Papers by Keyword: MgB₂

Abstract: We report the phase formation and electrical resistivity of MgB₂ superconductor samples. Method of synthesis was conventional solid-state reaction employing crystalline β-rhombohedral boron (B) and magnesium (Mg) with a stoichiometric ratio of Mg:B=1:2. The two precursors were mixed and sintered at various temperatures from 600°C to 900°C for an hour. All samples were characterized employing XRD, SEM, and Cryogenic Magnetometer. It is shown that the MgB₂ phase begins to form at a sintering temperature of 700°C. The highest peak intensity of the MgB₂ phase was observed in a sample sintered at 900°C indicates the largest fraction of the superconducting phase among all synthesized samples. Electrical resistivity values were carried out to investigate the superconducting properties of the samples. It is also shown the samples sintered at a temperature of 800°C and 900°C possess superconducting properties with a critical temperature of ~ 43 K

Abstract: MgB₂ superconductor is a superconductor with a critical temperature of around 39K and has the potential to replace Nb₃Sn and NbTi as superconducting coils to produce high magnetic fields. In this study, monofilament wires have been made to analyze the doping effect of SiC and Carbon Nanotubes (CNT) in its manufacture using Powder-In-Tube (PIT) method. Stainless Steel (SS-316) tube was used as a tube filled with powders of starting materials of Mg, B, SiC and CNT. A total of 8 samples were prepared with variations in the addition of SiC, and CNT as much as 5, 10, and 15 wt %, and also the variations in the addition of Mg composition by 0 and 10 mol % from normal stoichiometric values. The samples were rolled and sintered at 800°C for 3 hours. The samples then were analyzed using SEM (Scanning Electron Microscopy) to analyze the surface morphology, XRD (X-Ray Diffractometer) to analyze the formed phases and crystal structures, and then resistivity versus temperature using cryogenic systems to analyze their superconductivity properties. Based on the results of the XRD analysis, the MgB₂ phase is the major phase in the samples and the SiC doping causes the formation of minor phases of Mg₂Si and Fe₃C. The addition of SiC causes a decrease in crystalline properties of the MgB₂ phase due to reaction with SiC, while the addition of CNT does not cause the formation of a new phase. Based on the results of the analysis of resistance versus temperature, it is seen that the addition of SiC causes a decrease in T_C value. While the addition of CNT causes the improvement in the nature of superconductivity, but it also causes the decrease of its T_C values.

Abstract: MgB₂ superconductor with relatively high critical temperature (Tc=40 K) has been developed for possibilities utilization in various practical applications such as Magnetic Resonance Imaging. In order to enhance the process, the material was prepared by Powder-In-Tube (PIT) method, while the superconducting properties was improved by incorporating 0 wt.%, 10 wt.% and 20 wt.% SiC nanoparticles into MgB₂ structure. This study aimed at analyzing the effect of sintering temperature on the microstructure, resistivity and phase of Fe-sheathed MgB₂ superconducting wires. Three different compositions of MgB₂ powders were inserted into Fe tube with inner ø of 4 mm and outer ø of 6 mm. This tube was then rolled and drawn into a ø 2.5 mm wire. Wire samples with three different compositions of SiC were heat treated at 600°C and 800°C respectively. All samples were characterized to analyze the morphology, resistivity and crystal structure. X-ray diffraction (XRD) analysis showed that some Mg may react with SiC to form MgSi and with oxygen to form MgO. Scanning electron microscope (SEM) images revealed that with no addition of SiC, MgB₂ was formed and dispersed uniformly in wire, but with 10 wt.% and 20 wt.% SiC nanoparticles, the whisker morphology was observed resulting in degradation of the superconducting properties.

Abstract: 100nm thin Mg/B precursor films were prepared on SiC substrates in ZZSX-500 vacuum coating machine. They were annealed by electron-beam(EB) which only took fractions of a second. In this paper the best annealing duration to fabricate the superconducting MgB₂ thin films was investigated. Under the optimized annealing condition(accelerating voltage 15kV, electron beam current 5mA, annealing duration 0.7s), the superconducting MgB₂ thin film with critical temperature Tc^onset~35.3 K and transition width ∆Tc~1K was fabricated. Besides that, a nano-bridge (about 100×200nm²) was etched on the superconducting MgB₂ thin film by Focused Ion Beam (FIB). It’s a relative simple and efficient method. The nano-bridge exhibited the effect of Josephson junction with RSJ characteristics. At the same time a little loss of superconducting property was detected.

Abstract: MgB₂ powder was fabricated by sintering the mixture of pure Mg and B powder with atomic ratio of Mg : B=1:2. The magnetic property of the powder indicated that it was superconducting and its critical transition temperature was 39K. Titanium based MgB₂ films were obtained by electrophoretic deposition method using Ni sheet as anode and titanium tapes as cathode. The films were annealed at 500°C for 2 hours, subjected to argon-hydrogen (95%Ar+5%H2) gas flow. The results of X-ray diffraction (XRD) analysis showed that the composition of the film was mainly MgB₂. The observation under scanning electron microscopy (SEM) showed that the film of MgB₂ was uniform and dense. The electrical resistivity of double-side MgB₂ film was about 5.280×10^-8Ω/m.

Abstract: The structural and superconducting properties of iron sheathed mono-filamentary superconducting wires of MgB₂ with and without Fe addition processed at a relatively low temperature of 600 °C were investigated. The transport critical current density (J_C) of the superconducting composite wires is found to increase steadily with an increase in Fe content to an optimum of 10 wt.% is reached. The magnetic J_C and flux pinning analysis of the samples carried out up to a field of 9 T also show significant enhancements throughout the entire field of study. Another observation is that the T_C of the composites doesn’t vary much, indicating that the added Fe has not gone in to the MgB₂ lattice.

Abstract: In this study, as much as 10 and 15 wt.% nanosized silicon and carbon (Si+C) were reacted with (Mg+2B) at 650°C and 850°C, respectively, for 1 hour. The phase formation, surface morphology and superconducting properties of these samples were evaluated. The relative peak intensity as calculated from the XRD patterns indicates the formation of large Mg₂Si volume fraction at low sintering temperature. MgB₄ phase was detected in the samples sintered at high temperature as a result of Mg deficiency. The C substitution level as estimated from the lattice parameters, was shown to increase in the samples reacted with a higher amount of (Si+C) at high temperature. Scanning electron micrograph showed that (Si+C) co-addition had refined the grain size and improved the grain coupling of MgB₂. The superconducting transition temperature was found to decrease with increasing addition level. The superconducting transition width was also broadened because of a large volume fraction of secondary phases. The improved field dependent critical current density at both 5 K and 20 K is accounted to enhanced scattering by C substitution and grain boundary pinning.

Abstract: MgB₂ is a candidate for the fabrication of magnetic coils used in medical applications. Our review indicate that oxide additions based on the rare earth or metalloid elements show improvement of the MgB₂ critical current density (J_c) and the irreversible magnetic field (H_irr) without significantly affecting the critical temperature (T_c) However, the characteristics of the additions and the technological approaches show a strong influence in controlling superconducting properties. Both additions and the technology need a careful and complex optimization in order to enhance the J_c and H_irr.

Abstract: We report on the fabrication and characterization of disk-shaped bulk MgB₂ superconductors with high performance as superconducting bulk magnets. Several samples of diameters 20 mm, 30 mm and 40 mm were fabricated using a solid state reaction in pure Ar atmosphere at 775°C for 3h. The magnetization measurements confirmed that all the samples exhibited a sharp superconducting transition with T_c (onset) at around 38.5 K. The samples showed respective critical current density (J_c) values of 176 kA cm^-2 and 55 kA cm^-2 at 20 K in self field and 1T. The J_c values increased further to 250 kA cm^-2 and 100 kA cm^-2 with decreasing temperature down to 10 K. MgB₂ samples 20 mm and 30 mm in diameter and 7 mm in thickness exhibited trapped field values of 1.15 T and 1.3 T at 25 K, respectively. Microstructural observations with scanning electron microscopy (SEM) revealed that the samples are highly porous. And hence, continuing development of large-sized bulk MgB₂ with higher density will lead to promising industrial applications.

Abstract: MgB₂-based superconducting composites with magnetic nanoparticles were fabricated by spark plasma sintering technique. Two methods have been used to create nanoparticles within MgB₂ matrix: i) direct insertion of passivated magnetic nanoparticles; ii) growth of magnetic nanoparticles by thermolysis of polymers or metallo-organic precursors. These composites display an enhanced critical current density due to the additional magnetic pinning generated by the magnetic interaction with the flux lines.