Effect of the Content of B<sub>4</sub>C on the Oxidation Resistance of MgO–C at High Temperatures

This study investigates the oxidation behavior of MgO-C refractories containing a combined antioxidant system of Al (2wt%) and B4C (0~4wt%). Oxidation tests were conducted under air conditions at 1200°C, 1300°C, and 1400°C for 60 and 180 minutes. As the temperature was increased from 1200°C to 1400°C, the non-oxidized area increased by 1.4, 3.3, and 14.1 times, respectively. The weight loss ratio decreased with the B4C content and the temperature. Above 3wt% of added B4C, the weight loss ratio remained the same. At 1200°C, the weight loss ratio decreased from 14.2% to 9.9% as the addition of B4C was increased to 3wt%. At 1300°C, the weight loss ratio decreased from 14.8% to 6.7%. At 1400°C, the weight loss ratio decreased from 16.0% to 1.88%. These findings demonstrate that the effect is significant as the temperature increases. After the experiments, an XRD analysis confirmed the formation of Al2O3, B2O3, Mg2B2O5, Mg3B2O6, and MgAl2O4. Thermodynamics analysis indicates that Mg3B2O6 melts at 1400°C, enabling effective pore sealing. At 1300°C, however, the combined reaction between Al2O3 and magnesium borates generates low-melting phase that provides a remarkably strong antioxidation effect even at this lower temperature, making 1300°C the critical point where the Al-B4C system becomes highly effective. However, at 1200°C, only B2O3 is present as a liquid and subsequently forms solid magnesium borates with MgO, offering only a limited improvement in oxidation resistance.