1,720,989 research outputs found
Magnetic relaxation of type-II superconductors in a mixed state of entrapped and shielded flux
No full textThe magnetic relaxation has been investigated in type-II superconductors when the initial magnetic state is realized with entrapped and shielded flux contemporarily. This flux state is produced by an inversion in the magnetic field ramp rate due to, for example, a magnetic field overshoot or undershoot. The investigation has been faced both numerically and by measuring the magnetic relaxation in BSCCO tapes. Numerical computations have been performed in the case of an infinite thick strip and of an infinite slab, showing a quickly relaxing magnetization in the first seconds. As verified experimentally, the effects of the overshoot (or the undershoot) cannot be neglected simply by cutting the first 10–100 s in the magnetic relaxation. On the other hand, at very long times, the magnetic states relax toward those corresponding to field profiles with only shielded flux or only entrapped flux, depending on the amplitude of the field change with respect to the full penetration field of the considered superconducting samples. In addition, we have performed numerical simu- lations in order to reproduce the relaxation curves measured on the BSCCO(2223) tapes; this allowed us to interpret correctly also the first seconds of the M(t) curves
Effects of impurities addition in MgB2/Nb tapes on flux jumps instability and critical current density
No full textIn order to understand the effect of impurities inclusions on the transport properties of MgB(2) tapes, by means of magnetization measurements we have analysed non-commercial monofilamentary tapes in which titanium (Ti), tungsten (W) and silicon carbide(SiC)normal particles were included. All the samples under analysis have the same cross section and heir MgB(2) filament is embedded in a superconducting niobium matrix. For all the tapes a magnetic field (H(a)) up to 65 kOe has been applied parallel to the filament, and we have compared their magnetization loops M (H(a)) measured in the temperature range from 2 K up to 30K. The results show that the process of adding normal particles in the material, in order to increase the transport properties, produces at low field opposite effects to those at higher field. Moreover, all the particles included produce the common result of an enhancement in the thermomagnetic instability, and consequently a decrease of the transport properties, at low temperature and magnetic fields
Crystal structures, magnetic and superconducting properties of the RuSr2NdCu2Ox and RuSr2GdCu2Oy compounds
No full textWe report the magnetization and the susceptibility measurements of the RuSr2GdCu2Oy and RuSr2NdCu2Ox perovskite materials. We find that RuSr2GdCu2Oy compound exhibits a magnetic transition at Tn = 135 K followed by a superconducting one with an onset Tc = 35 K. Samples of RuSr2NdCu2Ox material have shown neither a superconductivity nor a magnetic transition. XRD measurements show that in RuSr2NdCu2Ox the Nd ions tend to be substituted by Sr ions in very high percentages. The relevance of this phenomenon on the absence of superconductivity in RuSr2NdCu2Ox is discussed. © 2002 Elsevier Science B.V. All rights reserved
Numerical calculation of the critical state in superconducting tapes above the full penetration field
No full text
Ion-beam Sputtering for the surface modification of heterogeneous nanodispersed Catalysts
Full text linkInterface science is crucial for the development of new technologically advanced materials. In particular, this study shows that ion beam sputtering can be used as an effective technique for the controlled surface modification of solid heterogeneous catalysts. The surface properties of these nano materials can be tailored to enhance their catalytic performance leading to better resistance to aging and a reduction of the PGM loading. The technique has been applied on catalysts of relevant interest like the ones applied in the emission control (e.g. Pt/Ce0.7Zr0.3O2 catalyst). The effect of the different parameters of ion bombardment (type of ions, energy, doses) on the catalytic activity has been investigated. Modeling of the treatment has also been introduced to the describe erosion of the surface through ion sputtering and deeply understand the correlations between the parameters of the bombardment and the observed enhanced catalytic activity
- …
