REBCO (RE = rare earth) based high temperature superconducting (HTS) wires are now being utilized for the development of electric and electromagnetic devices for various industrial, scientific and medical applications. In the last several years, the increasing efforts in using the so-called second generation (2G) HTS wires for some of the applications require a further increase in their engineering current density (Je). The applications are those typically related to high magnetic fields where the higher Je of a REBCO wire, in addition to its higher irreversibility fields and higher mechanical strength, is already a major advantage over other superconducting wires. An effective way to increase the Je is to decrease the total thickness of a wire, for which using a thinner substrate becomes an obvious and attractive approach. By using our IBAD-MOCVD (ion beam assisted deposition-metal organic chemical vapor deposition) technology we have successfully made 2G HTS wires using a Hastelloy® C276 substrate that is only 30 μm in thickness. By using this thinner substrate instead of the typical 50 μm thick substrate and with a same critical current (Ic), the Je of a wire can be increased by 30% to 45% depending on the copper stabilizer thickness. In this paper, we report the fabrication and characterization of the 2G HTS wires made on the 30 μm thick Hastelloy® C276 substrate. It was shown that with the optimization in the processing protocol, the surface of the thinner Hastelloy® C276 substrate can be readily electropolished to the quality needed for the deposition of the buffer stack. Same in the architecture as that on the standard 50 μm thick substrate, the buffer stack made on the 30 μm thick substrate showed an in-plane texture with a Δϕ of around 6.7° in the LaMnO3 cap layer. Low-temperature in-field transport measurement results suggest that the wires on the thinner substrate had achieved equivalent superconducting performance, most importantly the Ic, as those on the 50 μm thick substrate. It is expected the 2G HTS wires made on the 30 μm thick Hastelloy® C276 substrate, the thinnest and with the highest Je to date, will greatly benefit such applications as high field magnets and high current cables.

No abstract

No abstract

Two methods are available for the quantitative determination of benzoic acid. The first is based on the removal of dicarboxylic acids on a silica-gel column. For benzoic acid contents lower than 2 %, sublimation a t 250 " C must first be carried out. A solution of the crude product in pyridine or of the sublimate in chloroform is introduced into the column. The benzoic acid in the eluate is determined volumetrically (0.02 N alcoholic potassium hydroxide solution, thymol blue) for contents greater than 0.2 %, and spectrophotometrically for contents between 0.02 and 0.2 %.The second method is based on the separation of benzoic acid withbenzene astheeluent onwhatmanpaperpurified with acetic acid, followed by spectrophotometric determination. Phthalic acid is best determined fluorimetrically without chromatographicseparation.The small quantity of isophthalic [VB 36 I€]acid in the end product does not interfere.

No abstract