Paul J. McGinn

microstructure and critical current density of zone melt textured YBa2Cu3O6+x

Zone melting has been used to produce texture in extruded YBa2Cu3O6+x wires. Highly aligned microstructures are produced with a‐b planes oriented along the axis of the wires. Microstructural observations show that changes in alignment orientation can occur, and can result in the inability to carry a transport current. Pulsed transport Jc measurements on oriented samples indicate a zero field critical current density greater than 4×104 A/cm2.

Texture processing of extruded YBa2Cu3O6+x wires by zone melting

Abstract Zone melting has been used to produce texture in extruded YBa 2 Cu 3 O 6+ x wires. By controlling the directional solidification of the molten zone, oriented structures are produced that show a large magnetic hysteresis at 77 K compared to unaligned extruded YBa 2 Cu 3 O 6+ x wires. A magnetization critical current density of 1.8 × 10 4 A/cm 2 in an applied field of 20 kOe has been achieved.

Microstructure and critical current density of zone melt textured YBa2Cu3O6 + x with Y2BaCuO5 additions

Abstract Extruded wires of YBa 2 Cu 3 O 6 + x With Y 2 BaCuO 5 (211) additions were zone melted to produce textured microstructures. Excess 211 was introduced in order to observe its effect on the transport properties and the microstructure. Highly aligned microstructures can be produced with a−b planes oriented along the axis of the wires. 211 additions appear to modify the microstructure, with YBCO platelet thickness decreasing with increasing 211 additions. Magnetization and transport measurements show a decrease in J c with increasing 211 additions.

Texture processing of YBa2Cu3O7−x by Joule heat zone melting

Abstract Joule heat zone melting has been used to produce texture in YBa2Cu3O7−x polycrystalline bars. X-ray diffraction analysis shows the zone melted bars consist of tetragonal YBa2Cu3O7−x, BaCuO2, and CuO. A 900°C homogenization and 600°C anneal in oxygen are found to produce a nominally single phase structure of orthorhombic YBa2Cu3O7−x. SEM examination shows a platelet morphology is produced.

The effect of PtO2·H2O additions on the Y2BaCuO5 morphology in melt textured YBa2Cu3O7−χ

Abstract YBa 2 Cu 3 O 7−χ (123) pellets doped with 0.5 wt.% of PtO 2 ·H 2 O were melt textured to determine the effects of PtO 2 additions on the microstructure of melt textured 123. The addition of PtO 2 ·H 2 O resulted in both a refinement and a change in the morphology of the Y 2 BaCuO 5 (211) phase. The 211 particles are more acicular in melt textured PtO 2 -doped 123 than in undoped melt textured 123. The 211 particles were found to segregate and form tracks in the melt textured PtO 2 -doped 123 samples.

Removal of oil droplets from contaminated water using magnetic carbon nanotubes

Water contaminated by oil and gas production poses challenges to the management of Americas water resources. Here we report the design, fabrication, and laboratory evaluation of multi-walled carbon nanotubes decorated with superparamagnetic iron-oxide nanoparticles (SPIONs) for oil-water separation. As revealed by confocal laser-scanning fluorescence microscopy, the magnetic carbon nanotubes (MCNTs) remove oil droplets through a two-step mechanism, in which MCNTs are first dispersed at the oil-water interface and then drag the droplets with them out of water by a magnet. Measurements of removal efficiency with different initial oil concentration, MCNT dose, and mixing time show that kinetics and equilibrium of the separation process can be described by the Langmuir model. Separation capacity qt is a function of MCNT dose m, mixing time t, and residual oil concentration Ce at equilibrium: [Formula in text] where qmax, kw, and K are maximum separation capacity, wrapping rate constant, and equilibrium constant, respectively. Least-square regressions using experimental data estimate qmax = 6.6(± 0.6) g-diesel g-MCNT(-1), kw = 3.36(± 0.03) L g-diesel(-1) min(-1), and K = 2.4(± 0.2) L g-diesel(-1). For used MCNTs, we further show that over 80% of the separation capacity can be restored by a 10 min wash with 1 mL ethanol for every 6 mg MCNTs. The separation by reusable MCNTs provides a promising alternative strategy for water treatment design complementary to existing ones such as coagulation, adsorption, filtration, and membrane processes.

Texture processing of bulk YBa2Cu3O6+x by zone melting

Abstract Zone melting has been used to produce texture in bulk YBa 2 Cu 3 O 6+ x . By controlling the directional solidification of the molten zone, oriented structures are produced that consist of domains of aligned grains, with some misalignment between domains. Scanning electron microscopy and optical microscopy show a high degree of texture produced by this technique. Magnetization measurements show a large increase in hysteresis at 77 K compared to unaligned polycrystalline YBa 2 Cu 3 O 6+ x . The use of BaCuO 2 as a solvent to aid the texturing process is discussed.

Microstructure and critical current density of zone melt textured YBa2Cu3O6+x/Y2BaCuO5 with BaSnO3 additions

Additions of BaSnO3 have been made to YBa2Cu3O6+x/Y2BaCuO5 composite wires to examine its potential for improving solidification processing and enhancing pinning. Zone melting has been used to produce texture in extruded YBa2Cu3O6+x (Y‐123) wires with Y2BaCuO5(211) and BaSnO3 additions. BaSnO3 additions markedly improve the magnetization properties over similarly textured Y‐123 or Y‐123+211 wires in low fields, but do not show a noticeable improvement at higher fields (≳2 T). Microstructural effects of BaSnO3 include the growth of much larger Y‐123 grains, and a substantial reduction in size of 211 precipitates. Magnetic critical current densities (Jc) in excess of 1.2×105 A/cm2 in zero field, and 3.0×104 A/cm2 at 1 T are observed.

Transport critical current density and microstructure in extruded YBa2Cu3O7−x wires processed by zone melting

YBa2Cu3O7−x compounds were extruded into long wires with the diameter of 1 mm after sintering. The sintered wires were subsequently zone melted to develop a highly textured microstructure. Magnetization experiments at 77 K indicated a Jc value of 1×105 A/cm2 at 1 T. Transport measurements at 77 K showed a greatly enhanced field dependence of the critical current density. Transmission electron microscopy revealed an important grain‐boundary feature which eliminated the weak‐link behavior. Large amounts of dislocations have also been found in the zone‐melted sample which may contribute to flux pinning in the system.

Morphology of Y2BaCuO5 and segregation of second phase particles in melt-textured YBaCu oxides with/without BaCeO3 addition

Abstract Trapping behaviour of second phase (Y2BaCuO5 and BaCeO3) particles was investigated in undoped and BaCeO3-added YBaCu oxide prepared by the melt-texture processing. The segregation of second phase particles with a typical pattern is observed in both samples. The Y2BaCuO5 and BaCeO3 particles were trapped in the interior of textured YBa2Cu3O7−y domains and in the liquid phase remained at the high angle grain boundaries where textured YBa2Cu3O7−y domains met. The segregated pattern varied with a crystallographic orientation of the grown YBa2Cu3O7−y domain. This segregation appears to be related to the growth mechanism of the YBa2Cu3O7−y domain from the melt.