Processing and characterisation of long-length silver/bismuth-2223 tape for electric power applications
The potential of high temperature superconductivity (HTS) to raise efficiencies in electric power utilisation is dependent on the availability of HTS materials in a form which can be engineered into devices. This paper reviews a program of continuous process and product improvement which has enabled tape with lengths up to 1000 m and appropriate engineering properties to be reproducibly processed using the powder-in-tube technique. Underpinning this development of a large scale process capability, tape development on a small scale was necessary in the areas of innovative tape design, metal forming optimisation and heat treatment. In addition, techniques for the characterisation of long lengths of tape were developed. These techniques included the modelling of the effect of the self-field generated by the tape under test at 77 K to enable zero field Ic data to be determined.
Properties of `z-stack' elongate (Bi2−xPbx)Sr2Ca2Cu3O10−δ/Ag high temperature superconductors manufactured by the `tape-in-tube' technique
Abstract Multifilamentary z-stack samples of tape-in-tube wires and tapes have been prepared using a flat tape re-stacking procedure. Self-field I C measurements at 77 K show values of 24±2 A and 22±1 A for 2×11 multifilamentary z-stack tapes and round wires, respectively. These I C measurements correspond to J C values=1.62×10 8 A m −2 and 7.7×10 7 A m −2 , respectively, for tape and wire configurations. While most of the fabrication factors (such as the superconducting packing fraction) were found to be similar to those found in conventional powder-in-tube (Bi 2− x Pb x )Sr 2 Ca 2 Cu 3 O 10− δ /Ag composites, some of the tape properties such as the 5% ( e =0.46) reversible bend strain limit, showed an improvement from conventional powder-in-tube tape values. Measurements in magnetic fields show that twisting z-stack filaments in a round wire format can reduce the magnetic field anisotropy of tape-in-tube tapes compared to conventional powder-in-tube tapes.
Enhanced flux pinning through a phase formation-decomposition-recovery process in Ag-sheathed Bi(Pb)SrCaCuO wires
A high-critical temperature, T/sub c/, phase formation-decomposition-recovery (PFDR) process has been developed for fabrication of Ag-sheathed (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10+y/ (2223) wires with a short period of melt during the heat treatment. A critical current density, J/sub c/, of 40000 A/cm/sup 2/ at 77 K and 0 T and of 9000 A/cm/sup 2/ at 77 K and 1 T has been achieved. The irreversibility line for the PFDR tape is shifted to much higher temperature than those for normal tape and powder sample for fields up to 6 T. The PFDR processed samples contain a large amount of small spheres of Sr- and Ca-rich phase with a diameter of 1 mu m to 3 mu m, well aligned 2223 grains, highly dispersed, textured 2212 and high concentrations of dislocations (10/sup 10//cm/sup 2/) and stacking faults. The strong coupling between grains is attributed to the interfacial pinning.<<ETX>>