A Statistical Approach for Estimation of Fusion Behavior of Alumino-Thermic Ferrochrome Slags
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THE fusion behavior of slags is presented in terms of four characteristic temperatures, viz., initial deformation temperature (IDT), signifying surface stickiness of the slag; softening temperature (ST), signifying start of plastic deformation of the slag; hemispherical temperature (HT), which represents the liquidus temperature of the slag signifying its sluggish flow; and flow temperature (FT), signifying its liquid mobility.[1] The relevance of these characteristic temperatures in smelting and refining processes along with the experimental procedure to measure them using a hot-stage microscope in accordance with German standard 51730 have been presented in a previous article.[2] The said article also discusses the effects of significant variables, Al2O3/CaO ratio, and MgO and CaF2 contents, on the fusion behavior of synthetic slags resembling the slag generated during alumino-thermic production of ferrochrome in the industry. It is obvious that for efficient continuation of a pyrometallurgical process, the fusion behavior of the resulting slag is of greater importance compared with its melting point.[3] The melting point of a slag at the operating temperature provides a measure of the superheat contained in the slag that influences the slag fluidity and the slag–metal reactions/separations. On the other hand, ST indicates the aerodynamics in the reduction unit that influences the heat-and-mass transfer aspect, which is a measure of the efficiency of an extraction process. The difference between FT and HT would indicate whether the slag, after it melts, would need higher thermal energy for its free flow and subsequent S.K. SAHOO, Assistant Professor, J.N. TIWARI, Ph.D. Student, and U.K. MOHANTY, Professor, are with the Department of Metallurgical & Materials Engineering, NIT Rourkela, Rourkela 769008, Odisha, India. Contact e-mail: [email protected] Manuscript submitted September 27, 2012. Article published online August 14, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
effective separation from the metal. For example, a ‘‘short-slag’’ with a small difference between the FT and HT, would acquire liquid mobility without the necessity of the availability of high thermal energy in the system after it melts. This would not only assist effective slag– metal separation, would also enhance slag–metal exchanges, the flowing slag creating fresh interfaces with the metal during the course of its easy flow.[2] This aspect of the flow behavior of the nonmetallic oxides that combine to melt to form the slag is of immense importance in the alumino-thermic production of ferroalloys, where the generation of slag, production of metal and their separation, take place almost instantaneously when the charge is ignited. Another example to establish the relevance of flow behavior of the slag over its melting point lies in the production of iron in the blast furnace route. The significance of a ‘‘short-slag’’ is examined in great detail.[2,4,5] Thus, the importance of fusion behavior of slag and its determination pertaining to extractive metall
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