Phase Composition and Formation Mechanism of Slag Crust in Blast Furnace

Abstract

Copper stave damage is common problem in blast furnace operations, and the formation of slag crust is beneficial to reduce the damage of copper stave. Therefore, an in-depth understanding of phase composition and formation mechanism of slag crust is helpful to clarify the protection mechanism of copper stave, so as to control the growth of the slag crust and to increase the service life of copper staves. In this study, the slag crust from a copper stave blast furnace was sampled, and the phase composition and structure of the slag crust were characterized in detail through XRD analysis and SEM-EDS. The results indicated that the slag crust presented apparent layer structure as the solid slag layer and viscous layer, which primarily consisted of gehlenite (Ca₂Al₂SiO₇), calcium aluminate (CaAl₄O₇), magnesia-alumina spinel (MgAl₂O₄), pleonaste (Mg_0.7Fe_0.23Al_1.97O₄), kaliophilite (KAlSiO₄) and metallic iron. In addition, the ternary phase diagram analysis of CaO–SiO₂–Al₂O₃ showed that the primary crystal phase of the slag is in the gehlenite region, and that the primary crystal region migrates to the calcium aluminate region with the increasing of Al₂O₃ content, which are beneficial to the slag crust formation. Finally, the formation mechanism of slag crust was proposed.