Kinetic study of factors affecting in situ reduction of silica in carbon-silica mixtures for refractories

We report a systematic investigation on in situ reduction kinetics of silica in carbon based materials for refractories as a function of system parameters. The objective of this fundamental study was to establish factors influencing gasification of refractories, which in turn could lead to carbon depletion and refractory degradation. Experiments were carried out on silica-graphite mixtures for refractory applications as a function of temperature, compacting pressure, carrier gas flow rate, and additional oxides. The off gases (CO, CO2) generated from silica reduction and carbon oxidation processes were analysed using an infrared detector to estimate overall reaction rate constants. Additional oxides such as Al2O3 and ZrO2, had a significant effect on the reduction kinetics. The rate of SiO2 reduction was found to be mixed controlled by chemical reaction and mass transfer. Overall activation energy of bulk reactions taking place in the silica-graphite mixtures during initial stages of contact was estimated to be 153 kJ/mol.