부산대학교 도서관

In this study, the effect of the size of B powder on the critical current density (Jc) of MgB2 prepared by an in situ reaction process was investigated. Various combinations of B powders were made using a micron B, ball-milled B and nano B powders. Micron B powder was reduced by ball milling and the milled B powder was mixed with the micron B or nano B powder. The mixing ratios of the milled B and micron or nano B were 100:0, 50:50 and 0:100. Non-milled micron B powder was also mixed with nano powder in the same ratios. Pellets of (2B+Mg) prepared with various B mixing ratios were heat-treated to form MgB2. Tc of MgB2 decreased slightly when the milled B was used, whereas the Jc of MgB2 increased with increasing amount of the milled B or the nano powder. The used of the milled B and nano B power promoted the formation MgB2 during heat treatment. In addition to the enhanced formation of MgB2, the use of the powders reduced the grain size of MgB2. The use of the milled and nano B powder increased the Jc of MgB2. The highest Jc was achieved when 100% nano B powder was used. The Jc enhancement is attributed to the high volume fraction of the superconducting phase (MgB2) and the large grain boundaries, which induces the flux pinning at the magnetic fields.