This study demonstrates the effect of addition of Fe particles of different sizes on the critical properties of the superconductor MgB2. Bulk MgB2 is synthesized by ball milling Mg and B powders with Fe particles at 900oC. When Fe particles with size less than 10 μm are added in MgB2, they easily react with B and form the FeB phase, resulting in a reduction in the amount of the MgB2 phase and deterioration of the crystallinity. Accordingly, both the critical temperature and the critical current density are significantly reduced. On the other hand, when larger Fe particles are added, the Fe2B phase forms instead of FeB due to the lower reactivity of Fe toward B. Accordingly, negligible loss of B occurs, and the critical properties are found to be similar to those of the intact MgB2.

MgB2 bulk superconductors are synthesized by the solid state reaction of (MgB4+xMg) precursors withexcessive Mg compositions (x=1.0, 1.4, 2.0 and 2.4). The MgB4 precursors are synthesized using (Mg+B) powders. Thesecondary phases (MgB4 and MgO) present in the synthesized MgB4 are removed by HNO3 leaching. It is found thatthe formation reaction of MgB2 is accelerated when Mg excessive compositions are used. The magnetization curves ofMg1+xB2 samples show that the transition from the normal state to the superconducting state of the Mg excessive sam-ples with x=0.5 and x=0.7 are sharper than that of MgB2. The highest Jc-B curve at 5 K and 20 K is achieved forx=0.5. Further addition of Mg decreases the Jc owing to the formation of more pores in the MgB2 matrix and smallervolume fraction of MgB2.

The crystallization effects of boron (B) powder on the phase, full width at half maximum (FWHM) values, and critical properties were investigated for in-situ reacted MgB2 bulk superconductors. The semi-crystalline B powder was heat-treated at different temperatures of 1000, 1300 and 1500˚C for 5 hours in an Ar atmosphere. Then, using as-received and heat-treated B powders, the MgB2 samples were prepared at 600˚C for 40 hours in an Ar atmosphere. As the heat-treatment temperature of the B powder increased, both the particle size of the B powder and crystalline phase increased. In the case of MgB2 samples using B powders heat-treated at above 1300˚C, unreacted magnesium (Mg) and B remained due to the improved crystallinity of the B powder. As the heat-treatment temperature of B powder increased, the critical current density of MgB2 decreased continuously due to the reduction of grain boundary density and superconducting volume caused by unreacted Mg and B.

The effects of nano addition to superconducting properties of processed superconductors was examined. 0.1 wt.% and 1 wt.% nano powders were mixed with boron and magnesium powders by ball milling. The powder mixtures were made into pellets by uniaxial pressing. The pellets were heat-treated at in argon atmosphere for formation. It was found by powder X-ray diffraction that the raw powders were completely converted into after the heat treatment. The superconducting transition temperature () and critical current density (), estimated from susceptibility-temperature and curves, were decreased by nano addition. The and decrease by nano addition are attributed to the incorporation of iron and carbon with lattices (Fe substitution for Mg and C substitution for B) due to the high reactivity of the nano powder.

This paper deals with the phase analysis of bulk using spark plasma sintering process after ball milling. Mg and amorphous B powders were used as raw materials, and milled by planetary-mill for 9 hours at argon atmosphere. In order to confirm formation of phase, DTA and XRD were used. The milled powders were fabricated to bulk at the various temperatures by Spark Plasma Sintering. The fabricated bulk was evaluated with XRD, EDS, FE-SEM and PPMS. In the DTA result, reaction on formation of phase started at . This means that ball milling process improves reactivity on formation of phase. The MgO and FeB phases were characterized from XRD result. MgO and FeB were undesirable phases which affect formation of phase, and it's distribution could be confirmed from EDS mapping result. Spark Plasma Sintered sample for 5 min at was relatively densified and it's density and transition temperature showing super conducting property were and 21K.