Heat and Mass Transport in Undercooled Melts of Germanium and Silicon

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Containerless processing by a levitation method has been used for materials science and technological applications such as rapid solidification, purification and thermophysical properties measurement of melts. An electromagnetic levitation method (EML) can be used to levitate a relatively large size of a metallic melt in a given atmosphere. However, independent control for the temperature and spatial position of the specimen is difficult and the strong Lorentz force yields electromagnetic stirring in the melt and destabilizes the shape of the melt Recently, a novel method for levitating a metallic melt by EML under a static magnetic field was developed in order to damp the convection and vibration in the melt by the Lorentz force. In the present study, stabilizing of position and shape of a levitated melt for silicon and germanium was succeeded by the new EML method, and convection in each melt was strongly damped by the strong magnetic field.Measurements of the density and thermal conductivity of a pure silicon melt over a wide temperature range were performed by the EML, while those properties for germanium showed large data spreads due to higher evaporation rate of the melt. The emissivity of the melt showed almost constant to temperature. The determined density for silicon melt showed a linear relation with temperature, and no anomalous increase near the melting point was observed In addition the thermal expansion coefficient agreed well with the value calculated based on the metallic liquid model. Since the thermal conductivity of the melt agreed roughly with values estimated by the Wiedemann-Franz law, free electrons in a silicon melt obviously affect the thermal conductivity. In the result it was concluded that silicon melt even in an undercooled state showed metallic characteristic.