LAUSR

Metal carbon eutectic cells (high-temperature fixed points, HTFPs) (Machin in AIP Conf Proc 1552:305, 2013) are being considered for use as reliable high-temperature references for non-contact thermometry above the copper point ($$1084.62\,^{\circ }\hbox {C}$$1084.62∘C). Recent studies have demonstrated the concept of using doped metal carbon eutectic cells as artefacts suitable for temperature scale comparisons (Teixeira et al. in AIP Conf Proc 1552:363, 2013; Teixeira et al. in Int J Thermophys 35:467–474, 2014; Machin et al. in Int J Thermophys 36:327–335, 2015). When using such artefacts, the participating institutes do not know the realization temperature of the doped HTFP cell, because it has been modified by the addition of a selected dopant at a definite concentration. The use of such fixed points can critically evaluate the real measurement capability of the institutes in any comparison. The pyrometry laboratory of Inmetro developed a set of doped Ni–C eutectic cells in 2012 and 2013. This paper describes the long-term stability of a Sn-doped Ni–C cell constructed in 2012, which accumulated more than 220 h above $$1300\,^{\circ }\hbox {C}$$1300∘C amounting to more than 50 cycles of melts and freezes. The cell remained stable, well within the measurement uncertainty, throughout the evaluation period demonstrating the utility of such cells for scale comparison purposes.