Properties Of Bi-2223 Tapes Research Articles

The Critical Current Degradation of Bi-2223 Superconducting Tapes Due to Fatigue Cycles at Different Strain Range

The critical current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> ) of high temperature superconductors is an important parameter for practical application, such as magnets, cables and transformers. The degradation of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> under the tensile strain is measured at 77 K as well as under the compressive strain. It is found that the properties of Bi-2223 tapes are superior in the compressive strain to that in the tensile strain. The fatigue degradation behaviors of Bi-2223 tapes are studied in the symmetrical strain cycles and the unidirectional strain cycles. Both of the tests are conducted at 77 K. It is observed that the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> after thousands of cycles in the unidirectional strain cycles is much higher than that of the symmetrical strain cycles. Finally, a round bending test is employed to determine the degradation of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> when Bi-2223 tapes are wound around a mandrel. A critical radius of about 50 mm is found in the experiment.

Fabrication and properties of Bi2223 tapes with CuO barrier formed by the in situ oxidation method

Although Ag sheathed Bi2223 tapes have the performances of I c values over 100 A and length of 1000 m which are enough for prototype applications, their AC loss is still too high for practical applications. To reduce the AC loss, the introduction of high resistive barrier between filaments and the filament twisting are effective. In this study, the Bi2223 tapes with CuO barriers between filaments were fabricated through the in situ oxidation method. Mono-core wires covered with metal Cu were stacked and deformed to form 19-filamentary tapes. These tapes were sintered, and the metal Cu layer was oxidized to form CuO barrier layer. Although the CuO grains in barrier layer easily agglomerated during sintering, the continuity of CuO barrier could be kept well by decreasing total sintering time and by the use of thick barrier layer. However the conversion ratio from Bi2212 to Bi2223 became low by increasing the barrier thickness. In addition, XRD analysis revealed that the impurity phase of (Sr, Ca) 14Cu 24O x phase easily formed in the thick barrier tape. The J c value of over 1 × 10 4 A/cm 2 at 77 K, 0 T was achieved in CuO barrier tape with the initial thickness of 20 μm. The proper control of initial thickness and sintering conditions is important to achieve high J c and good continuity of barrier.

Fabrication and properties of Bi2223 tapes with high resistive barrier formed by the in situ oxidation method

Ag sheathed Bi2223 tapes have the performances of I c values over 100 A and length of 1000 m which are enough for prototype applications. However, their AC loss is still too high for practical applications. To reduce the AC coupling loss, the introduction of high resistive barrier between filaments and the filament twisting are effective. In this study, the Bi2223 tapes with CuO and NiO barriers between filaments were fabricated through the in situ oxidation method, and the effect of 2223 addition in precursor on the formation of Bi2223 was also investigated. Mono-core wires covered with metal Cu or Ni were stacked and deformed to form 7-filamentary tapes. These tapes were sintered, and the metal Cu and Ni layer were oxidized to form CuO and NiO barrier layer, respectively. The continuity of CuO and NiO barriers were kept well in the final tapes, although the CuO grains in barrier layer easily agglomerated during sintering compared to NiO. The formation speed of Bi2223 phase was increased by the addition of Bi2223 in precursor. However, the formation speed of the tape with barrier was slower than that without barrier. This difference should be considered to control the processing for high J c value.

Abnormal Stress–Strain Properties of Bi-2223 Tapes

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.

Electromechanical and Thermal Properties of Bi2223 Tapes

High temperature superconductor (HTS) tapes, e.g. Bi2223, are increasingly used for technical applications. A high variety of tape designs and compositions exists according to the special demands, e.g. for magnet coils or current leads. To use this material it is necessary to determine the thermal, mechanical and electrical properties in the temperature range planned for the application. Several types of available tapes are examined with respect to their mechanical properties at room temperature and at 77 K. Thermal properties, like thermal expansion and heat conductivity, in the temperature range from 5 K up to 300 K are given. In addition the effect of tensile loads in tape direction on the critical current is investigated.

Mechanical and Superconducting Properties of Bi-2223 Tape for 19 T Cryogen-Free Superconducting Magnet

We have started a new project to develop a cryogen-free 19 T superconducting magnet with a 52-mm room temperature bore. The magnet is designed to be consisting of three sections, i.e., the innermost high-T/sub c/ superconducting coil section, the middle Nb/sub 3/Sn section and the outer NbTi section. The electromagnetic hoop stress is applied to the superconducting wire due to the magnetic field generation. It is described to the products of magnetic field, transport current density, and winding radius. The maximum electromagnetic stress is estimated to exceed 200 MPa in the middle Nb/sub 3/Sn section and 50 Pa in the high-T/sub c/ section. It is important to explore the mechanical characteristics to design the magnet. In this study, mechanical properties, i.e., stress-strain characteristics and stress dependence of the critical current, were investigated for oxide superconducting tapes.

Transversal compressive force and superconducting transition properties of Bi-2223 tapes

Abstract Transversal compressive force was applied to a face of Bi-2223 tape, and V–I characteristics and mechanical properties of the tape were measured. Contact conditions between the tape and pushing parts are two kinds (a line-contact and a face-contact). Based on measured data dependence of critical currents and n-values of the Bi-2223 tape on the transversal compressive force and deformation of the tape was experimentally studied. From the results of the line-contact condition between the tape and the pushing parts, 25 N of the force to the tape decreased the critical current and the thickness of the tape by 90% and 0.6% of the initial value, respectively. The data under the face-contact condition showed little degradation of the tape’s critical currents because of the small stress to the tape. After those experiments the tape was cut along the longitudinal direction of the tape and Bi filaments were observed microscopically in the cross-section.

Characterization of the thermal conductivity and mechanical properties of sheath alloy materials for Bi-2223 superconductor tapes

We evaluated the effects of adding alloying-element to the Ag sheath on the thermal conductivity and mechanical properties of Bi-2223 tapes. The thermal conductivity of Ag and Ag-alloys was evaluated by using the thermal integral method in the temperature range of 10 to 100 K, and correlated to the indirectly-measured values obtained from the density, specific heat, and thermal diffusivity. It was observed that the additions of Au, Pd, and Mg to the Ag sheath significantly decreased thermal conductivity at low temperatures, probably due to the presence of alloying-elements. Specifically, the thermal conductivity of the Ag/sub 0.92/Pd/sub 0.06/Mg/sub 0.02/ and Ag/sub 0.973/Au/sub 0.025/Mg/sub 0.002/ alloys at 30 K was 28.9 and 59.2 (W/(m/spl middot/K)), respectively, which is about 17 to 35 times lower than that of Ag (997.2 (W/(m/spl middot/K))). At the same time, these additions to the Ag sheath, improved its mechanical strength. It is believed that this improvement is related to the presence of dispersed alloying-elements which leads to a smaller grain size.

Development and characterization of sheath alloys for Bi-(Pb)-Sr-Ca-Cu-O superconductor tape

The effect of alloying element additions to Ag sheath on mechanical and thermal properties of Bi-2223 tapes has been evaluated. Additions of Au, Pd, Mg and Al to Ag increased hardness and strength, while reducing workability and thermal conductivity. Hardness and tensile strength of Ag/sub 0.92/Pd/sub 0.06/Mg/sub 0.02/ and Ag/sub 0.973/Au/sub 0.025/Mg/sub 0.002/ sheath alloys improved to 92.5(Hv), 397 MPa and 81.9(Hv), 236 MPa, respectively. On the other hand, the corresponding values of Ag were 55.4(Hv) and 135 MPa. In addition, microstructural observation showed that the additions of alloying elements to Ag significantly reduced grain size from 240 /spl mu/m to 10/spl sim/100 /spl mu/m. The improvements in hardness and strength of Ag alloys are believed to be due to the smaller grain size and combined effects of solid solution hardening and dispersion hardening. Thermal conductivity of Ag alloys was measured by the thermal integral method and observed to decrease with increasing content of alloying elements.

The influence of processing parameters and tensile stresses on the properties of Bi-2223 tapes with Ag and AgMn sheaths

Multifilamentary Bi-2223 tapes with an inner Ag sheath immediately surrounding the filaments and an outer AgMn sheath containing 0.06-0.4 wt.% Mn have been fabricated by using the oxide-powder-in-tube technique. In some cases the filaments were additionally surrounded by a second AgPdAu sheath. The forming parameters employed to the rolling of the tapes and consequently the density evolution of the filaments during rolling were optimized aiming to avoid filament sausaging and at the same time to provide a high filament density in tapes of the final dimensions. After the parameters of the thermomechanical treatment were optimized too, similar values of the critical current densities could be achieved for tapes with a Ag/Ag-alloy sheath as for those with a pure Ag sheath. J/sub c/ values above 20 kA/cm/sup 2/ (77 K, 0 T) were measured on tapes over the whole length of 300 m. The tolerable tensile stresses and strains employable to conductors at room temperature without causing essential J/sub c/ degradation at 77 K were determined to /spl sigma//spl ap/90-110 MPa and /spl epsiv/=0.2% for tapes with an outer Ag-0.15 wt.% Mn sheath.

Fabrication and properties of Bi-2223 tapes

Bi-2223 tapes in different variations represent a good basis to build up prototypes for power applications. With respect to these applications we produce 55 filament tapes of lengths up to 600 m carrying currents of 57 A. A statistical analysis confirms reproducibility and quality. In 1 m samples the critical current density reaches 40 kA/cm/sup 2/. An overview of the fabrication process of the tapes is given. Besides the mechanical and microstructural properties of different Ag/Ag-alloy tapes we present the current carrying capability in different magnetic fields and at different temperatures. Additionally the tapes are characterized regarding to their AC losses. These tapes of long lengths are used to fabricate power transmission cables, transformers and motors.

Effect of V, Ir-doping on the J/sub c/ properties of Bi2223 tapes

We prepared Ag-sheathed mono-core tapes and multifilamentary tapes with 19 filaments by the powder-in-tube method, using V- and Ir-doped Bi2223 powder with a doping amount x less than 0.15. In the doped tapes two effects are overlapped: One is the decrease in J/sub c/ due to some weak links caused by precipitates such as Sr-V-O oxides, and the other is the increase in J/sub c/ with the doping content due to the enhancement of Bi2223 phase formation. This results in a minimum in J/sub c/ at x=0.05. The second effect becomes stronger in the V-doping, because of the great enhancement of Bi2223 phase formation. In the Ir-doped tapes the J/sub c/ values decrease monotonically with the doping content. For the multifilamentary tapes the V-doping is very effective to obtain high I/sub c/ values.

Effects of powder calcination on the properties of Bi-2223 tape

The effects of powder calcination on the properties of Bi-2223 tape have been investigated. The transport property of the tape was found to depend strongly on the condition for powder calcination. The tape fabricated with powder calcined at lower temperature resulted in a microstructure with a larger grain size and higher transport critical current. The development of the microstructure of the tape in the subsequent heat-treatment process is correlated with the constituents in the starting powder. The magnetization of samples characterized by SQUID indicates that the magnetic property is also correlated to the microstructures of the tape. An anomalous flux disturbance occurring at 70 K was observed on the zero-field cooling curves of all samples.