Noncontact Laser Calorimetry of High Temperature Melts in a Static Magnetic Field

Numerical simulations are widely used for high value-added materials processing such as semiconductor crystal growth, casting of super high-temperature alloys for a jet-engine turbine blade, and for welding in automobile manufacturing [1, 2]. Process modeling involving a liquid-to-solid transition requires precise thermophysical properties of materials in the solid and liquid state at temperatures near their melting points. However, high-temperature materials such as liquid silicon are chemically reactive and are easily contaminated by their containers and contact materials. Therefore, it remains extremely difficult to measure the thermophysical properties of high-temperature liquids. Especially, the thermal conductivity of a high-temperature liquid is a difficult property to measure because of the existence of the buoyancy and Marangoni convections in the liquid. Not only from process modeling but also from a scientific perspective, thermal conductivity data of high-temperature metallic or semiconductor liquids are important to investigate whether the Wiedemann—Franz law [3] is applicable to them.

Fecht et al. [4–7] developed modulation calorimetry for electromagnetically levitated metallic melts. The radio frequency (rf) coil's power was modulated to provide sinusoidal heating to the sample melt. The heat capacities and hemispherical total emissivities of the melts were determined at higher temperatures.However, convections existing in the droplets make it difficult to measure the true thermal conductivity of the melts. Yasuda et al. [8] reported that motion of the center of gravity, surface oscillation, and convection of an electromagnetically levitated liquid metal were suppressed in a static magnetic field because of the Lorentz force resulting from interaction between the fluid flows and the static magnetic field.