An Insight into Slag Structure from Sulphide Capacities
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The molar sulphide capacities CS = (mol pct S) (PO2 =PS2 )1/2 on four binary systems, MgO-SiO2, CaO-SiO2, MnO-SiO2 and FeO-SiO2 are elucidated so as to compare the magnitudes of the basicities of four metallic oxides and to estimate the temperature dependencies of the basicities of metallic oxides. The enthalpy changes of the reaction 2O = O + O2, viz. the been calculated from the slopes of the silicate polymerization reaction (denoted as DHð8Þ ) have 0 log CS vs 1/T curves for four binary silicates. The DHð8Þ value is considered in the present work to be an index of the basicity of silicate melts. The basicities obtained on the basis of the DHð8Þ values are in the order MgO < CaO < MnO < FeO, which are determined by two effects; (i) ionicity of chemical bonds between metallic and oxygen ions and (ii) clustering of metallic oxides in silicates. It is also found that the basicity of the FeO-SiO2 system is larger at higher temperatures. DOI: 10.1007/s11663-012-9713-8 Ó The Minerals, Metals & Materials Society and ASM International 2012
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INTRODUCTION
SLAGS are silicate melts that have been extensively used in the extraction and refining of metals. Structure and properties of slags have received a great deal of attention in the past decades. In steelmaking, for example, with higher demands on steel qualities, especially with respect to impurities such as sulphur and phosphorus as well as non-metallic inclusions in steels, understanding of the physics and chemistry of slags has become extremely important. Thermophysical and thermochemical properties of slags depend directly on the structure of slags. For example, viscosity, one of the most important thermophysical properties of steelmaking slags, decreases with an increase in basic oxide content and with elevating temperature. This phenomenon corresponds to a breakdown of the silica network structure. Thermochemical properties such as activity of a component in the slag melt and slag capacities are also relevant to the structure. In this paper, the present authors focus on the relationship between sulphide capacity and structure. The concept of sulphide capacity was first proposed by Fincham and Richardson[1,2] to quantify the desulphurizing capacity of slags, using the equilibrium
LI-JUN WANG, Lecturer, and KUO-CHIH CHOU, Professor, are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: [email protected] MIYUKI HAYASHI, Professor, is with the Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, Tokyo 152-8552, Japan. SESHADRI SEETHARAMAN, Professor Emeritus, is with the Department of Material Science and Engineering, Royal Institute of Technology, 10044 Stockholm, Sweden, and also Visiting Professor with the TU-Bergakademie, 09599 Freiberg, Germany. Manuscript submitted October 20, 2011. Article published online August 21, 2012. 1338—VOLUME 43B, DECEMBER 2012
reaction between molten slag and a gas phase with fixed sulfur and oxygen potent
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