Oxidation kinetics of MgO-C in air with varying ash content

MgO-C refractories are extensively used in metallurgical vessels in the steel industry. The graphite plays a vital role owing to its non-wettability with slag. Though quality is very important for graphite, little published data is available on the effect of varying ash content on oxidation. Since MgO-C bricks manufactured from graphite with different ash contents are regularly used for lining converters and steel ladles at SAIL plants, a study has been conducted to select an optimum graphite with low cost. Graphites with 2.8, 4.4, 12 and 20% ash content were used to make MgO-C samples in the laboratory, and oxidation properties were evaluated using an electrically heated tube furnace. Kinetic analysis shows that a chemical reaction mechanism operates in the earlier part of oxidation, followed by a diffusion mechanism in the latter part. MgO-C manufactured from graphite with 4.4% ash content was observed to have the best oxidation resistance, with an activation energy of 43.4 U mol(-1) during the earlier stage followed by 34.2 kJ mol(-1) in the latter.