Comparison of the realization of water triple point metallic cell through its preparation techniques in new modified adiabatic calorimeter at NIS-Egypt

Abstract

The triple point of water (TPW, temperature 273,16 K) plays a vital and critical role in thermometry, because of its triple functions. The first one, it defines the temperature unit, the Kelvin, it is the reference point in Standard Platinum Resistance Thermometer (SPRT) calibrations, according to the International Temperature Scale of 1990 (ITS-90) [1]. On the other side, TPW metallic-sealed cell is the link to determine Boltzmann constant through the acoustic resonance techniques. TPW is the connection point between the current definition of the Kelvin and the future one, based on the Boltzmann constant [2]. The uncertainty related to the realization of TPW will propagate in all fixed point defined by ITS-90 text. The thermal metrology laboratory, at the National Institute for Standards (NIS-Egypt), has been working during the last 5 years with the cooperation with LNE-France on the development of metallic-sealed cells for the realization of the TPW [1, 2, 3, 4]. Two techniques to solidify the water sample inside the cell were tested, the usual one; quenching (fast freezing) and a new modified smoothing (slow freezing starts at 90% of melted ice). The calculated value of impurities concentration was carried out; it is about of 1.29 × 10−6 mol. mole−1 which causes a deviation of about 142 μK. The uncertainty related to the realization of TPW has been improved up to ± 30 mK.