Imperfection of microstructural control in MgB 2 superconducting tapes fabricated using an in-situ powder-in-tube proces
- PDF / 1,621,227 Bytes
- 8 Pages / 595.276 x 790.866 pts Page_size
- 84 Downloads / 180 Views
Imperfection of microstructural control in MgB2 superconducting tapes fabricated using an in-situ powder-in-tube process: toward practical applications S. Hata • H. Sosiati • Y. Shimada • A. Matsumoto K. Ikeda • H. Nakashima • H. Kitaguchi • H. Kumakura
•
Received: 4 April 2012 / Accepted: 17 September 2012 / Published online: 28 September 2012 Ó Springer Science+Business Media New York 2012
Abstract MgB2 is a promising superconductor for future applications to superconduct wires and tapes used at the liquid hydrogen temperature (20 K). Because the maximal superconducting current (critical current) in MgB2 depends on its microstructure, an ‘‘in-situ’’ process to fabricate MgB2 based on a reaction between Mg and B is effective in controlling the microstructure. However, the critical current in the fabricated MgB2 wires and tapes is not sufficiently high for practical use. This may be attributed to the imperfectness of the microstructural control in MgB2 wires and tapes. In this paper, we will discuss the microstructural features of MgB2 tapes fabricated using a typical in-situ powder-in-tube process. By observing the early stage of microstructural evolution in detail, we can gain insights into the next strategy for improving the microstructure of MgB2 tapes with respect to their applications.
Introduction An MgB2 superconductor discovered in 2001 [1] is one of the promising materials for future superconducting wire applications. This material has several properties that are advantageous from the viewpoint of practical use: a simple S. Hata (&) Y. Shimada K. Ikeda H. Nakashima Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan e-mail: [email protected] H. Sosiati Nanomaterials Research Group, LPPT, Gadjah Mada University, Yogyakarta 55281, Indonesia A. Matsumoto H. Kitaguchi H. Kumakura National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
123
binary crystal structure; its superconducting transition temperature around 40 K that allows one to use liquid hydrogen (20 K) as a coolant instead of liquid helium (4.2 K); the superconducting current flow in a non-textured polycrystalline state unlike oxide superconductors such as Y–Ba–Cu–O; the superior values of the upper critical magnetic field required for high-field magnet applications [2]; the cost-effectiveness and light weight of the raw materials, Mg and B, etc. One can fabricate MgB2 wires using the following ex-situ process: fill a metal tube with MgB2 powder, and roll and heat the tube for the densification of the MgB2 compact inside it. However, the maximal (critical) superconducting current in the resultant MgB2 wire is not satisfactory for practical use. Because MgB2 is a type-II superconductor, its superconducting state remains even if the magnetic-flux lines penetrate MgB2, and the introduction of an appropriate microstructure in MgB2 to pin the flux lines can increase the critical current. Therefore, an in-situ process that uses a reaction between Mg
Data Loading...
