Electrical Conductivity and Electronic/Ionic Properties of TiO x -CaO-SiO 2 Slags at Various Oxygen Potentials and Tempe
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NTRODUCTION
THE electrical conductivity of molten slags plays an important role in understanding the structure of molten slags and operation of the electric smelting furnace. For instance, molten oxide electrolysis (MOE)[1–7] is a carbon–neutral electrochemical technique to decompose metal oxide directly into liquid metal and oxygen gas upon use of an inert anode. Compared to other technologies, its potential environmental advantage of no greenhouse gas emissions is the most important characteristic. For such electrometallurgy process, the electrical conductivity of molten slags is particularly important. The electrical conductivities of TiO2-BaO,[8] FexO-CaO-SiO2,[9–12] FexO-CaO-MgO-SiO2,[13] FexOCaO-SiO2-Al2O3,[14] NixO-CaO-SiO2,[15] and NixOCaO-MgO-SiO2[15] slags had been measured and reported in published literatures. Due to the high melting point of slags and the transfer of charge between the slag and the adsorbed gas species, the data regarding the electronic properties of TiOx-bearing slags are very limited. The objective of this work was to study the electrical and electronic conductivity of TiOx-CaO-SiO2 slags at various temperatures and oxygen potentials which was controlled by the ratio of CO/CO2. These fundamental researches will be used in the modeling and design of electric smelting furnaces.
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EXPERIMENTS
The compositions of slag samples are shown in Table I. In each group, the mass ratio of CaO/SiO2 remains constant, but the content of TiO2 gradually increases. Slag samples were prepared using reagent grade TiO2, SiO2, and CaCO3 powders (analytically pure, Sinopharm Chemical Reagent Co., Ltd, China), all of which were calcined at 1273 K (1000 °C) for 10 hours in a muffle furnace to decompose any carbonate and hydroxide before use. Then, about 12 g mixtures were precisely weighed according to the compositions shown in Table I, and mixed in an agate mortar thoroughly. To accomplish the electrical conductivity measurements, a four-terminal method was employed in this study. The measurement on the electrical conductivity of TiOx-CaO-SiO2 molten slags is extremely difficult because of its high melting point, reactivity, and conductivity. In order to get an accurate electrical conductivity value, 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, the contribution of the interfacial resistance is usually too large to be disregarded. The application of the four-electrode technique can avoid those difficulties. The electrical conductivity of the melts can be obtained by the following equation: r ¼ C=Rx ;
JUN-HAO LIU, Doctoral Student, GUO-HUA ZHANG, Associate Professor, YUE-DONG WU, Master Student, and KUO-CHIH CHOU, Professor, are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing 100083, China. Contact e-mail: [email protected] Manuscript submitted June 22, 2015. Article published online November 2, 2015. 798—VOLUME 47B, FEBRUARY 2016
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