Thermal Diffusivity Measurements of Oxide and Metallic Melts at High Temperature by the Laser Flash Method

The importance of heat transfer properties such as thermal conductivity or thermal diffusivity of various materials at high temperature is strongly emphasized, in parallel with recent progress in surface technology for several electronic devices. Such importance has been well recognized in many pyrometallurgical processes related to plant design and accurate control of continuous casting in steelmaking. For example, heat transfer properties of molten salts are essential to design applications to heat transfer fluids for fusion reactors, breeder reactors, and thermal energy storage systems. Then, thermal property data of molten salts with sufficient reliability are strongly required to select an optimum composition of salt mixture for the desired condition [1]. We also need thermal property data of molten iron at elevated temperature and continuous casting powder melts consisting of various oxide components; SiO2, CaO, MgO, Al2O3, etc. for further improving the present continuous casting process for steel [2].

In producing single crystals supplied for devices of semiconductor compounds such as GaAs and GaP, using Czochralski method, the components of high vapor pressure of P and As are likely to diffuse from the master melt, causing the original compositions to vary. To reduce such trouble, boron oxide melts have widely been employed as liquid capsules to encase the semiconductor master melt [3]. It is necessary to minimize the temperature gradient in the melt by accurate temperature control for producing high quality singlecrystals with a low dislocation density. Although the thermal diffusivity of a liquid capsule material is one of the important properties, no report is available on the value of thermal diffusivity of molten boron oxide within the best knowledge of the present authors.