From viscosity and surface tension to marangoni flow in melts
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9/11/03
11:33 AM
Page 517
From Viscosity and Surface Tension to Marangoni Flow in Melts* SHOUYI SUN, LING ZHANG, and SHARIF JAHANSHAHI This article covers some of our recent work on slag viscosity, the surface tension of liquid Cu-O alloys, and the relative role of Marangoni and bulk flow on refractory wear in iron-silicate slags. A viscosity model developed for slags containing SiO2, Al2O3, Fe2O3, CaO, MgO, MnO, FeO, PbO, NiO, Cu2O, ZnO, CoO, and TiO2 is capable of representing the effects of temperature, silica, and network-modifier cations within a wide range of temperatures and compositions. It forms a useful part of a computational package for multiphase-equilibrium (MPE) calculations and for predicting slag viscosities. The models are well applicable to a range of industrial slags (blast furnace, new iron making, base-metal and Platinum Group Metals (PGM) smelting, and coal-ash slags). The package has also some capability of predicting the viscosity of slags containing suspended solids. The surface tension of liquid copper–oxygen alloys has also been analyzed. The adsorption behavior of oxygen in liquid copper is well represented by the combined Langmuir–Gibbs isotherm. According to the rate data for silica-rod dissolution in liquid iron–silicate slags at 1573 K, the preferential attack at the slag line diminishes as the linear velocity of flow at the surface of the rotating silica rod reaches 9 to 16 cm/s. A tentative analysis gives the critical condition, that relates the critical Reynolds (Re) and Marangoni (Ma) number by the equation Re*2 0.13 Ma*.
I. VISCOSITY OF SILICATE SLAGS
ACCURATE data for, and predictive methods to determine, the viscosity of silicate melts are always desirable to meet operational demands. During the past decade, a slag-viscosity model has been developed for calculation of the viscosity of slags containing the oxide components of SiO2, Al2O3, Fe2O3, CaO, MgO, MnO, FeO, PbO, NiO, Cu2O, ZnO, CoO, and TiO2 at CSIRO Minerals and the former G.K. Williams Cooperative Research Centre for Extractive Metallurgy.[1–4] In the first step of modeling, the general behavior of viscosity in response to variations in the temperature and chemical composition of liquid slags was analyzed in detail based on a comprehensive collection of published viscosity data from binary to multicomponent silicate systems. It was revealed that, at a given temperature and when slags remain as homogeneous liquids, (1) SiO2 has the strongest effect on viscosity, and viscosity increases with increasing SiO2 content; (2) the effect of Al2O3 depends on the presence of the charge compensators, such as alkali, alkali-earth, and other mono- or divalent oxides; (3) the addition of metal-oxide components, such as TiO2, Fe2O3, CaO, MgO, MnO, FeO, PbO, NiO, Cu2O, ZnO, and CoO, tends to reduce viscosity. The classification of oxide components as glass formers (SiO2), modifiers
*This article is dedicated to Professor Ken Mills. The authors have been inspired by Ken and have benefited greatly from his encouragement in thei
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