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

Abstract

The effects of three antioxidants (AlB 2 –Al–Al 2 O 3 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 AlB 2 –Al–Al 2 O 3 composite powders is 28.33 mm, 25.34 mm and 12.00 mm, respectively, which implies that the AlB 2 –Al–Al 2 O 3 composite powder was the most effective antioxidant. The reason is that the Mg 3 B 2 O 6 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 MgAl 2 O 4 and Mg 2 SiO 4 with high melting points, and that of the oxidation zone with Al powder was MgAl 2 O 4 . 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.