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Nb-Based Superconductors
Published in David A. Cardwell, David C. Larbalestier, I. Braginski Aleksander, Handbook of Superconductivity, 2023
Gianluca De Marzi, Luigi Muzzi
If the pinning-force exponents are known or assumed, the flux pinning Equation B1.38 can be rearranged as: Jc1q∙B1-pq=-K1qBc2pq+1B+K1qBc2pq
c Conductors: The Alloy Nb–Ti
Published in David A. Cardwell, David C. Larbalestier, Aleksander I. Braginski, Handbook of Superconductivity, 2023
Lance D. Cooley, Peter J. Lee, David C. Larbalestier
Perhaps the ultimate manifestation of the artificial pinning centre concept is embodied in composites that use ferromagnetic pins. Because magnetism evolves from the interaction of electrons with aligned spins, it destroys the pairing of electrons with opposite spins associated with superconductivity. Therefore, superconductivity is suppressed completely within about 1 nm of the superconductor/ferromagnet interface. The flux-pinning force of a magnetic pin is thought to be close to the maximum possible pinning force, so very high critical current densities might be achieved. However, the pins must be widely separated to ensure that there are regions where superconductivity is unaffected by the pins, and this requirement limits the field range where ferromagnetic pins have maximum benefit. Several APC composites having Ni or Fe pins have been made [67, 70], and the best of these attains the highest bulk pinning force achieved at 4.2 K, 30 GN m−3, at 2 T field [57].
X-Ray Studies: Phase Transformations and Microstructure Changes
Published in David A. Cardwell, David C. Larbalestier, Aleksander I. Braginski, Handbook of Superconductivity, 2022
Christian Scheuerlein, M. Di Michiel
At the onset of detectability (at 540°C), the mean Nb3Sn crystallite size estimated from the Nb3Sn (200) peak width is about 60 nm. During the 700°C plateau, the average crystallite size increases from 110 nm to about 180 nm. At the same time, the Nb3Sn volume increases by about 35%, and the Nb3Sn lattice parameter increases from 5.3140 Å to 5.3156 Å. This indicates that the average Sn content increases by more than 1%, which in turn corresponds to a strong critical field Bc20 increase of 5 T [23]. At high magnetic field, such a strong Bc2 increase outweighs the reduction of flux pinning force due to the simultaneous Nb3Sn grains growth. Further increase in temperature and HT duration only slightly increases the Nb3Sn volume but has a detrimental influence on the Nb3Sn crystallite size, which results in limited Jc when flux pinning has a dominating influence.
Experimental Investigation of Bubble Oscillation and Leaping Driven by Thermocapillary Effects with Non-condensable Gas
Published in Heat Transfer Engineering, 2023
Ningxi Zhang, Daniel Orejon, Jionghui Liu, Khellil Sefiane
In Figure 16(a), when an oscillating bubble stops next to a stationary one the wall-characteristic temperature gradient at the oscillating bubble is at a minimum and left and right contact angles becomes of similar magnitude as the driving force is not enough to overcome bubble pinning to the wire. However, when Marangoni force is strong enough to overcome the main resistance to the motion the bubble then moves and oscillates along the wire. The contact line pinning force, is described by Eq. (6): where and is the advancing and receding contact angles (°) of the oscillating bubble respectively, is the surface tension and rb is the bubble base radius. In order to estimate the forces empowering the bubble motion, the rather small differences between advancing and receding contact angles were measured for each frame and the average values were used in the calculations.
An analytical model of grain growth considering the conjoint effects of precipitate pinning and solute drag in steel
Published in Philosophical Magazine Letters, 2022
A series of significant studies has been carried out on the pinning effect of second phase precipitate particle against grain boundary motion; especially by Zener [3], Hillert [4] and Gladman [5]. Taking into account the specific surface energy of the grain boundary and the size of the spherical precipitate particle, Zener [3] conceived the pinning force exerted by the particle with an analogy of surface tension. However, the resultant driving force appeared to be an overestimated one in Zener-model. Subsequently, Hillert [4] tried to correlate energy change and grain growth with a concept of critical radius beyond which the energy would tend to decrease. Accordingly, this approach found an application only in a situation where large grains tend to consume small grains, such as a situation in secondary recrystallisation. Furthermore, Gladman [5] came forward with a more detailed conceptualisation by at first formulating the energy changes accompanying the unpinning process and henceforth that for accompanying grain growth. Thereafter, these two aspects are combined to finally evaluate the overall energy change for grain growth and the critical radius initially conceptualised by Hillert [4]. However, this formulation proceeded towards a mathematical complicacy and the kinetics of grain growth in terms of grain size variation as a function of holding time could not be formulated analytically taking into account the precipitate pinning effect despite several subsequent attempts by other investigators [6–9].
Structural and electrical investigations of novel CdFeO/(Bi,Pb)-2212 superconductor composite
Published in Phase Transitions, 2022
S. Abbas, H. Basma, R. Awad, M.S. Hassan
Masnita et al. [14] have examined the influence of addition of antiferromagnetic FeS on the superconducting properties of Bi1.6Pb0.4Sr2CaCu2O8+δ (Bi-2212), where 0.00≤x ≤ 5.0 wt%. The powder X-ray diffraction (XRD) patterns showed that the Bi-2212 phase was optimal in samples for x ≤ 0.2 wt% (≥92% volume fraction). The highest zero resistivity temperature, Tc0 and onset temperature, Tc were 72 K and 83 K, respectively for the pure sample. The ac-magnetic susceptibility measurements revealed an increase in the flux pinning force for x ≤ 0.2 wt%. Whereas, the Bi-2212 phase showed a semiconducting-like behavior without any superconducting transition for x=5.0 wt%. Furthermore, Suazlina et al. [15] have investigated Bi-2223 superconductors doped with Fe2O3 at Cu-site. The doping of Fe does not support the formation of high Tc phase. The values of Tc and the critical current density Jc of the samples decrease with high doping concentrations. Regarding the XRD analysis, the volume fraction of the 2223 phases was reduced and the volume fraction of the 2212 phases was enhanced with the increase of Fe doping.