Effect of heat removal along the rod on uniformity of the inner interface thickness during the crystallization initiation

The optimum procedure for realization of metal freezing points accepted by the CCT and WG1 is used for realization of the ITS-90 in the national institutes. One of the basic principles of the method consists in formation of two interfaces during crystallization and initiation of the inner interface by means of short-term exposure of cold rods in the thermometer well of a cell. Since the upper part of the inserted rod is outside the central area of the furnace at the temperature much lower than the metal temperature, the axial temperature gradient appears. The presence of the temperature gradient during initiation of the metal crystallization can lead to different intensity of the solid phase formation throughout the metal height and, as a consequence, to different thickness of the frozen metal layer on the thermometer well surface. Insertion of two and more cold rods to form a continuous inner interface increases this difference. This aspect of the initiation process of inner interface is not accounted fo...