Analysis of the protective behavior and mechanism of MgO-C-Mg film for crude magnesium smelting

A major problem facing the magnesium melting process is to address the oxidative combustion of magnesium. At present, there are still some problems in the method used to protect magnesium smelting. For example, the reaction of covering flux with magnesium melt is likely to produce a large number of toxic and harmful gasses (Cl₂ and HCl), the cost of such reaction is high, and there is a lack of clarity on the protection mechanism of CO₂ acting as the protective gas of magnesium melt. Therefore, a new process is proposed in this paper to isolate the air on the surface of magnesium melt using MgO-C-Mg film. Based on the thermodynamic theory of MgO-C-Mg film formation during crude magnesium smelting, an investigation is conducted into the effect of different experimental conditions on the protective effect of magnesium. Not only is the protective mechanism of MgO-C-Mg film revealed, it is also verified that the MgO-C-Mg film can produce a more pronounced protective effect at suitable temperature. According to thermodynamic analysis, magnesium melt reacts with CO₂ to form magnesium oxide and C. CO₂ consumes C when the experimental temperature exceeds 700 °C. This is contrary to the purpose of the experiment as it should be maintained at about 700 °C. The experimental results show that an obvious protective effect can be produced on the magnesium melt by the MgO-C-Mg film generated under the following conditions of 90% CO₂–10% Ar, smelting temperature of 700 °C, holding time of 60 min, and stirring time of 20 min.