Combustion synthesis of B4C/Al2O3/C composite powders and their effects on properties of low carbon MgO-C refractories

To improve the dispersity and oxidation resistance of nano carbon black (CB) in low carbon MgO-C refractories, B4C/Al2O3/C composite powders were prepared by a combustion synthesis method using B2O3, CB and Al powders as the raw materials. The phase compositions and microstructures of the synthesized products were characterized by X-ray diffraction (XRD), Raman spectroscopy, and a scanning electron microscopy/energy dispersive spectrometry (SEM/EDS). The results show that an 80 wt% excess of CB is the maximum amount of CB that can be added under the condition of a self-propagating combustion wave, and the phase compositions of the products are B4C, alpha-Al2O3 and CB. B4C particles with uniform sizes and cubic polyhedral structures are embedded in the Al2O3 matrix. The combustion-synthesized B4C/Al2O3/C powders and mechanically mixed B4C/Al2O3/C powders were added to the low carbon MgO-C refractories, and their corresponding properties were compared. The apparent porosity (AP) of the refractories with the synthesized powders (labelled as M3) is lower than those of the refractories with mechanically mixed powders (labelled as M2) and without composite powders (labelled as M1). The oxidation ratio and slag erosion depth of M3 were lower than those of M2 and M1. The thickness of the decarburized layer of M3 was 10.2% and 22.4% less than that of M2 and M1, respectively. The penetration depth of M3 was 12.0% and 27.9% less than that of M2 and M1, respectively. The thermal shock resistance of M3 was better than that of M2 and M1. The residual strength ratio of M3 was 15.8% and 17.2% more than that of M2 and M1, respectively. These results suggest that the combustion-synthesized B4C/Al2O3/C composite powders can be used as new and promising additives for low carbon MgO-C refractories.