The critical current density of advanced internal-Mg-diffusion-processed MgB2 wires

Recent advances in MgB2 conductors are leading to a new level of performance. Based on the use of proper powders, proper chemistry, and an architecture which incorporates internal Mg diffusion (IMD), a dense MgB2 structure with not only a high critical current density Jc, but also a high engineering critical current density, Je, can be obtained. In this paper, a series of these advanced (or second - generation, "2G") conductors has been prepared. Scanning electron microscopy and associated energy dispersive X-ray spectroscopy were applied to characterize the microstructures and compositions of the wires, and a dense MgB2 layer structure was observed. The best layer Jc for our sample is 1.07x105 A/cm2 at 10 T, 4.2 K, and our best Je is seen to be 1.67x104 A/cm2 at 10 T, 4.2 K. Optimization of the transport properties of these advanced wires is discussed in terms of B-powder choice, area fraction, and the MgB2 layer growth mechanism.Comment: 13 pages, 3 tables, 7 figures (or 8 pp in published version

The Effect of Excess Carbon on the Crystallographic, Microstructural, and Mechanical Properties of CVD Silicon Carbide Fibers

Silicon carbide (SiC) fibers made by chemical vapor deposition (CVD) are of interest for organic, ceramic, and metal matrix composite materials due their high strength, high elastic modulus, and retention of mechanical properties at elevated processing and operating temperatures. The properties of SCS-6{trademark} silicon carbide fibers, which are made by a commercial process and consist largely of stoichiometric SiC, were compared with an experimental carbon-rich CVD SiC fiber, to which excess carbon was added during the CVD process. The concentration, homogeneity, and distribution of carbon were measured using energy dispersive x-ray spectroscopy (SEM/EDS). The effect of excess carbon on the tensile strength, elastic modulus, and the crystallographic and microstructural properties of CVD silicon carbide fibers was investigated using tensile testing, x-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM)

Superconductivity in MgB2 doped with Ti and C

Measurements of the superconducting upper critical field, Hc2, and critical current density, Jc, have been carried out for MgB2 doped with Ti and/or C in order to explore the problems encountered if these dopants are used to enhance the superconducting performance. Carbon replaces boron on the MgB2 lattice and apparently shortens the electronic mean free path of MgB2 and raising Hc2. Titanium forms precipitates of either TiB or TiB2 that enhance the flux pinning and raise Jc. Most of these precipitates are intra-granular in the MgB2 phase. For samples containing both C and Ti doping, the C appears to still replace B in the MgB2 lattice and the Ti precipitates out as a boride. If approximately 0.5%Ti and approximately 2%C are co-deposited with B to form doped boron fibers and these fibers are in turn reacted in Mg vapor to form doped MgB2, the resulting superconductor has μ0Hc2(T = 0) ∼ 25 T and Jc ∼ 10,000 A/cm2 at 5 K and 2.2 T.This is a manuscript of an article published as Wilke, R. H. T., S. L. Bud’ko, P. C. Canfield, M. J. Kramer, Y. Q. Wu, D. K. Finnemore, R. J. Suplinskas, J. V. Marzik, and S. T. Hannahs. "Superconductivity in MgB2 doped with Ti and C." Physica C: Superconductivity 418, no. 3-4 (2005): 160-167. DOI: 10.1016/j.physc.2004.11.022. Copyright 2004 Elsevier B.V. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Posted with permission