The melting and freezing behaviour of nickel was investigated using a vertical alumina crucible specially constructed for thermocouple calibration. The melting and freezing emfs coincided to within 0.02℃, and the freezing plateau depression was only 0.04℃ for 45 min. The effect of the thermocouple insulator was examined, and the heat loss through the insulator stem was estimated to lower the recorded temperature about 0.6℃ below the true freezing temperature. The expanded uncertainty for the calibration of a type B thermocouple was calculated to be about 2.1℃ (κ=2). The uncertainty factor related to the fixed-point temperature of nickel played a major role in the combined uncertainty. Exact determination of the true freezing temperature of nickel on the International Temperature Scale of 1990 (ITS-90) will reduce this uncertainty. From the observed results on the melting and freezing behaviour of the nickel cell, it is suggested that the Ni freezing point can be used as a new primary-grade fixed point at high temperature.
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