–Re) thermocouples are widely used in industry for measurements at high temperatures, up to $$2000\,^{\circ }\hbox {C}$$ . Since the electromotive force (emf) of a W–Re thermocouple is known to change during exposure at high temperatures, evaluation of the emf stability is essential for measuring temperature precisely and for realizing precise temperature control used to ensure the quality of products subject to annealing processes. To evaluate precisely the thermoelectric stability around $$2000\,^{\circ }\hbox {C}$$ , two Ru–C $$(1953\,^{\circ }\hbox {C})$$ cells (crucible and Ru–C eutectic alloy) were constructed in our laboratory. The key feature of the cells is that their dimensions are large to ensure there is sufficient immersion available to evaluate the homogeneity characteristics of the thermocouples. By using one of the Ru–C cells, the drift and inhomogeneity of Type C (tungsten–5 % rhenium vs tungsten–26 % rhenium) thermocouples during an exposure to high temperature around $$2000\,^{\circ }\hbox {C}$$ were evaluated. Furthermore, to explore possible applications of the eutectic point to other types of high-temperature thermocouples, the drift of an IrRh/Ir thermocouple (iridium–40 % rhodium vs iridium) was also evaluated using another Ru–C cell. The tests with W–Re and IrRh/Ir thermocouples demonstrate that the newly developed Ru–C cells can be used to successfully realize melting plateaux repeatedly. This enables the long-term drift measurements essential for the evaluation and improvement of high-temperature thermocouples. The results obtained in this study will also be useful for evaluating the uncertainty of thermocouple calibrations at around $$2000\,^{\circ }\hbox {C}$$ .
Databáze: OpenAIRE
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