An innovative technique to synthesize C-doped MgB₂by using chitosan as the carbon source

Abstract

Here, we report a new technique to synthesize carbon-doped MgB 2 powder. Chitosan was innovatively used as the carbon source during the synthesis of boron from boron oxide. This allowed the introduction of local defects, which later on served as pinning centers in MgB 2 , in the boron lattice itself, avoiding the traditional and time consuming ways of ex situ MgB 2 doping (e.g. ball milling). Two volume percentages of C-doping have been tried and its effect on the superconducting properties, evaluated by magnetic and transport measurements, are discussed here. Morphological analysis by scanning electron microscopy revealed nano-metric grains' distribution in the boron and MgB 2 powder. Mono-filamentary MgB 2 wires have been fabricated by an ex situ powder-in-tube technique by using the thus prepared carbon-doped MgB 2 and pure MgB 2 powders. Transport property measurements on these wires were made and compared with MgB 2 wire produced using commercial boron.

Size determination of superconducting MgB2powder from magnetization curve, image analysis and surface area measurements

“…The results of the BET measurements, expressed in m 2 /g were converted into the average diameter < d > using the formula (6): 6 d S ρ < >= * (6) In which S is the BET specific surface area and ρ is the true density, in the specific case the value of 2.63 g/cm 3 was used for the MgB 2 powders. The < d > value of each sample obtained through the BET analysis is really similar; this is due to the spherical shape approximation of the MgB 2 grains.…”

Nano-sized boron synthesis process towards the large scale production

“…Following the new boron synthesis process is possible to obtain a suitable precursor for MgB 2 -based conductor manufacturing with the same performance of conductors prepared using MgB 2 powders synthesized from commercial B precursor. In particular in previous articles we shown that the laboratory made B has the same critical current density (J c ) performance of milled MgB 2 powders [6][7][8].…”

Method for the production of pure and C-doped nanoboron powders tailored for superconductive applications

“…Subsequently, the freezedrying process (FDP) allows to remove the water and a homogenous dispersion of C in B 2 O 3 solid phase is obtained. The nanostructured B 2 O 3 is then reduced to pure or Cdoped nB by magnesiothermic process [20][21][22]. The fact that nanostructured boron is ideal for superconducting and other applications is related to the formation of nanosized boron grains, for which the following two conditions have to be satisfied:…”