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6/5/04

9:18

Page 461

Thermal Diffusivity Measurements of Some Synthetic CaO-Al2O3-SiO2 Slags ROBERT ERIKSSON and SESHADRI SEETHARAMAN In an attempt to systematize the knowledge of the heat conduction of liquid silicates, the effective thermal diffusivities of some synthetic slags containing CaO, Al2O3, and SiO2 have been measured, using the three-layer laser-flash method on a differential scheme in the temperature range of 1625 to 1825 K. The effective thermal diffusivities measured, which are a combination of the phononic and photonic heat-transfer mechanisms, were found to increase with increasing temperature for all the presently investigated slags. The slag compositions were chosen in such a way that the changes in the effective thermal diffusivities would reflect the changes in the structure of the slags. It was observed that, at a CaO/Al2O3 molar ratio of 4.42, an increase of the SiO2 content had very little effect on the effective thermal diffusivity values. On the other hand, addition of SiO2 to a slag with the CaO/Al2O3 molar ratio of 2.59 resulted in a significant increase in the effective thermal diffusivity. The addition of Al2O3 to slags with a constant CaO/SiO2 molar ratio resulted in a marked increase in the effective thermal diffusivity. Both these trends indicate that there might be an influence of the network formation in silicate melts on the effective thermal diffusivity.

I.

INTRODUCTION

IT has long since been recognized that access to highquality measurement data of various physical properties of metallurgical slags is essential for the design, modeling, and control of material processes, thus creating an increased demand for more-reliable measurements, over wider composition and temperature ranges. However, the investigation of thermal-property data of liquid silicate melts at high temperatures is still far from complete, as can be seen in the review on thermal conductivity and diffusivity data by Mills and Suza.[1] In the present work, high-temperature thermal diffusivity measurements were carried out on synthetic slags in the system CaO-Al2O3-SiO2, using the three-layered laserflash method. The choice of the CaO-Al2O3-SiO2 system for the present investigation was primarily due to the unique combination of a strongly basic, a strongly acidic, and an amphoteric oxide in the system, which would enable some structural insights. Second, this slag system is often encountered in ferrous as well as nonferrous metal production processes; hence, the results could be of great relevance to the modeling of heat-transfer phenomena in these processes. The laser-flash method has, over the years, been recognized as a versatile technique for thermal diffusivity measurements for a wide range of materials, such as metals, plastics, and silicates in both the solid and liquid state. A three-layered sample cell, consisting of the liquid slag sample sandwiched between an upper and a lower platinum crucible, has been employed in this present study. Unlike thermal diffusivity measurements on solid samples, wher