Influences of Na 2 O and K 2 O Additions on Electrical Conductivity of CaO-MgO-Al 2 O 3 -SiO 2 Melts
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NTRODUCTION
CURRENTLY, blast furnace ironmaking is still the main process to produce pig iron. Besides pig iron, a large amount of blast furnace slags are discharged at the same time. Normally, after being cooled by water/air, most of the slags are used as building materials, such as concrete. However, by this method, the abundance of sensible heats cannot get effective recycling. In order to recycle this energy, some researchers tried to use blast furnace slags to produce slag wool or microcrystalline glass with high added values.[1] However, to meet the composition requirement, composition adjustment was necessary. Some additives, such as silica and alkali metal oxides, were added into the liquid blast furnace slags.[1] During this process, the slag should be heated to melt all the additives. Electric heating with molybdenum electrodes is widely used. In order to perform more effective electric heating, as a prominent parameter, electrical conductivity of slags should be known in advance. Electrical conductivity data not only play a prominent role in the modeling and operation of electric smelting furnaces, but also can provide information about the structures of molten slag. However, relative to viscosity, much less attention has been paid to electrical conductivity. While many new experimental or modeling studies are performed on the subject of viscosity of molten slags every year, there are few for electrical conductivity. Limited data not only cannot provide enough fundamental supports to the practical production, but also may mislead the modeling work about electrical conductivity. For instance, when modeling electrical conductivity of molten slags, Thibodeau and GUO-HUA ZHANG, WEI-WEI ZHENG, and KUO-CHIH CHOU are with State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, China. Contact e-mail: [email protected] Manuscript submitted August 29, 2016. Article published online January 27, 2017. 1134—VOLUME 48B, APRIL 2017
Jung[2] stated that when CaO is gradually replaced by Al2O3 at constant SiO2 content in CaO-Al2O3-SiO2 melts, there is no minimum value of electrical conductivity, whereas the conductivity increases monotonically with increasing CaO/Al2O3 molar ratio. However, minimum values of electrical conductivity were found by the present authors both in CaO-Al2O3-SiO2[3] and CaO-FeOx-Al2O3-SiO2 melts.[4] Therefore, much more accurate data of electrical conductivity are urgently needed. In this study, influences of Na2O and K2O on electrical conductivity of blast furnace slags will be investigated.
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EXPERIMENTS
There are many methods to measure electrical conductivity of molten slags, such as centrally located pole electrode, two-electrode, and four-electrode techniques. In order to get accurate electrical conductivity values, it is necessary to exclude the resistances of lead wires and electrodes from the total measured resistance. If the current electrode is used in common for the potential one, contribution of interfacial resistance is usually
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