Abstract
An apparatus of high-pressure differential thermal analysis has been constructed. It operates under constant pressure up to 200MPa in the temperature range between 100K and 350K. Liquid 3-methylpentane is used as the pressure medium. Two holes symmetrically drilled in a copper-beryllium alloy block are fitted with sample and reference cells. The cell, made of stainless steel, has a re-entrant copper sheath soldered at the center of the bottom for accepting the thermocouple junction. The pressure inside of the block is sealed by the metallic cone connections and kept constant to within 0.1MPa during measurement by an automatic pressure control system. These contrivances made the sample replacement easy and increased the stability of the baseline. The results on ND4Br crystals showed the apparatus to be sensitive enough for use in most of the phase transition studies in the crystalline state. The heat capacity change≈10JK-1 mol-1 in the ND4Br crystal was resolved as a signal a few times larger than the noise level.
