Corrosion process of MgB2 superconductor in a moisture atmosphere

Abstract

The degradation behavior of polycrystalline magnesium diboride (MgB 2) superconductor in a highly humid air has been investigated. The MgB2 samples with grain size around 10 μm were exposed to the action of dry carbon dioxide, to water-vapour-saturated air and to water vapour in a closed system. It has been shown that prolonged exposure to highly humid air completely destroys superconductivity. Infrared transmission spectroscopy analyses indicate that water simply acts as a catalyst for the formation of magnesium carbonate (MgCO3) and diboride oxide (B2O 3) species, and the rate of degradation strongly depends on the water partial pressure in air. Microstructure analyses reveal that the degradation process was observed to initiate more likely at the surface and also at the grain boundaries of small MgB2 grains. Resistivity versus temperature measurements indicates that on exposure to humid air, the residual resistance ratio decreases and the material becomes insulator with prolonged exposure time. © 2004 WILEY-VCH Verlag GmhH & Co. KGaA, Weinheim.