was formed around the conductor in a solgel process. Reportedly,4 this technique improved the wire quality and lifted its thermal index to 280ºC; which exceeds the 240ºC index of conventional enamelled wire. The nanoparticle technology with magnetic (like Fe2O3) or functional particles (TiO2, CeO2, BaTiO3, CaCO3) uses various tailored chemical processes that avoid the disadvantages of agglomerates, donor enrichment and small molecule surface modifications. In this context it is important to mention that there are a number of reports on attempts to achieve “squeaky clean” nano wire, which does not collect water, oils or dust particles. The potential exists to extend the life time of coils and cores for motors and magnets in this way, utilizing a firing process for the wire surface. See Fig. 3. The metal powders with high conductivity (Cu, Ni, Al or Au) are used in extrusion compounds, conductive pastes, fillers and tapes in cable applications. Conventionally obtained by a crushing process, these powders are usually irregularly shaped, or flaked, and of non-uniform size. The semiconductive insulation layers for power cable design are used to “round up” interstices of the copper conductor in order to achieve a uniform electric field in the insulator. When the metal powders are applied to gain the required conductivity, it is necessary to either increase the overall volume of metal powder or use a more costly material such as silver. As a countermeasure, a uniformsized nanopowder (particle size: 200 nm or smaller) with an established method of fabrication, has been produced. This powder also finds applications in multi-layered structures, ceramic capacitors, electronic equipment and nano-imprinting technology for making circuits of submicron-wide wiring. Conductive nano-paste will be used in printing technology and also for applications to build up superconductor structures. Various smart mechanisms for parallel orientation of nanoparticles for improved barrier properties (i.e. gas and water) have been considered. The industry has developed a technology to produce magnetic powders with a particle size of several tens of nm. When a magnetic metal (such as nickel) is fabricated into nano-sized powder, each particle functions as a mini-magnet and forms chain-like structures. Also, heat conductivity toward a specific direction can be improved by aligning chain-like powders in that direction.
Using nanopowders in conductive layers, tapes or paste gives much lower resistance than with conventional methods. This means that the same resistance can be fabricated with less polymer volume allowing miniaturization and material savings. Superconductivity Diamagnetic materials with the unique ability to conduct electrical current with little or no resistance below a certain critical temperature are closely related to achievements in NT. The discovery of so called YBCOs ceramic-based High Temperature Superconductors (HTS) during the 1980s opened the possibility to achieve the superconducting state at temperatures of liquid nitrogen (77K), rather than the liquid helium required by the low temperature superconductors (4K). Applying this technology in power distribution networks and high field magnets, small motors, generators and magnetic levitation trains now become a reality. Using innovative DT (deformation texturing) technology, superconductor tape may carry over 1000 A/cm2 current level. There are basically three components in what is called the coated superconductor tape, namely the metal substrate (typically 25-50 μm thick nickel or Ni-based alloy produced by DT), followed by deposition of buffer layer and the superconducting YBCO or bismuth layer (produced by sol-gel and MOCVD). Many problems in superconductivity have been overcome through NT progress. A film that supports very high super-currents can now be grown in suitable lengths. Wires can be made by packing a bismuth-based superconductor into silver tubes which are then heated and rolled to make a more uniform microstructure. These wires are already used as current leads for ultra-cold superconducting magnets, much reducing the refrigeration power required. Science has gone well beyond stage one and two: finding the right material and checking out properties. Good progress is being made on stage three with some working installed lines starting to appear. But the critical stage four–integrating the HTS into working system–is still in its infancy. Extensive R&D efforts related to those materials and nano-processing of the tape technology are underway in the U.S., Europe and Asia.
text. Also, with respect to company ELKA and cable experts, now in retirement: .Juraj Trzec, Branko Paic and Rudolf Feis. References 1. D.R Lide, CRC Handbook of Chemistry and Physics, 1994 Edition. 2. J. F. Shackelford, Introduction to Materials Science for Engineers, Fourth Edition, 96. 3. V. Balzani, M.Venturi and A.Credi, “Molecular Devices and Machines,” WileyVCH 2003. 4. K. Suzuki, et al., “New Heath Resistant Magnetic Wire: Polyimide Silica Hybrid Enamelled Wire,” Hitachi Cable Review, No. 20, August 2001. 5. R. B. Greed, et al., “Microwave Applications of HT Superconductors,” GEC Review, Vol. 14, No. 2, 1999. 6. DTI Review of the UK National Program: “Superconductivity,” Jan. 1991. 7. G. Beyer, “Carbon nanotubes - a new class of flame retardants for polymers,” C & Wire Technology, Feb, 2001. 8. J. Grosman, New Generation of Nanocomposites for Thermoplastic Polymers, Oct 2004, Presentation for K2004, Düsseldorf. 9. H. Cizmic, HVDC vs HVDS: It’s all Down to Cable Design, W&C Technology International, Jan/Feb 2006. ■
Acknowledgement The author wishes to thank Grant Fry, nanotech enthusiast, for proof reading the MARCH 2007 199