High temperature heat treatment on boron precursor and PIT process optimization to improve theJcperformance of MgB2-based conductors

The promising results reported in our previous works led us to think that the production process of boron plays a crucial role in MgB 2 synthesis. A new method for boron preparation has been developed in our laboratory. This particular process is based on magnesiothermic reaction (Moissan's process) with the addition of an initial step that gives boron powder with nano-metric grain size. In this paper we report our efforts regarding optimization of the powder-in-tube (PIT) method for these nano-metric powders, and the resolution of problems previously highlighted such as the difficulty in powder packaging and the high friction phenomena occurring during cold working. This increases cracking during the tape and wire manufacture, leading to failure. Packaging problems are related to the amorphous nature of boron synthesized in our laboratory, so a crystallization treatment was applied to improve the crystallinity of the boron. To prevent excessive friction phenomena we synthesized non-stoichiometric MgB 2 and used magnesium as lubricant. Our goal is the J c improvement, but a global physical–chemical characterization was also made to analyse the improvement given by our treatments: this characterization includes x-ray diffraction, ρ( T ) measurement, and SEM imaging, besides magnetic and transport J c measurements.