Ken-ichi Sugioka

Normal spectral emissivity measurement of molten copper using an electromagnetic levitator superimposed with a static magnetic field

The normal spectral emissivity of molten copper was determined in the wavelength range of 780?920?nm and in the temperature range of 1288?1678?K, by directly measuring the radiance emitted by an electromagnetically levitated molten copper droplet under a static magnetic field of 1.5 T. The spectrometer for radiance measurement was calibrated using the relation between the theoretical blackbody radiance from Plancks law and the light intensity of a quasi-blackbody radiation source measured using a spectrometer at a given temperature. As a result, the normal spectral emissivity of molten copper was determined as 0.075 ? 0.011 at a wavelength of 807?nm, and it was found that its temperature dependence is negligible in the entire measurement temperature range tested. In addition, the results of the normal spectral emissivity and its wavelength dependence were discussed, in comparison with those obtained using the Drude free-electron model.

Thermal conductivity measurement of molten copper using an electromagnetic levitator superimposed with a static magnetic field

The thermal conductivity of molten copper was measured by the periodic laser-heating method, in which a static magnetic field was superimposed to suppress convection in an electromagnetically levitated droplet, to extend the measurement range of the method up to a relatively high thermal conductivity. Before measuring the thermal conductivity, the optimum conditions for static magnetic field, the laser frequency of periodic heating and sample diameter were investigated by numerical simulation both for the flow and thermal fields in an electromagnetically levitated droplet and for the periodic laser heating of the droplet in the presence of melt convection. As a result, the temperature dependence of the thermal conductivity of molten copper was proposed in the temperature range between 1383 and 1665 K. In addition, by comparing our results with those of previous studies, it was demonstrated that the present method of measuring thermal conductivity is also available for molten materials with a relatively high thermal conductivity, such as molten copper.

Noncontact Laser Modulation Calorimetry for High-Purity Liquid Iron

The heat capacity and thermal conductivity of liquid iron were measured the using recently developed method of noncontact laser modulation calorimetry. An iron sample was levitated using an electromagnetic levitator. Then the convection in the levitated droplet was suppressed to measure the thermal conductivity by the application of a dc magnetic field. High-purity iron (99.9972 mass %) prepared using an ion exchange method was used for measurements. The molar heat capacity of liquid iron at constant pressure was measured to be 45.4 ±3.2 Jmol-1K-1 (1848–1992 K) in low dc magnetic fields because a semi-adiabatic condition was achieved, assisted by the remaining convection in the liquid. The apparent thermal conductivity of liquid iron decreased concomitantly with the increasing dc magnetic field. It finally converged to 39.1 ±2.5 Wm-1K-1 (1794–2050 K) at 9 T or higher. The experimental uncertainties in the molar heat capacity and thermal conductivity are double the standard deviation.

Radiation Heat Transfer Analysis in a Semitransparent Single Crystal with Specular Surfaces: Application of REM2

In this work, to numerically analyze radiation heat transfer in the Czochralski (CZ) single crystal growth of oxide, the radiation element method by ray emission model (REM2) was considered for application. Here, REM2 was improved so that the radiation heat transfer through a transparent specular interface between media with arbitrary three-dimensional configurations and different refractive indices can be analyzed. The improved method was verified of its validity by comparing its results with the numerical results of previous works. Then, the effects of the optical thickness and refractive index of oxide crystals on the temperature distributions in the crystals were numerically investigated, considering a simplified model of the CZ furnace.

Effect of Static Magnetic Field on Recalescence and Surface Velocity Field in Electromagnetically Levitated Molten CuCo Droplet in Undercooled State

The recalescence events of phase-separated Co-rich phases in undercooled molten CuCo droplets electromagnetically levitated under various static magnetic fields were observed directly using a high-speed camera, and also the surface velocities on the levitated droplets were measured by tracing the trajectories of the phase-separated Co-rich phases as tracer particles. In addition, numerical simulations of melt convection in a spherical electromagnetically levitated CuCo droplet exposed to a static magnetic field were performed assuming laminar flow. We observed the emergence of many intermittent bright spots due to recalescence on the entire surface of the levitated droplet, and the frequency of the bright spots decreased markedly as the static magnetic field increased, with no bright spots observed at fields larger than 1.5xa0T. Also, the Reynolds numbers were evaluated from the measured and calculated velocities in the droplet for various static magnetic fields and compared with the critical Reynolds number of approximately 600, at which the laminar–turbulent transition of a magnetohydrodynamic (MHD) flow in an electromagnetically levitated droplet occurs, as proposed by Hyers et al. The above results clearly revealed that the marked change in the phase separation structures in undercooled molten CuCo droplets at approximately 1.5xa0T is due to a convective transition from turbulent flow to laminar flow in the levitated droplets, as speculated in our previous work.

Study on the Effect of Melt Convection on Phase Separation Structures in Undercooled CuCo Alloys Using an Electromagnetic Levitator Superimposed with a Static Magnetic Field

We studied the effect of melt convection on phase separation structures in undercooled Cu80Co20 alloys by using an electromagnetic levitator, where a static magnetic field was applied to control convection in the molten alloys. It was found that, when the static magnetic field was relatively small, dispersed structures with relatively fine Co-rich spheres distributed in the matrix of the Cu-rich phase were observed. However, a few large, coalesced Co-rich phases appeared in the Cu-rich matrix when the magnetic field exceeded axa0certain value, i.e., approximately 1.5xa0T in this study. The mean diameter of the droplet-shaped Co-rich phases distributed in the matrix of the Cu-rich phase increased gradually with the magnetic field and increased rapidly at approximately 1.5xa0T. Moreover, it was speculated from the result of periodic laser heating that the marked change in the phase separation structures at approximately 1.5xa0T might be due to a convective transition from turbulent flow to laminar flow in the molten sample, where the time variation of temperature in the lower part of the electromagnetically levitated molten sample was measured when the upper part of the sample was periodically heated.

Development of a Global Model of Heat Transfer in the Czochralski Furnace Taking into Account Specular Reflection at the Crystal Surface

In this study, a global model of heat transfer for the Czochralski crystal growth of oxides is developed by integrating the conventional model and the improved radiation element method by the ray emission model (REM2) in which radiative heat transfer in semitransparent crystals with a specular surface, that is, reflection and refraction at the crystal surface, is considered. The validity of the present model is verified by comparing it with the conventional model. Then, the effects of the optical thickness and the refractive index of the crystal on the temperature distribution in the furnace and on the melt/crystal interface shape are numerically investigated.