Novel nano-composite bulk superconductors for high field engineering applications

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).

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.