| Research Abstract |
Thermophysical properties of molten refractory metals such as hafnium, rhodium, ruthenium, tantalum, and rhenium have been measured using a containerless method. Their high melting temperatures and the risk of chemical reaction with a container make it difficult to measure such thermophysical properties as density, heat capacity, heat of fusion, surface tension, and viscosity. Containerless processing circumvents the above problems and offers suitable conditions for thermophysical properties determination of refractory metals. Moreover, these properties can be obtained in the undercooled region, which is not possible with conventional techniques.
Among the existing levitation methods, electrostatic levitation, which uses Coulomb force to counter gravity, is the most appropriate for thermophysical properties measurements of electrically conducting materials. However, because a potential minimum does not exist for the sample position (Earnshaw's theorem) and since a high-speed position control system is necessary, this technique is very challenging. For this reason, the development of the electrostatic levitation system has been slower than that of other instruments.
In this research, a rotation control system has been implemented to an existing electrostatic levitation furnace and thermophysical properties have been measured with high accuracy. Moreover, density data of molten ceramics (BiFeO_3 and BaTiO_3) at high temperatures have been measured.
The data reported in this research cover wide temperature ranges including the undercooled region. This includes the viscosity of ruthenium, which was measured for the first time in the world. Moreover, these data show good agreement with the quantum calculation based on the hard-sphere model. These results can also be utilized to estimate the thermophysical properties of other refractory metal.
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