Effect of Crystallization on the Abrupt Viscosity Increase during the Slag Cooling Process

Abstract

The abrupt viscosity increase during the slag cooling process may jeopardize the stability of industrial operation. However, the underlying mechanism has not been completely understood yet. In the present work, the viscosity of basic oxygen furnace (BOF) slags with different additions, i.e. Al₂O₃ and SiO₂, was measured via a rotational rheometer. The slag crystallization behavior was observed in-situ via confocal laser scanning microscope (CLSM). Microstructural features, i.e. crystal fraction, shape and size in the slag, were identified through characterizing the water-quenched slag sample. The present results show that the abrupt viscosity increase occurs only when the crystal fraction exceeds a threshold (defined as critical volume fraction of solid, Φ_c), at which crystals start to interfere with each other and form solid aggregates/clusters. The critical solid fraction varies between 0.33 and 0.51 for the investigated samples and is found to decrease with increasing crystal aspect ratio, which varies between 1.43 and 2.17 in our samples.