In-situ formation of MgO whiskers on the surface of magnesium alloy powders

MgO whiskers with diameters of 100–300 nm and lengths of 1–3 μm were formed during in-situ sintering of a mixture with 15:4 mole ratio of magnesium alloy powder AZ91D to H3BO3 in Ar atmosphere at 800 °C. The magnesium alloy powder AZ91D evaporates and reacts with trace oxygen to form MgO vapor as the temperature exceeds the melting temperature of Mg and a low supersaturation is required for the growth of MgO whiskers. The growth of MgO whiskers begins at about 700 °C. During the growth process of MgO whiskers, the preformed MgO films act as substrates and both the melted B2O3 and magnesium alloy on the surface of magnesium alloy powder AZ91D serve as catalysts. The growth process of MgO whiskers is dominated by a vapor–liquid–solid (VLS) mechanism.