Papers by Keyword: Magnesium Diboride

Abstract: In this paper, solid state method was using to synthesize the of magnesium diboride (MgB₂) added in Bi _1.6Pb _0.4Sr₂Ca₂Cu₃O_δ(Bi-2223) superconductor from 0.00 to 0.10 wt.%. The effect on additions were investigated through X-ray Diffraction (XRD), resistance-temperature (R-T) measurement and Scanning Electron Microscope (SEM). From the XRD result, volume fraction of Bi-2223 showed the highest volume percentage was 76 % correspond to addition with MgB₂=0.02 wt.% and slightly decreased the percentage while increased the additions. From the R-T measurement, all samples showed the metallic behavior in the normal state. Morphology images showed that the grains were flaky plates and the size slightly increased. These results revealed that, additions of magnesium diboride change the microstructure and decrease the superconducting transition.

Abstract: Our investigations show that the addition of Ti, polyvalent titanium oxides or TiC powders (0.1-40 mm, amount: 10 wt%) can affect the formation of MgB_x (x³4) inclusions and a redistribution of admixed oxygen resulting in the appearance of dispersed inclusions with near MgBO stoichiometry in the MgB₂ matrix and thus influencing the critical current density and the critical magnetic fields of the materials. The highest B_c2 and B_irr were obtained when powdered polyvalent titanium oxides (synthesized by electroerosion dispersion) or powdered titanium were added, but the critical magnetic fields were somewhat lower in the case of Ti additions. We show that Mg diffuses during the synthesis inside the grains of polyvalent titanium oxide, titanium carbide or titanium, which can affect the redistribution of boron and oxygen in the superconducting matrices and thus influence pinning and the superconducting properties.

Abstract: Magnesium diboride obtained from magnesium and boron oxide by magnesium-thermal reduction in SHS mode under the high-pressure inert gas (argon) was investigated. The effect of pressure of inert gas on the temperature of synthesis and the yield of final product (magnesium diboride) was determined. As energy additives were used powerful oxidizers - potassium chlorate salt (KClO₃) and ammonium nitrate (KNO₃) to increase the reactivity of the system Mg - B₂O₃. The composite material containing up to 20% of magnesium diboride phase was obtained. The acidic separation of final product from impurities was suggested. The microstructure and characteristic of particle size was defined. The products had a dense grain structure with a particle size 200-500 nm.

Abstract: Auger and SEM studies show that with increasing of MgB₂ manufacturing temperature from 600÷800 °C to 1050÷1100 °C the Mg-B-O nanolayers which are present in the MgB₂ matrix transform into distinct dispersed Mg-B-O inclusions. On the other hand the sizes of inclusions of higher magnesium borides (MgB_x, x=7 ÷ 25) which are also present in the MgB₂ matrix. The tendency is observed in a wide range of synthesis pressures (0.1 MPa-2 GPa). The described structural transformations are accompanied by an increase in critical current density, j_c, in low and medium magnetic fields and by transition from the grainboundary to the point pinning. The Ti addition results in a further increase in j_c due to: Ti promotes the formation of higher magnesium boride inclusions and localization (or segregation) of oxygen in MgB₂ matrix, and, hence, facilitates the formation of a homogeneous MgB₂ matrix with lower oxygen content, but with an increased number of Mg-B-O and MgB_x pinning centers. At low synthesis temperature Ti absorbs hydrogen forming titanium hydrides, thus preventing the formation of MgH₂ and provides the material densification. The positive effect of Ti addition is connected with the high ability of Ti to absorb hydrogen, oxygen, and magnesium. The results of the critical current and AC loss study by transformer method using rings from MgB₂ are discussed.

Abstract: The present study suggests the use of high energy ball milling to mix (to dope) the phase MgB2 with the AlB2 crystalline structure compound, ZrB2, with the same C32 hexagonal structure than MgB2, in different concentrations, enabling the maintenance of the crystalline phase structures practically unaffected and the efficient mixture with the dopant. The high energy ball milling was performed with different ball-to-powder ratios. The analysis of the transformation and formation of phases was accomplished by X-ray diffractometry (XRD), using the Rietveld method, and scanning electron microscopy. As the high energy ball milling reduced the crystallinity of the milled compounds, also reducing the size of the particles, the XRD analysis were influenced, and they could be used as comparative and control method of the milling. Aiming the recovery of crystallinity, homogenization and final phase formation, heat treatments were performed, enabling that crystalline phases, changed during milling, could be obtained again in the final product.

Abstract: Superconducting thin films of magnesium diboride (MgB2) has been synthesized on various substrates such as gold, silver, copper and silicon using a novel electroless plating technique. The microstructures and the superconducting properties of these films have been characterized using X-ray diffraction, scanning electron microscopy and temperature dependent magnetometry. X-ray diffraction measurements confirm that the films are crystalline magnesium diboride with some impurity phases. Clear evidence for a superconducting transition in the magnetization measurements was observed.

Abstract: The effect of purity of amorphous boron raw materials on properties of the hot pressed SiC doped MgB2 superconductor was investigated. MgB2 superconductors with magnetic Jc over 106 A/cm2 and remaining Jc of 105 A/cm2 at 4.2 K and 5 T were fabricated by hot pressing using both high purity (99.00%) and low purity (88.84%) boron powders. XRD analysis shows that purity of the boron powders has little effect on phase component of the MgB2 samples. If the main impurity in amorphous boron is Mg, low purity low cost boron powder is suitable as one of the raw materials for fabricating MgB2. Particle sizes of boron has significant effect on microstructure and properties of MgB2. Smaller boron particle size leads to smaller grain size of MgB2, higher density, higher lattice distortion, and thus higher magnetic Jc.

Abstract: In this work oxidized and oxide-free amorphous boron (a-B) powder and elemental Mg were used in an attempt to directly synthesize the Mg(BH4)2 complex hydride by controlled reactive mechanical alloying (CRMA) under hydrogen in a magneto-mill up to 200h. The particle size was refined to the 100-200nm range. Nanocrystalline MgH2 (~6nm crystallite size) was formed within the particles when an oxidized a-B is used. In contrast, a mixture of MgB2 and an amorphous hydride MgHx was formed when an oxide-free a-B was used. Differential scanning calorimetry (DSC) test up to 500°C produced a single endothermic heat event at 357.7°C due to hydrogen desorption. In addition, desorption conducted in a Sieverts-type apparatus revealed ~1.4wt.% of hydrogen release. The X-ray diffraction pattern after DSC test of the 200h milled sample made with oxide-free boron showed the presence of MgB2.

Abstract: In spite of the relatively short time dedicated to the development of MgB2 conductors since its discovery in 2001, a remarkable progress has been already achieved in terms of critical current density, homogeneity of the conductors and reproducibility of the results over long lengths. Unlike other HTS and LTS materials, MgB2 conductor processing is more open to a number of improvements and modifications that help in making it more attractive for several DC and AC applications. Up to now our work has been focused on the improvement of the production capacity in order to allow for the assembly of large prototype magnets to test the capability of MgB2 to maintain the present level of performance over very long lengths. Long MgB2 tapes of about 1600 m with superconducting and mechanical properties suitable for making low field magnets are already available. Presently we are focusing on the enhancement of the irreversibility field. This would open the possibility of using MgB2 also for high field applications.