The internal Mg diffusion (IMD) process produces a high-density MgB 2 layer with high critical current properties, which makes it an attractive and promising method for fabricating MgB 2 wires. We have obtained high critical current properties in our previous research. However, IMD-processed MgB 2 wires can have unreacted B particles remain in the reacted layer due to the long Mg diffusion distance in the B layer during heat treatment. A reduction in the amount of unreacted B particles is expected to enhance the critical current properties. In this study, we attempted to disperse Mg powder in the B layer as an additive in order to decrease the Mg diffusion distance. We found that a 6 mol% Mg powder addition to a B layer drastically decreased the amount of unreacted B particles and enhanced the critical current density to twice the value for IMD-processed MgB 2 wire with no Mg powder added. An analysis is presented that relates the microstructure to the critical current density.

MgB 2 powders were treated for different amount of time in diluted water (water-ethanol mixture) with two different water-to-ethanol ratios of 12 : 18 and 6 : 24 to investigate the effect of diluted water-treatment on the superconducting properties of MgB 2 . The diluted water-treatment did not affect the phase composition of the powder. The magnetic moment measurement of both untreated and treated MgB 2 powders showed the degradation of irreversible magnetic moment of the powders as the treatment time increases. The change of irreversible magnetic moment was explained by the dissolution of Mg and B into the diluted water during the treatment. The amount of dissolved substances after the treatment measured by chemical analyses (ICP MS) showed that the concentration of B dissolved in the diluted water is much larger than that of Mg, as the treatment time increases. The contact of MgB 2 with the water or moisture has to be considered in the design of the superconducting devices based on the MgB 2 to prevent the degradation of the superconducting properties of the devices.Index Terms-Diluted water treatment, irreversible magnetic moment, magnetic moment, MgB 2 superconductor.