Fabricating MgB2 superconductors using spark plasma sintering and pulse magnetization

Since the discovery of the superconductivity phenomena in 1911, scientists have been on the lookout for feasible materials that reach their superconducting state at higher temperatures, enabling them to be operated with cheaper coolants or advanced cryocoolers. Out of the many types of viable materials, MgB₂ superconductors have an operating temperature of 39 K, which lies between conventional metallic superconductors and high-temperature cuprate superconductors. It occupies a unique position where its intermediate operating temperature is offset by its unique material and electric properties.

MgB₂ superconductors are non-toxic, lightweight materials that can be fabricated by simple sintering processes and have current densities similar to that of conventional metallic superconductors. These properties make them suitable for applications that require cheap and lightweight superconductors such as space applications and electric machines. However, the sintering of MgB₂ superconductors is performed at ambient pressures, and it results in a highly porous material that has less than optimal superconducting properties. More specifically, the porous nature of the superconductor limits the magnetic field it can trap and hold.

Now in a study published in Materials Science and Engineering: B, researchers from Shibaura Institute of Technology, Japan, enhanced the trapped magnetic field in bulk MgB₂ superconductors by fabricating highly dense, non-porous MgB₂ bulks. Using spark plasma sintering (SPS), the researchers heated commercially available MgB₂ powder with pulsed electrical current at high pressures of 50 MPa. The results were fascinating: “It is the first study in which large, 40 mm diameter MgB₂ bulks with 99.8% packing ratio were fabricated via SPS,” explains Prof. Muralidhar Miryala, who led the study.

The prepared sample was of similar quality to those prepared by conventional sintering methods and had very little impurities. The high packing density was found to improve the current density and the strength of the material. On comparing their samples with dense bulks prepared via an alternative high pressure hot isostatic pressing (HIP) technique, the researchers found that the SPS bulks displayed superior strengths and had bending strengths eight times that of the HIP processed bulks.

A similar improvement in trapped field (TP) performance was noticed in the highly dense samples where their increased current density enhanced their ability to trap and hold magnetic fields. On examining the TP performance by magnetizing the samples and measuring the TP at temperatures of 14 and 20 K, the researchers found that the MgB₂ bulk showed high TP for external magnetic fields up to 1.6 tesla. However, when large external magnetic fields were applied, the poor thermal conductivity of the material caused the material to overheat and the TP value to drop.

Despite its thermal limitations, the highly dense MgB₂ superconductors are a significant improvement over the conventionally sintered counterparts. Commenting on the importance and novelty of their findings, Prof. Miryala explains: “The large SPS MgB₂ bulks produced this way can have wide applications as superconductors and our study also paves the way for further enhancing and realizing the commercialization of these superconductors.”

Indeed, space exploration and electric transport, which necessitate cheaper, lighter, and more affordable superconductors, may soon be made more efficient using these impressive MgB₂ superconductors.

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Reference

DOI: https://doi.org/10.1016/j.mseb.2021.115390

About Shibaura Institute of Technology (SIT), Japan

Shibaura Institute of Technology (SIT) is a private university with campuses in Tokyo and Saitama. Since the establishment of its predecessor, Tokyo Higher School of Industry and Commerce, in 1927, it has maintained “learning through practice” as its philosophy in the education of engineers. SIT was the only private science and engineering university selected for the Top Global University Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology and will receive support from the ministry for 10 years starting from the 2014 academic year. Its motto, “Nurturing engineers who learn from society and contribute to society,” reflects its mission of fostering scientists and engineers who can contribute to the sustainable growth of the world by exposing their over 8,000 students to culturally diverse environments, where they learn to cope, collaborate, and relate with fellow students from around the world.

Website: https://www.shibaura-it.ac.jp/en/

About Professor Muralidhar Miryala from SIT, Japan

Dr. Muralidhar Miryala is a Professor at the Graduate School of Science and Engineering and Board of Councilor at Shibaura Institute of Technology (SIT). He is an active researcher in solid state physics and material science with a focus on high temperature superconductivity. He has published over 500 research items including patents, books, review-articles, articles etc., He has received several awards for his research contributions, including the prestigious 2021 Pravasi Bharatiya Samman Award by the President of India.

Funding Information

This study was partly supported by Shibaura Institute of Technology (SIT) International Research Center for Green Electronics and Grant-in-Aid FD research budget code: 721MA56383.