New Experimental Technique for the Study of Phase Transition Evolution in Fixed-Point Cells

Abstract

A new advanced technique was developed at the Hungarian Metrological Institute (MKEH), devoted to optimizing the realization of the International Temperature Scale ITS-90. The work was performed within the framework of the European project “Novel techniques for traceable temperature dissemination.” The paper is devoted to describing this new measurement technique and its setup. The time evolution of the solid fraction and melt fraction along the phase transformation has been followed, using a technique based on the difference of the electrical conductivity between the solid and liquid phases of the metal. The measurement technique provides electrical signals, which are suitable for improving the quality of the freezing plateaus realized in the case of different fixed-point realizations, covering the temperature range from $-39\,^{\circ }\mathrm{C}$ to $962\,^{\circ }\mathrm{C}$. The ideal section of the freezing plateau can be maintained by ensuring a continuous flow of mass and energy of the fixed-point substance in the axial direction. The intervention is achieved by modifying the temperatures of the different zones of the furnace controller with more degrees, with the aid of developed intervening devices. Recent developments permit the selection of the ideal section of a freezing plateau and, what is more, the increase of this plateau section to practically unlimited for all metal fixed points.