Formation of MgO whiskers on the surface of bulk MgB2 superconductors during in situ sintering
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Magnesium oxide (MgO) whiskers (with diameters of about 60–80 nm) formed on the surface of bulk polycrystalline MgB2 superconductor at a relative low temperature (720 °C) during in situ sintering process. The reaction between Mg and B powders begins at a temperature below melting point of Mg and maintains till about 750 °C. The residual Mg powders evaporate and react 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 preformed MgB2 and MgO crystals act as substrates and the melted Mg powders on the surface of them serve as catalysts during the growth process of MgO whiskers. The growth process of MgO whiskers is dominated by a self-catalytic vapor–liquid–solid (VLS) mechanism.
KeywordsWhisker Growth MgB2 Superconductor Bulk MgB2 MgB2 Phase Bulk MgB2 Superconductor
The authors would like to thank the National Nature Science Foundation of China (granted No. 50401003), the Natural Science Foundation of Tianjin City (granted No. 07JCZDJC01200), the Keygrant Project of Chinese Ministry of Education (granted No. 707012) and Program for New Century Excellent Talents in University for financial support.
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