Materials Science Forum Vol. 721

Abstract: Superconducting (SC) and mechanical properties of spark plasma (or SPS) produced MgB₂ –based materials allow their efficient applications in fault current limiters, superconducting electromotors, pumps, generators, magnetic bearings, etc. The synthesized from Mg and B at 50 MPa, 1050 °C for 30 min material has a density of 2.52 g/cm³, critical current density, j_c = 7.1•10⁵ A/cm² at 10 K , 5.4 •10⁵ A/cm² at 20 K, and 9•10⁴ A/cm² at 35 K in zero magnetic field; at 20 K its field of irreversibility B_irr(20)=7 T and upper critical field B_c2(20)=11 T; microhardness H_V=10.5 GPa and fracture toughness K_1C =1.7 MPa•m^1/2 at 4.9 N-load. SPS-manufactured in- situ MgB₂-based materials usually have somewhat higher jc than sintered ex-situ. The pressure variations from 16 to 96 MPa during the SPS-process did not affect material SC characteristics significantly; the j_c at 10-20 K was slightly higher and the material density was higher by 11%, when pressures of 50-96 MPa were used. The structure of SPS-produced MgB₂ material contains Mg-B-O inclusions and inclusions of higher borides (of compositions near MgB₄, MgB₇, MgB₁₂, MgB₁₇, MgB₂₀), which can be pinning centers. The presence of higher borides in the MgB₂ structure can be revealed by the SEM and Raman spectroscopy.

Abstract: This paper presents the design of a novel high speed propulsion system for UAQ4 magnetic levitating train, the feasibility of which has been successfully tested and confirmed in laboratory. A direct-current linear stepper motor that uses permanent magnets distributed on the central beam of track as the stator and the direct current power supplied coils on-board the vehicle as the rotor is proposed and analyzed. The motor performances are evaluated by varying the system parameters by carrying out a finite element numerical model refined with experimental data. The main components of a real scale motor with speed up to 580 km/h for the UAQ4 train application is measured and discussed.

Abstract: The paper presents the results of our experiments with novel devices, which may open a new path for advanced applications by using continuous, perfectly closed superconducting YBCO loops. With this solution we wanted to examine whether it is possible to create novel fault current limiter, 3-phase self-limiting transformer. We considered the significance and efficiency of the perfect closed loop made from YBCO wire. The used superconducting wire was produced at SuperPower, Inc. in New York, USA. Type: SF 12050.

Abstract: A complete solution is presented for the boundary value problem of two perfect conductor spheres in a uniform magnetic field of arbitrary orientation. Expressions are given for the scalar magnetic potential and for the field intensity. They can readily be applied for calculating the forces between the spheres. Benchmark numerical results of specified accuracy are generated, which are also useful for validating various approximate numerical methods.

Abstract: The results of experimental study of the critical current and AC losses in high pressure-synthesized MgB₂ bulk superconductors are presented. The method is based on the use of the transformer configuration and suitable for samples in the form of hollow superconducting cylinders and rings. It was shown that the critical current measured by the transformer method is an order of magnitude lower than the value given by the magnetization technique. The obtained dependencies of the losses on current and frequency reveal the deviations from the critical state model behavior and reflect structural peculiarities of the investigated MgB₂ samples.

Abstract: A coupled thermal electromagnetic finite element analysis has been used to numerically simulate the electromagnetic characteristics of an MgB2 SMES coil. Magnetic field distribution data and current density predictions of the numerical model were compared with the literature and with the superconducting properties of explosively consolidated MgB2 samples measured experimentally. The material Jc characteristics were determined by applying Bean’s critical state model on the material magnetisation measurements conducted on a superconducting quantum interference device (SQUID).

Abstract: M-Heff full curves up to 19T for the permanent magnets composed of Nd-Fe-B were very precisely observed by using specially designed magnetizer. The pulsed magnetic field directions were safely reversed with the same coil-end to ground side of coil positive and negative field directions. The coercivity enhancements were observed by 15% in high pulsed field applications.

Abstract: We shown that by means of the two pulse sequence, the spin system of a liquid entrapped into nanosize cavities can be prepared in quasi-equilibrium states of high dipolar order. Then the dipolar order relaxes to thermal equilibrium with the lattice with a relaxation time T1d. It was shown that large number of spins T1d increases as the square to the concentration of the molecules C and decreases as inverse of the number of spins, T1d - C²/N. Study of spin lattice relaxation of dipolar energy in a spin system under the bounded region is important for extracting very useful parameter characterized nanomaterials from NMR experimental data.

Abstract: Recently, progress of the intelligent materials plays a big role in development of science and technology. We have ever tried to develop ferromagnetic shape memory alloys to expand application range of the common non-magnetic shape memory alloys, which are typical intelligent material. However the saturation magnetization and the shape memory effect were in a relation of trade-off, so we couldn’t get a good result. In this research, we tried to develop ferromagnetic shape-memory alloys as a composite material by using the single-roll melt spinning technique. They are bilayer ribbons, which have both shape memory layer and magnetic layer.