Biomass-derived carbon doping to enhance the current carrying capacity and flux pinning of an isotopic Mg^(11)B_(2)superconductor

Low activation isotopic boron(11B)based magnesium diboride(Mg^(11)B_(2))superconductors doped with biomass-derived activated carbon were synthesized using11B and magnesium powder via solid-state reaction.The effect of carbon doping on the lattice structure and superconducting properties of Mg^(11)B_(2)bulks were evaluated using X-ray powder diffraction,high resolution transmission electron microscopy,scanning electron microscopy and magnetization measurements.Precise refinement of structural parameters indicates successful substitution of carbon in Mg^(11)B_(2)bulks.The critical current density(Jc)of carbon doped Mg^(11)B_(2)synthesized at 650℃was enhanced more than two times compared with the pure Mg^(11)B_(2)bulk.Similar improvement was observed for the Mg^(11)B_(2)bulks heat-treated at 800℃.This enhancement is due to successful substitution of biomass-derived carbon with high surface area into Mg^(11)B_(2)lattice.The flux pinning mechanism of pure and doped Mg^(11)B_(2)bulks were investigated using the Dew-Hughes model.This study provides information regarding enhancement of the Jc of low activation Mg^(11)B_(2)superconductors suitable for next-generation fusion magnets.

Interplay between cold densification and malic acid addition (C4H6O5) for the fabrication of near-isotropic MgB2 conductors for magnet application

The effect of cold high pressure densification(CHPD)on anisotropy of the critical current density(Jc)in《in situ》single core binary and alloyed MgB2 tapes has been determined as a function of temperatures at 4.2 K,20 K and 25 K as well as at applied magnetic fields up to 19 T.The study includes binary and C4H6O5(malic acid)doped MgB2 tapes before and after CHPD.It is remarkable that the CHPD process not only improved the Jc values,in particular at the higher magnetic fields,but also decreased the anisotropy ratio,Г=JC^///JC^⊥In binary MgB2 tapes,the anisotropy factor F increases with higher aspect ratios,even after applying CHPD.In malic acid(C4H6O5)doped tapes,however,the application of CHPD leads only to small enhancements ofГ,even for higher aspect ratios.This is attributed to the higher carbon content in the MgB2 filaments,which in turn is a consequence of the reduced chemical reaction path in the densified filaments.At all applied field values,it was found that CHPD processed C4H6O5 doped tapes exhibit an almost isotropic behavior.This constitutes an advantage in view of industrial magnet applications using wires with square or slightly rectangular configuration.

Combustion performance of hybrid rocket fuels loaded with MgB_(2)and carbon black additives

Paraffin-based fuel has a great potential for several innovative missions,including space tourism,due to its safety,low environmental impact,high performance and low cost.Despite the fact that liquefying solid fuels increases the regression rate of hybrid rocket motors,incorporating energetic materials into solid fuel can still improve the performance.The objective and scope of this study is to increase the performance characteristics of the paraffin-based fuel by using magnesium diboride(MgB_(2))and carbon black(CB)additives.The cylindricalport fuel grains were manufactured with various additives percentages in mass(wt%:CB-2%and MgB_(2)-10%)and tested using a laboratory-scale ballistic hybrid motor under gaseous oxygen.The mechanical performance results revealed that adding CB and MgB_(2) improved the ultimate strength and elastic modulus of paraffin-based fuels.The addition of these fillers increased the hardness of fuel by developing a strong interaction in the paraffin matrix.Thermogravimetry(TG)results showed that CB inclusion improved the thermal stability of the paraffin matrix.The average regression rates of fuels loaded with CB and MgB_(2) were 32%and 52%higher than those of unmodified paraffin wax,respectively.The characteristic velocity efficiency was found in the range of 68%e79%at an O/F ratio of 1.5e2.6.The MgB_(2) oxidation/combustion in the paraffin matrix was described by a four-step oxidation process ranging from 473 K to 1723 K.Finally,a combustion model of MgB_(2) in the paraffin matrix was proposed,and four-step oxidation processes were discussed in detail.

Effect of Nano-SiC and Nano-Si Doping on Critical Current Density of MgB_2

The discovery of superconductivity in magnesium diboride (MgB2) has opened up a new field in materials science research. It offers a possibility of a new class of high performance superconducting materials for practical applications because of the relatively low cost of fabrication, high critical current densities (Jc) and fields, large coherence length, absence of weak links, higher Tc(TC = 39K) compared with Nb3Sn and Nb-Ti alloys (two or four times that of Nb,,Sn and Nb-Ti alloys). However, the weak flux pinning in the magnetic field remains a major challenge. This paper reports the most interesting results on nanomaterial (SiC and Si) doping in magnesium diboride. The high density of nano-scale defects introduced by doping is responsible for the enhanced pinning. The fabrication method, critical current density, microstructures, flux pinning and cost for magnesium diboride bulks, wires and tapes are also discussed. It is believed that high performance SiC doped MgB2 will have a great potential for many practical applications at 5K to 25K up to 5T.