High-Pressure Apparatus Using Pressure Generated by Restraining Thermal Expansion

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A mechanical type of high-pressure apparatus has usually been used for studies and productions. However, this type of apparatus requires a large hydraulic press and becomes large in size and complicated in structure. Furthermore, countermoves for frictional force and pressure leakage are the problem.An apparatus using pressure generated by restraining thermal expansion is not accompanied with frictional force and pressure leakage. The author has proposed this type of apparatus which consists of a conductor ball surrounded by a hard insulating cylinder. In the apparatus only an inside ball is heated by induction. However, the apparatus requires much work for set-up and pressure measurements, because it is necessary to make the pressure vessel of insulator. Furthermore, the ball used as pressure source requires good conductivity.In this study, a new type of high-pressure apparatus based on thermal energy was devised. In this apparatus, the pressure vessel was made of steel and a furnace was inserted in the pressure chamber. High pressure was generated by restraining thermal expansion of NaCl and LiF inserted in the pressure chamber. A method of calculating pressures generated in the apparatus was established. The apparatus was designed in detail using the calculating method and it was built as a trial.Results obtained from the calculations are as follows.1. A furnace with homogeneous temperature distribution was designed.2. A furnace which consists of SiC is suitable for the apparatus.3. When NaCl and LiF are used as pressure source, high pressures of 2.4 and 4.2 GPa are generated at 1000 ^ﾟC respectively.Furthermore, it was confirmed by the measurements using the pressure dependence of melting point of Pb that the apparatus produces a high pressure of 1GPa at 400^ﾟC.