Evaluation of Joint Resistance Between Bi-2223/Ag Superconducting Tapes
We fabricated Bi-2223/Ag jointed tape and evaluated its current carrying capacity and joint resistance at 77.3 K as a function of the contact length. The tapes were jointed by the conventional resistive joint method with 40Pb-60Sn solder as an insert material and their joint resistance was measured by two different techniques, i.e., the standard four-probe and field decay methods. It was observed that the current carrying capacity and joint resistance were significantly dependent on the contact length. As the contact length increased, the current carrying capacity improved and increased to the level of critical current in the unjoined tape at the contact length of 5 cm. On the other hand, the joint resistance linearly decreased as the contact length increased. In addition, the joint resistances measured by the two methods were similar to each other (7.3times10-9 Omega~8.0times10-9 Omega), indicating that the standard four-probe method maintained a moderate degree of accuracy at the level of resistance of 10-9 Omega
A Process for Developing Long-Length Superconducting Joint Tube Assembly of Bi-2223 (10 wt% Ag)
A process for developing long-length joint tube assembly of Bi-2223 (10 wt% Ag) superconductor is presented. The process involves sintering of tubes fabricated from cold isostatic pressing of the partially preformed Bi-2223 (10 wt% Ag) superconducting powder. The joint was made between these sintered tubes. For making joints, sintered tubes were physically joined by connecting together on a common superconducting bush coated with a superconducting paste. Subsequently, the combination of the bush and the physically joined portion were sintered. The superconducting properties and phase identification/phase composition of the component tubes and of the joint portions have been investigated. The diametral fractural strength of the component tubes and of the joint portion was also evaluated. In the joint obtained according to this method, it is possible to retain the superconducting properties and the fractural strength of the joint high-temperature superconducting tubes. This technique is very useful for fabrication of very large sized superconducting apparatuses such as external magnetic shielding, transmission cables and electrical current leads, etc.
Fabrication and characterization of the joining of Bi-Pb-Sr-Ca-Cu-O superconductor tape
We evaluated the effects of the joining process on the electrical and mechanical properties of Bi-2223 superconductor tape fabricated by the powder-in-tube technique. The joining of tapes was carried out by a lap-joint method. In the process, tapes were masked and etched to expose the superconductor cores in windows located near or at the end of the tape. The exposed cores of the two tapes were brought into contact, uniaxially pressed in the range 140-4000 MPa and sintered. The current carrying capacity of the jointed tape was evaluated as a function of uniaxial pressure and the shape of windows. It was observed that the current carrying capacity was reduced in the transition region of the jointed tape because of the non-uniform microstructure during the pressing. In addition, the current carrying capacity was significantly dependent on the uniaxial pressure. The highest current carrying capacity was obtained to be ~90% for the jointed tape to the tape itself by optimizing the window shape and pressure. It is believed that the highest value of current carrying capacity results from improvements in interface uniformity, core density, contacting area and grain alignment. The strain tolerance of the jointed tape was also evaluated, and the irreversible strain was measured to be 0.1%, which is lower than that of the unjointed tape. The decrease in the strain tolerance for jointed tape is believed to be due to the irregular interface and Ag intrusion in the transition region which acts as a stress concentration.