Formation and Evaluation of Protective Layer Over Magnesium Melt Under SF^sub 6^/Air Atmospheres

Molten magnesium oxidizes rapidly when exposed to air causing melt loss and handling difficulties. The use of certain additive gases such as SF^sub 6^, SO2, and CO2 to form a protective MgO layer over a magnesium melt has been proposed. The oxidation behavior of molten magnesium in air containing various concentrations of SF^sub 6^ was investigated. Measurements of the kinetics of the oxide layer growth at various SF^sub 6^ concentrations in air and temperatures were made. Experiments were performed using a thermogravimetric analysis unit in the temperature range of 943 K to 1043 K (670 °C to 770 °C). Results showed that a thin, coherent, and protective MgF^sub 2^ layer was formed under SF^sub 6^/Air mixtures, with a thickness ranging from 300 nm to 3 [mu]m depending on SF^sub 6^ concentration, temperature, and exposure time. Rate parameters were calculated and a model for the process was developed. The morphology and composition of the surface films were studied using scanning electron microscope and energy-dispersive spectroscope.[PUBLICATION ABSTRACT]