Superconducting cryo-magnets processed by spark plasma sintering and texturing

In this chapter, two main superconducting compounds have been studied. The first study was focused on the preparation of magnesium diboride (MgB2) cryo-magnets by Spark Plasma Sintering (SPS). The role of the starting powder on the superconducting properties of MgB2 is investigated. Different sets of bulk MgB2 material were processed from: (i) a commercial available 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 tungsten carbide molds, varying the processing conditions by the modulation of the temperature, the dwell time, and the applied pressure. The microstructures of the samples were investigated by SEM and TEM and correlated to their superconducting properties. The best sample was prepared at 850°C, 20min, and 100MPa. At 20K its critical current density (Jc) was 500 kA/cm2. Herein, we demonstrate that MgB2 is an excellent candidate to make cryo-magnets, maintaining 3.9T at 20K at the surface of a 20mm diameter disk. The SPS was modified with the aim of obtaining textured lamellar compounds with Bi2Ca2Sr2CuO8 superconductor ceramics. The new process is referred to as “Spark Plasma Texturing” (SPT). During SPT, the bulk material can freely deform itself. As a result, the formation of an inter-grain preferential crystallographic orientation is favored. The superconducting properties were measured and discussed in correlation with textured microstructure analysis.