Viscosity Measurements on Some Fayalite Slags

Abstract

In the present study, viscosity measurements on Fe–O–Si slags have been carried out using rotating cylinder method. The slag samples for viscosity measurement were prepared by pre-melting appropriate stoichiometric amounts of Fe, Fe₂O₃ and SiO₂ in an iron crucible under argon atmosphere, which ensured that Fe ions in the slag were predominantly in the valence state of +2. The viscosities of the pre-melted slag samples were measured in iron as well as nickel crucibles under argon atmosphere at different temperatures. The measured viscosity values obtained in the two kinds of crucibles were found to be in good agreement, indicating thereby that nickel crucibles can be successfully used for viscosity measurements. In order to investigate the effect of oxidation of Fe²⁺ to Fe³⁺, the binary Fe_nO–SiO₂ slag was kept in a nickel crucible under oxidising conditions using a CO/CO₂ atmosphere and viscosity measurements were carried out dynamically as a function of time at 1 623 and 1 673 K. With time, Fe³⁺ concentration in the slag increased and hence the viscosity changed progressively. The rate controlling step for the oxidation reaction was considered to be the mass transfer of CO₂ in the gas stream to the slag–gas interface. A simple kinetic analysis was used to predict the concentration of Fe³⁺ in the slag with time. The measured viscosity with time indicated that the viscosity remains almost the same during initial period of oxidation. The viscosityraises sharply when the Fe³⁺ concentration in the slag, calculated as Fe₂O₃ reached around 7 mass%.