Improvement of critical current density of MgB₂ bulk superconductor processed by Spark Plasma Sintering

Abstract

Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and optimization of the sintering kinetics and therefore makes it possible to obtain MgB2 bulk superconductor with tailored microstructures consisting of grains with either spherical or elongated morphology. In this contribution, the role of the precursor powders on the superconducting properties of MgB2 is investigated. Three sets of bulk MgB2 material were processed from: (i) a commercially available MgB2 powder; (ii) a mixture of Mg metal and amorphous B using a single‐step solid‐state reaction process and (iii) a mixture of amorphous boron coated with carbon and Mg metal. The samples were prepared in the same SPS processing conditions. The microstructure of the samples was investigated by X‐ray diffraction, SEM and TEM and correlated to their superconducting properties. The critical current density of the best sample at 20K was Jc = 500 kA/cm2 in self‐field, which is one of the highest critical current density reported for MgB2 bulk superconductors.

Review on the Use of Superconducting Bulks for Magnetic Screening in Electrical Machines for Aircraft Applications

“…However, for the MgB 2 [41], KFeSe [33], Bi 2 Sr 2 Ca 2 Cu 3 O x (Bi2223) [49], and CaK-FeAs [50], we observe a certain value of the applied field for each material at which the B 1 is maximized, which implies that for a machine made with these materials, an increase in the HTS coil size can lead to a decrease in the magnetic loading and the machine power. This is caused by the decay of the J c with the magnetic field.…”

“…In the other side, poly-crystalline bulks are widely prepared by sintering, a very quick, simple, and cheap method [41,50,78]. This also allow the preparation of very large samples scale, tens of centimeters or even more, and with a totally free shape.…”

“…At the same time the sample is pressed between the current lead with the same order of pressure than used for the Hot Pressing technique, whereas hours are needed for sintering a sample using a furnace, only tens of minutes to an hour are needed using the SPS technique. Furthermore, the resulting sample has a very high density, easily above 80% of the theoretical density [31,41] or even above 95% [80], a very good grain connectivity, and a very good homogeneity. The consequence is a huge improvement of the critical current and the mechanical properties to reach a level closed to the one of a single crystal with only a tiny fraction of the preparation time.…”

“…• The MgB 2 compound [39] with a T c of 39 K, an acceptable H c2 and a very high J c [40,41] has a good potential as trapped field permanent magnet [42,43].…”

“…Simulated amplitude of the flux modulation fundamental harmonic in the air gap versus applied magnetic field for different superconducting materials. The material properties are extracted from the works in[33,41,45,47,49,50].…”