Size reduction of boron particles by high-power ultrasound for optimization of bulk MgB₂

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 MgB2 via sintering at 775 °C. Effect of boron powder ultra-sonication on superconducting properties of the bulk MgB2 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 MgB2 with only small traces of MgO. Around 36% improvement in Jc at 20 K and Tc close to 39 K were observed in MgB2 bulk prepared with boron ultra-sonicated for 15 min. Microstructure studies showed numerous nanometre sized MgB2 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 MgB2 can be achieved without reduction in T c via employing a cheap boron, reduced in size by high-energy ultra-sonication.

An Improved Smart Meta-Superconductor MgB2

“…It can be seen from Figure 6 (a) that JC of pure MgB2 and doped samples decreases with the increase of temperature, which is consistent with the results in literature [34,58,59]. JC of pure MgB2 is 8.5x10 4 A/cm 2 at 20K, which is comparable to literature [60,61]. At this time the JC of 0.9 wt% luminescent inhomogeneous phase doped sample is 8.83 x10 4 A/cm 2 .…”

Critical Current Density and Meissner Effect of Smart Meta-Superconductor MgB2 and Bi(Pb)SrCaCuO

“…The J C of a MgB 2 , b MgB 2 , and c MgB 2 are 8.9 × 10 4 , 7.8 × 10 4 , and 7.2 × 10 4 A/cm 2 at 20 K. As observed, the J C of pure MgB 2 and doped samples decreases with the increase in temperature, which is consistent with the results of [ 28 , 47 , 48 ]. The J C of pure MgB 2 is comparable to references [ 49 , 50 ]. The J C decreases slowly when the temperature is lower, and the decreasing rate increases with the rise in temperature.…”

Pinning behavior in bulk MgB2 prepared using boron powder refined via high-energy ultra-sonication

“…Fifteen minutes of ultra-sonication is best for obtaining high-performance MgB 2 bulk. The self-field J c value was around 300 kA/cm 2 , by 35% more than in a normal bulk-220 kA/cm 2 [21]. Longer ultra-sonication resulted in boron agglomeration that led to large MgB 2 grains reducing J c .…”

“…Longer ultra-sonication resulted in boron agglomeration that led to large MgB 2 grains reducing J c . A more detailed explanation can be found elsewhere [21].…”

“…Regular conventional boron (Furu-uchi Chemicals, 300 mesh) was ultra-sonicated in ethanol for 15 min and used to fabricate sintered bulk MgB 2 . Details of boron ultra-sonication can be found elsewhere [21]. Mg powder and HEU boron powder were mixed in a glove box in argon atmosphere.…”