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Superconducting cables with a new twist
RESEARCH NEWS
Superconducting cables with a new twist ELECTRONIC MATERIALS
Power transmission efficiency and lowinductance magnet applications could be significantly improved by bundling high-temperature superconductor cables. Unfortunately, cabling techniques used so far have led either to fragile cables that are flexible, or robust cables that are stiff. US researchers have now shown that it is possible to create mechanically robust and flexible superconducting cables by making the cables from a conductor coated with a high-temperature superconductor. The cables, developed by researchers at the University of Colorado and the National Institute of Standards and Technology, both in Boulder, Colorado, can be made much thinner and more flexible than demonstration cables used in the electric power grid [van der Laan et al., Supercond Sci Technol (2011) 24, 042001; doi:10.1088/0953-2048/24/4/042001]. In work supported by the US Department of Energy, the Boulder team has wound multiple HTS-coated conductors around a multi-strand copper core, with superconducting layers of “GdBa2Cu3O7-δ” forming spirals in alternating directions. Although the prototype cables are wound by hand, several manufacturers say mass production is feasible.
Cross-section of a 7.5 mm high-temperature superconducting cable with a copper core and nylon and plastic insulation. Credit: Xifeng Lu/NIST.
The single most innovative step in producing these compact cables is in their tolerance for compressive strain, which allowed the team to use an unusually slender copper core. One prototype superconducting cable is just 6.5 mm in outer diameter but can carry 1200 A, while a second cable 1 mm thicker can sustain a current of more than twice that, at 2800 A at a
temperature of 76 K. Conventional electrical transmission cables operate at below 1000 A, but these newly wound cables are a tenth of the diameter of the demonstration superconducting cables tested so far. For example, a three-phase cable installed in Columbus, Ohio, uses bismuth-strontium copper oxide tapes wound around a large core to form a 70 mm cable that can carry an average current of 3000 A at 73 K. NIST researchers are now developing prototype compact HTS cables for the military, which require small size and light weight, as well as the flexibility to pull transmission lines through conduits with tight bends. Tests on the new cables showed them to potentially have a bend radius of just 125 mm. Besides power transmission, the flexible cabling concept could be used for superconducting transformers, generators, and magnetic energy storage devices that require high-current windings. The compact cables might be used in high-field magnets for medical applications such as next-generation magnetic resonance imaging and proton cancer treatment systems, and perhaps even in fusion reactors. David Bradley
Dyeing silk BIOMATERIALS New research into intrinsically colored and luminescent silk could provide a cost-effective and environmentally friendly approach to producing a new class of functional silk, as well as offering a better understanding of the effect of molecular properties on the biological incorporation of various molecular materials into silk fibroin. This is the first study that demonstrates how the coloration in silk from silkworms fed on a dyecontaining diet is due to the uptake of dye in the fibroin, a type of protein created by silkworms when making silk. This novel method for dyeing silk may also help bring about the large-scale production of new biomaterials that have added functionalities. Silk, with its softness, lustrousness and strength, has been widely applied as a biomaterial, used in suturing for thousands of years, and also more recently as tissue engineering scaffold. In most applications, the utility of silk is greatly enhanced by adding other
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substances into the core silk filament, fibroin, so this study was keen to identify a simple and effective method of incorporating functional materials into silk, using dyes as model compounds. Traditionally, when silk products are finished, the color is added by carrying out a dyeing process on the fibroin, including the removal of excess dye molecules and restoring properties that were affected by the dyeing. However, this research shows how an in vivo uptake of dyes into domesticated silkworms can lead to the direct production of intrinsically colored silk by the silkworms. The paper, published in Advanced Materials [Tansil et al., Adv Mater (2011) doi: 10.1002/ adma.201003860], points out that “The biological incorporation of dyes into silk fibroin is a greener method of producing colored silk because it eliminates the need for an external dyeing process, along with the resources (water, energy, additional chemicals) and post-treatments associated with it.”
APRIL 2011 | VOLUME 14 | NUMBER 4
A number of different fluorescent dyes were used as model compounds to investigate their selective uptake into fibroin or sericin through fluorescence imaging and spectroscopic quantification. The team hopes that the incorporation of other functional molecules into silk to yield novel silk materials will also be possible in the future. This work could lead to novel functional biomaterials, such as silk materials that contain stimuli-sensitive dyes and various drugs that can be added to produce wound dressings with monitoring or sensing features. Also, antibacterial, anticoagulant or anti-inflammatory agents can be added to tissue engineering scaffolds to result in better performance. The team hopes to work with a range of commercial partners to test the color fastness of the silk yarns, and also investigate the scale-up and implementation of the method in largescale silk farms.
Laurie Donaldson
Superconducting cables with a new twist ELECTRONIC MATERIALS
Power transmission efficiency and lowinductance magnet applications could be significantly improved by bundling high-temperature superconductor cables. Unfortunately, cabling techniques used so far have led either to fragile cables that are flexible, or robust cables that are stiff. US researchers have now shown that it is possible to create mechanically robust and flexible superconducting cables by making the cables from a conductor coated with a high-temperature superconductor. The cables, developed by researchers at the University of Colorado and the National Institute of Standards and Technology, both in Boulder, Colorado, can be made much thinner and more flexible than demonstration cables used in the electric power grid [van der Laan et al., Supercond Sci Technol (2011) 24, 042001; doi:10.1088/0953-2048/24/4/042001]. In work supported by the US Department of Energy, the Boulder team has wound multiple HTS-coated conductors around a multi-strand copper core, with superconducting layers of “GdBa2Cu3O7-δ” forming spirals in alternating directions. Although the prototype cables are wound by hand, several manufacturers say mass production is feasible.
Cross-section of a 7.5 mm high-temperature superconducting cable with a copper core and nylon and plastic insulation. Credit: Xifeng Lu/NIST.
The single most innovative step in producing these compact cables is in their tolerance for compressive strain, which allowed the team to use an unusually slender copper core. One prototype superconducting cable is just 6.5 mm in outer diameter but can carry 1200 A, while a second cable 1 mm thicker can sustain a current of more than twice that, at 2800 A at a
temperature of 76 K. Conventional electrical transmission cables operate at below 1000 A, but these newly wound cables are a tenth of the diameter of the demonstration superconducting cables tested so far. For example, a three-phase cable installed in Columbus, Ohio, uses bismuth-strontium copper oxide tapes wound around a large core to form a 70 mm cable that can carry an average current of 3000 A at 73 K. NIST researchers are now developing prototype compact HTS cables for the military, which require small size and light weight, as well as the flexibility to pull transmission lines through conduits with tight bends. Tests on the new cables showed them to potentially have a bend radius of just 125 mm. Besides power transmission, the flexible cabling concept could be used for superconducting transformers, generators, and magnetic energy storage devices that require high-current windings. The compact cables might be used in high-field magnets for medical applications such as next-generation magnetic resonance imaging and proton cancer treatment systems, and perhaps even in fusion reactors. David Bradley
Dyeing silk BIOMATERIALS New research into intrinsically colored and luminescent silk could provide a cost-effective and environmentally friendly approach to producing a new class of functional silk, as well as offering a better understanding of the effect of molecular properties on the biological incorporation of various molecular materials into silk fibroin. This is the first study that demonstrates how the coloration in silk from silkworms fed on a dyecontaining diet is due to the uptake of dye in the fibroin, a type of protein created by silkworms when making silk. This novel method for dyeing silk may also help bring about the large-scale production of new biomaterials that have added functionalities. Silk, with its softness, lustrousness and strength, has been widely applied as a biomaterial, used in suturing for thousands of years, and also more recently as tissue engineering scaffold. In most applications, the utility of silk is greatly enhanced by adding other
130
substances into the core silk filament, fibroin, so this study was keen to identify a simple and effective method of incorporating functional materials into silk, using dyes as model compounds. Traditionally, when silk products are finished, the color is added by carrying out a dyeing process on the fibroin, including the removal of excess dye molecules and restoring properties that were affected by the dyeing. However, this research shows how an in vivo uptake of dyes into domesticated silkworms can lead to the direct production of intrinsically colored silk by the silkworms. The paper, published in Advanced Materials [Tansil et al., Adv Mater (2011) doi: 10.1002/ adma.201003860], points out that “The biological incorporation of dyes into silk fibroin is a greener method of producing colored silk because it eliminates the need for an external dyeing process, along with the resources (water, energy, additional chemicals) and post-treatments associated with it.”
APRIL 2011 | VOLUME 14 | NUMBER 4
A number of different fluorescent dyes were used as model compounds to investigate their selective uptake into fibroin or sericin through fluorescence imaging and spectroscopic quantification. The team hopes that the incorporation of other functional molecules into silk to yield novel silk materials will also be possible in the future. This work could lead to novel functional biomaterials, such as silk materials that contain stimuli-sensitive dyes and various drugs that can be added to produce wound dressings with monitoring or sensing features. Also, antibacterial, anticoagulant or anti-inflammatory agents can be added to tissue engineering scaffolds to result in better performance. The team hopes to work with a range of commercial partners to test the color fastness of the silk yarns, and also investigate the scale-up and implementation of the method in largescale silk farms.
Laurie Donaldson