Abstract: Magnesia-calcia (MgO-CaO) refractories are widely used in tundish linings and continuous casting furnaces owing to their high melting point, thermal stability, resistance to slag corrosion, and effectiveness in purifying molten steel. However, their susceptibility to hydration in humid environments severely limits their practical applications. To enhance the hydration resistance of MgO-CaO materials, this study presents a novel one-step catalytic chemical vapor deposition method using soybean oil as a carbon source and cobalt (Co) as a catalyst to synthesize carbon nanotubes (CNTs) and calcium carbonate (CaCO3) co-coated superhydrophobic MgO-CaO grains. The effects of pyrolysis temperature, catalyst loading, and holding time on the microstructure and hydration resistance of the modified MgO-CaO grains were systematically investigated. The results indicate that the optimal synthesis conditions for the CNTs-CaCO3 co-coated superhydrophobic MgO-CaO grains are as follows: a reaction temperature of 700?°C, a holding time of 1?h, and 2?wt% Co catalyst loading. Under these conditions, the modified aggregates exhibited a water contact angle of 155°, and a minimal hydration-induced weight gain of only 0.73?wt% after exposure to 70?°C and 85% relative humidity for 24 h, representing a 9.47-fold improvement in hydration resistance compared to unmodified grains. The synergistic protective effects of the hydrophobic CNT layer and the CaCO3 shell effectively hindered moisture ingress and subsequent hydration reactions. This study provides an facile and efficient approach for enhancing the hydration resistance of MgO-CaO refractories.

Key words: MgO-CaO grains, Hydration resistance, CNT/CaCO₃ co-coated, Co catalyst