New Insights into Magnesia-Carbon Reaction in Refractory: Role of Superoxide Free Radicals in Magnesia

Magnesia-carbon refractories have been widely used in smelting processes. However, they undergo more severe oxidation and degradation under low oxygen pressure. In this study, the oxidation behavior of MgO–C samples prepared from different magnesia in a protective inert atmosphere at 1600 °C and the effect of superoxide free radicals on the magnesia-carbon reaction were studied. Magnesia with MgO content of 98, 97 and 90 wt pct were used for the experiment. The results indicate that oxygen vacancies in magnesia can promote the formation of superoxide free radicals. Superoxide free radicals significantly increase the oxidation activity of magnesia and accelerate the magnesia-carbon reaction. Compared with sintered magnesia of the same grade (MgO content is 97 wt pct), the oxidation activity of fused magnesia increases owing to more superoxide free radicals. Magnesia containing spinel has low oxidation activity due to the consumption of superoxide free radicals in the spinel reaction. It is expected to improve the oxidation resistance and prolong the service life of magnesia-carbon refractories.