Oxidation and Diffusion in Selected Pitch-Bonded Magnesia Refractories

A conventional and an improved (Mg-containing) BOF refractory, of commercial pitch-bonded magnesia type, were evaluated to determine their Mg diffusion and carbon oxidation characteristics. MgO dense-zone formation was characterized experimentally for various firing times at 1650°C, from which Mg diffusion coefficients in the range 1.4x10^-9 to 8.13x10^-10cm²/s were determined. The data indicate that the Mg diffusion in the system is of the extrinsic type, controlled by the impurities in the MgO, such as Al³⁺, Fe³⁺, and Cr³⁺. The effects of Mg vaporization and MgO condensation, preceding dense-zone formation, were observed to initiate at 1200°C. The dense-zone thickness and the amount of unoxidized carbon were greatest for the Mg-containing refractory.