Kinetic parameters estimation of MgO-C refractory by shrinking core model

Kinetics of oxidation of MgO-C refractories was investigated by shrinking core modeling of the gas-solid reactions taking place during heating the porous materials to the high temperatures. Samples containing 4.5 similar to 17 wt pct graphite were isothermally oxidized at 1000 similar to 1350 degrees C. Weight loss data was compared with predictions of the model. A mixed 2-stage mechanism comprised of pore diffusion plus boundary layer gas transfer was shown to generally control the oxidation rate. Pore diffusion was however more effective, especially at graphite contents lower than 10 wt pct under forced convection blowing of the air. Model calculations showed that effective gas diffusion coefficients were in the range of 0.08 to 0.55 cm(2)/s. These values can be utilized to determine the corresponding tortuosity factors of 6.85 to 2.22. Activation energies related to the pore diffusion mechanism appeared to be around (46.4 +/- 2) kJ/mol. The estimated intermolecular diffusion coefficients were shown to be independent of the graphite content, when the percentage of the graphite exceeded a marginal value of 10.