Pure Nickel Fixed Points for Contact Thermometry Calibrations

A robust fixed point using pure nickel contained in an alumina crucible has been developed for thermocouple calibrations. It was observed that a deep supercool often caused the freezing plateau to be short and have a large slope. A procedure for realizing the pure nickel fixed points was developed that reserved a small amount of nickel in the solid state to act as a seed for nucleation of the freeze. This procedure was found to allow freezing plateaus that were suitably long and flat to make them useful for calibrating thermocouples. Using a calibrated Pt/Pd thermocouple, the freezing temperature of nickel was determined to be \(1455.22\,^{\circ }\hbox {C}\) with a \((k = 2)\) uncertainty of \(0.8\,^{\circ }\hbox {C}\).