Oxidation and corrosion resistance of resin-bonded magnesia-based refractories reinforced by CaB6 addition for secondary refining

Excellent properties are required for refractories used for secondary refining because of the harsh service conditions. The current study investigated the effect of calcium boride (CaB₆) on the properties of magnesium oxide (MgO)‒based refractories. The sample with 0.4 wt.% CaB₆ exhibited excellent properties. It possessed the highest bulk density indicating that a suitable content of CaB₆ can increase the compactness of the refractories. The in-situ formation of aluminum oxycarbonitride (Al₃CON) at high temperatures in the MgO-based refractories was from the reaction of Al, Al₄C₃, AlN, and Al₂O₃ due to the addition of Al powders, which endowed them with high strength. The refractory containing 0.4 wt.% CaB₆ also exhibited the highest hot modulus of rupture (HMOR) of 26.6 MPa, which was around 2.5 times the strength of commercial MgO‒CaO bricks and 1.5 times that of the samples without CaB₆ addition. In addition, it exhibited the best oxidation resistance revealed by the minimum thickness of the decarbonization zone, because the addition of CaB₆ promoted the formation of a dense magnesium aluminate spinel (MgAl₂O₄, MA) layer between the oxidized and non-decarburized zone in the refractories, thereby promoting the resistance of the samples to oxidation. It also exhibited excellent thermal shock resistance, and the residual strength ratio reached 76.6%. The corrosion depth of the sample containing 0.4 wt.% CaB₆ was 9.8% that of the MgO‒CaO bricks. This work indicates a potential alternative for producing high‒performance resin‒bonded MgO-based refractories with CaB₆ in secondary refining furnaces.