No abstract

Articles you may be interested inThe critical parameters in in-situ MgB2 wires and tapes with ex-situ MgB2 barrier after hot isostatic pressure, cold drawing, cold rolling and doping Doping effect of nano-Ho2O3 and naphthalene in MgB2 superconductor prepared by powder-in-sealed-tube method A new scaling relation for n-AlN doped superconducting MgB2 Effect of thermal strain on Jc and Tc in high density nano-SiC doped MgB2 J. Appl. Phys. 109, 07E108 (2011); 10.1063/1.3549590 Superconductivity and the disorder effect in Ag and Al double doped Mg B 2Undoped and carbon-doped magnesium diboride (MgB 2 ) samples were synthesized using two sets of mixtures prepared from the precursors, amorphous nanoboron, and as-received amorphous carbon-doped nanoboron. The microscopic defect structures of carbon-doped MgB 2 samples were systematically investigated using X-ray powder diffraction, Raman and electron paramagnetic resonance spectroscopy. Mg vacancies and C-related dangling-bond active centers could be distinguished, and sp 3 -hybridized carbon radicals were detected. A strong reduction in the critical temperature T c was observed due to defects and crystal distortion. The symmetry effect of the latter is also reflected on the vibrational modes in the Raman spectra. V C 2015 AIP Publishing LLC.

Defect structure of MgB2 bulk and ultrafine particles, synthesized by solid state reaction route, have been investigated mainly by the aid of X-band electron paramagnetic resonance spectrometer. Two different amorphous Boron (B) precursors were used for the synthesis of MgB2, namely, boron 95 (purity 95%–97%, <1.5 μm) and nanoboron (purity >98.5%, <250 nm), which revealed bulk and nanosized MgB2, respectively. Scanning and transmission electron microscopy analysis demonstrate uniform and ultrafine morphology for nanosized MgB2 in comparison with bulk MgB2. Powder X-ray diffraction data show that the concentration of the by-product MgO is significantly reduced when nanoboron is employed as precursor. It is observed that a significant average particle size reduction for MgB2 can be achieved only by using B particles of micron or nano size. The origin and the role of defect centers were also investigated and the results proved that at nanoscale MgB2 material contains Mg vacancies. Such vacancies influence the connectivity and the conductivity properties which are crucial for the superconductivity applications.

. (2015). Significantly enhanced critical current density in nano-MgB2 grains rapidly formed at low temperature with homogeneous carbon doping. Superconductor Science and Technology, 28 (5), 055005-1-055005-7.Significantly enhanced critical current density in nano-MgB2 grains rapidly formed at low temperature with homogeneous carbon doping AbstractHigh performance MgB 2 bulks using carbon-coated amorphous boron as a boron precursor were fabricated by Cu-activated sintering at low temperature (600 °C, below the Mg melting point). Dense nano-MgB 2 grains with a high level of homogeneous carbon doping were formed in these MgB 2 samples. This type of microstructure can provide a stronger flux pinning force, together with depressed volatility and oxidation of Mg owing to the low-temperature Cu-activated sintering, leading to a significant improvement of critical current density (J c ) in the as-prepared samples. In particular, the value of J c for the carbon-coated (Mg 1.1 B 2 )Cu 0.05 sample prepared here is even above 1 x 10 5 A cm −2 at 20 K, 2 T. The results herein suggest that the combination of low-temperature Cu-activated sintering and employment of carbon-coated amorphous boron as a precursor could be a promising technique for the industrial production of practical MgB 2 bulks or wires with excellent J c , as the carbon-coated amorphous boron powder can be produced commercially at low cost, while the addition of Cu is very convenient and inexpensive.Keywords carbon, homogeneous, nano, density, current, critical, enhanced, temperature, low, doping, formed, significantly, rapidly, grains, mgb2 Disciplines Engineering | Physical Sciences and Mathematics Publication DetailsLiu, Y., Lan, F., Ma, Z., Chen, N., Li, H., Barua, S., Patel, D., Shahriar, M., Hossain, A., Acar, S., Kim, J. & Dou, S. Xue. (2015). Significantly enhanced critical current density in nano-MgB2 grains rapidly formed at low temperature with homogeneous carbon doping. Superconductor Science and Technology, 28 (5) AbstractsHigh performance MgB 2 bulks using carbon-coated amorphous boron as boron precursor were fabricated by Cu-activated sintering at low temperature (

Sub-micron sized TiB2 ceramic powders were prepared via self-propagating high-temperature synthesis (SHS) followed by HCl leaching at different temperatures. Purified powders obtained using optimum process parameters were consolidated by field assisted sintering technology / spark plasma sintering (FAST/SPS) technique. Phase and microstructural analyses of both the powder and sintered samples were carried out by X-ray diffractometer (XRD) and scanning electron microscope (SEM). The chemical analyses and particle size measurements of the specimen were conducted by inductively coupled plasma-mass spectrometry (ICP-MS) and dynamic light scattering (DLS) techniques. The final properties of the sintered sample were determined in terms of density and microhardness. The effects of different HCl leaching temperatures on the formation, microstructure, particle size, purity and sintering behavior of the SHS-produced TiB2 powders were investigated. The SHS reaction of TiO2-B2O3-Mg powders as a starting mixture yielded MgO, Mg3(BO3)2 and Mg beside the desired phase TiB2. All three magnesium containing by-products were completely removed by performing hot HCl leaching. TiB2 powders after SHS reaction and leaching with 9.3 M HCl for 30 min at 80°C revealed a minimum purity of 98.4 % and a homogenous particle size distribution with an average particle size of 536 nm. In the ultimate SPS experiment which was conducted at 1500°C for 5 min under a pressure of 50 MPa, a relative density of 94.9 % and a micro-hardness value of 24.56 GPa were achieved.