Novel nano-composite bulk superconductors for high field engineering applications

Lead Research Organisation: University of Cambridge
Department Name: Engineering

Abstract

Multi-specimen combinations of large, melt processed YBCO single grains of 25 mm diameter have been shown to trap stable magnetic fields as high as 17 T at 29 K in research-grade samples, which are simply not achievable in conventional iron-based permanent magnets (limited practically to less than ~ 1.5 T). Unfortunately, achieving and maintaining a bulk, superconducting device operating temperature of less than 65 K is difficult from a practical point of view and not particularly cost-effective. It is necessary, therefore, to develop materials with improved flux pinning (and hence field trapping) properties that can be fabricated economically for deployment in industrial applications based either on cryo-cooler technology, or on systems that use liquid nitrogen as a cryogen (boiling point, 77 K). Large single grains can be incorporated directly into existing sustainable engineering applications such as flywheels, magnetic bearings, permanent magnets for MRI/NMR, non-contact magnetic stirrers for high purity biological solutions and magnetic separators provided they can trap at least 2.0 T at 77 K. The closer the operating temperature to the transition temperature of the large single grain (typically ~ 90 K), however, the greater the requirement for effective artificial flux pinning centres in the large grain microstructure that prevent the motion of magnetic flux within the sample. The optimum size of such pinning centres is typically around a few nano-metres at 77 K. The most common method of introducing pinning centres into large YBCO grains involves engineering the size of Y2BaCuO5 (Y-211) phase inclusions in the bulk microstructure, which are produced as part of the Y-123 peritectic decomposition process during melt processing. The technique is limited fundamentally, however, by the tendency of Y-211 particles to ripen at elevated temperature, which conflicts directly with attempts to refine their size to the nano-scale. This results inevitably in a significant reduction in control of the melt process, and hence to limitations in sample performance. The PI has been involved in two important recent developments of the processing of large grain (RE)BCO superconductors. These are the development of a suitable non-211 phase that forms effective nano-scale artificial flux pinning centres, and in the development of an entirely new type of seed crystal that enables every member of the (RE)BCO class of materials to be grown in the form of large single grains by a practical techniques for the first time. The primary objective of this highly challenging project, therefore, is to fabricate mechanically stable, large, state of the art samples of single grain YBCO and other (RE)BCO melt processed superconductors than has been possible previously that contain novel (i.e. non Y-211-based), effective nano-scale artificial flux pinning centres by a practical processing technique. This will enable for the first time the cost-effective application of bulk superconductors in sustainable engineering devices that operate at, or around, 77 K. Additional objectives of this challenging proposal are to fabricate complex-shaped, new nano-phase composites for be-spoke applications for the first time using a novel multi-seeding technique, also underdevelopment at Cambridge by the PI, and to establish for the first time an effective recycling process for multi-grain samples. The project will involve extensive collaboration with four Cambridge science departments (Engineering, Materials Science, Physics and Chemistry) and with three international institutions (ATI Vienna, ICMAB Barcelona and the Boeing Company Seattle).

Planned Impact

The outcome of the project will be the availability of cost-effective technology for the fabrication of superconducting nano- composites in the form of large bulk grains that can carry high currents for direct application to a wide range of sustainable engineering devices. The impact of this project would be significant for both industry and academia world- wide, including commercial and government sectors of the various communities. The following institutions and application areas will benefit directly from this project: 1. UK and European engineering industries involved in the manufacture of stable magnetic bearings, flywheel energy storage systems, high field permanent magnet devices and magnetic ore separation units; 2. Medical applications: Potential magnets for designing portable MRI or NMR scanners; 3. Motors and generators: High efficiency, compact, iron-free devices for large-scale applications; 4. Researchers working on magnetic and transport properties, solidification and phase kinetics of various (RE)BCO and other HTS; 5. The defence industry: the development of transportable, high-energy storage devices with a high power output has significant potential for battle-field applications; 6. The wider public: Bulk materials provide a graphic demonstration of superconductivity leading to increased awareness of an emerging technology. Increasing awareness of the need to develop sustainable engineering devices over the past few years has brought research on high temperature superconductors to the forefront of many international communities, including the USA, Japan, PR China and South Korea. This has involved policy makers within these countries both at the local level and across countries and continents to formulate practical collaborative projects (e.g. between PR China and South Korea, Japan and the USA and PR China and Europe). These potential impacts are hugely important, and it is essential to establish a capability in the short term if full domestic benefit is to be obtained (currently there is no government-funded research in bulk (RE)BCO in the UK). Government agencies have a potential interest in applications of bulk HTS to defence, in particular, which increases the profile of these materials significantly. The development of state of the art bulk (RE)BCO superconductors has potential to contribute significantly to global wealth and that of the UK, in particular. Some estimates put the potential market at 5 billion Euro (http://www.conectus.org/flyer.html), of which bulk materials can be reasonably expected to contribute 500 million euro in the short to medium term. The efficiency benefits of bulk HTS technology offer a clear potential benefit to the economic competitiveness of the UK. Established applications such as MRI, which already utilize low temperature superconducting materials, will benefit from the availability of high, stable fields at 77 K, which will enhance directly the quality of life. The PI will communicate the potential of the emerging technology widely with the interested communities, in collaboration with the project partners. This will have indirect benefit to employers within the energy generating industry. Collaboration arrangements are already in-place with the Boeing Company, which is currently developing a number of sustainable devices that incorporate bulk superconductors on an industrial scale, including energy storage flywheels. The materials developed as part of this project will be exploited via two existing patents, under Cambridge ownership. These will protect the background knowledge and enabling IPR. The PI and the Cambridge group has an excellent track record in the field of bulk superconductors, which will maximize the chances of success of the very challenging and relatively high risk project.

Publications

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Shi Y (2013) A Comparison of 0°-0° and 45°-45° bridge-Seeded, YBCO single grains in Journal of the American Ceramic Society

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Shi Y (2011) A simple method for recycling GdBCO-Ag single grain bulk superconductors in Superconductor Science and Technology

 
Description • A new route to synthesise powders (Y123 and Y211) used for fabricating superconducting single grains has been developed. Carbon nano-tubes have been used as templates in fabricating Y123 and Y211 precursor powders in solution for the first time. The trapped field of an YBCO single grain, 16 mm in diameter, fabricated using nano Y211 powder was a world record.
• A new arrangement of seeds in a novel multi-seeding process has been developed to increase the current flow across the grain boundaries. 0°-0° and 45°-45° oriented bridge seeds of different lengths have been employed to multi-seed YBCO grains. The superconducting properties were measured and the sample microstructures were analysed using SEM and optical microscopy. The results show that the 45°-45° seeds arrangement is superior to that of 0°-0° in the multi-seeding process.
• A world record of trapped field in bulk MgB2 of >3 T, at 20 K has been achieved. The MgB2 sample was hot-pressed using optimized parameters.
• Simple methods to recycle YBCO and GdBCO-Ag grains have been developed. Failed GdBCO-Ag samples can now be recycled using a capping pellet of the same composition as the starting powder. The trapped field of the recycled single grain can be as high as 80% of that fabricated using the original precursors.
• Hardness tests have been performed to determine the mechanical properties of (RE)BCO single grains used for high field applications. Systematic tests have been carried out on single grains of YBCO, YBCO-Ag, GdBCO, GdBCO-10%Ag and GdBCO-15%Ag at room temperature and 77 K, respectively. The results show that hardness can be used as a easy and quick method to assess the mechanical properties of superconducting single grains used in high field.
• Single grains containing novel 2411(M) pinning centres have been fabricated. The addition of the Y-2411(M) phase to the precursor composition complicates the melt-processing of single grains. We investigated and compared the growth rate of single YBCO grains containing Y-2411(Bi) phase inclusions and Y2O3. The superconducting properties of these large single grains have been measured specifically to investigate the effect of Y2O3 on broadening the growth window of these materials (which is important for the continued development of a practical melt process).
• A comprehensive modelling framework has been developed to simulate various magnetisation processes of bulk HTS, including pulsed field magnetisation (PFM) techniques. With this tool, magnetisation using a novel split-coil arrangement, developed in collaboration with the University of Oxford, can be studied thoroughly. The geometrical conditions for designing an effective split-coil arrangement have been established, and the mechanisms of a split-coil magnetisation process, which consist of two distinct regimes of flux penetration, are now understood.
Exploitation Route Bulk superconductor demonstration kits primarily for schools and a levitation platform have been developed as part of the project. GdBCO-Ag single grains have been used in fly wheels for energy storage and MgB2 will be used potentially in future applications of MRI. Bridge seeding may help develop multi-seeding technique and basic theoretical reseach.
Sectors Energy

URL http://www-g.eng.cam.ac.uk/bulk_sucon/index.php
 
Description A new arrangement of seeds in a novel multi-seeding process had been developed to increase the current flow across the grain boundaries in EP/H049657/1. This technique has been further developed in current running EP/K02910X/1. A buffer aid bridge seeding technique, which combines bridge seeding and the newly developed buffering technique, is now used to fabricate multi-seeded YBCO and GdBCO-Ag bulk samples. Buffers, which are sintered thin pellets, have replaced long bridge seeds cut from single SmBCO single grains. The complicated and time consuming process of making bridge seeds is now not needed. Most importantly, multi-seeded YBCO and GdBCO-Ag quasi-single grains up to 31 mm in diameter have been fabricated successfully. The simple methods for recycling failed YBCO and GdBCO-Ag grains developed in EP/H049657/1 has been renewed with a generic reliable recycling technique for any (RE)CO-Ag systems (RE = Sm, Gd and Y) by replenishing the liquid phase lost during the primary growth process. The success rate of this method on batch recycling is close to 90%. The superconducting property, trapped field, of the recycled samples has reached 70% of the values of the samples in primary growth. This technique is use in helping recycling failed samples from Adelwitz Technologiezentrum GmbH (ATZ).
First Year Of Impact 2010
Sector Environment
Impact Types Economic

 
Description Novel, multi-­seeded bulk superconductors for sustainable engineering applications
Amount £472,525 (GBP)
Funding ID EP/K02910X/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 11/2013 
End 10/2016
 
Description Atominstitut der Oester Universitaet 
Organisation Vienna University of Technology
Department Institute of Atomic and Subatomic Physics (Atominstitut)
Country Austria 
Sector Academic/University 
Start Year 2004
 
Description Boeing-Cambridge collaboration 
Organisation Boeing
Country United States 
Sector Private 
PI Contribution The contribution was part of an on-going collaboration on the development of bulk superconductors for applications. We have transferred processing technology to Boeing and have provided bulk superconductors for incorporating in a flywheel energy storage device by Boeing.
Collaborator Contribution Boeing developed the flywheel system that incorporates our samples.
Impact The further development pf the Boeing energy storage flywheel.
 
Description IFW Desden 
Organisation Leibniz Association
Department Leibniz Institute for Solid State and Materials Research
Country Germany 
Sector Academic/University 
Start Year 2004
 
Description Slovak Academy of Science 
Organisation Slovak Academy of Sciences
Country Slovakia 
Sector Public 
Start Year 2004
 
Description University of Liege 
Organisation University of Liege
Country Belgium 
Sector Academic/University 
Start Year 2004