Effects of Al–Si alloy powders on mechanical properties and slag resistance of unfired magnesia refractories: In air and carbon-embedded atmospheres

Ultra-low carbon magnesia refractories used in working lining of ladle are crucial components to meet the smelting requirements for producing purity steel. However, the decreased carbon content weakened thermal shock resistance and slag resistance of refractories, resulting in the hampered practical applications. To resolve the mentioned problems, Al–Si alloy powders were introduced into unfired magnesia refractories with glucose and citric acid as binders to form combination of oxides and non-oxides, and performances of refractories were researched systematically in air and carbon-embedded atmospheres according to different service conditions, respectively. The results show that reaction mechanisms in 2 atm led to different effects on microstructure of refractories with added Al–Si alloy powders. The formation of AlN whiskers and plate-shaped MgAl2O4 and Mg2SiO4 with intersecting structure resulted in higher mechanical strength, fracture surface energy and thermal shock resistance of refractories in air atmosphere than that in carbon-embedded atmosphere. The in-situ formed ceramic phases (AlN, MgAl2O4 and Mg2SiO4) in pores led to enhanced slag resistance for refractories. Meanwhile, in carbon-embedded atmosphere, the reduced reactions of Fe2O3 in molten slag increased slag viscosity, presenting higher slag penetration resistance for refractories than that in air atmosphere. Considering the lowered compactness of refractories with excessive alloy powders by large volume expansion from the formation of ceramic phases, refractories with 3 wt% alloy powders showed high mechanical properties, thermal shock resistance and slag resistance. This study provides a reference for the development of ultra-low carbon magnesia refractories used in working lining of ladle, and the research results also indicated that the evaluation of different atmosphere conditions is important for the design of high performance refractories.