Effect of Al Antioxidant on the Rate of Oxidation of Carbon in MgO–C Refractory

Kinetics of air oxidation of MgO–C–Al refractory at 600°–1300°C were investigated using the software based on the modified shrinking core model (KDA). Commercial bricks containing 88.5% MgO, 10% residual carbon, and 1.5% aluminum anti‐oxidant were oxidized isothermally with air. Combination of experimental data with model calculations indicated gas diffusion through solid material and pores as a major controlling step. Previously observed chemisorption process was eliminated from the rate‐controlling mechanism with addition of aluminum antioxidant. Comprehensive rate equations were devised for MgO–C–Al and MgO–C oxidation reactions. Overall activation energies of Q id (internal diffusion)=139.15 kJ/mol at T ≤800°C and Q pd (pore diffusion)=25.48 kJ/mol at T >800°C were obtained for MgO–C–Al oxidation reactions. Corresponding values were determined to be Q id =134.85 kJ/mol and Q ca (chemical adsorption)=66.69 kJ/mol at T ≤800°C and Q pd =18.95 kJ/mol and Q ca =66.69 kJ/mol at T >800°C for MgO–C oxidation reactions. Addition of aluminum anti‐oxidant indicated a reducing effect on oxidation of MgO–C bricks at 800°C≤ T ≤1250°C. Reverse behavior was observed at T ≤700°C.