Recent advances in long length Bi-2223 HTS multifilamentary composite wire development

Phase evolution and microstructure development in silver-clad Bi-2223 composite conductors have been investigated as a function of filament count (mono, 19, 85 and 361), precursor powder type (metallic powder or oxide powder), oxygen partial pressure (<10-3 to 0.13 atm), temperature (790-855 °C) and time (0-6000 min). Favourable conditions for rapid Bi-2223 phase formation and stability were achieved with an oxygen partial pressure around 0.08 atm, regardless of precursor type or filament count. In general, the rate of the Bi-2223 formation reaction increased and the width of the temperature window for rapid kinetics became broader as the filament count increased. The most rapid kinetics and the broadest heat treatment window were observed for the 361-filament metallic powder composite. These trends in Bi-2223 formation rate and stability are believed to be associated with the increased proximity of powder to silver as the filament count increases and the filament transverse dimensions become smaller. For each conductor type (in terms of precursor form and filament type) there was an optimum processing temperature in ca 0.08 atm O2 that produced a well-developed Bi-2223 grain colony microstructure with the least amount of second-phase. This optimum temperature was near the peak of the reaction rate versus temperature profile.

Section: Introductionmentioning

confidence: 99%

Phase formation and microstructure development in silver-clad Bi-2223 multifilament composite conductors

Merchant¹,

Luo²,

Fischer³

et al. 1999

“…While much fundamental research is being focused on the development of new materials with higher critical temperatures, the critical current is receiving more attention from the industrial community. At liquid nitrogen temperatures, values of 69 000 A cm −2 have been reported for short lengths [1] of Bi-2223 and 13 000 A cm −2 over a 1 km length [2]. More recently, the possibility of much higher critical currents have been illustrated independently by groups at Los Alamos and Oak Ridge who succeeded in controlling [3] the grain orientation of YBCO during growth, giving critical current densities higher than 10 6 A cm −2 .…”

Section: Introductionmentioning

confidence: 99%

Calorimetric ac loss measurements of silver sheathed Bi-2223 superconducting tapes

Dolez

Aubin

Willen

et al. 1996

A new calorimetric method has been developed to measure ac losses in superconductors. Calibration of the losses requires a reference heater of the same size and shape as the superconductor mounted in a symmetric environment. Its main advantage is the direct determination of the total losses. Variations of the method include a null technique and averaging of the main Fourier component to reduce noise effects. The method has been tested on Bi-2223 tapes and gives the expected hysteresis losses as well as a frequency independent loss which can be attributed to flux creep. The measured losses are similar to those obtained by other groups with other methods.

“…The bending stress/strain occurs in the superconducting wires or tapes when they are transferred from one drum to another or wound on a bobbin for the construction of a coil after the final heat treatment to form superconductors. Many experiments have been carried out on the bending strain effect on the critical current, I c , in the research and developments of high-temperature superconductor wires or tapes worldwide [1][2][3][4][5]. In these experiments, however, test conditions such as the bending method, the specimen mounting method for the I c measurement and the sequence of bending and the I c measurement are not always the same among laboratories.…”

Section: Introductionmentioning

confidence: 99%

Complementary analysis of the results of a bending strain effect round robin-test on the critical currents of Ag alloy-sheathed Bi-2223 tapes

Kuroda¹,

Itoh²,

Kumakura³

et al. 2003

As a result of the first round robin-test (RRT) on the bending strain effect in Ag alloy-sheathed Bi-2223 superconducting tapes, it has been found that the scatter in the critical current data reported from 12 participant laboratories is not very large; the coefficient of variation (COV) is, for example, less than 6% at a bending strain of 0.6%. However, the bending strain limit, which is practically a more important parameter and is defined as a strain where the critical current degrades by 10%, has been found much scattered (17% in COV) in the first RRT. To clarify the origins of data scatter and finally reduce it, complementary analysis and tests on the effects of thermal stress relating to the sequences of the bending of the specimen and critical current measurements have been carried out. Additionally, it has been found that the sample inhomogeneity in mechanical properties contributes to some part of data scatter.