Abstract
The oxide films formed on the molten Mg-Ca alloy were investigated by using an optical microscope, scanning electron microscope (SEM), X-ray diffraction and X-ray photoelectron spectroscopy (XPS) in order to elucidate the effect of Ca addition on the suppression of ignition and burning of the molten metal. While the pure Mg almost always ignited and burnt before melting down, the Ca addition increased the ignition temperature by about 250K, at which a very thin and uniform oxide film was formed on the molten Mg-5mass%Ca alloy, X-ray diffraction and XPS revealed that the oxide film on the Mg-5mass%Ca alloy consisted of two layers ; most upper layer of CaO and mixed layer of MgO-CaO under the CaO layer. The former was very thin and its thickness was independent of the exposure time at 973K in air, but the latter gradually grew with the exposure time. It appeared that the CaO film first formed depressed the volatilization of Mg and the permeation of oxygen gas, which made the molten alloy incombustible and manipulatable in air.
