Freezing points of pure metals as defining points of International Temperature Scale ITS-90

Abstract

Melting and freezing temperatures are one of the most important features of metals, both in production and application. For the extremely pure metals where purity higher than 99.9999% is reached, difference between the melting and the freezing temperature is less than 1 mK (1/1000 °C). This virtue has been used for establishment of the temperature fixed points, on which the Practical temperature scales were laid upon. Temperatures of the fixed points are determined on the basis of thermodynamics. The temperature fixed points are used for the calibration of thermometers, which are then in turn used for interpolation between the fixed points. Every realization of the Practical temperature scale is an independent experiment. In this sense, this paper describes mathematical modeling and equipment used for the realization of the temperature scale in the Republic of Croatia in the range from −0 °C to 660 °C, accompanied with the measurement uncertainties.

Keywords

• international temperature scale
• melting and freezing temperatures
• pure petals