Characterization of the protective surface films formed on molten magnesium in air/HFC-134a atmospheres

The surface films formed on molten magnesium in an air/HFC-134a gas mixture at 700 °C were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Auger electron spectroscopy (AES). The results showed that there was a protective film on molten magnesium surface, which can prevent molten magnesium from oxidation and ignition. The surface film contained primarily four elements: magnesium, fluorine, oxygen and carbon, and was composed of MgF2, MgO and C. The film properties depended on the HFC-134a concentration in the gaseous mixture and exposure time. The thickness of the film formed after exposure to air containing 0.5% HFC-134a for 10 min was about 1–2 μm.