Modeling Viscosities of CaO-MgO-FeO-MnO-SiO 2 Molten Slags
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temperature metallurgical systems, the viscosity of the molten slag is an important physical property and plays a prominent role in both fundamental research and industrial operations. During the basic oxygen steelmaking process, a suitable viscosity is important for both foaming and the successful separation of metal from slag. Furthermore, the attack of the refractory lining is also inversely dependent on slag viscosity. Thus, there are pressing demands for slag viscosity data. Because viscosity measurements are both time consuming and difficult at high temperatures, it is not possible to provide viscosity data for slag compositions in the many metallurgical processes; hence, the need for a reliable model to estimate slag viscosities. Silicate melts exhibit a complicated variation between viscosity and composition. Generally, the viscosity decreases with increasing basic oxide content and with increasing temperature. It has been pointed out that the activation energy is a nonlinear function of composition for binary silicate melts[1] and shows an abrupt decrease near pure silica. For silicate melts, the viscosity is a reflection of the structure and a decrease in viscosity corresponds to a breakdown of the network structure, where the addition of basic oxide results in a change from GUO-HUA ZHANG, PhD Graduate Student, and KUO-CHIH CHOU and QING-GUO XUE, Professors, are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, 100083 Beijing, P.R. China. Contact e-mail: [email protected] KENNETH C. MILLS, Professor, is with the Department of Materials, Imperial College, London SW7 2AZ, UK. Manuscript submitted June 3, 2011. Article published online October 19, 2011. 64—VOLUME 43B, FEBRUARY 2012
a random network to a more depolymerized structure containing chains and rings. Fincham and Richardson[2] proposed that the structure of silicate melts contained three types of oxygen, namely (1) nonbridging oxygen bonded only to one silicon atoms, (2) bridging oxygen bonded to two silicon atoms, and (3) free oxygen bonded to no silicon atom. The addition of basic oxides to pure silica results in a gradual decrease in the number of bridging oxygen and to a decrease in viscosity. Consequently, a viscosity model should account for the influence of structure on the viscosity, and it should reflect the nonlinear behavior of activation energy with composition. Several models have been developed to estimate the viscosity of multicomponent slags. Riboud et al.[3] expressed the activation energy as the linear addition of network-former components denoted SiO2 (= SiO2 + PO2.5 + TiO2 + ZrO2), but this does not reflect the nonlinear variation of activation energy with composition. Urbain[4] expressed the activation energy dependency on composition as a polynomial expression of composition containing three terms, but many parameters are adopted with fewer structure factors. Models by Iida et al.[5] and those based on the optical basicity concept[6–8] have narrow application ranges. The structural
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