The effect of addition of Al2O3 on the viscosity of CaO-FeO-SiO2-CaF2 slags

• The viscosities of CaO-FeO-SiO2-CaF2 slags with various amounts of alumina addition were measured using a rotating-cylinder method in the temperature range 1714-1757 K. The first part of the experiments was conducted by measuring the viscosities under equilibrium conditions after small additions of Al2O3. Similar experiments were also conducted with one commercial mould flux in order to compare the results. In both cases, the viscosities were found to increase with the addition of Al2O3 at all the experimental temperatures, the increase in viscosity being somewhat linear with Al2O3 addition. In the case of the commercial mould flux, even an addition of 2.6 mass% Al2O3 led to a significant increase in the viscosity. Some isothermal experiments were also conducted with the above set of slags in the dynamic mode, wherein, the changes in the slag viscosities were monitored as a function of time as an Al2O3 disc dissolved continuously into the slag. The experiments were so designed that the dissolution of alumina occurred mainly along the vertical direction. The rate of dissolution of alumina is discussed in the light of the rate of change of viscosity as well as the composition profile in the slag after the experiments. An examination of the Al2O3 disc revealed the counter diffusion of the slag components into the solid alumina and that the dissolution took place by the solid product dissolving in the melt.

Nyckelord

viscosity

dissolution of Al2O3

fluoride volatilisation

mould flux

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