Antioxidant properties of low-carbon magnesia-carbon refractories containing AlB2–Al–Al2O3 composites

Abstract The effects of three antioxidants (AlB2–Al–Al2O3 composite powders and Al and Al/Si composite powders) on the oxidation resistance of low-carbon magnesia-carbon refractories were investigated. First, thermodynamic calculations were performed to analyze the product compositions of the oxidized zone of low-carbon magnesia-carbon refractories with three antioxidants. Then, the oxidation zones were analyzed by X-ray diffraction, field emission scanning electron microscopy and energy spectrum analysis. The results show that the thickness of the decarburization layer of low-carbon magnesia-carbon bricks with Al powder, Al/Si composite powders and AlB2–Al–Al2O3 composite powders is 28.33 mm, 25.34 mm and 12.00 mm, respectively, which implies that the AlB2–Al–Al2O3 composite powder was the most effective antioxidant. The reason is that the Mg3B2O6 phase is formed in the products of the oxidation zone, and its melting point is 1360 °C. Therefore, it melts at 1400 °C and shows excellent oxidation resistance by filling the pores and blocking the oxygen channel. The products of the oxidation zone with Al and Al/Si composite powders were MgAl2O4 and Mg2SiO4 with high melting points, and that of the oxidation zone with Al powder was MgAl2O4. These products are still solid particles at 1400 C. The oxygen channel has a weaker blocking effect than the melt, so the oxidation resistance of Al/Si composite powders and Al powders is weaker.