共查询到20条相似文献,搜索用时 15 毫秒
1.
W. M. Chen D. Q. Shi Y. C. Guo X. K. Fu H. K. Liu T. Silver S. X. Dou 《Journal of Superconductivity》2001,14(4):539-543
Three Ag sheathed Bi-2223 multifilamentary tapes were produced by a processing method that consists of two sintering treatments with an intermediate deformation, involving sandwich rolling (SR), pressing (P), or normal rolling (NR). The magnetic field dependence of the critical current density J
c was measured with the magnetic field H applied parallel to both the ab plane (H ab) and the c-axis (H c) of the Bi-2223 grains. Experimental results show that J
c of the pressed (P) tape (J
cP) for both H ab and H c is about 1.5–1.8 times higher than that for the NR tape (J
cNR) and the SR tape, although J
cSR is always larger than J
cP. The ratio of J
cSR/J
cNR for H c increases rapidly with the applied magnetic field and reaches a maximum of about 12 at 0
H 900 T. The calculated density of the pinning force F as a function of magnetic field shows that curves of F for SR, NR, and P tapes all have their maximum F
max at different magnetic fields and the magnitudes of F
max are also different from each other. The SR tape has the largest value of F
max, while NR has the smallest. XRD analysis shows that an intermediate deformation can destroy the grain alignment, and the larger the deformation, the worse the grain texture will be. Our experimental results, however, clearly show that J
c for Bi-2223 multifilamentary tapes is independent of grain alignment. The significant differences in J
c for tapes processed using the three different intermediate deformation procedures are dependent on the density of the pinning force and cannot be attributed to the grain alignment. Our experimental results support the view that SR processing is the best method for fabricating Ag/Bi-2223 tapes of high quality. 相似文献
2.
High-T
c superconducting joints between Ag-clad Bi-2223 tapes have been developed for persistent current applications. Two presintered tapes with one side of the silver stripped were lapped and then wrapped by a silver foil. The complex was uniaxially pressed followed by appropriate sintering to form a high-T
c superconducting tape joint. It was found that the ratio of critical currents through the joint to that of the tape,I
cj/Ic, depended on the uniaxial pressure and the sintering conduction. At liquid-nitrogen temperature 77 K,I
cj/Ic=99% has been achieved. Persistent current loops formed by Bi-2223 tapes have also been fabricated and tested. Joint resistance of a loop was determined to be 4×10–13 between the decay time of 120 and 3600 sec. 相似文献
3.
To improve on present critical current (J c) performance, multifilamentary Ag/Bi-2223 tapes with a large range of reduction rates were manufactured. The relative core mass density D was calculated, dependent on the measured geometric dimensions of the tapes. Experimental results, D vs. J c, D vs. maximum pinning force density F max , and D vs. irreversible magnetic field B irr, are quantitatively formatted. In particular, the magnetic field dependence of J c is critically dependent on its core density. If the core density increases by 10%, J c of the tapes in this experiment is enhanced by as much as 100%. Therefore, in the present state of the technological process for manufacturing Ag/Bi-2223 tape, increasing the core density is clearly a significant strategy in improving the electronic and magnetic properties of the tapes and enhancing the capacity for carrying current at high magnetic fields. The limit of the bulk self-field-J c can be calculated by the relationships of J c vs. D. The limit is estimated to be on the order of 200 kA/cm2 for multifilamentary Bi-2223 tapes, which was supported by magneto-optical (MO) magnetization measurements results. It is a hard task to approach this limit with the present state of the art in manufacturing Ag/Bi-2223 tape, and it is the time to suggest some new ideals for Bi-2223 tapes to promote large-scale applications. 相似文献
4.
O. Ozogul 《Journal of Superconductivity》2004,17(4):513-517
The Anderson–Kim model for a granular superconductor was employed to calculate both temperature and magnetic field dependencies of the AC susceptibility of a Bi-2223 superconductor. Moreover, similar calculations were performed for the magnetization. The prediction of the model, including the intergranular and intragranular contribution, for susceptibilities and magnetizations was consistent with experimental data very well by considering the temperature-dependent effective volume fraction. The temperature-dependence of fitting parameters was shown to obey almost quadratic power relation (1–T/T
c)
with 2. 相似文献
5.
A practical Bi-2223 superconducting magnet, working in liquid nitrogen (L.N2), was designed and fabricated. Bi-2223 tape with a critical current of 147 A was prepared by a controlled overpressure (CT-OP) process at 77.3 K in self-field. Ten double-pancake coils were resistively connected by copper terminals. The bore diameter was 54 mm?, the magnet outer diameter was 122 mm?, the height of the magnet was 124 mm, and the weight of the magnet was about 3 kg. The maximum magnetic field at the center of the bore was 0.48 T with an operating current of 50 A. The experimental results agree well with design predictions calculated by finite element method. AC operation was also performed, and no distortion of the voltage waveform was observed. Therefore, this Bi-2223 superconducting magnet is a suitable replacement for copper magnets designed for applications in science and technology. 相似文献
6.
This paper introduces an enriched Boundary Element Method in which functions are introduced that are known to model singularities or discontinuities from a priori knowledge of the solution space. Additional fundamental solutions are introduced to solve for the additional unknowns created by enrichment and a numerical integration routine is outlined for the evaluation of strongly singular and hypersingular enriched boundary integrals. The solution of a curved crack in an infinite domain by Muskhelishvili is used to assess the accuracy of the method. Using an appropriate technique to evaluate J1 and J2 integrals, it is found that very good agreement with the exact solution is seen with improvements in accuracy over similar FEM implementations. 相似文献
7.
本文对国内某公司高温Bi-2223超导线材的典型宏观缺陷进行了观察,用EDS对缺陷成分进行了分析,并测试了缺陷处临界电流Ic值,结果表明,点缺陷和鼓泡两种典型缺陷都使Bi-2223超导线材缺陷处临界电流值出现了衰减,在点缺陷处Zr元素出现了偏析. 相似文献
8.
The upper critical field H
c2, based on Ginzburg–Landau theory at medial magnetic fields, can be calculated from the relationship of the magnetization intensity M(H) versus magnetic field H if M is linear with ln0
H. For Ag/Bi-2223 tapes, the measured M(H) was found to be linear with ln0
H. In this case, the values of H
c2(T) may in principle be determined. To do this, we will meet another problem in that the obliquity of crystal planes is not equal for different grains in tapes, and values of grain-oblique angle will appear in the calculated H
c2. Obviously, for Ag/Bi-2223 tapes is an uncertain parameter and hard to determine. To avoid the effects of , we only study the H
c2 in the c axis direction and the projections of H onto the c axis is taken as the actual applied fields. Thus, the effects of grain-oblique angle may be counteracted when measuring critical current density J, if the external magnetic fields are applied to the tape along both the parallel to and perpendicular to the c axes directions (on the narrow surfaces of the tape). On medial fields (H = 0 – 3 T), the upper critical fields H
c2(T) on c axis for the Ag/Bi-2223 tape are obtained and fitted as 0
H
c2(T) = 830 e
–0.07T
. The average slope d[0
H
c2(T)]/dT – 8T/K is found to be as large as that of Bi-2212. On extrapolating the relation to T = 0 K, the value of 0
H
c2(0) 800T. The coherence length
ab
is determined from H
c2(c), and
ab
(0) = 0.63 nm at T = 0 K. 相似文献
9.
V. íma E. Pollert V. Plecháek J. Chval K. Kníek L. Martini L. Bigoni S. Zannella 《Journal of Superconductivity》1998,11(2):253-258
The processing of Ag/Bi(Pb)-2223 tapes via the prevailing solid state reaction was investigated. A precursor powder of the composition Bi1.86Pb0.26Sr1.96Ca1.95Cu2.97O10+ containing mainly Bi-2223 phase was employed. Particular attention was devoted to the microstructural properties of the tapes subjected to rolling and subsequent heat treatment in one, two, and three steps, respectively. A sharp texturing gradient exists in the superconducting cores, and the repeated treatment leads to deterioration of the superconducting properties. The latter effect is ascribed to the formation of periodic defects arising during the repeated rolling of the sintered superconducting core. 相似文献
10.
Multifilament Ag-sheathed BiPbSrCaCuO (2223) superconducting tapes containing 49 filaments were fabricated by the powder-in-tube route and the roll-anneal process. The transport critical current densityJ
c
was 1.3×104 A cm–2 at 77 K and 7×104 A cm–2 at 4.2 K in self-field. A 12-m-long tape was used to construct superconducting solenoids (50, 28, and 14 mm internal diameters) generating dc fields 380–1070 G at 4.2 K. Measurements of the variation ofJ
c
with field (0–1.6 T) and bend strain (0–5%) are used to explain the performance of the solenoids. The critical bend strain of tapes was about 1.5%. 相似文献
11.
Internally assembled ring-bundle-barrier Bi-2223 tapes with a Rutherford type stranded structure were optimised with respect to low coupling losses. They had resistive barriers of a mixture of SrCO3 and SrZrO3 around the strands and around the central Ag core. From these tapes small test coils were wound and the ac losses were measured with a sinusoidal ac transport current at 77 K. The loss measurement was performed by the standard magnetization technique. A calorimetric calibration yielded the correct absolute values of the losses. The results show that the main loss component is hysteretic, and coupling losses do not contribute significantly to the total losses. The suppression of coupling losses due to the resistive barriers leads however to a small critical current of the tapes and further optimisation with respect to losses and critical current is necessary. 相似文献
12.
Optimization heat-treatments have been performed on multi-filament Bi-2223/Ag superconducting tapes under 1 bar total gas pressure, the oxygen partial pressure being 8.5%. In a first heat-treatment (HT1), the tapes were sintered within 822-838 °C for 1-50 h. After intermediate deformation, all the samples underwent the second heat-treatment (HT2) at 825 °C and 830 °C for 20 h followed by a thermal sliding procedure. The relative content of the phases present in HT1 samples was measured by XRD. It was found that the Bi-2212 phase content after HT1 strongly influences the values of Jc after HT2. There is a correlation between the amount of Bi-2212 phase after HT1 and the final Jc values after HT2. A maximum of Jc was found for a ratio of 0.15 between Bi-2212 and Bi-2223. 相似文献
13.
Multifilamentary HTSC tapes are important for their applications in various electrical devices. Powder-in-tube technique with
improved optimized synthesis parameters is regarded as one of the most promising ways to prepare long-length multifilamentary
Bi-2223/Ag tapes. Nevertheless, usefulness of such tapes depends on their electrical and mechanical properties. Critical current
density of a Bi-2223/Ag tape with 37 filaments has been studied at 77 K with field, field orientation, thermal cycling and
bending strain as parameters. Results have been discussed in light of various mechanisms and models. A small pancake coil
has been fabricated out of the same tape and the test results presented. 相似文献
14.
B. Krunavakarn P. Udomsamuthirun S. Yoksan I. Grosu M. Crisan 《Journal of Superconductivity》1998,11(2):271-273
We give an analytical expression for the gap-to-T
c ratio (R) of a superconductor with a van Hove singularity in the density of states. Our calculation yields R in very good agreement with the results obtained numerically by S. Ratanaburi et al. [J. Supercond. 9, 485 (1996)]. 相似文献
15.
B. Ruzicka P. Calvani M. Capizzi S. Lupi P. Maselli A. Paolone 《Journal of Superconductivity》1996,9(4):393-396
Polaronic absorption features, induced by excess charges in both electron and hole doped cuprates, have been measured. The features here reported include additional phonon-like peaks in the far infrared and a broad overtone band centered at 1000 cm–1 (d band). The peaks in the far infrared are attributed to local modes. Thed band is produced by overtone and combination bands of a few of these local modes and is well fitted in a polaron model. Most of these polaronic contributions survive in the metallic phase, where they are superimposed on the Drude term due to free carriers. 相似文献
16.
W. M. Chen F. Wang F. Lin S. S. Jiang Y. C. Guo H. K. Liu S. X. Dou 《Journal of Superconductivity》2000,13(3):441-446
For polycrystalline Ag/Bi-2223 tapes, the preferential orientation of grains is a very important issue. The platelike grains in the tapes are generally believed in a high-order alignment. However, microstructural observation by SEM shows that the grain alignment is far from perfect. Theoretically, upper critical field, H
c2, for H parallel to ab plane and c axis was calculated form the relation of M(H). However, the ratio of H
c2 (H//ab) to H
c2(H//c) depends on the angle () between the ab plane of grains and the broad surface of the tapes. Based on the ratio, the orientation distribution of grains is obtained. The results show that grains in Ag/Bi-2223 tapes can grow with ab plans at any angle between 75° > > –75°, but no grain can grow with its ab plane perpendicular to the tape broad surface. The overall distribution is that: >90% grains orient in the angle range of || < ± 75°, about 5% grains at ±75° || ±85°, and no grains at || > ±85°. 相似文献
17.
U Syamaprasad M S Sarma A R Sheeja Nair P Guruswamy P S Mukherjee J Koshy A D Damodaran 《Bulletin of Materials Science》1995,18(5):517-529
Silver clad Bi-2223 tapes with consistently high critical current densities of over 30,000 A/cm2 at 77 K and zero field were prepared by powder-in-tube (PIT) technique. Powder XRD, electron microscopy, a.c. susceptibility
and critical current measurements were used to study the phase assemblage, microstructure and transport properties of these
tapes at various stages of processing. The precursor powder for PIT process was prepared by a sol-gel route by acrylate method
using freshly prepared nitrates of Bi, Pb, Sr, Ca and Cu. The carbon content in the powder was minimized by subjecting it
under dynamic vacuum calcination followed by heating in free flow of oxygen for long durations with intermittent grindings.
The choice of initial stoichiometry, high reactivity of the precursor, effective removal of carbon, choice of phase assemblage
at the filling stage and the multistage thermomechanical processing at optimized conditions were found to be responsible for
the high critical current density.
The work was done under the National Superconductivity Programme funded by the Department of Science and Technology (DST),
New Delhi. 相似文献
18.
The onset of superconductivity is 49 K in Cu-doped (but cuprate-plane-free) Sr2YRuO6, almost the same as the 45 K onsets in GdSr2Cu2RuO8 and in R2 – z
Ce
z
Sr2Cu2RuO10 (for R = Gd or Eu), implying that the superconductivity in all four compounds originates in the SrO layers, not in the cuprate-planes. Muon studies show that the superconducting condensate in YBa2Cu3O7 is either s-wave or extended s-wave, not d-wave, confirming earlier work. 相似文献
19.
Vladimir Z. Kresin Stuart A. Wolf Yu. N. Ovchinnikov 《Journal of Superconductivity》1996,9(3):329-333
The value of the critical temperature of the cuprates correlates with the doping level and is affected by the interplay of two competing factors: (1) the increase in carrier concentration, and (2) the pair-breaking effect of magnetic impurities. An analysis of the temperature dependence of the critical field leads to the conclusion that magnetic impurities are present even in a sample with the maximum observed value ofT
c.A new parameter, intrinsicT
c (T
cintr), which is its value in the absence of magnetic impurities, is introduced. The maximum value ofT
cintr, which corresponds to the maximum doping level, appears to be similar for different cuprates and to be equal to 160–170 K. This is the upper limit ofT
c in the cuprates. 相似文献
20.
When a current is applied above the critical current lc of a superconductor, the material is in its normal state and has a finite resistance. Below lc the material becomes a superconductor with zero resistance. Switching between these two states can be achieved by modulating a current through the sample. Various high Tc superconducting (HTS) line structures have been made. In the normal state these structures are ordinary resistors with resistances ranging from 10 μ to 100 kμ. The critical currents are in the range 10 μA–100 mA. Switching behaviour has been observed in a simple divider circuit using the HTS lines at 77 K. Applications of the current controlled HTS switch to digital and logic circuits are discussed. 相似文献