Size reduction of boron particles by high-power ultrasound for optimization of bulk MgB<sub>2</sub>
Sai Srikanth Arvapalli, M. Muralidhar, M. Jirsa, M. Murakami
Abstract
Abstract Critical current density, J c , in superconductors is strongly connected with size of defects in the material. Frequently, the smaller defects, the higher J c . In this work, we tried to reduce the size of cheap commercial boron precursor powder using high energy ultra-sonication in ethanol media. The resulting powder was then utilized in synthesizing bulk MgB 2 via sintering at 775 °C. Effect of boron powder ultra-sonication on superconducting properties of the bulk MgB 2 was studied and discussed. SEM of ultra-sonicated boron showed fine particles with sharp edges (high-energy surfaces), irregular shapes and clustering of fine particles occurred for longer ultra-sonication durations. XRD proved a high quality of MgB 2 with only small traces of MgO. Around 36% improvement in J c at 20 K and T c close to 39 K were observed in MgB 2 bulk prepared with boron ultra-sonicated for 15 min. Microstructure studies showed numerous nanometre sized MgB 2 grains in the bulk. Other bulks (made of boron ultra-sonicated longer, for 30, 45, and 60 min) have larger grains. It resulted in slightly lower J c , anyway, still by 22% higher than in reference bulk. The present results demonstrate that the high performance bulk MgB 2 can be achieved without reduction in T c via employing a cheap boron, reduced in size by high-energy ultra-sonication.