The economic growth and future sustainable development of global community require use of new materials improving quality of life. Superconductivity in general allows for 100% current transmission without losses. This is a super resource for sustainability in many aspects. The high-temperature superconducting materials (HTSC), crucial for the future day-life applications, are convenient also from the view-point of the sustainable development goals (SDG’s). Superconducting super-magnets can be used as compact high-field magnets, hearts of mobile diagnostic devices such as magnetic resonance imaging, nuclear magnetic resonance, or magnetic drug delivery. Furthermore, these magnets will be crucial for the development of compact electric motors, hybrid-type superconducting magnetic bearings for rotating machinery, compact magnetic field generators, shielding plates etc. Among the existing superconducting systems, MgB2 superconductors are very interesting for their easy fabrication, tunability, low cost, raw materials availability, light-weight etc. These characteristics indicate the commercial significance of MgB2 superconductors, which possess some special characteristics to full fill the sustainable developmental goals. In any case, all applications require high values of trapped field, which is governed by the critical current density (Jc). In the very beginning, we optimized the sintering conditions to 775-815oC/3 hours to obtain good Jc, which became the standard heat treatment for our MgB2 fabrication. Then, we learned the role of boron precursor in the solid-liquid reaction of B and Mg and started to employ nano-sized precursors. Initially, we used a commercial nano-amorphous boron that resulted in astonishing Jc of 408 kA/cm2 at 20 K, self-field. SEM micrographs identified nano-sized grains in the final microstructure, evidently responsible for self-field pinning improvement. We also tried different dopants to improve the high field pinning, high field Jc, and irreversibility field Hirr such as MgB4, carbon, silver etc. We systematically doped MgB2 with MgB4 as, 1, 2, 3, 4, 5, and 10 wt% and observed that 1 wt% of MgB4 showed a high self-field critical current density of 385 and 315 kAcm-2 at 15 and 20 K, respectively. Flux pinning diagrams confirmed domination of grain boundary pinning and supported our assumption that a tiny amount (1 wt%) of MgB4 is optimal for high-field point-like pinning in refined grains. The most popular carbon substitution had a serious issue in doping inhomogeneity. To overcome this problem, we prepared carbon-encapsulated boron (CEB) made by pyrolysis of diborane, hydrogen and gaseous hydrocarbon. It was found that a low wt% carbon coating such as 1.5wt% resulted in a uniform carbon distribution in the matrix and enhanced a high-field Jc and Ha. 1.5 wt% carbon-encapsulated-boron-based MgB2 bulk showed tremendous Jc of 660 and 250 kA/cm2 observed at 0 and 2 T; 10 K. To further improve this result, our group studied the effect of co-dopants such Ag and CEB. Microstructural analysis identified Ag-Mg phases formed in the matrix and optimum performance was observed for 4 wt% Ag. To compensate the loss of Mg reacting with Ag, as well as to increase the Ag-Mg phase fraction, we studied the optimization of Mg precursor concentration. 7.5 wt% excess of Mg resulted in the best result, with highest Ag-Mg phase (2 wt%), high irreversibility field (Hirr) of 4.76 Tesla and large Jc such as 440 kA/cm2 at 20 K, self-field. SEM analysis confirmed existence of nanoscopic secondary Ag-Mg phases (20-40 nm) which acted as pinning centers. In order to make the processing cheap while maintaining high performance, we explored a novel technique of high-energy ultra-sonication. We successfully produced nano-sized boron via ultra-sonication, and arrived at high Jc in the final bulk. Beside size refinement, the obtained fine boron powder was free of B2O3 and other contaminations, due to which the MgB2 bulks were of high quality and high Jc performance (36 % improvement). In addition, we have fabricated 20 to 40 mm in diameter, MgB2 bulk via spark plasma sintering (SPS), with 99.8% density and studied its trapped field behavior. The bulk showed superior mechanical as well as superconducting properties compared to regular bulk material and gave the prospects for commercial exploration of the material. The present talk elucidates the progress in fabrication of high-performance bulk MgB2 superconductors around 20 K, with special respect to the sustainable development goals (SDG’s).
Keywords: Sustainable development goals, Super-magnets, MgB2, Trapped Field