Kinetics and Thermodynamics of Carbon Isothermal and Non-isothermal Oxidation in MgO-C Refractory with Different Air Flow

Today, MgO-C bricks are widely used in steel industry due to their excellent resistance to slag corrosion and thermal shock increased particularly by the carbon content. The presence of carbon makes these bricks very susceptible to oxidation, leading to a reduction of the strength and to the penetration of metal and/or slag. The aim of this paper is to investigate the processes of carbon oxidation of MgO-C commercial bricks containing 7 and 14 pct C by both isothermal and non-isothermal methods. The results show that carbon oxidation of the samples is limited by diffusion through the pores only. If the carbon content does not have a greater influence on the oxidation process at lower temperatures, then at higher temperatures the weight loss increases with increasing carbon content. Both types of commercial bricks oxidize directly in a lower temperature range and indirectly at higher temperatures. That means that the indirect oxidation does not exist alone, but is initiated by direct oxidation of carbon. Activation energy and diffusion coefficient for different bricks have been determined and compared with literature data. The results of the investigation of the non-isothermal carbon oxidation show that for one and the same final thermal state of the refractory the carbon oxidation can be essentially minimised by choosing specific heating-up rates.