Thermal Conductivity Measurements of Ladle Slag Using Transient Hot Wire Method
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he steelmaking process, good temperature control is essential. Accident increasing or decreasing of the steel temperature can result in poor steel quality, faster erosion of the refractory material, and increased energy consumption. While ladle slag plays very important roles in steel refining, the slag layer also protects the liquid steel from reoxidation and acts as an insulator during teeming. Great effort is currently made to control the ladle thermal state through the whole steelmaking chain.[1–3] Some of these works focus on the development of dynamic model for the teeming process.[4–6] Because of the lack of thermal conductivity data, the function of ladle slag is very often excluded in the model. To improve model predictions of the steel temperature and the cooling behavior, accurate physical property data are needed. In the teeming process, convection in the slag is rather limited. Hence, the reliability of a dynamic thermal model necessitates reliable thermal conductivity data for ladle slag. To the knowledge of the present authors, no thermal conductivity data have been reported for ladle slags. Ladle slag is usually chosen in the high CaOcontaining region in the quaternary system, Al2O3-CaOMgO-SiO2. The present work focuses on the measurements of some Al2O3-CaO-MgO-SiO2 slags in the temperature range 1773 K to 1923 K (1500 °C to 1650 °C). Different experimental methods can be used to measure the thermal conductivity. These methods can BJO¨RN GLASER, Researcher, and DU SICHEN, Professor, are with the Department of Materials Science and Engineering, Royal Institute of Technology, 10044, Stockholm, Sweden. Contact e-mail: [email protected] Manuscript submitted July 24, 2012. Article published online December 1, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
be divided into three groups, namely steady state (e.g., linear and radial heat flow methods), non-steady state (e.g., radial wave and modulated beam methods), and transient methods (e.g., laser pulse and line source methods).[7] Steady state and non-steady state methods are usually not used for liquids due to the difficulties of excluding convection during the measurements. The transient hot wire (THW) method and the laser pulse (LP) method are often used for slag systems. However, as pointed by Professor Ken Mills in the 9th International Conference on Molten Slags, Fluxes and Salts in Beijing (China), the measured conductivity values using the LP method are approximately ten times higher than the values measured by the THW method. This huge difference could be attributed to the radiation associated with the LP technique. Because of its high accuracy and suitability for high temperature slag measurements as reported by many researchers,[8–10] the THW method was adopted in the present work. A sketch of the experimental setup is given in Figure 1. Figure 1(a) shows the whole setup and Figure 1(b), the measuring cell. To be able to calculate the conductivity values from the measurements, the resistivity of the hot wire needs to be known. The wire resistivity in th
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