Novel nano-composite bulk superconductors for high field engineering applications

经熔融处理的直径为25 mm的YBCO大颗粒的多个样品组合在研究级样品中可以捕获在29K时高达17T的稳定磁场，这在传统的铁基永磁体(实际上限制在~1.5T以下)中是无法实现的。不幸的是，从实用的角度来看，实现并维持一个整体超导设备的工作温度低于65K是困难的，而且不是特别划算。因此，有必要开发具有改进的磁通钉扎(从而场俘获)性能的材料，这种材料可以经济地制造出来，用于工业应用，无论是基于低温制冷机技术，还是基于使用液氮作为制冷剂的系统(沸点，77K)。大单晶可直接应用于现有的可持续工程应用中，如飞轮、磁轴承、用于磁共振/核磁共振的永磁体、用于高纯度生物溶液的非接触式磁搅拌器和磁选机，前提是它们能在77K下捕获至少2.0T。在77K下，这种钉扎中心的最佳尺寸通常在几个纳米左右。将钉扎中心引入大的YBCO颗粒的最常见方法是在块体组织中设计Y2BaCuO5(Y-211)相夹杂物的尺寸，这是熔体加工过程中Y-123包晶分解过程的一部分。然而，这项技术从根本上受到了Y-211粒子在高温下成熟的趋势的限制，这与将其尺寸细化到纳米级的尝试直接冲突。这不可避免地导致熔融过程控制的显著减少，从而限制了样品的性能。PI参与了大颗粒(RE)BCO超导体加工的两个重要发展。这些都是开发合适的非211相，形成有效的纳米级人工磁通钉扎中心，以及开发一种全新类型的种子晶体，使(RE)BCO类材料的每个成员首次能够通过实用技术以大单晶的形式生长。因此，这个极具挑战性的项目的主要目标是通过实用的加工技术制造机械稳定的、大的、最先进的单晶YBCO和其他(RE)BCO熔融处理的超导体样品，其中包含新的(即非Y-211基)、有效的纳米级人工磁通钉扎中心。这将首次使块状超导体在77K或左右运行的可持续工程设备中具有成本效益的应用。这项具有挑战性的提案的其他目标是首次使用一种新的多晶种技术制造用于辐条应用的复杂形状的新型纳米相复合材料，该技术也是国际电工研究所正在开发的，并首次建立了一种有效的多颗粒样品回收工艺。该项目将涉及与四个剑桥科学系(工程系、材料科学系、物理系和化学系)以及三个国际机构(ATI维也纳、巴塞罗那国际人与生物圈计划和西雅图波音公司)的广泛合作。

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).