Texturing Crystal Growth in Vertical Thermal Gradients

1989 ◽  
Vol 169 ◽  
Author(s):  
N. X. Tan ◽  
A. J. Bourdillon ◽  
N. Sawides
Keyword(s):  
Crystal Growth ◽  
Critical Current ◽  
Grain Growth ◽  
Thermal Gradient ◽  
Thermal Gradients ◽  
Ceramic Superconductor ◽  
Downward Motion ◽  
Current Densities ◽  
Molten Phase

AbstractTexture growth in incongruently melting ceramic superconductor materials, such as YBa2Cu3O7‐χ can be combined with zone refinement in thermal gradients to increase critical current densities. In gravity aided texture growth (GATEG), a vertical thermal gradient is used with downward motion of the partially molten specimen (relative to the furnace) so that the molten phase recrystallizes with grain growth. The oxidation features of Y‐Ba‐Cu‐0 and Bi‐Sr‐Ca‐Cu‐0 can be explained by Madelung potentials.

GRAVITY AIDED TEXTURE GROWTH IN CERAMIC SUPERCONDUCTORS

1989 ◽  
Vol 03 (14) ◽  
pp. 1053-1060 ◽  
Author(s):  
A. J. BOURDILLON ◽  
N. X. TAN ◽  
N. SAVVIDES ◽  
J. SHARP
Keyword(s):  
Critical Current ◽  
Grain Growth ◽  
Thermal Gradient ◽  
Thermal Gradients ◽  
Ceramic Superconductor ◽  
Downward Motion ◽  
Ceramic Superconductors ◽  
Current Densities ◽  
Molten Phase

Texture growth in incongruently melting ceramic superconductor materials, such as YBa 2 Cu 3 O 7−x, can be combined with zone refinement in thermal gradients to increase critical current densities. In gravity aided texture growth (GATEG), a vertical thermal gradient is used with downward motion of the partially molten specimen (relative to the furnace) so that the molten phase recrystallizes with grain growth.

Bi2Sr2CaCu2O8+x films prepared by fluorinated precursors in dry ambient

1992 ◽  
Vol 7 (11) ◽  
pp. 2956-2961 ◽  
Author(s):  
L.S. Hung
Keyword(s):  
Mass Transport ◽  
Critical Current ◽  
Grain Growth ◽  
Abnormal Grain Growth ◽  
Liquid Phases ◽  
Current Densities

Bi2Sr2CaCu2O8+x films were prepared by mixing 2-ethylhexanoate precursors with heptafluorobutyric acid and annealing at 820 °C in dry ambient. The films underwent substantial mass transport and exhibited abnormal grain growth, indicating that some liquid phases might be involved in the process. It was found that the high atomic mobilities during annealing significantly improved in-plane orientations and consequently increased critical current densities.

Crystal Growth and Critical Current Densities of Polycrystalline<tex>$rm MgB_2$</tex>Superconductor

2005 ◽  
Vol 15 (2) ◽  
pp. 3300-3303 ◽  
Author(s):  
M. Maeda ◽  
K. Mizuno ◽  
A. Takashi ◽  
D. Uchiyama ◽  
T. Kawakami ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Critical Current ◽  
Current Densities

A two-powder process for Bi-2223 precursors

1996 ◽  
Vol 11 (1) ◽  
pp. 28-38 ◽  
Author(s):  
T. G. Holesinger ◽  
K. V. Salazar ◽  
D. S. Phillips ◽  
B. L. Sargent ◽  
J. K. Bremser ◽  
...  
Keyword(s):  
Critical Current ◽  
Grain Growth ◽  
The Other ◽  
Fine Grained ◽  
Current Densities ◽  
Precursor Route ◽  
Blending Process ◽  
Multi Phase

A two-powder process is described for the production of uniform, fine-grained Bi2Sr2Ca2Cu3Oy (Bi-2223) powders. One powder is the Bi2.1−xPbxSr1.9−yCayOz (2:2 Cu-free) phase. The other is a multi-phase powder of approximate overall composition SrCaCu3Oy. The 2:2 Cu-free is one of the first Bi-containing phases to form from a nominal Bi-2223 mixture of oxides and carbonates. This precursor route was chosen for investigation because (1) the powders have very similar particle morphologies and (2) the mixing volumes are closely matched. Both of these characteristics facilitate the milling and blending process. This precursor mix was found to be stable in that explosive grain growth of undesirable phases was not observed during sintering. Critical current densities up to 26,900 A/cm2 in self field at 75 K were obtained in tapes.

Fission Gas Bubbles in Fractured UO2

1968 ◽  
Vol 26 ◽  
pp. 286-287
Author(s):  
O. M. Katz
Keyword(s):  
Electron Microscopy ◽  
Thermal Gradient ◽  
Gas Bubbles ◽  
Inert Gas ◽  
Thermal Gradients ◽  
Fission Gas ◽  
Beam Heating ◽  
Limited Application ◽  
Bubble Characteristics ◽  
Electron Beam Heating

The swelling of irradiated UO2 has been attributed to the migration and agglomeration of fission gas bubbles in a thermal gradient. High temperatures and thermal gradients obtained by electron beam heating simulate reactor behavior and lead to the postulation of swelling mechanisms. Although electron microscopy studies have been reported on UO2, two experimental procedures have limited application of the results: irradiation was achieved either with a stream of inert gas ions without fission or at depletions less than 2 x 1020 fissions/cm3 (∼3/4 at % burnup). This study was not limited either of these conditions and reports on the bubble characteristics observed by transmission and fractographic electron microscopy in high density (96% theoretical) UO2 irradiated between 3.5 and 31.3 x 1020 fissions/cm3 at temperatures below l600°F. Preliminary results from replicas of the as-polished and etched surfaces of these samples were published.

Facet Topography and Dislocation Structure as a Possible Source for Electrical Heterogeneity in [001] TILT Bicrystals of YBa2Cu3O7-δ

1996 ◽  
Vol 54 ◽  
pp. 338-339
Author(s):  
I-Fei Tsu ◽  
D.L. Kaiser ◽  
S.E. Babcock
Keyword(s):  
Grain Boundary ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Electromagnetic Properties ◽  
Length Scale ◽  
Density Values ◽  
Current Densities ◽  
Applied Fields ◽  
A Current

A current theme in the study of the critical current density behavior of YBa2Cu3O7-δ (YBCO) grain boundaries is that their electromagnetic properties are heterogeneous on various length scales ranging from 10s of microns to ˜ 1 Å. Recently, combined electromagnetic and TEM studies on four flux-grown bicrystals have demonstrated a direct correlation between the length scale of the boundaries’ saw-tooth facet configurations and the apparent length scale of the electrical heterogeneity. In that work, enhanced critical current densities are observed at applied fields where the facet period is commensurate with the spacing of the Abrikosov flux vortices which must be pinned if higher critical current density values are recorded. To understand the microstructural origin of the flux pinning, the grain boundary topography and grain boundary dislocation (GBD) network structure of [001] tilt YBCO bicrystals were studied by TEM and HRTEM.

Toward living nanomachines

2018 ◽  
Author(s):  
Christof Mast ◽  
Friederike Möller ◽  
Moritz Kreysing ◽  
Severin Schink ◽  
Benedikt Obermayer ◽  
...  
Keyword(s):  
Molecular Evolution ◽  
Thermal Gradient ◽  
Molecular Level ◽  
Minimal System ◽  
Thermal Gradients ◽  
Temperature Oscillations ◽  
Fluid Convection ◽  
Inanimate Matter ◽  
High Concentrations ◽  
Periodic Temperature

How does inanimate matter become transformed into animate matter? Living systems evolve by replication and selection at the molecular level and this chapter considers how to establish a synthetic, minimal system that can support molecular evolution and thus life. Molecular evolution cannot be explained by starting with high concentrations of activated chemicals that react toward their chemical equilibrium; persistent non-equilibria are required to maintain continuous reactivity and we especially consider thermal gradients as an early driving force for Darwinian molecular evolution. The temperature difference across water-filled compartments implements a laminar fluid convection with periodic temperature oscillations that allow for the melting and replication of DNA. Simultaneously, dissolved molecules are moved along the thermal gradient by an effect called thermophoresis. The combined result is an efficient molecule trap that exponentially favors long over short DNA and thus maintains complexity. Future experiments will reveal how thermal gradients could actively drive the Darwinian process of replication and selection.

scholarly journals Improved critical current densities in MgB2 tapes with ZrB2 doping

2006 ◽  
Vol 89 (13) ◽  
pp. 132510 ◽  
Author(s):  
Xianping Zhang ◽  
Zhaoshun Gao ◽  
Dongliang Wang ◽  
Zhengguang Yu ◽  
Yanwei Ma ◽  
...  
Keyword(s):  
Critical Current ◽  
Current Densities

Extraction of anisotropic critical current densities and flux pinning potentials

Cryogenics ◽  
1994 ◽  
Vol 34 (4) ◽  
pp. 329-334
Author(s):  
H.L Ji ◽  
Z.X Shi ◽  
Z.Y Zeng ◽  
X Jin ◽  
H.C Fan ◽  
...  
Keyword(s):  
Critical Current ◽  
Flux Pinning ◽  
Current Densities
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