Abstract

Al₂O₃-Cr₂O₃ refractories have been widely used in the harsh areas of thermal equipments such as petrochemical and steelmaking due to their excellent slag corrosion resistance. Molten slag, which is the primary cause of Al₂O₃-Cr₂O₃ refractories degradation, has great effect on the corrosion of refractories at high temperature with thermal fluctuation. To discuss the comprehensive effects of chromium oxide content, additives and microstructure on the slag resistance of Al₂O₃-Cr₂O₃, eight kinds of commercial Al₂O₃-Cr₂O₃ refractories were selected with Cr₂O₃ mass fraction of 10%, 12%, 30%, 50%, 60%, 75%, 90% and 95%, respectively. Some of the speciments had small amount of zirconia as an additive, and some had the microstructure with microporous. All the specimens were installed in the same rotary slag-resistant furnace, using intermittent heating process to realize the test temperature fluctuated between 200 ℃ and 1600 ℃. By adding CaO-SiO₂-Al₂O₃-Fe₂O₃-MgO slag as the corrosion slag, the corrosion resistance of Al₂O₃-Cr₂O₃ refractories was researched under the simulated thermal fluctuation condition. The erosion degree and thermal shock fracture of corroded refractories were evaluated through observation and measurement. The microstructure and chemical composition of the specimens were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The pore size distribution of virgin refractories were measured by mercury porosimetry. The interfacial reactions of refractory materials with slag were investigated by thermodynamic modeling using FactSage^TM software. The results showed that the degradation of Al₂O₃-Cr₂O₃ refractories was affected by comprehensive factors, including chemical erosion, physical dissolution, thermal spalling caused by penetration. With the increase of Cr₂O₃ content, the slag corrosion rate of Al₂O₃-Cr₂O₃ material decreased, which indicated that the Cr₂O₃ content played a decisive role in the slag resistance of Al₂O₃-Cr₂O₃ material. Dense spinel layer was formed by the reaction of Cr₂O₃ with Fe₂O₃ and MgO, which had a high melting point and prevented the further infiltration of slag into the materials. Thermodynamic evaluation also showed that the content of Cr₂O₃ in refractories had a significant influence on the formation of dense spinel layer. Morover, the additives had benefit on improving the slag penetration resistance because it effectively suppressed the microcrack propagations under the condition of temperature fluctuation. Additionally, microporous structure improved the slag penetration resistance and thermal shock resistance of the materials. Therefore, it will be also an effective way to promote slag resistance of Al₂O₃-Cr₂O₃ refractories with lower content of Cr₂O₃ by the designation and preparation of microporous structural materials.