Thermophysical properties of liquid Co measured by electromagnetic levitation technique in a static magnetic field

Abstract

Density, normal spectral emissivity, heat capacity, and thermal conductivity of liquid Co were measured by an electromagnetic levitation technique in a static magnetic field. High-purity Co (99.9995 mass%) prepared by an anion exchange method was used for the measurements. Uncertainty analysis was conducted for all experimental data. The emissivity data at 807 nm deviated from the Drude model, owing to interband transitions of electrons. The heat capacity was successfully measured at a low magnetic field of 3 T with some residual convection within the droplet. However, for thermal conductivity measurements, a larger magnetic field was required to suppress convection, which made the levitation unstable owing to the magnetic force. Although the thermal conductivity data showed a relatively large scatter, the data agreed with the Wiedemann–Franz law at low temperatures. At higher temperatures, the experimental data deviated from the Wiedemann–Franz law. For heat capacity measurements, translational motion of the Co droplet should be suppressed, while thermal transportation by convection flow in the droplet should be preserved. Conversely, for thermal conductivity measurements, the convection flow should also be suppressed. Therefore, in this study, the heat capacity and thermal conductivity of Co were measured under static magnetic fields of 3 and 9 T, respectively. Moreover, our experimental results were compared with free electron models, namely, the Drude model and Wiedemann–Franz law.