Investigation of the Reproducibility of Melting and Freezing Curves for Tin in a Miniature Cell

We studied the possibility of realizing the International Temperature Scale 1990 tin fixed point using a miniature cell and a portable temperature calibrator to improve the calibration accuracy of small high-precision platinum resistance thermometers so that it is equal to that of a Class 2 resistance thermometer. We show that the melting curves for 99.999% pure tin in a miniature cell cannot be used for this purpose. We determined the amount by which the liquidus temperature for Russian-produced commercial-grade tin is reduced due to impurities. We used the calibration methods developed in this paper to determine the optimum conditions for reproducibility of the freezing curve, and studied the properties of these curves.