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1.
《低温学》2002,42(6-7):377-382
We are developing Bi-2223/Ag tapes with a high engineering critical current density by optimizing the powder-in-tube process and are studying its application to coil and current leads. We have fabricated 250 m-long tape and investigated optimized processing conditions to enhance engineering critical current density. More bubbling was found when the tape was heat-treated with a higher heating rate. Different kinds of superconducting joints were fabricated with multi-filamentary Bi-2223/Ag tapes, and 58% of retained Ic was achieved using the insertion of Bi-2223 core between two exposed tapes. Current decay property of the persistent mode HTS coil was investigated. Rapid current decay was observed when the operating current is in a flux-flow range. We could successfully fabricate a low heat leak type HTS current lead with Bi-2223/Ag–Au tapes by employing a stepped geometry. Using this lead, safe operation of 2 kA current transport was confirmed.  相似文献   

2.
10-meter-long Ag?CNi bimetallic sheathed (Bi,Pb)-2223 tapes with outer nickel sheath and inner silver sheath have been successfully fabricated by the ??Powder in tube?? technique. Microstructure and phase evolution studies by means of SEM and XRD, as well as critical current density (J c ) measurements have been performed. It is found that the nickel sheath and dwell time in the first sintering process have great influences on the texture evolution, phase transformation and J c of the Bi-2223/Ag/Ni tapes. Mono-filament (Bi,Pb)-2223 tape with a J c of 6656?A?cm?2 and 61-filament tape with a J c of 12420?A?cm?2 are obtained. Although using composite bimetallic sheaths can reduce production costs and improve mechanical properties of the Bi-2223 tapes, the Bi-2223 content and J c of Bi-2223/Ag/Ni tapes are relatively lower than that of traditional Bi-2223/Ag tapes. Meanwhile, due to higher Bi-2223 content and better alignment of Bi-2223 grains, tapes with 61-filament have higher J c than mono-filament tapes.  相似文献   

3.
The influence of green tape thickness on the Bi-2223 phase formation and texture evolution in Ag/Ni composite-sheathed tapes fabricated by the “powder-in-tube” technique has been studied. Microstructural observations by SEM as well as critical current density (J c) measurements at 77 K, 0 T have been performed to analyze the performance of the tapes. The results show an important influence of the green tape thickness on the critical current depending on the content and texture of Bi-2223 phase. The J c increases with decreasing thickness. Moreover, texture measured by omega scans shows that the texture of the Bi-2223 phase is significantly influenced by the thickness of the green tape after the first and final sintering processes. Alignment of Bi-2223 grains in the thin tapes is much better. Higher performance of Ag/Ni composite-sheathed Bi-2223 tapes can be obtained by controlling the thickness of the green tapes.  相似文献   

4.
This paper summarizes the experimental investigations on the critical current of two jointed Bi-2223/Ag superconducting tapes connected by Sn63Ag2Pb solder. Different lap lengths of contact surface were studied. The joint resistance was measured to be in the range of 0.059??0.76????, and the critical current of the jointed Bi-2223/Ag HTS tapes was measured with different charging rates using standard four-point-method in a zero-applied magnetic field applying 1 ??V/cm criterion. The experimental results showed that the longer the lap length was, the smaller the joint resistance was and the nearer the critical current approached that of Bi-2223/Ag superconducting short-sample. On the other hand, the critical current decreased with the increasing of the charging rate.  相似文献   

5.
The secondary sintering of a Bi-2223/Ag ribbon, following the stages of primary sintering and rolling to a strain of ε∼18%, was studied by methods based on the acoustic emission, thermal expansion, and magnetic susceptibility measurements. During the second thermal treatment, a signal of acoustic emission from the ribbon was detected in a temperature range from 570 to 660°C. The process of liquid-phase healing of the rolling cracks in the ribbon material is considered as a reason of the acoustic emission. The possibility of using the acoustic emission measurements for nondestructive testing in the Bi-2223/Ag ribbon fabrication technology is considered.  相似文献   

6.
Thirty-seven-filamentary AgAu-sheathed Bi-2223 tapes were fabricated by a powder-in-tube (PIT) process. And, the round wires (? 1.86 mm) were rolled to 0.35-mm tapes with 12, 7, 5, and 4 rolling passes through flat rolling, respectively. The influences of different rolling passes on the core density, deformation, and transport properties of Bi-2223/AgAu tapes were systematically investigated. It was noticed that after rolling, the Vickers microhardness of the superconducting core and deform homogeneity along both the horizontal and vertical directions on the cross section of seven-pass rolled tape were better than those on the tapes with other passes, which proved the larger core density and uniform deformation with the seven-pass rolling process. Meanwhile for the wires with 12 and 7 passes, the AgAu/superconducting core interfaces were much flatter. With the rolling passes decreasing from 12 to 4, the critical current density (Jc) first increased and then decreased. Due to the better homogeneity and flatter interfaces, Jc reached the maximum value of 17.3 kA/cm2 on the seven-pass sample. Meanwhile, the enhancement of current capacities in magnetic field applied parallel to the Bi-2223/AgAu tape surface could also be recognized as the evidence of improving intergrain connections due to the higher density in seven-pass rolled tapes.  相似文献   

7.
《低温学》2003,43(10-11):549-553
Bi-2223/Ag tapes with different lead content (Pb=0.2–0.4) powders were fabricated. The microstructural development and Jc properties were studied with starting precursor powder prepared in different conditions. The experimental results indicate that the variations of lead content extremely influence the reactivity of precursor powders, which is closely related to the formation rate of 2223 phase, microstructure and Jc values of Bi-2223/Ag tapes. In addition, the particle size distribution of precursor powders has a large effect on the transport properties. By optimizing these powder parameters, Jc values above 60,000 A/cm2 (77 K, 0 T) in short tapes were achieved.  相似文献   

8.
The stress–strain properties of Bi-2223 tapes directly relate to its applications, but have not been systematically studied yet. Three tapes sheathed by Ag and Ag alloys were manufactured for the study of stress–strain. X-ray diffraction analyses were used to determine the amorphous and Bi-2223 phases for the three tapes before and after sintering. Tensile experiments were performed to study the stress–strain properties as well. Micro-morphologies of the three tapes were observed and recorded by scanning electron microscopy. The experimental results show green tapes with a linear stress–strain relation. It is suggested that this relation comes from the sheathed metal’s properties. The mechanical properties of Ag/Mg sheathed tapes are like those of a rigid body, which do not present plasticity and elasticity. The phenomena of outgrowth and bridges were observed in Ag and Ag/Sb sheathed tapes. Also, Ag and Ag/Sb sheathed tapes showed abnormal stress–strain properties, which were subjected to micro-cracks existing in the sheathed metals and imperfections of Bi-2223 crystals.  相似文献   

9.
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.
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   

11.
F ChovanecP Usak 《低温学》2002,42(9):543-546
A sudden drop of the coil voltage and a hysteresis of I-V curve were observed in measurement of one-layer Bi-2223/Ag coils cooled by liquid nitrogen at currents well above critical current region. Their temporal behavior indicates, that the improvement of the cooling and corresponding decrease of temperature after the jump takes place. To study this phenomenon we measured I-V curves of two Bi-2223/Ag coils made from tapes with various degree of critical current homogeneity and analogical curves of two non-superconducting coils made from thin Cu tapes having various widths. In Cu coils we really observed a sudden drop of the temperature, measured in parallel with Cu resistance drop, after reaching heat flux of about 0.4 W cm−2 during current ramping up. In spite of non-superconducting character of the tape, the hysteresis, i.e. difference between increasing branch and decreasing branch of I-V curves, was observed too! Approximately the same value of heat flux, at current corresponding to the jump, was found also in superconducting coil on segment with least value of local critical current. We conclude that observed voltage drop of the Bi-2223/Ag does not bear upon superconducting nature of the coil and, as that for Cu coil, can be explained by dynamics of heat transfer to liquid nitrogen and its history.  相似文献   

12.
The process of cooling of a Bi-2223/Ag ribbon after secondary sintering at 1000 K is studied by the method of acoustic emission (AE). The acoustic response is observed below 500 K and increases in intensity with decreasing temperature. It is established that the AE signal variation reflects the plastic flow in the silver coating caused by a difference between the thermal expansion coefficients of silver and the ceramic core of the Bi-2223/Ag ribbon.  相似文献   

13.
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   

14.
The effect of the partial substitution of Ca by Sm in the Bi-2223 superconducting samples have been investigated in terms of X-ray diffraction (XRD), EDXRF (Energy Dispersive X-ray Fluorescent), magnetoresistivity, critical temperature, transport critical current density, and ac susceptibility measurements. The samples were prepared by the conventional solid-state reaction method. XRD patterns are used to calculate lattice parameters and phase ratio of the Bi-2223 samples. The volume fraction was determined from the intensities of Bi-2223 and Bi-2212 peaks. The room temperature XRD patterns of the samples showed the presence of Bi-2223 phase decreases with increasing the Sm content. We estimated the transition temperature of the samples from the resistivity versus temperature measurements in dc magnetic fields up to 0.6 T. We observed that transition temperature, T c , and transport critical current density, , depend on the Sm substitution. They both decrease with increasing the Sm substitution. We extracted the peak temperature, T p , and the pinning force density from our previous ac susceptibility measurements. The pinning force density decreased with increasing the Sm content. The possible reasons for the observed decreases in critical temperature and critical current density due to Sm substitution were discussed.  相似文献   

15.
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   

16.
T.-M. Qu  Y. Song  L. Zhao  P. Li  Z. Han 《低温学》2007,47(2):127-131
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   

17.
The effect of the addition of SnO2 nano-particles on Bi-2223 phase formation has been studied. Tin oxide was added at different intervals of the synthesis process. It is shown that the addition of SnO2 inhibits the Bi-2223 phase formation regardless of when it is introduced to the system. SnO2 partially reacts with calcium to form the Ca2SnO4 phase. This phase is stable throughout the synthesis process. As a consequence, the formation of the Bi-2223 phase is compromised for the benefit of secondary phases such as Bi-2212, Ca2SnO4, Sr0.15Ca0.85CuO2 and Cu2SrO2. The c parameter of the Bi-2223 phase increases when tin is added. A possible explanation is a partial substitution of Cu2+ by Sn4+.  相似文献   

18.
The microstructure, phase composition, and superconducting properties of Bi-2223 ceramics doped with 0.05–0.5 wt % TaC were investigated. The materials were heat-treated at 840°C in three steps (10 + 24 + 24 h). By optimizing the TaC content and heat-treatment conditions, the 77-K critical current density of the Bi-2223 ceramics in zero field was raised by a factor of 2.  相似文献   

19.
Sinter forging has been employed to improve critical current density of Bi-2223 bulks. After that, optimal post annealing is also very important to get good performance. Different annealing schedules have been used to produce Bi-2223 sinter-forged bulks in different atmospheres. In this paper, Bi-2223 long bulks were prepared by a combination of cold isostatic pressing (CIP) and sinter-forging techniques. The samples were undergone deformation rates from 50 to 90% totally. The effect of post annealing in atmosphere of 7.5% O2/N2 on critical current density Jc for such (Bi, Pb)2Sr2Ca2Cu3Oy long bulks was investigated. Their microstructure features and phase changes were also studied.  相似文献   

20.
Sinter forging has been employed to improve critical current density of Bi-2223 bulks. After that, optimal post annealing is also very important to get good performance. Different annealing schedules have been used to produce Bi-2223 sinter-forged bulks in different atmospheres. In this paper, Bi-2223 long bulks were prepared by a combination of cold isostatic pressing (CIP) and sinter-forging techniques. The samples were undergone deformation rates from 50 to 90% totally. The effect of post annealing in atmosphere of 7.5% O2/N2 on critical current density Jc for such (Bi, Pb)2Sr2Ca2Cu3Oy long bulks was investigated. Their microstructure features and phase changes were also studied.  相似文献   

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